Experimental investigation of injection-induced fracturing during supercritical CO2 sequestration. (August 2017)

• Record Type: Journal Article
• Authors: Wang, Lei; Yao, Bowen; Xie, Haojun; Kneafsey, Timothy J.; Winterfeld, Philip H.; Yin, Xiaolong; Wu, Yu-Shu
• Is Part Of: International journal of greenhouse gas control. Volume 63(2017)
• Page Start: 107
• Page End: 117
• Publication Date: 2017-08
• Subjects: CO2 sequestration and storage -- Supercritical CO2 -- Fracturing -- Geomechanics -- True tri-axial stress -- Caprock; Greenhouse gases -- Environmental aspects -- Periodicals; Air -- Purification -- Technological innovations -- Periodicals; Gaz à effet de serre -- Périodiques; Gaz à effet de serre -- Réduction -- Périodiques; Air -- Purification -- Technological innovations; Greenhouse gases -- Environmental aspects; Periodicals; 363.73874605
• DOI: 10.1016/j.ijggc.2017.05.006
• Languages: English
• ISSNs: 1750-5836

Abstract

Highlights: A systematic experimental procedure was developed for scCO2 injection-induced fracturing monitoring and characterization. ScCO2 induced fracturing is controlled by the tri-axial stress heterogeneity and affected by low fluid viscosity. Poroelastic mechanics model matches the scCO2 breakdown pressure of low porosity and permeability concrete blocks. 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 injection-induced 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.