Modelling of Multistage Hydraulic Fracture Operations in Unconventional Resources – The Application of Geomechanics and Field Data to the Optimization of Fracture Spacing and Production

Abstract

Massive multistage hydraulic fracturing using horizontal wells has been an integral part of the natural resource industry in Canada. The process uses long horizontal wells divided into many stages to access large volumes of oil and gas bearing formations. Each well is divided into fracture stages. Fluids are pumped down into each stage of the well to generate a fracture which increases the porosity and permeability of the formation to allow economic resource extraction. The in situ geomechanical stresses of the formation do not remain static during the fracturing of the rock. Each fracture creates a volume change within the formation which in turn leads to alteration of the stress and strain conditions within the rock mass. There is the possibility that the alteration of stress conditions will have an effect on the initiation and propagation of subsequent stages of the multi-stage hydraulic fracture operation. This phenomenon is known as ‘stress shadowing’. Stress shadowing occurs when the minimum compressive stress in the formation is increased due to the fracturing of the rock. Increasing the minimum compressive horizontal stress can have several effects, including the rotation or diversion of fracture propagation, stages that do not initiate, thinner fractures, and reduced porosity and permeability within the fracture stage. Currently, many hydraulic fracture operations do not invest in advanced mathematical models of geomechanics. Some pressure monitoring is carried out during operations, but the data are inadequate to warrant advanced numerical methods to predict stress change and its effects. This thesis presents a semi-analytical solution for the stresses around an ellipsoid (the Eshelby Solution) for use in predicting fracture geometry and stress shadow effects. The program is quick to use and can be linked to field data. A study of field data from the Montney Formation is presented. The algorithm developed in this thesis is used to evaluate stress changes within the Montney Formation and the outputs are compared to the stress changes seen in the hydraulic fracture pressure data.