Experimental Investigation of Crack Extension Patterns in Hydraulic Fracturing with Shale, Sandstone and Granite Cores

Abstract

Abstract:Hydraulic fracturing is an important method of reservoir stimulation in the exploitation of geothermal resources, and conventional and unconventional oil and gas resources. In this article, hydraulic fracturing experiments with shale, sandstone cores (from southern Sichuan Basin), and granite cores (from Inner Mongolia) were conducted to investigate the different hydraulic fracture extension patterns in these three reservoir rocks. The different reactions between reservoir lithology and pump pressure can be reflected by the pump pressure monitoring curves of hydraulic fracture experiments. An X-ray computer tomography (CT) scanner was employed to obtain the spatial distribution of hydraulic fractures in fractured shale, sandstone, and granite cores. From the microscopic and macroscopic observation of hydraulic fractures, different extension patterns of the hydraulic fracture can be analyzed. In fractured sandstone, symmetrical hydraulic fracture morphology could be formed, while some micro cracks were also induced near the injection hole. Although the macroscopic cracks in fractured granite cores are barely observed by naked eye, the results of X-ray CT scanning obviously show the morphology of hydraulic fractures. It is indicated that the typical bedding planes well developed in shale formation play an important role in the propagation of hydraulic fractures in shale cores. The results also demonstrated that heterogeneity influenced the pathway of the hydraulic fracture in granite cores.

An Experimental Investigation of Hydraulic Fracturing in Shale Considering Anisotropy and Using Freshwater and Supercritical CO2

“…In our experimental design, hydraulic fracturing experiments using freshwater and SCO 2 were conducted on shale cores with different bedding angles to investigate the fracture propagation. As remarked by [38]: "The depth of the shale formation to be hydraulically fractured is usually thousands of meters, so proper retrieval of shale cores is sometimes impossible and quite costly. In addition, the size of the cores may also be too small to meet the requirements of the experimental apparatus".…”

“…As remarked by [38]: "The depth of the shale formation to be hydraulically fractured is usually thousands of meters, so proper retrieval of shale cores is sometimes impossible and quite costly. In addition, the size of the cores may also be too small to meet the requirements of the experimental apparatus".…”

Numerical Simulations of Fracture Propagation in Jointed Shale Reservoirs under CO2 Fracturing

“…Nitrogen fracturing experiments were conducted on shale samples vertical and parallel to the bedding plane; the results indicated that a relative complex fracture surface is formed in the shale sample vertical to the bedding plane [32]. He et al [33] performed hydraulic fracturing on shale with bedding planes; the results showed that the bedding planes in shale formation have a significant influence on the propagation of hydraulic fractures. However, the mechanism of the fracture initiation and propagation in kinds of jointed reservoirs is not well investigated.…”

Investigation of Hydraulic Fracturing Behavior in Heterogeneous Laminated Rock Using a Micromechanics-Based Numerical Approach

“…This technology depends on multiple parameters, and fracture formation is dominated by several factors, e.g., the in-situ stress, the rock mass properties, and the injection rates [1,2]. The seepage pathway of fluid flow in a fractured rock mass is mainly controlled by the geometry, pattern, and heterogeneity of the hydraulic fracture network [3][4][5][6]. Therefore, the quality of the artificially modified fracture network is a critical factor in practical applications [7,8].…”

“…Despite this arsenal of insights, techniques, and specialized knowledge, there is still a lack of understanding of the dynamic fracture propagation and the failure mechanisms in shale formations. Additionally, there are still a lack of satisfactory models that can explicitly represent the heterogeneity characteristics of shale formations and simulate the coupling between stress, fluid flow, and damage in ways that can be easily visualized [4].…”