The Use of Microseismicity To Understand Subsurface-Fracture Systems and To Increase the Effectiveness of Completions: Eagle Ford Shale, Texas
- John Detring (MicroSeismic Incorporated) | Sherilyn Williams-Stroud (MicroSeismic Incorporated)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- September 2013
- Document Type
- Journal Paper
- 456 - 460
- 2013. Society of Petroleum Engineers
- 1.10 Drilling Equipment, 3 Production and Well Operations, 4.6 Natural Gas, 4.1.2 Separation and Treating, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.8.4 Shale Oil, 5.1.5 Geologic Modeling
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Existing natural fractures often have a significant impact on both thestimulation and the production of oil and gas wells. The effective exploitationof unconventional reservoirs requires understanding of the local tectonichistory and the present-day stress regime. Signal strength; high-qualityreflection seismic, microseismic imaging; and the moderate structuralcomplexity of the liquids-rich gas and tight oil Eagle Ford Shale make it anexcellent place to study hydraulic fracturing in tight rocks.Microseismic-monitoring results showed clear structural trends relating to thereactivation of existing faults and fractures, and rock-failure mechanismsdetermined through source mechanism inversion of events. These results providedcritical information to the operator for optimizing the hydraulic-fracturedesign. Microseismic data collected by use of a surface array allowed the fullgeometry of the result to be viewed with no directional bias. The geometry ofthe microseismicity trends related to fracturing developed during thestimulation treatment was representative of the true geometry of the structure.The large aperture and wide azimuth of the monitoring array facilitated thedetermination of source mechanisms from every event detected, which providedfull coverage of the focal sphere of each source mechanism. The eventsidentified two different source mechanisms, indicating a failure mechanism forfractures that is different from that for reactivated faults. Microseismicitywith a northeast/southwest (NE/SW) orientation is interpreted to be related toeither induced or reactivated faults or fractures. Microseismicity also formedtrends that are contiguous across more than one wellbore in aneast-northeast/west-southwest (ENE/WSW) direction. These trends areinterpretedto have formed as a result of fault reactivation. Source mechanismsfrom fracturing parallel to SHmax have failureplanes that strike NE/SW with normal dip-slip failure on steeply dippingplanes. Those from fault reactivation have strike-slip failure onENE/WSW-striking failure planes. The NE/SW-striking, dip-slip fractures areparallel to extensional Gulf of Mexico (GOM) growth -faulting, and theENE/WSW-striking, strike-slip faults are at an angle of approximately 258 tothe dominant fracturing trends. Microseismicity trends associated with faultsare used to project where faults will intersect adjacent wells. Theidentification of these faults in the reservoir by means of microseismicmapping allows operators to modify their treatment parameters and stage spacingto avoid geologic hazards. The operator combines thetreatment-pump parametersfor the wells with the additional structural understanding gained from theanalysis of fracture trends and source mechanisms to identify zones that shouldbe avoided in subsequent treatments. In addition, the mapped microseismicityprovides critical information that was used to modify well spacing forsubsequent wells, thereby optimizing the completion plan and dramaticallycutting costs.
|File Size||794 KB||Number of Pages||5|
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