New Chemical Package Produces an Improved Shale Inhibitive Water-Based Drilling Fluid System

Abstract

Abstract Quantitative shale stability performance data based on a new testing procedure (Dynamic Pellet Test or DPT) were used to quantitatively rank the shale stability performance of over 30 chemical species. Shale stability performance of over 3500 aqueous solutions or muds on over 20 different shale or clay samples was done. The test results allowed the following four conclusions about shale stability induced by inorganic and polymeric chemicals to be drawn:inorganics alone are inadequate,potassium ion is significantly better than any other cation in shale stability performance,hydrogen bonding polymers are most effective and,high molecular weight polymers (up to the limit of solubility) are most effective. From the results of this work, a particularly effective shale stabilizing additive package for aqueous muds was identified. The exceptional shale stabilizing performance of these chemical structures is based on a chemical synergism uncovered through DPT testing. Typical drilling fluid formulations and their laboratory properties will be discussed, including tests conducted on a heated/pressurized flow loop. Introduction During well drilling procedures, formations are frequently encountered which lose physical integrity when exposed to aqueous drilling fluids. In almost all cases these are uncemented or young shales. Prior to the introduction of oil-based muds, great difficulty was encountered in drilling through these types of shales. The first use of oil drilling fluids is obscure (1), however early patent activity dates from 1919 (2). In spite of this early use of oil muds, their application was mainly restricted to coring and release of stuck pipe until emulsion muds were introduced in 1950 (3). These emulsion and invert emulsion muds made drilling through problem shales possible, but the hydrocarbons they contained posed safety and environmental hazards. In the 1970's, significant efforts to develop low toxicity and low flammability muds have been made by replacing the diesel and crude oils with refined oils that were less toxic to aquatic life, in large part due to the lower aromatic content of the refined oils (3a, 3b). However, in spite of the advances in this technology, oil muds still have several disadvantages;oil muds are significantly more expensive than many water-based muds,oil muds interfere with some well logging procedures,oil muds are combustible,even low toxicity oil-based muds have some adverse environmental effects. The use of modern water-based inhibitive muds began with the observation that potassium ion retarded the disintegration of problem shales. These observations, made by Nowak and Krueger and others (4-7) between 1950-1970, led the way to the currently used inhibitive water-based muds (8-9). The reported use of these more recent water-based inhibitive muds beginning about 1969 (8), made use of polymers and potassium ion. P. 341^