Stimulation and Sequestration Mechanism of CO₂ Waterless Fracturing for Continental Tight Oil Reservoirs

Abstract

CO2 fracturing is a promising technology for oil field development in tight, continental deposits, with potential advantages of enhanced oil recovery (EOR), CO2 sequestration, and water conservation. Compared with CO2-EOR techniques, such as CO2 huff and puff and CO2 flooding, CO2 can interact with reservoir rock and fluid under higher pressure conditions during fracturing, resulting in CO2 stimulation and sequestration effects that differ from those that occur during conventional CO2-EOR. In this paper, the CO2 interactions between CO2 and reservoirs in continental tight oil reservoirs under fracturing conditions are systematically studied through laboratory experiments. The results show that under high pressure, CO2 effectively changes the pore structure through the extraction of hydrocarbons, dissolution of the rock matrix, and migration of minerals. CO2 dissolution of the rock matrix can significantly increase the number and complexity of fractures. Furthermore, CO2 has a higher solubility in formation fluid under high-pressure conditions. Given the higher pressures, CO2 forms a miscible phase with crude oil, diffuses more deeply into the formation, and reacts fully with the reservoir minerals and fluid during CO2 fracturing. Accordingly, CO2 can improve the permeability of the reservoir and flowability of crude oil significantly. Hence, CO2 fracturing can enhance oil recovery and CO2 sequestration more effectively. Core displacement experiments indicate that oil recovery of CO2 soaking process after CO2 fracturing is 36%, which is 12% and 9% higher than those of CO2 huff and puff and CO2 flooding with 5 pore volume, respectively. Field tests show that average oil production after CO2 fracturing is 1.42 times higher than that after CO2 flooding, which further validates the advantage of CO2 fracturing and demonstrates its huge application potential.

Laboratory Study of the Influence of Fluid Rheology on the Characteristics of Created Hydraulic Fracture

“…In case of Liquid nitrogen (LN 2 ) injection, thermal stress plays a significant role in reducing a fracture initiation and propagation pressure by generating enormously high-tensile hoop stress and causing extensive rock damage [18,19]. Injection of supercritical carbon dioxide (CO 2 ) demonstrates a strong thermal gradient, generating local tensile stress in the rocks surrounding a borehole [20].…”

CO2-assisted technologies for the development of tight gas reservoirs: The implication on CCUS

“…As a result of these reactions, reservoirs may become more porous and permeable, and the flow of natural gas commences. Gas recovery factor is enhanced and CO 2 is permanently stored in the geological formations (Tao et al, 2021). Tight reservoirs and other unconventionals are characterized by high temperature especially when the depth exceeds 1000 m where the temperature and (31.1 C,7.38 MPa,respectively).…”

Main Control Factors of Fracture Propagation in Reservoir: A Review

“…130 The chemical composition of fracturing fluids can affect the dissolution and corrosion properties of rocks. Unlike water-based fracturing fluids, under high pressure, CO 2 can extract hydrocarbons from tight oil reservoir rocks, dissolve the rock matrix and minerals, 134 large water consumption and the generation of a significant amount of wastewater may lead to regional seismicity, water lock reactions, and damage to formations 135 air prone to generating fracture branching and larger surface roughness 53 poor carrying capacity of proppants 136 LPG no fluid loss, resulting in better effective fractures 136 generates a large amount of flammable propane N 2 -based can enhance the connectivity of pore and fracture networks, can quickly clean without impacting the environment, L-N 2 has a large compression coefficient and strong expansion ability, and has high elasticity 137−139 poor carrying capacity of proppants, not suitable for use in plastic formations 140 CO 2 -based good permeability, low viscosity, generates finer and more complex fracture networks, increases methane and hydrocarbon production, and favorable for carbon sequestration 77,141 poor carrying capacity of proppants, leading to significant loss and leakage, strict requirements for fracturing equipment, preparation and transportation of carbon dioxide 31 and migrate, which can effectively alter the pore structure 131 (Figure 18). SC-CO 2 has a much lower viscosity than waterbased fracturing fluids, and its surface tension is close to zero, resulting in a much higher permeability as compared to waterbased fluids.…”

“…The chemical composition of fracturing fluids can affect the dissolution and corrosion properties of rocks. Unlike water-based fracturing fluids, under high pressure, CO 2 can extract hydrocarbons from tight oil reservoir rocks, dissolve the rock matrix and minerals, and migrate, which can effectively alter the pore structure (Figure ). SC-CO 2 has a much lower viscosity than water-based fracturing fluids, and its surface tension is close to zero, resulting in a much higher permeability as compared to water-based fluids.…”

“…SEM analysis of CO 2 infiltration into organic matter in rock indicates that, with increasing infiltration time, CO 2 can generate more etching pores within the organic matter and cause mineral migration. Reprinted with permission from ref . Copyright 2021 ACS Publications.…”