CT Identification and Fractal Characterization of 3‐D Propagation and Distribution of Hydrofracturing Cracks in Low‐Permeability Heterogeneous Rocks

Abstract

Understanding and characterization of the three‐dimensional (3‐D) propagation and distribution of hydrofracturing cracks in heterogeneous rock are key for enhancing the stimulation of low‐permeability petroleum reservoirs. In this study, we investigated the propagation and distribution characteristics of hydrofracturing cracks, by conducting true triaxial hydrofracturing tests and computed tomography on artificial heterogeneous rock specimens. Silica sand, Portland cement, and aedelforsite were mixed to create artificial heterogeneous rock specimens using the data of mineral compositions, coarse gravel distribution, and mechanical properties that were measured from the natural heterogeneous glutenite cores. To probe the effects of material heterogeneity on hydrofracturing cracks, the artificial homogenous specimens were created using the identical matrix compositions of the heterogeneous rock specimens and then fractured for comparison. The effects of horizontal geostress ratio on the 3‐D growth and distribution of cracks during hydrofracturing were examined. A fractal‐based method was proposed to characterize the complexity of fractures and the efficiency of hydrofracturing stimulation of heterogeneous media. The material heterogeneity and horizontal geostress ratio were found to significantly influence the 3‐D morphology, growth, and distribution of hydrofracturing cracks. A horizontal geostress ratio of 1.7 appears to be the upper limit for the occurrence of multiple cracks, and higher ratios cause a single crack perpendicular to the minimum horizontal geostress component. The fracturing efficiency is associated with not only the fractured volume but also the complexity of the crack network.

A Review of Hydraulic Fracturing Simulation

“…More recently, CT-scan techniques have been increasingly used in experiments to detect natural fractures and stimulated hydraulic fracture network [40,125,162,196,198,397]. Liu et al [196] identified 3D propagation and distribution of hydraulic fractures in heterogeneous rocks and found the rock heterogeneity and horizontal in situ stress ratio have a significant influence on the stimulated fracture network. Luo et al [198] conducted CT-scan on carbonate rock specimens before and after the hydraulic fracturing to investigate the shear slippage behaviour of the natural fractures.…”

Research on 3D crack segmentation of CT images of oil rock core

“…Zhu et al [ 12 ] proposed a novel co-regularized unsupervised feature selection algorithm. Liu et al [ 13 ] used the multithresholding image segmentation method to identify the cracks. In [ 14 ], the CT data was segmented into a binary volume using the automatic Otsu method.…”

Three-Dimensional Ultrasonic Imaging and Acoustic Emission Monitoring of Hydraulic Fractures in Tight Sandstone

“…If these key mechanical problems can be grasped and understood, the process of fracture development can be predicted and evaluated, thus providing important references for optimizing hydraulic fracturing plans and improving recovery efficiency. By conducting hydraulic fracturing experiments in the laboratory, the influence of environmental factors can be reduced, and the dynamic development process and distribution ranges of fractures can be obtained using multiple physical means, such as acoustic emission monitoring, ultrasonic velocity, and X-ray tomography [2][3][4][5].…”