CO2 injection-induced fracturing in naturally fractured shale rocks

Abstract

Niobrara shale cubes of 20 cm from Colorado were employed to investigate gas and supercritical CO 2 injection-induced fracturing in naturally fractured caprocks of deep aquifers/depleted reservoirs and fractured shale reservoirs. Under tri-axial stresses, gas or supercritical CO 2 was injected into the center of the cubes to induce fracturing. Real-time pressure and temperature, acoustic wave, pressure decay, fracture coloring, and gas fracturing were used to characterize the fracturing process and fracture morphology. Without pore pressure, CO 2 injection-induced fracturing occurred and completed instantly, accompanied by an evident temperature drop. Strongly bonded fractures barely affected transverse fracture propagation, whereas weakly bonded or open fractures arrested the injected fluid first and then allowed it to generate new fractures perpendicular to the minimum horizontal stress. Breakdown pressures for cubes with preexisting fractures using gas and supercritical CO 2 are much lower than both poroelastic predictions and slick-water fracturing pressure, and some are even lower than the minimum horizontal stress. This is attributed to unconformable preexisting fractures and the low viscosity of CO 2. Moreover, decreasing tri-axial stress levels and increasing stress differences tend to lower the breakdown pressure. This study is instructive for understanding and tackling geomechanical issues related to CO 2 geological storage and fracturing of shale reservoirs.

Effects of injection parameters on heat extraction performance of supercritical CO2 in enhanced geothermal systems

“…The result in Figure shows that the permeability of the rock sample increases with increasing injection pressure. When the SCCO 2 injection pressure increases and exceeds the breakdown pressure of the preexisting fractures, it causes the propagation and damage of the micro‐fractures . In addition, an increase in the temperature of the injected SCCO 2 results in its volume expansion and viscosity reduction, accompanied by a decrease in the fracture temperature .…”

The role of supercritical carbon dioxide for recovery of shale gas and sequestration in gas shale reservoirs

“…[204][205][206][207] Due to its low viscosity and lack of surface tension, SC-CO 2 used as a fracture stimulation fluid, has the potential to lower the formation breakdown pressure and create more irregular multiple fractures compared to liquid CO 2 or water. Wang, et al 208 used the Niobrara shale to conduct fracturing experiments with gaseous and SC-CO 2 , as well as slickwater with the same confining pressures and temperature. They found that gaseous and SC-CO 2 induced fracturing occurred at much lower pressures than slickwater fracturing, which were 6.6 MPa, 9.6 MPa and 11.0 MPa, respectively.…”

Study on crack propagation of the CO2 presplitting blasting empty hole effect in coal seam

“…CO 2 presplitting blasting of a coal and rock mass with empty holes is completed under the combined action of stress waves and explosive gases 30,31 . If the tangential tensile stress derived from radial displacement exceeds the tensile strength of the coal and rock mass, it will generate radial cracks in the coal and rock mass; then, the explosive gas is filled the initially formed radial crack, and the crack propagates under a gas‐driven mode 32,33 . The physical model of CO 2 blasting in the entire empty hole of the coal and rock mass is expressed by Equations .…”