Study on Collapse Pressure Prediction of Fractured Strata

The Xujiahe Formation in western Sichuan has complex geological characteristics, fractures and fractures, and is prone to collapse in drilling. In this paper, the in-situ stress field around the wellbore, pore pressure, internal pressure in the wellbore and additional stress field generated by fluid flow are taken into account, and combined with the mechanical strength of rock in the target block, the in-situ stress parameters are calculated, the collapse pressure model of fractured formation is established, and the formation pressure profile of the well area is obtained, so as to predict the safe drilling fluid density window. The results show that the accuracy of the in-situ stress model is high, and the maximum error is 1.3%, which meets the engineering requirements. In the target block, the collapse pressure of Section 5 of Xinsheng 101 well and Section 5 – Section 3 of Xin601 well is high, reaching 1.8 g/cm3, and the safe drilling fluid density is narrow. Therefore, the drilling fluid density should be carefully designed to ensure the stability of borehole wall and prevent the occurrence of borehole wall collapse caused by too low drilling fluid density.