Numerical analysis of the effect of natural microcracks on the supercritical CO2 fracturing crack network of shale rock based on bonded particle models. (30th June 2017)

• Record Type: Journal Article
• Authors: Peng, Peihuo; Ju, Yang; Wang, Yongliang; Wang, Shaoqin; Gao, Feng
• Is Part Of: International journal for numerical and analytical methods in geomechanics. Volume 41:Number 18(2017)
• Page Start: 1992
• Page End: 2013
• Publication Date: 2017-06-30
• Subjects: bonded particle model (BPM) -- distribution uniformity index (DUI) -- mechanical properties -- natural microcracks -- supercritical CO2 fracturing; Soil mechanics -- Mathematics -- Periodicals; Rock mechanics -- Mathematics -- Periodicals; 624.1510151
• DOI: 10.1002/nag.2712
• Languages: English
• ISSNs: 0363-9061

Abstract

Summary: The problem of predicting the geometric structure of induced fractures is highly complex and significant in the fracturing stimulation of rock reservoirs. In the traditional continuous fracturing models, the mechanical properties of reservoir rock are input as macroscopic quantities. These models neglect the microcracks and discontinuous characteristics of rock, which are important factors influencing the geometric structure of the induced fractures. In this paper, we simulate supercritical CO2 fracturing based on the bonded particle model to investigate the effect of original natural microcracks on the induced‐fracture network distribution. The microcracks are simulated explicitly as broken bonds that form and coalesce into macroscopic fractures in the supercritical CO2 fracturing process. A calculation method for the distribution uniformity index (DUI) is proposed. The influence of the total number and DUI of initial microcracks on the mechanical properties of the rock sample is studied. The DUI of the induced fractures of supercritical CO2 fracturing and hydraulic fracturing for different DUIs of initial microcracks are compared, holding other conditions constant. The sensitivity of the DUI of the induced fractures to that of initial natural microcracks under different horizontal stress ratios is also probed. The numerical results indicate that the distribution of induced fractures of supercritical CO2 fracturing is more uniform than that of common hydraulic fracturing when the horizontal stress ratio is small. Highlights: A bonded particle model was used to simulate supercritical CO2 fracturing of rock. The distribution uniformity index (DUI) was proposed to characterize fractures. The supercritical CO2 fracturing processes with different DUIs were analyzed. The dependence of fracturing induced cracks on initial microcracks was probed. The CO2 fracturing created more uniformly distributed cracks than hydrofracturing.