页岩储层超临界二氧化碳压裂裂缝形态研究

doi:10.11743/ogg20190316

摘要/Abstract

摘要： 目前超临界CO₂压裂技术尚不成熟，裂缝形成与扩展机理尚不明确。为深入认识超临界CO₂压裂裂缝延伸规律及空间形态，基于位移间断边界元方法，通过引入Pen-Robinson方程来实现超临界CO₂压裂过程的模拟。结合室内物理模拟实验，初步探讨了页岩储层水力压裂与超临界CO₂压裂裂缝扩展形态的差异。研究结果表明，由于超临界CO₂的扩散性及良好的渗透能力，通过增加围岩孔隙压力，从而减少了地应力对裂缝扩展的约束，使裂缝起裂压力低于水力压裂。超临界CO₂压裂时产生的体积应变增量与压后裂缝破坏程度比水力压裂更高，使得在裂缝形态复杂程度高于水基压裂液。同时，超临界CO₂压裂裂缝断面复杂、不平整，裂缝表面粗糙度比水力压裂更大。

关键词: 裂缝扩展, 裂缝形态, 天然弱面, 超临界二氧化碳, 水力压裂, 页岩储层

Abstract: The supercritical CO₂ fracturing technology is yet to be improved,and the mechanisms of fracture generation and propagation are still not clear at present.In order to get an in-depth understanding of hydraulic fracture propagation behaviors and geometry under supercritical CO₂ fracturing,we introduced the Pen-Robinson equation to simulate the process of supercritical CO₂ fracturing,based on the displacement discontinuity boundary element method.Combined with lab physical simulation experiments,the differences of hydraulic fracture propagation behaviors and geometry between conventional fracturing with water-based fluid and fracturing with supercritical CO₂ in the shale reservoir were discussed.The results show that the pressurization in the pores of surrounding rocks will function to reduce the constraint of in-situ stress on fracture propagation,thanks to the diffusivity and good permeability of supercritical CO₂,and in turn the initiation pressure for fractures is lower than that of conventional fracturing.The incremental volumetric strain generated during and the failure of fractures after supercritical CO₂ fracturing are higher than those under conventional fracturing,thus the fracture geometry under supercritical CO₂ fracturing is more complex than that under fracturing with water-based fluid; meanwhile,the fracture plane under supercritical CO₂ fracturing is more complex and uneven,and has higher tortuosity than that under conventional fracturing with water-based fluid.

Key words: fracture propagation, fracture geometry, natural weak plane, supercritical CO₂, hydraulic fracturing, shale reservoir

中图分类号:

TE357.1

苏建政,李凤霞,周彤. 页岩储层超临界二氧化碳压裂裂缝形态研究[J]. 石油与天然气地质, 2019, 40(3): 616-625. doi: 10.11743/ogg20190316 Su Jianzheng,Li Fengxia,Zhou Tong. Hydraulic fracture propagation behavious and geometry under supercritical CO₂ fracturing in shale reservoirs[J]. Oil & Gas Geology, 2019, 40(3): 616-625. doi: 10.11743/ogg20190316

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