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M A H M O U D A B D U L - B A Q I / G I A N T G A S F I E L D S O F S A U D I A R A B I A 145

Giant Gas Fields of Saudi Arabia

In this chapter describing the recent discovery of several giant gas fields in the Paleozoicof Saudi Arabia, Mahmoud Abdul-Baqi highlights the progressive evolution of technicaleffort in the Kingdom. Early technical work had been led by expatriates seconded to Aram-

co. Over the years, Saudis gradually moved to technical and leadership positions, and nowSaudi Aramco has become a modern major oil company.

Significant research capabilities have evolved within Saudi Aramco to support its explo-

ration effort. This exploration effort to discover non-associated natural gas has been so suc-

cessful that it has shifted the national strategy for Saudi energy usage from oil to gas.

In its early years, Saudi Arabia wanted and needed outside assistance. Modern Saudi Aramco welcomes (but does not need) outside assistance. This evolution of the company

mirrors changes in the country, and can be a model for other oil-rich developing nations.

— M. W. Downey

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exploration, for drilling to begin as soon as a suit-able structure was found, and for construction of a refinery after oil was discovered.

In 1933, ground and air reconnaissance start-

ed in earnest (Figures 2, 3). The use of airplaneswas an essential part of the early exploration cam-paign due to the large concession area. In fact,Socal sought permission to use them early on dur-ing the original negotiations. By the followingyear, 1934, a small group of enthusiastic explorershad been assembled, working for Socal’s new sub-sidiary, California Arabian Standard Oil Company

(Casoc), later to become Aramco and eventuallySaudi Aramco.

Among the early explorers was MaxSteineke (Figure 4), “a big man with a big arm

and a big voice,” whose contribution to under-standing the geology of the Arabian Peninsulawould later shape the exploration efforts in thisarea. Aiding that group were Saudis in a widevariety of jobs, such as Khamis Rimthan (Figure5), a rugged, determined, and effective fieldguide “whose head was a human compass,”according to early explorers (to this day, the

Rimthan Field remains the only field in SaudiArabia named after a person).

Early exploration activities were difficult, butground and air reconnaissance continued, and cul-

minated in several field maps that describe thesurface structures (Figure 6) and located a suitablespot to drill. In April 1935, the first well,Dammam Well No. 1, commenced drilling (Figure7) on the Dammam Dome structure (Figure 8).The well, unfortunately, produced no more thatabout 100 bbl of oil a day from the CretaceousWasia Formation, which was hardly a commercial

Figure 1. Signing of the concessionagreement between Saudi Arabia and

Socal in Khuzam Palace, Jiddah, in 1933.

Pictured are the Saudi Finance Minister,

Abdullah Al-Sulayman, and Lloyd N.

Hamilton, a senior Socal lawyer.

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148 Discoverers of the 20th Century: Perfecting the Search

Figure 2. Early field mapping party.Much of the early geology was

mapped by crews similar to this field

mapping party. Surface expressions

of geologic structures were identified

and their limits surveyed. Work

progressed forward in an area bigger

than Texas. Mapping was done under

difficult conditions. Both heat and

sandstorms often confined the

geologists to their field tents, until

mapping conditions improved.

Figure 3. Early aviation. Airreconnaissance provided invaluable

help in mapping the vast concession

areas in early exploration. Picture

taken in 1935.

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success in Saudi Arabia, and was completed as agas well, producing gas from a shallow horizonfor domestic cooking and heating. It is interestingto note that the first well ever to be drilled in

Saudi Arabia was a gas discovery!Of course, at that time, the focus was on dis-

covering commercial quantities of oil for export,and so several other wells were planned to bedrilled to test the same structure. The followingyear, Dammam Well No. 7 started drilling, target-ing the Jurassic Arab formation, and in March of 1938, it flowed 3800 bbl/day from that formation

(Figure 9). Lucky No. 7 was a tough well to drill,encountering several operational problems duringdrilling, but it turned out to be a steady and reli-able producer and the start of a new era for SaudiArabia and the oil industry. In fact, it was stillcapable of producing 1800 bbl/day when it wastaken out of production in 1989, even after turn-ing out more than 32 million bbl of production inalmost 45 years of service.

The following year, in 1939, His Majesty KingAbdul-Aziz paid his first visit to the newly con-structed oil installation (Figure 10), and, in 1944,the company changed its name to Arabian Amer-ican Oil Company, abbreviated as Aramco. With-out His Majesty’s guidance and vision, the entireenterprise would not have been possible.

Gas Exploration and theNon-associated Gas Program

Numerous oil and gas discoveries were made inthe years that followed. The first commercial gasdiscovery, though, was in 1957 in Dammam WellNo. 45, which flowed 22 mmcf of gas per dayfrom the deeper Permian Khuff Formation. Othermajor gas discoveries include Haradh (1971), ‘Ain

Dar (1975), Hawiyah (1979), Shedgm (1979), and‘Uthmaniyah (1980). These discoveries are part of one: The greater Ghawar Field, the largest oil fieldin the world and one of the biggest gas fieldsworldwide (Figure 11).

More recently, with the change of emphasisfor in-Kingdom energy consumption towards gas,

the current non-associated gas program started inearnest in 1994. This deep-gas exploration pro-gram started in 1994 with the discovery of sweetgas in the Devonian sandstones along the eastflank of the giant Ghawar anticline — a fault andunconformity truncation play of the Devonian Jauf sandstones. By the end of 2001, the program

Figure 4. MaxSteineke, “a big

man with a big

arm and a big voice.” Picture

taken in 1937.

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had drilled 28 wildcat and deeper pool wells, tar-geting Permian to Silurian reservoirs at depths of 12,000 to 18,000 ft (3660 to 5490 m) (Figure 11).

The program made 15 significant discoveries,

9 in deep, four-way closures, 4 in combinationstructural/stratigraphic traps, and 2 deeper pools,amounting to an exploration success rate of 54%.The program has added 44 tcf of non-associatedgas reserves, and led to a recent commissioning of a gas plant in Hawiyah with a capacity of 1.6 bcf/day, while a second plant with the samecapacity in the vicinity of Haradh is under con-struction.

Permian Khuff Gas Play

The late Permian Khuff Formation is the domi-nant non-associated gas reservoir in Saudi Arabia.The Khuff Formation is primarily composed of carbonates, evaporites, and lagoonal shales, andrepresents shallow-water deposits containing 5

major depositional cycles. Each cycle starts gradu-ally with a transgressive subtidal grainstone,which comprises the reservoir, and ends graduallywith regressive intertidal and supratidal carbonatemuds and evaporites, which make up the reser-voir seals (Figure 12). High porosities found inthese depositional cycles are associated withleached oolitic limestones and high-energy grain-stones, which are commonly dolomitized. TheKhuff A, B, and C are the main gas reservoirs inthe Khuff.

Within Saudi Arabia, the Khuff Formationranges in thickness from 430 to 3100 ft (130 to 950m). The total isopach of the Khuff is illustrated inFigure 13. The Khuff thickness increases to thenorth and east of Ghawar, and also increases intothe Rub’ Al-Khali basin to the southeast. Local


Figure 5. Khamis Rimthan, afield guide with the

equivalent of a human

compass in his head. Picture

taken in 1938.

Figure 6. 1935 fieldmap compiled by Koch

and Steineke. Early

exploration was based

on surface structure

maps like this.

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Figure 7. Dammam Well No. 1.


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variations in thickness caused by pre-Khuff fault-ing and tectonics are also common.

The first Khuff gas field in the Middle Eastwas discovered in 1948, in Awali, Bahrain, by

drilling the Bahrain Well No. 52 to the Khuff For-mation at a depth of 10,078 ft (3072 m). Followingthe successful gas discovery at Dammam Dome in1957, a period of regional study and detailed out-crop work on the Khuff reservoir was undertakenand culminated in a new round of exploratorydrilling. In 1971, the giant Haradh Khuff Gas Fieldwas discovered in the southern portion of Ghawar (Figure 14), and this was followed by thediscovery of 4 more giant Khuff gas fields on thegreater Ghawar structure (Table 1).

Today, Saudi Aramco continues to exploreand develop the Khuff gas reservoir in and aroundGhawar. The first Khuff horizontal well wasdrilled in 1997; since then, horizontal drilling hasproved to be very useful in the gas developmentstrategy. An ongoing and extensive study of the

depositional facies and diagenetic controls onKhuff reservoir porosity continue today with databased on detailed core description, facies correla-tion, and thin-section analysis. Additionally, geo-


Figure 8.Dammam Dome

structure. Current

Saudi Aramco

headquarters are

located just about

the top of the

dome.

Table 1. Major historical gas field discoveries.

Field Discovered Reservoir

Dammam 1957 KhuffHaradh 1971 Khuff, ‘UnayzahAin Dar 1975 Khuff Hawiyah 1979 Khuff, Jauf Shedgum 1979 Khuff, Jauf ‘Uthmaniyah 1980 Khuff, Jauf Berri 1978 Khuff Qatif 1981 Khuff, Jauf

GreaterGhawarfield

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Figure 9. Dammam Well No. 7. The first commercial oil discovery,1938.

Figure 10. His Majesty King Abdul-Aziz visiting newly constructed oilfacilities in the eastern Province in 1939.

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physical research aimed at improving seismicimaging of the Khuff reservoir is showing goodresults at Saudi Aramco (Figure 15).

Pre-Khuff Paleozoic PlaysThere are 2 major plays in the pre-Khuff Paleozoicsiliciclastic sandstones of eastern Saudi Arabia:The Devonian Jauf and the Carboniferous toLower Permian ‘Unayzah. The source rocks forboth plays are the Lower Silurian Qusaiba “hotshale.” The plays exist on and at the flanks of thegiant Ghawar anticline and in adjacent satellite

structures. The trap styles range from simple four-way closures to complex combinations of strati-graphic and structural traps (Figure 16), includingdownthrown fault plays.

‘Unayzah Gas Exploration

The Lower Permian ‘Unayzah Formation isquickly becoming the second major non-associ-ated gas reservoir in Saudia Arabia, with 10 gasfields discovered or showing significant exten-sion potential since 1994 (Figure 17). The mostrecent discovery is the Mazalij Field, located 60miles (95 km) west of Ghawar (Figure 11). In theMazalij Field, non-associated gas in commercialquantities was discovered in the downthrownfault block of the main Mazalij structure (Figure18). The upthrown block was drilled in the

1970s and proved to be barren of the ‘Unayzahsands due to a combination of erosion and non-deposition.

The ‘Unayzah Formation is a thick sequenceof continental sediments that were deposited onthe pre-’Unayzah (Hercynian) unconformity. The‘Unayzah is composed of a mix of facies types,ranging from fluvial and eolian sandstones, silt-

stones, and mudstones, to debris-flow conglomer-


Figure 11. Recentgas discoveries

in the non-

associated gasprogram.

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ates and caliche paleo-soil deposits. The best‘Unayzah gas reservoirs are mainly found in thebraided and meandering stream sands, and theeolian dune sand facies. The non-reservoir silt-stones and mudstone facies are associated withlocal playa lake deposits. The top seal for the‘Unayzah reservoirs are mainly the overlyingtransgressive shales and carbonates of the basal

Khuff formation.

Devonian Jauf Gas Exploration

Two giant gas fields in the Devonian Jauf reser-voirs have been discovered on the east flank of Ghawar in Shedgum and Hawiyah fields. In 1980,the Giant Shedgum (Jauf) gas field; and in 1994,the giant Hawiyah (Jauf) gas field were added to

the impressive list of giant gas reservoirs associat-

ed with Ghawar field. The trapping style for the Jauf reservoir is erosional truncation at the Her-cynian unconformity, with transgressive shalesand carbonates of the overlying basal Khuff For-mation acting as both lateral and top seals.

The Devonian Jauf sandstones have the mostfavorable pre-Khuff reservoir development in theGhawar area. The Jauf reservoir consists of fine-

to-medium grained sandstones that are weaklycemented by authigenic illite clays. The high levelof silica cementation and quartz-overgrowthdevelopment, often associated with Paleozoic-aged sandstones, appears to have been inhibitedby the presence of illite clays in the Devonianreservoir.

Exploration for additional gas fields in the

Jauf reservoir is continuing by Saudi Aramco,

along the regional Jauf truncation limits. Majorimprovements in seismic imaging technologyare allowing enhanced seismic imaging of the Jauf truncation and reducing exploration drillingrisk.

Energy NeedsAs mentioned above, Saudi Arabia is shifting its

local energy use emphasis from oil to gas (Figure19). Supplying the new local gas need, (which isincreasing significantly and is expected to contin-ue to increase over the coming years) are 5 oper-ating gas plants in Berri, Shedgum, Abqaiq, ‘Uth-maniyah, and Hawiyah, and one plant under con-struction in Haradh (Figures 11, 20).

The success of the gas exploration program

has prompted a shift in national strategy to

Figure 12. The variousdepositional facies types

comprising the Khuff

Carbonate Ramp model areshown here. Each Khuff

facies type is well

documented by available

core data.

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Figure 13. A regional isopach of the Khuff Formation shows the influence of Paleozoic tectonics on Khuff deposition. Note the thinning onto the Ghawar anticline and also major thickness increase into the Rub’

Al-Khali basin located to the southeast.


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expand the petrochemical industries and rely onnatural gas for power generation and seawaterdesalination. The success also encouraged interna-tional oil companies to put forward proposals to

participate in the Kingdom’s non-associated gasexploration, development, and utilization pro-grams. Currently, the local consumption of gas isabout evenly divided between electric power gen-eration, petrochemical plants, water desalinationplants (which also produce power), and otherindustrial activities (Figure 21).

Technology Challengesand SolutionsThe non-associated gas program proved the

deep Khuff and pre-Khuff gas potential of theArabian basin, and has been an exploration anddevelopment success. This success, however,has not been without challenges. Some of thesechallenges include the difficulty in estimatingthe highly variable ‘Unayzah and Jauf reservoirquality, inter-bed seismic multiples (ghost reflec-tions) contaminating most seismic sections, seis-

mic velocity heterogeneity of the near-surface

layers (causing severe statics problems), and thedifficulty in estimating the intensity and orien-tation of subsurface fractures, which highlyinfluences the flow rate in several reservoirs.

In order to tackle these challenges, SaudiAramco researchers developed some innovativetechnologies and tools, 4 of which are highlighted.

Coherence and DETECT

Coherence analysis is a useful way of detectinganomalous areas within the seismic data. By

emphasizing edges in the seismic data, insight is

Figure 14. The HaradhGas field area is

associated with a

southeast-plunginganticline. Currently a

very intensive

development program of

the Khuff and Pre-Khuff

gas reservoirs is ongoing.

At the same time, Saudi

Aramco is undergoing

major construction of theHaradh gas plant,

scheduled for

commissioning in 2003

at a 1.6 bcf of gas per

day production level.

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Figure 15. A detailed view of the greaterGhawar anticlinal structure at top Khuff

level. The entire Ghawar structure has been

covered by 3-D seismic surveys and merged

into a seismic supercube. The many faults

and structures comprising the Ghawar field

can be seen.

Figure 16. Paleozoic gas plays.


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ever, interest renewed, fueled not only by disap-pointments in classical artificial intelligence meth-ods in solving large, complicated systems, but alsoencouraged by many innovations in neural com-

puting; and these days, neural networks havewide-ranging applications in several fields.

One of the major difficulties with conven-tional neural networks is that their performancehas been inconsistent due to the significantamount of parameter tweaking required toachieve satisfactory results. The reason is thatlarge networks, trained for a long time, tend to

overfit the data, producing a rough solution that is

not useful as a predictive model. Saudi Aramcoscientists developed an enhanced type of neuralnetwork (regularized neural networks) thatimposes natural smoothness on the solution and

thus alleviates the overfitting problems. Figure 28shows a blind test in two wells. The regularizednetwork solution (red) remains stable and close tothe true porosity measured at the well, while theconventional network prediction (blue) has wildoscillations around the true solution, reflecting theoverfitting problem. As a whole, the regularizedsolution leads to a 22% increased accuracy over

the conventional network output in this area.

Integration

Of course, technology is only useful when utilizedeffectively. Therefore, it has always been para-mount that technology is absorbed and assimilat-ed within our daily routines, and that proper ven-ues for effective technology integration are estab-lished. Among these are several visualization

rooms (Figure 29) that bring together experts from

Figure 19. Seawater desalination plant ineastern Saudi Arabia.

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Figure 20. Daily gas feed capacity from the 6Saudi Aramco gas plants. Haradh plant is still

under construction.

Figure 21. Current gas usage by sector inSaudi Arabia. Electrical power generation and

water energy needs consume approximately

half of the daily gas production in Saudi

Arabia

Figure 22. Left : Coherence slice from a commercial package. Right : Same slice from Saudi Aramco’s in-house developed DETECT package. Note the clarity of the channels in the

DETECT picture.

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Figure 23. Faults and sinkholes appear vividly in a coherenceslice from DETECT.

Figure 24. Subsurface impact craters from geologic time, in aDETECT slice.

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Figure 25. Top : Seismic section processed by conventional deconvolution.Bottom : Same section processed by fractal deconvolution. Note clarity and

continuity of the events, especially those marked by the arrows.


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Figure 26. Various geological and geophysical sources of data are integratedinto an estimate of the reservoir potential utilizing an algorithm based on

fuzzy logic.


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Figure 27. Reservoir porosity is estimated between the wells using regularized neural networks. Theresult is a geocellular model of the porosity heterogeneity of the reservoir.

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various disciplines (geology, geophysics, engineer-ing, computer science, etc.) to discuss challengesand problems, analyze them from different per-spectives, and prescribe remedies and solutionsthat draw from the expertise of the whole group.These visualization rooms have been an effectivetool of technology integration, and have had a sig-nificant impact on our ability to tackle the techni-cal and operational challenges.

SummarySaudi Aramco’s exploration program has proventhe gas potential of the deep Paleozoic reser-

voirs in the Arabian basin. The program hasadded 44 tcf of non-associated gas reserves dur-ing the past 8 years in and around the GreaterGhawar area, with an overall exploration suc-cess rate of 54%, having drilled a total of 28exploration wells resulting in 15 new gas fields.The program also substantially improved under-standing of the Paleozoic geology of the region.

The technical challenges faced, particularly indeep seismic imaging, have spawned significantresearch by Saudi Aramco and its partners inindustry and academia. In fact, the success of the gas exploration program has prompted ashift in national strategy to expand the petro-chemical industries and rely on gas for powergeneration and seawater desalination. It also

encouraged international oil companies to putforward proposals to participate in the King-dom’s non-associated gas exploration, develop-ment, and utilization programs.

AcknowledgmentsThe author acknowledges the significant contri-bution of Muhammad Saggaf, Martin Rademak-ers, and Abdulkader Afifi for helping with the

Figure 28. In a blindtest, comparison of the

true well porosity

(green), that estimated

by conventional neuralnetworks (blue), and that

estimated from

regularized neural

networks. The latter

avoids the wild

oscillations of the

conventional solution.

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Figure 29. Effective technological integration is key to successful tackling of challenges.


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preparation of this chapter. Scott Mussett andNasser Al Maddy are acknowledged for preparingthe graphics. The author also acknowledges all of the Exploration Organization staff at Saudi Aram-co, present and past, for their contribution as well

as the many unpublished internal company re-ports utilized in this chapter. Thanks is expressedto the Ministry of Petroleum and MineralResources and the Saudi Arabian Oil Company(Saudi Aramco) for permission to publish.

References Janahi, I. A., and B. A. Dakessian, 1985, Develop-

ment of the Khuff Gas Reservoir, Bahrain Field:SPE 1985 Middle East Oil Technical Conference,SPE paper 13679, p. 25–32.

Jum’ah, A. S., 2002, Hawiyah Gas Plant RecognitionCeremony, Executive Speech.

Luo, Y., S. Al-Dossary, and M. Marhoon, 2001, Seis-mic Edge Detection Using Generalized HilbertTransform: 63rd Meeting, European Association

of Exploration Geophysicists, Session: P627.McGillivary, J. G., and M. I. Husseini, 1992, The

Paleozoic-Carboniferious Glacial Deposits inSouthern Saudi Arabia: AAPG Bulletin, v. 76, p.1473–1490.

Saggaf, M., N. Toksoz, and H. Mustafa, 2000, Esti-mation of reservoir properties from seismic databy regularized neural networks: 70th AnnualInternational Meeting, Society of Exploration

Geophysicists, p. 1422–1425.Saggaf, M. M., and E. A. Robinson, 2000, A unified

framework for the deconvolution of traces of

nonwhite reflectivity: Geophysics, v. 65, 1660–1676.

Saggaf, M., and E. Nebrija, 2001, Estimating the res-ervoir potential through integration of multipleattributes: 71st Annual International Meeting,

Society of Exploration Geophysicists, p. 540–543.

Videtich, P. E., 1994, Dolomatization and H2S Gen-eration in the Permian Khuff Formation, Off-shore Dubai, UAE: Carbonates and Evaporites,v. 9, n. 1, p. 42–57.

Wender, L. E., J. W. Bryant, M. F. Dickens, A. S.Neville, and A. M. Al-Moqbel, Paleozoic (Pre-Khuff) Hydrocarbon Geology of the Ghawar

Area, Eastern Saudi Arabia: GeoArabia, v. 3, n.2, p. 273–302.

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