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In 1980 and again in 1985, on the occasions of the 50th

anniversary of the Society of Exploration Geophysicistsand the 50th anniversary of publication of GEOPHYSICS, spe-

cial issues of that journal were published. In both those times,as now, the science was flourishing. The science described inthose issues was directed toward exploration, but many of themethods were to form the basis for a new application, herecalled reservoir geophysics. In 1980, oil prices were at recordhighs, and in 1985 they were about to plummet; at the time ofthis writing, prices are again at local highs, accompanied bya renewed enthusiasm for the sound application of the sci-ence.

The acceptance of 3D seismology as a cost-effective toolfor reservoir management was the single most importantaspect in the growth of reservoir geophysics. As such, mostof the history of reservoir geophysics parallels the history of3D seismology. On the other hand, a wide variety of differenttechniques within specialty areas of geophysics was developedsimultaneously; although these are not as widespread or well-known as 3D seismic, they are extremely valuable tools in thearsenal of reservoir management.

This brief history first describes the evolution of the accep-tance of 3D seismic techniques for reservoir management, andthen summarizes a number of other geophysical techniquesused for reservoir engineering purposes. Of course, any ret-rospective is strongly colored by the personal experiences andbiases (whether or not they are recognized as such) of theauthor, who assumes full responsibility for any errors, par-ticularly errors of omission.

Defining reservoir geophysics. Reservoir geophysics can bedefined as the application of geophysical techniques within a knownhydrocarbon reservoir. This implies that at least one well has beendrilled into that reservoir, and may (or may not) be availablefor geophysical applications. It is this access to wells and/orto internal information about the reservoir that distinguishesreservoir geophysics from exploration geophysics, as well asthe overall scale of the surveys. We can further subdivide“reservoir geophysics” into “development” and “production”geophysics, depending on the immediate application:Development geophysics is applied to the initial efficientdevelopment of a field, whereas production geophysics isapplied to the understanding of the field as it evolves duringproduction. (In some instances, authors may use the termreservoir geophysics as a synonym for “time-lapse seismic.”This usage should be discouraged; time-lapse seismic is sim-ply one aspect of production geophysics.)

In 1980, the typical sequence of reservoir development fol-lowed a “classical” flow of information from one specialty toanother, as shown in Figure 1.

In 1980, the flow of information was linear, from one per-son (and specialty) to another. There was very little feedbackbetween, say, the engineers involved in development and thegeophysicists who may have been able to assist them.

This has changed, of course. In fact, the new edition of thePetroleum Engineering Handbook, to be published by the Society

of Petroleum Engineers, will include a chapter on reservoirgeophysics, specifically to inform engineers of the assistancethat geophysicists can provide. While the transition from exclu-sively exploration-oriented geophysics to reservoir geophysicsmay seem fast and furious, concentrated in the 1990s, a more-detailed reflection indicates that the movement had alreadybegun by the early 1980s, when several developments tookplace in academia, industry, and the economy.

The academic role in developing reservoir geophysics. Threekey participants were:

1) By 1977, Amos Nur had founded the Rock Physics groupat Stanford, and was later rejoined by his former student,Gary Mavko. An expansion into borehole geophysics in1986 created SRB, the Stanford Rock Physics and BoreholeGeophysics Project. This group has done (and continuesto do) much to allow the interpretation of geophysicaldata in terms of rock and fluid properties, and of stressesaround boreholes, both key applications of reservoir geo-physics.

2) In 1982, M. Nafi Toksöz at the Massachusetts Institute ofTechnology founded the Earth Resources Laboratory,which by 1984 included the Full-Waveform AcousticLogging Consortium under Arthur Cheng, and by 1985the Reservoir Delineation Consortium under RogerTurpening. Both these consortia actively developed andtested new geophysical methods for the evaluation ofreservoir and nonreservoir rocks through borehole geo-physical techniques.

3) In 1985, Tom Davis formed the Reservoir CharacterizationProject at the Colorado School of Mines using multicom-ponent (and, later, time-lapse) seismic studies in reser-voirs to define internal attributes such as fracture densityand fluid content. This group is now on its tenth “phase,”having studied at least seven different fields.

These and other groups in many different countries laid

The rapid rise of reservoir geophysicsWAYNE D. PENNINGTON, Michigan Technological University, Houghton, USA

Figure 1. Schematic workflow for the development of a petroleum reservoir,circa 1980.

the foundation for much of the seismic work now included inreservoir geophysics. Their timing was good for the science,although funding was always (and presumably continues to be)a challenge. But the combination of new methods of seismicacquisition and processing with new and evolving interpreta-tional aspects of rock physics was key to the ease of industryacceptance of the seismic aspects of reser-voir geophysics. It was fortunate for theindustry at large that a few far-sightedprofessionals within various companieschampioned these and other consortia ata time when funding was scarce and theapplications of the science were notalways entirely apparent.

The education of geophysicists in uni-versities continued during the low-hiringperiod of the mid-to-late 1980s, providinga workforce for those companies that didhire them. In part due to the poor job mar-ket, most schools were training their stu-dents broadly, without early specializationinto certain niches, allowing them breadthof choice in employment upon gradua-tion. This ran counter to the demands ofsome recruiters, who tended (and stilltend) to request students who weretrained in one specific software packageor one highly specialized niche area, inorder to fill a certain immediate need. Thegeneralized backgrounds of many of thesestudents served them and their companieswell when the discipline rapidly evolved,and these new employees migrated intointerdisciplinary positions bridging geol-ogy, geophysics, and engineering.

The oil and gas industry. In the 1980s, the big money was beingput into exploration, not reservoir, geophysics. There was awidespread conviction that the price of oil would never drop,and that finding new oil was the best way to make money. Butthen, suddenly, the Ekofisk platform in the North Sea wasobserved to be “sinking” due to subsidence associated withreservoir compaction. Understanding the interior of the reser-voir was suddenly a multibillion dollar question, at least for onecompany, and all large oil companies became aware of their lim-ited knowledge of reservoir-rock dynamics. Many geophysi-cists had been schooled in earthquake seismology, and thetransition to reservoir mechanics was natural. As it turned out,petroleum engineers also needed input for well-completiondesigns, and this was becoming available through full-waveformacoustic logging. Once again, the classical earthquake trainingof many industry geophysicists made them well-suited forunderstanding the normal-mode propagation of waves in theborehole (compared with the ray-theoretical approximationssuitable for most surface reflection studies) and the strength ofrock and stresses in the formations—these values were neededby engineers working on hydraulic-fracture design, predictionsof wellbore stability, and simulation studies incorporating thecompressibility of the reservoir rock.

Many engineers and geophysicists developed good work-ing relationships within their companies as a result of thesemutual interests and capabilities, and each learned the advan-tages the other could bring to their work. These relationships

proved to be extremely useful in the next stage—the acceptanceof 3D seismic studies by the engineering community. (While 3Dseismic methods were gaining the most popularity and atten-tion, there were significant advances in several other aspects ofreservoir geophysics, including borehole-based seismic, micro-gravity, electrical, electromagnetic, and passive seismic; these will

be discussed in a later section of thispaper.)

The first 3D seismic surveys were per-formed as subjects of research and havebeen discussed in various reminiscencespublished in TLE’s “From the Other Side”column. Most geophysicists knew by thelate 1970s or early 1980s that 3D seismicwas technically feasible, and some dra-matic examples were shown at variousmeetings, mostly directed toward enhanc-ing exploration, rather than production(see, for example, the abstract describing3D seismic exploration in the Austin Chalkby Calcote and others in SEG’s 1982Expanded Abstracts). By 1983, the SEGAnnual Meeting and Expanded Abstractsincluded a session “Seismic 16” (availablefor online browsing through the SEGDigital Library) with seven papers pre-sented on 3D seismic methods and casehistories. Of these, about half could beconsidered applicable to reservoir geo-physics, and about half to exploration.One of the papers described the first time-lapse seismic study reported in the liter-ature: “A study of fireflood efficiency”(Greaves and others, paper S16.1; also laterpublished in GEOPHYSICS). A number ofpresentations at the 1983 Annual Meeting

(sessions Seismic 20 and Seismic 21) also described computertechniques that allowed interpreters to manage and view 3D seis-mic data, a necessary feature for wide application, of course.

Although the value of 3D seismic for field development wasrecognized publicly as early as 1984 (“The value of 3D seismicin field development” by Gaarentstroom, SPE 13049), an impor-tant milestone occurred with the publication of “Modern tech-nology in an old area: Bay Marchand revisited” by Abriel andothers (first, as an abstract, RES 2.7 in 1990, then as a paper inTLE in 1991). In this study, the Chevron team demonstrated that3D seismic studies and interpretation applied to a field—one thathad been under production since 1949 and in decline since theearly 1970s—resulted in nearly doubling the daily productionand clearly demonstrating that reservoir geophysics was a cost-effective tool for the management of producing assets.

But the real confirmation that the industry was going toadopt the new technology and apply it to reservoir develop-ment and production arrived in 1991 when Shell described itsexperiences with 3D seismic. Figure 2 is from Nestvold’s “3DSeismic: is the promise fulfilled?” SEG Expanded Abstract whichstated that “... it is recognized that 3D is a powerful tool forappraising a field and for providing valuable input into thedevelopment plan itself.” It was inferred that Shell wouldconduct 3D seismic surveys over every major asset, as well asbeing used earlier in the exploration process. This caught theattention of the managements of most oil companies, and geo-physicists were finally brought into the discussion of reser-

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Figure 2. The growth of 3D seismic surveys inShell (outside of North America), from theexpanded SEG abstract published by Nestvold in1991.

voir engineering and production on a larger scale.Most producing companies had, by this time (1991), devel-

oped some experience with 3D seismic methods, and con-tractors were able to deliver the service worldwide. Theadditional pieces required to make reservoir geophysics amainstream aspect of reservoir management were (1) confi-dence of management in the geophysicists’ capability to under-stand and appreciate reservoir engineering needs, and (2)direct lines of communication between the geophysicists andengineers. Fortunately, in many companies, these were alreadyin place as a result of their earlier experiences in geomechan-ical and well-completion studies. Most companies werealready familiar with the appropriate technologies throughparticipation in academic consortia, if not through their ownefforts. The rest, as they say, is all in the details. Of course, thedetails varied among companies and even among differentmanagement groups. Some companies and managers madeopening of the lines of communication easy; others, no doubt,made it difficult.

The gorilla in the room—economic issues. The developmentof many of the techniques that ultimately found applicationsin reservoir geophysics had begun when the price of oil wasvery high, in the late 1970s and early 1980s. But then the priceof oil collapsed in 1986, and the attention of most oil compa-nies and oil-service companies was directed to cutting costs... to the bone. Exploration was a primary target of cost-cut-ting, because of its long payback time. Reservoir geophysicswas seen by those geophysicists remaining in the business asa possible avenue to continued relevance and employment.Companies had to be convinced that there was actually an eco-nomic benefit to be realized in applying reservoir geophysics.The correlation between the drop in oil prices and the rise inuse of 3D seismic surveys (Figure 3) is only partially spuri-ous, but the dramatic rise in seismic surveys applied for reser-voir studies was no doubt accelerated by the need to developexisting assets as budgets tightened.

How did this affect the geophysicists who were needed toapply their science to the improved development of reservoirs?A few scientists actually found positions as geophysicistsattached to engineering departments, but this was the excep-

tion, rather than the rule. Strong economic pressures helpeddrive geophysicists into making use of their talents in wayswhich they had not previously envisioned, in areas such asfull-waveform acoustic logging, borehole stability, reservoirgeomechanics, and rock-physics integration with reservoirsimulation. These applications all became directly engaged inwhat we now call reservoir geophysics.

As companies began to depend more on increasing pro-ductivity from their existing assets and less from finding newfields, the pressure also increased on reservoir engineers toensure that they made use of all the relevant data that couldbe obtained. Their relationships with some geophysicistsallowed them to have confidence (although perhaps limited)in the field in general, and most were open to considering theuse of geophysics in their reservoir evaluations.

Following the oil-price collapse of the 1980s, oil pricesremained more-or-less steady through 2003 (Figure 4),although volatile in the short term. The groundwork for reser-voir geophysics was laid during the price collapse of the 1980s.The science matured during the postcollapse period of the1990s, and this continues today. (Speculation about the rela-tionship of reservoir geophysics with the oil-price run-upunder way in 2004-2005 is premature at this time, and will notbe attempted by this author!)

As reservoir geophysics matured, it became increasingly“standard operating procedure” at most companies. Withincreased scrutiny of asset statements, it is likely to becomemore integrated with traditional reservoir managementschemes over time. Although hard figures are impossible tocome by, it may be that more financial and human resourcesare being invested in reservoir geophysics than in explorationgeophysics at this time ... less than 20 years after the phrasecame to popular attention.

Specific aspects of reservoir geophysics. Reservoir geophysicsdiffers from exploration geophysics in three main areas: wellcontrol, rock-physics control, and survey scope and design.The targets of reservoir geophysical surveys are more clearlyidentified, and the existence of at least one well means thatthe surveys can be focused, calibrated to depth, and calibratedfor rock physics correlations. The availability of one or more

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Figure 3. Comparison of the growth in 3D seismic surveys (approximatedfrom Figure 2) and the price of oil (first-purchaser's cost, in constant year-2000 dollars; from the Energy Information Agency, U.S. Department ofEnergy).

Figure 4: Price of oil (first-purchaser's cost, in constant year-2000 dollars;from the Energy Information Agency), showing short-term volatility andlong-term stability from 1986 through 2003.

wells also opens up new geometrical options for the surveys.As a result of these factors, reservoir geophysics has expandedthe application of 3D seismic and opened new opportunitiesfor borehole seismic and nonseismic techniques.

Many of these techniques are due largely to the tenacityof a few dedicated visionaries of geophysics. Each specialtyhas repeatedly been declared “dead” by practitioners andmanagement, only to resurface again with improved tech-nology and resolution. The dedication of these people cannotbe overstated, and the field of reservoir geophysics owes themtheir appreciation. Their funding sources varied, but includedtheir own personal credit, corporate support, venture capital,and government funding. Government funding for the devel-opment or improvement of many of these techniques wasoften through the U.S. Department of Energy and its nationallaboratories, in an effort to decrease the decline of US-basedpetroleum resources (for author’s disclaimer, see acknowl-edgments). Currently, research support in reservoir geophysicsis also provided through the European Union, reflecting theimportance of North Sea assets.

3D surface seismic has five main benefits:

• Attributes: While seismic attributes have become increas-ingly important for exploration geophysics, they are derigueur for reservoir geophysics. Spatial variations in lithol-ogy and fluid content are among the primary goals of reser-voir geophysics, and these are typically established throughcalibrated seismic attributes, including inversion results.

• Geostatistics: With well calibration comes the opportunityto provide estimates of confidence in the results of corre-lation of rock properties through (calibrated) rock-physicsrelationships.

• Time-lapse seismic: The repeated surveying of a reservoir hasallowed changes in attributes to be related to changes inreservoir properties due to production. Some changes arethe result of fluid substitutions, while others are due to pres-sure changes, and still others may, in some unusual cir-cumstances, be due to chemical and physical changes inthe reservoir matrix material.

• Ultrathin beds: As the targets become more focused, the abil-ity to use the natural bandwidth within the seismic waveletincreases. Commonly grouped under the label of “spectraldecomposition,” these methods exploit the highest-fre-quency components of the wavelet and their tuning effectsin thin beds, rather than just the dominant frequency com-ponent.

• Multicomponent seismology: The use of three-componentreceivers, whether to record shear waves generated by aspecialized source or shear waves generated by conversionupon reflection, has been demonstrated to enable imagingbeneath gas clouds that overlie some reservoirs and tomap fracture patterns and densities.

Borehole seismic has three primary functions:

• 3D VSPs: Getting either the receiver or the source closer tothe imaging target (and below the weathered layer) resultsin a much higher-resolution image. Placement of a stringof seismic receivers in the borehole (vertical seismic pro-filing or VSP) or a source in the borehole (reverse VSP)accomplishes this, and allows for 3D imaging if the sur-face components (sources for VSP and receivers for reverseVSP) occupy appropriate large swaths of the surface.

Development of extremely high-quality multichannelreceiver strings has made the service affordable by mini-mizing acquisition time, which often requires loss of pro-duction.

• Crosswell seismic imaging: The deployment of a string ofreceivers in one well, and a source in another well, allowsthe imaging of the plane between the two wells. The tim-ing of the first arrivals allows a 2D image of interval veloc-ities to be obtained as a velocity tomogram, and thereflected events can then be migrated into proper positionsfor a crosswell reflection image. The primary advantagecomes from a tremendous increase in resolution, oftenexceeding a full order of magnitude improvement over thesurface data in the same area.

• Passive seismic monitoring: Some reservoir managementactivities result in microseismic (and occasionally macro-seismic) activity—small earthquakes—usually notdetectable at the surface of the earth. Deployment of sen-sors in boreholes has allowed detection of these events.When the seismic events that accompany stimulation forhydraulic fracturing are located, the result is a temporallychanging map of the fracture during its creation. The map-ping of events from other reservoir practices (usually,although not always, injection) can also be accomplished,although the relationship of these events to information thatis deemed useful to the improvement of reservoir perfor-mance is not always apparent. While hydraulic-fracturemonitoring services can be considered “routine” by reser-voir-geophysics standards, the application of other micro-seismic services is still developing.

Electrical and electromagnetic surveys. The single most sig-nificant physical property that distinguishes hydrocarbonsfrom brine is resistivity—hydrocarbons are virtually insula-tors while brine is an excellent conductor. The differences canbe orders of magnitude (compare this with the fractional dif-ferences of seismic properties), and mapping of reservoir flu-ids from electrical and electromagnetic should be easy, it seems.The problems with using these techniques are associated withtheir inherent poor resolution (they should be considered dis-persive, with essentially very large wavelengths) and theprevalence of steel-cased wells in oil fields. Still, amazingprogress has been made, and, while not quite routine, time-lapse electromagnetic surveys of reservoirs are now possible,and case histories have been published. This area can beexpected to continue to improve in capability and availabil-ity in the future, as improvements continue to be made andcase studies conducted.

The role of SEG. SEG promotes the advancement of the scienceof geophysics and the ethical practice of applied geophysics. Itis strongly driven by the desires and needs of its membership.But the word “exploration” is in its name. In the 1980s, a smallgroup of geophysicists decided that the overwhelming atten-tion paid to exploration geophysics was resulting in the neglectof geophysics applied to reservoir development and production,and they formed a new committee, called the Development andProduction Committee, to address their needs. (This is howthings work in SEG. If there is a need for something, a groupcan be formed to address it. It is a highly democratic institu-tion.) This committee rapidly grew in size to more than 200 mem-bers, almost all of whom were active in one form or another. Itinitiated the “Development and Production Forum” (D&P

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Forum) in 1991, where attendees were united by common goals,rather than common technologies. In this sense it was remark-ably unique and beneficial—the participants in these week-longmeetings (held at resort locations) included geophysicists, geol-ogists, engineers, and occasionally management. They were vir-tually forced to sit through presentations and discussionsinvolving technologies with which they were not necessarily veryfamiliar, because there were no alternative sessions (other thantruancy, which was frowned upon). The effect was a tremen-dous cross-fertilization of ideas and expertise. For example, theelectromagnetic researchers learned how to present results inways that reservoir engineers could see a benefit. Seismologistslearned about the problems facing the engineering community,and found out that these were not always the same as the “prob-lems” that the geophysicists had been working on. And so on.Most meetings were highly successful, although some did notbreak even financially, causing a strain on the concept of dedi-cated small meetings sponsored by the larger society.

A brief timeline drawn from session titles of SEG AnnualMeetings and special sections of TLE shows a number ofaccomplishments (see box, right).

There were times that the D&P Committee recommendedthat the SEG Executive Committee change the name of SEG tosomething more encompassing (my personal favorite is SEG:the Society of Extraordinary Geophysicists—where we are allabove average). This proposal was usually met with disdain, butoccasionally good-natured laughter. The D&P Committee nolonger feels the need to exert its influence in these matters.Instead, the question presently facing the group is this: Now thatdevelopment and production geophysics has become a majorforce—perhaps the major force—in petroleum geophysics, isthere still a need for such a committee? Should the committee“declare victory and go home”? We are nearly all reservoir geo-physicists now.

Suggested reading. The best contemporary accounts of the devel-opment of reservoir geophysics can be found in the annual specialsections of TLE from 1992 through 2004. The journal is available forbrowsing through the SEG Digital Library (http://segdl.org/). Somereaders may be interested in comparing the reflections made in thispaper with the predictions made by Gordon Greve in “Geosciencein reservoir development—a sleeping giant” (TLE, 1992). @75

Acknowledgments: The author gratefully acknowledges all the people whoworked on the D&P Committee through the years, and who actively pro-moted the discipline of reservoir geophysics. Each person’s recounting of thehistoric record will vary, and this article presents just one view. Preparationof this manuscript was supported by project DE-FC26-04NT15508 fromthe U.S. Department of Energy, Fossil Energy Program, through the Tulsaoffice of the National Energy Technology Laboratory with Purna Halder asprogram manager. The views and opinions of the author expressed hereindo not necessarily state or reflect those of the United States Government orany agency thereof.

About the author: Wayne Pennington has degrees in geology and geophysicsfrom Princeton, Cornell, and the University of Wisconsin-Madison. Hiscareer has been divided between academic and industry employers and heis currently a professor of geophysical engineering and department chair atMichigan Technological University. He was an early advocate of reservoirgeophysics and chaired the 1992 D&P Forum on Monitoring ReservoirChanges Over Time. Pennington was guest editor for several TLE specialsections on development and production geophysics and wrote the reservoirgeophysics chapter in the new Petroleum Engineering Handbook (soonto be published by SPE).

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Examples of typical advertisements published in GEOPHYSICS during the 1940s.