Reservoir Recovery Optimization and Carbon Dioxide Reduction: Opportunities Using Carbon Dioxide Huff-N-Puff Technique
Authors: Zheng W. , Gurpinar O. , Banerjee R. , Wang J. , Khneigera J. , Malpani R. , Krishnamurthy J. 
Published: November 2023

Abstract
Today, most mature fields are past their peak production periods, and the traditional field management practices are no longer sufficient. Without enhanced oil recovery (EOR) techniques, large volumes of oil could be left unrecoverable. Unlike conventional reservoirs, unconventional reservoirs face sharp decline challenges, and EOR considerations should come as early as well design. And the utilization of captured carbon dioxide (CO2) is immediate and beneficial for CO2 reduction. The objective of this study is to investigate unconventional reservoirs that had been previously stimulated with hydraulic fracturing, the application of CO2 huff-n-puff technique and provide reservoir recovery optimization recommendations.
Because accurate subsurface understanding is critical for unconventional reservoir development, in this paper, a calibrated 3D mechanical earth model with petrophysical properties was used for the study. This was followed upon fracture, reservoir, and geomechanical coupling for reservoir simulation and production forecast. A CO2 huff-n-puff application was evaluated numerically for wells located in the Permian Basin and Bakken Formation. For the Permian Basin case study, an unconventional fracture model (UFM) was used to simulate seven wells, along with a numerical reservoir simulation through unstructured perpendicular bisection (PEBI) grids to capture the simulated fracture properties. A compositional reservoir model was used for production history matching and forecasting over a 5-year period. The CO2 huff-n-puff was applied to determine the well performance and recovery factor arising from the reservoir fluid viscosity reduction and gas expansion. For the Bakken Formation case study, a parent-child well scenario was simulated using a planar3D hydraulic fracture model, and a finite-element reservoir geomechanics coupling technique was applied to capture induced depletion effects caused by the parent well production. With a sensitivity study over the CO2 huff-n-puff timing schedules, injection rates, injection compositions, and comparison with gas reinjection, the application of the CO2 injection to recovery systems in the low-permeability reservoir medium was captured.
In this study we found that: 1) CO2 can compare favorably to gas reinjection as an EOR agent. Increasing the injection rate can help improve the recovery factor (RF) but up to certain limits and is driven by the price of oil or the economic environment. 2) EOR should be implemented early in field production to achieve maximum benefits for unconventional reservoirs. 3) Infill well can be further improved if the EOR method of CO2 huff-n-puff is used over various time periods of production. 7% extra RF was observed when the nonmiscible CO2 was used, while 65% extra RF was observed when CO2 and wet hydrocarbon (C3 to C5) mixture was used as compared to production dependent only on hydraulic fracture stimulation. 4) Using a numerical reservoir simulation study coupled with a fracture simulation model presents insights into improving the RF through CO2 injection and can be reliable for field forecasts and critical to increase the long-term economic benefits. This approach can be applied to formations in other basins to improve the RF, meanwhile facilitating the decarbonization goal.