Leveraging Oil and Gas Legacy for Advanced CCS in Japan: Realistic CO2 Storage Simulation in the Higashi-Niigata Gas Field

Abstract Japan is advancing carbon dioxide capture and storage (CCS) initiatives to achieve carbon neutrality by 2050, identifying depleted oil and gas fields as promising storage sites. Among these, the Higashi-Niigata gas field – known for its long production history and extensive subsurface data — has been selected as a candidate site under the Advanced CCS Projects program led by the Japan Organization for Metals and Energy Security (JOGMEC). Due to Japan's unique geological conditions, storage reservoirs are not always as favorable as those found in other countries. However, the Higashi-Niigata field, being a depleted gas field with a long production history and abundant data, offers a distinct advantage over data-scarce aquifers for precise storage planning. In this study, Japan Petroleum Exploration Co., Ltd. (JAPEX) and MITSUBISHI GAS CHEMICAL COMPANY, INC.(MGC) jointly conducted a comprehensive reservoir evaluation to assess the feasibility of CCS implementation at the Higashi-Niigata field. Before initiating a reservoir evaluation, the seal integrity and fault stability were evaluated using geological and production history data. A geological model was constructed, and a reservoir simulation model was developed through history matching, despite the complexity of the interbedded sand and mud formations characteristic of the field. By leveraging extensive subsurface data and incorporating multiple geological realizations calibrated through history matching, the study achieved a highly accurate CO2 storage plan. This plan enabled the quantitative assessment of injection performance, pressure evolution, and storage capacity. The inclusion of case studies involving pressure relief wells further highlighted optimization strategies for preserving reservoir integrity and enhancing storage potential. The study demonstrated that the Higashi-Niigata gas field is a suitable and strategic candidate for CCS in Japan, with reliable injectivity, capacity, and integrity confirmed through simulation and data analysis.