海上窄压力窗口控压固井浆柱结构设计方法

Design method of slurry column structure of managed pressure cementing at offshore gas wells with narrow pressure window

摘要:

针对海上油气井窄压力窗口固井顶替效率低下的技术难题，通过轻钻井液的施加以优化浆柱结构以及施加环空回压的方法实现安全高效固井的目标。考虑停泵压胶塞环空回压值≯5 MPa、冲洗液环空紊流接触时间>10 min以及注替结束井筒自压稳3个关键技术要求，合理优化固井浆柱结构，计算控压固井全过程井筒当量循环密度（ECD），使井筒ECD在安全密度窗口内，形成了海上窄压力窗口控压固井浆柱结构设计方法。以乐东10-1气田某高温高压井为例，优化设计了该井的浆柱结构，并模拟计算了控压固井全过程井筒ECD及紊流接触时间。结果表明：轻钻井液用量为14~50 m³且密度在1.822~2.142 g/cm³之间、冲洗液用量>13 m³且密度在2.36~2.45 g/cm³之间、水泥浆密度在2.4~2.51 g/cm³之间，可实现冲洗液紊流接触时间>10 min且满足压稳不漏的固井要求。该设计方法可实现海上窄压力窗口井安全施工和提高固井顶替效率的要求。

Abstract:

Aiming at the technical problem of poor cementing quality of offshore gas wells with narrow pressure window， the goal of safe and efficient cementing is achieved through the application of light drilling fluid to optimize the slurry column structure and the application of annular backpressure. Three key technical requirements are considered in this paper： the annular backpressure value during the pump stopping process should not exceed 5MPa， the turbulent contact time of the flushing fluid should be greater than 10 minutes， and the wellbore should be self-stable after cementing ending. Then the optimized slurry column structure and the calculated wellbore equivalent cycle density （ECD） with managed pressure cementing （MPC） technology were conducted by which a design method of cementing slurry column structure of MPC for offshore gas wells with narrow pressure window was formed. Taking a high-temperature and high-pressure well in Ledong 10-1 Gas Field as an example， the cementing slurry column structure was optimized， and the wellbore ECD and turbulent contact time was simulated during the entire MPC process. The results indicate that： the requirements of turbulent contact time greater than 10 minutes and leakproof pressure stability can be achieved under the following three conditions： the volume of light drilling fluid is 14~50m³ and the density is 1.822~2.142g/cm³， the volume of the pad fluid is greater than 13m³ and the density is 2.36~2.45g/cm³ and the density of cement slurry is 2.4~2.51g/cm³. The goal of improving the efficiency of cementing displacement and safety construction is feasible with this method.