What can we infer about a hydraulic fracture from microseismic? Towards a microseismic interpretation framework
Microseismic monitoring has been established as the ‘go to’ technology for mapping hydraulic fractures. With the rapid expansion of massive hydraulic stimulation of horizontal wells, fracture diagnostics are critical for understanding the hydraulic fracture geometry. Indeed, microseismic observations have led to a paradigm shift towards complex fracture networks developing and injection interacts with pre-existing fractures (for example see Maxwell, 2014, and references therein). In this light, basic microseismic data often tends to be qualitatively interpreted in terms of estimating hydraulic fracture dimensions including an estimate of the stimulated reservoir volume (SRV). In addition to the fracture geometry inferred from microseismic hypocentral locations, magnitudes are also a useful attribute. Magnitudes are typically used to quantify the sensitivity of the recording, identify potential fault activation and have also been related to ultimate production from the well. In application of seismic monitoring for hydraulic fracture induced seismicity, magnitudes are generally used to trigger alerts for traffic light protocols. Microseismic source mechanisms are also increasingly commonplace to deduce orientations of the seismically-active fractures. Various advanced interpretations have also been put forward based on mechanisms and moment tensor inversions. For example, moment tensor inversions and estimates of fracture opening modes have also been postulated to assist in deducing fracture effectiveness, although this particular aspect will be critically reviewed later in the article.