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Extensive rainfall can lead to the discharge of untreated mine drainage from abandoned mines. The Ministry of Economy, Trade and Industry aims to promote environmental impact assessments in scenarios where untreated mine drainage discharges may occur due to extensive rainfall. This study aims to develop a risk assessment method for these events, focusing on 26 abandoned mine drainages without responsible parties. We estimated metal concentrations at discharge points under the assumption that untreated drainage is released. A tiered system was used for the risk assessment: Tier 0 evaluates risks using river flow rates during droughts, while Tier 1 uses simulated post-rainfall river flows via AIST-SHANEL. In the Tier 0 assessment, two mine drainages (No. 5 and No. 8) exhibited Cd, Pb, As, Cu, Zn, Fe, and Mn concentrations below environmental standards, indicating that high dilution effect contributed to a low-risk discharge even after a certain period following extensive rainfall. In the Tier 1 assessment, even for mine drainages assessed as high-risk in the Tier 0 assessment, some mine drainages, which initially assessed as high-risk in Tier 0, showed metal concentrations below environmental standards for up to 7 days following peak rainfall, suggesting that high flow rates can mitigate discharge risks. For practical application, simulating river flow during extensive rainfall would allow predictions of heavy metal concentrations at discharge and water use points. Our approach would enable the setting of appropriate discharge periods and volumes, even in situations where untreated discharges are unavoidable, contributing to minimize environmental impacts downstream.
Depleted reservoirs are one of the targets for CCUS projects. Hirai area in Higashi-Kashiwazaki gas field onshore Japan was selected for a CO2 storage reservoir of Kashiwazaki blue hydrogen and ammonia production and usage demonstration project. A highly depleted current reservoir condition after historical hydrocarbon gas production and highly heterogeneous reservoir quality of the volcanic formation posed technical challenges for the completion work of wells drilled in the Hirai gas field as follows: Perforation under an overbalanced pressure condition which make heavy mud loss and skin damageHigh uncertainty of reservoir quality to obtain sufficient CO2 injectivityRisk of damaging fiber optic cables installed along production casing for monitoring. This paper presents a case study of oriented Tubing Conveyed Perforation (TCP) perforation followed by acidizing operation to overcome above technical challenges. To obtain sufficient well productivity and injectivity, prior to operation a feasibility study of oriented perforation was conducted, considering both of wireline and TCP perforation operation. The study suggested that TCP was a better choice with a better penetration depth, while wireline perforation would not exceed a mud invasion zone which was expected due to depleted reservoir pressure. To mitigate the risk of damage on fiber cables, oriented perforation was considered. Most critical aspect of oriented perforation was to determine fiber optic cable mapping accurately. Both of gyro wireline tool and wireline with electromagnetic field measurement were combined and System Integrity Test (SIT) was performed before actual operation to optimize wireline operation parameters to detect fiber optic cable efficiently. Because current reservoir pressure was lower than hydrostatic pressure, mud loss after gun fire was concerned and it would make additional skin damage on the well. Kill well operation with CaCO3 was considered to prevent continuous mud loss through perforation interval. As CaCO3 could be dissolved by acid, combination of kill well operation with CaCO3 and acid treatment was adopted. Proposed operation approach achieved high well productivity by minimizing skin damage. The use of depleted reservoirs for CCUS has several attractive attributes compared to the use of saline aquifer, e.g., lower pressure, existing infrastructure, and better understanding in the reservoir. Nevertheless, some of these attribute poses technical challenges. It is believed that our integrated approach from perforation to acidizing job could be referred as one of approaches to solve such challenges for other CCUS field.
The results of pioneering carbon dioxide capture and storage（CCS）projects such as Sleipner and Gorgon are widely recognized as milestones in the early days of CCS. The reservoir formations of the pioneering projects are characterized by homogeneous sandstones that develop over several hundred meters thick. On the other hand, sandstone formations expected to work as reservoirs for CCS in Japan are characterized to be more heterogeneous and thinner than those of pioneering projects as above because of the tuffaceous sandstones typical of volcanic arcs. In addition, the geological formations in Japan that separated by complex faults in active continental margins might not be suitable for CCS reservoirs. However, we will have to make CCS feasible against these "challenging" formations. In this paper, examples of multidisciplinary approaches for geological evaluation of domestic depleted oil fields obtained from a joint study with INPEX are shared, and we hope that those findings would help future CCS projects in Japan.
JOGMEC's official name is supposed to be changed to "Japan Organization for Metals and Energy Security" on 14th November 2022 according to the coming into effect of revised JOGMEC Act". Furthermore, JOGMEC is supposed to be added its functions of equity investment for production and storage of hydrogen and ammonia, as well as for carbon dioxide capture and storage(CCS). Technical business strategy is being updated to accommodate with current situation in terms of energy security and carbon neutral requirements.
