Research on CO2 Emission and Sequestration in the Development of Low-Maturity Shale

Abstract Globally, low-maturity shale resources are abundant in reserves. Both the United States and China have developed oil shale resources with relatively shallow burial depths, and China is now conducting the development of low-maturity shale resources with greater burial depths. Once technical and theoretical breakthroughs are achieved, low-maturity shale resources are expected to become an important strategic replacement resource. However, during the development process, in addition to oil, natural gas, and water, a large amount of CO2 is generated, and some is even produced along with production, which increases global carbon emission pressure and is not conducive to mitigating climate change. Maximizing the in-situ sequestration of generated CO2 underground is one of the key issues that must be considered in future low-maturity shale development. Based on the traditional electric heating development method, this study proposes a development model combining high-temperature CO2 injection with electric heating by re-injecting emitted CO2 underground, and clarifies the CO2 emission and sequestration capacity using numerical simulation methods. The results show that: the electric heating method has a good short-term heating effect but a limited sweeping range; the high-temperature CO2 injection method can achieve long-term and large-scale thermal sweeping, which is favorable to the in-situ conversion. Through CO2 re-injection, a net-zero CO2 emissions in the in-situ conversion process is achieved. With the increase in heating time, the CO2 emission rate shows a trend of first increasing and then decreasing, while the sequestration efficiency gradually decreases. After 5.5 years of heating, under standard conditions, the cumulative emission volume is 76.1 million cubic meters, and the sequestration volume is 457 million cubic meters, with a sequestration efficiency of 83.3%. This study reveals the laws of CO2 emission and sequestration during the development of low-maturity shale, realizes net-zero CO2 emissions, and is of great significance to global carbon emission and sequestration as well as mitigating global climate change.