3D Modeling of Fracturing and Refracturing in Unconventional Reservoirs

Abstract

Unconventional gas reservoirs considered in this thesis include low and ultralow permeability shales and tight reservoirs. Gas production from unconventional reservoirs has grown dramatically in the United States during the last decade and has helped that country to become a top gas producer around the world. Extensive use of natural gas has in turn reduced CO2 emissions to levels not seen in the United States since the 1990s. This has happened due to innovations associated with two main technologies: (1) Drilling of horizontal wells and (2) multistage hydraulic fracturing. This success in the United States has inspired the primary objective of this thesis: Finding means of improving gas rates and recoveries by fracturing and refracturing unconventional reservoirs. To this end, the thesis presents the development of an original 3D fracture propagation model that helps to understand hydraulic fractures and their growth in unconventional reservoirs. Results from the 3D fracture propagation model are calibrated with microseismic data and are used in (1) an original hybrid hydraulic fracture (HHF) simulation model for estimating stimulated reservoir volume (SRV), (2) reservoir modeling with a fully coupled HHF-geomechanics model, and (3) a comparison of refracturing vs. infill drilling. The thesis closes with an evaluation that discusses the economic aspects of refracturing. It is concluded that the fracture propagation model developed in this thesis provides valuable information regarding fracturing and refracturing of unconventional reservoirs. Furthermore, it generates useful input data for fluid flow simulations, and improvements in production rates and recoveries of natural gas from unconventional tight and shale reservoirs.