Fractal Evolution Characteristics on the Three-Dimensional Fractures in Coal Induced by CO2 Phase Transition Fracturing

IF 4.7 3区材料科学 Q1 ENGINEERING, ELECTRICAL & ELECTRONIC ACS Applied Electronic Materials Pub Date : 2024-05-04 DOI:10.3390/fractalfract8050273

Zhen Zhang, Gaofeng Liu, Jia-Chi Lin, George Barakos, Ping Chang

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Abstract

To analyze the transformed effect of three-dimensional (3D) fracture in coal by CO2 phase transition fracturing (CO2-PTF), the CO2-PTF experiment under a fracturing pressure of 185 MPa was carried out. Computed Tomography (CT) scanning and fractal theory were used to analyze the 3D fracture structure parameters. The fractal evolution characteristics of the 3D fractures in coal induced by CO2-PTF were analyzed. The results indicate that the CO2 phase transition fracturing coal has the fracture generation effect and fracture expansion-transformation effect, causing the maximum fracture length, fracture number, fracture volume and fracture surface area to be increased by 71.25%, 161.94%, 3970.88% and 1330.03%. The fractal dimension (DN) for fracture number increases from 2.3523 to 2.3668, and the fractal dimension (DV) for fracture volume increases from 2.8440 to 2.9040. The early dynamic high-pressure gas jet stage of CO2-PTF coal influences the fracture generation effect and promotes the generation of 3D fractures with a length greater than 140 μm. The subsequent quasi-static high-pressure gas stage influences the fracture expansion-transformation effect, which promotes the expansion transformation of 3D fractures with a length of less than 140 μm. The 140 μm is the critical value for the fracture expansion-transformation effect and fracture generation effect. Five indicators are proposed to evaluate the 3D fracture evolution in coal caused by CO2-PTF, which can provide theoretical and methodological references for the study of fracture evolution characteristics of other unconventional natural gas reservoirs and their reservoir stimulation.

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二氧化碳相变压裂诱发煤炭三维裂缝的分形演化特征

为分析二氧化碳相变压裂（CO2-PTF）对煤中三维（3D）裂缝的改造效果，进行了压裂压力为 185 兆帕的 CO2-PTF 试验。利用计算机断层扫描（CT）和分形理论分析了三维断裂结构参数。分析了 CO2-PTF 诱导的煤中三维裂缝的分形演化特征。结果表明，CO2 相变压裂煤具有裂缝生成效应和裂缝扩展-变形效应，使最大裂缝长度、裂缝数量、裂缝体积和裂缝表面积分别增加了 71.25%、161.94%、3970.88% 和 1330.03%。压裂数量的分形维度（DN）从 2.3523 增加到 2.3668，压裂体积的分形维度（DV）从 2.8440 增加到 2.9040。CO2-PTF 煤的早期动态高压气体喷射阶段影响了裂缝生成效果，促进了长度大于 140 μm 的三维裂缝的生成。随后的准静态高压气体阶段影响了裂缝扩展-转化效应，促进了长度小于 140 μm 的三维裂缝的扩展转化。140 μm 是压裂膨胀转化效应和压裂生成效应的临界值。提出了评价 CO2-PTF 作用下煤炭三维裂缝演化的五项指标，可为其他非常规天然气储层裂缝演化特征及其储层激励研究提供理论和方法参考。

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来源期刊

ACS Applied Electronic Materials Multiple-

CiteScore

7.20

自引率

4.30%

发文量

567

期刊介绍： ACS Applied Electronic Materials is an interdisciplinary journal publishing original research covering all aspects of electronic materials. The journal is devoted to reports of new and original experimental and theoretical research of an applied nature that integrate knowledge in the areas of materials science, engineering, optics, physics, and chemistry into important applications of electronic materials. Sample research topics that span the journal's scope are inorganic, organic, ionic and polymeric materials with properties that include conducting, semiconducting, superconducting, insulating, dielectric, magnetic, optoelectronic, piezoelectric, ferroelectric and thermoelectric. Indexed/Abstracted： Web of Science SCIE Scopus CAS INSPEC Portico

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