碳酸盐岩裂缝性水驱气藏水锁实验研究

WATER-LOCK EXPERIMENTS OF CARBONATE FRACTURED GAS RESERVOIRS WITH WATER DRIVE

我国多数碳酸盐岩裂缝性气藏属有水气藏。在气藏水侵过程中 ,天然气渗流经过的孔隙、裂缝和溶洞都会产生水封 ,造成水锁。实验研究表明 ,对同一块岩心 ,含水饱和度增大 ,气体突破压差增加 ,而且增幅加快 ,气相渗透率降低 ;对不同岩心 ,绝对渗透率越小 ,气体突破压差越大 ,气相渗透率也越低 ;无裂缝岩心的突破压差比有裂缝岩心的增加更大 ,气相渗透率下降幅度更快。由于在气驱水过程中存在巨大能量损失 ,水驱气的气相相渗比气驱水高得多 ,而两种条件下水相相渗几乎相同 ,说明用气挤水很困难 ,封闭气解封阻力较大。无裂缝岩心水驱气效率比有裂缝岩心的高 ,说明水驱气过程中岩心越均质有利于水的均匀推进 ,防止水窜 ,减少水封气。因此 ,当边水和底水进入储层发生水淹后 ,气相渗透率将极大降低 ,存在较强的水锁效应。降压解封方法可以减小水锁效应 ,封闭气解封首先出现在裂缝和溶洞系统 ,采出基质中的气需要更大的解封压差。

Most of carbonate-fractured reservoirs belong to water drive ones in China. In the water invading process of the gas reservoirs, water seal will happen to the pores, fractures and caves where gas will pass through. As a result, water lock will be formed. Experiments show: for the same core sample, the pressure difference of gas breakthrough increases, and the pressure differential margin increases faster, and the gas phase permeability decreases as the water saturation increases. For different core samples, the smaller the absolute permeability is, the bigger the pressure difference of gas breakthrough is, and the lower the gas phase permeability. The pressure difference of gas breakthrough for the cores without fractures increases faster than that for fractured cores. And the gas phase permeability decreases faster, too. Since energy loss is big while gas drives water, and the gas phase permeability while water drives gas is much higher than that while gas drives water, and the water phase permeability is almost the same in the two states, that is why squeezing water by gas is difficult, and the resistance of seal eliminating for closed gas is bigger. The efficiency of water driving gas for the cores without fractures is higher than that for fractured cores. That means while water drives gas, more homogeneous cores favors water progressing homogeneously to prevent water channeling, and decrease water-sealing gas. So, after reservoir watering out as edge water and bottom water enters, the gas phase permeability will decrease greatly, and strong water lock effect will happen. With the method of pressure fall to eliminate seal, the water lock effect can be reduced. The seal eliminating for closed gas will first happen in the system of fractures and caves. The bigger pressure difference of seal eliminating will be needed to recover the gas in the matrix.