Assessment indicator system for siting of geologic CO2 sequestration in low-porosity and low-permeability saline aquifers: A case study of the Ordos Basin

ObjectiveCO2 injection and geologic sequestration in deep saline aquifers as underground spatial resources represents an important means of achieving the targets of greenhouse gas emission reduction and carbon neutrality. Current assessments of the siting and potential for geologic CO2 sequestration in saline aquifers focus primarily on the macroscopic basin and regional scales, with the assessment indicator system scarcely accounting for the suitability of low-porosity and low-permeability strata. MethodsUsing data from 192 wells in the Yusheng area, Ordos Basin, this study conducted the division and correlation of intervals bearing no hydrocarbon, carried out lithologic and physical interpretations of these intervals, and identified aquifer reservoirs. Then, this study investigated dominant aquifer reservoirs, including stratigraphic characteristics, sealing performance of cap rocks, sequestration potential, and surface environment. Accordingly, this study developed and quantified assessment indicators for the siting of geologic CO2 sequestration in saline aquifers that account for the developmental characteristics of low-porosity, low-permeability reservoirs. Results and ConclusionsThe proposed assessment indicator system consists of three first-level indicators, namely geologic sequestration, sequestration capacity, and socio-environmental conditions. These indicators, consisting of second-level indicators, are used to characterize the injectivity, sequestration capacity, and surface feasibility, respectively of saline aquifers. The second-level indicators of the geologic sequestration conditions include reservoir lithology, reservoir thickness, porosity, and permeability; those of the sequestration capacity conditions encompass the sealing performance of cap rocks, burial depth, sequestration potential, and faults, and those of the socio-environmental conditions comprise the current status of underground resource development, land use conditions, collapse and disaster areas, source-sink matching, and public acceptance. The assessment system for the target area- and site-scale siting of CCS projects, established based on the current low-porosity and low-permeability sandstone reservoirs in the Ordos Basin, will provide a basis and guide for the implementation of the industrial projects of geologic CO2 sequestration in saline aquifers.