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Fast Evaluation of Caprock Strength Sensitivity to Different CO2 Solutions Using Small Sample Techniques
Rock Mechanics and Rock Engineering ( IF 6.2 ) Pub Date : 2021-09-16 , DOI: 10.1007/s00603-021-02641-6
Laura Edvardsen 1 , Mohammad H. Bhuiyan 1 , Pierre R. Cerasi 1 , Ruben Bjørge 1
Affiliation  

The Draupne shale is a rock formation functioning as overburden for gas reservoirs in the Norwegian Sea and potentially as caprock for future CO2 storage locations as well. In this paper, the Draupne shale was exposed to several fluids: CO2 gas, supercritical CO2, CO2 gas dissolved in brine, supercritical CO2 dissolved in brine, as well as brine and dry air. The motivation for the exposure tests was to investigate whether injected CO2 in a reservoir coming into contact with the caprock could change the caprock’s mechanical properties and increase the risk for leakage of the stored CO2. In addition, a systematic exposure study will provide more insight into the various processes susceptible of altering the shale’s shear strength and acoustic velocity, such as clay hydration, mineral dissolution, and capillary forces. Due to the low permeability of the shale, experiments were conducted on mm-sized disk samples, reducing fluid diffusion into the shale, and allowing for many repeated tests on disks close by in the original core. The punch method, where a small circle is punched out of the shale, was used to assess shear strength, while continuous wave technique was used to assess ultrasonic velocity. Results show that the shale is not noticeably sensitive to CO2, in the sense that no additional weakening is observed in the presence of CO2 as compared to brine exposure. This last weakening effect is probably due to poor matching between pore fluid salinity and exposure brine strength.



中文翻译:

使用小样本技术快速评估盖层强度对不同 CO2 溶液的敏感性

Draupne 页岩是一种岩层,可作为挪威海气藏的覆盖层,也可能作为未来 CO 2储存地点的盖层。在本文中,Draupne 页岩暴露于多种流体:CO 2气体、超临界 CO 2、溶于盐水的CO 2气体、溶于盐水的超临界 CO 2以及盐水和干燥空气。暴露测试的动机是研究在与盖层接触的储层中注入的 CO 2是否会改变盖层的机械特性并增加储存的 CO 2泄漏的风险. 此外,系统的暴露研究将更深入地了解易改变页岩剪切强度和声速的各种过程,例如粘土水化、矿物溶解和毛细管力。由于页岩的低渗透性,在毫米大小的圆盘样本上进行了实验,减少了流体扩散到页岩中,并允许在原始岩心附近的圆盘上进行多次重复测试。从页岩中冲出一个小圆圈的冲压方法用于评估剪切强度,而连续波技术用于评估超声波速度。结果表明,页岩对 CO 2不是很敏感,因为在 CO 2存在下没有观察到额外的弱化与盐水暴露相比。最后一种减弱效应可能是由于孔隙流体盐度与暴露盐水强度之间的匹配不佳。

更新日期:2021-09-16
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