Geomechanical Simulation of Stress Shadows for Improved Hydraulic Fracture Design

Abstract

Hydraulic fracturing is a common stimulation procedure to enhance hydrocarbon production in unconventional reservoirs. However, the contribution of each fracturing stage to production can vary significantly. This variation may in part be caused by the development of stress shadows; local changes to the regional stress state near hydraulic fractures, following their opening. An incomplete understanding of these changes may lead to undesired effects in stimulation treatment. To quantify the stress shadow effects, we perform Finite Element (FE) simulations using Abaqus FEA software. In the workflow, we combine a field-scale geomechanical model populated with calibrated distribution of rock mechanical properties and realistic hydraulic fracture geometries. The 3D stress response is obtained by increasing the net pressure within the fracture plane to magnitudes monitored during the field operations. This new workflow allows visualization and quantification of stress shadow effects for each stress component. In addition to purely linear elastic simulations, fractures can be numerically propped after opening. Sensitivity assessments using this workflow show that significant changes in Young's Modulus or Poisson's Ratio, as well as changes in principal stress ratios, have a minor effect on the stress redistribution. Furthermore, stress shadows are concentrated between hydraulic fractures: laterally, away from the fracture plane, stress shadow effects diminish almost immediately. Consequently, for simple frac geometries, the stress shadow can be quantified with respect to net fracture pressure, and fracture length, height and spacing ratios. A frac optimization work was carried out for production in the Montney formation (AB, Ca.). The results highlight the potential importance of the stress shadow on hydraulic fracture geometries. For instance, fracture spacing must be optimized to avoid out-of-zone growth or inappropriate stimulation treatment. At the same time, stress shadow development may have a local stabilizing effect on critically stressed natural fractures, as it decreases the differential stress between the successive stages. Finally, with a stress shadow-updated frac design the FE analysis can be revised and improved to re-evaluate the stress redistribution and its effects on the surrounding rocks, as well as calibrating it to production.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016