致密气充注聚集机理及数理模型

Tight gas charging and accumulation mechanisms and mathematical model

致密气的气-水分布和产出非均质性虽已从实验和地质观察角度总结了相应认识规律,但一直缺少定量的数理模型揭示其聚集机理。从驱替-核磁物理模拟、考虑物质平衡和力学平衡的数值模拟以及实际地质观察3方面论证致密气充注聚集机理,结果显示致密气充注聚集时会在源-储界面附近优先形成含气饱和度稳定带,气源不足时,从源-储界面起,依次形成含气饱和度降低带和未充注带。源岩条件越好,排气量越多、超压越大,致密储集层含气饱和度稳定带和降低带越厚,整体含气饱和度越高;源岩条件有限时,致密储集层条件越好,孔渗越高、孔喉越大,含气饱和度稳定带和降低带厚度越薄,但含气饱和度高。致密气“甜点”有利层段发育在靠近源岩的优质储集层中,对应含气饱和度稳定带。基于数理模型的数值模拟结果很好地吻合了驱替-核磁物理模拟结果,并合理解释了松辽盆地徐家围子断陷深层和鄂尔多斯盆地临兴—皇甫致密气区的气-水分布和产出规律。

The gas-water distribution and production heterogeneity of tight gas reservoirs have been summarized from experimental and geological observations,but the charging and accumulation mechanisms have not been examined quantitatively by mathematical model.The tight gas charging and accumulation mechanisms were revealed from a combination of physical simulation of nuclear magnetic resonance coupling displacement,numerical simulation considering material and mechanical equilibria,as well as actual geological observation.The results show that gas migrates into tight rocks to preferentially form a gas saturation stabilization zone near the source-reservoir interface.When the gas source is insufficient,gas saturation reduction zone and uncharged zone are formed in sequence from the source-reservoir interface.The better the source rock conditions with more gas expulsion volume and higher overpressure,the thicker the gas saturation stabilization and reduction zones,and the higher the overall gas saturation.When the source rock conditions are limited,the better the tight reservoir conditions with higher porosity and permeability as well as larger pore throat,the thinner the gas saturation stabilization and reduction zones,but the gas saturation is high.The sweet spot of tight gas is developed in the high-quality reservoir near the source rock,which often corresponds to the gas saturation stabilization zone.The numerical simulation results by mathematical model agree well with the physical simulation results by nuclear magnetic resonance coupling displacement,and explain the gas-water distribution and production pattern of deep reservoirs in the Xujiaweizi fault depression of the Songliao Basin and tight gas reservoirs in the Linxing-Huangfu area of the Ordos Basin.