Drilling Fluids Containing an Admixture of Polyethoxylated, Sulfurized Fatty Acids and Polyalkylene Glycols

This invention relates to aqueous drilling fluids. More particularly, this invention relates to aqueous drilling fluids having incorporated therein a minor amount of an admixture of a polyethoxylated sulfurized fatty acid and a polyalkylene glycol as hereinafter more fully described. In another embodiment this invention is directed to an improved drilling operation employing the modified drilling fluids described above.

In a drilling operation, such as in a rotary drilling operation, a drilling fluid is forced down the drill string, about the drill bit at the bottom of the borehole and then back up to the surface. The drilling fluid employed in such a drilling operation usually is an aqueous drilling fluid and is compounded of various materials in order to impart certain desirable physical and chemical properties to the drilling fluid. For example, there is usually incorporated in an aqueous drilling fluid a hydratable clayey material, such as a bentonite clay, to impart desirable viscosity and gel strength properties to the drilling fluid so as to better enable the drilling fluid to carry away the drilling cuttings from the bottom of the borehole. Other materials such as weighting agents, e.g., barium sulfate, are employed to increase the density of the drilling fluid so as to make the drilling operation more effective and safer by overcoming the fluid pressure within the formation being drilled. Other materials such as water loss improving agents, e.g., carboxymethylcellulose, hydrolyzed starch, etc. are added to reduce the loss of fluid from the drilling fluid into the formation during the drilling operation. Still other materials such as corrosion inhibitors, bactericides and drill bit lubricants are incorporated in the drilling fluid in order to improve the drilling operation and the drilling fluid.

Although a wide variety of aqueous drilling fluids containing materials designed to increase the lubricity of these fluids have been proposed and used in the field, all of these modified drilling fluids suffer from one or more disadvantages.

In accordance with this invention an improved aqueous drilling fluid is provided by incorporating therein a minor amount of a water soluble or water dispersible admixture of a polyethoxylated sulfurized fatty acid and a polyalkylene glycol as hereinafter defined.

As used in the specification and in the accompanying claims, the expression "an admixture of a water soluble polyethoxylated sulfurized fatty acid and a polyalkylene glycol" refers to

(1) An unsaturated fatty acid containing from about 14 to 18 carbon atoms therein such as myristoleic, the various hexadecenoic acids including palmitoleic, the various octadecenoic acids including oleic, elaidic, isoleic, linoleic, linolenic, elaeostearic, ricinoleic and the like; and

(2) Wherein the polyethoxy content of each unsaturated fatty acid can vary from about 10 to about 13 moles of ethylene oxide, preferably between 10 and 12 thereof, per mole of the unsaturated fatty acid moiety; and

(3) Wherein the sulfur content of the unsaturated fatty acid can vary from about 2 to about 6% by weight, based on the weight of the unsaturated fatty acid with the polyethylene oxide units and preferably about 3-5% by weight,

A water soluble polyalkylene glycol having an average molecular weight in the range of from about 300 to about 1200, preferably between about 400 and 1000, preferably a polyethylene glycol.

A drilling fluid of this invention may be prepared by the addition of a water soluble polyethoxylated sulfurized fatty and a polyalkylene glycol described above to an aqueous drilling fluid or to an aqueous drilling fluid containing a clay dispersed therein.

Polyethoxylated fatty acid precursors of the sulfurized water soluble fatty acid component of the admixture of the present invention are available commercially from Emergy Industries Inc., Cincinnati, Ohio under the trade designations Emerest 2646, 2647 and 2648. Sulfurization of the water soluble polyethoxylated fatty acid precursor was accomplished by known methods such as by heating the precursor to a temperature in the range of from about 150.degree.-200.degree. C. and adding thereto slowly the requisite amount of elemental sulfur and maintaining the resulting heated admixture for two hours followed by a cooling period to let the sulfurized product reach room temperature. This product was used.

The polyalkylene glycol component of the admixture is used in a weight ratio of from about 2 up to about 4 parts per part of the sulfurized polyethoxylated fatty acid component. In general it has been found necessary to maintain the glycol-fatty acid ratio at 2 or more parts by weight of the glycol per part by weight of the fatty acid component so as to maintain the rheology of the drilling fluid within acceptable limits.

The amount of the admixture of the water soluble polyethoxylated sulfurized fatty acid and polyalkylene glycol added to the well drilling of the invention is a minor but sufficient amount to substantially increase the lubricity of the said drilling fluid as measured, for example, by torque reduction. The amount to be added to the well drilling fluid is in the range of from about 0.5 to about 5 pounds thereof, per barrel of drilling fluid, preferably from about 1 to about 2 pounds per barrel.

It has been found that the drilling fluids containing the novel additives of the present invention exhibit a high degree of lubricity with little or no abnormal distortion of mud properties. Moreover the drilling fluids do not generate an abnormal amount of foam, so that any foaming can be controlled by the use of conventional defoamers which are compatible with drilling fluid systems. The drilling fluids containing the novel additives of this invention show tolerance and stability over wide ranges in pH and electrolyte concentrations and they perform satisfactorily in the various mud systems (i.e. drilling fluid systems) in general use today, e.g., low pH, salt water, as well as nondispersed and inhibitive mud systems.

An aqueous drilling fluid, the Base Mud in the following Tables, was prepared using a top hole mud from the West Cote Blanche Bay Field, St. Mary Parish, La., which was treated with 6 pounds per barrel of the ferrochrome lignosulfonate dispersant "Q-Broxin", its pH raised to about 9.5 with caustic, and aged overnigh at 150.degree. F. before use.

There was added thereto varying amounts of the admixture of the water soluble polyethoxylated sulfurized fatty acid and the polyalkylene glycol. The physical properties of the resultant drilling fluids in terms of lubricity and drilling fluid rheology were measured using a lubricity tester.

A machine was designed to simulate borehole conditions. The torque on a steel shaft rotating in a formation type core in the presence of a circulating drilling fluid was measured.

The torque produced by dry friction is considered to be linearly dependent on the normal force independent of velocity area, and fluid properties such as plastic viscosity and yield point.

Viscous friction is caused by viscous drag of the shaft rotating in the circulating mud system. This type of drag is proportional to the surface area; and depends upon velocity, and film thickness which together can be considered as the velocity gradient; and depends on fluid properties such as plastic viscosity and yield point. Viscous drag is dependent on the normal force only in an indirect manner through its effect on the film thickness. That is, increasing the normal force decreases the film thickness which in turn increases the velocity gradient thus increasing the required torque.

The major components of the test machine consist of a steel shaft turned by a cradle mounted motor with a Zero-Max (0-800 rpm) speed control, and a swivel mounted core. The motor was arranged so torque readings could be taken on a spring scale attached to the end of a lever arm.

The core is mounted on a bracket which pivots about a stationary point on one end. A cable is attached to the other end of the bracket. This cable runs over a pulley and weights are hung on the end. From a balance of moments and forces, the load on the pulley or applied load can be related to the load on the shaft or the normal force holding the shaft and core in contact.

To torque-load relation for the laboratory machine is linear. Thus the dry friction model adequately described the process under consideration, and the change of the coefficient of friction between the base mud and the treated mud runs gives an indication of the effectiveness of the additive under consideration.

The results obtained are reported as % Reduction in Torque.

The results were recorded and are summarized in the following tables.

The data presented in Table I above show that ethoxylated fatty acids alone (Examples 1, 2, 9 and 10) are ineffective as lubricity additives or (Ex. 2) less than 10% effective, as measured by the % reduction in torque.

The data obtained with sulfurized ethoxylated fatty acids (Examples 4-8) indicate some improvement in lubricity but concomitantly the rheology of the drilling fluids have been substantially impaired. These data indicate the sulfurized ethoxylated fatty acid materials are likewise unsatisfactory as lubricity additives. The data in the Table further show the criticality of the ethylene oxide content of the fatty acid, both unsulfurized and sulfurized (Examples 9-16) using the 14 mole ethylene oxide oleic acid material Emerest 2660, resulted in little or no beneficial effects in terms of lubricity or satisfactory rheology properties, except for Example 14.

The data in Table II above show that satisfactory lubricity values and drilling fluid rheology are obtained by the novel additive admixtures of the present invention. In all instances, except for Examples 17, 21, 25 and 29, the drilling fluid rheology was within acceptable limits in terms of Plastic Viscosity and Yield Point values and the lubricity properties obtained were good, ranging from 19% to 31.5% reduction in torque (Examples 18, 22, 26 and 30).