Oil-Based Drilling Fluid Technology for High Pressure Brine Layer in Kuqa Piedmont of the Tarim Oilfield

High friction and stuck pipe have been persistent problems when drilling through the deep gypsum-salt layer of the Tarim piedmont structure. What has been observed is that invasion of high-pressure brine deteriorates the properties of high-density drilling fluid, resulting in those characteristic downhole complexities such as friction and sticking. Generally, the measure of drainage pressure relief is used to reduce the pressure of high pressure brine lens, but that poses higher requirement on the brine invasion resistance of oil-based drilling fluids. To solve the problem, a single-chain multi-cluster new emulsifier was developed to improve the emulsification efficiency by increasing the number of hydrophilic groups in the molecular structure of emulsifier, hence improving the brine invasion capacity limit of oil-based drilling fluids. The results of laboratory evaluation show that the density of oil-based drilling fluid system formed by this new emulsifier can be as high as 2.85 kg/L, the resistance to brine pollution is over 60%, and has good high-temperature stability. The oil-based drilling fluid technology applied in several ultra-deep wells drilling (including Well Keshen 1101). During the treatment, the properties of oil-based drilling fluid were stable, there was no pipe string stucking or other accidents caused by drilling fluids. Studies suggest that this oil-based drilling fluid system has good rheology, sedimentation stability and brine pollution resistance. It can handle mud contamination in the massive gypsum-salt layer or high-pressure brine formation of deep wells, and can be promoted and applied in the Kuqa piedmont drilling of the Tarim Oilfield.