Hydraulic Fracture Growth and Containment Design in Unconventional Reservoirs

Abstract

Hydraulic fracture growth in permeability challenged reservoirs often results in irregular and complex fracture geometries as indicated by microseismic observations. In general, fracture characteristic such as length, height growth, extent and conductivity, which in turn contributes to the overall complexity of the resulting fracture network, are controlled by a combination of operational parameters and local geology/subsurface conditions. The operational parameters include well spacing, well orientation, number of stages, number of clusters, treatment rates, and fluid characteristics among others. These parameters are optimized to maximize hydrocarbon recovery and Conductive Reservoir Volume (CRV) and in the meantime fractures are contained within the target zones and subsurface integrity is maintained. This optimization, however, needs to be evaluated within the context of local geology and subsurface conditions. For example, presence of natural fracture swarms, mega fractures (or faults), and stress anisotropy can present hydraulic fracture design challenges that need to be carefully addressed by advanced geomechanical analysis.

In this paper, a 3D hydraulic fracture propagation code is utilized to quantify the impact of operational parameters and subsurface conditions on the resulting hydraulic fracture growth/containment and engineering design considerations. Extensive sensitivity analysis investigates the effect of each operational parameters and subsurface conditions. Examined effects include vertical stress contrast, fracturing fluid properties, completion design, mechanical interactions between multiple stages and/or neighboring wells, and interactions between natural fracture and hydraulic fracture.

The model results show that the hydraulic fracture growth, containment (vertical or horizontal containment) and the resulting quality of the CRV is primarily a function of the in-situ stress profile, stimulation design parameters (simultaneous or sequential injection, zipper fracturing), well architecture (number and spacing of stages/clusters, well spacing and location), and the reactivation of pre-existing natural fractures. Results show that, if not designed properly or contained, fractures can grow in and out of zones, intersect with the pre-existing fracture networks, interact with existing hydraulic fractures, and interfere with existing wells and thus significantly impacting resulting CRV.

Introduction

Advanced technologies, such as horizontal drilling and hydraulic fracturing, are developed and widely used to increase hydrocarbon extraction from low-permeability formations. Recent industry practices in North America prove that hydraulic fracturing is essential for economic production from permeability challenged reservoirs [1, 2]. However, microseismic (MS) data demonstrate that hydraulic fractures (HF) often develop irregular and complex fracture geometries [3-7] that reduce the stimulation efficiency.