Integrating Reservoir and Geomechanical Models to Compare the Productivity of Shale Reservoirs Using Different Fracture Techniques

Abstract

AbstractThe ultra-tight nature of shale gas reservoirs has made hydraulic fracturing inevitable. Whilst most of the gas industry is driven by the success of hydraulic fracturing, alternate fracturing techniques have repeatedly been overlooked. In hydraulic fracturing, only 20–30% of the injected water is recovered during clean-up, and this causes a concern over the fracture efficiency. Additionally, the overbalanced pressure during fracturing poses a threat towards damaging the fracture sand face. A potential alternative to eliminate these drawbacks is a forgotten technology-pulsed gas fracturing. The pulsed fracturing (through high pressure gas) also makes the clean-up much faster/simpler. Although the stimulated reservoir volume (SRV) resulting from pulsed fracturing might not be comparable to the one resulting from hydraulic fracturing, it is suspected that the former technique would be more efficient especially in ductile shale where the industry lacks efficient stimulation technique as hydraulic fracturing fails to be successful.Hydraulic fracturing involves a relatively slow loading rate and this usually results in bi-wing fracture geometries. On the other hand, explosive fracturing involves very rapid loading of formation that can trigger multiple fractures. However, due to extreme stress/heat that is generated during the explosion, near wellbore region may reach the plastic limit which inhibits fracture growth away from the wellbore. The pulsed fracturing loading rate and peak load (via high energy gas or propellants) lies in between hydraulic and explosive fracturing processes. This technique has the potential to shatter ductile shale(s): in particular by triggering a ductile to brittle transition: at an optimized pulse rate at a certain depth.Through coupling of geomechanical and reservoir models, a workflow to predict the generated fracture networks and to quantify the productivity/efficiency of the same has been established. Additionally, in order to account for the various phenomena that are expected to occur during transient production, parameters such as desorption and stress dependent permeability have been considered and are presented in this paper.This paper serves as a platform to compare the models depicting the established process of hydraulic fracturing versus an alternate fracturing technique like pulsed gas fracturing.