Case Study: Successful TCP and Acidizing Operation into Depleted Gas Reservoir for CCUS Project

Abstract 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.