扩散在低孔渗致密砂岩气成藏中的作用和贡献探讨

Discussion on role of gas diffusion and its contribution in low porosity-permeability tight sandstone gas reservoirs

根据气体在浓度梯度作用下进行自由扩散的原理,开展浓度梯度驱动下的天然气扩散运移物理模拟实验,对扩散在低孔渗致密砂岩气成藏中的作用和贡献、低孔渗致密储层天然气成藏机制进行探讨。结果表明:浓度梯度驱动下的天然气扩散运移模拟实验后低孔渗致密砂岩最大含气饱和度与物性总体呈负相关关系,渗透率≤0.1×10-3μm2时最大含气饱和度与孔隙度具有更好的负线性相关性,渗透率>0.1×10-3μm2时最大含气饱和度与渗透率具有更好的负线性相关性;当低孔渗致密砂岩的孔隙度小于0.6%、空气渗透率小于0.01×10-3μm2时,扩散可能对低孔渗致密砂岩含气饱和度的增加起主要作用和贡献;扩散是低孔渗致密储层天然气成藏的重要机制之一,是中低丰度低孔渗致密储层大面积含气的重要原因之一。

Assuming that gas diffusion is controlled by its concentration gradient, the physical simulation experiments of gas difussion driven by concentration gradient were conducted, and the role of gas diffusion and its contribution in low po-rosity-permeability tight sandstone gas reservoirs, as well as forming mechanisms of low porosity-permeability tight gas res-ervoirs were discussed. The results show that the maximum gas saturation in the simulations has overall negative linear cor-relation with the gas physical properties: it correlates with the gas porosity when permeability is less than 0. 1×10-3μm2;and correlates with the gas permeability when permeability is larger than 0. 1 × 10-3μm2 . Gas diffusion may become the main mechanism for gas saturation increment in low porosity-permeability tight sandstone reservoir, when porosity is less than 0. 6% and permeability is less than 0. 01×10-3μm2. Gas diffusion is one of the important forming mechanisms of low porosity-permeability tight gas reservoir, and one of the important reasons for low porosity-permeability tight reservoir with large gas bearing area.