Evaluation Method of Shale Water-Based Drilling Fluid Plugging Based on «Thick Mud Cake» Simulation

The preparation of true shale cores is limited by the characteristics of shale formations, such as the development of bedding and micro-fractures, poor cementation, and fragility. Artificial cores cannot meet the requirements of shale at the nanometer scale and are not representative. Existing plugging evaluation methods have problems such as cumbersome steps, long time consumption, and low evaluation accuracy. Therefore, this paper proposes a shale plugging evaluation method based on the simulation of “thick mud cakes”. This method analyzes the effects of factors such as bentonite dosage, type and dosage of treatment agent, barite content and particle size distribution on mud cake parameters through approximation experiments, establishes a standard slurry formula for “thick mud cakes”, and prepares a standard “thick mud cake” with a thickness of 10.03 mm and a permeability of 4.79·10 -4 mD to evaluate the plugging effect by the reduction rate of permeability. Based on this method, four plugging agents were selected and combined to obtain the best compound plugging agent. The drilling fluid system plugging evaluation was carried out on both the standard “thick mud cake” and thin mud cake, and the microscopic plugging mechanism of shale was analyzed. The results show that this method is simple to operate, has good reproducibility and high accuracy in plugging evaluation results, and has strong application potential.