Chemical treatment and gas huff-n-puff for enhanced oil recovery in oil shale reservoirs
Shale oil contributes more than 60% to the US oil production. Shale oil production has been feasible because of technological development for horizontal wells with multistage hydraulic fracturing. However, after primary production, more than 90% of the oil is left behind in shale oil reservoirs due to ultra-low permeability. For an average well the oil production rates fall sharply in the first year because of the extremely low permeability, micro-fracture closure, and large flow resistance at the matrix-fracture interface. To sustain oil production from shale oil, it is essential to develop enhanced oil recovery (EOR) techniques for unconventional reservoirs. In this dissertation, lab experiments were conducted to investigate the effect of chemical treatment, gas huff-n-puff, and/or both on EOR in shale oil reservoirs. Surfactant treatment on shale was studied. Static adsorption experiments were performed to investigate the adsorption behavior of surfactant on shale samples. An additive model was built to estimate the adsorption capacity given the mineral composition and TOC of shale samples. A series of surfactant screening process, including aqueous stability tests, contact angle measurements, interfacial tension measurements, and spontaneous imbibition experiments, was used to compare the performance of surfactants at reservoir conditions. Surfactant blends were compared with single surfactants, and the surfactant blends showed improved oil recovery compared to most single surfactants. Chemical blends showed good EOR potential in Eagle Ford formation, and the effects of solvents in chemical blends were investigated via spontaneous imbibition process. Chemical blends with solvents showed improved recovery compared to the brine-only controlled case, and the Green Solvent showed the most promising results among the five solvents tested. Cyclic gas injection was investigated with CO₂ and hydrocarbon gases. CO₂ huffn-puff showed about 40% oil recovery, and it was observed that the huff pressure to which the cores were pressurized with CO₂ did not affect the oil recovery significantly as long as the pressure was high enough. A combination of chemical blend with CO₂ was more effective compared to pure CO₂ huff-n-puff (40% → 64%). The hydrocarbon gas (60% C1 + 35% C2 + 5% C3) showed a similar effectiveness as CO₂, which can be used to replace CO₂ depending on availability and cost. Also, a numerical simulation model was built to investigate the key parameters in the gas huff-n-puff qualitatively. The learning from these simulations can be used for future experimental design.
Enhanced oil recovery, Chemical blend, CO₂ huff-n-puff, Shales, Hybrid EOR methods
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