岩溶型地热资源开采过程水岩反应对储层孔渗演变影响研究

Study of the effect of water-rock reaction on reservoir pore-permeability evolution during exploitation of karst geothermal resources

岩溶型地热开采过程中,储层内的水岩反应会改变储层孔渗,影响系统产能。为探究岩溶型热储开采过程中水岩反应对孔渗演变的作用机制,搭建了考虑孔隙变形的碳酸盐岩热流化多场耦合模型。揭示了热流化耦合作用下水岩反应对储层孔渗演变的作用机制,研究了孔渗参数的演变特征及其演变对系统取热性能的影响。结果表明:欠饱和注入下,注入井和波及前沿区域发生溶解反应,中间区域发生沉淀反应,致使储层浓度和孔隙度呈环状分布。开采30年时,注入井处孔隙度和渗透率分别增大了19.3%和73.6%,生产井处分别降低了0.11%和0.32%;考虑孔隙变形案例的注采压差比不考虑孔隙变形案例低21.7%。本研究可为碳酸盐岩岩溶型热储产能的精确预测和开发方案优化提供参考依据。

Water-rock reactions within the reservoir during karst-based geothermal exploitation can lead to variation of porosity and permeability,affecting the system's thermal performance.A multi-field coupled thermal-hydraulic-chemical model considering the pore changes was developed to investigate the mechanism of water-rock reaction on the evolution of pores and permeability during the production process of karst-based geothermal reservoirs.The mechanism of water-rock reaction on reservoir pore-permeability evolution under thermal-hydraulic-chemical coupling is revealed,and the evolutionary characteristics of pore-permeability parameters and their evolutionary impact on the system heat extraction performance are investigated.The results show that under undersaturated injection conditions,the concentration and porosity distribution present a ring shape,which is caused by dissolution reactions occurring in the injection wells and swept front regions,and precipitation reactions occurring in the intermediate regions.After 30 years of production,the porosity and permeability at the injection wells increased by 19.3%and 73.6%,respectively,and the porosity and permeability at the production wells decreased by 0.11%and 0.32%,respectively.The injection-production differential pressure of the case considering pore deformation was 21.7%lower than that of the case without considering pore deformation.This study is instructive for the accurate prediction of carbonate karst-based reservoir production and development program optimization.