致密砂岩气藏渗流特征及转化临界条件研究

The Transformation Conditions of Different Flow Effect in Tight Sandstone Gas Reservoir

我国大多数致密砂岩气藏具有高含水饱和度特点,导致其渗流机理与常规气藏比较表现出不同的非线性渗流特征。掌握低渗致密高含水砂岩气藏渗流特征及定量确定不同非线性渗流特征相互转化临界条件对于指导该类气藏开发具有重要意义。以四川盆地须家河组某低渗致密砂岩气藏为研究目标,通过建立定量化渗流机理实验测试技术及渗流机理诊断分析技术,采用实际储层岩样开展79样次渗流机理实验测试及分析,通过对实验测试结果分析建立不同渗流特征相互转化临界条件。研究表明,不同的岩样条件下,气体渗流表现出不同的渗流特征;低渗高含水砂岩气藏普遍存在四种渗流特征:阈压效应、滑脱效应、达西渗流及高速非达西渗流特征;当气相有效渗透率小于0.02 m D、有效气相孔隙度小于6.5%储层,存在明显阈压效应;不同渗流效应相互转化临界条件不仅与储层物性有关,更重要的是受储层含水饱和度的影响。

The developed gas reservoirs are almost with water saturation at present, which formation characteris- tics cause the filtration mechanisms with different non-linear flow characteristics compared with the conventional gas reservoir. Therefore, it is significant to be explicit the flow characteristics and to quantify the critical conditions of reciprocal transformation among different non-linear filtration effects for low-permeable gas reservoir with high water saturation. Taking the Xu-Jiahe formation in Guang-an gas filed located in Sichuan Basin for the research objec- tives, the critical conditions of reciprocal transformation among different filtration effect was established by the tes- ting results through developing the quantitative flow mechanism experiment testing technique and diagnosis tech- nique for low mechanism, carrying out 79 flow mechanism experiment test and analysis by using actual reservoir samples. The results demonstrate that the gas flow has different flow characteristic under different sample condi- tions, the low-permeable gas reservoir with high water saturation has 4 flow effect in general as follows： threshold pressure effect, slippage effect, Darcy flow effect and non-Darcy flow effect. When the effective permeability of the gas phase is less than 0.02 mD, the effective porosity or gas factor is less than 6.5%, the reservoir has obvious threshold pressure effect. The critical condition of transformation between threshold pressure effect and slippage effect, the critical condition of transformation between slippage effect and Darcy flow effect is related to the experi- ment pressure gradient. The critical condition of transformation between Darcy flow effect and non-Darcy flow effect is related to the flow velocity of gas phase. The transformation condition between different percolation effects is not only related to the reservoir properties, but also is more importantly affected by the reservoir water saturation.