Resource Analysis and Screening for Potential CO2 Storage Targets in Low-Porosity Saline Aquifers, Yulin, China

Abstract The Ordos Basin, a crucial energy base in China, leads the nation in oil, gas, and coal production, consequently leading to high carbon emissions. This establishes it as a key prospective region for implementing CO2 geological storage (CCS) to facilitate regional emissions reductions. However, the basin is predominantly characterized by low-porosity and ultralow-permeability reservoirs, which limit the applicability of current site selection criteria, largely derived from successful international projects involving high-porosity and high-permeability reservoirs. There is a lack of systematic site selection research tailored to such low-quality reservoirs. Therefore, this study focuses on screening target areas for the CO2 storage. On the basis of well-logging and geological data from 192 wells in the Yulin area of the Ordos Basin, we systematically conducted lithostratigraphic correlation, reservoir property interpretation, and deep saline aquifer identification. This resulted in the identification of two saline aquifers: the Chang 10-3 Submember of the Yanchang Formation (with an average porosity of 8.3% and a maximum permeability of 12.3 mD) and the Qian 5 Member of the Shiqianfeng Formation (with an average porosity of 8.5% and a maximum permeability of 8.3 mD). We then developed the low-porosity and low-permeability evaluation index system (LOWEIS), a dedicated framework integrating and quantifying more than ten key indicators, including the sand-to-formation ratio, single-layer thickness, porosity, permeability, shale-to-formation ratio, and social environmental constraints. Applying the LOWEIS for hierarchical evaluation and spatial overlay analysis across the 14,000 km2 area of Yulin, China, we preliminarily identified 8 favorable storage targets with the highest implementation potential. This work complements existing site selection techniques for CO2 geological storage and provides a targeted evaluation framework for low-porosity and low-permeability saline aquifers.