Physical Simulation Experiment Research for Hydraulic Fracturing in Tight Sandstone Reservoir Under Different Stress Conditions and Nature Fracture Combinations
Authors: Fan Pingtian , Liu Yuetian , Lin Ziyu , Wang Jingru , He Yuting , Zhang Bowei 
Published: August 2024

ABSTRACT:
Hydraulic fracturing is an essential stimulation technique for the effective exploitation of tight oil and gas reservoirs. The fracturing performance is closely related to the degree of reservoir remodeling. However, the mechanical mechanisms of fracture propagation and permeability enhancement under different differential stresses and natural fracture configurations remain elusive. To elucidate the physical processes and basic mechanisms of hydraulic fracturing of tight sandstones under different stress differentials, we conducted hydraulic fracturing simulation experiments on representative tight sandstone cores from the Ordos Basin. In order to gain insight into the influence of natural fractures (NF), bedding laminations, and stress states on the initiation of hydraulic fracturing, we conducted hydraulic fracturing experiments on core samples with dimensions of 300mm×300mm×300mm and 200mm×200mm×200mm. The experiments were conducted under realistic triaxial stress conditions. The results demonstrate that hydraulic fracturing in tight sandstones primarily induces a single dominant fracture. For rock samples containing natural fractures (NF), hydraulic fracturing (HF) preferentially initiates along the NF. For samples without NF but with developed bedding laminations, HF tends to initiate along the laminations. In the absence of these two features, HF is primarily controlled by the current stress state.

1. INTRODUCTION
The tight sandstone reservoir formations are widely distributed in the Ordos Basin of China, with abundant reserves and enormous exploration and development potential (Lyu, W. et al., 2019). Hydraulic fracturing is a key technology for the development of such oil and gas reservoirs (Warpinski, N.R. et al, 2009; Yang, X. et al, 2016). During the fracturing process, the natural fracture (NF) within the reservoir interacts with the induced hydraulic fracture (HF) (Wang, H., 2019; Taleghani, A. D. and Olson, J. E., 2014), connecting the matrix porosity to the wellbore and playing a crucial role in subsequent production.
To investigate the influence of NF on hydraulic fracture propagation, a series of simulation experiments were conducted to study the propagation behavior and fracture geometry of HF in naturally fractured reservoirs (Zhou, J. et al., 2008; Lin, M. et al., 2015). Concrete analog simulation experiments were conducted to investigate the influence of natural fracture development, dip and strike angles, and differential stresses on fracture propagation. The experiments were performed on pre-fabricated 300 mm cubic cement samples with NF (Hou, B. et al., 2014; Dehghan, A. et al., 2015). Some numerical simulation methods using DFN have been established. These studies have found that HF is significantly influenced by the presence and orientation of NF (Basirat, Goshtasbi, and Ahmadi., 2019). Additionally, the interaction between the NF and HF has been analyzed (Liu, C., et al, 2020; Wang, Y., Li, X., and Tang, C. A., 2016).