Experimental and Numerical Investigation on Fracture Propagation Sensitivity Parameters in Deep Coal Seams

ABSTRACT: Hydraulic fracturing is the primary method for increasing hydrocarbon production in the extraction of deep coal bed methane. Understanding the initiation and propagation mechanisms of hydraulic fractures in deep coal seams, as well as developing design principles for hydraulic fracturing operations, can improve the efficiency of such operations. This study aims to identify the key factors affecting hydraulic fracture initiation and propagation in deep coal seams through indoor experiments and numerical simulations of deep coal seam wells. The study conducted an indoor experiment on hydraulic fracturing, using CT three-dimensional reconstruction technology and a two-dimensional fractal dimension analysis method to analyze the fracture morphology of deep coal seams. The study assessed the impact of various parameters, including fracturing displacement, fracturing fluid viscosity, lithology, and well trajectory, on hydraulic fracture initiation and fracture propagation. Additionally, a numerical model of fracture propagation was established to simulate hydraulic fracture initiation and propagation in typical wells in deep coal seams. The study also employed a two-dimensional fractal dimension analysis method and weight analysis method to analyze sensitivity parameters affecting fracture complexity and identified the main controlling factors of fracture initiation and propagation in deep coal seams. This study explores the basic principles of complex fracture propagation mechanisms through small-scale indoor hydraulic fracturing experiments. It aims to identify the key operational parameters that can enhance the complexity of fracture networks in hydraulic fracturing. The study also uses numerical simulations to analyze the important factors that influence the complexity of fractures through well-scale numerical simulations of fracture propagation. This approach provides design tools and theoretical insights for optimizing hydraulic fracturing design in deep coal seams. 1. INTRODUCTION Coalbed methane is an unconventional oil and gas resource. More than 47.6 trillion cubic meters of coalbed methane resources exist in coal reservoirs buried at a depth of more than 1500 meters (Zuo H.C, 2015). Coal seams have a unique bedding and cutting development system and usually require hydraulic fracturing methods to obtain a high yield. Deep coal seams have poor physical properties, high stress, low permeability, and strong adsorption capacity, so the effect of conventional fracturing transformation is not acceptable.