Fault friction and slip stability not affected by Co₂ storage: Evidence from short-term laboratory experiments on North Sea reservoir sandstones and caprocks

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• 作者：Jon Samuelson ; ^{jonesamuelson@gmail.com} ; ^{samu0034@hotmail.com} ; ^{J.E.Samuelson@uu.nl} ; Christopher J. Spiers
• 关键词：Rate and state friction ; Fault strength ; Fault stability ; CCS ; CO2 water rock interaction
• 刊名：International Journal of Greenhouse Gas Control
• 出版年：2012
• 出版时间：November, 2012
• 年：2012
• 卷：11
• 期：supp_S
• 页码：S78-S90
• 全文大小：1324 K

文摘

We conducted velocity stepping direct-shear experiments on 5 separate simulated fault gouges made using 3 caprock samples, 1 reservoir rock, and 1 mixture of reservoir and caprock. Our aim was to understand the frictional strength and velocity dependent slip behavior of faults within and lateral to a potential pilot CO₂ sequestration reservoir situated in the Netherlands sector of the North Sea. To analyze fault mechanical properties prior to CO₂ injection, and to gain an understanding of the potential short-term influence of CO₂ after injection, experiments were conducted under a variety of pore fluid conditions; dry, dry-pressurized with supercritical CO₂, brine-saturated, and brine-saturated plus pressurized with supercritical CO₂. Experiments were conducted at in situ effective stress (35 MPa) and temperature (115 ¡ãC) for the potential pilot project. Results indicate that the coefficient of friction (¦Ì) for the studied caprock material is highly dependent on mineralogy, with ¦Ì increasing as a result of increasing quartz content and concomitant decrease in clay content. Quartz-rich reservoir rock exhibited the highest value for ¦Ì, and a 50/50 (wt. % ) mixture of caprock and reservoir rock showed ¦Ì values lying directly between those of the two end-member compositions (0.47 and 0.61). Saturation of clay-rich gouges with a brine solution led to weakening compared to dry gouges, whereas quartz rich gouges showed no clear weakening upon brine saturation. The addition of supercritical CO₂ to dry and to brine saturated gouges had no clear influence on frictional strength. The friction rate parameter (a ? b) as defined by the rate- and state-dependent friction laws was measured in low shear velocity steps (0.2-1-10-1-0.2 ¦Ìm/s) for all materials and pore fluid conditions, and indicates that all tested materials exhibit predominantly velocity strengthening behavior, and that neither the addition of brine nor supercritical CO₂ has any clear, strong influence on friction velocity dependence, indicating that reservoir faults should behave aseismically both before and after the addition of CO₂.