Date of Award

January 2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Petroleum Engineering

First Advisor

kegang Ling

Abstract

Unconventional reservoirs, such as the Bakken and Three Forks formations, present significant challenges due to their ultra-low permeability and complex fracture networks, which limit primary oil recovery to less than 10%. To enhance hydrocarbon extraction while simultaneously facilitating carbon dioxide (CO₂) storage, this study investigates the mechanisms governing CO₂ Huff-n-Puff (HnP) and associated storage under various operational conditions. A comprehensive approach integrating experimental analysis, numerical simulations, multiphase flow modeling, and geochemical interactions is employed to optimize CO₂-EOR and storage strategies. The experimental phase focuses on evaluating the performance of different injected gases (CO₂, ethane, and propane) in the Upper Three Forks (UTF) and Middle Three Forks (MTF) formations. A series of experiments are applied under different constraints. The parameters that are examined include the effect of soaking time at immiscible and miscible conditions, the effect of fluid state (vapor, supercritical), injection pressure, selected gases (CO2, ethane, and propane), target formations (Upper Three Forks (UTF) and Middle Three Forks (MTF)), and the effect of pore size distribution on the recovery factor. During the Huff-n-Puff process, the Nuclear Magnetic Resonance (NMR) technique was used to analyze the microscopic oil production and the micro residual oil distribution before and after CO2 injection. NMR measurements reveal that soaking time plays a pivotal role in mobilizing oil from diverse pore structures, particularly under or near the minimum miscibility pressure (MMP), while higher injection pressures above the MMP attenuate the benefits of soaking. Moreover, propane demonstrates the highest recovery factor at low pressures, followed by ethane and CO₂, though the performance of lighter gases improves significantly at higher pressures. Additionally, the physical properties of the rocks can undergo significant alteration during the CO2 injection and soaking stage. While the interaction between brine, rock, and CO₂ has been widely studied, there is limited understanding of how the buffering capacity of carbonate-rich and silicate-rich rocks influences these interactions and alters pore-scale properties, fluid flow, brine chemistry, and mineralogical composition under the complex mineralogy of Bakken rocks. To address this problem, we present an experimental investigation on how supercritical CO2 (Sc-CO2) influences mineralogy, fluid flow, pore structure, and brine chemistry in carbonate-rich and silicate-rich samples from the Bakken Formations. Carbonate-rich rocks display notable dissolution of calcite and a concomitant reduction in acidity that favors clay stability, whereas silicate-rich samples exhibit pronounced clay dissolution and subsequent quartz precipitation. Extended soaking times (up to 30 days) prove essential for the penetration of CO₂ into micropores, although precipitation of salt crystals in macropores diminishes fluid mobility in both rock types, most notably in formations with lower buffering capacity. Although horizontal drilling and multistage hydraulic fracture (HF) have significantly increased the primary production, field data also indicate substantial well interference arising from HF overlaps (HFO) in the multi-well pad (MWP). During the CO2 Huff-n-Puff (HnP) process, poor conformance management can lead to early CO2 breakthrough, causing injected CO2 to promptly migrate to adjacent wells without effectively contacting the designated HnP well. Moreover, gas relative permeability hysteresis, which depends on alternating drainage (injection) and imbibition (production) under varied complex HF interference can redistribute the CO2 mobilization, hence, impacting oil recovery and CO₂ trapping mechanism. Simultaneously, geochemical interactions among CO₂, brine, and rock can alter reservoir properties, and injectivity, potentially complicating interference patterns. This study develops a 3D field geological model for the Bakken formation using conventional logs and petrophysical analysis. A compositional simulation was subsequently performed on a MWP (4 wells) for history matching. Following that, three HFO Schemas (low, medium, and high) were conducted to investigate the impact of injection rate and offset well operations on well interference under varying degrees of overlap. Gas hysteresis was integrated using Land’s trapping function to assess the influence of hysteresis-induced trapping on the efficiency of MWP interference performance. Additionally, Henry's law for CO2 solubility in brine was coupled with aqueous and mineral reactions, providing an in-depth perspective on reactive transport effects on porosity, permeability, and the overall CO2-EOR and storage effectiveness in complex HF networks. The results indicate that the multi-well pad study highlights how partial closure of offset wells increases average reservoir pressure, improves CO₂ solubility in oil, and enhances the efficiency of both oil recovery and CO₂ storage. Relative permeability hysteresis aids in creating residual gas saturation, improving overall storage, yet can reduce injectivity near the Huff-n-Puff well. Furthermore, geochemical reactions, including calcite dissolution, affect reservoir properties such as porosity and permeability, thus influencing both CO₂ migration and oil recovery. The findings of this study contribute to optimizing gas injection strategies for unconventional reservoirs by identifying the most effective injection parameters and enhancing the understanding of gas-oil-rock interactions. The research provides a systematic framework for improving CO₂-EOR efficiency while maximizing CO₂ storage potential, supporting both economic hydrocarbon recovery and long-term carbon management initiatives. The insights gained will aid in developing more effective CO₂ injection designs, minimizing early gas breakthroughs, and advancing sustainable energy practices in the Bakken Formation development.

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