Shale-gas plays and other unconventional resources have gained significant importance worldwide. Historically, synthetic-base drilling fluids (SBM) are used in these plays when no environmental concerns are in place and are preferred when wellbore stability is necessary. In this paper, we study the use of an improved water-base drilling fluid (WBM) that is simple in formulation and maintenance that shows excellent rheological properties, maintains wellbore stability, and a good environmental profile. A combination of well-known and economically affordable materials is combined with new technology to achieve desired rheological properties and wellbore stability. The use of nanoparticles to decrease shale permeability by physically plugging nanoscale pores holds the potential to remove a major hurdle in confidently applying water-base drilling fluids in shale formations, adding a new advantage to the studied fluid. Silica nanomaterials were investigated for this purpose. Due to their commercial availability, these materials can be engineered to meet the specifications of the formation. Characterization of the nanoparticles was completed with Transmission Electron Microscopy (TEM), dynamic light scattering, and X-ray photoelectron spectroscopy. Rheological properties and fluid loss are studied together with other important properties such as shale stability and anti-accretion properties. The authors will describe new laboratory methods used to investigate these properties, from a modified API fluid loss test to the Shale Membrane Test that measures both fluid loss and plugging effects and illustrate additional future research that includes adding reactive species, and anchoring them to the pores, thus stabilizing the shale further.

SPE Members Abstract New applications of structurally unique organic cationic materials (OCMs) have provided a highly efficient and economical technology for inhibiting the swelling and yielding of hydratable shales. These OCMs are compatible with all common drilling fluid additives, thermally stable, and environmentally acceptable. The laboratory determined properties and field tests of the OCMs are discussed in detail. Introduction For a variety of reasons, including economics, convenience, and logistics, it has always been desirable to drill with water-based muds whenever possible. However, drilling in certain environments, particularly in water-sensitive shale formations, with water-based muds has often been difficult to impossible, and has often been very costly. When water-sensitive shales are exposed to aqueous fluids, they adsorb water, which results in swelling and/or disintegration of the shale. Typical drilling problems which result from these phenomena are bit balling, high torque and drag, and stuck pipe. Historically, because water-based muds sufficiently inhibitive to eliminate or minimize the hydration of these shales have not been available, the only alternative for drilling such sensitive formations has been oil-based muds. Although more expensive than water-based muds, oil-based muds are very effective in controlling water-sensitive shales and generally allow trouble-free drilling through these difficult formations, thereby ameliorating the higher cost. Over the past several years, environmental regulations and concerns have increasingly restricted the use of oil based muds worldwide, making them a much less attractive alternative than before. These increasing environmental demands have resulted in greatly intensified interest in the development of highly inhibitive water-based drilling fluid systems, with the eventual goal of replacing oil-based muds. The drilling fluid industry's search for inhibitive waterbased mud systems has been a continuous endeavor for some time. Many approaches have been taken over the years, including the use of: calcium treated muds, such as lime and gypsum muds; relatively high concentrations of inorganic salts, such as NaCl, KCl and CaCl2 modified asphalts and gilsonites; a variety of polymeric additives, such as the functionally anionic PACs and PHPAs, functionally cationic polymers such as polyquaternary amines, amphoteric polymers (which exhibit both anionic and cationic characteristics) such as polyamino acids, and nonionic polymers such as polyols, glycerols, glucosides, polyvinyl alcohols (PVA), and HECs. However, even these approaches have not been completely successful in inhibiting the hydration of highly reactive water-sensitive shales and alleviating the resulting problems. Additionally, the usage of many of these materials is increasingly restricted for environmental reasons. P. 623

No abstract

Ultrahigh-temperature/ultrahigh-pressure (uHT/uHP) conditions have a different definition, depending on the region, the operator, and the service company. In this paper, the definition used for uHT/uHP fluid performance is that the fluid be able to perform above 500 F and 30,000 psi. This paper describes the development of innovative drilling fluids that are specific to these well conditions.When bottomhole temperatures exceed 400 F, the design and engineering of drilling fluids can be challenging. Drilling fluids that destabilize can cause a variety of fluid-control problems that could lead to drilling and completion issues. With invert-emulsion fluids, the major challenges encountered with these conditions are related to the thermal degradation of the emulsifier and wetting package that can lead to gelation and syneresis. Another challenge is fluid loss that is related to the emulsion stability and to the degradation of the fluid-loss-control additives. Finally, efficient control of the rheological properties-critical to the success of any well-also can be challenging when effects from emulsion instability, filtration-control degradation, and rheology-control-additive degradation are coupled with increases in drilled solids, rapidly leading to rheological instability. This can manifest itself as high-fluctuating rheologies and gelation or the loss of rheological properties that can give rise to sag of weight material, both potentially leading to associated well-control problems.The paper describes the development of the new fluid system designed for such uHT/uHP environments (highlighting the chemical differences) and compares the test data of the system with more-conventional high-temperature/high-pressure (HT/HP) invert-emulsion fluids. Data are presented that show the stability and performance of the new fluid with extended exposure to temperature >500 F, demonstrating a tolerance to various contaminations and showing the rheological behavior and stability to 600 F and 40,000 psi.

Ultra high temperature, high pressure (uHTHP) conditions have a different definition depending on the region and the operator and Service Company. In this paper the definition used for uHTHP fluid performance is that of a fluid able to perform above 500°F and 30,000 psi. This paper describes the development of innovative drilling fluids specific to these well conditions. When bottomhole temperatures exceed 400°F, the design and engineering of drilling fluids can be challenging. Drilling fluids that destabilize can cause a variety of fluid control problems that could lead to drilling and completion issues. With Invert emulsion fluids, the major challenges encountered under these conditions are related to the thermal degradation of the emulsifier and wetting package that can lead to gelation and syneresis. Another challenge is fluid loss which is related to the emulsion stability and to the degradation of the fluid loss control additives. Finally, efficient control over the rheological properties – critical to the success of any well - can also be challenging, where effects from emulsion instability, filtration control degradation and rheology control additive degradation are coupled with increases in drilled solids, rapidly leading to rheological instability. This can manifest itself as high fluctuating rheologies and gelation, or loss of rheological properties that can give rise to sag of weight material, both potentially leading to associated well control problems. The paper describes the development of the new fluid system designed for such uHTHP environments, highlighting the chemical differences and compares the test data of the system with more conventional HTHP invert emulsion fluids. Data is presented showing the stability and performance of the new fluid over extended exposure to temperature >500°F, demonstrating tolerance to various contaminations and showing the rheological behavior and stability to 600°F and 40,000 psi.