| abstract |
The present invention provides a modified liquid phase drilling fluid having desirable properties of shale swelling inhibition, lubrication, and high temperature performance. The fluid does not rely on the incorporation of inorganic salts or high molecular weight water soluble polymers for control of shale swelling or shale disintegration and exhibits performance characteristics, approaching those of oil base drilling fluids, without the objectionable properties of hydrocarbon oils or its potential hazardous impact on the environment. The fluid is comprised of the following: (1) a liquid phase containing: (a) a water phase comprising fresh water, seawater, brine, simulated brine, or mixtures thereof; and (b) a water-soluble component selected from the class consisting of polyhydric alcohols, glycol, glycol ethers, polypropylene glycols, polyethylene glycols, ethylene oxide-propylene oxide copolymers ("EO-PO"), alcohol-initiated EO-PO copolymers and/or mixtures thereof, the ratio of said water-soluble component in the total liquid phase being from about 5% to about 50% by volume; (2) a viscosifier for suspension of solids in said liquid phase; and (3) a filtration control agent. The fluid with the water soluble component will exhibit a lubricity coefficient lower than that for substantially the same fluid without the water soluble component as determined by the American Petroleum Institute's "Procedure for Determination of Lubricity Coefficient (Tentative)" (1980), and the linear swelling on a reconstituted "gumbo" shale inserted for about 60 minutes of said drilling fluid being from lower than that for substantially the same fluid without the water soluble component, as measured by the "Swelling Test", "Rigsite Shale Evaluation Techniques for Control of Shale-related Wellbore Instability Problems", SPE/IADC Paper No. 16054, pages 52-53, (1987). |