High-Efficiency and Safe Drilling Technologies for Development Wells in the Beibuwan Basin

The Beibuwan Basin in the western South China Sea has well developed micro-fractures and strong water sensitivity, which leads to frequent drilling complexities, especially wellbore instability in the second member of the Weizhou Formation. In order to improve the drilling efficiency of development wells in Beibuwan Basin, drilling technologies and practices were summarized. The wellhead was constructed by sidetracking the riser of the abandoned wellhead slot, so as to make full use of the wellhead slot; the seawater polymer drilling fluid system was used to drill the surface casing section while reducing the borehole size of surface casing section, and to achieve deep drilling of this section; the strong plugging full oil-based drilling fluid was used to penetrate the target layer which named Weizhou 2 Formation; the casing program was optimized, and the intermediate casing and production casing were integrated, so as to improve the drilling safety of the target layer and reduce the operation time. Thus, high-efficiency and safe drilling technologies for development wells in Beibuwan Basin were finally formed. With these technologies applied in more than 30 wells in several oilfields in Beibuwan Basin, the waste of wellhead slot resources was avoided, the drilling fluid cost for surface casing section was reduced, the complex accident ratio of the target layer was reduced, the ROP of the whole well was improved by more than 20%, and the drilling period of development well was shortened by nearly 25%. These drilling technologies could provide technical references for the efficient development of similar oilfields.