Characterization of Microseismic-Derived Discrete Fracture Networks Through Topological Approaches

Abstract

Hydraulic fracturing in unconventional reservoirs seeks to create a network of drainage pathways such that hydrocarbons can efficiently and effectively be produced from tight formations. With reference to the tri-linear model of fracture stimulations, where there is a near-wellbore region of high fracture complexity, a further region of enhanced permeability, and a third region of negligible permeability enhancement, understanding the evolving nature of the enhanced fracture distribution is critical to understanding which volumes within the reservoir are being accessed, and therefore critically impactful on decisions regarding well and stage spacing as well forecasting overall decline. In order to constrain and characterize this enhanced discrete fracture network (DFN), high quality microseismic data can be used; this allows for the determination of seismic moment tensors (SMT) to be determined. Each event is a rupture of a discrete fracture whose size scale and orientation can be inferred from the microseismic data. With these approaches in hand, we have the ability to build a DFN from the events that we are able to constrain. We use a topological approach to define the character of the DFN, characterizing the intersections of the network: fractures are either isolated (I), have branching intersections (Y), or have crossing intersections (X). Tabulating the instances of these different interactions, we construct IYX ternary plots for the microseismic DFN. There are some underlying assumptions and restrictions that need to be examined if we are to take the next step towards network characterization. First is that with the high-quality microseismic data, we are limited to examining a certain size scale of a few meters to tens of meters, although extending the SMTI-based orientation to lower quality data can extend the characterization to scale lengths around a meter. Second is that we derive our scale lengths with respect to a model of a penny-shaped crack. We address both of these points through scaling our fractures and calibrating the response of the fracture network to the trilinear model. We will show how the character of the SMTI-derived DFN changes along the axis of a stimulated zone through these IYX ternary plots which then facilitate relating our observations to predications based on percolation thresholds.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017