考虑气体溶解效应的持续套管压力预测与分析

Predicting and analyzing sustained casing pressure while taking into consideration the gas dissolution effect

水泥环失效是导致持续套管压力的重要原因之一,严重威胁油气井的安全生产。基于气体渗流方程,利用水泥环综合渗透率表征水泥环失效程度,建立了考虑气体溶解的持续环空压力预测模型,通过与现场实测数据的对比表明模型具有较高的预测精度。考虑气体溶解可准确预测进入环空的气体泄漏量,溶解效应对于压力早期建立过程具有重要影响,随着溶解度的增加预测误差增大,适当增加压力测试数据有利于减小预测误差。利用建立的模型对陵水气田进行了持续套管压力预测,结果表明,随着水泥环综合渗透率的增加,持续套管环空压力上升速度明显加快,环空流体密度减小会导致持续最大环空压力升高,预置环空体积可以延缓环空压力的上升。从工程角度,保证气井整个服役期水泥环的完整性和考虑钻井液沉降的影响对于环空压力管理具有重要意义。

Cement sheath failure is one of the important reasons for the generation of sustained casing pressure(SCP)and it seriously threatens the safety production of oil and gas wells.Based on the gas flow equation,the SCP prediction model considering gas dissolution was established by using the composite cement sheath permeability to characterize the failure degree of cement sheath.The comparison between the calculation results and the field measurement data show that this newly established model has higher prediction accuracy.By taking the gas dissolution into consideration,the gas leakage in the annulus can be predicted accurately.Dissolution effect has an important influence on the early pressure building up process,and with the increase of the dissolubility,the prediction error increases,so increasing the amount of pressure testing data appropriately is beneficial to reduce the prediction error.The SCP prediction model considering gas dissolution was used to predict the SCP in the Lingshui Gasfield.It is indicated that with t he increase of the composite cement sheath permeability,the rising speed of the sustained casing annulus pressure increases obviously. The reduction of the annulus fluid density can lead to the increase of the maximum sustained annulus pressure. Presettingthe annulus volume can slow down the increase of the annulus pressure. From the view point of engineering, ensuring cement sheathintegrity in the whole service life of gas well and taking into consideration the effect of drilling fluid settlement are of greatsignificance to annulus pressure management.