44 Oilfield Review

Global Warming and the E&P Industry

Melvin CannellCentre for Ecology and HydrologyEdinburgh, Scotland

Jim FilasRosharon, Texas, USA

John HarriesImperial College of Science, Technology and MedicineLondon, England

Geoff JenkinsHadley Centre for Climate Prediction and ResearchBerkshire, England

Martin ParryUniversity of East AngliaNorwich, England

Paul RutterBPSunbury on Thames, England

Lars SonnelandStavanger, Norway

Jeremy WalkerHouston, Texas

For help in preparation of this article, thanks to DavidHarrison, Houston, Texas, USA; Dwight Peters, Sugar Land,Texas; and Thomas Wilson, Caracas, Venezuela. Specialthanks to the Hadley Centre for Climate Prediction andResearch for supplying graphics that were used as a basisfor some of the figures appearing in this article.

The question as to what extent man-made emissions of greenhouse gases may be

causing climate change has stirred intense debate around the world. Continued shifts

in the Earth’s temperatures, predicted by many scientists, could dramatically affect the

way we live and do business. This article examines the evidence and the arguments,

and describes some of the mitigating actions being taken by the exploration and pro-

duction (E&P) industry.

Scientists use language cautiously. They tend toerr on the side of understatement. During themid-1990s, in the Second Assessment Report ofthe Intergovernmental Panel on Climate Change(IPCC), leading scientists from around the worldexpressed a consensus view that “the balance ofevidence suggests a discernible human influenceon global climate.” In July 2001, for the IPCCThird Assessment Report, experts took this con-clusion a step further. Considering new evidence,and taking into account remaining uncertainties,the panel stated “most of the observed warmingover the last 50 years is likely to have been dueto the increase in greenhouse-gas concentra-tions.”1 The word ‘likely’ is defined by the IPCC asa 66 to 90% probability that the claim is true.

An important and influential segment of theglobal scientific community firmly believes thathuman activity has contributed to a rise in theEarth’s average surface temperature and a result-ing worldwide climate change. They contend thatsuch activity may be enhancing the so-called‘greenhouse effect.’ Other distinguished scien-tists disagree, some dismissing the IPCC view as simplistic.

The Greenhouse and EnhancedGreenhouse EffectsThe greenhouse effect is the name given to theinsulating mechanism by which the atmospherekeeps the Earth’s surface substantially warmerthan it would otherwise be. The effect can beillustrated by comparing the effects of solar radiation on the earth and the moon. Both areroughly equidistant from the sun, which suppliesthe radiation that warms them, and both receiveabout the same amount of heat energy persquare meter of their surfaces. Yet, the earth ismuch warmer—a global average temperature of15°C [59°F] compared with that of the moon, -18°C [-0.4°F]. The difference is largely due to thefact that the moon has almost no atmospherewhile the Earth’s dense atmosphere effectivelytraps heat that would otherwise escape into space.

Climatologists use a physical greenhouseanalogy to explain how warming occurs. Energyfrom the sun, transmitted as visible light, passesthrough the glass of a greenhouse without hin-drance, is first absorbed by the floor and con-tents, and then reemitted as infrared radiation.

1. Climate Change 2001: The Scientific Basis: TheContribution of Working Group I to the Third AssessmentReport of the Intergovernmental Panel on ClimateChange. New York, New York, USA: Cambridge UniversityPress (2000): 10.

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Because infrared radiation cannot pass throughthe glass as readily as sunlight, some of it istrapped, and the temperature inside the green-house rises, providing an artificially warm envi-ronment to stimulate plant growth (right).

In the natural greenhouse effect, the Earth’satmosphere behaves like panes of glass. Energycoming from the sun as visible short-wavelengthradiation passes through the atmosphere, just asit does through greenhouse glass, and isabsorbed by the surface of the earth, which thenreemits it as long-wavelength infrared radiation.Infrared radiation is absorbed by naturally occur-ring gases in the atmosphere—water vapor, carbon dioxide [CO2], methane, nitrous oxide,ozone and others—and reradiated. While someenergy goes into outer space, most is reradiatedback to earth, heating its surface.2

An enhanced greenhouse effect occurs whenhuman activities increase the levels of certainnaturally occurring gases. If the atmosphere ispictured as a translucent blanket that insulatesthe earth, adding to the concentration of thesegreenhouse gases is analogous to increasing thethickness of the blanket, improving its insulatingqualities (below).

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Visible energy from the sun passes through the glass, heating the ground.

Some reemitted infrared radiation is reflected by the

glass and trapped inside.

> The greenhouse analogy. A greenhouse effectively traps a portion of thesun’s energy impinging on it, raising the interior temperature and creating anartificially warm growing environment.

Absorption of outgoingradiation by indigenousatmospheric gases

Incomingshort-wavelength

radiation

Natural Greenhouse Effect Enhanced Greenhouse Effect

Reradiationinto space

Reradiationto earth

Outgoinglong-wavelength

radiation

Enhancedabsorption bygreenhouse gases

Reradiationinto space

Incomingshort-wavelength

radiation

Reradiationto earth

Outgoinglong-wavelength

radiation

> Natural and enhanced greenhouse effects. In the natural greenhouse effect (left), indigenous atmospheric gases contribute to heating of the Earth’s surface by absorbing and reradiating back some of the infrared energy coming from the surface. In the enhanced greenhouse effect (right), increased gasconcentrations, resulting from human activity, improve the atmosphere’s insulating qualities.

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Autumn 2001 47

Man-made emissions of greenhouse gasesoccur in a number of ways. For example, carbondioxide is released to the atmosphere when solidwaste, wood and fossil fuels—oil, natural gasand coal—are burned. Methane is emitted by decomposing organic wastes in landfill sites, during production and transportation of fossilfuels, by agricultural activity and by dissoci-ation of gas hydrates. Nitrous oxide is ventedduring the combustion of solid wastes and fossil fuels (above left).

Carbon dioxide is the most important, dueprincipally to the fact that it has an effective life-time in the atmosphere of about 100 years, and isthe most abundant. Every year, more than 20 bil-lion tons are emitted when fossil fuels areburned in commercial, residential, transportationand power-station applications. Another 5.5 bil-lion tons are released during land-use changes,such as deforestation.3 The concentration of CO2

in the atmosphere has increased by more than30% since the start of the Industrial Revolution.

Analysis of air trapped in antarctic ice capsshows that the level of carbon dioxide in theatmosphere in pre-industrial days was about 270parts per million (ppm). Today, readings taken atthe Mauna Loa Observatory in Hawaii, USA,place the concentration at about 370 ppm.4

Concentrations of methane and nitrous oxide,which have effective lifetimes of 10 and150 years, respectively, also have increased—methane more than doubling and nitrous oxiderising by about 15% over the same time span.Both are at much lower levels than CO2—methane at 1.72 ppm and nitrous oxide at0.3 ppm—but they exert a significant influencebecause of their effectiveness in trapping heat.Methane is 21 times more effective in this regardthan CO2, while nitrous oxide is 310 times moreeffective, molecule for molecule.5

The global-warming potential of a gas is ameasure of its capacity to cause global warmingover the next 100 years. The warming effect ofan additional 1-kg [2.2-lbm] emission of a green-house gas discharged today—relative to 1 kg of

CO2—will depend on its effective lifetime, theamount of extra infrared radiation it will absorb,and its density. On this basis, experts calculatethat, during this century, CO2 will be responsiblefor about two-thirds of predicted future warming,methane a quarter and nitrous oxide around atenth (above right).6

2. The description above is a simplification. In fact, about25% of solar radiation is reflected back into space beforereaching the Earth’s surface by clouds, molecules andparticles, and another 5% is reflected back by the Earth’ssurface. A further 20% is absorbed before it reaches theearth by water vapor, dust and clouds. It is the remain-der—just over half of the incoming solar radiation—thatis absorbed by the Earth’s surface. The greenhouse anal-ogy, although widely used, is also only partly accurate.Greenhouses work mainly by preventing the natural pro-cess of convection.

3. Jenkins G, Mitchell JFB and Folland CK: “The GreenhouseEffect and Climate Change: A Review,” The Royal Society(1999): 9-10.

4. Reference 1: 12.5. “The Greenhouse Effect and Climate Change: A Briefing

from the Hadley Centre,” Berkshire, England: HadleyCentre for Climate Prediction and Research (October1999): 7.

6. Reference 5: 7.

Methane 24%

Nitrous oxide 10%

Others 3%

Carbon dioxide 63%

> Relative warming projected from differentgreenhouse gases during this century. Of the various greenhouse gases, carbon dioxide is pre-dicted to have the greatest capacity for causingadditional global warming, followed by methaneand nitrous oxide.

Carbon dioxide

Methane

Nitrous oxide

Chlorofluorocarbons

Ground-level ozone

Aerosols

Combustion of fossil fuels and woods Land-use changes

Production and transport of fossil fuelsDecomposing wasteAgricultureDissociation of gas hydrates

Combustion of fossil fuelsCombustion of waste

Production

TransportIndustrial emissions

Power generationTransport

100 years

10 years

150 years

100 years

3 months

2 weeks

Atmospheric constituent Source Lifetime

> Man-made emission sources and lifetimes forgreenhouse gases. Various gases and aerosolsare emitted daily in commercial, industrial andresidential activities. Carbon dioxide is the mostimportant, because of its abundance and effec-tive lifetime in the atmosphere of about 100 years.

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Measuring and Modeling Climate ChangeIPCC scientists believe that we are already expe-riencing an enhanced greenhouse effect.According to their findings, the Earth’s globalaverage surface temperature increased by about0.6°C [1.1°F] during the last century. They main-tain that this increase is greater than can beexplained by natural climatic variations. Thepanel believes there is only a 1 to 10% probabil-ity that inherent variability alone accounts for thisextent of warming. Most studies suggest that,over the past 50 years, the estimated rate andmagnitude of warming due to increasing concen-trations of greenhouse gases alone are compara-ble to, or larger than, the observed warming.7

To better understand the physical, chemicaland biological processes involved, scientistsinvestigating climate variations construct complexmathematical models of the Earth’s weather sys-tem. These models are then used to simulate pastchanges and predict future variations. The moreclosely that simulations match historical climaterecords built from direct observations, the moreconfident scientists become in their predictivecapabilities (left).

Greater emphasis on diagnosing and predict-ing the impact of global warming has resulted inincreasingly sophisticated simulations. For exam-ple, a state-of-the-art, three-dimensional (3D)ocean-atmosphere model developed at theHadley Centre for Climate Prediction andResearch in Berkshire, England, appears to repli-cate—with reasonable precision—the evolutionof global climate during the late 19th and 20thcenturies. This simulation matches records thatclearly show that the global mean surface airtemperature has increased by 0.6°C ± 0.2°C[1.1°F ± 0.4°F] since 1860, but that the progres-sion has not been steady. Most of the warmingoccurred in two distinct periods—from 1910 to1945, and since 1976—with little change in theintervening three decades.

When factors that impact the Earth’s climatevary—concentrations of greenhouse gases, butalso heat output from the sun, for example—they exert a ‘forcing’ on climate (see “Increasesin Greenhouse Forcing,” next page). A positiveforcing causes warming, a negative one resultsin cooling. When researchers at the HadleyCentre and the Rutherford Appleton Laboratory,near Oxford, England, simulated the evolution of 20th century climate, they concluded that, by themselves, natural forcings—changes in volcanic aerosols, solar output and other phenomena—could not account for warming

48 Oilfield Review

Update and refine model

Comparison and

validation

Climate-system model

Computersimulation

Predictedbehavior

Observedbehavior

> Climate simulations. Scientists use sophisticated models and computer sim-ulations of the Earth’s climate system to confirm historical, and predict future,temperature changes. Results are validated by comparison with actual tem-perature measurements. Such analyses form a basis for updating and refiningthe reliability of simulations.

1.0ModelObservations

0.5

0.0

–0.5

–1.01850 1900

Tem

pera

ture

ano

mal

ies,

C

Tem

pera

ture

ano

mal

ies,

C

Natural factors only

1950 2000

1.0ModelObservations

ModelObservations

0.5

0.0

–0.5

–1.01850 1900

Human factors only

1950 2000

1.0

0.5

0.0

–0.5

–1.01850 1900

Human and natural factors

1950 2000

> Observed and simulated global warming. Neither natural nor man-made effects alone account forthe evolution of the Earth’s climate during the 20th century. By combining the two, however, theobserved pattern is reproduced with reasonable accuracy.

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Autumn 2001

in recent decades. They also concluded thatanthropogenic, or man-made, forcings alonewere insufficient to explain the warming from1910 to 1945, but were necessary to reproducethe warming since 1976. However, by combiningthe two simulations, researchers were able toreproduce the pattern of temperature changewith reasonable accuracy. Agreement betweenobserved and simulated temperature variationssupports the contention that 20th century warm-ing resulted from a combination of natural andexternal factors (previous page, bottom).8

In addition to examining the global mean tem-perature, researchers at the Hadley Centre also

compared geographic patterns of temperaturechange across the surface of the earth. Theyused models to simulate climate variationsdriven by changes in greenhouse-gas concentra-tions and compared the ‘fingerprint’ producedwith patterns of change that emerge from obser-vation. Striking similarities are evident betweenthe fingerprint generated by a simulation of thelast 100 years of temperature changes and thepatterns actually observed over that period (above).

Despite many advances, climate modelingremains an inexact science. There is concernthat, at present, simulations may not adequatelyrepresent certain feedback mechanisms, espe-cially those involving clouds. Researchers, like

those at Hadley, do not claim that close agree-ment between observed and simulated tempera-ture changes implies a perfect climatic model,but if today’s sophisticated simulations of climate-change patterns continue to closelymatch observations, scientists will rely to agreater extent on their predictive capabilities.

7. Reference 1: 10.8. Stott PA, Tett SFB, Jones GS, Allen MR, Mitchell JFB

and Jenkins GJ: “External Control of 20th CenturyTemperature by Natural and Anthropogenic Forcings,”Science 290, no. 5499 (December 15, 2000): 2133-2137.

90˚ N

45˚ N

90˚ S

45˚ S

90˚ NSimulated

Observed

45˚ N

90˚ S

45˚ S

90˚ W 0˚ 90˚ E 180˚ E

–0.5 0.5 1 1.5 20–1

90˚ W 0˚ 90˚ E 180˚ E

180˚ W

180˚ W

–0.5 0.5 1 1.5 20–1

> Observed (top) and simulated (bottom) surface air temperature changes.Computer models closely resemble the global temperature signature pro-duced by measurements of the change in air temperature. Values increasefrom negative to positive as the color scale moves from blue to red.

Increases in Greenhouse Forcing

Early this year, scientists at the ImperialCollege of Science, Technology and Medicine inLondon, England, provided the first experimen-tal observation of a change in the greenhouseeffect. Previous studies had been largely limitedto theoretical simulations.1 Changes in theEarth’s greenhouse effect can be detected fromvariations in the spectrum of outgoing long-wavelength radiation, a measure of how theearth gives off heat into space that also carriesan imprint of the gases responsible for thegreenhouse effect.

From October 1996 until July 1997, an instru-ment on board the Japanese ADEOS satellitemeasured the spectra of long-wavelength radia-tion leaving the earth. The Imperial Collegegroup compared the ADEOS data with dataobtained 27 years earlier by a similar instru-ment aboard the National Aeronautics andSpace Administration (NASA) Nimbus 4meteorological satellite. The comparison of thetwo sets of clear-sky infrared spectra provideddirect evidence of a significant increase in theatmospheric levels of methane, carbon dioxide,ozone and chlorofluorocarbons since 1970.Simulations show that these increases areresponsible for the observed spectra.

1. Harries JE, Brindley HE, Sagoo PJ and Bantges RJ:“Increases in Greenhouse Forcing Inferred from theOutgoing Longwave Radiation Spectra of the Earth in1970 and 1997,” Nature 410, no. 6832 (March 15, 2001):355-357.

49

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The Opposing View Not all scientists accept the IPCC findings. Many distinguished researchers argue that thepanel’s approach is too simplistic. For instance,Dr Richard Lindzen, Alfred P. Sloan Professor ofMeteorology at the Massachusetts Institute ofTechnology (MIT) in Cambridge, USA, suggeststhat clouds over the tropics act as an effectivethermostat and that any future warming becauseof increased carbon dioxide concentration in theatmosphere could be significantly less than cur-rent models predict.

Scientists have voiced strong objections thateven sophisticated circulation models do notadequately describe the complexity of the mech-anisms at work. A group of researchers at theHarvard-Smithsonian Center for Astrophysics inCambridge, Massachusetts, for example, claimsthere are too many unknowns and uncertaintiesin climate modeling to have confidence in theaccuracy of today’s predictions. The group arguesthat even if society had complete control over how much CO2 was introduced into the atmosphere, other variables within the climatesystem are not sufficiently well-defined to pro-duce reliable forecasts. The researchers are nottrying to disprove a significant man-made contri-bution, but rather contend that scientists do notknow enough about the complexity of climatesystems, and should be careful in ascribing toomuch relevance to existing models.9

New scientific studies are shedding morelight on the problem. For example, previousinvestigations have concluded that the Earth’sclimate balance is upset not only by emissions ofman-made greenhouse gases during processessuch as the combustion of fossil fuels, but alsoby small particles called aerosols, such as thoseformed from sulfur dioxide, which cool the Earth’ssurface by bouncing sunlight back into space.But, new findings suggest that things may not bethat simple. A researcher at Stanford University,California, USA, states that black carbon, or soot,emissions from the burning of biomass and fossilfuels are interfering with the reflectivity ofaerosols, darkening their color so that theyabsorb more radiation. This reduces the coolingeffect, and could mean that black carbon is amajor cause of global warming, along with car-bon dioxide and other greenhouse gases.

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9. Soon W, Baliunas S, Idso SB, Kondratyev KY andPostmentier ES: “Modelling Climatic Effects ofAnthropogenic Carbon Dioxide Emissions: Unknowns and Uncertainties.” A Center for Astrophysics preprint.Cambridge, Massachusetts, USA: Harvard-SmithsonianCenter for Astrophysics (January 10, 2001): to appear asa review paper in Climate Research.

10. Jacobson M: “Strong Radiative Heating due to theMixing State of Black Carbon in Atmospheric Aerosol,”Nature 409, no. 6821 (2001): 695-697.

11. Reference 1: 2-4.12. Reference 1: 12-13.13. Climate Change 2001: Impacts, Adaptation and

Vulnerability: Contribution of Working Group II to theThird Assessment Report of the IntergovernmentalPanel on Climate Change. New York, New York, USA:Cambridge University Press (2001): 5.

Atmospheric computer simulations usuallyassume that aerosols and soot particles are sep-arate, or externally mixed. An internally mixedstate—in which aerosols and soot coalesce—also exists, but no one has yet successfully deter-mined the relative proportions of the two states.The Stanford researcher ran a simulation inwhich black carbon was substantially coalescedwith aerosols. His results were more consistentwith observations than simulations that assumedmainly external mixing. Although this could meanthat black carbon is a significant contributor towarming, there is a bright side to the discovery.Unlike the extended lifetime of carbon dioxide,black carbon disappears much more rapidly. Ifsuch emissions were stopped, the atmospherewould be clear of black carbon in only a matter ofweeks (left).10

Radiation into space

Radiation into space

Radiation from Earth's

surface

Radiation from Earth's

surface

Coalesced state

Soot

Aerosol

Coalesced sootand aerosolconstituents

(internal mixing)

Separate sootand aerosolconstituents

(external mixing)

> Impact of aerosols and soot. Temperature simulations that take into account an internallymixed, or coalesced, accumulation of aerosolsand soot (right) are more consistent with obser-vations than separate, or externally mixed, accumulations (left).

Global-averagesurface temperature

change(1900 to 2000)

Results:

10% decrease in snow cover(since the late 1960s)

2-week shorter annual ice cover

0.1- to 0.2-m sea-level rise

0.5 to 1% increase in precipitation per decade (Northern Hemisphere)

+0.6 C

> Observed impact of global warming. The 0.6°C temperature rise observed during the last100 years has been postulated as the cause ofdecreased snow and ice cover, higher sea levelsand increased precipitation.

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Autumn 2001 51

Predicting the Future Impact of Global WarmingThe IPCC has described the current state of sci-entific understanding of the global climate sys-tem, and has suggested how this system mayevolve in the future. As discussed, the panel con-firmed that the global-average surface tempera-ture of the earth increased by about 0.6°C duringthe last 100 years. Analyses of proxy data fromthe Northern Hemisphere indicate that it is likelythe increase was the largest of any century in thepast millennium. Because of limited data, less isknown about annual averages prior to the year1000, and for conditions prevailing in most of theSouthern Hemisphere prior to 1861.

The IPCC report states that temperatureshave risen during the past four decades in thelowest 8 km [5 miles] of the atmosphere; snowcover has decreased by 10% since the late1960s; the annual period during which rivers andlakes are covered by ice is nearly two weeks

shorter than at the start of the century; and aver-age sea levels rose by 0.1 to 0.2 m [0.3 to 0.7 ft]during the 1900s. The report further states that,during the last century, precipitation increased by0.5 to 1% per decade over most middle and highlatitudes of Northern Hemisphere continents,and by 0.2 to 0.3% per decade over tropical landareas (previous page, bottom).11

While these changes may appear to be mod-est, predicted changes for this century are muchlarger. Simulations of future atmospheric levels ofgreenhouse gases and aerosols suggest that theconcentration of CO2 could rise to between 540and 970 ppm. For all scenarios considered by theIPCC, both global-average temperature and sealevel will rise by the year 2100—temperature by1.4°C to 5.8°C [2.5°F to 10.4°F] and sea level by0.09 to 0.9 m [0.3 to 2.7 ft]. The predicted tem-perature rise is significantly greater than the 1°Cto 3.5°C [1.8°F to 6.3°F] estimated by the IPCCfive years ago. Precipitation is also forecasted toincrease. Northern Hemisphere snow cover is

expected to decrease further, and both glaciersand ice caps are expected to continue to retreat.12

If climate changes occur as predicted, seriousconsequences could result, both with respect tonatural phenomena, such as hurricane frequencyand severity, and to human-support systems. TheIPCC Working Group II, which assessed impacts,adaptation and vulnerability, stated that if theworld continues to warm, we could expect watershortages in heavily populated areas, particularlyin subtropical regions; a widespread increase inthe risk of flooding as a result of heavier rainfalland rising sea levels; greater threats to healthfrom insect-borne diseases, such as malaria, andwater-borne diseases, such as cholera; anddecreased food supply as grain yields dropbecause of heat stress. Even minimal increases intemperature could cause problems in tropicallocations where some crops are already near theirmaximum temperature tolerance (above).13

Water shortages

Decreased food supply

Greater exposure to disease

Increase in frequency and intensity

of severe weather

Increased flooding

> Future impact of global warming. IPCC scientists predict a number of consequences if climate changestrack the latest simulations, ranging from water shortages to flooding and decreased food supply.

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Sea-level rises could threaten five parts ofAfrica that have large coastal population cen-ters—the Gulf of Guinea, Senegal, Gambia,Egypt and the southeastern African coast. Even asomewhat conservative scenario of a 40-cm[15.8-in.] sea-level rise by the 2080s would add75 to 200 million people to the number currentlyat risk of being flooded by coastal storm surges,with associated tens of billions of dollars in prop-erty loss per country.14

Africa, Latin America and the developingcountries of Asia may have a two-fold problem,being both more susceptible to the adverseeffects of climate change and lacking the infras-tructure to adjust to the potential social and economic impacts.

The IPCC Working Group II has ‘high confi-dence’ that:• Increases in droughts, floods and other

extreme events in Africa would add to stresseson water resources, food-supply security,human health and infrastructures, and con-strain further development.

• Sea-level rise and an increase in the intensityof tropical cyclones in temperate and tropicalAsia would displace tens of millions of peoplein low-lying coastal areas, while increasedrainfall intensity would heighten flood risks.

• Floods and droughts would become more frequent in Latin America, and flooding would increase sediment loads and degradewater quality.

The Working Group has ‘medium confidence’that:• Reductions in average annual rainfall, runoff

and soil moisture would increase the creationof deserts in Africa, especially in southern,northern and western Africa.

• Decreases in agricultural productivity andaquaculture due to thermal and water stress,sea-level rise, floods, droughts and tropicalcyclones would diminish the stability of foodsupplies in many countries in the arid, tropicaland temperate parts of Asia.

• Exposure to diseases such as malaria, dengue fever and cholera would increase inLatin America.15

Not all impacts would be negative, however.Among projected beneficial effects are highercrop yields in some mid-latitude regions; anincrease in global timber supply; increased wateravailability for people in some regions, like partsof Southeast Asia, which currently experiencewater shortages; and lower winter death rates inmid- to high-latitude countries.16

Other studies—such as the US GlobalResearch Program’s report “Climate ChangeImpacts on the United States,” and the EuropeanCommunity-funded ACACIA (A Consortium forthe Application of Climate Impact Assessments)Project report—are consistent with future IPCCforecasts, and provide a more detailed picture forparticular regions.

According to the US study, assuming there areno major interventions to reduce continued growthof world greenhouse-gas emissions, temperaturesin the USA can be expected to rise by about 3°C to5°C [5.4°F to 9°F] over the next 100 years, com-pared with the worldwide range of 1.4°C to 5.8°C[2.5°F to 10.4°F] suggested by the IPCC.17

Assuming there are no major interventions,other predictions include the following:• Rising sea levels could put coastal areas at

greater risk of storm surges, particularly in thesoutheast USA.

• Large increases in the heat index, the combi-nation of temperature and humidity, and in thefrequency of heat waves could occur, particu-larly in major metropolitan cities.

• Continued thawing of permafrost and meltingof sea ice in Alaska could further damageforests, buildings, roads and coastlines.

In Europe, negative climate changes areexpected to impact the south more than thenorth. Sectors such as agriculture and forestry

will be affected to a greater extent than sectorssuch as manufacturing and retailing, andmarginal and poorer regions will suffer moreadverse effects than wealthy ones.

The ACACIA report, which provided the basisfor the IPCC findings on impacts in Europe, makesthe following predictions for southern Europe: • Longer, hotter summers will double in fre-

quency by 2020, with a five-fold increase insouthern Spain, increasing the demand for air conditioning.

• Available water volumes will decrease by 25%,reducing agricultural potential. Careful plan-ning will be essential to satisfy future urbanwater needs.

• Desertification and forest fires will increase.• Deteriorating air quality in cities and excessive

temperatures at beaches could reduce recre-ational use and associated tourist income.

Predictions for northern Europe include thefollowing:• Cold winters will be half as frequent by 2020.• Northern tundra will retreat and there could be

a loss of up to 90% of alpine glaciers by theend of the century.

• Conversely, climate changes could increaseagricultural and forest productivity and wateravailability, although the risk of flooding couldincrease (above).18

52 Oilfield Review

Rising sea levelsHigher heat index

Droughts Floods Decreased food supply Expanding deserts Sea-level rise

Hotter summers Reduced water supply Increase in forest fires Deteriorating air quality

Floods Increased rainfall Intense cyclones Decreased food supply

Floods Droughts Degraded water quality

Retreating glaciers Thawing of permafrost Melting of sea ice

> Impact of global warming by region. All continents will be affected significantly if global warmingcontinues. The type and severity of specific impacts will vary, as will each continent’s or country’scapacity to use infrastructure and technology to cope with change.

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Autumn 2001 53

The Sociopolitical Debate and Its Impacton Process and TechnologyOn balance, the potential dangers and adverseeffects of global warming far outweigh any pos-sible benefits. Both legislative and technicaloptions are being explored to mitigate theimpacts of future climate change.

With its 100-year effective lifetime, CO2 con-centration in the atmosphere is slow to respondto any cut in emissions. If nothing is done toreduce emissions, the concentration would morethan double over the next century. If emissionsare lowered to 1990 levels, the concentrationwould still rise, probably to more than 500 ppm.Even if emissions were slashed to half that leveland held there for 100 years, there would still bea slow rise in concentration. Best estimates sug-gest it would take a reduction of 60 to 70% of the1990 emission levels to stabilize the concentra-tion of CO2 at the 1990 levels.19

Against this backdrop, there have been polit-ical attempts to grapple with the problem fornearly a decade. These have achieved, at best,modest results. Although an in-depth discussionof global-warming politics is beyond the scope ofthis technically focused article, conferences heldto date and their resulting protocols illustrate thechallenges that will be faced by new-generationoilfield processes and technologies, and by busi-ness and industry in general (above).

The political movement toward global con-sensus began in 1992 at the United NationsConference on Environment and Developmentheld in Rio de Janeiro, Brazil. This conferenceresulted in the United Nations FrameworkConvention on Climate Change (UNFCCC), astatement of intent on the control of greenhouse-gas emissions, signed by an overwhelmingmajority of world leaders. Article II of the con-vention, which came into force in 1994, said thesignatories had agreed to “achieve stabilizationof greenhouse-gas concentrations in the atmo-sphere at a level that would prevent dangerousanthropogenic interference with the climate sys-tem…within a time frame sufficient to allowecosystems to adapt naturally to climate change,to ensure that food production is not threatened,and to enable economic development to proceedin a sustainable manner.” The developed nationstaking part also committed themselves to reducetheir emissions of greenhouse gases in the year2000 to 1990 levels.

A more ambitious target was set in 1997 inthe Kyoto Protocol, an agreement designed to

commit the world’s 38 richest nations to reducetheir greenhouse-gas emissions by an average ofat least 5% below 1990 levels in the period from2008 to 2012.20 The Kyoto Protocol put most ofthe burden on developed countries, which, as agroup, had been responsible for the majority of greenhouse gases in the atmosphere. Itexcluded more than 130 developing countries,even though many poorer nations were adding tothe problem in their rush to catch up with thedeveloped world. European Union (EU) countriesagreed to a reduction of 8%, and the USApromised a 7% cutback, based on 1990 levels. Totake effect, it was agreed that the Protocol mustbe ratified by at least 55 countries, includingthose responsible for at least 55% of 1990 CO2

emissions from developed countries.The targets set in Kyoto are more rigorous

than they might first appear since many devel-oped economies have, until very recently, beengrowing rapidly and are emitting greater volumesof greenhouse gases. In 1998, for example, theUS Department of Energy forecasted that USemissions in the year 2010 would exceed theKyoto target by 43%.

The November 2000 talks in The Hague onimplementing the Kyoto Protocol collapsed whenthe EU rejected a request that the estimated310 million tons of CO2 soaked up by forests inthe USA be set against its 7% commitment. TheEU suggested instead that the USA be allocateda 7.5-million ton offset.

In July 2001, 180 members of the UNFCCCfinally reached broad agreement on an opera-tional rulebook for the Kyoto Protocol at a meet-ing in Bonn, Germany. The USA rejected theagreement. If the Protocol is to go forward, thenext step would be for developed-country

governments to ratify it so that measures couldbe brought into force as soon as possible, possi-bly by 2002.

One issue resolved at the Bonn meeting washow much credit developed countries couldreceive towards their Kyoto targets through theuse of ‘sinks’ that absorb carbon from the atmo-sphere. There was agreement that activities thatcould be included under this heading includedrevegetation and management of forests, crop-lands and grazing lands. Individual country quotaswere set so that, in practice, sinks will accountonly for a fraction of the emission reductions thatcan be counted towards the target levels.Similarly, storage options exist for carbon dioxidethat offer attractive alternatives to sinks undercertain conditions (see “Mitigating the Impact ofCarbon Dioxide: Sinks and Storage,” page 54).The conference also adopted rules governing theso-called Clean Development Mechanism (CDM)through which developed countries can invest inclimate-friendly projects in developing countriesand receive credit for emissions thereby avoided.

Conference

_____

Outcome

1992

Rio de Janeiro,Brazil

_________

Statement of intent on controlof greenhouse

gases

1997

Kyoto,Japan

_________

Protocol onreduction levels

for specific commitment

period

2000

The Hague,The Netherlands

_________

Collapse ofimplementationplan for Kyoto

Protocol

2001

Bonn,Germany

_________

Broad agreement on rulebook

for implementing Kyoto protocol(except USA)

> Major international global warming conferences. A concerted effort ataddressing the sociopolitical implications of global warming in a forum ofnations began in 1992 in Rio de Janeiro, Brazil. The most recent conference,held in July 2001 in Bonn, Germany, was the latest attempt to reach sometype of formalized agreement on reducing greenhouse-gas emissions.

14. Reference 13: 13-14.15. Reference 13: 14-15.16. Reference 13: 6.17. Climate Change Impacts on the United States, The

Potential Consequences of Climate Variability andChange: Foundation Report, US Global Change ResearchProgram Staff. New York, New York, USA: CambridgeUniversity Press (2001): 6-10.

18. Parry ML (ed): Assessment of Potential Effects andAdaptations for Climate Change in Europe. Norwich,England: Jackson Environment Institute, University ofEast Anglia, 2000.

19. Jenkins et al, reference 3: 10.20. Kyoto Protocol, Article 31, available at Web site:

http://www.unfccc.de/resource/docs/convkp/kpeng.html

(continued on page 56)

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54 Oilfield Review

In the short to medium term, the world will continue to depend upon fossil fuels as cheapenergy sources, so there is growing interest inmethods to control carbon dioxide emissions—for example, the creation of carbon sinks andstorage in natural reservoirs underground or inthe oceans.1

Carbon sinks—Carbon sinks are newlyplanted forests where trees take CO2 from theatmosphere as they grow and store it in theirbranches, trunks and roots. If too much CO2 isbeing pumped into the atmosphere by burningfossil fuels, discharge levels can be compen-sated for, to some extent, by planting new treesthat soak up and store CO2.

In 1995, the IPCC estimated that some345 million hectares [852 million acres] of newforests could be planted between 1995 and 2050that would sequester nearly 38 gigatons of car-bon. These actions would offset about 7.5% offossil-fuel emissions. The IPCC added that othermeasures, like slowing tropical deforestation,could sequester another 20 to 50 gigatons.Taken together, new forests, agroforestry, regen-eration and slower deforestation might offset 12to 15% of fossil-fuel emissions by the year 2050.An attractive feature of this approach is that, ifimplemented globally, it buys time during whichlonger term solutions can be sought to meetworld energy needs without endangering the climate system.

There are, however, other factors that mustbe considered, such as how to quantify theamount of carbon being sequestered, how toverify sequestration claims and how to deal with‘leakage.’ Leakage occurs when actions toincrease carbon storage in one place promoteactivities elsewhere that cause either adecrease in carbon storage (negative leak) or an increase in carbon storage (positive leak).Preserving a forest for carbon storage may, forinstance, produce deforestation elsewhere (neg-ative leakage) or stimulate tree planting else-where to provide timber (positive leakage). Thecarbon-sink process is reversible. At somefuture date, some forests could become unsus-tainable, leading to a rise in CO2 levels.

Carbon storage—Carbon dioxide is producedas a by-product in many industrial processes,

usually in combination with other gases. If theCO2 can be separated from the other gases—atpresent, an expensive process—it can be storedrather than released to the atmosphere. Storagecould be provided in the oceans, deep salineaquifers, depleted oil and gas reservoirs, or onland as a solid. Oceans probably have the great-est potential storage capacity. While there are no real engineering obstacles to overcome, the environmental implications are not ade-quately understood.

For years, carbon dioxide has been injectedinto operating oil fields to enhance recovery,and normally remains in the formation. The useof depleted oil or gas reservoirs for CO2 storage,however, has a further advantage in that thegeology is well-known, so disposal takes place inareas where formation seals can contain the gas.

The first commercial-scale storage of CO2 inan aquifer began in 1996 in the Sleipner naturalgas field belonging to the Norwegian oil com-pany Statoil. The project is named SACS (SalineAquifer CO2 Storage) and is sponsored by theEU research program Thermie. A million tons, a year of CO2 production, are removed from thenatural gas stream using a solvent-absorptionprocess and then reinjected into the Utsirareservoir, 900 m [2950 ft] below the floor of the North Sea (above). According to a report bythe Norwegian Ministry of Petroleum andEnergy, the Utsira formation is widespread and about 200 m [660 ft] thick, so it can theo-retically accommodate 800 billion tons of CO2—equivalent to the emissions from allnorthern European power stations and majorindustrial establishments for centuries to come(next page, bottom).

Mitigating the Impact of Carbon Dioxide: Sinks and Storage

NORWAY

DENMARK

GERMANY

UNITED KINGDOM

NORTH SEA

Stavanger

Statfjord

Gullfaks

Frigg

Heimdal

Ula

Ekofisk

Sleipner

Sleipner West

Sleipner East

> Sleipner field location.

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Autumn 2001 55

To monitor the CO2-injection area,Schlumberger is conducting four-dimensional(4D), or time-lapse, seismic studies that com-pare seismic surveys performed before and dur-ing injection. A survey acquired in 1994, twoyears before injection began, served as the base-line for comparison with a 1999 survey acquiredafter about 2 million tons of CO2 had beeninjected. Higher seismic amplitudes in the 1999survey show the location where gas has dis-placed brine in the Utsira formation. Another4D survey is scheduled for late 2001 (right).

The Sleipner CO2 sequestration projectalready has inspired other oil and gas compa-nies to consider or plan similar efforts in south-east Asia, Australia and Alaska.

1. Cannell M: Outlook on Agriculture 28, no. 3: 171-177.

Depth, m

Sleipner T Sleipner A

CO2 injection well

Utsira formation

Heimdal formation

CO2

0

500

1000

1500

2000

2500

0

0 1640 3280 4920 ft

500 1000 1500 m

Sleipner East productionand injection wells

> Carbon dioxide injection well in Utsira. The Utsira formation is about 200 m [660 ft] thick and can hold the equivalent of all carbon dioxide emissionsfrom all northern European power stations and industrial facilities for centuries to come.

1994 1999

Sleipner CO2 injection siesmic monitoring E-W section preliminary raw stack

after injecting 2 millIon tons of CO2 since 1996no change above this level

Velocity push-down beneath CO2 cloud

–250 m

Injection point

Top Utsira formation

500 m

> Seismic responses due to carbon dioxide injection. A 1994 seismic survey (left)served as a baseline for a 1999 survey (right) that showed the pattern of brinedisplacement by carbon dioxide following injection of 2 million tons of the gas.

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The Kyoto Protocol includes a compliancemechanism. For every ton of gas that a countryemits over its target, it will be required to reducean additional 1.3 tons during the Protocol’s sec-ond commitment period, which starts in 2013.Some reports contend that concessions made atthe conference reduced emissions cuts requiredby the Protocol from 5.2% to between 0 and 3%in 2010. The UNFCCC is more cautious in itsstatements. As of August of this year, its secre-tariat had not calculated how the Bonn agree-ments might affect developed-country emissionreductions under the Kyoto Protocol, and indi-cated that this would not be known with any pre-cision until the 2008-2012 target period.

E&P Company InitiativesToday, many oil and gas companies are takingglobal warming seriously, convinced that it is sen-sible to adopt a precautionary approach. Othershave taken a more conservative stance: theyagree that climate change may pose a legitimatelong-term risk, but argue that there is still insuffi-cient scientific understanding to make reasonablepredictions and informed decisions, or to justifydrastic measures. All agree that a combination ofprocess changes and advanced technologies willbe required within the industry to meet the typesof emission standards being proposed.

BP and Shell have implemented strategiesbased on a judgment that while the science ofclimate change is not yet fully proven, it is pru-dent to behave as though it was. Both companieshave established ambitious internal targets forreduction of their own emissions. The KyotoProtocol calls for an overall reduction of green-house-gas emissions of at least 5% by 2008 to2012, compared with 1990. BP has undertaken to

reduce its greenhouse-gas emissions by 10% bythe year 2010, against the 1990 baseline. Shellintends to reduce emissions by 10%, against thesame baseline, by 2002.

Companies are choosing to cut emissions inseveral different ways. The BP emissions reduc-tion program, for instance, includes ambitiouscommitments:• Ensure that nothing escapes into the environ-

ment that can be captured and, ideally, usedelsewhere. BP intends to stop the deliberateventing of methane and carbon dioxide wher-ever possible. This may involve redesigning orreplacing equipment, and identifying and elim-inating leaks.

• Improve energy efficiency. Engineers are exam-ining all energy-generating equipment toensure that the company is making the bestpossible use of hydrocarbon fuels and the heatthat is a by-product of energy generation.

• Eliminate routine flaring. It is better to flare gasthan vent it directly to the atmosphere, but it is still a waste of hydrocarbons—althoughsome flaring may still be necessary for safety reasons.

• Develop technology to separate carbon dioxidefrom gas mixtures, then reuse it for enhancedoil recovery or store it in oil and gas reservoirsthat are no longer in use, or in saline forma-tions (above).

Integrated oil companies also are trying tohelp customers reduce greenhouse-gas emissionsby increasing the availability of fuels with lowercarbon content and offering renewable energyalternatives, like solar and wind-driven power.

Some companies, including BP and Shell,have introduced internal greenhouse-gas emis-sions trading systems. The attraction of emissionstrading is that it allows reductions to be achievedat the lowest cost; companies for whom emis-sions reductions are cheap can lower their

emissions and sell emission rights to firms thatwould have to pay more to decrease emissions.

The BP emissions trading system is based ona cap-and-trade concept, and was primarilydesigned to provide BP with practical experiencedealing with an emissions trading market and tolearn about its complexities. At its simplest level,a cap is set each year to steer the group towardthe most efficient use of capital to meet its 2010target of 10%. Say, for example, increased pro-duction is planned from an offshore platform,thereby causing emissions above its allocatedallowance. If the platform’s on-site abatementcosts are higher than the market price of CO2, thecompany may decide to purchase CO2

allowances for that unit. Similarly, if a down-stream unit has upgraded its refinery and emitsless CO2 than its allowances cover, it is econom-ically desirable to both companies if the lattersells its allowances to the former (below).

The operation of these systems will beclosely followed not only by other oil and gascompanies but also by governments, since theprinciples behind emissions trading are broadlythe same whether trading takes place within asingle company, among companies within a sin-gle country, among companies internationally orbetween nations.

Oilfield Technology Development and ApplicationWorking with oil and gas companies, major oil-field service suppliers have been at the forefrontin addressing a range of health, safety and envi-ronmental issues—from reducing personnelexposure to risks at the wellsite, to application of‘green’ chemicals that provide equal or enhancedperformance while decreasing ecological impact,and to methods for cutting or eliminating emis-sions resulting from processes such as burningoil and flaring gas during well-testing operations.

56 Oilfield Review

BP Emissions-Reduction Program_________

Capture and reuse emissions.

Stop deliberate venting of carbon dioxide and methane.

Improve energy efficiency.

Eliminate routine flaring.

Develop technologies to separate carbon dioxide from gas mixtures.

> Cutting emission levels. BP has undertaken anaggressive, multifaceted program to reduceemissions, ranging from improved energy effi-ciency to elimination of routine gas flaring.

Company A Company B

Each companyinitially is

allocated 50 permits to emit

50 tons

Units sold

Units boughtEmission limit before trading

Emission limit after trading

Carb

on d

ioxi

de e

mis

sion

s

–10

40 50

+10

> Emissions trading system. This process strives to reduce emissions at thelowest cost by permitting the buying and selling of emissions rights betweenvarious units within a given company or between companies.

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Autumn 2001 57

Solutions to eliminate flaring—Burning oiland flaring natural gas during testing operationsnot only are costly due to lost revenue, but alsoproduce large quantities of carbon dioxide. Smallamounts of toxic gases, soot and unburnedhydrocarbons are also released. Eliminating oilburning and, ultimately, gas flaring not only cre-ates a safer working environment, but also helpsreduce the key constituent, carbon dioxide,thought to be associated with global warming.

Recently, a Schlumberger team in the MiddleEast, working closely with a major operator in theregion, addressed the flaring problem for produc-tion testing where an existing export pipelinewas available. Considering the nature of the test-ing program, there were several key challengesthat had to be overcome. Wells are typicallyhighly deviated or horizontal, and penetrate mas-sive carbonate formations. Large quantities ofacid are used to treat the zones, giving rise tolong cleanup periods and an erratic initial flow ofmixtures of spent acid, emulsions, oil and gas.

Traditionally, the wells were flowed until suffi-cient oil was produced at sufficient pressure togo directly into the production pipeline, requiringburning of oil in the interim. Care had to be takenthat the fluid’s pH was high enough so as not tocause corrosion problems.

A three-stage program to eliminate flaringand simultaneously solve associated well-testingproblems was undertaken. In the first stage,beginning in 1998, the goal was to pump sepa-rated oil into the pipeline from the outset,instead of burning it. This required the design ofspecialized, dual-packing centrifugal pumps thatwere run in series to achieve the required pres-sure for oil injection into the pipeline. Naturalgas was still flared, and separated water dis-carded. Residual oil and water emulsionsremained a problem, since a single separatorwas insufficient to break them.

In the second stage of the project, a neutral-izer and breaker system was designed for treat-ment of the emulsion phase prior to entering the

main separator. Remaining gas and oil were thenflowed through the separator. A skimmer andchemical injection system were employed toreduce the oil content in the water underflowstream from 3000 ppm to less than 80 ppm,allowing safe disposal of all residual water. Oilproduced through emulsion breaking waspumped into a surge tank and then into the pro-duction pipeline, saving additional oil that wouldhave otherwise been discarded.

In the third stage, currently under way, thegoal is for complete elimination of flaring byusing advanced multiphase pumping technologywith multiphase metering. When the wellheadpressure is insufficient to route gas back throughthe line after the multiphase meter, a variable-drive multiphase pump—that can handle a vari-ety of flow rates and pressures—would beintroduced so that both oil and gas can beinjected into the production pipeline (above).

Gas

Oil

Water and oil emulsion

Series of pumps

Series of pumps

Produced fluidPipeline

Flaring

Separator

Disposal

Gas

Pipeline

Flaring

Skimmer

SeparatorProduced fluid

Stag

e 1

Stag

e 2

Stag

e 3

Gas and oilNeutralizer and emulsion breaker

Neutralizer and emulsion breaker

Broken emulsion

Broken emulsion

Oil

Oil

Oil

Clean water

Clean water

Disposal

Surge tank

Pipeline

Skimmer

Produced fluid Gas and oil Gas and oil

Disposal

Surge tank

Multiphase flowmeter Multiphase pump

> Three-stage program to eliminate flaring. A Schlumberger team in the Middle East committed to first reduce and then fully eliminate flaring of gas andburning of oil and, at the same time, generate greater revenue for the operator by increasing pipeline throughput.

50387schD01R1 11/29/01 5:26 AM Page 57

In the first year of implementation of the initialstages of the project, the operator was able to sellan additional 375,000 barrels [59,600 m3] of oilthat otherwise would have been burned, generat-ing more than $11 million in increased revenues.21

Zero-emission testing—The next frontier is ageneralized solution for zero-emission testing forexploration and appraisal wells where an exportpipeline is not available. Here, the challenge is totake a quantum step beyond improved burnertechnology. The goal is elimination of all emis-sions by keeping produced hydrocarbons con-tained either below surface or the mudline, or inspecial offshore storage vessels. Through the useof advanced downhole measurements and tools,high-quality test data and samples could still be captured.

There are several approaches to downholecontainment. In particular, three options are

currently undergoing intensive investigation. Thefirst is closed-chamber testing. Here, test fluidsflow from the formation into an enclosed portionof a tool or pipestring. A short flow period isachieved as the chamber fills and its original con-tents become compressed. Flow stops as thechamber reaches equilibrium, allowing analysisof the subsequent buildup. This method, applica-ble to both oil and gas wells, is simple, and theshort test duration limits rig time compared witha conventional test. But, there are drawbacks.With only a small flowed volume due to capacitylimitations of the test string or wellbore, only alimited radius of investigation near the wellborecan be evaluated. Lack of thorough cleanup afterperforating can potentially affect the quality ofcollected samples. If the formation is not well-consolidated, hole damage or collapse may occurbecause of high inflow rates (below left).

A second method is production from one zoneand reinjection into the same zone, known asharmonic testing. Here, fluid is alternately with-drawn into a test string and then pumped backinto the reservoir at a given periodic frequency.The reservoir signature is determined point-by-point as a function of frequency by varying thefrequency during testing. The advantage is that a

58 Oilfield Review

Pressure gauge

Packer

Produced fluid and initial liquid cushion

Gas-liquid interface

Test valve

Surface valve

> Closed-chamber testing. Test fluids from theformation enter an enclosed space until the con-tents compress and reach equilibrium. This briefflow period is then followed by a second stage ofpressure buildup.

Tubing

Circulating valve

Barrier valve

Upper packer

Circulating valve

Ball valve

Downholepump assembly

Lower packer

Sand screen and gravel pack

Flow direction

> Continuous production and reinjection. A spe-cially designed tool allows produced fluid fromone zone to be continuously injected into anotherusing a downhole pump to provide a prolongedtesting period. Samples can be retrieved, andflow and pressure data are measured downholefor subsequent analysis.

21. The team that spearheaded this project won thePerformed by Schlumberger Chairman’s Award 2000, the top award in a company-wide program to strengthenthe Schlumberger culture of excellence. Client teammembers included Abdullah Faddaq, Suishi Kikuchi,Mahmoud Hassan, Eyad Al-Assi, Jean Cabillic, Graham Beadie, Ameer El-Messiri and Simon Cossy.Schlumberger team members included Jean-FrancoisPithon, Abdul Hameed Mohsen, Mansour Shaheen,Thomas F. Wilson, Nashat Mohammed, Aouni El Sadek,Karim Mohi El Din Malash, Akram Arawi, Jamal AlNajjar, Basem Al Ashab, Mohammed Eyad Allouch,Jacob Kurien, Alp Tengirsek, Mohamed Gamad andThomas Koshy.

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Autumn 2001 59

separate zone for disposal of the produced fluidis not needed, but defining the pressure-responsecurve would require more time than for a con-ventional test and may not be cost-effective.Advanced signal processing may be able toreduce the time required, but still may not makethe process economically viable.

The third method is to continually producefrom one zone and inject the produced fluid intoanother zone. Reservoir fluids are never broughtto surface, but are reinjected using a downholepump. Drawdown is achieved by pumping fromthe production zone into the disposal zone.Buildup is provided by simultaneously shutting inthe production zone and stopping the downholepump. If injectivity can be maintained, this con-tinuous process emulates a full-scale well test. Alarger radius of investigation is possible due tolarger flow volumes, with the potential to inves-tigate compartmentalization or even reservoirlimits. A longer flow period improves cleanupprior to sampling. Flow and pressure are mea-sured downhole and analyzed with conventionalmethods for radial flow. It is possible to capturesmall pressure-volume-temperature (PVT)-qualitysamples and larger dead-oil samples downhole.Drawbacks include a somewhat complex toolstring, an inability to handle significant quantitiesof gas and no time-saving over a conventionalwell test. The key factor is having a suitableinjection zone that provides sufficient isolation(previous page, bottom right).

Two joint industry programs have been estab-lished to investigate each of the three methods indetail, with participation by BP, Chevron, NorskHydro and Schlumberger. The first, conducted bySchlumberger, is assessing downhole tool design

and capability requirements. The second, a three-year program at Imperial College in London,England, is defining the interpretation packagesand procedures that would be required to capturethe maximum amount of reliable informationfrom the data.

Once the selection of the preferred method isfinalized, the next step will be a proof-of-conceptfield experiment that mirrors the requirements ofa variety of well-test conditions. Currently, thecontinuous production-reinjection option looksmost promising.

Modules mounted on the deck or in the holdof a suitable floating vessel are being investi-gated for storing fluids collected offshore duringtesting. Fluid-processing facilities also would beprovided onboard. Large discoveries, marginalfields and deepwater prospects are targetedapplications. Equipment would be designed tohandle a broad range of testing conditions anddurations. The vessel would receive and storegas and liquids, and offload the contents at theend of the well test or at intervals during the test.This concept could completely eliminate the needfor flaring, and generate revenues from sale ofproduced fluids that would otherwise be lost. Theprocedures for handling and storing liquids havealready been successfully demonstrated inextended well tests in fields such as BP’sMachar—proving both the feasibility and finan-cial viability of the approach. Gas handling andstorage, however, pose additional challengesthat would probably require compression and transfer facilities to create compressed natural gas. This is a costly proposition and may not be economically viable at current gas prices (above).

With growing emphasis on eliminating alltypes of gas emissions, particularly carbon diox-ide, these areas of investigation are expected tocontinue to receive close attention and signifi-cant industry funding.

Future ChallengesIn the near future, governments around the worldwill receive the IPCC Synthesis Report which willattempt to answer, as clearly and simply as pos-sible, 10 policy-relevant scientific questions.Perhaps the pivotal question, as stated by theIPCC, is: “How does the extent and timing of theintroduction of a range of emissions-reductionactions determine and affect the rate, magnitudeand impacts of climate change, and affect globaland regional economies, taking into account his-torical and current emissions?”

In another five years, the IPCC is expected topublish its Fourth Assessment Report. By then,climatologists may have resolved some of theuncertainties that limit today’s climate models.They should, for example, be able to provide abetter description of the many feedback systemsassociated with climatic phenomena, particularlyclouds. Greater understanding could lead toreduced uncertainty about a causal connectionbetween increased greenhouse-gas concentra-tions and global warming. This would be a majorstep forward.

In the interim, oil and gas companies, working closely with oilfield service companies,will continue to be proactive in developing technologies and operational procedures forreducing emissions. —MB/DEO

Storage modules andprocessing facilities

Drilling andproduction unit

Export flowline

Dynamically positionedstorage or shuttle tanker

Rigid productionriser

BOP or subseatest tree

> Offshore storage-module concept. A vessel for storing and offloading fluids collected in closed modules during testing operations might offer an approach to eliminate the need for flaring while generating increased revenues.

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