Impact of through-layer fracturing on CO2 storage efficacy of interbedded reservoirs in inclined formations

Abstract

Large-scale carbon dioxide geological storage (CGS) is an effective means of mitigating global warming. However, inconsistencies between the distribution of high-quality reservoirs and CO₂ source locations hinder the large-scale implementation of CGS. Studies indicate that saline aquifer sequestration plays a dominant role in geological storage, yet not all saline aquifers serve as high quality reservoirs for CO₂ sequestration. Sandstone-mudstone interbedded deposits are common in natural formations. What kind of engineering measures can improve the CO₂ injection performance of such an interbed reservoir is a challenging problem. This study targets sandstone-mudstone interbedded reservoirs, and proposes a new interbedded reservoir modification concept using through-layer fracturing in horizontal wells. A three-dimensional numerical model was developed to systematically evaluates the effectiveness of fracturing in enhancing CO₂ storage under various dip angles, accounting for formation dip angle and fracture height. Results show that fracturing increases both the CO₂ migration distance and injection volume within the reservoir across different dip angles. In this study, migration distance increased by up to 66.7 %, and injection volume by up to 67.5 %. Compared to horizontal formations, inclined formations exhibit more significant injection enhancement, with a maximum enhancement of 12.5 %. An analysis of post-modification injection safety indicates that localized pressures may exceed safe injection thresholds due to the impact of fracture planes and formation slope. Adjusting injection well pressure effectively prevents this occurrence. The findings provide new insights and methodologies for optimizing CGS site selection and improving reservoir sequestration performance.