利用环空压力测试数据评价高温高压气井固井水泥环的密封完整性

Cement integrity evaluation of HTHP gas wells based on annulus pressure diagnosis test

摘要:

目前，高温高压气井在生产期间环空异常带压现象频发，气井环空异常带压表明井内出现窜漏，其完整性受到削弱，将影响气井安全生产。气井环空异常带压的根本原因是井屏障部件受损。通过对异常环空压力进行现场诊断测试，根据测试数据评估各个环空的窜漏程度，为环空异常带压潜在风险控制措施的制定提供指导。首先，分析了气井环空带压的5种模式，并基于气液多相流和达西渗流理论，建立了水泥返至井口和未返至井口2种环空介质条件下气体渗流数学模型。结合实例井不同环空压力诊断测试数据，评估了固井水泥环的密封完整性。该方法可通过反向拟合现场实测压力数据，预测各环空压力的变化趋势，并评估固井水泥环的整体泄漏程度，可用于指导固井工程设计及现场作业。

关键词:高温高压气井;环空异常带压;诊断测试;数学模型;水泥环;密封完整性

Abstract:

At present， sustained casing pressure （SCP） occurs frequently in the development of high temperature and high pressure gas wells， indicating that leakage happens along the well， and the well integrity is damaged. The basic cause for sustained casing pressure is failure of the well barrier， which leads to abnormal annular pressure in gas wells and hence threatens safe production of gas wells. It makes sense to analyze the annular pressure build up test data to evaluate the leakage rate of cement sheaths and control the risk of SCP. Five SCP modes were analyzed， with the mathematic model established for gas infiltration flow in the two cases where both cement returns and doesn’t returns to surface. The cement integrity was evaluated using the annulus pressure diagnosis test data， which could not only predict the trend of the annulus pressure， but also obtain the equivalent leakage rate of the cement sheaths. The results of this paper can be used to conduct the cementing design and provide references for management and control of sustained casing pressure.

Key words:high temperature and high pressure gas wells;sustained casing pressure;diagnosis test;mathematic model;cement;sealing integrity