Drilling Geological Risk Analysis and Measures Taken in the South Yellow Sea

The South Yellow Sea Basin is the only sea area of the four major sea areas in China that has not seen significant oil and gas discoveries at present, and its exploration degree is very low. So far, nearly 30 wells have been drilled, most of them are about 3 000 m, which are shallow wells. In order to further explore the hydrocarbon accumulation situation in this sea area, under the guidance of geophysical data, more exploration wells need to be arranged in vantage point. According to the drilling operation, the upper strata of the sea area is continental tectonic deposit and the lower strata is marine tectonic deposit. Geological deposit and plate movement have caused many drilling geological risks, including downhole leakage, borehole wall collapse, abnormal pressure and H₂S. In the early stage of drilling, there have been corresponding downhole complications. In this paper, aiming at these geological risks, according to the theoretical study of geological sedimentation, the causes of these drilling geological risks are discussed, and the characteristics and types of formation leakage, the mechanism of wellbore collapse, the nature of abnormal pressure and the formation conditions of H₂S are analyzed. Based on the analysis results and the drilling technology currently used, the countermeasures of drilling construction in the later stage are put forward, which can provide technical guarantee for the later exploration operation in the South Yellow Sea.