Assessment of brittleness and comparison of hydrofracturing potential of water and non-aqueous alternative- CO2 in coal

Abstract

Hydraulic Fracturing (HF) is a significant method used for enhancing the oil and gas recovery from low permeability reservoirs. The selection of specific injecting fluid impacts the reservoir permeability enhancement, long-term production efficiency and fracture propagation potential of the reservoir. This study compares the fracture propagation potential of water and non-aqueous alternative- supercritical CO₂, using Perkins-Kern-Nordgren (PKN) and the Khristianovic-Geertsma-de-Klerk (KGD) fracture models in low permeability coal and shale reservoir. Reservoir compatibility for performing HF operations is identified by studying the brittleness of the reservoir based on the elastic parameters (i.e., poisson’s ratio $\left(v\right)$, young’s modulus (E)). Brittleness is highly influenced by tensile strength, modulus of elasticity, poisson’s ratio, and coal composition. Based on the analysis of elastic parameters, coal samples are found to be high to moderately brittle in nature, indicating the suitability of Jharia coalfield for carrying out HF operations. Comparing two injecting fluids, CO₂ shows 116 % greater fracture propagation length than water using the PKN model, whereas the difference is ∼90 % when tested using the KGD model. The results indicate that the fracture propagation ability of the reservoir primarily depends on Poisson’s ratio $\left(v\right)$, shear modulus (G), Young’s modulus (E), temperature of the reservoir and viscosity of injecting fluid ($\mu )$.