Modeling Near-Wellbore Hydraulic Fracture Behaviors Under Combined Impacts of Wellbore Perforation and Natural Fractures
Authors: Fu W. , Damjanac B. , Radakovic-Guzina Z. , Finnila A. , Podgorney R. , McLennan J. 
Published: August 2024

ABSTRACT:
Hydraulic fracture trajectory near the wellbore directly influences the efficiency of fluid flow into and out of the well. Modeling the near-wellbore hydraulic fracture behaviors has been challenging due to the combined impacts of wellbore perforation placement, stress concentration around the wellbore and perforation tunnels, in-situ stress conditions, as well as pre-existing fractures in the subsurface that interact with hydraulic fractures. In this paper, we have built numerical models to take into account the aforementioned factors and investigate near-wellbore fracture growth and fluid pressure characteristics. The numerical models use a distinct element method (DEM) approach that explicitly represents the well casing, cement sheath, and perforation tunnels, with natural fractures represented by Smooth Joint Model. The results show that natural fractures intersecting the perforation tunnels at a favorable angle with respect to in-situ stress directions can facilitate fracture initiation in hard rocks. Multiple initiation points may occur, while one fracture becomes dominant at a later time in the simulated case. In addition, the simulation results show the termination of hydraulic fracture growth in the highly fractured zone, as well as hydraulic fractures crossing natural fractures that have small effective sizes at the interaction location. This study also demonstrates the efficacy of the near-wellbore model to represent detailed wellbore elements, consider complex discrete fracture networks, and capture the fundamental mechanisms that influence near-wellbore hydraulic fracture behaviors.

1. INTRODUCTION
The trajectory of hydraulic fractures near the wellbore directly influences the efficiency of fluid flow into and out of the well, making it a crucial factor that can impact several critical aspects in unconventional reservoirs and enhanced geothermal systems, such as reservoir connectivity, fluid circulation, proppant transportation, and energy production efficiency. Modeling near-wellbore fracture initiation and propagation has been challenging due to complex influencing factors that need to be considered, including the casing-cement sheath-perforation tunnel-rock structure, stress concentrations resulting from the wellbore and perforation tunnels, interference, competition, and merging of hydraulic fractures, interactions within the hydraulic discrete fracture network, and in-situ stress conditions. A model must span multiple scales to accurately capture different fracture behaviors, from fracture initiation along perforation tunnels at a millimeter scale to fracture propagation near the wellbore at a meter scale.
In this study, a numerical model was established to investigate hydraulic fracture behaviors in the near-wellbore region. Utilizing a distinct element method (DEM) lattice approach, we analyzed hydraulic fracture initiation and propagation behaviors under the combined impacts of wellbore perforation and discrete fracture network (DFN). The model is based on hydraulic fracturing tests conducted at the Utah FORGE Site. Well casing, cement sheath, and perforation tunnels were explicitly represented in the simulation, and fluid pressure characteristics and corresponding fracture behaviors are discussed in detail.