Integrated Experimental and Simulation Study of Miscible Gas Flooding in Multi-Layered Light Oil Reservoir, Onshore Oil Field Thailand

Abstract

Abstract The remote area in Thailand’s onshore oil field has been under waterflooding. The improved oil recovery study was initiated to seek opportunities for infill well drilling, waterflood improvement, and enhanced oil recovery (EOR). The technical EOR screening results show that the miscible hydrocarbon gas injection is the most suitable EOR method. This study aims to conduct an integrated laboratory and simulation research of hydrocarbon gas injection in this area. The integrated laboratory studies include PVT analysis, oil swelling test, asphaltene deposition test, minimum miscibility pressure (MMP) measurement, and three gas coreflood tests at a pressure of 2,500 psi (at MMP), 3,000 psi (above MMP), and 2,000 psi (below MMP). The coreflood results are used to calibrate the input parameters in the core-scaled simulation before utilizing them in the field-scaled compositional simulation model. The gas injection scenarios include gas injection alone and water-alternating-gas (WAG) and are sensitized based on injector locations, injection rates, and WAG parameters to identify the optimal injection strategy. The SARA analysis shows an asphaltene content of 0.2%, and the asphaltene onset measurement test suggests the potential of asphaltene deposition when mixing live oil with injection gas. The slim tube tests indicate that an MMP of 2,535 psi is required to achieve the miscibility state. From the coreflood tests, the gas injection at a pressure of 3,000 psi is the most favorable condition, which could achieve the highest oil recovery factor at 95%. After gas injection, the permeability reduction is observed between 4 – 7%, and a small trace of asphaltene solid was detected from core thin-section images. From the simulation study, the optimal strategy is injecting water-alternating-gas (WAG) at updip locations by converting two existing producers, yielding an incremental recovery factor of 3.4%. This study presents the integrated laboratory and simulation study workflow of hydrocarbon gas injection in complex multi-layer light oil reservoirs. The investigation of asphaltene deposits and their impacts is included.