考虑有效应力与含水饱和度的致密砂岩气层供气能力

Gas Supply Capacity of Tight Sandstone in Considering Effective Stress and Water Saturation

致密砂岩天然气资源丰富,但渗透率低,纵向上气层多,采用多层合采时,各层供气能力存在差异。气藏开采过程中气层压力下降快,含水饱和度也会发生变化,影响各气层供气能力。选取鄂尔多斯盆地上古生界典型致密砂岩岩样,开展含水饱和度对致密砂岩岩样供气能力的影响实验,对比分析了有效应力与含水饱和度对不同渗透率级别岩样供气能力的影响。结果表明,有效应力增加,渗透率相对较低岩样产气贡献率明显下降,相对高渗岩样增加,有效应力增加加剧了岩样间供气能力差异;在原地有效应力条件下,随着含水饱和度升高,岩样供气能力显著下降,渗透率越低,供气能力下降也就越显著;渗透率级差越大,渗透率相对较低岩样产气贡献率就越低。

Although there is abundant of natural gas in tight sand matrix,the gas supply capacity of each layer is different when adopting commingling production in the multi-layer of tight sand gas reservoir. The gas supply capacity of each layer may be impacted by rapid decrease of reservoir pressure and change of water saturation during production. We select the tight sandstone samples from Ordos basin to conduct the experiments so as to test the effect of water saturation on gas supply capacity,and take a contrast of water saturation and effective stress on gas supply capacity of the tight sandstone samples with different permeability. The results show that the effective stress severely impacts the gas supply capacity; with effective stress increase, the gas production for low permeability cores decreases, but the gas production for high permeability cores increase. So the effective stress increase aggravates the difference between gas supply ca- pacities of different permeability rocks. Under in-situ effective stress condition,the gas supply capacity de- creases significantly with water saturation increase and permeability decrease. The smaller the permeability is, the more significant the gas supply capacity decreases. The bigger the permeability range of core sample groups is, the more different the contribution rate of gas production is.