ASSESSING HYDRAULIC FRACTURE SYSTEM GEOMETRY USING INDUCED MICROSEISMICITY: NEW TECHNIQUES TO CHARACTERIZE MICROSEISMIC EVENTS

In the United States, stimulation of wells by hydraulic fracturing is common practice, particularly in tight gas formations. Often the only measure of fracturing success is an increase in production. Therefore, proper characterization and understanding of the created fracture geometry is essential to the effectiveness of any stimulation program. Microseismic monitoring of hydraulic fractures can now provide extensive diagnostic information on fracture development and geometry. Critical elements of a monitoring system include three-component receivers and a telemetry system. Equally important is the accuracy of the velocity model used to process acquired data.

Geology is a fundamental element in the design and completion of a stimulation program as well as the interpretation of its results. Rock properties govern the fluid types to be injected in the formation as well as the pumping schedule. Rock layering controls monitoring device positioning, establishes the depth at which perforations should be located, and determines how hydrocarbons flow within the formation. Despite these facts, the effect rock characteristics may have on the stimulation results is frequently overlooked, because it is often assumed that stimulated fractures have a symmetric planar geometry.

Newly developed techniques such as full-waveform moment tensor inversion and multiplet analysis provide essential aid in describing geological relationships between induced microseismic events. Full-waveform moment tensor inversion allows assessing the asymmetry and detection threshold, fault plane orientations, and principal stress directions of the induced microseismic events. Multiplet analysis helps highlight regions of repeated activity and reduce the apparent complexity of induced microseismicity. We apply these techniques to a dataset recently acquired during a hydraulic fracture monitoring campaign in the continental United States. We show how these new techniques, in addition to traditional fracture models and prorated production-rate transient analyses, improve our understanding of natural and induced fracture systems.