The inter-salt shale refers to a series of shale reservoirs mainly composed of argillaceous shales supported by upper and lower salt rocks. Inter-salt formation is widely distributed in the Qianjiang formation of Jianghan Basin in China with intricate rhythmic strata. Inter-salt shale layers are composed of various minerals with high salt contents. The fracture characteristic of this kind of stratum is not clear.

This research tests many core samples of the inter-salt shale from different rhythmic layers by using the rock mechanics triaxial compression test system. It also tests the mechanical behaviours under different confining pressures and analyses the fracture mechanism of the inter-salt shale. By using the segmentation module of Avizo, a set of advanced visualization software, this study identifies more clearly the fractures and their propagation morphology inside the core from a microscopic point of view.

The core rock mechanics parameters of different rhythmic layers are greatly different. There is an obvious anisotropy in the mechanical characteristics of inter-shale shale. From the microscopic perspective, the macroscopic rupture of inter-sale shale is developed by the expansion of its internal pores and micro-cracks. The types of rupture are mostly the shear fracture. The approach of combining Avizo with triaxial compression test and CT scanning enriches the research methods for rock mechanics parameters and can provide a new way for studying the fracture morphology of different rhythmic layers of inter-salt shale.

1 Introduction

With the advancements in exploration and development technologies year by year, unconventional oil and gas reservoirs have drawn extensive attention. Hydraulic fracturing is one of the effective means to obtain ideal capacities for unconventional reservoirs (Zhang et al., 2019; Hou et al., 2019). Many scholars all over the world have made lots of researches on the rock mechanism characteristics and fracture modes of unconventional reservoirs (Niandou et al., 1997; Li et al., 2012; Hou et al, 2019). The shale reservoir is a kind of common low porosity and low permeability unconventional oil and gas reservoirs. As a kind of reservoirs of shale oil in Jianghan Oilfield, the inter-salt shale is characterized by multiple bedding planes, low rock strength, complicated mineral compositions and high heterogeneity of rock mechanics (Fan et al., 2019).

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