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Role of CO2 in geomechanical alteration of Morrow Sandstone across micro–meso scales
International Journal of Rock Mechanics and Mining Sciences ( IF 7.2 ) Pub Date : 2023-01-20 , DOI: 10.1016/j.ijrmms.2022.105311
G.L. Manjunath, A.T. Akono, I. Haljasmaa, Birendra Jha

We study the effect of CO2 on the mechanical properties of Morrow Sandstone in Farnsworth Unit oilfield in Texas, where supercritical CO2 is being injected for sequestration and enhanced oil recovery (EOR) applications. We conduct mechanical compression tests with acoustic monitoring and microscratch tests on core samples taken from two wells in the Farnsworth field to quantify the role of CO2 on poroelastic moduli and fracture toughness across micro-to-meso scales. We quantify dynamic poroelastic moduli at different effective stresses and temperatures using argon and CO2 as saturating pore fluids and analyze the effect of the fluid type on property alteration. Variation in the effective stress is achieved by varying the confining stress from 5 MPa to 20 MPa and varying the pore pressure over 0–20 MPa range. The temperature is varied from 23 degC to 75 degC, which is relevant for sequestration-EOR applications. Microscratch tests are performed to investigate the nonlinear fracture behavior and estimate the change in the scratch toughness resulting from CO2 exposure. Scanning electron microscopy shows evidence of nonlinear fracture mechanisms. Using the Size Effect Law for fracture analysis, we find that scratch-induced deformation transitions from ductile to brittle regime as the penetration depth increases. We observe a 29%–45% reduction of the scratch toughness in the bedding-parallel direction and a 60%–82% reduction in the bedding-perpendicular direction, both of which are larger in magnitude compared to the 8%–10% increase in the dynamic elastic modulus at mesoscale due to injection-induced cooling. The grain orientation affects the fracture behavior and CO2-induced geomechanical alterations: a greater decrease in fracture toughness is observed in the bedding-perpendicular orientation.



中文翻译:

CO 2 在莫罗砂岩微观-中尺度地质力学变化中的作用

我们研究了 CO 的影响2个得克萨斯州 Farnsworth Unit 油田 Morrow 砂岩力学特性的研究,超临界 CO2个正在注入封存和提高石油采收率 (EOR) 应用。我们对取自 Farnsworth 油田两口井的岩心样本进行机械压缩测试、声学监测和微划痕测试,以量化 CO 的作用2个关于微观到中观尺度的多孔弹性模量和断裂韧性。我们使用氩气和 CO 量化不同有效应力和温度下的动态多孔弹性模量2个作为饱和孔隙流体并分析流体类型对性质变化的影响。通过在 5 MPa 到 20 MPa 之间改变围压以及在 0-20 MPa 范围内改变孔隙压力来实现有效应力的变化。温度在 23 摄氏度到 75 摄氏度之间变化,这与螯合-EOR 应用相关。进行微划痕测试以研究非线性断裂行为并估计由 CO 引起的划痕韧性的变化2个接触。扫描电子显微镜显示非线性断裂机制的证据。使用尺寸效应定律进行断裂分析,我们发现随着穿透深度的增加,划痕引起的变形从韧性状态转变为脆性状态。我们观察到沿层理平行方向的划痕韧性降低了 29%–45%,沿层理垂直方向降低了 60%–82%,两者的幅度都大于 8%–10% 的增加由于注射引起的冷却,在中尺度的动态弹性模量。晶粒取向影响断裂行为和CO2个-引起的地质力学改变:在层理垂直方向上观察到断裂韧性的更大降低。

更新日期:2023-01-21
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