Experimental Study on Water-based Drilling Fluid for Horizontal Drilling of the Shuijingtuo Shale Formation in West Hubei

A high performance water base drilling fluid was required to drill the well EYIYE-1 from which a high flow rate of shale gas was obtained. This well penetrated the Shuijingtuo formation of the Cambrian system. A series of laboratory work has been conducted to formulate an appropriate drilling fluid for the designed shale gas drilling. An outcrop of the Shuijingtuo shale formation, obtained from Zigui County, Hubei Province, was analyzed with XRD and SEM methods. Mud additives, such as clay, salts, nanomaterials, filter loss reducer, MMH and surfactants were selected through experiments. A high performance water base drilling fluid, SWDF, was formulated based on electric inhibition and wettability control. The SWDF drilling fluid was evaluated for its rheology, filtration property, lubricity, high temperature stability, shale inhibitive capacity and contamination resistance. It was found that 1) the Shuijingtuo shale formation is mainly composed of quartz, feldspar, and calcite etc.; the total amount of these brittle minerals accounts for 55%-67% of the shale sample. Illite is the main component of the clay minerals, which accounts for 13%-27% of the total clay. The shale formation contains no montmorillonite, and is therefore a weak-swelling formation. 2) the shale formation is developed with pores and micro-fissures which provided channels to drilling fluid invasion. 3) the SWDF drilling fluid has appropriate viscosity and gel strength, API filter loss of only 7.2 mL and friction coefficient of 0.21. SWDF is resistant to high temperature of 120 ℃, and shows good inhibitive capacity to shale hydration and high resistance to salt, calcium and formation clay (drilled cuttings) contamination; it is therefore suitable for use in drilling the horizontal Shuijingtuo shale formation in west Hubei area.