Physical Simulation Experiments of Hydraulic Fracture Initiation and Propagation under the Influence of Deep Shale Natural Fractures

Abstract

Horizontal wells’ multi-section and multi-cluster hydraulic fracturing plays an important role in the efficient development of shale gas. However, the influence of the perforating hole and natural fracture dip angle on the process of hydraulic fracture initiation and propagation has been ignored in the current researches. This paper presents the results related to a tri-axial large-scale hydraulic fracturing experiment under different natural fracture parameters. We discuss the experimental results relating to the near-wellbore tortuosity propagation of hydraulic fractures. Experimental results showed that the triaxial principal stress of the experimental sample was deflected by the natural fracture, which caused significant near-wellbore tortuosity propagation of the hydraulic fractures. The fractures in most rock samples were not perpendicular to the minimum horizontal principal stress after the experiment. As well, the deflection degree of triaxial principal stress direction and the probability of hydraulic fractures near-wellbore tortuosity propagation decreased with the increase of the natural fracture dip angle. After hydraulic fractures’ tortuous propagation, the hydraulic fractures will propagate in the direction controlled by the triaxial stress in the far-wellbore area. For reservoirs with natural fractures, proppant in hydraulic fracturing should be added after the fractures are fully expanded to prevent sand plugging in tortuous fractures. When the permeability of natural fractures is low, the volume of fracturing fluid entering natural fractures is small, and hydraulic fractures are easy to pass through the natural fractures.

A Review of Macroscopic Modeling for Shale Gas Production: Gas Flow Mechanisms, Multiscale Transport, and Solution Techniques

“…This heterogeneity leads to variations in pore types (round pores, slit pores, fissures) and pore sizes (from nanometer kerogen pores to micrometer fractures) [9]. Thirdly, gas flow and well performance are highly dependent on the properties of hydraulic fractures in shale, and hydraulic fractures may communicate with local natural fractures to form a complicated fracture network, further amplifying reservoir heterogeneity [10][11][12]. The accurate modeling of a fracture network is another essential component for the forecast of shale gas production.…”

Research on the impact of pre‐existing geological fractures on hydraulic fracturing in high in situ stress environments

“…11 In addition, the samplemaking method is usually relatively simple, 12 and most of the hydraulic fracturing samples are cut and then spliced, which cannot properly restore the mechanical characteristics of hydraulic fractures in the formation, and the interface characteristics after splicing will greatly interfere with the expansion path of hydraulic fractures. 13 In addition, even if the pre-existing fracture is embedded in the hydraulic fracturing sample, it is only a piece of paper or other material to replace the natural fracture, but this can only simulate the influence of microfractures, and can not study other complex preexisting fractures, let alone study the impact of preexisting fracture properties on hydraulic fracturing. 14 There are four types of numerical simulation methods in hydraulic fracturing: extended finite element (XFEM), boundary element (BEM), discrete element (DEM), and finite element discrete element method (FDEM).…”