Abstract
Geomechanical modelling of stress changes during multi-stage hydraulic fracturing (MSHF) can help optimize the design of hydrocarbon extraction operations in unconventional low permeability low porosity reservoirs. Stress changes which occur during a single stage of MSHF have been known to affect subsequent fracturing stages. If an understanding and modeling capability of the effects of induced stress changes can be achieved, optimization of hydraulic fracture operations becomes feasible. Given uncertainty and limited monitoring data, calibration and history matching with reservoir models are used to help design MSHF operations. Data from "similar" wells to those that will be later encountered are used to create a semi-empirical "model" that may have predictive value in design, but because the basis in physics of such models is weak, their predictive capabilities rapidly disappear if conditions are significantly different from those used to develop the empirical calibration factors.
This paper will examine the stress shadow effects during MSHF in unconventional reservoirs and the possibility of fracture spacing optimization. The study aims to examine previous stress shadow models to identify the most commonly agreed upon effects of stress shadowing, as well as any noted differences in stress changes during different completion methods. Field data is then examined to identify any of these effects, including but not limited to, increase in instantaneous shut in pressure which may indicate an increase in minimum horizontal stress, and fluctuations in treatment pressure which could show stress changes during the fracture propagation.
Both a complex mathematical model and a simple two dimensional model are introduced which will be used to compare efficiency and results in future studies. Recommendations are made concerning simplifying assumptions when it comes to MSHF and reservoir modelling in tight formations.
1. INTRODUCTION
Massive multistage hydraulic fracturing in low permeability formations using horizontal wells has become one of the most commonly used method to extract natural gas in Canada. The use of horizontal wells has improved the efficiency of resource extraction by increasing the numbering of hydraulic fracture stages within a single well along several hundred meters of a producing formation.
