北部湾盆地开发井高效安全钻井技术

南海西部北部湾盆地地层微裂缝发育，水敏性强，尤其是涠洲组2段地层井眼失稳问题突出，导致井下故障频发。为了提高北部湾开发井钻井效益，使用废弃井槽，在隔水导管内开窗侧钻建立井口，以高效利用槽口资源；表层井段使用海水聚合物钻井液，同时减小其井眼直径，达到增加表层井段钻深的目的；目的层井段使用强封堵全油基钻井液钻穿涠洲组2段地层；在优选钻井液的基础上，将三开井身结构优化为二开井身结构，提高了目的层井段钻井安全，同时提高了机械钻速、缩短了钻井周期，最终形成了北部湾盆地开发井高效安全钻井技术。该技术在北部湾盆地多个油田30余口井进行了现场应用，避免了槽口资源浪费，降低了表层井段钻井液成本和目的层井段发生井下故障的概率，全井段机械钻速提高超过20%，钻井周期缩短近25%。北部湾盆地开发井高效安全钻井技术为类似油田的高效开发提供了技术借鉴。 

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.