低渗砂岩气藏开发中的压敏效应问题

利用弹性力学、渗流力学理论建立了毛细管受压模型，推导出了渗透率与有效压力之间的本构关系式。通过室内模拟实验，证明该关系式与实验结果非常吻合；同时结合气井的生产参数，利用推导出的考虑压敏效应的低渗砂岩气藏的产能公式，预测了降压生产时气井产气量的变化情况。从考虑压敏效应的流入动态曲线可以看出：当有效压力较低时，流入动态曲线的形态与常规流入动态曲线的形态接近，随着有效压力的增大，曲线逐渐地表现出一个明显的拐点，井底流压以此拐点为临界点，当井底流压大于此临界点值时，流量随着井底流压的降低而增大；但当井底流压小于此临界点值时，流量不在随着井底流压的降低而增大，甚至出现急剧的下降现象。由此可见，压敏效应对气井开发效果有一定程度的影响，拐点的井底流压即是合理开采气藏的临界井底流压。因此，在实际生产中，应找出临界井底流压，建立合理的生产制度，避免因压力下降过快而造成储层伤害。

Pressure-sensitive effect in development of low permeability sandstone gas reservoir

Based on the elasticity and fluid mechanics in porous medium,a capillary pressure model is established and the relational expressions between permeability and effective pressure are derived.It can be proved that the relations are very agreement with the experiment result through the experiment.Combined with the productive parameters of gas well,the production change of gas well is predicted during the production of pressure release according to the productivity formulas derived by considering the pressure-sensitive effect of low permeability sandstone gas reservoir.The analysis of inflow performance curve of pressure-sensitive effect shows that the pattern of inflow performance curve is close to the pattern of conventional inflow performance curve when the effective pressure is low.But with the increase of effective pressure,the curve gradually presents an apparent break point.When the bottom-hole flowing pressure is higher than the value of critical point,taking the break point as the critical point of bottom-hole flowing pressure,the deliverability will increase with the decrease of bottom-hole flowing pressure.The deliverability will not increase with the decrease of bottom-hole flowing pressure when the bottom-hole flowing pressure is less than the value of critical point,even showing a quick drop.This shows that the pressure-sensitive effect has a curtain influence on the development effect of gas well and the bottom-hole flowing pressure of break point is critical bottom-hole flowing pressure of reasonable gas reservoir production.So the critical bottom-hole flowing pressure should be found out and the reasonable production rules should be set up to avoid the reservoir damage caused by rapid pressure decline in the process of practical production.