Hydraulic fracturing experiment and numerical simulation were conducted to investigate the factors influencing vertical extension of hydraulic fracture in bedding shale formation. It is observed experimentally that, hydraulic fracture would cross the beddings under high stress difference of 12MPa and propagate along the beddings under low stress difference of 3MPa. The combined effects of flow rate and viscosity resulted to single fracture for 1.00ml/s and 120mPa.s, non-planar fracture for 0.166ml/s and 120mPa.s, complex fracture for 0.166ml/s and 3mPa.s, and complex fracture network for 1.0ml/s and 3mPa.s. From numerical simulation, layered formation with different material properties have got horizontal stress contrast between layers and the deformation appeared in layers with the high Poisson's ratio and less Young's modulus. It is predicted that any failure which will happen may occur in the layer with less minimum stress distribution and stiffness. By adding the pore pressure in each side of the model, the poroelastic effects resulted in increased stress magnitudes in some layers, which had an impact on fracture dimensions such as height, length and width during fracture propagation.

1. Introduction

Stimulation by hydraulic fracturing in a low permeability shale gas reservoir with presence of beddings and natural fractures can significantly affect hydraulic fracture propagation. Theoretical, experimental and numerical simulations of both geological and engineering parameters were investigated to investigate hydraulic fracture initiation and propagation behaviors.

Many researchers discussed hydraulic fracture behaviors when encountered a single natural fracture (Blanton 1986; Warpinski and Teufel, 1987; Dehghan et al., 2016; Hou et al., 2019). Three types of interactions between hydraulic fractures and pre-fracture were observed: arrested, opening and dilating. They concluded that the main factors for controlling propagation behavior and geometry were horizontal differential stress and the angle of approach to the pre-fractures. To predicte a natural fracture response affecting by a propagating hydraulic fracture, various criteria have been proposed, such as Warpinski criterion (Warpinski and Teufel, 1987), Gu criterion (Renshaw and Pollard, 1995), and Zhou criterion (Gu and Weng, 2010). To investigate fracture extension in naturally fractured reservoirs, Hou (2015) conducted experimental and numerical simulation in complex fracture network of shale formations. They found that fracture complexity increased with the increasing of natural fracture density and fracture length. Hou (2015) studied the influence of natural fracture network on hydraulic fracture propagation in carbonate formations. They concluded that hydraulic fractures perpendicularly crossed parallel and symmetric pre-fractures under large horizontal differential stress and large angle between natural fractures and maximum horizontal principal in situ stress. Hou (2017) conducted a series of rock mechanical tests to study the rock mechanical properties of different lithologies under different temperatures. Based on groups of triaxial experiments in shale outcrops, Hou (2019) presented that hydraulic fracture geometries in the vertical direction could be classified into four scenarios: simple fracture, fishbone-like fracture, fishbone-like fracture with fissure opening, and multilateral fishbone-like fracture network.

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