近井塑性带应力状态与地层损害关系

油、气井测试及生产过程中，井筒周围储集层应力应变状态发生变化，这是造成地层损害的不可忽略的因素。地层被钻开后，井筒周围存在塑性应变带和弹性应变区，前者渗透率大大低于后者，地层被严重损害，被损害地层的范围与塑性带的宽度密切相关。塑性带宽度（半径）除与储集层的岩石力学性质和流体物性有关之外，还随测试或生产流速的增加而增大。对任何类型的砂岩储集层，存在一个不使其发生坍塌破坏和出砂的临界流速，该临界值的大小取决于储集层的胶结强度和地层流体的粘度等因素。当测试或生产流速接近临界值时，塑性带宽度急剧增大，导致地层损害范围急剧加大。因此，将测试或生产流速控制在低于临界流速的范围内，在钻井过程中尽量控制井喷、井涌，是避免储集层发生灾难性损害的关键。储集层胶结强度对临界流速影响很大，对可能因酸化而大幅度降低胶结强度的储集层，不宜酸化；可进行酸化的，酸化后应考虑胶结强度降低对临界流速的影响，将测试流速控制在合理范围内。图４参７（郭海莉摘

The relation of stress condition and formation damgage in near wellbore plastic area.

By analyzing the stress distribution around well bore for poorly consolidated sand formation during testing and producing, this paper points out the errors existing in some previous work. There exists a critical flow rate for any poorly consolidated sand formation, over which the formation would suffer disastrous damage. The critical flow rate is determined by the formation mechanics and fluid properties, such as the consolidation strength, the fluid viscosity and the inner friction ratio of formation. When the flow rate is less than its critical value, there also exists a plastic zone around well bore. The radius or width of plastic zone grows with the increase of flow rate, and increases rapidly when the flow rate is near to its critical value. The plastic zone will result in formation damage because the permeability of plastic zone is much less than that in elastic zone. And the damage will increase with the increase of plastic zone. Therefore, controlling the flow rate of testing and producing is the key to control formation damage in test and production.