Simulation study on enhanced oil recovery with CO2 gas mixtures from offshore field in thailand

Abstract

The research is driven by the dual incentives of mitigating climate change impacts while storing CO₂ underground and obtaining more oil recovery. Currently, the field flares a CO₂-rich produced gas stream, which contributes to greenhouse gas emissions and increases the carbon footprint. Instead of burning this gas, the study explores reinjection for EOR purposes, transforming an emissions liability into an opportunity for hydrocarbon recovery and carbon tax mitigation - integrating waterflooding as part of the overall field development strategy. This study assesses the application of carbon dioxide enhanced oil recovery (CO₂-EOR) and water-alternating-gas (WAG) injection techniques for an offshore solution-gas drive reservoir. The modeling is conducted over a 20-year period utilizing the Petrel E-300 compositional simulator. The primary objectives include simulating the performance of CO₂-EOR across various injection gas compositions and evaluating the influence of key parameters such as gas composition, injection rate, WAG ratio, and well spacing on recovery efficiency. Minimum miscibility pressure (MMP) is estimated using empirical correlations and PVTi equation-of-state calculations. Reservoir simulations are performed using Eclipse and Petrel RE, with input parameters of the offshore field. The model validation is achieved through the history matching, with average deviations of 1.2% in bottom-hole pressure, 7.2% in gas-oil ratio, and 3.9% in cumulative oil production. MMP analysis confirms that all tested CO₂ compositions ranging from 95% to 25% purity, including practical and balanced impurity blends remain immiscible at reservoir pressure (~1,700 psia). The evaluation reveals that standalone CO₂-EOR is unsuitable due to significant increases in gas-to-oil ratio (GOR). Conversely, CO₂-WAG injection with 2:1 water-to-gas ratio, using 0.4 million standard cubic feet per day of 95% CO₂, achieves a total recovery factor of 42.9%, while maintaining GOR within the facility’s operational limits. The analysis identifies GOR as the key operational constraint. Beyond its technical contributions, this study provides a reference database for applying CO₂-EOR methods using impure, field-derived gas mixtures.