Heloise Lynn

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Heloise Lynn
Image-lynn.jpg
MSc Geophysics
PhD Geophysics
MSc university Stanford University
PhD university Stanford University

Heloise B. Lynn started working in reflection seismic in the oil/gas industry in 1975, processing seismic data at Texaco, in Houston, Texas. In 1978, she completed her MS in Exploration Geophysics, Stanford University, and in December, 1979, she completed her PhD in Geophysics, also at Stanford University, in (post-stack) depth migration and interpretation issues within migration algorithms. Lynn worked for Texaco, Amoco, BP, and then in 1984, she and her husband, Walt, formed Lynn Incorporated. Her consulting experience includes working in North America, Hungary, Qatar, Kuwait, Saudi Arabia, Pakistan, Australia, Thailand, China, and Japan. She specializes in the use of 3D multiazimuth and/or multicomponent data to obtain structure, lithology, porosity, pore fluids, in-situ stress, and aligned porosity (aka natural fractures). She also includes conventional VSP data processed for split-shear waves in these projects because there is nearly always a source-generated S-wave or a near-source mode-converted S-wave, and/or mode-conversions at impedance boundaries.

In the mid-1990s, the U.S. Department of Energy funded three projects, wherein she served as principal geophysicist, to document how to use reflection seismic to characterize naturallyfractured gas reservoirs. Her current interests include the co-rendering of high dimensional seismic datasets for interpretation (mid-2000s). "Where you sit governs what you see," and two subsequent articles, by H.B. Lynn and Ping Chen and Chenyi Hu, in The Recorder, Canadian SEG, July 2003, discuss the visualization of high-dimensional datasets.

Heloise is the 2015 recipient of the the Reginald Fessenden Award and served as the SEG 2019 Honorary Lecturer and the Fall 2004 SEG Distinguished Lecturer. She is a member of SEG, EAGE, the Geophysical Society of Houston (GSH), AAPG, and SPE.

2019 SEG Honorary Lecturer, North America

Azimuthal P-P seismic measurements: Past, present, and future

Azimuthal(az’l) seismic analyses give rise to better imaged data and insights into the in-situ stress field and the aligned porosity (fractures) that flow fluids. Ignoring azimuthal seismic information, which in the past was quite easy to do, is now inexcusable because of vast improvements in: (a) platforms to view, map, and analyze az’l prestack or partial stack data; (b) acquisition (more data); and (c) processing algorithms (e.g., orthorhombic prestack depth migration [PSDM]).

Understanding the past gives insight into today. In 1986, the first “Anisotrophy” session of the SEG Annual Meeting featured five paradigm-shifting Amoco papers and one paper from Stuart Crampin, an early anisotropy pioneer. The Amoco papers documented six years of confidential applied research into shear-wave splitting, as visible in S-wave reflection seismic data. Shear-wave splitting, specifically, the two different shear moduli for vertically propagating S-waves, and more generally, the effects of aligned porosity (vertical penny-shaped cracks or squashed vertical pancake porosity), is the cause of azimuthal variations in seismic measurements. The porosity geometry is the root cause of shear-wave splitting and all azimuthal P-P seismic. The P-wave velocity depends on the bulk modulus and the shear modulus (as influencing various elastic constants): when these moduli vary by azimuth and angle of incidence, then the P-wave velocity varies by azimuth and angle of incidence.

In 1995, Lynn et al. published the case history of two orthogonal 2D 9C lines, deliberately laid out in the principal planes of the az’l anisotropy: one line parallel the maximum horizontal stress (N30W) and fracture parallel, and the other line perpendicular to that direction, in the Bluebell-Altamont field, Utah [US DOE Contract No. DE-AC21-92MC28135]. The S-S reflections traveled as S1-S1 or S2-S2 depending on the azimuth of their particle motion (SH or SV). The birefringence of the rock layers was directly measured in the difference between the S1 versus S2 interval traveltimes between key reflectors. In the Upper Green River (the zone of interest), the az’l change of the PP AVA gradient at the tie-point was proportional to the contrast in S-wave layer-birefringence (contrasts in fracture density) at the boundary. In the following decade, the AVA gradient change by azimuth (AVAZ) became an industry standard for detecting and describing natural fracture sets.

Closer to the present, in 2017, the use of az’l anisotropy to obtain better imaged 3D P-P reflection seismic has been most recently demonstrated in 4C 3D offshore Vietnam and Bohai Bay: both complex geology settings. Lynn and Goodway (2018) published az’l P-P reflection seismic amplitudes wherein the effect of vertical aligned porosity in a naturally fractured carbonate oil reservoir has a specific effect upon the az’l variation of the gradients as well as the near-angle (6-20° incident angles) amplitudes. In the Bluebell-Altamont 1995 data set, az’l variation in the P-P near-angle amplitudes at the tiepoint was also observed, below the zone of interest. The az’l variation of the near-angle amplitudes is currently controversial. More geophysicists need to examine their own az’l seismic, with calibration data, and publish!

The future: as affordable compute power continues to increase, the ability to view, analyze, and process 3D P-P data from 0 to 360° shall become the norm, especially in complex geology settings. Continual improvements in imaging will drive this advance. Furthermore, the ability to record, analyze, process, map, and interpret the effect of dipping aligned fractures (that is, “dipping faults,” aka “growth faults”) shall be realized: at first through the P-S1, P-S2, reflections (already processed from azimuths 0-360), and also by the P-P reflections processed 0-360 and tied to the P-S1 and P-S2 reflections. We will learn how to better remove the effect of the birefringent near-surface (weathering layer, or top ~1000 ft). 4D seismic shall routinely become time-lapse azimuthal seismic because the most compliant (easily changed) part of the rock-pore-fluid system is the pore-fluid space. The pore space and the pore shape change when fluids are removed or introduced into a reservoir. Along tectonic plate boundaries, stresses alter with time – this alters the pore geometry (the fracture populations) so time-lapse azimuthal seismic shall become stress-monitoring. People don’t like no-warning earthquakes.

The world is filled with new and exciting opportunities. With each new technology advance, new production is discovered. In the 33 years since the first SEG session on anisotropy, we have made a good start, but the best is still to come. All explorationists are incurable optimists; it is a job requirement!

Additional Resources

A recording of the lecture is available.[1]

Listen to Heloise discuss her lecture in Anisotropy without tears featuring Heloise Lynn, Episode 62[2] of Seismic Soundoff, in-depth conversations in applied geophysics.

SEG Reginald Fessenden Award 2015

Heloise Lynn is presented the Reginald Fessenden Award for her 35-year career of translating the anisotropic behavior of seismic waves into practical applications that allow stress fields, fracture systems, and geomechanical properties to be characterized in targeted rock systems. She has described her research findings in many oral presentations and in 47 published papers that collectively create an invaluable knowledge base for scientists, researchers, students, teachers, and exploration geophysicists.

Biography Citation for the SEG Reginald Fessenden Award 2015

by Leon Thomsen

Heloise Lynn graduated from Stanford University in 1980 with a Ph. D. thesis in conventional exploration seismics. But on joining Amoco’s domestic Exploration and Production office in Houston, Texas, she was given a new type of data set to process, one that had defeated more experienced geophysicists. It had been recorded in the folded Appalachian Mountains of Pennsylvania, two crossing 2D lines of “shear data.” This was in the early, naïve days of shear-wave exploration, and everybody thought that such surveys should have a horizontal crossline source, creating “SH” reflection data. This had been executed on both lines so that at the tie-point, the two lines had near-orthogonal polarization.

Heloise produced, on each line separately, a well-defined subsurface image, clear down to 20,000 ft. This in itself was a triumph, since the Conoco Shear-Wave Group Shoot had demonstrated, only a few years previously, that most such data was uninterpretable. In fact, the Amoco Research Acquisition Party 45 had been outfitted with horizontal vibrators, specifically to investigate this negative result.

But Heloise was not satisfied with her apparent technical success, since the two images, at the tie point, did not tie each other. A gradual mis-tie developed with traveltime, growing to 60 ms at 4 s. Working together with Amoco’s Tulsa Research Center, she concluded that this was the first observation ever (in exploration data) of “shear-wave splitting” at near-vertical incidence. And she was able to explain why her success was consistent with the Conoco Group Shoot’s failures. This led directly to six years of intensive, secret Amoco development of shear-wave understanding and know-how before other companies began to catch on.

When we finally went public, at the now-famous “Amoco Anisotrophy Technical Session” of the 1986 SEG convention, Heloise’s contribution was essential to helping the industry understand this fundamental feature of shear-wave propagation in realistic anisotropic formations. But Heloise had moved on, leaving Amoco to found Lynn Inc. (with husband Walt Lynn).

Lynn Inc., has prospered for more than 30 years as a “boutique firm,” specializing in the design and processing and interpretation of multi-azimuth and/or multi-component seismic data sets. An early project was a wide-azimuth (land) 3D P-wave survey, which Heloise processed to reveal the now well-known ellipse of azimuthal variation of moveout velocity. This was one of the first observations of its kind; the effect has now been seen in many contexts, especially with today’s high-quality wide-azimuth marine surveys. Unless the effect is accounted for, most wide-azimuth surveys will result in nonoptimal images.

(As an aside, Heloise was the first, to my knowledge, to propose multiboat marine surveys for wide-azimuth acquisition. The year was about 1995, i.e., long before BP’s first such surveys. Her suggestion was made to me in a casual conversation; I dismissed it out of hand as economically unfeasible. That was a mistake; decisions like this should be based on costs versus benefits, not on costs alone. Heloise understood this principle, in this context, before anybody else did.)

Recently, Heloise has published data demonstrating the azimuthal variation of velocities (and the associated P-wave azimuthal amplitude effects) in a carbonate oil-resource data set and has correlated those seismic signatures with various calibration data sets at the detailed reservoir scale. Analysis like this is a valuable step toward learning how to actually explore for the sweet spots of production of the shale resource too. As the industry learns how to explore in the shale resource, instead of blindly drilling on a grid and fracking everywhere, we will begin to realize the promise of that resource in an economically viable way. Creative minds like Heloise show the way.

"Heloise B. Lynn, 2008"

Fall 2004 SEG Distinguished Lecturer

The Winds of Change: Anisotropic Rocks...their Preferred Direction of Fluid Flow and their Associated Seismic Signatures

Although 20 years ago it was politically incorrect to admit that horizontal permeability anisotropy resulting from aligned connected porosity was linked with seismic anisotropy (azimuthal anisotropy), the winds have changed.

Our industry now has a respectable worldwide effort in research, acquisition, processing, interpretation, and modeling that pursues precisely that linkage. The current thought process is that unequal horizontal stresses and/or vertical aligned fractures can provide the aligned connected porosity which may result in horizontal permeability anisotropy. The presence of vertical aligned fractures and/or unequal horizontal stresses typically causes azimuthal anisotropy.

The earliest efforts pursued the azimuthal variation of PP and SS traveltimes and amplitudes, because these pure-mode seismic waves measurements are the "easiest" measurements our industry can process and interpret, and we believe we understand traveltimes and amplitudes. Thus our documentation of the relationship of azimuthal PP and split shear-wave measurements was founded. As time went on, the PS modes (P-S1 and P-S2) or the split C-wave (converted wave—P down and S up), were used to document the shear-wave anisotropy arising from unequal horizontal stress and/or vertical aligned fractures.

Now, however, our industry is grappling with what researchers point out as the "biggest" anomaly that links horizontal permeability anisotropy to seismic anisotropy—azimuthal variation in attenuation. However, attenuation has usually received cursory dismissal. We don't like "dim zones" being "pay," because (1) they are "too hard" to map, (2) there are too many other reasons for dim zones rather than azimuthal attenuation, and (3) attenuation is too hard to quantify and attribute to any one cause per se. In the past, we have often used trace equalization, AGC, spectral whitening, and other very powerful processing techniques to remove dim zones. Processors worth their salt made those pesky dim zones look nice and bright and sharp!

In the past, attenuation has been a classic problem, and not in any guise a "solution" to anything. Now, however, we can glide forward on the next wave of multi-component multi-mode multi-azimuth 3D and 4D seismic powered by the winds of change.

Honorable Mention (Geophysics) 1990

H. B. Lynn and L. A. Thomsen received 1990 Honorable Mention (Geophysics) for their paper Reflection shear-wave data collected near the principal Axes of Azimuthal anisotropy.[3]

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