The impact of geological heterogeneity on horizontal well-triplet performance in CO2-circulated geothermal reservoirs

CO2 circulated geothermal production can be integrated with CO2 geological sequestration as a utilization method to offset cost. Investigation of heterogeneity impact is limited to CO2 sequestration and its effect on CO2 circulation and associated heat recovery is unclear. This study is aimed to improve the understanding of this problem by numerical experiments. A set of spatially correlated heterogeneous porosity fields is generated using a variety of geostatistical parameters, i.e., variance, correlation lengths, anisotropy and azimuth. Heterogeneous fields of intrinsic permeability and initial/residual water saturation are derived from porosity using equations regressed from a field dataset. Twenty combinations of injection pressure and well space obtained by Latin-Hypercube sampling are deployed in each heterogeneous field, generating a suite of numerical geothermal reservoir models. Performance indicators, including lifespan, net stored CO2, produced heat flux, and total recovered heat energy in lifespan, are calculated from each model simulation. The simulation results suggest that geologic heterogeneity could develop highpermeable CO2 flow paths, causing bypass of the hot low-permeable zones, shortened lifespan and reduced total recovered heat energy. Depending on the azimuth, anisotropy can create either flow barriers or preferential flow paths, increasing or decreasing heat sweeping efficiency. The relative angle between horizontal wells and the axis of maximum continuity of the heterogeneity can be optimized to maximize heat recovery efficiency. These finds provide useful insights of interplay between geological heterogeneity, well placement and operation of CO2 circulated geothermal production.

Automated summary

This study improves the understanding of the impact of geological heterogeneity on CO2 circulated geothermal production through numerical experiments. It reveals that geological heterogeneity can affect CO2 flow paths, shorten production lifespan, and reduce heat recovery.