非常规储层超临界CO2压裂复杂裂缝扩展模型

Complex fracture propagation model of supercritical CO2 fracturing in unconventional reservoirs

蔡鑫

中国石化胜利油田分公司博士后科研工作站，山东 东营 257001 中国石化胜利油田分公司勘探开发研究院，山东 东营 257001

Postdoctoral Research Station, Shengli Oilfield Company, SINOPEC, Dongying 257001, China Research Institute of Petroleum Exploration and Development, Shengli Oilfield Company, SINOPEC, Dongying 257001, China

超临界CO2压裂是一种很有前景的非常规储层开采技术，由于其具有黏度低、流动能力强的特征，使得压裂时产生多分支的复杂裂缝。目前大多数水力裂缝扩展模型需要指定裂缝扩展路径和方向，无法得到实际的复杂裂缝扩展结果，因此文中在考虑超临界CO2低黏度特性的基础上，建立了非常规储层超临界CO2压裂流￣固耦合复杂裂缝扩展模型。该模型通过建立弱形式有限元公式和有限差分公式，实现了岩石变形和流体运移的耦合计算；同时，在裂缝分支处引入Kirchhoff定律，实现了复杂裂缝分支处的流量守恒。数值模拟与实验结果吻合程度良好，验证了模型的准确性。通过研究发现，超临界CO2压裂时，裂尖区域有更高的流体压力用来造缝，裂缝分叉处产生大量剪切破坏裂缝。

Supercritical CO2 fracturing is a promising production technology of unconventional reservoirs. Supercritical CO2 has advantages of low viscosity and high flow capacity, which will lead to complex fractures with multiple branches during fracturing. So far, most of the hydraulic fracturing propagation models need pre-set propagating path and direction, and are not able to give true complex fracture morphology. In this paper, based on the low viscosity characteristics of supercritical CO2, the hydro-mechanical coupled complex fracture propagation model of supercritical CO2 fracturing in unconventional reservoirs is established. In this model, weak-form finite element formula and finite-difference formula are established to realize the coupling calculation of rock deformation and fluid migration, and the Kirchhoff law is introduced to realized the flow conservation in the complex fracture junctions. The numerical simulation results is in good agreement with the experimental results, which verifies the accuracy of the model. The research shows that there is a higher fluid pressure near the crack tip area to drive fracture propagation in supercritical CO2 fracturing, and lots of shear failed cracks are produced in the fracture junctions.

10.6056/dkyqt202201018