Stability Analysis of Salt Structure Drilling and Its Application to the Keshen 10 Block of Kuqa Depression in Tarim Basin

Due to the creep and weak mechanical strength of the salt, perturbations or anomalies of stress and pore pressure often occur in the sediments around salt, leading to the risk of wellbore drilling and even drilling failure. The drilling problem near salt structures still has not been well solved, and has become a challenge in petroleum drilling engineering. To study the effects of stress field in salt basins on wellbore stability and drilling trajectory, we built a three-dimensional conceptual salt hemisphere finite element model to simulate stress fields of the salt structure under different background stress environments, investigate these stress fields and their perturbations around salt, and analyze their effects on the safe mud weight window in the salt system. The results show that the safe mud weight window is the widest under thrust-fault background stress environment, but the narrowest under normal fault background stress environment; it is in the middle under strike-slip fault background stress environment. For a subsalt reservoir under the strike-slip fault background stress environment, the use of directional well can not only avoid the stress anomaly area at the top of the salt sphere, but also improve the drilling stability because of a wider safe mud weight window for the inclined well than that for the vertical well. Our results also suggested that in the Keshen 10 Block of Tarim Basin, the directional well drilling and the inclined well drilling in the regions to the south of the salt structure are the preferred well trajectory.