Hybrid Gas EOR in Onshore Thailand: Bridging Experiments and Simulations for Compartmentalized Reservoirs

This study explores the implementation of hybrid gas injection in the low-permeability, compartmentalized, multi-layer reservoirs within Thailand's largest onshore oilfield. The full and complete integration of experimental and simulation studies is performed to rigorously assess and optimize various injection strategies and injection gas types. The fluid characterization study involves PVT analysis, oil swelling, and asphaltene deposition tests. The minimum miscibility pressure (MMP) tests are extensively conducted using conventional methods (Slim Tube and Rising Bubble Apparatus tests) and a new innovative micromodel method, which reduces testing time from months to a day and enables testing with different gas formulas. Three gas injection coreflood tests are performed and calibrated with a 1D coreflood simulation. The field-scale simulation models are developed, history-matched, and used to design optimal enhanced oil recovery (EOR) methods. Numerous EOR strategies, including waterflood, gas injection, Water-Alternating-Gas (WAG), and Double Displacement Process (DDP), are evaluated. PVT tests indicate an oil swelling factor of up to 30% and a twofold viscosity reduction when mixed with 60% hydrocarbon gas, enhancing oil mobility. The MMP of the reservoir oil and hydrocarbon gas ranges between 5,000 and 5,500 psi, exceeding the current reservoir pressure of 3000 to 4000 psi. Coreflood tests, calibrated with core-scale simulations, demonstrate high one-dimensional oil recovery of 96% at 5,000 psi (MMP), which decreases to 89% at 4,000 psi and 71% at 3,000 psi. These findings underscore the importance of maintaining high-pressure conditions to achieve miscibility and optimize gas-oil displacement efficiency. In the field-scale simulation, the gas injection at the well level was allocated through SIMPLEX optimization algorithm to achieve the highest oil recovery. The optimal strategy for enhanced oil recovery is the updip WAG and downdip water injection, increasing the effective recovery factor by 4.5%. This approach leverages the combined benefits of oil displacement by injected gas and water while maintaining reservoir pressure in favorable conditions. Enriched LPG gas can double the recovery factor, as MMP is tremendously reduced by multiple folds. This study establishes a comprehensive framework for hybrid gas EOR, bridging laboratory experiments to field-scale applications and offering valuable insights for making informed decisions in brownfield development planning. It represents the first PTTEP full-loop technical evaluation of gas EOR, providing rapid and robust MMP estimation, coreflooding experiments, and field-scale simulations. This framework can serve as a prototype for future projects, advancing knowledge and practices in the petroleum industry.