Microseismic hydraulic fracture imaging: The path toward optimizing shale gas production

Abstract

Economic shale gas production involves hydraulic fracture stimulation in order to create permeable flow paths within these low-permeability reservoirs. Microseismic monitoring has shown that often these “fracs” consist of complex fracture networks, with large surface contact areas with the reservoir. Optimized production is therefore dependent on the ability of the stimulation to activate an extensive fracture network. Much of the current attention around hydraulic fractures focuses on microseismic imaging of the activated network; however, the path toward optimized shale gas production also requires methods to both predict and model the fracture networks. Along the path, engineers will be able to close the loop for an optimally designed stimulation: being able to predict, monitor, and assess the stimulated fracture network. As an industry, we are just starting down this path, and this paper describes a few case studies that highlight recent advancements. Before we can ultimately predict the fracture network that will result from a specific injection, we first need to understand the factors that control the variability in hydraulic fracture networks that are routinely observed. To this end, two case studies are described integrating microseismic imaging with seismic reservoir characterization, both of which show that the hydraulic fracture geometries are controlled by pre-existing fractures and stresses. Many engineering tools exist to model the performance of a fracture network, and one of the case studies describes a reservoir simulation investigation of the production sensitivity to various ways of characterizing the stimulated hydraulic fracture network. To begin, however, because microseismic is the basis of these case studies and will likely remain the primary hydraulic fracture monitoring technique, some general comments are first made regarding microseismic specific to shale gas.