New Method for Evaluating Filtration and Mud Cake Building Performance of Drilling Fluid for Shale Drilling

To satisfy the need for filtration control performance test with dense low permeability media, a test required for shale gas drilling, a simulated low permeability mud cake formed in shale formation has recently been prepared using barite of millimicron in particle size and commercial barite as solid particle materials, and laboratory high-speed mixer and HTHP filter press as experiment equipment. The permeability of the mud cake was gradually reduced by improving the dispersing stability of the millimicron barite and adjusting the mass ratio of the two barites. The final formulation for making the mud cake was as follows:1,000 mL water + 100 g millimicron barite + 10 g polyacrylamide + 50 g sodium polyacrylate + 200 g commercial barite + 7 g plugging agent. The mud cake made with this formulation had average thickness of 2.24 mm, and average permeability of 1.42×10^-7 D. The process of making the mud cake had good stability and repeatability. Using the prepared mud cake, several commonly used water base drilling fluids were tested for their filtration performance, further proving that the mud cake prepared with this method was suitable for use in simulating shale formations with developed micro pores and micro fractures, and in effectively evaluating the filtration and wall building performance of drilling fluids across the shale hole sections.