Experimental investigation of injection-induced fracturing during supercritical CO2 sequestration

Abstract

Leakage risk assessment is an inevitable procedure in permanent sequestration and storage of CO2 in deep saline aquifers and depleted oil and gas reservoirs, where the integrity of caprock is most critical. Low porosity and low permeability concrete cubes were employed as caprock analogs to investigate the supercritical CO2 injection-induced fracturing processes under true tri-axial stress conditions. A systematic experimental procedure, consisting of active acoustic emission measurement, pressure decay, injection pressure and temperature monitoring, fracture coloring, and gas fracturing, is formulated to qualitatively and quantitatively characterize the injectioninduced fracturing processes and fracture morphology. Occurrence of injection-induced fracturing can be directly identified from peaks of borehole pressure profiles as well as sharp drops on temperature profiles due to CO2 expansion, but generally there was no fracture propagation plateau appearing for the 20 cm rock cubes with zero pore pressure. Acoustic wave signatures, including both waveform change and arrival time delay, can effectively capture the extension of induced fractures inside the opaque rock. Initiation and propagation of supercritical CO2 injection-induced fractures are highly dominated by the tri-axial stresses, following the general trend of continuum mechanics at high stress levels with large stress difference. As the stress difference decreases, induced fractures branch off in relatively arbitrary directions. For these supercritical CO2 injection-induced fracturing experiments, poroelastic mechanics model makes a decent fit with the measured breakdown pressure of the caprock analogs. Findings in this study are valuable for risk analysis and operation optimization of geological CO2 sequestration and storage as well as for CO2 fracturing design and implementation in shale and tight reservoirs.

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

“…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 . These changes lead to an increase in permeability.…”

Study on the influence of mechanical characteristics of multi-rhythm inter-salt shale oil on fracture propagation in Qianjiang formation, China

“…Fracture direction and development are controlled by stress direction and magnitude, and the sample in homogeneities controls the hydraulic fracture development (Yashwanth et al 2013). The initiation and propagation of fractures caused by supercritical CO 2 injection are mainly controlled by triaxial stress, which conforms to the general trend of continuum mechanics at high stress levels with large stress difference (Wang et al 2017). Higher injection rate leads to higher breakdown pressure, while higher deviatoric stress leads to lower breakdown pressure .…”

Full-Sample X-ray Microcomputed Tomography Analysis of Supercritical CO2 Fracturing in Tight Sandstone: Effect of Stress on Fracture Dynamics

“…Under a triaxial condition, the plane of fracture or parting first tends to be perpendicular to the least principal stress. 26,43 The formation breakdown pressure (P b ) can be expressed as, 44 σ σ σ…”

“…Conventional fracture mechanics and continuum mechanics typically expresses fracture initiation as a function of the stress loading and tensile strength of the rock. Under a triaxial condition, the plane of fracture or parting first tends to be perpendicular to the least principal stress. , The formation breakdown pressure ( P b ) can be expressed as, where σ h and σ H refer to the least and greatest horizontal stresses, respectively, σ t is the tensile strength of rock, and P p is the pore pressure. If the core sample is treated as an elastic medium with no pore spaces or pore pressure, P b can be simplified as However, if there is natural pore pressure or fluid permeating into rock, the above equation (H–W) can be modified as, , where η = α (1 – 2υ)/(1 – υ) is a function of α and υ.…”