Abstract:

Complex problems such as leakage and overflow often occur during the cementing process of shale gas horizontal wells in a particular oilfield in the Permian Shanxi Formation，severely impacting cementing quality. The existing method for calculating casing pressure under concentric wellbore conditions cannot be used to accurately calculate wellbore pressure. A wellbore pressure calculation model is urgently required that considers actual downhole conditions throughout the cementing process to accurately predict and evaluate the distribution of wellbore pressure in real-time，ensuring cementing safety and improving cementing quality. This study considers the effects on wellbore static pressure and circulation friction of various fluid injections under eccentric casing conditions during the cementing process. A correction coefficient for eccentric annulus friction pressure drop is developed，and a calculation model for annulus flow during cementing process with eccentric casings is established. The impact of eccentric casing conditions on annular pressure is analyzed using eccentric casing data from well A. The results show that the annular friction pressure drop under eccentric casing conditions is reduced by 22.7%－33.42% compared to concentric annuli. The predicted values of the pressure calculation model under eccentric casing conditions align well with the actual pump pressure，and the calculation error is within 1.37%. The principle of pressure stability and no leakage during the whole cementing process has been insured with the proposed calculation model. The correctness of the established cementing pressure prediction model and calculation method is verified，providing important guidance for cementing operations in low-pressure and leak-prone formations，avoiding downhole complexities，and ensuring the safety of cementing operations.

Key words:

cementing, eccentric casing , annular flow, circulating pressure, pressure prediction

摘要：

某油田二叠系山西组页岩气水平井注水泥过程中易出现漏失和溢流等复杂问题，严重影响固井质量，现有套管居中条件下井筒压力计算方法难以满足井筒压力精确计算要求。亟需建立一套考虑实际井下工况的注水泥全过程井筒压力计算模型来准确预测、实时评价井筒压力分布特征，以确保固井安全与提高固井质量。考虑套管偏心工况下注水泥过程中多种流体注入对井筒静压和循环摩阻的影响，引入偏心环空摩阻压降修正系数，建立了考虑套管偏心条件下注水泥环空流动计算模型，结合计算A井套管偏心数据，分析了套管偏心对环空压力的影响。结果表明，套管偏心条件下环空摩阻压降比同心环空降低了22.7%~33.42%，套管偏心条件下压力计算模型的预测值与实际泵压吻合度高，计算误差在1.37%以内，采用该计算方法确保了注水泥施工过程中的压稳不漏原则。验证了建立的注水泥全过程压力预测模型与计算方法的准确性，成果对低压易漏地层固井施工具有重要指导意义，避免了井下复杂情况发生，确保固井施工安全。

关键词:

固井, 套管偏心, 环空流动, 循环压力, 压力预测