南海北部陆坡浅水流评估及深水钻井防治措施

深水钻井中浅水流喷发会对钻井安全产生很大影响。基于浅水流形成条件和南海北部陆坡古地质环境,分析目标海域浅水流的潜在风险。根据水流喷出速率,量化浅水流危害等级,并建立能够模拟浅水流上喷或喷出的数值模拟模型,分析典型工况下浅水流层压力、规模、孔渗条件及钻速对其喷出过程的影响。结果表明:南海北部陆坡存在浅水流形成的古地质条件,但浅水流规模较小,压力系数较低,钻进中发生严重浅水流危害的概率较低;浅水流喷发具有"压力-水瞬间高速释放"的特征;采用低密度海水钻井液钻进,钻遇压力系数为1.15的浅水流层,钻井液停止循环后水流喷出速率和喷出量可达70 m~3/h和60 m~3;浅水流喷发主要受其压力和规模控制。针对目标海域浅水流特征及控制因素,提出了控制浅水流危害的措施。

Shallow water flow hazard assessment in the northern slope of the South China Sea and control measures during deepwater drilling

Shallow water flow (SWF) can greatly influence the safety of deepwater drilling. In this study, the occurance and its potential risk of SWF on drilling safety in the northern slope of the South China Sea was analyzed based on SWF formation conditions and paleogeological characteristics. A numerical simulation model of SWF blowout was established, and the effects of the over-pressure, geologic parameters and the size of SWF formation, and penetration rate on water blowout were investigated. SWF hazards were then classified quantitatively according to water blowout rates. The results show that there are paleogeological conditions for the formation of SWF in the target area. However, the scale and pressure of SWF formations would be low so that there are low probabilities for serious SWF hazards to be confronted. SWF blowout is characterized with spontaneous release of water and pressure, and the water blowout rate and volume can be up to 70 m³/h and 60 m³ during drilling through a typical SWF formation with a formation pressure coefficient of 1.15 using sea water as drilling fluid. SWF blowout is mainly controlled by its over-pressure and the size of the SWF formation.