Microseismic monitoring is a valuable tool in understanding the efficacy of hydraulic fracture treatments. Determination of event locations and magnitudes leads to estimations of the geometry of the fracture zone and certain dynamics of the fracturing process. With sufficient resolution, the hypocenters may even reveal failure planes or other underlying structures controlling the distribution of events and of interest to petroleum engineers to test various hypotheses on fracture growth.

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Microseismic monitoring has been used to image hydraulic fracture growth in the Barnett Shale. The Barnett is a naturally fractured shale reservoir, which causes significant complexity in fracture growth during well stimulation operations. Several Barnett treatments have been successfully imaged between March 2000 and December 2001. In this paper, examples will be given to illustrate the complexity and variability which is developed during the treatment as the slurry interacts with the pre-existing fracture sets. The microseismic images explain why the stimulations occasionally grow at an angle to the assumed fracture orientation and into neighboring wells. Differences in production rates from various wells could also be related to the fracture geometry. The implications of the images to reservoir management highlight the benefit of imaging individual fracture networks to avoid overlapping and for targeting potential new well locations. Introduction Fracture diagnostics is critical in understanding the details of actual subsurface fracture growth, especially in cases of fracture complexity. Several diagnostic techniques exist, although microseismic imaging perhaps offers the best resolution to image fracture complexity. Even with relatively simple fracture geometries (i.e. a Perkins-Kern type fracture geometry), fractures can grow asymmetrically, have variable confinement across geologic interfaces, and change orientation. However, fracture growth in a naturally fractured reservoir can exhibit additional complexities associated with interaction between the hydraulic fracture and the pre-existing fracture network. In this paper, we describe the results of microseismic imaging of hydraulic fractures in Devon Energy's (formerly Mitchell Energy) Barnett Shale Gas Field, Texas1–4. The images are the first successful microseismic images in the Barnett, recorded between March 2000 and December 2001. The field is in the Fort Worth Basin, comprising the Mississippian shale lying between the Viola Limestone and the Marble Falls Limestone. The shale varies between 300' to 1000' thick, and is extremely low permeability (approximately 0.0001 millidarcies). Large scale hydraulic fracturing is required to stimulate production in the field to economic levels1. The objective of the microseismic imaging was to define the fracture growth characteristics during these well stimulations. The large scale hydraulic fractures, combined with infill drilling on spacing as tight as 27 acres and apparenent fracture complexity related to interaction with pre-existing fractures, resulted in a need to better understand the fracture geometry5. To image the actual fracture behavior in the field, a series of stimulations have been imaged using passive microseismic imaging to determine the fracture geometry and growth characteristics. Here, we present selected examples from images collected during numerous stimulations over a period of two years, which demonstrate substantial fracture complexity resulting from interaction with the natural fractures in the field. The paper reports the fracture geometry and complexity, comparisons with the final well production, and implications for field management.

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Carbon capture and storage (CCS) is currently one of several candidate technologies for reducing the emission of industrial [Formula: see text] to the atmosphere. As plans for large-scale geological storage of [Formula: see text] are being considered, it is clear that monitoring programs will be required to demonstrate security of the [Formula: see text] within the storage complex. Numerous geophysical monitoring techniques are currently being tested for this purpose, including controlled-source time-lapse reflection seismology, satellite synthetic aperture radar interferometry, electromagnetic sounding, gravity, and others. Passive seismic monitoring is an additional technique under consideration that complements these other techniques, and has potential as a cost-effective method of demonstrating storage security. This is particularly true over longer periods of time, as passive seismic arrays cost relatively little to maintain. Of the large-scale CCS pilot projects currently operational, thus far only the IEA GHG Weyburn-Midale [Formula: see text] Monitoring and Storage Project has included passive seismic monitoring. Here we present the results from five years of passive seismic monitoring at Weyburn, and discuss the lessons learnt that can be applied when deploying passive seismics to monitor future CCS operations.