储层含水条件下致密砂岩/页岩无机质纳米孔隙气相渗透率模型

MODEL FOR GAS TRANSPORT IN NANOPORES OF SHALE AND TIGHT FORMATION UNDER RESERVOIR CONDITION

页岩及致密砂岩储层富含纳米级孔隙,且储层条件下页岩孔隙(尤其无机质孔隙)及致密砂岩孔隙普遍含水,因此含水条件下纳米孔隙气体的流动能力的评价对这两类气藏的产能分析及生产预测具有重要意义.本文首先基于纳米孔隙内液态水及汽态水热力学平衡理论,量化了储层孔隙含水饱和度分布特征;进一步在纳米孔隙单相气体传质理论的基础上,考虑了孔隙含水饱和度对气体流动的影响;最终建立了含水饱和度与气相渗透率的关系曲线.基于本文岩心孔隙分布特征,计算结果表明:储层含水饱和度对气体流动能力的影响不容忽视,在储层含水饱和度20%的情况下,气相流动能力与干燥情况相比将降低约10%;在含水饱和度40%的情况下,气相流动能力将降低约20%.

The formations of shale gas and tight gas are abundant in the nanopores of shale and tight sandstone, and the pores are partially saturated with water under reservoir conditions, so the evaluation of gas flow capacity by considering water saturation is important to gas production forecast. Based on the thermodynamic equilibrium theory between liquid and vapor in formation nanopores, we quantify the distribution of reservoir pores water under ultra-low water saturation condition, and establish the relation between water saturation and gas phase permeability. Results show that the impacts of water saturation on the gas flow can be divided in two forms：（1）bound water film in large pores will reduce the effective pore diameter for gas flow;（2）capillary water in small pore will block the entire gas flow channel. And the effect of water saturation on gas flow capacity cannot be ignored. In case that water saturation is 20%, the gas flow capacity will reduce10%, compared with the dry conditions. Under the condition that water saturation is 40%, the gas flow capacity will be reduced by about 20%. The results calculated by the models in this paper are in agreement with the experimental results in a newly-published article.