Quantitative analysis of slope stability of drilling sites with complex topography in the Qiongdongnan continental slope

Abstract

Due to the large slope angle and the weak strength of submarine soils, Qiongdongnan deepwater continental slopes face great instability problems. In continental slope area, evaluating the stability of the slope before drilling is important as slope instability threatens the drilling safety. Taking the Lingshui deepwater well site as an example, 2D and 3D submarine slope stability calculation models, which consider the vertical heterogeneity of soil strength, were established based on the strength reduction method and Flac3D. The vertical profile of the soil shear strength was obtained via cone penetration and geotechnical tests. The effect of returned cuttings and drilling disturbance on slope stability were analyzed, and the safety factor of the slope was calculated. In addition, the position of potential slip surfaces and the possible slip directions were analyzed. Based on this, the location of the well was determined. The results indicate that the minimum safety factor of slope, which crosses the well, is 1.32. Moreover, the risk of submarine landslide is low. One potential landslide mass exists. However, the slope near the well is stable, and the slip direction of the landslide mass does not point to the well. The returned cuttings from the borehole decrease the safety factor and increase the risk of slope instability near the well.