#2 Using Seismic Azimuthal Anisotropy to Find Fractures

#2 Using Seismic Azimuthal Anisotropy to Find Fractures

Geomechanics Breakfast Series No 2
←  SPE - Calgary Section

Geomechanics Breakfast Series No 2:
Using Seismic Azimuthal Anisotropy to Find Fractures

Date: Thursday, 20th of February 2020
Speaker: David Gray, Principal Geophysicist, Ikon Science
Location: Calgary Petroleum Club (329- 5th Ave SW)
Time: 7:30am – 9:30am
Cost:Member - $40, Non-Members $50 Students $15
Special Three Geomechanics Series: Members - $100, Non Members - $130


Abstract:

Many unconventional gas plays rely on the presence of natural fractures to enhance or create permeability in the reservoir. These fractures cause significant, measureable changes in 3D seismic data.  These changes appear as variations in seismic amplitudes and velocities with shot-receiver azimuth and are known as seismic azimuthal anisotropy. 

Figure: AVAZ results overlaid as “plates” on an acoustic impedance inversion.  The coloured plates indicate seismic anisotropy, which is an indicator of open fractures.  The size and colour of the plates is proportional to the intensity of the seismic anisotropy, with the anisotropy following the same colour scale as the acoustic impedance (shown at the bottom of the figure).  Low acoustic impedance (grey) indicates coals, moderate acoustic impedance (brown) indicates shales, and high acoustic impedance (blue) indicates sands in this section.

Examples of the seismic identification of fractures are shown for a Mannville coal, unconventional shales from Alberta, and the tight gas sands of the Pinedale Field in Wyoming, which is an analog to Alberta’s Deep Basin.  In the latter example, seismic fracture estimates are shown to be the best predictors of well EUR (Estimated 

Ultimate Recoverable) and therefore they are used to predict EUR in 3D space from the seismic data.

The technology to measure seismic azimuthal anisotropy is 20 years old and ready to be used to pinpoint areas of more dense natural fractures in reservoirs such as unconventional shales and other tight rocks, and coalbed methane.   The seismic azimuthal anisotropy response is driven by the interaction of today’s stress field with the paleo-fractures generated in the past.  A discussion of how to interpret today’s open fractures from this anisotropy will use this concept.  This can result in complex fracture behavior, as can be seen in the figure.  The described interpretation of the seismic anisotropy allows for understanding that leads to better pad and well design.

Seismic azimuthal anisotropy measurements have achieved a technical success rate for identifying fractures upwards of 80% in unconventional gas plays.  This can significantly impact economic success of wells in areas where success rates are variable. 


Speaker Bio:

David Gray is Principal Geophysicist, Canada for Ikon Science.   During the 2018-19 school year, David was honored to give the CSEG Canadian Distinguished Lecture on Seismic Geomechanics at 24 Universities and Research Institutes across Canada.  In 2015, David was selected as the honoree of the 4th annual CSEG Symposium for his contributions to showing value in geophysics.  Many of David’s recent talks address the value that geophysical work can bring both monetarily and societally.   In 2018, he was given the award for the best CSEG Luncheon talk, and has he has been co-author of several papers that have won similar awards.  David is a founding member and Secretary of the CSEG’s Value of Integrated Geophysics Committee, whose mandate is to show ways that geophysics adds value to industry and society.  He has made significant contributions to: quantitative interpretation, where three AVO equations have his name on them; seismic fracture characterization, where in 1999 he related azimuthal variations in 3D seismic to fractures in the borehole and where he holds a patent; and, seismic geomechanics where in 2009 he showed that all three principal stresses can be estimated from 3D seismic data and where he also holds a patent.  He has presented over 100 papers at various technical conferences and luncheons for CSEG, SPE, AAPG, EAGE, HGS, and RMAG.    Previously, David was Senior Geophysical Advisor at Nexen, where he contributed AVO work on the 6 billion bbls of reserves discovered in the last 4 years by the Guyana JV of Exxon, Hess, and CNOOC, and where he made significant advances proving that geophysics adds value in Oil Sands.  Prior to that, he did 17 years of research for Veritas and CGGVeritas in reservoir characterization and seismic signal analysis using experience gained as AVO specialist and seismic data processor for Veritas, Geo-X Systems, and Seismic Data Processors, as well as from his internship in the special projects group at Gulf Canada. David received a Bachelor of Science degree in Honors Geophysics from the University of Western Ontario (1984) and a Masters of Mathematics degree in Statistics from the University of Waterloo (1989).   David is a member of SPE, SEG, CSEG, EAGE, and APEGA and is a registered Professional Geophysicist in the Province of Alberta.  In his spare time, he enjoys spending time with his family, writing and presenting technical papers, working with students and young professionals, and competing in volleyball and grassroots motorsports.

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February 20, 2020
From 7:30 AM to 9:30 AM
Calgary Petroleum Club
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