Directional hydraulic fracturing (DHF) using oriented perforations: The role of micro-crack heterogeneity

Abstract

This study presents numerical investigations about the role of micro-crack heterogeneity in hydraulic fracture (HF) development and directional hydraulic fracturing (DHF) creation. By comparing the results of heterogeneous models (named DFN models) with the associated homogeneous models, the behavior is categorized into three modes: DFN models, which consume more (A), comparable (B), and much lower (C) energy than the associated homogeneous models. Variation of micro-crack distributions, which determines HFs interaction in the stress shadow zone, contributes to the difference in HF morphologies and injection energy consumption. The connection process, where one HF connects the other, predominates the energy cost in the DHF. Offset-related interactions usually occur between HFs and DFN in case of favorable distribution of micro-cracks, which guides the HFs to propagate through the interaction zone, thus favoring the connection process and improving the DHF efficiency. Adverse distribution of local cracks (even a single crack) with dilation-related interactions near the connection zone can produce extremely high stress due to the opening of the cracks, which significantly deteriorates the connection process and reduces the DHF efficiency. Therefore, a limited variation of crack distribution near the connection zone could cause a pronounced effect on HF connection and the associated energy consumption. Due to the limited sizes and shear slips of the micro-cracks in these simulations, deformation energy and fracture energy dissipation dominate the energy conversion during the injection, while frictional energy consumption plays a secondary role. The two-stage injection strategy can be a promising method to weaken the stress shadow effect, i.e., subsequent HFs extend directly to the previous one by taking advantage of the stress state produced in the first stage. The frictional resistance of micro-cracks also plays a significant role in DHF creation. Weak cracks allow the HFs to go through the interaction zone and avert the strict connection process, consequently improving the DHF efficiency.