基于数值模拟探讨提高咸水层CO_2封存注入率的途径

Numerical investigation for enhancing injectivity of CO_2 storage in saline aquifers

咸水层CO2地质封存是减少大气中CO2排放量的有效途径。CO2注入率是衡量咸水层中CO2注入能力的有效因素,因此,研究注入速率的变化规律及提高的措施是很有工程价值的。在很多区域,地层的低渗透性限制了CO2的注入率。针对鄂尔多斯盆地的水文地质条件,通过数值模拟,探讨在低渗透性咸水层中提高CO2注入率的途径,包括改变储层中的盐度、采用水平井注入、增加注入井段的长度以及采取水力压裂等工程措施。其中改变储层中的盐度可通过在注入CO2前向储层中注入一定量的水来实现。模拟结果表明,这些方式可以有效地提高CO2注入率,其中水平井改造方式和水力压裂工程措施效果显著,盐度改造措施在地层初始含盐度较高时,会有更好的效果。研究结果可为鄂尔多斯盆地和类似地区的咸水层CO2地质封存项目提供参考。

CO2 storage in deep saline aquifers is considered to be an imperative practical mean for reducing greenhouse gas emissions. Injectivity is one of key factors for determining the feasibility for storage of CO2 in a brine field. Research into the injection rate variation rules and the measures to improve is of great value. Many saline aquifers have relatively low permeability which limits the injection rate of CO2 to the aquifers. In this paper, numerical simulation studies of carbon dioxide storage in brine-saturated reservoirs have been conducted to investigate the approaches for enhancing injectivity through changing the fluid salinity in aquifer, using horizontal well or longer injection screen, and introducing hydraulic fracturing for storage aquifer improvement. Changing fluid salinity can be implemented through injecting a slug of fresh water prior to commencement of CO2 injection. Setup of the models is loosely based on the hydrogeological conditions in Ordos basin. Modeling results indicate that these approaches can effectively improve the injectivity. Use of horizontal well and hydraulic fracturing shows obvious injectivity enhancement. The effect of changing salinity could be more significant when the initial salinity of aquifer is high. The findings may provide helpful hints to the CO2 geologic sequestration in saline aquifer in Ordos basin or similar areas.