地层孔隙压力变化对井壁稳定性的影响研究

Study on the Effects of Changes in Pore Pressure on Wellbore Stability

受长期注采工程作业的影响,地层孔隙压力将发生大幅度波动,从而导致地层的岩石强度、地应力相对开采初期已发生较大变化,且横向分布更为复杂,进而诱发、加剧井壁失稳,井下复杂状况频发。理论与实验相结合研究了孔隙压力变化对砂岩地层岩石强度及地层坍塌压力的影响,结果表明:(1)岩石强度与地层孔隙压力呈负相关,随地层孔隙压力增大,地层岩石强度、弹性模量呈线性递减;(2)地层孔隙压力变化将影响调整井的井壁稳定状态,压裂、注水、注聚等工程作业导致井周地层孔隙压力增大,将加剧井眼失稳;而在一定限度内,油气的压力衰减式开采将降低地层坍塌压力,利于井眼保持稳定。

Long-term injection/projection operations cause large fluctuations in pore pressure, which in turn cause relatively large changes in rock strength and ground stress in the strata compared to the initial stage of mining. Furthermore, the complexity in the horizontal distribution of pore pressure induces and exacerbates wellbore instability and results in frequent occurrences of complex downhole situations. We carried out a combined theoretical and experimental study to understand the effects of pore pressure changes on the rock strength and stratum collapse pressure of sandstone strata. The results show that:(1) Rock strength is negatively correlated with pore pressure. As pore pressure increases, stratum rock strength and elastic modulus show a linear decrease.(2) Changes in pore pressure affect wellbore stability. Fractures, water injection, and polymer injection operations result in increased pore pressure around the well, which exacerbates wellbore instability. In addition, pressure-attenuated mining of oil and gas within a certain range decreases the stratum collapse pressure, which is beneficial for maintaining wellbore stability.