Optimized schemes of enhanced shale gas recovery by CO2-N2 mixtures associated with CO2 sequestration

Abstract

In response to the growing demand for CO2 mitigation and unconventional natural gas, the oil and gas industry is researching for the viability to enhance shale gas recovery (ESGR) and sequester CO2 in depleted reservoirs. Previous research has shown that a CO2-N2 mixture can be employed as a desired injection fluid to concurrently address both industrial issues. Due to the infancy of ESGR operations, there is no thorough knowledge of field-level optimized strategies using CO2-N2 for the ESGR associated with CO2 sequestration. In this study, the commercial reservoir simulator GEM and CMOST by CMG were adopted to conduct ∼ 120 simulation scenarios based on the Barnett shale formation in order to comprehend the impacts of three dominating operational parameters and propose the corresponding solutions. This study reveals four major findings. Firstly, a larger N2 concentration corresponds to a better recovery factor of shale gas but a shorter breakthrough time that causes the worse CO2 storage performance. Secondly, an injection rate is initially proportional to the shale gas recovery and CO2 storage performance but beyond a threshold rate, it can inversely affect both outcomes. Thirdly, the influence of a soaking period is limited in a short term and negligible in a long term for both ESGR and CO2 sequestration. Lastly, by selecting an appropriate combination of an injection rate and a CO2-N2 ratio, the income of a project can significantly be improved by 22 % under the current carbon tax policy. This study provides shale gas operators with a guideline for implementing large-scale ESGR projects employing CO2-N2 mixtures.