Investigation of Swelling and Elastic Property Changes Resulting from CO2 Injection into Cuboid Coal Specimens

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• 作者：Brijes Mishra ; Bongani Dlamini
• 刊名：Energy & Fuels
• 出版年：2012
• 出版时间：June 21, 2012
• 年：2012
• 卷：26
• 期：6
• 页码：3951-3957
• 全文大小：438K
• 年卷期：v.26,no.6(June 21, 2012)
• ISSN：1520-5029

文摘

To study and quantify the effect of CO₂ injection on sorption-induced strain (swelling) and coal elastic properties, specifically ultrasonic velocity (V_p and V_s) and elastic moduli, an experimental approach was followed. Two cuboid coal specimens with approximate dimensions of 25 cm (9.8 in.) 脳 17 cm (6.7 in.) 脳 6 cm (2.4 in.) were prepared. The coal specimens used were from the Lower Sunnyside Coal Seam of the Books Cliffs Coalfields in Utah. A specially designed steel frame was used to contain the specimens. Two extreme cases were tested using the specimens. For case one, a high injection pressure and a high confining pressure were used, and for case two, both injection pressure and confining pressure were dramatically decreased. The conventional pulse transmission method was used to determine P- and S-wave velocities. This method uses transducers to send an ultrasonic wave through the specimen, where corresponding transducers on the other end of the specimen then pick up the signal. Pre-injection measurements of ultrasonic velocity (V_p and V_s) were taken using the OYO New Sonic-Viewer. From V_p and V_s, other pre-injection properties, such as Poisson鈥檚 ratio and shear, bulk, and Young鈥檚 moduli (dynamic), were calculated. Digital deformation gauges were also strategically placed on the specimens to measure strain during the injection phase. CO₂ was injected into the first specimen at a high confining pressure and a high injection pressure, while both confining and injection pressures were dramatically lowered. Injection proceeded for 5 days for each of the specimens (25 h of actual injection). An increase in compressional velocity (as high as 21%) was measured at 12.41 MPa confining pressure and 4.14 MPa injection pressure. Because the dynamic elastic moduli are influenced by velocity, increases in elastic moduli were also observed with velocity increases. Adsorption strain as high as 0.9% was measured at 12.41 MPa confining pressure and 4.14 MPa injection pressure. It was also noted that significant changes in confining and injection pressures influenced the adsorption strain rate as well as the rate of change of compressional velocity and elastic moduli. At high injection pressure (4.14 MPa) and high confining pressure (12.41 MPa), adsorption strain, compressional velocity, and bulk modulus all had high rates of change. The opposite was observed at low injection pressure (1.8 MPa) and low confining pressure (1.8 MPa), with adsorption strain, compressional velocity, and bulk modulus all having low rates of change.