Index

Introducing Fracture Network Engineering

In recent years, ASC and Itasca have developed advanced, groundbreaking techniques for correlating microseismic field observations with simulated microseismicity from Itasca's models. On the one hand, data acquisition and microseismic processing are used to map a disturbed or enlarging fracture network in space, magnitude, and evolution using techniques developed by ASC for signal processing and interpretation. The feedback provides "first order" information to engineers, potentially in real time, so that decisions on project design can be made and revised effectively and efficiently. On the other hand, a Synthetic Rock Mass (SRM) numerical model is developed. The SRM is enhanced and updated by the information provided by the microseismic information. SRM models employ Itasca's PFC2D/PFC3D codes to create an assembly of bonded particles that represent the rock mass on a large scale (e.g. 10-100m). A Discrete Fracture Network is embedded within the bonded assembly to represent joints, faults, or other pre-existing fractures as smooth, frictional (or cohesive) planar features. SRM samples that are subjected to the same mechanical or fluid disturbance expected in the field produce synthetic seismicity that can be compared directly with microseismic data collected in the field.

This approach can effectively monitor the rock mass disturbance as it is developed on site, and has two principal objectives:

1. to use the models to better interpret the causal effects of the microseismicity by analyzing the micromechanics occurring within the numerical model framework (recognizing that in the model we observe all activity within the configured boundary conditions, whereas field observations record only a portion of the activity depending on the sensitivity of the monitoring system);
2. to use the observed microseismicity to feed back into the development of the models, and so validate their results, in order to develop robust predictive models for engineering the fracture network (both for the project in hand or for future projects).

The image below illustrates how this technique, which we term Fracture Network Engineering, is used in a hydraulic fracturing campaign to provide results and interpretations that feed back into the design and operation of the project.

Both ASC and Itasca have been aggressively pursuing the expansion and growth of Fracture Network Engineering. We define this new discipline as the design, analysis, modeling, and monitoring of in-field activities that enhance or inhibit permeability and/or promote disintegration of rock masses through fluid injection, blasting, or excavation. The validation of predictive models resulting from the SRM technique makes it possible to develop robust guidelines for engineering fracture networks based on in situ conditions, rock mass properties, and operational controls.

We believe the opportunities inherent in this discipline are of great benefit in any field where the behavior of in situ rock masses subject to fracturing can have critical impact on the design, efficiency and success of industrial operations: hydraulic fracturing for petroleum extraction in oil reservoirs, stimulation of rock at depth for extraction of geothermal energy, examination of rock mass behavior around underground excavations (tunnels, caverns, storage facilities), and blast design, to name a few. And the potential applicability only extends from there.