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Experimental and numerical investigation of hydrocarbon gas huff-n-puff in unconventional reservoir
Fu, Qinwen
Fu, Qinwen
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Abstract
Unconventional resources have become an important and irreplaceable part of the energy supply for industry and the public. The Eagle Ford play in Texas has been one of the most productive unconventional reservoirs in North America. To continue unlocking potential barrels of oil from unconventional reservoirs, research and development of production technology and understanding of production mechanisms are the top priorities. Gas huff-n-puff injection technique has been attracting industry interest because of the convenience, efficiency, and potential of carbon sequestration. This dissertation focuses on studying the phase behavior, mass transfer mechanism, and operation parameters during hydrocarbon gas huff-n-puff injection in the Eagle Ford play. It included several parts.First, phase behavior between injection gas and reservoir stock-tank oil was analyzed experimentally and numerically. A pressure-volume-temperature (PVT) cell was used for phase behavior experiments between oil and gas fluid systems, CMG WinProp™ software was used to tune heavy components’ critical properties as well as other Peng-Robinson equation of state (PR-EOS) properties, and CMG GEM was used for minimum miscibility pressure (MMP) slim tube modelling. Accurate characterization of reservoir fluids in refined EOS models and MMP for huff-n-puff injection pressure design were studied.Second, experimental measurement and analysis of pressure, oil recovery factor, and produced fluid compositions from six cycles of hydrocarbon gas huff-n-puff injection in three Eagle Ford core samples at reservoir conditions were conducted. The recovery factors for the three samples were 57.5%, 56.7%, and 51.7%, respectively. A significant gap existed in defining diffusion coefficients coupled with rock tortuosity. Numerical study with focuses on fracture complexity, lithological variations, and diffusion mechanism was carried out by history matching model to experimental data at the core scale in Schlumberger ECLIPSE®. A comprehensive study was performed on three representative litho-facies from Lower Eagle Ford rock samples to measure effective within phase and cross-phase diffusion coefficients.Third, the numerical model was scaled up from core scale to field scale for sensitivity analysis and predictions in Schlumberger PETREL. The field model was history matched with huff-n-puff pilot test in the Eagle Ford then diffusion mechanism was incorporated with the model. 2.2% higher oil recovery factor was observed by adding diffusion mechanism in the simulation model for five cycles of hydrocarbon gas huff-n-puff. Smaller fracture spacing promoted diffusion mechanism leading to higher oil recovery. Depletion level prior to huff-n-puff injection for the producer also affected ultimate recovery efficiency with an optimum time for each case of live and dead oil systems. Parameter analysis on puff production periods and soaking times suggested that longer production time per cycle slightly increased oil production, while shorter soaking time accelerates oil production and had minimal difference in ultimate oil recovery after huff-n-puff. Injection gas comparisons ranked y-grade CO2 ≈ hydrocarbon gas lean gas for maximizing oil production. The study contributes insights into upscaling and offers huff-n-puff pilot design recommendations in the Eagle Ford formation.
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Date
2023-12-31
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University of Kansas
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Keywords
Petroleum engineering, Chemical engineering, Petroleum geology, Diffusion, Eagle Ford, Enhanced Oil Recovery, Huff-n-puff, Reservoir Engineering, Unconventional Reservoir