Hele-Shaw Modeling of CO2-Assisted Gravity Drainage with Bottom-Water Support: An Experimental Study

Document Type

Conference Proceeding

Publication Date

1-1-2026

Abstract

Gas-assisted gravity drainage (GAGD) has emerged as a promising enhanced oil recovery (EOR) method that utilizes the natural buoyancy of injected gas to mobilize oil in gravity-dominated systems. The scope of this work is to experimentally evaluate the performance of CO2-assisted GAGD in the presence of bottom-water support, a common reservoir condition that complicates gas flooding efficiency. The primary objectives are to (i) assess the impact of injection pressure and oil production rate on oil recovery, (ii) determine the operational conditions that maintain gravity dominance and delay breakthrough, and (iii) identify the trade-offs between maximizing recovery and minimizing gas losses. A Hele-Shaw glass model was employed to simulate a reservoir system consisting of an oil zone underlain by an active water aquifer. A Free-Fall Gravity Drainage experiment served as the baseline for comparison. CO2 injection tests were then performed by systematically varying injection pressure (0.5–2 psig) and production rate (50% and 100% valve openings). To ensure efficient experimental design, Hammersley Sequence Sampling was applied to distribute test conditions evenly across the operational space. Flow dynamics were captured with time-sequence images, while cumulative oil recovery and breakthrough times were monitored. Statistical analyses, including analysis of variance (ANOVA) and multiple linear regression, were conducted to quantify the relative contributions of the studied parameters and to validate experimental observations. The experimental results demonstrate that injection pressure is the most influential parameter controlling ultimate recovery, while production rate primarily affects breakthrough timing and frontal stability. Maximum recovery of 88.4% was achieved at an injection pressure of 2 psig combined with a restricted production rate. At low pressures, production rate showed limited effect, but at higher pressures, unrestricted production accelerated breakthrough and destabilized the oil bank, leading to early gas channeling and reduced sweep efficiency. Image analysis confirmed that higher injection pressure accelerated oil displacement but introduced risks of unstable flooding without controlled production. Statistical analysis reinforced the qualitative findings, with Analysis-Of-Variance (ANOVA) confirming the dominance of injection pressure and regression models accurately predicting recovery trends. The combined insights emphasize the operational trade-offs: while higher injection pressures increase recovery potential, production restrictions are essential to avoid premature gas override and sustain stable displacement fronts. This study provides new experimental insights into CO2-assisted GAGD performance under bottom-water support, an area rarely addressed in the literature. The integration of Hele-Shaw physical modeling with statistical analysis and flow visualization offers a novel approach for quantifying operational parameters and their interactions. The findings not only highlight practical strategies for optimizing GAGD field operations but also expand the fundamental understanding of gravity-driven CO2 flooding processes in reservoirs with active aquifers.

Publication Source (Journal or Book title)

Proceedings SPE Symposium on Improved Oil Recovery

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