苏里格低渗致密气藏阈压效应

低渗致密气藏孔吼细小,束缚水饱和度普遍较高,气-水关系复杂,存在阈压效应。采用苏里格低渗致密储层的岩样,开展了低渗致密气藏阈压效应的研究。实验采用气泡法与压差流量法相结合测试并研究了阈压梯度及其引起的气体非线性渗流特征。通过核磁共振和恒速压汞实验测试了赋存水的分布规律和岩样孔喉结 构,分析了阈压效应产生的机理及其影响因素。实验结果表明可动水和孔喉特征是影响阈压效应的主要因素,可动水比例越高、孔喉越致密,阈压梯度越大,阈压效应越强。并得出了通过气藏的绝对渗透率和含水饱和度定量表征苏里格低渗致密气藏阈压梯度的公式,进一步建立了通过渗透率和含水饱和度预测存在阈压效应的气井产能数学模型。IPR曲线表明,阈压效应会降低气藏的储量动用程度,导致一定的产能损失,因此减少气藏含水饱和度是提高开发效果的有效途径。

Threshold pressure effect of low permeability tight gas reservoirs in Sulige gas field

Threshold pressure effect exists in the low-permeability tight gas reservoirs with small pore throat, high irreducible water saturation and complicated gas-water relation. Rock samples of low-permeability tight gas reservoirs from Sulige gas field were used to study the threshold pressure effect of low-permeability tight gas reservoirs. The experiment was carried out in combination with gas bubble method and differential pressure flow method to test and investigate the threshold pressure gradient and the resulting gas non-linear percolation characteristics. The distribution law of occurring water and pore throat structure of rock samples were tested with the use of nuclear magnetic resonance and constant-rate mercury injection experiment, based on which the occurrence mechanism and influence factors of threshold pressure effect are analyzed in this study. The experimental results show that movable water and pore throat characteristics are primary controlling factors. The higher the percentage of movable water is, and the tighter the pore throat is, the greater the threshold pressure gradient will be, and the stronger the threshold pressure effect will be. Moreover, the absolute permeability and water saturation of gas reservoirs are used to characterize the threshold pressure gradient of low-permeability tight gas reservoirs in Sulige gas field, and the related function has been obtained. The mathematical model was further established to predict the gas well productivity under threshold pressure effect. IPR curves indicate that threshold pressure effect can decrease the producing degree of gas reservoirs, leading to a certain loss of productivity. Thus, development results can be effectively improved through the reduction of water saturation in gas reservoirs.