In this paper we review the workflow used for anisotropic moment tensor inversion and visualization applied to a dual well monitoring survey from the West Pembina field in Alberta. The workflow makes use of an exact, dynamic, layered VTI ray-tracer that allows for constant dip. Included are a description of VTI model calibration, moment tensor inversion, moment tensor decomposition and visualization. Interpretation of the results is ongoing.
The source mechanism of induced microearthquakes is of interest to the oil and gas industry because of what it may reveal about the hydraulic fracturing process. The process of recovering the source mechanism of earthquakes is known generally as “moment tensor inversion”, and techniques have been published applied to microseismic events (Urbancic et al., 1996, Trifu et al., 2000, Nolen-Hoeksema and Ruff, 2001, Eisner et al., 2010). These techniques have made use of a time domain isotropic ray theory Green function. Full waveform approaches for the moment tensor inversion problem have also been studied, using finite-difference Green function computations in isotropic media (e.g. Kim, 2011). Due to the computational burden, compressive sensing techniques have been investigated for waveform inversion (Vera Rodriguez et al., 2012). Rössler et al. (2007) described a time-domain inversion for earthquake sources in anisotropic media using ray theory Green functions, but the mechanism considered was limited to a displacement discontinuity source, which is an incomplete moment tensor. Recently a frequency domain inversion for the complete moment tensor was described (Leaney et al., 2011; Leaney and Chapman, 2013) that makes use of anisotropic Green functions computed with a VTI ray tracer. In that work anisotropy was found to have a significant distorting effect on the inverted source mechanism. In this paper we describe a time-domain moment tensor inversion that makes use of the same VTI ray tracer for the Green function. We review the workflow on a real dual well monitoring job from the West Pembina field in Alberta. Included are a description of VTI model calibration, moment tensor inversion, moment tensor decomposition and visualization. Interpretation of the results is ongoing.
About the Author(s)
Chris Chapman is a consultant with Schlumberger. His research interests are in theoretical seismology with applications ranging from exploration to earthquake seismology. He is interested in all aspects of seismic modelling but particularly in extensions of ray theory, anisotropy and scattering with applications in high frequency seismology. He has held academic positions at the Universities of Alberta and Toronto, and Professor of Geophysics at the University of Cambridge before joining Schlumberger as a Scientific Advisor in 1991. He was awarded the Gold Medal (Geophysics) of the Royal Astronomical Society in 2013.
Les Bennett is Microseismic Principal Geophysicist for Schlumberger and is located in Houston, Tx. He provides global operational support and training for microseismic operations in emerging markets and interfaces with Schlumberger microseismic engineering and software development centers. Les has served as instructor in various microseismic workshops including Doodletrain and Microseismic Bootcamp. He has B.S. and M.S. degrees from University of Mississippi in electromagnetic theory and a M.S. degree from University of Texas at Dallas in computer science. (Bennett5@slb.com).
Shawn Maxwell is Microseismic Advisor for Schlumberger, based in Calgary. Through previous positions with various service companies he has been a pioneer in the introduction of commercial microseismic hydraulic fracturing imaging services to the oil and gas industry and was a Lecturer at Keele University in England. Shawn was awarded a Ph.D. in microseismology from Queen’s University in Canada. He serves on various microseismic focused committees and workshops around the globe, and is currently passive seismic associate editor for Geophysics. Shawn is also a 2013 SPE Distinguished Lecturer (What Have We Learned About Fracturing Shales After 12 Years Of Microseismic Mapping?) and the 2014 SEG Distinguished Instructor Short Course (Microseismic Imaging of Hydraulic Fracturing: Improved Engineering of Unconventional Shale Reservoirs). (SMaxwell@slb.com).
Jim Rutledge received a BS in Geology from Pennsylvania State University and an MS in Geophysics from the University of Arizona. From 1984 to 2012 he worked as a contractor and staff seismologist at Los Alamos National Laboratory. From 2004 to 2012 he also worked as a consultant for Schlumberger Cambridge Research and MEQ Geo, Inc. Since October 2012 he has been employed by Schlumberger’s Microseismic Services. His research interests include: induced seismicity, the mechanics and interpretation of hydraulic fracture microseismicity, wave propagation in layered media, sensor systems, and borehole seismology.
John Duhault is a “hunter finder” who graduated with a Bachelor of Science in Geological Engineering in 1979 from the University of Manitoba and has over 34 years of industry experience in Canada and overseas. He has worked for and consulted to integrated senior and intermediate producers (Chevron, CS, Pengrowth and Canadian Hunter) and he has also found oil and gas for several junior independents. He founded and led two private juniors (Dragonheart Energy and Dragonheart Resources) and is currently working for Lightstream Resources on their Alberta/BC team. Mr. Duhault has presented papers for the CSEG, SEG, CSUR and ASET on integrated geophysical image interpretation and microseismic analysis. Mr. Duhault is a member of CSEG, SEG, CSPG, and APEGA.