The Integrity Evaluation of Geological Body for CCUS Technology Based on Microseismic Monitoring Technology

Abstract The integrity of geological bodies is a fundamental condition for the long-term and highly efficient storage of CO2. Geological body integrity of CO2 injection areas is indirectly judged by such conventional methods as primarily assessing contamination degree of water and gas in shallow layers, as well as changes in carbon flux in soil and the atmosphere. Direct identification methods for leakage pathways of inter-layers and faults are relatively limited. This paper puts forward a evaluation method for geological body integrity of Carbon Dioxide Capture, Utilization, and Storage (CCUS) based on microseismic monitoring technology. This technique utilizes downhole geophones to collect data of target intervals, and employs perforation signals of adjacent wells for polarization analysis of P-waves. Then we correct the direction of the downhole geophones with three-components, optimize the velocity model. Subsequently, microseismic signals generated during the CO2 flooding process are located by adopting the method of multi-wave joint orientation technology. By analyzing the sequences and spread conditions of microseismic events, the spread distribution of CO2 flooding front is grasped, and the channeling condition of inter-layers is determined. This technology has been applied in the CO2 flooding test areas in Jilin Oilfield, which is the largest CCUS demonstration area in PetroChina. It is designed with 12-stage geophones, with a longitudinal monitoring range covering the top and bottom boundaries of the oil reservoir. The lateral monitoring range is approximately 1500m, and the monitoring period is 60 days, covering two complete water-gas alternating injection cycles, each cycle lasting 30 days. By statistically analyzing the time sequence and magnitude attributes of microseismic events, a total of 539 effective microseismic events have been acquired, with magnitudes ranging from -3.13 to -0.906. In the vertical direction, the locations of microseismic events are concentrated in producing reservoir areas, with no continuous microseismic events occurring across the cover layer, indicating good integrity performance of the formation. The successful application of this technology effectively evaluates the geological integrity of CCUS systems, which is of significant importance in guiding the subsequent location selection for CCUS/CCS technologies. Additionally, it provides effective data support for understanding the flow patterns of CO2 injected into the formation, and also the basis for the mapping of subsequent development plans.