Well Treatment Pellets

1. Field of the Invention

The present invention is broadly concerned with solid, high specific gravity, low solubility well treatment composites used for oil and gas well treatments. More particularly, the composites of the invention have a high melting point, thus eliminating the problem of ambient air melting, are sufficiently dense so as to readily sink in typical well fluids, and have a low solubility that generates a slow release of the composite ingredients into the well fluid. The composites of the invention preferably comprise a nonylphenol ethoxylate and a fatty acid amide, and also further include a weighting agent such as barium sulfate or sodium chloride, and active ingredients selected from the group consisting of corrosion inhibitors, scale inhibitors, bactericides, scale converters, foaming agents, and mixtures thereof.

2. Description of the Prior Art

Oil wells require the periodic addition of treatment agents, such as scale and corrosion inhibitors, in order to facilitate smooth, trouble-free operations. Such agents are often in liquid form, and are commonly added into the annular space between the well sidewall and the internal well casing. Well operators use a number of expedients for such additions, such as introduction through a side arm flush associated with the well fluid removal system. Because conventional treating agents tend to float on the well fluid, it is a common practice to add excess well fluid after addition of the treatment agent in order to drive the agent downwardly to a subterranean level adjacent the lower end of the well casing. As can be appreciated, this practice largely or completely shuts down well production, and it is not uncommon to thereby lose an entire day's production during the treatment process.

The foregoing difficulty is particularly acute in the case of low fluid wells having a relatively low static fluid level, in that relatively large amounts of fluid must be added atop the agent in order to drive the agent down to an operative level. However, the problem can also be significant in high fluid wells, because of the need to drive the active chemical downwardly through relatively long columns of fluid. Indeed, it is sometimes impossible in such situations to drive the chemical down far enough into the well formation, and the chemical may be significantly diluted before it reaches the downhole pump.

Weighted treatment agents have been used in the past in an effort to overcome this problem. These materials are in fluid form, but include glycerine or molasses in order to give the fluid a higher specific gravity. Unfortunately, this tends to be an expensive process, and such weighting agents have a tendency to adhere to the outside of the well tubing and casing.

Solid composites have also been utilized to provide a method for downhole treatment. For example, mold inhibitors such as the commercial product Iconol NP-100 Pastille FD (a nonylphenol ethoxylate available from BASF Corp.) have been mixed with active ingredients (such as corrosion inhibitors or bactericides) and formed into pellets. The melting point of NP-100 is approximately 69.degree. C. However, when the active ingredients are added to NP-100 and the mixture is formed into pellets, the melting point of the entire pellet composite is only about 54.degree. C. This results in pellets which melt easily in hot weather and dissolve quickly downhole.

The present invention overcomes the problems noted above, and provides solid well treatment composites having a specific gravity greater than typical well fluids, thus causing the composites to sink in well fluids. Furthermore, the composites of the invention do not melt in ambient air during hot weather and dissolve slowly over the course of several weeks after downhole placement, depending on the downhole conditions.

More particularly, the composites of the invention comprise a nonylphenol ethoxylate having at least about 50 moles, and preferably from about 50-150 moles of ethylene oxide per mole of nonylphenol, and a fatty acid amide. The nonylphenol ethoxylate component should be present in the composites at a level of from about 20 to about 75%, preferably from about 25 to about 60%, and more preferably from about 30 to about 50% by weight, based on the total weight of the composite. A particularly preferred nonylphenol ethoxylate having about 100 moles of ethylene oxide per mole of nonylphenol is available from BASF under the tradename Iconol NP-100 Pastille FD.

The fatty acid amide should be present in the composites at a level of from about 20 to about 75%, preferably from about 25 to about 60%, and more preferably from about 30 to about 50% by weight based on the total weight of the composite. The preferred fatty acid amides are those having 16-20 carbon atoms, with fatty acid amides having 18 carbon atoms being particularly preferred. One particularly preferred 18 carbon atom fatty acid amide is oleamide (an unsaturated fatty monoamide derived from oleic acid and having the formula cis-CH.sub.3 (CH.sub.2).sub.7 CH:CH(CH.sub.2).sub.7 CONH.sub.2). Oleamide is commercially available under the tradename KEMAMIDE.RTM. from the Humko Chemical Division of the Witco Corp. in Memphis, Tenn.

In the composites of the invention, the ratio of nonylphenol ethoxylate:fatty acid amide should be from about 1:3 to 3:1, preferably from about 0.5:1 to 1.2:1, and more preferably about 1:1.

In one embodiment, the composites further include active ingredients selected from the group consisting of corrosion inhibitors, scale inhibitors, bactericides, scale converters, foaming agents, and mixtures thereof. While the concentration of each active ingredient can be altered as desired, the total concentration of all active ingredients should be from about 10 to about 50% by weight, preferably from about 20 to about 40% by weight, and more preferably from about 28 to about 30% by weight based on the total weight of the composite.

While any corrosion inhibitor known in the art is suitable with the composites of the invention, particularly preferred corrosion inhibitors include tallow diamine ethoxylates (such as Pluradyne.RTM. Cl 1010 from BASF), imidazolines (such as Pluradyne.RTM. Cl 1019 from BASF), and tallow-1,3-propylene diamines (such as Adogen.RTM. 570 S from Sherex Chemical Co. in Dublin, Ohio). Any bactericide known in the art will work with the composites of the invention, but preferred bactericides include coco diamines (such as Adogen.RTM. 580 from Sherex Chemical Co.) and 3-alkoxy(12-15)-2-hydroxy-N-propyltrimethyl ammonium chloride (available under the name WWT 1902C from JACAM Chemical Partners, Ltd., Sterling, Kans.). The preferred scale inhibitors of the composites include polyacrylates, phosphate esters such as WSI 3400 (JACAM Chemical Partners, Ltd.), and organic phosphonates such as Unihib 106 (LONZA, Inc., Fair Lawn, N.J.), Unihib 305LC (LONZA, Inc.), and Unihib 905 (LONZA, Inc.). These organic phosphonates can also function as a corrosion inhibitor as discussed above.

In another embodiment, the composites further include a weighting agent such as powdered NaCl or barium sulfate. One preferred barium sulfate weighting agent is BAROID.RTM. available from NL Baroid/NL Industries, Inc. in Houston, Tex. The weighting agent should be present in the composites at a concentration of from about 5 to about 35%, preferably from about 10 to about 30%, and more preferably from about 13 to about 17% by weight based on the total weight of the composite.

The composites in accordance with the invention have a specific gravity of at least about 1.16, preferably about 1.19-1.35, and more preferably about 1.2-1.3. It will be appreciated that because the specific gravity of the composites is greater than that of the well fluid, the composites will readily sink into the well fluid to a level adjacent or below the lower end of the well casing. Furthermore, the mixture of a nonylphenol ethoxylate and a fatty acid amide unexpectedly provides a well treatment pellet with an increased melting point. Particularly, the composites have a melting point of at least about 75.degree. C., preferably at least about 78.degree. C., and more preferably at least about 88.degree. C. in order to prevent the composites from melting in hot weather. The composites dissolve in approximately 2-4 weeks, depending on the downhole temperature, rather than dissolving in 4-24 hours as is the case with currently available well agent treatments. Finally, the composites are preferably formed into pellets wherein the largest surface dimension of the pellets average from about 75 to about 750 mm, and more preferably from about 100 to about 500 mm.

The composites are formed by mixing a quantity of melted nonylphenol ethoxylate with a quantity of melted fatty acid amide in the concentration ranges and ratios previously described. Alternately, the two solid compounds can be mixed together and the resulting mixture can be melted by heating to about 88-95.degree. C. The desired active ingredients (corrosion inhibitors, scale inhibitors, bactericides, scale converters, foaming agents, and mixtures thereof) are then added to the melted mixture followed by stirring for approximately 15 minutes. The chosen active ingredients and their concentrations can be varied depending on the condition of the well to be treated. However, the total concentration of all active ingredients should be such that it falls within the ranges set forth above.

After mixing, the desired weighting agent should be added to the mixture followed by further mixing until a substantially homogeneous mixture is obtained. The hot material is then poured into a belt mold or ball mold and allowed to cool, forming pellets of the desired size and shape. The finished pelleted composites can then be used immediately or packaged for later use.

Any known method of introducing a treatment agent into a well is suitable for treating wells using the composites of the invention. Advantageously, the most preferred introduction method is simply dropping the composites into the well fluid. Because they have a specific gravity of at least about 1.16, the composites readily sink into the well fluid and slowly dissolve over the course of several weeks.

The following examples illustrate preferred aspects of the present invention. It is to be understood, however, that these examples are presented by way of illustration only, and nothing therein should be taken as a limitation upon the overall scope of the invention.

One hundred pounds of Iconol NP-100 Pastille FD (a nonylphenol ethoxylate having about 100 moles of ethylene oxide per mole of nonylphenol, available from BASF) was melted by heating to about 75.degree. C. Likewise, 100 pounds of KEMAMIDE.RTM. (available from Witco Corp., Humko Chemical Division, Memphis, Tenn.) was melted by heating to about 85.degree. C. The two melted compounds were mixed together, and the following compounds were added to the mixture:

The resulting mixture was mixed for 15 minutes followed by the addition of 45 pounds of BAROID.RTM. (barium sulfate weighting material). Mixing was continued until a substantially homogeneous dispersion was obtained. The hot material was then poured into belt molds where it was cooled. The resulting pellets were removed from the molds and packaged. Tests conducted on the final product showed that the pellets had a specific gravity of 1.3 and a melting point of 70-74.degree. C.

One hundred pounds of Iconol NP-100 Pastille FD was mixed with 100 pounds of KEMAMIDE.RTM.. The mixture of two solids was melted by heating to about 85.degree. C. To the melted mixture, the following compounds were added:

The resulting mixture was mixed for 15 minutes followed by the addition of 45 pounds of BAROID.RTM.. Mixing was continued until a substantially homogeneous dispersion was obtained. The hot material was then poured into belt molds where it was cooled. The resulting pellets were removed from the molds and packaged. Tests conducted on the final product showed that the pellets had a specific gravity of 1.3 and a melting point of 68-72.degree. C.