BACKGROUND OF THE INVENTION Drilling mud is used in the sinking of boreholes including deep boreholes sunk in the search for hydrocarbons. The drilling mud lubricates the drill pipe and acts as a carrier for excavated drill cuttings. The drilling mud is pumped down the drill pipe through nozzles in the drill bit at the bottom of the borehole and up the annulus between the drill pipe and the borehole wall. Drilled cuttings generated by the drill bit are transported by the drilling mud to the surface of the borehole where they are separated from the drilling mud and discarded. The drilling mud may then be cleaned and re-used.

In addition to its function as a carrier for cuttings, a drilling mud operates to lubricate the drill pipe and bit as well as the wall of the borehole, thereby reducing torque, overpull, and wear as well as the sticking of the drill pipe in the borehole.

The drilling mud further provides a hydrostatic balance with the geological structure being drilled thereby minimizing the possibility of cave-ins and keeping high pressure hydrocarbons from entering the borehole before a casing is run.

The drilling mud additionally forms an impermeable membrane on the borehole to prevent the liquid phase in the drilling fluid from migrating to the geological formation, causing clays and shales to swell. In addition, the drilling mud acts to cool the drill bit and other high pressure wear areas. The drilling mud should possess a suitable viscosity so as to suspend the drill cuttings when the drilling mud pumps are stopped. To enhance these functions, the drilling mud may incorporate additives such as hydrocarbon oil lubricants and polymers for controlling flow characteristics of the drilling mud.

A satisfactory drilling mud should be chemically inert, non-toxic, and nonpolluting. Oil based muds are known to have superior lubricating qualities to water based muds, but generally have unacceptable toxicity and pollution levels.

In recognition of this fact, U. S. Patent No. 5,401,719 discloses a drilling mud which excludes components that are harmful to the environment. The drilling mud additive of the aforementioned patent further improved the lubricating qualities of water based drilling muds to approach those of oil based products.

However, this prior art system suffers from various deficiencies. Although the lubrication of the disclosed additive improved upon that of prior water based additives, it is still desirable to improve the lubricating and water repellent properties of the additive.

A further difficulty of pre-existing systems, including that of the aforementioned U. S. patent, is the necessity of continuous operator monitoring.

Continuous monitoring has been necessary because previous systems have been insufficiently water repellent to coat the formation thereby preventing chemical reaction. The possibility of the occurrence of a chemical reaction renders continuous operator monitoring necessary.

SUMMARY OF THE INVENTION It is accordingly an object of the invention to provide a chemically inert, non-polluting, nontoxic mud system.

It is a further object of the invention to provide a mud system having improved lubricating and water repellent properties.

It is still a further object of the invention to provide a mud system which eliminates the need for continuous operator monitoring of drilling operations.

To achieve the foregoing objects, and in accordance with the purpose of the invention as embodied and broadly described herein, there is provided a mud system that comprises a water based fluid and water repellent particles interspersed in the water based fluid. The water repellent particles comprise a combination of graphite, a silicate material, a silicone material, and processed wax treated with polyglycol. The system coats a geological formation such that it is sealed from the drilling fluid.

In yet another aspect, a method of the invention comprises the steps of providing a drilling fluid, combining an additive with the drilling fluid, and allowing the drilling fluid and the additive to fill and level contact areas, thereby reducing

torque values. The additive comprises water repellent particles interspersed in the drilling fluid, the water repellent particles comprising a combination of graphite, a silicate material, a silicone material, and processed wax treated with polyglycol.

These and other objects and advantages of the preferred embodiments will become apparent through the detailed description of the invention and its preferred embodiments.

DETAILED DESCRIPTION According to an embodiment of the invention, a drilling fluid is provided which is preferably water-based in order to minimize polluting effects. The water- based drilling fluid of this embodiment includes weighting minerals to increase fluid density and viscosifiers to enhance viscosity. Suitable weighting materials include, but should not be limited to barite, calcium carbonate, ferrous oxide, and hematite. Suitable viscosifers include biodegradable environmentally friendly materials including, but not limited to carboxy methyl cellulose (CMC) and polyanionic cellulose (PAC) polymers. An additive is combined with the drilling fluid in order to enhance water repellency and minimize surface tension. The additive is preferably chemically inert and exhibits low surface tension characteristics of approximately 20 Dynes/cm2. All components of the additive are chemically inert, non toxic, and nonpolluting.

In a preferred embodiment, the additive includes natural graphite, a silicate material, a silicone material, and a processed wax treated with polyglycol. The graphite component is preferably 100% natural crystalline flake graphite having a particle size of less than 25 microns. However, synthetic and/or amorphous graphite can also be used. The silicate material components falls within the micaceous mineral group and may include koalinite or phlogophite and preferably has a particle size smaller than 15 microns and more preferably less than one micron. The processed wax is a non sticky, brittle waxy solid treated with a polyglycol. The processed wax exhibits pliable and coating properties. When the graphite is impregnated with the processed wax, the combined materials act as an initial binding to metal to form a thin pliable film on the metal components in

the borehole. The silicone component is a dimethyl polysiloxane based emulsion listed in the Merek Index as symethycone, and is also known as PMDS. The dimethyl polysiloxane enhances the water repellency or hydrophobic nature of the impregnated graphite and silicate particles. When dispersed in a drilling fluid, these particles increase surface tension between the predominately water wet surface in the borehole. Surfaces with a difference in surface tension tend to repel each other, thereby enhancing lubrication. Furthermore, when the particles are dispersed in the fluid, the fluid forms a membrane that coats the geological formation to seal it from the drilling fluid and prevent formation reaction.

The graphite and silicate particles combined may constitute between 70% to 80%, and preferably about 75% of the mass of the additive. The PMDS composition may be up to 22% of the mass and the processed wax may range from 1 % to 3% of the mass of the additive. The specific gravity of the additive is preferably between 1.6 and 2.0 kg/dm3. The pH of the additive is preferably between 8.0 and 8.5 (10% by weight in water).

The above-described additive composition is a powder type lubricant that is added to the above-described drilling fluid. Lubrication is effected by filling, dressing and leveling action, thereby separating the opposing contact surfaces, increasing the actual load bearing area, and thereby decreasing the actual load.

Reduced load values result in lower friction and torque values or simultaneously protecting the opposing surfaces. As opposed to a liquid type lubricant, powder type lubricants fill and level uneven surfaces to increase the load bearing area and lower the load per unit area. The pliable particles of the above-described additives have an affinity for metal and coat metal surfaces forming a thin layer.

As the particles of the additive have a very low surface tension, the difference in surface tension of the thin layer between the drill string and borehole improves lubrication and consequently minimizes rotary torque and friction.

Additionally, the above-described powder type lubricant is stable in temperatures in excess of 500 °F, whereas liquid type lubricants generally are not. Furthermore, the additive lowers the high temperature/high pressure filtrate values in any drilling fluid and has an effect on long term filtration rates and

minimizing filtrate invasion. The additive further has a direct reduction effect on seepage losses.

A further benefit of the above-described additive is the stabilization of rheological properties. This stabilization leads to greater hole cleaning efficiency.

Water based drilling fluids and in particular viscous fluids or salt containing fluids are susceptible to air entrapment. The surface area of the dispersed air forms an emulsion that contracts and expands with changes in pressure and temperature.

This fluctuation in rheology and density is undesirable and is minimized by the additive described above.

Additionally, the above described additive has a strong defoaming action and maximizes air and gas breakout. The additive minimizes the viscosifying effect of the entrapped air and stabilizes the viscosity after the entrapped air is removed. Due the above described release of air and gases and the coating ability of the additive, the corrosion rate of the metal surfaces is very low. Due to reduction in surface tension, the invention imparts an effective defoaming action thereby ensuring air and gas removal. This action ensures a de-serated drilling fluid and protects polymeric additives from being damaged by high temperature oxygen degradation. The additive further helps to extend the temperature stability of the polymers by providing improved heat transmission and transfer medium, thereby increasing the temperature range of polymers.

The adhesive properties of the additive causes it to coat and smear the entire surface of the casing and drill string and to establish a presence throughout the borehole wall thereby minimizing downhole frictional forces. The filling and coating action of the additive creates smoother surfaces and thereby reduces wear between surfaces and the borehole. The smoother surfaces additionally cause a reduction in torque and drag and eliminate previously existing downhole vibrations and shock. The smoother surfaces further reduce wear on the drill string and the drilling tools and bit, thereby reducing premature metal and seal failures. By preventing borehole problems as described above, the system optimizes logging operations and cementing operations.

Because the particles of the additive are predominantly water repellent and create a water repellent film that coats clay type material in the well bore, the

additive assists in physical inhibition. The particles of the additive are forced into pores or microfractors in the clay by differential pressure and downhole dynamics. This process forms a seal and reduces fluid invasion into the clay formation. The particles of the additive thereby stabilize mechanically troublesome shales.

With regard to drilled solids, the coating effect of the additive reduces dispersion of the solid and the drilling fluid. Furthermore, the drilled solids are firmer and in better physical condition due to the reduction in degradation caused by the protective coating. The improved condition of the drill solids allows more accurate visual analysis and evaluation by geologists.

Additionally, the above described additive has positive effects oh drilling equipment. Due to the coating effect of the water repellent particles, membranes also known as thin filter cakes eliminate pipe sticking tendencies. Due to lubrication properties, the additive enhances conditions for gaining maximum performance from directional tools and drill string design. The lubrication effect further protects tools and reduces premature failures of steering, measuring, and telemetric downhole tools.

The low surface tension of the particles of the additive creates several additional positive effects. First, the particle cause reduction or elimination of bit and bottom hole assembly balling between metal and drilled claimed minerals.

Thus, the time for tripping, logging, and casing run operations is shortened.

Additionally, diamond and PDC bits can be used because of the surface tension effect with optimum performance comfortable to that in oil based muds. The low surface tension further insures maximum lift-off and reduces formation damage and clean up time.

The non-polluting, environmentally friendly, and chemically inert properties provide great advantages over oil based mud systems. Legislation governing the use of hydrocarbon based drilling fluids increases the demand for the development of such a product. Because the particles of the additives are totally chemically inert, they are not absorbed into the food chain or any form of aquatic life. The system is extremely low or totally free of hydrocarbon content. In particular, the additive has less than 25 ppm residual.

The system described above also maximizes the usage of available drilling horsepower. In the case of offshore drilling operation from existing platforms, it provides the operator with far more options to reach reserves of hydrocarbon previously unreachable. The fluid system further gives the operators both land and offshore, the option to utilize smaller drilling package design that can alter the economics of bringing hydrocarbon reserve into production. Finally, the drilling fluid can be used without any chemistry knowledge or chemical additive management.

It will be apparent to those skilled in the art that various modifications and variations can be made in the system and method of the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided that they come within the scope of the appended claims and their equivalents.