超低压水平井井壁稳定性研究与应用——以崖城13-1气田为例

在气田开发中后期的调整井钻井中,由于储层压力衰竭,会产生与常压或异常高压地层中不同的井壁稳定问题,主要体现在钻进中容易漏失,导致井下复杂情况或钻井事故。崖城13-1气田在开发10余年后,主力储层压力系数衰减为0.47左右,是典型的超低压力气藏。针对该气田储层压力衰竭情况,建立了调整井井壁稳定力学分析方法,对崖城13-1气田某大位移调整井压力衰竭后的坍塌压力、破裂压力和漏失压力情况进行了分析。计算结果表明,地层压力降低导致坍塌压力和破裂压力均有不同程度下降,使钻井中坍塌风险降低,漏失风险增加。因此,在压力衰竭储层段钻井液密度设计中需要以压力衰竭后的坍塌压力、破裂压力及漏失压力为参考。实际钻井情况表明,考虑压力衰竭条件下的井壁稳定性分析在崖城13-1气田水平井的应用取得了良好效果。

Wellbore Stability Research and Application in Ultralow Pressure Horizontal Wells of Yacheng 13-1 Gas Field

In the adjustment well drilling at the late stage of oil or gas field development,there existed different wellbore instability problems in normal pressure or abnormal high pressure formations due to reservoir pressure depletion,and the main problem was easy to lost circulation in drilling,by which downhole complex condition and well drilling accidence were induced.After development of more than 10 years in Yacheng 13-1 Gas Field,the pressure coefficient of main reservoirs decreased to about 0.47,and it became typical ultralow pressure gas reservoir.In allusion to the pressure depletion of the gas-field,wellbore stability mechanical analysis method for adjustment wells was established.The collapse pressure,fracture pressure and leakage pressure of depleted reservoir of an extended reach adjustment well were calculated.The results show that a collapse pressure and fracture pressure are reduced to different degrees caused by formation pressure depletion,by which risk of borehole collapse is reduced and risk of fracturing is raised.Therefore,drilling fluid density design in depleted reservoirs should be according to the calculation results of collapse pressure,fracture pressure and leakage pressure considering pressure decreasing.Actual drilling condition shows that good results are achieved in application of wellbore stability analysis in depleted reservoirs of Yacheng 13-1 Gas Field.