Vertical fracture propagation behavior upon supercritical carbon dioxide fracturing of multiple layers
Vertical fracture propagation behavior upon supercritical carbon dioxide fracturing of multiple layers
复制标题
多层超临界二氧化碳压裂垂直裂缝扩展行为
DOI：
10.1016/j.engfracmech.2022.108913
复制
发表时间：
2023-01-21
影响因子：
5.4
通讯作者：
Cui, Zhuang
中科院分区：
文献类型：
--
作者：
Hou, Bing;Cui, Zhuang
鄂尔多斯盆地延长组砂岩-页岩互层中蕴藏着丰富的非常规油气资源。但砂岩-页岩互层储层界面发育，非均质性强，超临界二氧化碳裂缝高度增长难以预测。为了提高砂岩-页岩互层储层产能，有必要明确Sc-CO2裂缝演化机制。针对砂岩-页岩互层Sc-CO2压裂过程，提出了一种全局嵌入零厚度黏结元数值模拟方法，研究了应力差、界面强度、射孔位置对裂缝垂向扩展模式的影响。这些结果使我们得出三个主要结论。(1)采用全局嵌入内聚单元法结合非线性本构方程建立压裂模型，解决了内聚单元不能有效模拟Sc-CO2裂缝随机扩展的问题。(2)在地应力和天然软弱面共同作用下，裂缝扩展模式呈现“工字型”、“十字型”和“单字型”三种典型模式。此外，主裂缝与层间界面之间存在6种相互作用模式。当主裂缝穿过砂岩-页岩界面时，容易形成分支裂缝和微裂缝。(3)垂向应力差大于4 MPa，无因次综合界面强度在0.3 ~ 0.4之间，页岩和砂岩同时射孔是裂缝高度充分扩展的有利因素。研究结果为砂岩-页岩互层储层Sc-CO2压裂层位选择提供了理论指导。
There are abundant unconventional oil and gas resources in the sandstone-shale interbed of the Yanchang Formation in Ordos Basin. However, it is difficult to predict the growth of supercritical carbon dioxide (Sc-CO2) fracture height in sandstone-shale interbed reservoirs due to the developed interface and strong heterogeneity. To enhance the productivity of sandstone-shale interbed reservoirs, it is necessary to clarify the Sc-CO2 fracture evolution mechanism. In this study, a global embedded zero-thickness cohesive element method is proposed for numerical simulation of Sc-CO2 fracturing of sandstone-shale interbeds, and the effects of stress difference, interface strength, and perforation position on fracture vertical propagation pattern are investi-gated. The results lead us to three main conclusions. (1) The fracturing model is established using the global embedded cohesive element method combined with the nonlinear constitutive equa-tion, which solves the problem that the cohesive element cannot effectively simulate the random propagation of Sc-CO2 fractures. (2) Under the combined influence of in situ stresses and natural weak surfaces, there are three typical fracture extension patterns: I-shaped, cross-shaped, and single-shaped. In addition, there are six interaction modes between the main fracture and the interlayer interface. Branch fractures and microfractures are easily formed when the main frac-ture penetrates the sandstone-shale interface. (3) The vertical stress difference is greater than 4 MPa, and the dimensionless comprehensive interface strength is between 0.3 and 0.4, so the simultaneous perforation in shale and sandstone is a favorable factor for the full expansion of fracture height. The results provide theoretical guidance for selecting the Sc-CO2 fracturing ho-rizon of sandstone-shale interbed reservoirs.