NOVEL STRONTIUM CARBONATE BRIDGING MATERIALS AND METHODS FOR MAKING AND USING SAME

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 61/721,017, filed Oct. 31, 2012 (31 Oct. 2012).

[0002] 1. Field of the Invention

[0003] Embodiments of this invention relate to drilling fluids including a base fluid, a weighting agent and/or a bridging agent, and a thickening agent, and methods making and using same.

[0004] More particularly, embodiments of this invention relate to drilling fluids including a base fluid, a weighting agents and/or a bridging agent, and a thickening agent, where the weighting agent or bridging agent comprises a particulate strontium carbonate and methods making and using same.

[0005] 2. Description of the Related Art

[0006] A variety of drilling fluids and weighting agents are presently on the market. Generally, drilling fluids have an aqueous or hydrocarbon base. One principal requirement of a good drilling fluid is that it is able to suspend a sufficient amount of weighting additives so as to meet desired density requirements particularly with respect to preventing gasification and blow-outs, while remaining pumpable. With respect to aqueous base drilling fluids, a variety of water thickeners are also known. Examples are organic materials such as xanthan gums, aluminum containing compositions, such as hydrous aluminum oxide, polyacrylates, polyacrylamides and a variety of cellulose derivatives. Examples of known weighting materials include barite, hematite, calcium carbonate; zinc, potassium or sodium halides or phosphates and formates.

[0007] In rotary drilling of wells, a drilling fluid is usually circulated down the drill string and back up the annulus between the drill string and the wellbore face. The drilling fluid can contain many different chemicals, but will most often contain a viscosifier, such as bentonite. When a casing string or liner is to be cemented into the wellbore, any drilling fluid and remnants of the viscosifier present in the wellbore are preferably removed to aid the bonding of the cement between the casing string or liner and the wellbore. In removing this drilling fluid from the wellbore and to clean the annulus, a wash or spacer fluid can be introduced ahead of a cement slurry.

[0008] U.S. Pat. No. 4,584,327 disclosed high density fluids including water; a gelling agent selected from the group consisting of oxides of antimony, zinc oxide, barium oxide, barium sulfate, barium carbonate, iron oxide, hematite, other irons ores and mixtures thereof wherein said gelling agent has an average particle diameter size in the range of from about 0.5 to about 10.0 micrometers; hydraulic cement wherein said hydraulic cement has an average particle size in the range of from about 30 to about 200 micrometers wherein said hydraulic cement and said gelling agent have a physical makeup with regard to fine particle size, high density and intersurface attraction properties sufficient to create a slurry with the water that has a gel strength of at least 10 pounds per 100 square feet; and a weighting material selected from the group consisting of iron powder, hematite, other iron ores, steel shot, tungsten, tin, manganese, iron shot, and mixtures thereof wherein said weighting material has an average particle diameter size of from about 2 to about 20 times the average particle size of the gelling agent; said fluid having a density of from 24 pounds per gallon to about 40 pounds per gallon.

[0009] Even though there are many drilling fluids and many weighting agents, there is still a need in the art for drilling fluids with alternate weighting agents, which permit easier filter cake removal and improved tailoring and optimized drilling fluids.

[0010] Drilling fluids including a base fluid, a thickening system, a weighting system, where the weighting system includes an effective amount of strontium carbonate weighting agents or a mixture of a calcium carbonate weighting agent and strontium carbonate weighting agent. The strontium carbonate weighting agent includes particles less than or equal to about 5000μ.

[0011] Drilling fluids including a base fluid, a thickening system, a weighting system, and a bridging system, where the weighting system includes an effective amount of calcium carbonate weighting agent, a strontium carbonate weighting agent or a mixture of a calcium carbonate weighting agent and strontium carbonate weighting agent. The strontium carbonate weighting agent includes particles less than or equal to about 5000μ. The strontium carbonate bridging agent includes a single strontium carbonate mode or a mixture of single strontium carbonate modes, where the modes are particles having sized of D50 of 2μ, 10μ, 20μ, 50μ, 100μ, 200μ, 500μ, 1000μ, 2000μ, 3000μ, 4000μ and 5000μ. In certain embodiments, the strontium carbonate includes equal amounts of particle modes having D50 of 2μ, 10μ, 20μ, 50μ, 100μ, 200μ, 500μ, 1000μ, 2000μ, 3000μ, 4000μ and 5000μ. These types of equal particle size distributions are effective for use in formation zones, screens, gravel packs, or similar structures having pore sizes that range from 2μ to 5000μ. For formation zones, screens, gravel packs, or similar structures having a given pore size distribution, the strontium carbonate weighting and/or bridging agents may be tailored by adding different amount of each mode to substantially mimic the pore size distribution. In other embodiment, the strontium carbonate agent has a mono-modal distribution or a poly-modal distribution tailored to effectively plug a given pore size distribution of a formation, a screen, a gravel pack, or other similar structure.

[0012] Methods for making drilling fluids including a base fluid, a thickening system, a weighting system, where the weighting system includes an effective amount of strontium carbonate weighting agents or a mixture of a calcium carbonate weighting agent and strontium carbonate weighting agent, where the methods involve mixing the ingredients together at desired levels to produce a drilling fluid of this invention. The strontium carbonate weighting agent includes particles less than or equal to about 5000μ.

[0013] Methods for making drilling fluids including a base fluid, a thickening system, a weighting system, and a bridging system, where the weighting system includes an effective amount of calcium carbonate weighting agent, a strontium carbonate weighting agent or a mixture of a calcium carbonate weighting agent and strontium carbonate weighting agent, where the methods involve mixing the ingredients together in desired levels to produce a drilling fluid of this invention. The strontium carbonate weighting agent includes particles less than or equal to about d000μ. The strontium carbonate bridging agent includes a single strontium carbonate mode or a mixture of single strontium carbonate modes, where the modes are particles having sized of D50 of 2μ, 10μ, 20μ, 50μ, 100μ, 200μ, 500μ, 1000μ, 2000μ, 3000μ, 4000μ and 5000μ. The methods may also include measuring a pore size of the formation, screen, gravel pack, or other structure and formulating a strontium carbonate composition having a particle size distribution that is the same or substantially same as the pore size distribution. The strontium carbonate bridging agent includes a single strontium carbonate mode or a mixture of single strontium carbonate modes, where the modes are particles having sized of D50 of 2μ, 10μ, 20μ, 50μ, 100μ, 200μ, 500μ, 1000μ, 2000μ, 3000μ, 4000μ and 5000μ. In certain embodiments, the strontium carbonate includes equal amounts of particle modes having D50 of 2μ, 10μ, 20μ, 50μ, 100μ, 200μ, 500μ, 1000μ, 2000μ, 3000μ, 4000μ and 5000μ. These types of equal particle size distributions are effective for use in formation zones, screens, gravel packs, or similar structures having pore sizes that range from 2μ to 5000μ. For formation zones, screens, gravel packs, or similar structures having a given pore size distribution, the strontium carbonate weighting and/or bridging agents may be tailored by adding different amount of each mode to substantially mimic the pore size distribution. In other embodiment, the strontium carbonate agent has a mono-modal distribution or a poly-modal distribution tailored to effectively plug a given pore size distribution of a formation, a screen, a gravel pack, or other similar structure.

[0014] Methods for using drilling fluids including a base fluid, a thickening system, a weighting system, where the weighting system includes an effective amount of strontium carbonate weighting agents or a mixture of a calcium carbonate weighting agent and strontium carbonate weighting agent, where the methods involve circulating a drilling fluid of this invention while drilling an oil or gas well. The strontium carbonate weighting agent includes particles less than or equal to about 5000μ. The strontium carbonate bridging agent includes a single strontium carbonate mode or a mixture of single strontium carbonate modes, where the modes are particles having sized of D50 of 2μ, 10μ, 20μ, 50μ, 100μ, 200μ, 500μ, 1000μ, 2000μ, 3000μ, 4000μ and 5000μ. In certain embodiments, the strontium carbonate includes equal amounts of particle modes having D50 of 2μ, 10μ, 20μ, 50μ, 100μ, 200μ, 500μ, 1000μ, 2000μ, 3000μ, 4000μ and 5000μ. These types of equal particle size distributions are effective for use in formation zones, screens, gravel packs, or similar structures having pore sizes that range from 2μ to 5000μ. For formation zones, screens, gravel packs, or similar structures having a given pore size distribution, the strontium carbonate weighting and/or bridging agents may be tailored by adding different amount of each mode to substantially mimic the pore size distribution. In other embodiment, the strontium carbonate agent has a mono-modal distribution or a poly-modal distribution tailored to effectively plug a given pore size distribution of a formation, a screen, a gravel pack, or other similar structure.

[0015] Methods for making drilling fluids including a base fluid, a thickening system, a weighting system, and a bridging system, where the weighting system includes an effective amount of calcium carbonate weighting agent, a strontium carbonate weighting agent or a mixture of a calcium carbonate weighting agent and strontium carbonate weighting agent, where the methods involve circulating a drilling fluid of this invention while drilling an oil or gas well. The strontium carbonate weighting agent includes particles less than or equal to about 5000μ. The strontium carbonate bridging agent includes a single strontium carbonate mode or a mixture of single strontium carbonate modes, where the modes are particles having sized of D50 of 2μ, 10μ, 20μ, 50μ, 100μ, 200μ, 500μ, 1000μ, 2000μ, 3000μ, 4000μ and 5000μ. The strontium carbonate bridging agent includes a single strontium carbonate mode or a mixture of single strontium carbonate modes, where the modes are particles having sized of D50 of 2μ, 10μ, 20μ, 50μ, 100μ, 200μ, 500μ, 1000μ, 2000μ, 3000μ, 4000μ and 5000μ. In certain embodiments, the strontium carbonate includes equal amounts of particle modes having D50 of 2μ, 10μ, 20μ, 50μ, 100μ, 200μ, 500μ, 1000μ, 2000μ, 3000μ, 4000μ and 5000μ. These types of equal particle size distributions are effective for use in formation zones, screens, gravel packs, or similar structures having pore sizes that range from 2μ to 5000μ. For formation zones, screens, gravel packs, or similar structures having a given pore size distribution, the strontium carbonate weighting and/or bridging agents may be tailored by adding different amount of each mode to substantially mimic the pore size distribution. In other embodiment, the strontium carbonate agent has a mono-modal distribution or a poly-modal distribution tailored to effectively plug a given pore size distribution of a formation, a screen, a gravel pack, or other similar structure.

[0020] The following definitions are provided in order to aid those skilled in the art in understanding the detailed description of the present invention.

[0021] The term “mono-modal” particle size distribution means a particle size distribution having a single peak, which may be bell-shaped (Gaussian) or skewed to smaller or larger particle sizes.

[0022] The term “poly-modal” particle size distribution means a particle size distribution that includes more than one central peak. These distributions may be many peaks.

[0023] The term “equal or even” particle size distribution means a particle size distribution that has particles of all sizes within the range of the distribution which vary by no more that 20%. In other embodiments, an even or equal particle size distribution has particles of all sizes within the range of the distribution which vary by no more that 15%. In other embodiments, an even or equal particle size distribution has particles of all sizes within the range of the distribution which vary by no more that 10%. In other embodiments, an even or equal particle size distribution has particles of all sizes within the range of the distribution which vary by no more that 5%.

[0024] The term “about” means that the value is within about 10% of the indicated value. In certain embodiments, the value is within about 5% of the indicated value. In certain embodiments, the value is within about 2.5% of the indicated value. In certain embodiments, the value is within about 1% of the indicated value. In certain embodiments, the value is within about 0.5% of the indicated value.

[0025] The term “substantially” means that the value is within about 10% of the indicated value. In certain embodiments, the value is within about 5% of the indicated value. In certain embodiments, the value is within about 2.5% of the indicated value. In certain embodiments, the value is within about 1% of the indicated value. In certain embodiments, the value is within about 0.5% of the indicated value.

[0026] The term “drilling fluids” refers to any fluid that is used during well drilling operations including oil and/or gas wells, geo-thermal wells, water wells or other similar wells.

[0027] An over-balanced drilling fluid means a drilling fluid having a circulating hydrostatic density (pressure) that is greater than the formation density (pressure).

[0028] An under-balanced and/or managed pressure drilling fluid means a drilling fluid having a circulating hydrostatic density (pressure) lower or equal to a formation density (pressure). For example, if a known formation at 10,000 ft (True Vertical Depth—TVD) has a hydrostatic pressure of 5,000 psi or 9.6 lbm/gal, an under-balanced drilling fluid would have a hydrostatic pressure less than or equal to 9.6 lbm/gal. Most under-balanced and/or managed pressure drilling fluids include at least a density reduction additive. Other additives may be included such as corrosion inhibitors, pH modifiers and/or a shale inhibitors.

[0029] The term “gpt” means gallons per thousand gallons.

[0030] The term “ppt” means pounds per thousand gallons.

[0031] The term “ppg” means pounds per gallon.

[0032] The term “HTHP” means high temperature, high pressure.

[0033] The term “HPHT” means high pressure, high temperature.

[0034] The inventors have found that strontium carbonate (SrCO₃) is a successful weighting agent for higher density reservoir drilling fluids (RDF). The inventors have found that strontium carbonate based higher density RDFs have better acid solubility than corresponding calcium carbonate based higher density RDFs in laboratory tests. The inventors have also fount that neat strontium carbonate based higher density RDFs have less than 1% acid insoluble content and are ideal suited for use as acid soluble bridging materials. The inventors have also found that filter cake formed using strontium carbonate based higher density RDFs are easily removed by HCl. The inventors have also found that the properties of the strontium carbonate based higher density RDFs may be optimized for or tuned to specific field applications. The inventor have also found that acetic acid was less effective in dissolving strontium carbonate based higher density RDFs filter cakes than HCl. Applicants believe that the dissolution rate may related to acid strength, with slower dissolution rates for weaker acids and faster dissolution rates for stronger acids. Thus, additional time is required for filter cake dissolution using weaker acids than stronger acids permitting fluid optimization and tailoring based on formation needs. The inventors have also found that fluid loss increases with fluid density. The inventors have also found that the amount of starch and biopolymers may be increased in the fluids to control fluid loss of the strontium carbonate based higher density RDFs. The inventors have also found that the fluid loss is temperature dependent and that for HP starch and biopolymers, temperatures above about 250° F. result reduced fluid loss as the starch and polymers appear to break down at temperatures greater than or equal to 200° F.

[0035] Fluids with basic components including Xanthan, starch, and strontium carbonate or calcium carbonate were successfully formulated in the lab up to a density of 13.3 ppg. The fluids showed acceptable rheological and fluid loss properties. The filter cakes formed by the fluids were easily cleaned by hydrochloric acid, while larger percentage of filter cake residue was observed with acetic acid after a 4 hour soak time. Surprisingly, filter cakes formed using strontium carbonate based higher density RDFs are easier to clean up than filter cakes formed using calcium carbonate based higher density RDFs.

[0036] A high density weighting material is required to build high density reservoir drilling fluid (RDF). The material has to have a high specific gravity, stable chemistry, and be removable by acids dissolution. The weighting material must also have a proper particle size and particle size distribution to generate optimal bridging to reduce fluid loss. Calcium carbonate is widely used in the industry as a bridging material for reservoir drilling fluid; however, it has a low gravity. Therefore, the density increase afforded by the addition of calcium carbonate to a drilling fluid is limited. Strontium carbonate was identified as a novel weighting/bridging material. It has similar properties to calcium carbonate, but it has high specific gravity 3.8 and surprisingly, dissolves in acids at a faster rate than calcium carbonate. We tested a strontium carbonate sample in the laboratory and demonstrated that strontium carbonate has several advantages over calcium carbonate as a weighting/bridging material for use in reservoir drilling fluids: 1) strontium carbonate has higher specific gravity of 3.8 as compared to 2.7 for calcium carbonate, 2) strontium carbonate filter cakes dissolve more readily in acids than calcium carbonate filter cakes making strontium carbonate easier to remove by acids after drilling, and 3) the ease of strontium carbonate filter cakes removal reduces skin damage of formation surfaces.

[0037] Strontium carbonate was determined to be a successful bridging agent for low, medium and high density RDF (reservoir drill-in fluids). Several fluids have been made, tested using fluid loss apparatus with specific pore sized ceramic disks, the filter cake has been dissolved using an acid breaker, and these ceramic disks have been tested using a device to measure the return permeability time. The ceramic disks permeability will differ before fluid loss and after filter cake clean-up; these two are compared to return a percentage, the return permeability.

[0038] Strontium carbonate fluids are seen to maintain a better suspension than the same formulation with calcium carbonate substituted, regardless of particle size. Calcium carbonate tends to fall out of solution after hot-rolling for 16 hours. A separation is usually seen after this time. Strontium carbonate showed no signs of separation in fluid after several days.

[0039] Rheology will have specified maximum and minimum values not to exceed which will be able to be adjusted by lowering the xanthan gum and starch content as need be. As the amount of strontium carbonate is increased beyond 12 ppg, the starch and even xanthan gum amount will be needed to decrease. Plastic viscosities will need to be maintained at a low while yield points should be maintained between 20 and 35. The general formulation is below. Strontium carbonate maintained a more similar rheology before hot-rolling as it did after hot-rolling compared to calcium carbonate. Calcium carbonate had a rheology before hot-rolling that exceeded the limit of yield point range.

[0040] Strontium carbonate has shown excellent fluid loss for a bridging material, as low as 2 milliliters after 30 minutes and less than 20 milliliters over a four-hour period. The fluid loss is administered using an assortment of several different sized ceramic disks to mimic the vast range of potential pore sizes in the field. The smaller the fluid loss, the smaller will be the filter cake, which will in turn make a shorter digestion time. It was seen originally that a sample of neat strontium carbonate has less than 1% acid insoluble and is ideal as an acid soluble agent. In drilling fluids strontium carbonate shows excellent bridging qualities as seen from the extremely low fluid loss. The filtercakes are easily cleaned using a dilute 15% hydrochloric acid. After filter cake cleanup using hydrochloric acid, a larger percentage of filtercake residue is observed using calcium carbonate than there is using strontium carbonate. Also, hydrochloric acid is used for faster breaker/filter cake cleanup than acetic acid digestion, due to it being a stronger acid. Acid breaker time was completed after a 4 hour digestion time with strontium carbonate and hydrochloric acid. Fluid loss is completed at a temperature of 150° F. with a 500 psi differential, rheology at 120° F. Acid digestion is also done at 150° F. and 100 psi. Strontium carbonate outperformed calcium carbonate in similar formulas when tested for fluid loss.

[0041] Fluids were designed using different sizes of strontium carbonate particles to optimize the bridging ability.

[0042] These strontium carbonate reservoir drill-in fluids are made in both water-based as well as synthetic-based fluids. The basic components in both types of fluids will be additives such as xanthan gum, starch and strontium carbonate and have been successfully formulated in the lab up to 17 ppg. These fluids show ideal rheological and fluid loss properties.

[0043] Tests have been run to check whether the strontium carbonate is harmful to the environment, specifically via a total characteristic leeching procedure. This test, after administered showed a low sign of any hazardous leeching, far below the standard set by the Environmental Protection Agency.

[0044] Overall, strontium carbonate shows to be an acceptable substitute for calcium carbonate and to even exceed calcium carbonate in many instances. Below are first the original results obtained for strontium carbonate followed by the newest most recent data generated in the lab.

[0045] In drilling fluid embodiments, the base fluid compositions of this invention are used in a range between about 1 vol. % and about 100 vol. % (volume, v/volume, v) of the base fluid (the base fluid is the fluid into which all other components of the final fluid are added). In other embodiments, the base fluids are used in a range between about 10 vol. % and about 90 vol. %. In other embodiments, the base fluids are used in a range between about 30 and about 70 vol. %. In other embodiments, the base fluids are used in a range between about 40 vol. % and about 60 vol. %. In other embodiments, the base fluids make up greater than or equal to about 50 vol. % of the base fluid. In other embodiments, the base fluids make up greater than or equal to about 60 vol. % of the base fluid. In other embodiments, the base fluids make up greater than or equal to about 70 vol. % of the base fluid. In other embodiments, the base fluids make up greater than or equal to about 80 vol. % of the base fluid. In other embodiments, the base fluids make up greater than or equal to about 90 vol. % of the base fluid. In other embodiments, the base fluids make up about 100 vol. % of the base fluid.

[0046] Suitable aqueous base fluids for use in this invention includes, without limitation, freshwater, production water, seawater other sodium brines, non-sodium brines (phosphate, sulfate, nitrate, etc.), aqueous makeup systems, and mixture or combinations thereof.

[0047] Suitable oil based fluids for use in this invention includes, without limitation, synthetic hydrocarbon fluids, petroleum based hydrocarbon fluids, natural hydrocarbon (non-aqueous) fluids or other similar hydrocarbons or mixtures or combinations thereof. The hydrocarbon fluids for use in the present invention have viscosities ranging from about 5×10⁻⁶ to about 600×10⁻⁶ m²/s (5 to about 600 centistokes). Exemplary examples of such hydrocarbon fluids include, without limitation, polyalphaolefins, polybutenes, polyolesters, vegetable oils, animal oils, other essential oil, diesel having a low or high sulfur content, kerosene, jet-fuel, internal olefins (IO) having between about 12 and 20 carbon atoms, linear alpha olefins having between about 14 and 20 carbon atoms, polyalpha olefins having between about 12 and about 20 carbon atoms, isomerized alpha olefins (IAO) having between about 12 and about 20 carbon atoms, VM&P Naptha, Limpar, Linear paraffins, detergent alkylates and Parafins having between 13 and about 16 carbon atoms, and mixtures or combinations thereof.

[0048] Suitable polyalphaolefins (PAOs) include, without limitation, polyethylenes, polypropylenes, polybutenes, polypentenes, polyhexenes, polyheptenes, higher PAOs, copolymers thereof, and mixtures thereof. Exemplary examples of PAOs include PAOs sold by Mobil Chemical Company as SHF fluids and PAOs sold formerly by Ethyl Corporation under the name ETHYLFLO and currently by Albemarle Corporation under the trade name Durasyn. Such fluids include those specified as ETYHLFLO 162, 164, 166, 168, 170, 174, and 180. Well suited PAOs for use in this invention include blends of about 56% of ETHYLFLO now Durasyn 174 and about 44% of ETHYLFLO now Durasyn 168.

[0049] Exemplary examples of polybutenes include, without limitation, those sold by Amoco Chemical Company and Exxon Chemical Company under the trade names INDOPOL and PARAPOL, respectively. Well suited polybutenes for use in this invention include Amoco's INDOPOL 100.

[0050] Exemplary examples of polyolester include, without limitation, neopentyl glycols, trimethylolpropanes, pentaerythriols, dipentaerythritols, and diesters such as dioctylsebacate (DOS), diactylazelate (DOZ), and dioctyladipate.

[0051] Exemplary examples of petroleum based fluids include, without limitation, white mineral oils, paraffinic oils, and medium-viscosity-index (MVI) naphthenic oils having viscosities ranging from about 5×10⁻⁶ to about 600×10⁻⁶ m²/s (5 to about 600 centistokes) at 40° C. Exemplary examples of white mineral oils include those sold by Witco Corporation, Arco Chemical Company, PSI, and Penreco. Exemplary examples of paraffinic oils include solvent neutral oils available from Exxon Chemical Company, high-viscosity-index (HVI) neutral oils available from Shell Chemical Company, and solvent treated neutral oils available from Arco Chemical Company. Exemplary examples of MVI naphthenic oils include solvent extracted coastal pale oils available from Exxon Chemical Company, MVI extracted/acid treated oils available from Shell Chemical Company, and naphthenic oils sold under the names HydroCal and Calsol by Calumet.

[0052] Exemplary examples of vegetable oils include, without limitation, castor oils, corn oil, olive oil, sunflower oil, sesame oil, peanut oil, other vegetable oils, modified vegetable oils such as cross linked castor oils and the like, and mixtures thereof. Exemplary examples of animal oils include, without limitation, tallow, mink oil, lard, other animal oils, and mixtures thereof. Other essential oils will work as well. Of course, mixtures of all the above identified oils can be used as well.

[0053] Suitable base fluid compositions or solvent systems of this invention include, without limitation, blends of biodegradable, non-toxic, non-hazardous solvents including biodegradable paraffins, isoparaffins, olefins, naphthenes, esters, and oxygenates having a flashpoint ≧80° C. and a pour point of about 19° F. Exemplary examples include HF-1000™, ODC®, LPA®, terpenes and mixture of terpenes derived from citrus plants including d-limonenes, orange terpenes, lemon terpenes, grapefruit terpenes, orange oil, lemon oil, other citrus terpenes, other citrus oils, blends of HF-1000™, ODC®, and/or LPA® with the terpenes and mixtures of terpenes or mixtures and combinations thereof.

Particle Size Distributions of Strontium Carbonate Weighting and/or Bridging Agents

[0054] Suitable strontium carbonate weighting agents include, without limitation, particulate strontium carbonates. In certain embodiments, the particle size for the strontium weighting agents is less than or equal to about 5000μ (micron), where the particle size distribution is mono-modal, bi-modal, poly-modal or equally distributed (all particles sized equally represented). In other embodiments, the particle size for the strontium weighting agents is less than or equal to about 4000μ, where the particle size distribution is mono-modal, bi-modal, poly-modal or equally distributed (all particles sized equally represented). In other embodiments, the particle size for the strontium weighting agents is less than or equal to about 3000μ, where the particle size distribution is mono-modal, bi-modal, poly-modal or equally distributed (all particles sized equally represented). In other embodiments, the particle size for the strontium weighting agents is less than or equal to about 2000μ, where the particle size distribution is mono-modal, bi-modal, poly-modal or equally distributed (all particles sized equally represented). In other embodiments, the particle size for the strontium weighting agents is less than or equal to about 5000μ, where the particle size distribution is mono-modal, bi-modal, poly-modal or equally distributed (all particles sized equally represented). In other embodiments, the particle size for the strontium weighting agents is less than or equal to about 500μ, where the particle size distribution is mono-modal, bi-modal, poly-modal or equally distributed (all particles sized equally represented). In other embodiments, the particle size for the strontium weighting agents is less than or equal to about 250μ, where the particle size distribution is mono-modal, bi-modal, poly-modal or equally distributed (all particles sized equally represented). In other embodiments, the particle size for the strontium weighting agents is less than or equal to about 100μ, where the particle size distribution is mono-modal, bi-modal, poly-modal or equally modality distributed (all particles sized equally represented). In other embodiments, the particle size for the strontium weighting agents is less than or equal to about 50μ, where the particle size distribution is mono-modal, bi-modal, poly-modal or equally distributed (all particles sized equally represented). Strontium carbon may be purchased from at least Solvay Chemicals of Nuevo Leon, Mexico, Spectrum Chemicals & Laboratory Products, Shanghai Yixin Chemical Co., Ltd, Red Butterfly Strontium Industry Co., Ltd., GFS Chemicals, Inc., Columbus, Ohio, All-Chemie, Ltd., Mount Pleasant, S.C., City Chemical LLC, West Haven, Conn., Mil-Spec Industries Corp, Roslyn Heights, N.Y., NOAH Technologies Corporation, San Antonio, Tex., Service Chemical, Inc., Hatfield, Pa., Allan Chemical Corp., Ringwood, N.J., Barium & Chemicals, Inc., Steubenville, Ohio, Del Amo Chemical Co., Gardena, Calif., Espicorp Inc., Ashland, Oreg. Mallinckrodt, Inc., Hazelwood, Mo. Arlington International, Inc., Fort Collins, Colo., and Seaforth Mineral & Ore Co., Inc., Cleveland, Ohio.

[0055] In certain embodiments, the particles are ≦5000μ and the distribution in mono-modal-Gaussian distribution centered at a desired value less than or equal to 2500μ. In other embodiments, the particles are ≦4000μ and the distribution in mono-modal-Gaussian distribution centered at a desired value less than or equal to 2000μ. In other embodiments, the particles are ≦3000μ and the distribution in mono-modal-Gaussian distribution centered at a desired value less than or equal to 1500μ. In other embodiments, the particles are ≦2000μ and the distribution in mono-modal-Gaussian distribution centered at a desired value less than or equal to 1000μ. In other embodiments, the particles are ≦1000μ and the distribution in mono-modal-Gaussian distribution centered at a desired value less than or equal to 500μ. In other embodiments, the particles are ≦500μ and the distribution in mono-modal-Gaussian distribution centered at a desired value less than or equal to 250μ. In other embodiments, the particles are ≦250μ and the distribution in mono-modal-Gaussian distribution centered at a desired value less than or equal to 150μ. In other embodiments, the particles are ≦100μ and the distribution in mono-modal-Gaussian distribution centered at a desired value less than or equal to 50μ. In other embodiments, the particles are ≦50μ and the distribution in mono-modal-Gaussian distribution centered at a desired value less than or equal to 25μ.

[0056] Suitable strontium carbonate bridging agents include, without limitation, particulate strontium carbonate having particles size ranging between about 2μ and about 5000μ. The particulate strontium carbonate bridging agents may have a mono-modal, bi-modal, poly-modal or equally distributed modality (all particles sized equally represented). In certain embodiments, the bridging agents include strontium carbonate having a particle size distribution D50 of 2μ, 10μ, 20μ, 50μ, 100μ, 200μ, 500μ, 1000μ, 2000μ, 3000μ, 4000μ and 5000μ, or mixtures and combination thereof. The separate strontium carbonate agents may then be used separately or combined together to produce a desired particle size distribution (PSD) having particles ranging between about 2μ and 1000μ for appropriate bridging products. If the pore size distribution of the formation zone, the screen, the gravel pack, sand pack, or other structure is known or was determined, then the strontium carbonate weighting and/or bridging agent may be tailored by adding different amount of the different modes of strontium carbonate to mimic or substantially mimic the pore size distribution.

[0057] It should be recognized that each strontium carbonate material has a particle distribution determined by its D50. When preparing a given distribution of strontium carbonate particles, the amount of each material mixed to from the distribution will have to be adjusted so that the given distribution may be prepared.

[0058] Suitable hydratable polymers that may be used in embodiments of the invention include any of the hydratable polysaccharides. For instance, suitable hydratable polysaccharides include, but are not limited to, galactomannan gums, glucomannan gums, guars, derived guars, and cellulose derivatives. Specific examples are guar gum, guar gum derivatives, locust bean gum, Karaya gum, carboxymethyl cellulose, carboxymethyl hydroxyethyl cellulose, and hydroxyethyl cellulose. Exemplary examples of hydratable polymers include, but are not limited to, guar gums, hydroxypropyl guar, carboxymethyl hydroxypropyl guar, carboxymethyl guar, and carboxymethyl hydroxyethyl cellulose. Suitable hydratable polymers may also include synthetic polymers, such as polyvinyl alcohol, polyacrylamides, poly-2-amino-2-methyl propane sulfonic acid, and various other synthetic polymers and copolymers. Other suitable polymers are known to those skilled in the art.

[0059] The polymer may be a hydrolyzed polyacrylamide polymer. The polymer can be a scleroglucan, a modified scleroglucan, or a scleroglucan modified by contact with glyoxal or glutaraldehyde. The scleroglucans are nonionic water-soluble homopolysaccharides, or water-soluble anionic polysaccharides, having molecular weights in excess of about 500,000, the molecules of which consist of a main straight chain formed of D-glucose units which are bonded by β-1,3-bonds and one in three of which is bonded to a side D-glucose unit by means of a β-1,6 bond. These polysaccharides can be obtained by any of the known methods in the art, such as fermentation of a medium based on sugar and inorganic salts under the action of a microorganism of Sclerotium type A. A more complete description of such scleroglucans and their preparations may be found, for example, in U.S. Pat. Nos. 3,301,848 and 4,561,985, incorporated herein by reference. In aqueous solutions, the scleroglucan chains are combined in a triple helix, which explains the rigidity of the biopolymer, and consequently its features of high viscosity-increasing power and resistance to shearing stress.

[0060] It is possible to use, as source of scleroglucan, the scleroglucan which is isolated from a fermentation medium, the product being in the form of a powder or of a more or less concentrated solution in an aqueous and/or aqueous-alcoholic solvent. Scleroglucans customarily used in applications in the petroleum field are also preferred according to the present invention, such as those which are white powders obtained by alcoholic precipitation of a fermentation broth in order to remove residues of the producing organism (mycelium, for example). Additionally, it is possible to use the liquid reaction mixture resulting from the fermentation and containing the scleroglucan in solution. According to the present invention, further suitable scleroglucans are the modified scleroglucan which result from the treatment of scleroglucans with a dialdehyde reagent (glyoxal, glutaraldehyde, and the like), as well as those described in U.S. Pat. No. 6,162,449, incorporated herein by reference, β-1,3-scleroglucans with a cross-linked 3-dimensional structure produced by Sclerotium rolfsii).

[0061] The polymer can be Aquatrol V (a synthetic compound which reduces water production problems in well production; described in U.S. Pat. No. 5,465,792, incorporated herein by reference), AquaCon (a moderate molecular weight hydrophilic terpolymer based on polyacrylamide capable of binding to formation surfaces to enhance hydrocarbon production; described in U.S. Pat. No. 6,228,812, incorporated herein by reference) and Aquatrol C (an amphoteric polymeric material). Aquatrol V, Aquatrol C, and AquaCon are commercially available from BJ Services Company.

[0062] As indicated, mixtures of polymeric gel forming material or gellants may be used. Materials which may be used include water soluble crosslinkable polymers, copolymers, and terpolymers, such as polyvinyl polymers, polyacrylamides, cellulose ethers, polysaccharides, lignosulfonates, ammonium salts thereof, alkali metal salts thereof, alkaline earth salts of lignosulfonates, and mixtures thereof. Specific polymers are acrylic acid-acrylamide copolymers, acrylic acid-methacrylamide copolymers, polyacrylamides, partially hydrolyzed polyacrylamides, partially hydrolyzed polymethacrylamides, polyvinyl alcohol, polyvinyl acetate, polyalkyleneoxides, carboxycelluloses, carboxyalkylhydroxyethyl celluloses, hydroxyethylcellulose, galactomannans (e.g., guar gum), substituted galactomannans (e.g., hydroxypropyl guar), heteropolysaccharides obtained by the fermentation of starch-derived sugar (e.g., xanthan gum), ammonium and alkali metal salts thereof, and mixtures thereof. Preferred water soluble crosslinkable polymers include hydroxypropyl guar, carboxymethylhydroxypropyl guar, partially hydrolyzed polyacrylamides, xanthan gum, polyvinyl alcohol, the ammonium and alkali metal salts thereof, and mixtures thereof.

[0063] The hydratable polymer may be present in the fluid in concentrations ranging from about 0.10 wt. % to about 5.0 wt. % of the aqueous fluid. In certain embodiments, the hydratable polymer are present in concentrations ranging from about 0.20 wt. % to about 0.80 wt. %.

[0064] The pH of an aqueous fluid which contains a hydratable polymer may be adjusted as needed depending on the application. Typical materials for adjusting the pH are commonly used acids, acid buffers, and mixtures of acids and bases. For example, sodium bicarbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, and sodium carbonate are typical pH adjusting agents. Acceptable pH values for the fluid may range from neutral to basic, i.e., from about 5 to about 14. In certain embodiments, the pH is kept neutral or basic, i.e., from about 7 to about 14, more preferably between about 8 to about 12.

[0065] Suitable corrosion inhibitor for use in this invention include, without limitation: quaternary ammonium salts e.g., chloride, bromides, iodides, dimethylsulfates, diethylsulfates, nitrites, bicarbonates, carbonates, hydroxides, alkoxides, or the like, or mixtures or combinations thereof; salts of nitrogen bases; or mixtures or combinations thereof. Exemplary quaternary ammonium salts include, without limitation, quaternary ammonium salts from an amine and a quaternarization agent, e.g., alkylchlorides, alkylbromide, alkyl iodides, alkyl sulfates such as dimethyl sulfate, diethyl sulfate, etc., dihalogenated alkanes such as dichloroethane, dichloropropane, dichloroethyl ether, epichlorohydrin adducts of alcohols, ethoxylates, or the like; or mixtures or combinations thereof and an amine agent, e.g., alkylpyridines, especially, highly alkylated alkylpyridines, alkyl quinolines, C₆ to C₂₄ synthetic tertiary amines, amines derived from natural products such as coconuts, or the like, dialkylsubstituted methyl amines, amines derived from the reaction of fatty acids or oils and polyamines, amidoimidazolines of DETA and fatty acids, imidazolines of ethylenediamine, imidazolines of diaminocyclohexane, imidazolines of aminoethylethylenediamine, pyrimidine of propane diamine and alkylated propene diamine, oxyalkylated mono and polyamines sufficient to convert all labile hydrogen atoms in the amines to oxygen containing groups, or the like or mixtures or combinations thereof. Exemplary examples of salts of nitrogen bases, include, without limitation, salts of nitrogen bases derived from a salt, e.g.: C₁ to C₈ monocarboxylic acids such as formic acid, acetic acid, propanoic acid, butanoic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, 2-ethylhexanoic acid, or the like; C₂ to C₁₂ dicarboxylic acids, C₂ to C₁₂ unsaturated carboxylic acids and anhydrides, or the like; polyacids such as diglycolic acid, aspartic acid, citric acid, or the like; hydroxy acids such as lactic acid, itaconic acid, or the like; aryl and hydroxy aryl acids; naturally or synthetic amino acids; thioacids such as thioglycolic acid (TGA); free acid forms of phosphoric acid derivatives of glycol, ethoxylates, ethoxylated amine, or the like, and aminosulfonic acids; or mixtures or combinations thereof and an amine, e.g.: high molecular weight fatty acid amines such as cocoamine, tallow amines, or the like; oxyalkylated fatty acid amines; high molecular weight fatty acid polyamines (di, tri, tetra, or higher); oxyalkylated fatty acid polyamines; amino amides such as reaction products of carboxylic acid with polyamines where the equivalents of carboxylic acid is less than the equivalents of reactive amines and oxyalkylated derivatives thereof; fatty acid pyrimidines; monoimidazolines of EDA, DETA or higher ethylene amines, hexamethylene diamine (HMDA), tetramethylenediamine (TMDA), and higher analogs thereof; bisimidazolines, imidazolines of mono and polyorganic acids; oxazolines derived from monoethanol amine and fatty acids or oils, fatty acid ether amines, mono and bis amides of aminoethylpiperazine; GAA and TGA salts of the reaction products of crude tall oil or distilled tall oil with diethylene triamine; GAA and TGA salts of reaction products of dimer acids with mixtures of poly amines such as TMDA, HMDA and 1,2-diaminocyclohexane; TGA salt of imidazoline derived from DETA with tall oil fatty acids or soy bean oil, canola oil, or the like; or mixtures or combinations thereof.

[0066] The drilling fluids of this invention can also include other additives as well such as scale inhibitors, carbon dioxide control additives, paraffin control additives, oxygen control additives, or other additives.

[0067] Suitable additives for Scale Control and useful in the compositions of this invention include, without limitation: Chelating agents, e.g., Na⁺, K⁺ or NH₄⁺ salts of EDTA; Na⁺, K⁺ or NH₄⁺ salts of NTA; Na⁺, K⁺ or NH₄⁺ salts of Erythorbic acid; Na⁺, K⁺ or NH₄⁺ salts of thioglycolic acid (TGA); Na⁺, K⁺ or NH₄⁺ salts of Hydroxy acetic acid; Na⁺, K⁺ or NH₄⁺ salts of Citric acid; Na⁺, K⁺ or NH₄⁺ salts of Tartaric acid or other similar salts or mixtures or combinations thereof. Suitable additives that work on threshold effects, sequestrants, include, without limitation: Phosphates, e.g., sodium hexamethylphosphate, linear phosphate salts, salts of polyphosphoric acid, Phosphonates, e.g., nonionic such as HEDP (hydroxyethylidene diphosphoric acid), PBTC (phosphoisobutane, tricarboxylic acid), Amino phosphonates of: MEA (monoethanolamine), NH₃, EDA (ethylene diamine), Bishydroxyethylene diamine, Bisaminoethylether, DETA (diethylenetriamine), HMDA (hexamethylene diamine), Hyper homologues and isomers of HMDA, Polyamines of EDA and DETA, Diglycolamine and homologues, or similar polyamines or mixtures or combinations thereof; Phosphate esters, e.g., polyphosphoric acid esters or phosphorus pentoxide (P₂O₅) esters of: alkanol amines such as MEA, DEA, triethanol amine (TEA), Bishydroxyethylethylene diamine; ethoxylated alcohols, glycerin, glycols such as EG (ethylene glycol), propylene glycol, butylene glycol, hexylene glycol, trimethylol propane, pentaerythritol, neopentyl glycol or the like; Tris & Tetrahydroxy amines; ethoxylated alkyl phenols (limited use due to toxicity problems), Ethoxylated amines such as monoamines such as MDEA and higher amines from 2 to 24 carbons atoms, diamines 2 to 24 carbons carbon atoms, or the like; Polymers, e.g., homopolymers of aspartic acid, soluble homopolymers of acrylic acid, copolymers of acrylic acid and methacrylic acid, terpolymers of acylates, AMPS, etc., hydrolyzed polyacrylamides, poly malic anhydride (PMA); or the like; or mixtures or combinations thereof.

[0068] Suitable additives for CO₂ neutralization and for use in the compositions of this invention include, without limitation, MEA, DEA, isopropylamine, cyclohexylamine, morpholine, diamines, dimethylaminopropylamine (DMAPA), ethylene diamine, methoxy propylamine (MOPA), dimethylethanol amine, methyldiethanolamine (MDEA) & oligomers, imidazolines of EDA and homologues and higher adducts, imidazolines of aminoethylethanolamine (AEEA), aminoethylpiperazine, aminoethylethanol amine, di-isopropanol amine, DOW AMP-90™, Angus AMP-95, dialkylamines (of methyl, ethyl, isopropyl), mono alkylamines (methyl, ethyl, isopropyl), trialkyl amines (methyl, ethyl, isopropyl), bishydroxyethylethylene diamine (THEED), or the like or mixtures or combinations thereof.

[0069] Suitable additives for Paraffin Removal, Dispersion, and/or paraffin Crystal Distribution include, without limitation: Cellosolves available from DOW Chemicals Company; Cellosolve acetates; Ketones; Acetate and Formate salts and esters; surfactants composed of ethoxylated or propoxylated alcohols, alkyl phenols, and/or amines; methylesters such as coconate, laurate, soyate or other naturally occurring methylesters of fatty acids; sulfonated methylesters such as sulfonated coconate, sulfonated laurate, sulfonated soyate or other sulfonated naturally occurring methylesters of fatty acids; low molecular weight quaternary ammonium chlorides of coconut oils soy oils or C₁₀ to C₂₄ amines or monohalogenated alkyl and aryl chlorides; quanternary ammonium salts composed of disubstituted (e.g., dicoco, etc.) and lower molecular weight halogenated alkyl and/or aryl chlorides; gemini quaternary salts of dialkyl (methyl, ethyl, propyl, mixed, etc.) tertiary amines and dihalogenated ethanes, propanes, etc. or dihalogenated ethers such as dichloroethyl ether (DCEE), or the like; gemini quaternary salts of alkyl amines or amidopropyl amines, such as cocoamidopropyldimethyl, bis quaternary ammonium salts of DCEE; or mixtures or combinations thereof. Suitable alcohols used in preparation of the surfactants include, without limitation, linear or branched alcohols, specially mixtures of alcohols reacted with ethylene oxide, propylene oxide or higher alkyleneoxide, where the resulting surfactants have a range of HLBs. Suitable alkylphenols used in preparation of the surfactants include, without limitation, nonylphenol, decylphenol, dodecylphenol or other alkylphenols where the alkyl group has between about 4 and about 30 carbon atoms. Suitable amines used in preparation of the surfactants include, without limitation, ethylene diamine (EDA), diethylenetriamine (DETA), or other polyamines. Exemplary examples include Quadrols, Tetrols, Pentrols available from BASF. Suitable alkanolamines include, without limitation, monoethanolamine (MEA), diethanolamine (DEA), reactions products of MEA and/or DEA with coconut oils and acids.

[0070] The introduction of water downhole often is accompanied by an increase in the oxygen content of downhole fluids due to oxygen dissolved in the introduced water. Thus, the materials introduced downhole must work in oxygen environments or must work sufficiently well until the oxygen content has been depleted by natural reactions. For system that cannot tolerate oxygen, then oxygen must be removed or controlled in any material introduced downhole. The problem is exacerbated during the winter when the injected materials include winterizers such as water, alcohols, glycols, Cellosolves, formates, acetates, or the like and because oxygen solubility is higher to a range of about 14-15 ppm in very cold water. Oxygen can also increase corrosion and scaling. In CCT (capillary coiled tubing) applications using dilute solutions, the injected solutions result in injecting an oxidizing environment (O₂) into a reducing environment (CO₂, H₂S, organic acids, etc.).

[0071] Options for controlling oxygen content includes: (1) de-aeration of the fluid prior to downhole injection, (2) addition of normal sulfides to product sulfur oxides, but such sulfur oxides can accelerate acid attack on metal surfaces, (3) addition of erythorbates, ascorbates, diethylhydroxyamine or other oxygen reactive compounds that are added to the fluid prior to downhole injection; and (4) addition of corrosion inhibitors or metal passivation agents such as potassium (alkali) salts of esters of glycols, polyhydric alcohol ethyloxylates or other similar corrosion inhibitors. Exemplary examples of oxygen and corrosion inhibiting agents include mixtures of tetramethylene diamines, hexamethylene diamines, 1,2-diaminecyclohexane, amine heads, or reaction products of such amines with partial molar equivalents of aldehydes. Other oxygen control agents include salicylic and benzoic amides of polyamines, used especially in alkaline conditions, short chain acetylene diols or similar compounds, phosphate esters, borate glycerols, urea and thiourea salts of bisoxalidines or other compound that either absorb oxygen, react with oxygen or otherwise reduce or eliminate oxygen.

[0072] Suitable salt inhibitors for use in the fluids of this invention include, without limitation, Na Minus-Nitrilotriacetamide available from Clearwater International, LLC of Houston, Tex.

[0073] Determine whether Strontium Carbonate is an acceptable substitute for Calcium Carbonate. Tests were run to check acid solubility of neat product, flow properties, fluid loss values as compared to standard RDF (1 ppb HP Starch, 25 ppb calcium fine carbonate), and drilling fluid filter cake constructed with product. Basic rheology at 120° F., HTHP at 180° F. and 250° F., API and HTHP cake thicknesses should be checked.

[0074] Determine if the SrCO₃ has any solubility issues with potassium formate, like barite has shown.

[0075] Strontium Carbonate, white powder, supplied by Solvay.

[0076] The sample was characterized as strontium carbonate by XRD as shown in FIG. 1.

[0077] The specific gravity was determined to be 3.7941 by gas pycnometer at 25° C. as shown in FIG. 2.

[0078] The PSD was determined by Mastersizer 2000. D50 is 11.5μ (μm) and D90 is 240μ. It is noticed that the distribution has multiple peaks at 0.5μ, 8μ and 100μ as shown in FIG. 3.

[0079] A neat sample of both SrCO₃ and CaCO₃ were reacted with acetic and hydrochloric acids at room temperature. The acid insoluble solids were separated by centrifuge and weighted after drying. The SrCO₃ was provided by Solvay. The CaCO₃ used was 325-mesh.

[0080] In this experiment, neat SrCO₃ and CaCO₃ samples were tested at two different carbonate to acid ratios: 1:4 and 1:2. The acid insoluble solid in the strontium carbonate sample at the carbonate to acid ratio of 1:4 was determined to be below 0.7 wt. % as tabulated in Table I. The acid insoluble solid in the strontium carbonate sample at the carbonate to acid ratio of 1:4 was determined to be below 0.7 wt. % as tabulated in Table II.

TABLE I
Acid Insoluble - 1:4 Molar Ratios (Carbonate:Acid)
Weighting Agent	HCl (15% wt)	AcOH (10% wt)
SrCO3	0.64%	0.61%
CaCO3	0.54%	1.17%

TABLE II
Acid Insoluble - 1:2 Molar Ratios (Carbonate:Acid)
Amount Insoluble in Grams	HCl (15% wt)	AcOH (20% wt)
SrCO3	3.36%	49.25%
CaCO3	7.81%	17.57%

[0081] The data indicated that at a 1:4 mole ratio of strontium carbonate to acid, strontium carbonate is easier to clean-up than calcium carbonate, while at a strontium carbonate to acid mole ratio of 1:2, strontium carbonate is easier to clean-up in HCl than calcium carbonate, but harder to clean-up in acetic acid. Thus, drilling fluid including strontium carbonate as the weighting agent, will produce filter cakes that are readily dissolvable in acid solutions having a strontium carbonate to acid mole ratio of greater than 1:3, when pumped into a completed well. In certain embodiments, the acid solutions have a strontium carbonate to acid mole ratio of greater than 1:4, when pumped into a completed well.

[0082] Strontium carbonate RDFs having densities between 8.78 ppg to 13.28 ppg incremented by 0.5 ppg were prepared and tested. The rheology, API, HPHT at both 180° F. and 250° F., HPHT filter cake thickness at both temperatures were measured from all samples. The acid solubility in 20% acetic and 18.9% hydrochloric acids were tested as a percent of filter cake residue after acid exposure.

[0083] Tables IIIA&B tabulated the rheological properties of strontium carbonate based RDFs Examples S1, S3, S4, and S6 having densities of 8.78 ppg, 9.78 ppg, 10.28 ppg, and 12.78 ppg, respectively.

TABLE IIIA
SrCO3 RDF Compositions of Examples S1, S3, S4, and S6
	Example
		S1	S3	S4	S6
Constituent	Sp. Gr.	8.78 ppg	9.78 ppg	10.28 ppg	11.28 ppg
Water	1.00	337.00	322.00	314.50	299.50
Sodium	2.69	0.50	0.50	0.50	0.50
Carbonate
Caustic Soda	2.10	0.25	0.25	0.25	0.25
WEL-ZAN D	1.55	1.00	1.00	1.00	1.00
HP Starch	1.50	5.00	5.00	5.00	5.00
(Cargill)
WEL-CARB	2.71	8.00	25.00	8.00	8.00
Strontium	3.80	0.00	57.00	85.50	142.50
Carbonate
Total Mass	351.75	410.75	414.75	456.75
Total Volume	344.24	350.51	344.24	344.24
specific gravity	1.02	1.17	1.20	1.33

TABLE IIIB
Rheological Properties of Examples S1, S3, S4, and S6
	Example
	S1	S3	S4	S6
Hot Rolling (16 hrs)	BHR	AHR	BHR	AHR	BHR	AHR	BHR	AHR
Viscometer Temp	120	120	120	120	120	120	120	120
600 rpm	36	37	50	52	52	54	68	70
300 rpm	26	28	41	38	39	41	53	55
200 rpm	23	25	32	33	34	36	47	48
100 rpm	18	20	24	26	27	29	36	39
6 rpm	7	9	9	11	11	12	15	17
3 rpm	6	7	7	9	10	10	13	14
GELS 10″	6	6	6	8	8	9	12	13
GELS 10′	7	7	8	9	9	10	13	13
APPARENT VISC.	18	19	25	26	26	27	34	35
PLASTC VISC.	10	9	9	14	13	13	15	15
YIELD POINT	16	19	32	24	26	28	38	40
API	5.1	3.6	3.3	3.8
Fluid Loss Temp. (° F.)	180° F.	250° F.	180° F.	250° F.	180° F.	250° F.	180° F.	250° F.
HTHP Fluid Loss	14.4	33	13.4	44	17.2	65	22	91
Cake thicknes (in.)	1/32″	2/32″	1/32″	4/32″	1/32″	6/32″	3/32″	14/32″
pH	11.3	11.6	12.0	11.6
specific gravity (SG)	1.01	1.15	1.23	1.34

[0084] Tables IVA&B tabulated the rheological properties of strontium carbonate based RDFs Examples S7, S9, S11, and S12 having densities of 11.78 ppg, 10.28 ppg, 13.28 ppg, and 10.28 ppg, respectively.

TABLE IVA
SrCO3 RDF Compositions of Examples S7, S9, S11, and S12
	Example
		S7	S9	S11	S12
Constituent	Sp. Gr.	11.78 ppg	10.28 ppg	13.28 ppg	10.28 ppg
Water	1.00	292.00	300.10	269.50	314.50
Sodium	2.69	0.50	0.50	0.50	0.50
Carbonate
Caustic Soda	2.10	0.25	0.25	0.25	0.25
WEL-ZAN D	1.55	1.00	1.00	1.00	1.00
HP Starch	1.50	5.00	5.00	5.00	5.00
(Cargill)
WEL-CARB	2.71	8.00	125.00	25.00	25.00
Strontium	3.80	171.00	0.00	256.50	85.50
Carbonate
Total Mass	477.75	431.85	557.75	431.75
Total Volume	344.24	350.51	350.51	350.51
specific gravity (SG)	1.39	1.23	1.59	1.23

TABLE IVB
Rheological Properties of Examples S7, S9, S11, and S12
	Example
	S7	S9	S11	S12
Hot Rolling (16 hrs)	BHR	AHR	BHR	AHR	BHR	AHR	BHR	AHR
Viscometer Temp (° F.)	120	120	120	120	120	120	120	120
600 rpm	77	77	70	73	119	118	53	56
300 rpm	60	60	56	62	92	91	39	44
200 rpm	52	53	50	57	82	80	36	40
100 rpm	42	43	42	48	65	64	27	31
6 rpm	20	20	19	24	32	32	11	14
3 rpm	17	17	16	22	28	28	9	11
GELS 10″	14	15	16	21	27	27	8	12
GELS 10′	16	16	15	21	33	28	9	32
APPARENT VISC.	39	39	35	37	60	59	27	46
PLASTC VISC.	17	17	14	11	27	27	14	12
YIELD POINT	43	43	42	51	65	64	25	32
API	4.2	4.8	6.5	4.4
Fluid Loss Temp. (° F.)	180° F.	250° F.	180° F.	250° F.	180° F.	250° F.	180° F.	250° F.
HTHP Fluid Loss	30	138	25	34	82	147	47	63
Cake thicknes (in.)	5/32″	19/32″	4/32″	6/32″	18/32″	28/32″	8/32″	12/32″
pH	11.2	12.0	11.7	11.5
specific gravity (SG)	1.43	1.25	1.53	1.21

[0085] Tables VA&B tabulated the fluid compositions and the dissolution data in 18.9% hydrochloric acid. Examples S2, S5, S8, and S10 having densities of 9.28 ppg, 10.78 ppg, 12.28 ppg, and 13.28 ppg, respectively, were chosen to digest in both hydrochloric acid and acetic acid.

TABLE VA
SrCO3 RDF Compositions of Examples S2, S5, S8, and S10
	Example
		S2	S5	S8	S10
Constituent	Sp. Gr.	9.28 ppg	10.78 ppg	12.28 ppg	13.28 ppg
Water	1.00	329.37	306.95	284.50	277.00
Sodium	2.69	0.50	0.50	0.50	0.50
Carbonate
Caustic Soda	2.10	0.25	0.25	0.25	0.25
WEL-ZAN D	1.55	1.00	1.00	1.00	1.00
HP Starch	1.50	5.00	5.00	5.00	5.00
(Cargill)
WEL-CARB	2.71	25.00	25.00	25.00	25.00
Strontium	3.80	29.00	114.20	199.50	228.00
Carbonate
Total Mass	390.12	435.90	515.75	536.75
Total Volume	350.51	344.16	350.51	350.51
specific gravity (SG)	1.11	1.27	1.47	1.53

TABLE VB
Hydrochloric Acid Dissolution Properties of Examples S2, S5, S8, and S10
	Example
	S2	S5	S8	S10
Hot Rolling (16 hrs)	BHR	AHR	BHR	AHR	BHR	AHR	BHR	AHR
Viscometer Temp	120	120	120	120	120	120	120	120
600 rpm	43	46	63	61	88	88	103	111
300 rpm	32	34	44	47	85	68	82	87
200 rpm	28	29	38	41	70	60	71	77
100 rpm	21	23	31	34	59	48	57	61
6 rpm	8	10	13	15	29	23	28	32
3 rpm	7	8	11	12	26	19	25	27
GELS 10″	6	7	10	12	18	19	23	26
GELS 10′	7	8	10	12	18	19	26	27
APPARENT VISC.	22	23	32	31	44	44	52	56
PLASTC VISC.	11	12	19	14	3	20	21	24
YIELD POINT	21	22	25	33	82	48	61	63
API	4.2	3.6	4.9	6.1
Fluid Loss Temp. (° F.)	180° F.	250° F.	180° F.	250° F.	180° F.	250° F.	180° F.	250° F.
HTHP Fluid Loss	14	45	21	66	41	154	110	154
Cake Thickness (in.)	2/32″	4/32″	2/32″	11/32″	6/32″	26/32″	17/32″	24/32″
pH	11.4	11.7	11.9	12.0
18.9% HCl needed	172	394	618	689
Specific Gravity	1.10	1.28	1.49	1.48
HPHT filter temp @ 4 hr	B (g)	A (g)	B (g)	A (g)	B (g)	A (g)	B (g)	A (g)
180° F.-RT	5.79	0.0176	7.65	0.0093	14.5	0.0051	44.38	0.0815
180° F.-120° F.	5.84	0.0215	6.75	0.0356	15.73	0.003	39.42	0.0663
250° F.-RT	10.96	0.0129	26.32	0.0371	48.73	0.073	62.01	0.1752
250° F.-120° F.	9.81	0.0311	20.65	0.027	59.34	0.0798	63.53	0.1803
180° F.-RT	0.30%	0.12%	0.04%	0.18%
180° F.-120° F.	0.37%	0.53%	0.02%	0.17%
250° F.-RT	0.12%	0.14%	0.15%	0.28%
250° F.-120° F.	0.32%	0.13%	0.13%	0.28%

[0086] Tables VIA&B and table is dissolution in 20% acetic acid. Examples S2, S5, S8, and S10 having densities of 9.28 ppg, 10.78 ppg, 12.28 ppg, and 13.28 ppg, respectively. The one cell below in the 12.78 ppg mud had a much larger fluid loss than expected; this was most likely due to a temperature fluctuation while heating the cell.

TABLE VIA
SrCO3 RDF Compositions of Examples S2, S5, S8, and S10
	Example
		S2	S5	S8	S10
Constituents	Sp. Gr.	9.28 ppg	10.78 ppg	12.28 ppg	13.28 ppg
Water	1.00	329.37	306.95	284.50	277.00
Sodium	2.69	0.50	0.50	0.50	0.50
Carbonate
Caustic Soda	2.10	0.25	0.25	0.25	0.25
WEL-ZAN D	1.55	1.00	1.00	1.00	1.00
HP Starch	1.50	5.00	5.00	5.00	5.00
(Cargill)
WEL-CARB	2.71	25.00	25.00	25.00	25.00
Strontium	3.80	29.00	114.20	199.50	228.00
Carbonate
Total Mass	390.12	452.90	515.75	536.75
Total Volume	350.51	350.51	350.51	350.51
Sp. Gr. Calc.	1.11	1.29	1.47	1.53

TABLE VIB
Acetic Acid Dissolution Properties of Examples S2, S5, S8, and S10
	Example
	S2	S5	S8	S10
Hot Rolling (16 hrs)	BHR	AHR	BHR	AHR	BHR	AHR	BHR	AHR
Viscometer Temp	120	120	120	120	120	120	120	120
600 rpm	45	47	59	62	90	93	103	108
300 rpm	35	36	46	49	70	72	79	83
200 rpm	30	32	40	44	61	64	68	72
100 rpm	22	25	32	36	48	52	55	58
6 rpm	9	10	13	16	22	24	28	28
3 rpm	7	8	11	13	19	25	24	25
GELS 10″	7	8	10	13	17	21	23	25
GELS 10′	8	8	10	13	20	21	26	26
APPARENT VISC.	23	24	30	31	45	47	52	54
PLASTC VISC.	10	11	13	13	20	21	24	25
YIELD POINT	25	25	33	36	50	51	55	58
API	4.2	3.6	4.9	6.1
Fluid Loss Temp. (° F.)	180° F.	250° F.	180° F.	250° F.	180° F.	250° F.	180° F.	250° F.
HTHP Fluid Loss	12	52	18	82	27	144	38	140
Cake Thickness (in.)	2/32″	7/32″	6/32″	13/32″	9/32″	23/32″	10/32″	26/32″
pH	11.4	11.7	11.9	12.0
20% AcOH needed	268 g	571 g	961 g	1078 g
Specific Gravity	1.10	1.29	1.47	1.48
HPHT filter temp @ 4 hr	B (g)	A (g)	B (g)	A (g)	B (g)	A (g)	B (g)	A (g)
180° F.-RT	3.62	3.5189	4.99	4.0160	13.2	0.7052	12.01	0.2961
180° F.-120° F.	6.21	1.6244	6.66	0.9357	21.69	0.7102	24.6	0.1299
250° F.-RT	12.92	1.9801	13.78	5.3126	52.13		94.08	4.3985
250° F.-120° F.	15.77	1.6576	21.23	2.7310	59.19		54.37	1.7487
180° F.-RT	97.21%	80.48%	5.34%	2.47%
180° F.-120° F.	26.16%	14.05%	3.27%	0.53%
250° F.-RT	15.33%	38.55%		4.68%
250° F.-120° F.	10.51%	12.86%		3.22%

[0087] The CaCO₃ used in the formulations was 325-mesh ExCal CW CaCO₃ except the 10.28 ppg fluid, which used 50:50 blends of 325-mesh ExCal CW CaCO₃ and 200-mesh ExCal CaCO₃. From the TDS of these two carbonates it shows that the 200-mesh has 1.3% impurity of SiO₂, whereas the 325-mesh contains <0.01% SiO₂. This may be the cause of the greater insolubility of the carbonate in the purely CaCO₃ RDF compared with the 10.28 ppg SrCO₃ RDF. The results are shown in the following tables.

[0088] Two RDFs, both at 10.28 ppg, one using only CaCO₃ and the other using only SrCO₃ as the weighting agent were compared.

[0089] A strontium carbonate RDF and a calcium carbonate RDF having the density of 10.28 ppg were produced to compare the rheology and acid solubility properties. As one can see, the fluid loss is much greater in the formulation with SrCO₃; however, the rheology is slightly lower and the acid solubility is much greater. The high fluid loss may due to the PSD of strontium carbonate. The results of the tests are tabulated in Table VIIA&B.

TABLE VIIA
Comparison of SrCO3 RDF Example S13 and
CaCO3 RDF Comparative Example C1 at 10.28 ppg
	Examples
			S13	C1
	Constituent	Sp. Gr.	10.28 ppg	10.28 ppg
	Water	1.00	314.50	300.10
	Sodium Carbonate	2.69	0.50	0.50
	Caustic Soda	2.10	0.25	0.25
	WEL-ZAN D	1.55	1.00	1.00
	HP Starch (Cargill)	1.50	5.00	5.00
	WEL-CARB	2.71	25.00	125.00
	Strontium Carbonate	3.80	85.50	0.00
	Calcium Carbonate	2.70	0.00	85.50
	Total Mass		431.75	431.85
	Total Volume		350.51	350.51
	specific gravity		1.23	1.23

TABLE VIIB
Rheological Properties Strontium Carbonate
RDF v. Calcium Carbonate RDF
	Example
	S13	C1
	Sp. Gr.
	10.28 ppg	10.28 ppg
Hot Rolling (16 hrs)	BHR	AHR	BHR	AHR
Viscometer Temp	120	120	120	120
600 rpm	54	64	71	74
300 rpm	41	52	58	62
200 rpm	35	40	51	57
100 rpm	28	32	42	50
6 rpm	11	14	20	24
3 rpm	9	11	17	23
GELS 10″	8	11	16	23
GELS 10′	9	11	16	23
APPARENT VISC.	27	32	36	37
PLASTC VISC.	13	12	13	12
YIELD POINT	28	40	45	50
API	3.8	4.3
Fluid Loss Temp. (° F.)	180° F.	250° F.	180° F.	250° F.
HTHP Fluid Loss	16	86	16.8	34
Cake thickness (in.)	2/32″	12/32″	3/32″	6/32″
pH	11.5	11.4
specific gravity	1.23	1.23
15% HCl Acid	403 g	607.5 g
HPHT filter temp @ 4 hr	Insolubles
180° F.-RT	1.47%	9.79%
180° F.-120° F.	2.30%	13.54%
250° F.-RT	0.25%	8.47%
250° F.-120° F.	2.40%	7.27%

[0090] A sample of SrCO₃ sample used in the studies were analyzed to determine pore volume using helium gas as the probe gas. An 8.1723 g sample of the SrCO₃ was analyzed in helium gas at a temperature of 25.72° C. The equilibration rate as set at 0.005 psig/min. The sample was placed in a cell having a volume of 11.7000 cm³. The cell was purged five times with helium and the cell volume has expanded 8.4764 cm³. The data from each cycle is tabulated in Table VIII.

TABLE VIII
Total Pore Volume Determination of SrCO3
					Total Pore
	Pressure 1	Pressure 2	Volume	Density	Volume
Cycle#	(psig)	(psig)	(cm3)	(g/cm3)	(cm3/g)
1	19.636	10.402	2.1520	3.7975	0.7367
2	19.627	10.396	2.1529	3.7959	0.7366
3	19.654	10.410	2.1537	3.7945	0.7365
4	19.647	10.406	2.1551	3.7921	0.7363
5	19.618	10.390	2.1561	3.7902	0.7362
	Summary
	Data	Average	Standard Deviation
	Volume	2.1540 cm3	0.0015 cm3
	Density	3.7941 g/cm3	0.0026 g/cm3
	6202- Total solids concentration is Invalid; liquid density is greater-than or equal to solids density.

[0091] Referring now to FIG. 3, the particle size distribution (PSD) of the SrCO₃ sample was analyzed from 0.01μ to 3000μ. The particular SrCO₃ material used in these studies had a poly-modal distribution including a first mode of particles having particle between about 0.1μ and 1μ, a second mode of particles between about 1μ and about 30μ, a third mode of particles between about 30μ and about 250μ, and a fourth mode of particles between about 250μ and about 1000μ. The SrCO₃ sample had most of its particles of size within the second and third modes. The inventors believe that for bridging application, the SrCO₃ particles should have a single modal distribution.

[0092] Tables IXA&B list compositional data and rheological data for Examples S14 and S15 and Comparative Examples C2 and C3, where the compositions have different particle size distributions.

TABLE IXA
Comparison of SrCO3 RDF Examples S14 and S15 and CaCO3 RDF Comparative
Examples C2 and C3 with Different Particle Size Distributions
	Example		Example
Constituent	SG	S14	S15	Constituent	SG	C2	C3
Water	1.00	321.10	321.10	Water	1.00	311.47	311.47
Soda Ash	2.69	0.50	0.50	Soda Ash	2.69	0.50	0.50
Caustic Soda	2.10	0.25	0.25	Caustic Soda	2.10	0.25	0.25
WEL-ZAN XG	1.55	1.00	1.00	WEL-ZAN XG	1.55	1.00	1.00
WEL-STAR HP	1.50	6.00	6.00	WEL-STAR HP	1.50	6.00	6.00
SrCO3 2 μm	3.80	36.40	9.10	CaCO3 2 μm	2.71	36.40	9.10
SrCO3 10 μm	3.80	36.40	63.70	CaCO3 10 μm	2.71	36.40	63.70
SrCO3 20 μm	3.80	18.20	13.65	CaCO3 20 μm	2.71	18.20	13.65
SrCO3 50 μm	3.80	0.0	4.55	CaCO3 50 μm	2.71	0.0	4.55
Biocide*	1.06	0.25	0.25	Biocide*	1.06	0.25	0.25
Disk size	10 μm	20 μm	Disk size	10 μm	20 μm
Total Mass	419.85	419.85	Total Mass	410.22	410.22
Total Volume	350.00	350.00	Total Volume	350.00	350.00
Sp. Gr. Calc.	1.20	1.20	Sp. Gr. Calc.	1.17	1.17
ppg	10.0	10.0	ppg	9.78	9.78

TABLE IXB
Rheological Properties of Examples S14 and S15 and Comparative Examples C2 and C3
	Example		Example
	S14	S15		C2	C3
Constituent	RPM	BHR	AHR	BHR	AHR	Constituent	RPM	BHR	AHR	BHR	AHR
Soda Ash	600	56	58	58	60	Soda Ash	600	75	51	72	51
DF-00257	300	42	44	45	46	DF-00257	300	67	39	63	39
Caustic Soda	200	37	38	40	40	Caustic Soda	200	64	35	58	33
DF-00264	100	30	29	31	32	DF-00264	100	56	28	49	27
WEL-ZAN XG	6	10	12	12	13	WEL-ZAN XG	6	32	12	25	11
DF-01036	3	9	9	10	10	DF-01036	3	28	9	22	9
WEL-STAR HP	PV	14	14	13	14	WEL-STAR HP	PV	8	12	9	12
DF-00486	YP	28	30	32	32	DF-00486	YP	59	27	54	27
SrCO3 2 μm	10″	9	9	9	10	CaCO3 2 μm	10″	32	8	20	8
DF-00506	10′	10	9	10	10	DF-00740	10′	29	9	21	9
SrCO3 10 μm	4 hr FL	20*2 = 40	22*2 = 44	CaCO310 μm	4 hr FL	28*2 = 56	36*2 = 72

[0093] These first fluids were run side by side against calcium carbonate. Although the fluid loss was far from ideal this is a good comparison of the two different bridging materials. Also, notice the difference in low-end rheology, plastic viscosity, and yield points between the strontium carbonate compared to the calcium carbonate.

[0094] Tables XA&B list compositional data and rheological data for Examples S16 and S17 and Comparative Examples C4 and C5, where the compositions have different particle size distributions.

TABLE XA
Comparison of SrCO3 RDF Examples S16 and S17 and CaCO3 RDF Comparative
Examples C4 and C5 with Different Particle Size Distributions
	Example		Example
Constituent	SG	S16	S17	Constituent	SG	C4	C5
Water	1.00	320.87	320.87	Water	1.00	311.24	311.24
Soda Ash	2.69	0.50	0.50	Soda Ash	2.69	0.50	0.50
Caustic Soda	2.10	0.25	0.25	Caustic Soda	2.10	0.25	0.25
WEL-ZAN XG	1.55	1.00	1.00	WEL-ZAN XG	1.55	1.00	1.00
WEL-STAR HP	1.50	6.00	6.00	WEL-STAR HP	1.50	6.00	6.00
SrCO3 2 μm	3.80	38.00	15.00	CaCO3 2 μm	2.71	38.00	38.00
SrCO3 10 μm	3.80	37.00	60.00	CaCO3 10 μm	2.71	37.00	37.00
SrCO3 20 μm	3.80	16.00	16.00	CaCO3 20 μm	2.71	16.00	16.00
SrCO3 50 μm	3.80	0.0	9.00	CaCO3 20 μm	2.71	0.0	0.0
Biocide*	1.06	0.25	0.25	Biocide*	1.06	0.25	0.25
Disk size	10 μm	20 um	Disk size	10 μm	20 μm
Total Mass	419.87	419.87	Total Mass	410.24	410.22
Total Volume	350.00	350.00	Total Volume	350.00	350.00
Sp. Gr. Calc.	1.20	1.20	Sp. Gr. Calc.	1.17	1.17
ppg	10.0	10.2	ppg	9.78	9.78

TABLE XB
Rheological Properties of Examples S16 and S17 and Comparative Examples C4 and C5
	Example		Example
	S16	S17		C4	C5
Constituent	RPM	BHR	AHR	BHR	AHR	Constituent	RPM	BHR	AHR	BHR	AHR
Soda Ash	600	56	62	56	58	Soda Ash	600	80	60	82	58
DF-00257	300	43	47	43	47	DF-00257	300	74	55	76	47
Caustic Soda	200	37	41	37	42	Caustic Soda	200	69	52	70	43
DF-00264	100	28	32	28	34	DF-00264	100	61	44	62	36
WEL-ZAN XG	6	11	13	10	13	WEL-ZAN XG	6	38	23	38	18
DF-01036	3	9	10	8	9	DF-01036	3	35	20	35	16
WEL-STAR HP	PV	13	15	13	11	WEL-STAR HP	PV	6	5	6	11
DF-00486	YP	30	32	30	36	DF-00486	YP	68	50	70	36
SrCO3 2 μm	10″	9	10	8	9	CaCO3 2 μm	10″	38	14	34	15
DF-00506	10′	11	11	9	11	DF-00740	10′	35	3	34	14
SrCO3 10 μm	4 hr FL	21*2 = 42	20*2 = 40	CaCO3 10 μm	4 hr FL	22*2 = 44	27*2 = 54
DF-00505				DF-00743

[0095] After using a new starch the calcium carbonate shows a better fluid loss, its bridging ability, still does not compare with that of strontium carbonate.

[0096] Tables XIA&B list compositional data and rheological data for Examples S18 and S19 and Comparative Examples C6 and C7, where the compositions have different particle size distributions.

TABLE XIA
Comparison of SrCO3 RDF Examples S18 and S19 and CaCO3 RDF Comparative
Examples C6 and C7 with Different Particle Size Distributions
	Example		Example
Constituent	SG	S18	S19	Constituent	SG	C6	C7
Water	1.00	321.10	321.10	Water	1.00	311.47	311.47
Soda Ash	2.69	0.50	0.50	Soda Ash	2.69	0.50	0.50
Caustic Soda	2.10	0.25	0.25	Caustic Soda	2.10	0.25	0.25
WEL-ZAN XG	1.55	1.00	1.00	WEL-ZAN XG	1.55	1.00	1.00
WEL-STAR HP	1.50	6.00	6.00	WEL-STAR HP	1.50	6.00	6.00
SrCO3 2 μm	3.80	11.00	5.00	CaCO3 2 μm	2.71	11.00	5.00
SrCO3 10 μm	3.80	52.00	20.00	CaCO3 10 μm	2.71	52.00	20.00
SrCO3 20 μm	3.80	23.00	55.00	CaCO3 20 μm	2.71	23.00	55.00
SrCO3 50 μm	3.80	5.00	11.00	CaCO3 50 μm	2.71	5.00	11.00
Biocide*	1.06	0.25	0.25	Biocide*	1.06	0.25	0.25
Disk size	40 μm	50 μm	Disk size	40 μm	50 μm
Total Mass	419.85	419.85	Total Mass	410.22	410.22
Total Volume	350.00	350.00	Total Volume	350.00	350.00
Sp. Gr. Calc.	1.20	1.20	Sp. Gr. Calc.	1.17	1.17
ppg	10.0	10.0	ppg	9.78	9.78

TABLE XIB
Rheological Properties of Examples S18 and S19 and Comparative Examples C6 and C7
	Example		Example
	S18	S19		C6	C7
Constituent	RPM	BHR	AHR	BHR	AHR	Constituent	RPM	BHR	AHR	BHR	AHR
Soda Ash	600	65	55	62	55	Soda Ash	600	67	56	69	58
DF-00257	300	51	42	51	43	DF-00257	300	62	44	57	46
Caustic Soda	200	43	37	40	37	Caustic Soda	200	59	38	53	41
DF-00264	100	33	30	30	30	DF-00264	100	51	32	45	34
WEL-ZAN XG	6	13	12	11	12	WEL-ZAN XG	6	27	14	22	16
DF-01036	3	10	9	9	10	DF-01036	3	23	12	19	13
WEL-STAR HP	PV	14	13	11	12	WEL-STAR HP	PV	5	12	12	12
DF-00486	YP	37	29	40	31	DF-00486	YP	57	32	45	34
SrCO3 2 μm	10″	9	8	9	9	CaCO3 2 μm	10″	20	11	18	12
DF-01059	10′	11	9	10	10	DF-00740	10′	15	11	18	12
SrCO3 10 μm	spurt	3	11	CaCO3 10 μm	spurt	1	1
DF-00505	30 min	10	18	DF-00743	30 min	10	9
SrCO3 20 μm	1 hr			CaCO3 20 μm	1 hr
DF-01060	2 hr			DF-00742	2 hr
SrCO3 50 μm	3 hr			CaCO3 50 μm	3 hr
DF-01057	4 hr	21.5	32	DF-00750	4 hr	26.5	32
Biocide	Total	40	53	Biocide	Total	52	63

[0097] This run is the last comparison of the strontium carbonate with calcium carbonate. The strontium carbonate once again outperforms the calcium carbonate for the same ceramic disk size. Also, make not in the difference in rheologies before and after hot-rolling of the two different types of formulations, strontium and calcium.

[0098] These first three batches of formulations were made mainly for comparison, but also seeking out the perfect combination of sizes. Sizes were eventually found and tested for fluid loss. These are listed below.

[0099] Tables XIIA&B list compositional data and rheological data for Examples S20, S21, S22 and S23, where the compositions have different particle size distributions.

TABLE XIIA
SrCO3 Examples S20, S21, S22 and S23 Having
Different Particle Size Distributions
	Example
Constituent	SG	S20	S21	S22	S23
Water	1.00	321.10	321.10	321.10	321.10
Soda Ash	2.69	0.50	0.50	0.50	0.50
Caustic Soda	2.10	0.25	0.25	0.25	0.25
WEL-ZAN XG	1.55	1.00	1.00	1.00	1.00
WEL-STAR HP	1.50	6.00	6.00	6.00	6.00
SrCO3 2 μm	3.80	15.00	20.00	20.00	25.00
SrCO3 10 μm	3.80	31.00	26.00	30.00	26.00
SrCO3 20 μm	3.80	30.00	25.00	21.00	20.00
SrCO3 50 μm	3.80	15.00	20.00	20.00	20.00
Biocide*	1.06	0.25	0.25	0.25	0.25
Disk Size	40 μm	40 μm	40 μm	40 μm
Total Mass	419.85	419.85	419.85	419.85
Total Volume	350.00	350.00	350.00	350.00
Sp. Gr. Calc.	1.20	1.20	1.20	1.20
ppg	10.0	10.0	10.0	10.0

TABLE XIIB
Rheological Properties of Examples S20, S21, S22 and S23
	Example
	S20	S21	S22	S23
Constituent	RPM	BHR	AHR	BHR	AHR	BHR	AHR	BHR	AHR
Soda Ash	600	55	60	59	60	60	63	61	62
DF-00257	300	42	48	45	47	46	49	47	49
Caustic Soda	200	35	41	39	41	40	43	40	43
DF-00264	100	28	33	31	33	32	35	32	35
WEL-ZAN XG	6	9	15	13	15	13	15	13	15
DF-01036	3	8	12	11	13	11	12	11	13
WEL-STAR HP	PV	13	12	14	13	14	14	14	13
DF-00486	YP	29	36	31	34	32	35	33	36
SrCO3 2 μm	10″	8	11	9	12	9	13	10	12
DF-01059	10′	8	12	10	12	10	12	11	13
SrCO3 10 μm	spurt	0	0	0	0
DF-01058	30 min	3	1	2	2
SrCO3 20 μm	1 hr	6	4	5	5
DF-01060	2 hr	9	7.5	7.5	7.5
SrCO3 50 μm	3 hr	12	10	10.5	10.5
DF-01057	4 hr	14	12.5	12.5	13
BIOCIDE	Total	28	25	25	26

[0100] Tables XIIIA&B list compositional data and rheological data for Examples S24, S25, S26 and S27, where the compositions have different particle size distributions.

TABLE XIIIA
SrCO3 Examples S24, S25, S26 and S27 Having
Different Particle Size Distributions
	Example
Constituent	SG	S24	S25	S26	S27
Water	1.00	321.10	321.10	321.10	321.10
SodaAsh	2.69	0.50	0.50	0.50	0.50
CausticSoda	2.10	0.25	0.25	0.25	0.25
WEL-ZAN XG	1.55	1.00	1.00	1.00	1.00
WEL-STAR HP	1.50	6.00	6.00	6.00	6.00
SrCO3 2 μm	3.80	30.00	26.00	20.00	15.00
SrCO3 10 μm	3.80	26.00	25.00	25.00	26.00
SrCO3 20 μm	3.80	20.00	20.00	26.00	25.00
SrCO3 50 μm	3.80	15.00	20.00	20.00	25.00
Biocide*	1.06	0.25	0.25	0.25	0.25
Disk Size	20 μm	20 μm	20 μm	20 μm
	419.85	419.85	419.85	419.85
Total Volume	350.00	350.00	350.00	350.00
Sp. Gr. Calc.	1.20	1.20	1.20	1.20
ppg	10.0	10.0	10.0	10.0

TABLE XIIIB
Rheological Properties of Examples S24, S25, S26 and S27
	Example
	S24	S25	S26	S27
Constituent	RPM	BHR	AHR	BHR	AHR	BHR	AHR	BHR	AHR
Soda Ash	600
DF-00257	300
Caustic Soda	200
DF-00264	100
WEL-ZAN XG	6
DF-01036	3
WEL-STAR HP	PV
DF-00486	YP
SrCO3 2 μm	10″
DF-01059	10′
SrCO3 10 μm	spurt	10	13	0	0
DF-01058	30 min	15	17	1	0
SrCO3 20 μm	1 hr	Fluids	Failed
DF-01060	2 hr
SrCO3 50 μm	3 hr			9.5	7.5
DF01057	4 hr			11	9.5
BIOCIDE	Total	−10	−13	22	19

[0101] Due to the high fluid loss of the first two fluids, S24 and S25, the runs were stopped. The fluid lost was mostly white, which is due to the high content of strontium carbonate at 2 μm. The 2 μm particles merely seeped through the ceramic disks. The rheologies are in the range for which we need for these for these fluids in every run as of yet and thus will not be checked in these runs.

[0102] Before the fluid loss test is run a blank run is tested on the ceramic filter disk to check the time taken for 200 mL of 3% KCl to permeate through the disk after being saturated in 3% KCl for 30 minutes under negative pressure. Each ceramic disk will have a different permeability time, thus an average permeability time will be used with a percent error. After the fluid loss tests were run acid breaker is run four hours at 100 psi, followed by the final return permeability test. Each strontium carbonate filter cake dissolved faster than those with calcium carbonate. Also, 100% return permeability has been observed after breaker cleanup, however the minimum will be observed to be greater than 70%. The ceramic disks run with strontium carbonate have once again exceeded those run with calcium carbonate in terms of return permeability time.

[0103] All references cited herein are incorporated by reference. Although the invention has been disclosed with reference to its preferred embodiments, from reading this description those of skill in the art may appreciate changes and modification that may be made which do not depart from the scope and spirit of the invention as described above and claimed hereafter.