窄安全密度窗口重力置换漏喷函数研究

The Leakage Function of Gravity Displacement in the Narrow Safety Density Window

王存新 许佳欣 李勇 李皋 肖东

WANGCunxin XUJiaxin LIYong LIGao XIAODong

中国石化西南石油工程有限公司钻井工程研究院, 四川 德阳 618000 油气藏地质及开发工程国家重点实验室·西南石油大学, 四川 成都 610500

Research Institute of Drilling Engineering, Southwest Petroleum Engineering Co. Ltd., SINOPEC, Deyang, Sichuan 618000, China State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, Sichuan 610500, China

由于重力置换的原因，钻遇裂缝性地层时，井下经常发生漏喷同存，造成井下复杂情况，增大井控难度，损害地层，影响生产。建立了重力置换数学模型，并基于此形成了高压含气层窄安全密度窗口重力置换漏喷函数，利用地层-井筒耦合流动可视化实验装置对漏喷函数进行了验证。实验结果表明，建立的漏喷函数的计算结果与实验数据吻合度较高。当钻遇裂缝性地层时，无论是采用欠平衡钻井、平衡钻井工艺，还是过平衡钻井工艺，均无法避免重力置换现象的发生，但是将井筒压力维持在近平衡（微过）状态，能够显著降低重力置换现象的严重程度。研究成果对研究钻遇裂缝性地层时的井底复杂的物质交换规律及井筒压力的安全控制具有重要的指导意义。

Due to gravity displacement, overflow and lost circulation occur simultaneously in fractured formations. This not only causes complicated downhole conditions and increases the difficulty of drilling pressure control, but also damage the reservoir, which will cause adverse effect on production. This paper establishes a gravity displacement model. And based on gravity displacement model, a leakage function of the gravity displacement in the narrow safety density window of high pressure gas layer has been formed. Then an experiment has been designed to testify leakage function by using the test device development of wellbore-formation coupling flow. The experimental results show that the calculated results of the leakage function are consistent with the experimental data. When drilling in fracture development formation, whether it is underbalanced drilling, balanced drilling, or overbalanced drilling, gravity displacement can't be avoided. However, when we maintain the wellbore pressure close to equilibrium (slightly exceeding), the gravity displacement phenomenon can be significantly reduced. Results of this study have important guiding significance for the mechanism of complex material exchange laws and wellbore safety control of the bottom hole when encountering fractured formations during drilling operations.

10.11885/j.issn.1674-5086.2020.10.31.01