| There are unconsolidated reservoirs in upper formations and high-temperature high-pressure in lower formations of Yingge Sea Basin of western South China Sea. Lost circulation occurred easily in drilling through above formations, which caused frequent drilling accident that affected drilling speed and cementing quality. Therefore, it is necessary to predict fracture pressure accurately and study the influencing law of HTHP to fracture pressure.In this study the variation law of wellbore temperature, thermal stress calculation method, Transport of infiltration in borehole wall, and osmotic pressure calculation method were studied through investigating research status at home and abroad, numerical calculation and experimental analysis. In the study, some factors such as the effect of temperature, pore pressure, borehole wall permeability, and the interaction of shale and drilling fluid were considered. At last stress distribution rule was determined. Fracture pressure prediction mode of HTHP formations was established combined with formation failure criterion, and then a set of fracture pressure prediction technology was obtained for HTHP formations. The technology was applied in HTHP drilling of western South China Sea successfully, which improved the accuracy of fracture pressure prediction, and directed drilling designs of the HTHP wells. This technology also provided theoretical support and research method to accurate fracture pressure prediction of HTHP wells in other blocks. |
