基于微米CT的钻井液浸泡复兴陆相页岩裂缝扩展演化OA北大核心CSTPCD

Using micro-CT scanning technology,the characterization and evolution of the fractures in the Fuxing continental shales before and after high-temperature soaking are quantitatively analyzed.The continental shales are soaked in bentonite slurry,Nanodrill water based drilling fluid and white oil based drilling fluid,and are scanned with micro-CT at different soaking times.The effects of the different drilling fluids on the evolution of the fractures are analyzed.The study results show that the rock samples taken from the Liangshan Formation have more fractures than other rock samples,and different drilling fluids have different inhibitive capacities for the extension of the fractures.After soaking for 10 d in bentonite slurry,the percent layered fractures with the maximum width found in the rock samples is 12%,significantly higher than that of the rock samples in the white oil based drilling fluid,which is 6.13%,and the percent layered fractures with the maximum width of the rock samples in the water based drilling fluid lies in between the two.Using microscope,the distribution of the fracture widths of the rock samples before soaking is studied,and the percent increase of the fracture widths of the rock samples after soaking for 10 d is analyzed;the rock samples in the bentonite slurry have the highest percent increase in fracture width,which is 61.6%,the rock samples in the Nanodrill water based drilling fluid have the intermediate percent increase in fracture width,which is 52.1%,and the rock samples in the white oil based drilling fluid have the lowest percent increase in fracture width,which is 39.8%.Quantitative study on the distribution of the lengths of the fractures shows that the rock samples soaked in the bentonite slurry have the most fractures with lengths between 50 μm and 100 μm,and the numbers of the fractures with the same length distribution in the rock samples soaked in the Nanodrill water based drilling fluid and in the white oil based drilling fluid are basically remained unchanged.These data indicate that the white oil based drilling fluid has the best inhibitive capacity in inhibiting fracture extension in shales,with the Nanodrill water based drilling fluid inferior in inhibiting fracture extension to the oil based drilling fluid,and the bentonite slurry performs the poorest in this aspect.The results of this study can be used as a technical reference for efficient and safe drilling of the continental shale formations in the Fuxing area.