22 Oilfield Review

Information delivery is a business of balance.With too little information, problems remainu n s o l ved. With too much, the relevant partsm ay go unheeded. Too early may not be pos-sible, but too late might just as well be not atall. And giving confidential information tothe wrong party is unacceptable. Creatingthe perfect balance requires knowing what isneeded: wh i ch data and how much, wh e r eand when to send data, and to whom. And ofcourse, no data transfer is possible without ameans of conve ya n c e .

For the oil and gas industry, the scale of thei n f o r m a t i o n - d e l ivery challenge is global.Rigs, crews and vessels are able to acquirelog and seismic data at nearly every coordi-nate on the globe, but the decision-makersand end-users of these data are usually farfrom the acquisition site and often remove dfrom data-processing opera t i o n s .

The availability of the Wo r l d Wide We b ,satellites and high-speed transmission linesmakes delivery of distant oilfield informationpossible, but other elements of the balancingact must be weighed before the problem iscompletely solved—before the hard-wo ndata make their utmost contribution to ther e s o u rce optimization puzzle. Each disci-pline within the industry has specificrequirements for data type and amount. Eve nwithin a discipline, needs may vary withu r g e n cy and end use.

Interactive Exploration

Operating companies can now monitor from afar the pro g ress of their

seismic data acquisition and processing projects on a daily basis.

T h rough advances in secure computer network access, the searc h

for hydrocarbons is approaching a level of interactivity that allows

oil company experts to “virtually” participate in the acquisition and

p rocessing of their data in real time from the comfort of their offic e s .

For help in preparation of this article, thanks to ColinHulme and Robin Wa l k e r, Geco-Prakla, Gatwick ,E n g l a n d .Olympus-IMS, SEISMOS, SuperVision, TQ3D (To t a lQuality 3D) and T R I NAV are marks of Sch l u m b e r g e r.TWS (Trusted Web Service) is a mark of Omnes.N avigator and Enterprise are marks of NetscapeCommunications Corporation. Internet Explorer is amark of Microsoft Corpora t i o n .

Dilip BhattJohn KingstonG a t w i ck, England

Helge Bra g s t a dA s k e r, Norway

Dennis O’NeillHouston, Texas, USA

Winter 1997 23

24 Oilfield Review

In terms of seismic data, the demands forinformation can be classified according tothe stage of a surve y. The two stages with thegreatest needs for time-sensitive data, andthat lend themselves well to the constra i n t simposed by real-time transfer of information,are survey acquisition and data processing.In this article, we examine the data require-ments for these two crucial stages in theimaging of a reservoir and describe a newInternet-based system that allows opera t o r sto monitor in real time the progress of theirdata acquisition and processing.

R e q u i red While AcquiringUntil a well is drilled, the most reliable infor-mation available for identifying targets isgleaned from seismic data. Getting a high-quality seismic survey at a cost-effectiveprice is crucial. To ach i e ve this, opera t o r sneed details about survey progress duringseismic acquisition, whether on land or atsea. This may be for health, safety and env i-ronmental reasons, contract conditions, or

for monitoring and assessing data quality. Insome cases, timely operator response orinput is essential to the success of the surve y.

Some of the information operators requireis contained in the party ch i e f ’s log, wh i ch isa record of all significant events; the nav i g a-tion log, wh i ch documents the positioningprocess; and the daily production log, wh i chis a listing of the lines that were acquired andwhether they passed established qualityacceptance criteria.

Also vital, from a data-quality point of view,are Quantified Quality A s s u rance (QQA)reports that contain detailed analyses of thedata acquired and comparisons of these toquality standards that were set in the surve yplanning stage.1 Quality parameters have tra-ditionally been based on simple analysis ofb a ckground noise levels, but are increasinglybased upon the measured quality of recordeddata. Quality acceptance levels for para m e-ters such as signal-to-noise ratio, sourc ep ow e r, frequency content and coherencebetween adjacent traces are set prior to a sur-vey after a detailed evaluation of their impacton the ultimate objectives of the surve y.

In the course of a surve y, some shots orlines may not meet quality specific a t i o n s ,requiring a reshoot of the offending lines. Orc o nve r s e l y, some lines that do not initiallyappear to meet specifications based on back-ground noise levels may, in fact, be adequateafter some processing, and not requirereshooting. The opera t o r, usually someone inan office, decides whether the data are fit forthe processing and interpretation that follow.For maximum acquisition effic i e n cy ande c o n o my, making the decision that a lineneed or need not be reshot requires up-to-date information, so shooting can be donebefore the acquisition crew leaves the site.

■Covering the target. The surface overlying the target is divided into bins. The number ofre flection points that project up into a bin is tallied and called the coverage; often the term“fold” is also used to denote coverage.

1. For a review of seismic survey planning: Ashton CP,Bacon B, Mann A, Moldoveanu N, Déplanté C,Ireson D, Sinclair T and Redekop G: “3D SeismicS u r vey Design,” O i l field Rev i ew 6, no. 2 (April 1994): 19-32.

Winter 1997 25

In addition, periodically, a cove rage map—a plot showing the geographic area of thes u r vey and the density of seismic energyrecorded at every “point” on the map—isanalyzed to verify that the subsurface targetis being covered sufficiently by seismic data(p revious page). The points are actually smallareas called bins. As the survey comes to aclose, if holes are detected in the cove ra g e ,i n fill shooting is required. Infill shooting,wh i ch entails redeploying sources andr e c e ivers to areas already traversed in thes u r ve y, can represent up to 30% of ove ra l ls u r vey cost.

In the past, the party ch i e f ’s log, nav i g a t i o nlog and daily production log were printed onpaper and sent or faxed to the oil company.Data quality control (QC) analyses and cov-e rage plots were also printed and sent by faxor surface mail if color plots were produced.Decisions would be made based on thepaper output, and relayed as soon as possi-ble back to the service company contra c t o r.U n f o r t u n a t e l y, delays often occurred, andseismic crews were kept waiting or had toreturn to the site later for costly reshooting.

Input to Pro c e s s i n gData acquisition is not the only stage of aseismic survey that requires timely inputfrom the opera t o r. Data processing—whether run after acquisition, or as is nowmore common, concurrently with acquisi-tion—can benefit from real-time clienti nvo l ve m e n t .

The two processing steps that most typi-cally receive client attention are deconvo l u-tion and velocity analysis. Deconvolution isa filtering technique that removes certaintypes of noise and produces seismic tra c e swith features that more accurately corre-spond to the reflectors encountered. As atest, various deconvolution filters are appliedto a small amount of the seismic data. The fil-ter that gives the best result is then applied toall the data. The choice is usually made visu-ally from a plotted series of deconvo l u t i o npanels. Expert knowledge about theexpected geology is important in ch o o s i n gd e c o nvolution para m e t e r s .

Velocity analysis is part of the stacking pro-cess. Stacking is the summing, for the pur-pose of enhancing the signal-to-noise ra t i o ,of seismic traces acquired by differents o u rc e - r e c e iver pairs. On these tra c e s ,e choes originating from the same locationon a reflector appear at different times. Th etime difference across traces is directlylinked to the velocity at wh i ch seismic wave st ravel through the subsurface. Most ve l o c i t y

analysis schemes rely on picking the maxi-mum in a ve l o c i t y - versus-time plot (a b ove) .S e ve ral velocities are tested on small por-tions of the data. The velocity that producesthe greatest coherence is selected.

A 3D seismic survey typically requiresvelocity analysis at seve ral thousand loca-tions, between wh i ch the selected ve l o c i t i e sare interpolated to enable optimum stack i n gover the whole survey area. Selection of thevelocity function that maximizes coherencecan be done automatically by computer, butquality control must be performed visuallyby a geophysicist who can recognize a phy s-ically realistic velocity function. Quite fre-

quently clients participate directly in ve l o c i t yquality control, or pick the velocity functionst h e m s e l ves. This practice can sometimeslead to scheduling delays in the project.

In a growing industry trend, more surve y sare being shot and processed concurrently,reducing ove rall cycle time of the projectand speeding access to an interpretableresult. This drives the need for even fasterdecision-making, wh i ch in turn requiresfaster access to real-time acquisition andprocessing information by oil companyo f fice personnel.

■Velocity analysisc o h e rence plot. Aspart of stacking, avelocity functionthat varies withdepth is applied toseismic traces. If thevelocity function isthe correct one, thetraces will line up,and exhibit coher-ence, or similarity,f rom one to thenext. A mathemati-cal expression forc o h e rence is plottedh e re in velocity(horizontal axis)versus two-waytravel time (verticalaxis). Blue signifie slow coherence, yel-low is interm e d i a t eand red is high. Thevelocity functionthat gives the beststack is plotted as ayellow step-like line.

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Monitoring from AfarThe SuperVision project monitoring servicefrom Geco-Prakla delivers acquisition andprocessing updates that allow oil companydecision-makers to participate in projects inreal time (above). This new initiative uses off-the-shelf Web-browser software and theexplorationist’s own PC or workstation to

access a project “home page.” The client canmonitor and comment on project progressfrom an office or portable PC, anywhere inthe world and at any time of day or night.2

Connection between client sites and theSuperVision system is through one of a smallnumber of servers from the TWS Trusted WebService offered by Omnes. The TWS server is

linked to the Schlumberger intranet througha security firewall (below). Actual transmis-sion of data can be through the Internet orthrough dedicated high-speed integrated ser-vices digital network (ISDN) lines. Projectmonitoring data destined for client view arecollated onboard or at the field location,transferred on a regular basis via satellite to amaster server, then sent to the TWS server.Through the appropriate authenticationmechanism, authorized personnel log intothe home page of that survey, and use com-mercially available Internet tools, such asNavigator or Internet Explorer to view andbrowse the Web site.

Network security is obviously ofparamount importance. The security technol-ogy that controls SuperVision access wasdesigned by Geco-Prakla to work in thesecurity-unfriendly environment of the pub-lic Internet. The goals of the security mea-sures are privacy, authentication androbustness. Privacy means there is no unau-thorized access to confidential informationover the public network. Authenticationmeans that steps are taken to ensure thatusers are who they say they are and thatinformation originates from the source itclaims. Robustness means that a server willnot fail by attack from someone with physi-cal or network access.

Secure Web serverHSEQQA dataPersonnelCoverage dataSurvey planningProduction logsVessel descriptionGeneral file transfersSeismic dataQC data

■■Real-time seismic acquisition and processing project monitoring with secure access. TheWeb-based SuperVision service encourages interactive exploration by providing up-to-dateinformation on project status while preventing unauthorized access.

Fire wall

■■Extending client connectivity with the SuperVision system. Seismic data from acquisition units (left) are transferred on internal Web serversto data-processing centers on the Schlumberger intranet. Data are then archived on a TWS Trusted Web Service server. To access data, oilcompanies (right) may use the Internet or direct ISDN lines, following strict authentication measures to access the TWS server.

Winter 1997 27

The TWS service relies on three tech n o l o-g i e s — fire wall, Netscape Enterprise serve rand secure socket layer—to ensure properlycontrolled connectiv i t y. The fire wall restrictsp hysical access and monitors tra f fic to detectunauthorized access attempts. It also restrictsthe electronic communication between twodifferent machines, or Internet protocol (IP)addresses, to a certain class of conve r s a t i o n s ,or port numbers. For example, machine Amight be allowed to access Web pages onm a chine B, but not be able to do a remotelogin. The Netscape Enterprise server man-ages access control. The secure socket laye rmanages certified access and relies on pub-lic key encryption, digital certificates andpersonal smart cards to assure security.3

Digital certification for access to the G e c o - P rakla TWS server is administered bytrusted third-party authorities called certifi-cate authorities.

The certificate authority currently certifyingaccess to the TWS server is Verisign, Inc. ofMountain Vi e w, California, USA. Verisign isthe leading provider of digital authenticationservices and products for electronic com-m e rce and other forms of secure communi-cations. Verisign installs a unique fin g e r p r i n t ,or digital certificate, on the hard disk of thecomputer that will be used to access thes e r ve r. The certificate is registered with theWeb site at the time the authorized clientuser is issued a password. Certified access tothe TWS server requires identification of thatuser with that password on that mach i n ewith that digital certificate. Unless each ofthese is authenticated, there is no access. Ifmultiple machines are to access the We bsite, each must have a certificate registeredwith the TWS serve r.

Once the authorized user has accessed the SuperVision home page, the gateway isopen to a wealth of information. A tour of the home page set up for the fictitious XYZOil Company reveals the types of infor-mation available on acquisition and pro-cessing projects.

The first stop is the party ch i e f ’s log, anexact replica of its paper- c o py ancestor. A l s oon record here in chronological order are allthe logs for each day of the survey (a b ove) .The recent log selected—highlighted in theleft column—chronicles details of the surve y.Annotations include the party ch i e f ’s name,

■Party chief’s log from an XYZ Oil Company survey. The SuperVision system allows up-to-the-minute checks onacquisition status as well as a complete archive of all survey activity.

2. B ragstad H, Kingston J and O’Neill DM: “SeismicE x p l o ration and the World Wide We b ,” presented atthe 59th EAGE Conference and Te chnical Exhibition,G e n e va, Switzerland, May 26-30, 1997, paper B035.

3. For more on public keys, encryption and security:A rango G, Colley N, Connelly C, Greenes K, Pearse K, Denis J, Highnam P, Durbec C, Gutman L,Sims D, Jardine S, Jervis T, Smith R and Miles R:“ W h a t ’s in IT for Us?” O i l field Rev i ew 9, no. 3( Autumn 1997): 2-19.

28 Oilfield Review

weather conditions, number of sourc e s ,streamers and channels, streamer length,total number of points shot, comments onstreamer modifications made during the sur-vey and notes on the day ’s events. In thiscase, the difficult weather conditions pre-cluded a rendezvous with a supply boat.

A second type of update, the cove rage plot,presents seve ral panels with informationabout how effectively the survey is cove r i n gthe subsurface target (a b ove). The mainscreen shows each traverse of the vessel as avertical swath. Black indicates full cove ra g e ,according to the specifications of the surve y,and lighter colors flag zones of lower cove r-age. An inset panel explains the color legendand describes the details of the groupings ofshots within each vertical swath of the plot.The white step-like areas at the bottom ofe a ch swath are zones left without cove ra g eat the beginning of each line. The white areasin the middle of a black area are holes in thec ove rage. Holes of this nature can be createdby obstacles in the survey area. In this exam-ple, the holes result from having to nav i g a t earound an offshore platform.

As a type of page, the cove rage plot is com-pletely different from the party ch i e f ’s logbecause users can interact with it. Cove ra g e ,or the number of shots hitting a bin, is com-puted and plotted for a streamer offset ra n g e .But the cove rage could also be plotted for adifferent offset range using the same data.From the SuperVision cove rage plot, a newoffset range can be selected, and a new plotg e n e rated. This intera c t ive feature sets theS u p e r Vision project monitoring service apartfrom any fax or hard-copy delivery method.

A third type of acquisition project monitor-ing page available on the SuperVision systemis the real-time quality control plot (n ex tp a g e , t o p). The graphs in this example tra cksignal quality recorded in the streamer beingt owed on the port side of the vessel, andindicate shot points for wh i ch para m e t e r sselected in the survey planning stage exceeda prescribed value. The culprit in this case isa noise level spike just before shotpointnumber 2600.

Unlike the party ch i e f ’s log and cove ra g eplot, wh i ch are generated at regular inter-vals, quality control plots are generated asexception reports, and appear only when ap a rameter threshold has been surpassed.With this information available in real time,clients can evaluate the impact of the noisyshots on the final outcome of the processeds u r ve y. For this surve y, such conditionsoccurred in isolated shots on two lines, asindicated in the left window.

Acquisition updates are also available forland seismic surveys with the SuperVi s i o nservice. In a fictitious example over the cityof Amsterdam, the survey acquisition geom-etry with locations of sources and receive r shas been plotted on a basemap of the localcountryside (n ext page, bottom left). Th i ss h ows the locations of obstacles and otherc o n s t raints on the acquisition. During acqui-sition, cove rage can be monitored. Fo rexample, an area dominated by a lakeexhibits some low - c ove rage spots becauses o u rce positions were limited. A d e q u a t ec ove rage is plotted in red and orange, wh i l el ower cove rage shows up as ye l l ow, greenand blue (n ext page, bottom right).

■Interactive coverage plot. On the main screen, each traverse of the vessel appears as a colored, verticalswath. Black indicates full coverage and lighter colors show lower coverage. White areas in the middle of a black area are gaps in coverage created by obstacles in the survey area. The inset panel describes in more detail the four vertical subdivisions of each swath. The leftmost division of any swath shows thecoverage for the near- o ffset traces, with offsets between 180 and 1630 m. The second division gives c o v e rage for the near-to-mid offsets, from 1630 to 3080 m. The mid-to-far offsets (3080 to 4530 m) follow, and the rightmost division shows coverage for the far offsets (4530 to 6100 m).

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■Planning a seismic survey over Amsterd a m .Taking into account natural and man-madeobstacles, a grid of source (red) and re c e i v e r(purple) positions has been laid over a mapof the city.

■The coverage expected for the Amsterdam survey in one are adominated by a lake. Coverage decreases from red and oranget h rough yellow to green and blue.

■Exceptions to therule. When surveynoise parametersexceed establishedt h resholds, a QQAQ u a n t i fied QualityAssurance exceptionreport is generated.In this case, thesignal qualityre c o rded in the ports t reamer shows anoise level spike(center panel) n e a rshotpoint 2600.

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S e ve ral steps in the data-processing ch a i ncan also be monitored. The processing statusreport gives an overview of the processingproject (b e l ow). This display plots the pro-cessing tasks in chronological order, the timei n t e r val allotted for completion and a snap-shot of processing status. This excerpt from anoutput for a TQ3D Total Quality 3D marines u r vey indicates that the early tasks, includ-ing priority-area processing concurrent withacquisition, prestack testing and data merg-ing, have been completed. Milestones, suchas completion of acquisition, delivery of nav-igation data, meetings and steps requiringclient input, are marked by diamonds. A typ-ical processing project will have 20 to 40tasks, many of wh i ch overlap. The final stepsin this project, not plotted here, includevelocity field QC and data migra t i o n .

The crucial phase of velocity analysis fors t a cking requires seve ral itera t ive steps ande x changes of data between service companyand opera t o r. The SuperVision system allow sthese exchanges to be performed in a fra c-tion of the time previously required for faxand courier delivery of paper outputs. Th e

S u p e r Vision page houses a record of ve l o c-ity-analysis panels, and updates the arch ivewith all communications and data analysespertaining to the velocities that will be usedfor stacking and migration (n ext page). Th emultipanel display is standard output fromthe Geco-Prakla SEISMOS data-processingsystem. The velocity-depth panel on the lefts h ows coherence maxima picked as blue,red and black squares. The center panel plotsthe seismic data with the current ve l o c i t yfield applied. The seven panels on the rights h ow the results of applying seven differentc o n s t a n t - velocity fields to the data.

The Vi s i o nS u p e r Vision project monitoring delive r shigher quality seismic results than previousmethods, and does so more effic i e n t l y. Th efast turnaround in communication promotesclient input at crucial stages, producing ani m p r oved seismic product. Effic i e n cy isgained because the Web site takes less effortto update and to read. The data are ava i l a b l ewhen needed, and there is a unique, sharedversion that can be accessed by teams wo r k-

ing in different locations. The digital projecta rch ive can be stored and managed with theseismic data themselves, from acquisitionthrough processing and interpretation.C e r t i fied access to multiple locations allow so p e rator experts and partners, as well as con-t ractor offices and field sites, to participate increating a high-quality seismic dataset.

Because information is updated rather thanreplaced, an information arch ive is built upover the duration of a surve y, allowing acomplete retrospective view of the job todate. An added benefit is that by the end of aproject, most of the final report already existsin a standard and accessible format.

The SuperVision service aims to delive rproject monitoring to customer desktops,usually a personal computer, and to prov i d ea ny display that would normally be seen ona workstation in the instrument room of aseismic vessel or land acquisition unit, or ina processing center. An immediate benefit isbetter leve rage of experienced personnel:monitoring a survey no longer requiresabsence from the office for two or threemonths. Supervising a project via the We b

■Tracking processing status. This report gives an overview of the processing project, including tasks in c h ronological ord e r, the time allotted for completion, and a look ahead at meetings and other milestones.

Winter 1997 31

eliminates days, weeks, and potentiallymonths of dead time, postage costs and riskof misdirected pack a g e s .

With the desktop goal and speedy access inmind, data available through the SuperVi s i o nsystem are limited by their size. Raw seismicdata and large 3D cubes occupying hun-

dreds of gigabytes are not suitable for deliv-ery to the oil company interpreter’s desktopPC. But through the SuperVision page, forexample, a request can be made for the datato be delivered through a different path to alarge machine down the hall, with the optionof using high-fidelity compression tech-niques to shorten transmission times.

The near-term goal is to have every seismicproject accessible to clients through theS u p e r Vision system. This would be the nextstep toward the longer-term vision of com-p r e h e n s ive management of oil and gasr e s o u rces from the office desktop. — L S

■F rom velocity analysis. The multipanel display is standard output f rom the Geco-Prakla SEISMOS data-pro c e s s i n gsystem. The velocity and travel time panel on the left, which appeared earlier on page 25 shows coherence maximapicked as blue, red and black squares. The center panel plots the seismic data with the current velocity field applied.The seven panels on the right show the results of applying seven diff e rent constant-velocity fields to the data.