From Coreflooding and Scaled Physical Model Experiments to Field-Scale Enhanced Oil Recovery Evaluations: Comprehensive Review of the Gas-Assisted Gravity Drainage Process

Abstract

The gas-assisted gravity drainage (GAGD) process has been suggested to improve oil recovery in both secondary and tertiary stages through immiscible and miscible injection modes. In contrast to continuous gas injection and water-alternating gas, the GAGD process takes advantage of the natural segregation of reservoir fluids to provide gravity-stable oil displacement and improve oil recovery. In the GAGD process, the gas is injected through vertical wells at the top of the reservoir to formulate a gas cap that allows oil and water to drain downward to the reservoir bottom, where horizontal producer(s) are placed. Extensive experimental works and limited reservoir-scale evaluation studies have been conducted to test the effectiveness of the GAGD process performance. In this paper, a comprehensive literature review is presented to summarize all of the references about concepts, principles, and field-scale evaluations of the GAGD process. Particularly, this paper presents an introduction to the mechanisms of CO2–rock–fluid interactions, gas enhanced oil recovery injection approaches, the GAGD process physical model, the factors influencing the GAGD process, and a review of all of the previous field-scale evaluation studies. Furthermore, the validation of the GAGD process in reservoir-scale applications is fully discussed by focusing on its weaknesses with respect to the optimal implementation design for achieving maximum oil recovery.

Enhanced Gas Recovery in Kerogen Pyrolytic Pore Network: Molecular Simulations and Theoretical Analysis

“…With the dramatic development of modern industry, the consumption of traditional fossil energy sources (e.g., coal, oil, and natural gas) is significantly increasing worldwide, resulting in the worries of energy shortage. Meanwhile, the excessive emission of greenhouse gases (e.g., carbon dioxide) in the atmosphere is triggering global climate change, via effects such as global warming. , Nowadays, achieving the means to increase the energy supply and concurrently reduce the emission of greenhouse gas has become an urgent problem for almost all countries. Fortunately, the development of unconventional reservoirs such as shale gas, known as a clean energy source with huge reserves and energy conversion rates, , greatly alleviates this problem and plans a new blueprint for the future world energy pattern.…”

CO2 Sequestration and Enhanced Oil Recovery via the Water Alternating Gas Scheme in a Mixed Transgressive Sandstone-Carbonate Reservoir: Case Study of a Large Middle East Oilfield

“…The CO 2 -EOR contains different methods such as CO 2 -WAG, continuous CO 2 injection, CO 2 huff-n-puff (H-n-P), and gas-assisted gravity drainage (GAGD). , Furthermore, studies have been conducted to assess the performance of CO 2 -EOR techniques in oil-bearing reservoirs that showed that continuous CO 2 injection during CO 2 -EOR is highly effective for oil displacement and viscosity reduction. , However, this continuous CO 2 injection can cause CO 2 breakthrough that is induced by gravity segregation, thereby causing viscosity fingering and permeability reduction because of inorganic and asphaltene deposition . The GAGD is presented as a powerful CO 2 -EOR technique to improve oil recovery because of the density difference between the injected gas and the crude oil. , The main advantage of GAGD is the huge volume of CO 2 that can be injected into the subsurface formation, which leads to cutting down the large-scale emissions of CO 2 into the atmosphere and boosts the volumetric sweep efficiency. , The basic idea behind GAGD is to inject gas vertically to form a gas cap, then utilize gravity segregation to drive oil and water out of the reservoir by employing situated horizontal wells to extract the oil.…”

“…The GAGD is presented as a powerful CO 2 -EOR technique to improve oil recovery because of the density difference between the injected gas and the crude oil. , The main advantage of GAGD is the huge volume of CO 2 that can be injected into the subsurface formation, which leads to cutting down the large-scale emissions of CO 2 into the atmosphere and boosts the volumetric sweep efficiency. , The basic idea behind GAGD is to inject gas vertically to form a gas cap, then utilize gravity segregation to drive oil and water out of the reservoir by employing situated horizontal wells to extract the oil. In contrast, the presence of methane in the reservoir will cause to reduce the dissolved CO 2 in the crude oil, which results in reducing oil swelling . Also, decrease in oil viscosity occurs when CO 2 is saturated with the oil reservoir at high pressure.…”

“…Also, decrease in oil viscosity occurs when CO 2 is saturated with the oil reservoir at high pressure. In addition, the effectiveness of gravity segregation is decreased because of the density reduction of oil and water because of the reaction of CO 2 and water in the reservoir. , …”

Performance demonstration of gas-assisted gravity drainage in a heterogeneous reservoir using a 3D scaled model

“…5 Theoretical research and eld practice has demonstrated that GAGD can inhibit viscous ngering and increase swept volume and ultimate recovery factor. [6][7][8][9] GAGD is inuenced by many factors, [10][11][12][13] including heterogeneity, wettability, and water saturation of the reservoir, uid property, gas injection rate, and oil recovery factor. Dominant seepage zones or dominant seepage paths frequently occur in the reservoirs with high heterogeneity, leading to early gas breakthrough and sweep efficiency reduction during CGI or WAG.…”