Full-Sample X-ray Microcomputed Tomography Analysis of Supercritical CO2 Fracturing in Tight Sandstone: Effect of Stress on Fracture Dynamics,Energy & Fuels

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Full-Sample X-ray Microcomputed Tomography Analysis of Supercritical CO2 Fracturing in Tight Sandstone: Effect of Stress on Fracture Dynamics
Energy & Fuels ( IF 5.2 ) Pub Date : 2021-01-07 , DOI: 10.1021/acs.energyfuels.0c03554
Bing Yang ₁ , Haizhu Wang ₁ , Zhonghou Shen ₁ , Olufemi Olorode ₂ , Bin Wang ₂ , Yong Zheng ₁ , Wanjuan Yan ₁ , Zhaoyang Jia ₁

Affiliation

The commercial production from tight oil and gas reservoirs has been facilitated by the multistage hydraulic fracturing of horizontal wells. This process typically requires the pumping of large amounts of slick water into the subsurface, and this could be challenging in areas with a limited supply of water. Despite the commercial success of hydraulic fracturing with water, it still faces the problem of clay swelling and potential contamination of underground water. This has led to research studies and field applications of liquid or supercritical carbon dioxide (SC-CO₂) fracturing in unconventional oil and gas resources. Considering that the propagation and characteristics of these man-made fractures are controlled by the fracturing fluid and mechanical state of the reservoir, we performed a series of fracturing experiments on tight sandstones using water and SC-CO₂ at different stress magnitudes. To explore the morphology of the fractures and quantify their attributes, we proposed a novel full-sample fracture analysis approach, which is based on microcomputed tomography (CT) imaging. The results of this study indicate that the breakdown pressure is a linear function of the minimum principal stress and tensile strength. We observe that the pattern and geometry of the fractures created from SC-CO₂ fracturing is more complex than those of water fracturing under the same stress conditions. Our experimental results also indicate that smaller differential stresses lead to the creation of more fracture branches and that fracture propagation is significantly affected by the presence of initial bedding planes. Furthermore, our quantification of the fracture attributes (based on fracture extraction and digitization) indicates that SC-CO₂ fracturing leads to the creation of more complex fractures with rougher surfaces than water fracturing. This experimental study proposes a new full-sample fracture quantification approach, which can be implemented to analyze fracture attributes precisely and effectively. The results from this work could provide insights and guidance for the field application of SC-CO₂ fracturing in unconventional oil and gas resources.

中文翻译：

致密砂岩中超临界CO ₂压裂的全样品X射线微计算机断层扫描分析：应力对断裂动力学的影响

水平井的多级水力压裂促进了致密油气藏的商业生产。该过程通常需要将大量的光滑水泵入地下，这在水供应有限的地区可能具有挑战性。尽管水力压裂在商业上取得了成功，但它仍然面临着粘土膨胀和地下水潜在污染的问题。这导致了液态或超临界二氧化碳（SC-CO ₂）非常规油气资源的压裂。考虑到这些人为裂缝的传播和特征受压裂液和储层力学状态的控制，我们在不同应力大小下用水和SC-CO ₂对致密砂岩进行了一系列压裂实验。为了探索骨折的形态并量化其属性，我们提出了一种新颖的基于显微计算机断层扫描（CT）成像的全样本骨折分析方法。这项研究的结果表明，击穿压力是最小主应力和拉伸强度的线性函数。我们观察到由SC-CO ₂产生的裂缝的模式和几何形状在相同的应力条件下，压裂比水压裂更复杂。我们的实验结果还表明，较小的压差导致创建更多的裂缝分支，并且裂缝的扩展受初始层理面的存在显着影响。此外，我们对裂缝属性的量化（基于裂缝提取和数字化）表明，与水力压裂相比，SC-CO ₂压裂导致形成了更粗糙，表面更粗糙的裂缝。这项实验研究提出了一种新的全样本裂缝量化方法，可用于精确有效地分析裂缝属性。这项工作的结果可以为SC-CO的现场应用提供见识和指导₂压裂非常规油气资源。

更新日期：2021-01-21

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