Building a Discrete Fracture Network Utilizing Constraints Derived From Microseismicty Fracture Parameters

Abstract

Microseismic event locations are often used as input into geomechanical models to describe the effect of hydraulic stimulations, if only just to calibrate modelled fractures to the spatial microseismic response. While such methods are used to model production decline curves, and can be tuned through time with history matching observations, using only the distribution of microseismicity offers a relatively weak constraint on reservoir dynamics and ignores the potential benefits of utilizing the source characteristics associated with microseismic events. Specifically, each microseismic event location not only represents a point measure of failure in the reservoir but more correctly identifies the initiation point of a rupture on a fracture with dimensions and orientation that can be inferred through higher-order analyses such as Seismic Moment Tensor Inversion (SMTI) and source parameter analyses (eg., seismic moment, seismic energy, and stress release), where data quality are sufficiently sampled from a large azimuthal range (achieved through multi-array downhole deployments). Not every microseismic event detected by a array qualifies for SMTI and can to used to delineate fracture orientations. Some events rupture smaller fractures that result in less energy released and lower signal quality on the arrays, other events may be geometrically ill-favored for SMTI though their position relative to the monitoring arrays. In order to incorporate these features, we project these events onto features drawn from the distribution of SMTI derived fracture plane orientations. Construction of the discrete fracture network in this fashion offers a bridge between microseismic data collection and geomechanical modelling. This DFN describes the fractures that were favoured to slip through pressure and/or stress perturbations, and can be considered as the activated fracture set within the total fractures in the reservoir. By using SMTI-derived failure mechanisms (generally mixed-mode shear-tensile failures), constraints can also be applied to the DFN model development and be used to image the fractures that can accept proppant, and those fractures that are clamped. The question of how to extend this information on the style of fracturing to the sub-SMTI events is currently being investigated, and again drawing from the sampling of available fracture behaviours in a spatio-temporal sense will be key to further extending these constraints on DFN model development.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015