A new drilling fluid system for plugging argillaceous shale reservoirs

Argillaceous shale reservoir development is mainly based on extended reach horizontal wells, and has complex geological characteristics. In the process of long horizontal drilling, wellbore instability is easy to occur. In this paper, the mechanism of argillaceous shale instability is explored by testing the mineral composition of argillaceous shale. The method of plugging argillaceous shale with nano-sio2 is proposed, and a new nano plugging drilling fluid formulation system is constructed. The system mainly includes specially designed fluid loss additive SFL and EY, flow pattern regulator VBS, lubricant RH, bentonite, nano silica and inorganic salt. Through a series of experimental tests, the rheological property, thermal stability, anti pollution and plugging ability of the system were evaluated. Finally, with the help of SEM, the micro analysis of core profile before and after plugging with nano drilling fluid is carried out, and the plugging mode of nano drilling fluid is further elaborated. The comprehensive results show that nano-sio2 has good compatibility with water-based drilling fluid, and has good effect on inhibiting argillaceous shale expansion and plugging argillaceous shale fractures. It can play the role of stabilizing shale, effectively meet the needs of target block, and provide reference for the follow-up study of plugging argillaceous shale reservoir.