Research on the Calculation Method of CO2 Storage Volume and its Application in L Reservoir
Authors: WU Zangyuan , FENG Qihong , LIAN Liming , MENG Xiangjuan , XU YanLong , WANG Sen , WU Kuankuan , ZHOU Wei , LUO Min , LI Yang , FAN Jin , CHENG Ronghong , WU Mimi , HUANG Xingning 
Published: February 2025

This paper addresses the difficulty in calculating CO2 storage volume due to the complexity of CO2 occurrence states in the CCUS process. A method for calculating CO2 storage volume is proposed, designing well networks throughout the entire lifecycle of CCUS to meet the demands of both CO2 EOR and storage stages. This extends the implementation time of CO2 EOR to enhance oil recovery and ensures effective CO2 storage while maximizing oil production, aligning with the global strategy of green and low-carbon development.

Initially assuming that the pore volume of produced hydrocarbons is completely occupied by CO2 and considering dissolution retention and mineral reaction retention, the theoretical carbon storage volume of the target reservoir is predicted to determine the upper limit of storage volume. Building on flash calculation, utilizing equations of state-activity models, equations of state-equations of state models, and chemical reaction kinetics models, model parameters were fitted and corrected through experiments on CO2 multiphase non-isothermal flow, dissolution, solid-phase deposition, and mineral reactions to develop a CO2 storage volume prediction model and proprietary software. Finally, reliability verification was conducted using analogous block comparison methods.

The technology proposed in this paper has been applied in the integrated CO2 EOR and storage scheme for the L reservoir, predicting saturation fields, solubility fields, and various storage mechanisms during the CO2 flooding and storage process and providing three-dimensional field changes. Results indicate that the theoretical carbon storage upper limit for the L reservoir is 9.88 million tons; under current reservoir temperature and pressure conditions, CO2 dissolution loss in formation connate water is 0.05 t/m3, and in residual oil it is 0.32 t/t, resulting in an effective storage volume of 7.47 million tons (with analogous block comparison results at 7.78 million tons, verifying the reliability of the method). Dissolved CO2 and supercritical CO2 exhibit similar spatial and temporal distribution characteristics; buoyancy and overburden effects lead to upward CO2 migration. Sealing forms during CO2 flooding phase are dominated by structural and hydrodynamic sealing, supplemented by dissolution sealing and capillary sealing; mineral sealing is less effective in the short term. After millennia, mineral sealing becomes the dominant form at 47%, followed by dissolution sealing at 34%, capillary sealing at 12%, and structural and hydrodynamic sealing at 7%.

The "CO2 Storage Volume Calculation Method" proposed in this paper provides an effective means of predicting carbon storage volume for practical application in the integrated CO2 EOR and storage scheme of CCUS technology. The developed software can seamlessly integrate with mainstream reservoir numerical simulation commercial software, enabling storage simulation based on EOR, including various simulations of saturation, solubility, and the four major storage mechanisms, as well as dynamic visualization of three-dimensional field maps. Analogous block comparisons and on-site experimental results also confirm the effectiveness of this technology.