Research on the Damage Mechanism and Reservoir Protection Drilling Fluid System of Jurassic Reservoir in Zhenbei Oilfield

Low permeability oil and gas reservoirs have become increasingly prominent in China's oil and gas exploration and development and are an important area for reserve growth, and the Yanchang formation in the Ordos Basin is a low-permeability reservoir that contains abundant oil and gas resources. Jurassic reservoirs are widely distributed in the Ordos Basin, and the proportion of reservoir production has been increasing year by year. In this study, the mechanism of drilling fluid damage in Jurassic reservoirs was revealed through the analysis of physical parameters, rock characteristics, pore structure, and sensitivity. As a result, the reservoir properties are mainly intergranular pores and dissolution pores, with low displacement pressure, low porosity, and high permeability, and the overall physical properties are good. When foreign solid and liquid phases invade, it is easy to cause throat particle migration, leading to pore blockage and serious reservoir damage. Secondly, through the optimization of oil soluble temporary plugging agents and filter loss reducing agents, combined with experimental methods such as particle size analysis and scanning electron microscopy, a drilling fluid system for Jurassic reservoir protection in Zhenbei Oilfield was obtained, which includes temporary plugging agent G325 and self-degradable filter loss reducing agent. The medium pressure water loss of the drilling fluid system is 4.5 mL, with an average sealing rate of 71.06% and an average core permeability recovery rate of 97.80%. overall, the drilling fluid has excellent sealing performance and reservoir protection performance.