Research Into Lubricity, Formation Damage Promises to Expand Applications for Silicate Drilling Fluids

Abstract

Abstract Silicate drilling fluids have been used for more than 60 years. While the early versions of silicate-base systems proved very inhibitive, controlling mud properties was difficult because proper polymer additives were not available for maintaining rheology and fluid loss control. Furthermore, the solids control equipment available at the time was ineffective in removing solids. During the last decade, silicate-base systems have been re-engineered to provide a state-of-the-art and environmentally acceptable, water-base system that provides the inhibition approaching that of an invert emulsion field. The proposed mechanism of inhibition is the surface adsorption and chemical reaction of the silicate polymer with the formation surface. This "coating" effectively provides a thin pressure and chemical barrier on the surface of the wellbore. This formation/silicate interaction has raised a number of concerns regarding both the lubricity and the formation damage potential of the fluid. This paper investigates systematically both the lubrication characteristics of the fluid and the effect of silicate-base systems on formation production and evaluation. The results show promise in expanding the application of silicates as reservoir drill-in fluids and in the drilling of critical high-angle wells where lubricity is a primary design criterion. The data obtained in this study utilizes purpose-built lubricity and formation damage equipment to critically look at the problems. From this investigation the authors will reveal that the coefficient of friction of silicate fluids, as observed in the laboratory and measured in the field, does not differ significantly from that of other water-base fluids. Furthermore, the thin physical and chemical barrier formed during the reaction of the silicate polymer with the formation surface prevents fluids and fine particles from migrating into the formation, thereby minimizing damage to the producing zone. Introduction Silicate-based drilling fluids are probably the most misunderstood systems in the industry. Since the introduction of sodium silicate fluids in the the 1930's, silicate chemistry has demonstrated outstanding shale and formation inhibition characteristics. However, rheology and filtration properties had been difficult to control. Over the past few years, the development of modern polymer technology provided fluid design tools that proved effective in controlling both the rheological and filtration properties of silicate systems. Complementing advanced polymer technology was the design of new solids control and process technology that made silicate-base products effective well-bore stabilizing agents. Improvement in inhibition not only contributes to wellbore stability but also to minimizing dilution volumes, minimizing costs. The low dilution rates and toxicity of the system also provide an excellent fluid with minimal environment impact. In the 1980's, Wingrave's research on shale stability found that silicates, used in conjunction with the potassium ion and specific polymers, combined for an effective shale-stabilizing package.1 During the last decade the industry has effectively used sodium silicate in conventional polymer fluid formulations to provide an effective water-base shale stabilizing system.2,3,4,5 High-performance polymers and efficient solids removal equipment can now provide the required fluid performance and maintenance necessary for efficient and cost-effective silicate chemistry. Furthermore, its capacity to provide inhibition competitive with invert emulsion fluids makes silicate systems an ideal alternative for optimum wellbore stability, without the environmental limitations of an invert emulsion fluid.