高温高压固井第一界面径向胶结强度试验研究

Experimental Study on Radial Cementation Strength of the First Cementing Interface in HTHP Wells

针对水泥环在高温高压井工况下的受力状况,研制了全尺寸高温高压水泥环密封完整性评价试验装置,运用气窜法开展了高温高压下围压变化和套压变化对固井水泥环第一界面径向胶结强度的影响试验,揭示了围压变化和套压变化对第一界面窜流压力的影响规律。试验结果表明:在套压为10 MPa时,窜流压力随着围压的增大而呈非线性增长,且增长速度越来越快,窜流压力在围压70 MPa时达到最大值6.76 MPa,窜流压力随围压的减小呈非线性减小,窜流压力始终比同围压下加载时的窜流压力大;窜流压力在套压50 MPa时达到最大值6.43 MPa,最后趋于稳定;窜流压力随着套管压力的卸载而减小,卸载过程中窜流压力小于同套压状态下加载过程中的窜流压力。因此,在对油井开采及后续施工时要避免因较大的围压变化和套压变化而削弱第一胶界面的径向胶结强度,从而使井筒的密封完整性受到破坏。

In view of the stress status of cement ring in high-temperature and high-temperature (HTHP) wells, a set of full-size HTHP cement ring sealing integrity evaluation test equipment was developed. The influence of confining pressure and casing pressure on the radial bonding strength of the cement ring first interface was tested by use of gas channeling method in HTHP environment and the influence rule was concluded. The test results show that when the casing pressure is 10 MPa, the crossflow pressure increases nonlinearly with the increase of the confining pressure, and the growth rate is faster and faster. The crossflow pressure reaches the maximum of 6.76 MPa when the confining pressure is 70 MPa. The crossflow pressure decreases nonlinearly with the decrease of the confining pressure, and the crossflow pressure is always higher than the crossflow pressure during loading the same confining pressure. The crossflow pressure reaches the maximum of 6.43 MPa when the casing pressure is 50 MPa, and finally tends to be stable. The crossflow pressure decreases with the unloading of casing pressure, and the crossflow pressure during unloading is less than that during loading the same casing pressure. The results show that, during oil production and subsequent operations, big changes in confining pressure and casing pressure should be avoided because they will impair the bonding strength of the first cementing interface and damage the wellbore sealing integrity accordingly. This study could provide a theoretical guidance for oil and gas exploitation.