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WAFRA FIEID KUWAIT-SAUDI ARABIA NEUTRAL ZONE
by
Paul H. Nelson Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021
ABSTRACT
The Wafra field lies in the western part of the Kuwait-Saudi Arabia Neutral Zone in the northeastern part of the Arabian Peninsula. The field was discovered in 1953 by the American Independent Oil Company and Pacific Western Oil Company on the basis of corehole and seismic information. It is unique in being operated jointly under separate concessions from two coun tries, Kuwait and Saudi Arabia, granted to American Independent Oil Company and Getty Oil Company (formerly Pacific Western Oil Company) respectively. It is northwest - southeast trending anticlinal fold, and produces from four main zones, two in the Eocene and two in the Cretaceous. Accumulated pro duction to July 31, 1967 was 584,254,067 barrels of oil.
INTRODUCTION
The Wafra field is located in the west central part of the Kuwait Saudi Arabia Neutral Zone, some 50 airline miles south and slightly west of Kuwait City, Kuwait. It is about 30 miles inland and the oil produced is moved by pipeline northeast 35 miles to Mena Abdulla (Aminoil) and 30 miles east and slightly north to Mena Saud (Getty), for processing and loading to tankers. (Fig. 1) Wafra field is unique in being in territory jointly owned by two separate countries, Kuwait and Saudi Arabia, and has been developed under two concessions by two companies, although at pre~ent most of the field operations are carried out by a Joint Operations Co~ttee. It is also the only field on the southwest side of the Arabian Gulf producing from the Eocene, and although far from being of the caliber of its two giant neighbors, Burgan in Kuwait and Ghawar in Saudi Arabia, it has many inter esting features. This paper is a brief description of the stratigraphy, ... structure, and production of the Wafra field. :
HISTORY
The Neutral Zone between Kuwait and Saudi Arabia was established in late 1922, giving each country an undivided one half interest at a time when the only oil production in the region was some distance away in Iran. How ever, investigations in Kuwait to the north led to the discovery and early development of the great Burgan field in 1938-1940, and renewed development after World War II. This stimulated negoitations on the Neutral Zone which resulted in the awarding of a concession of the Kuwait one-half share of oil and gas to a group of American companies, called "Aminoil", in June 1948, and the Saudi Arabia portion to Pacific Western Oil Company (now Getty Oil Company) in January, 1949.
101 Exploration began in 1949 with a gravity survey, and based on that work, Wafra No. '1 well was spudded December 11, 1949. This well was loca ted on the top of a large gravity high similar to, and straight south of the Burgan field some 25 miles. Although it encountered the Burgan sands high to the oil-water contact of that field, they were found to contain water and the well was plugged and abandoned at 5,020 feet. Wafra No. 2 was drilled in 1950 at a location about two miles west and abandoned at 5,250 feet. This well ran high to No. 1 and actually found a small thick ness of Wara (First Burgan) Sand showing oil, but on a short test after plugging back it failed to produce. It now lies on the extreme northeast
side of the East Wafra sector of the field. Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021
A seismic crew was brought into the Neutral Zone and worked during 1950 and 1951, and in 1951 and 1952 a combined seismic and shallow core hole program was conducted over most of the Neutral Zone. Wafra No.3, on the south fringe of the present field, and FuwarisNo. 1 on the northern extremity of the present South Fuwaris field were drilled at this time but both were dry. Finally, on April 14, 1953 the Wafra No.4, located in what is now the south central part of the main Wafra field, was completed in the War a (First Burgan) Sand for 2,400 BOPD as the discovery for the field.
Later drilling has developed in addition to the Wara (Burgan) pay, two shallow pay zones in the Eocene and a deeper pay in the Ratawi Oolitic Limestone. Minor pay zones are found in the Upper Cretaceous Maestrichtian and in the Ratawi Limestone member.
STRATIGRAPHY POST EOCENE
Kuwait Beds:
The surface and near surface beds are fine to medium sands, often polished and well rounded, with beds of shale and occasional dense fresh water 1imes~one. Pebbles occur but gravels are not common. These beds are poorly indurated and a short string of large diameter pipe is set to avoid hole caving. The thickness ranges from 200 to 250 feet.
EOCENE
Dammam Formation:
The first indurated beds are the cherty upper layers, usually 10 to 25 feet thick, of the Dammam Formation. Below this cherty cap lies some 300 feet to 400 feet of white to tan limestone, fine crystalline to chalky, dolomitic in part and quite porous. It is often quite fossiliferous, with abraded foraminiferal fragments forming a soft spongy calcarenite. The . basal 150 to 200 feet of the Dammam, consisting of more dolomitic limestone, has been called the "Camerina" zone. At its base is found 20-30 feet of grey-green waxy shale which at times carries nummulites and forms a char acteristic "shale" pattern on the elctrical resistivity log just above the dense underlying anhydrite. The entire Dammam section is notorious for lost circulation problems, and in central and northern parts of the "Main Area" of the field erratic lenses containing gas have given a great deal of trouble.
102 Rus Formation:
The Rus Anhydrite, usually from 250-350 feet thick, is an alter nating series of white, crystalline anhydrite, and brown, dense, anhydritic limestone, with thin beds of blue to green marly shale.
Radhuma Formation:
This formation consists of an upper massive sequence of tan to buff, somewhat anhydritic and marly, dolomitic limestone, similar to the Dammam but darker in color and somewhat coarser grained; a middle section of some
100-150 feet of alternating anhydrite and anhydritic limestone in beds of Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021 20-30 feet thickness, and underlain by another thick dolomitic, calcarenitic limestone similar to the first. The lower part contains the Rotalia-Lock hartia fossil flood zone at whose base a characteristic 20' shale "sinus" is seen on the electrical log. In field nomenclature, these zones have been called the "First Eocene Limestone", the "Second Eocene Anhydrite", and the "Second Eocene Limestone" to identify the two major pay zones occurring in the limestone. A very minor zone occurs under the Rota1ia-Lockhartia zone and has been called the ''Third Eocene Limestone." It is generally more dense and crystalline than the upper limestone but develops vugular porosity. The total Radhuma section is about 1,400 feet thick.
UPPER CRETAC1!DUS
Tayarat Formation:
The Upper Cretaceous Tayarat Formation is normally 700 to 800 feet thick and has been divided in the field into a ''First Maestrichtian Shale" and "First Maestrichtian Limestone"; a "Second Maestrichtian Shale" and "Second Maestrichtian Limestone'" and an underlying liB" and "C" zones. The shales overlying their respective limestones are 20-30 feet thick, black to grey, with varying amounts of limy partings and some pyrite. The limestones are tan to grey, fine to medium crystalline in part but generally granular, and vugular in some areas. The "Maestrichtian 'B"' is a marly limestone sequence of 200 feet or more, underlain by the green-white, granular Hartha Limestone.
Hartha Formation:
The Hartha Formation, called ''Maestrichtian C" by the field usage, consists of 50 to 100 feet of grey-white, fossiliferous, cherty limestone. It is somewhat shaly and detrital in some developments.
UNCONFORMITY
Sadi and Rumaila Formations:
The Senonian - Cenomanian section as developed in the Wafra field is a complex and variable interval of 75 to 150 feet, composed of detrital limestone, Shale, and sandy shale, with the limestone granular and often porous. The upper portion corresponds to the Sadi Formation and the lower part probably to the Rumaila Formation. These beds are bounded both top and bottom by large unconformities, with a much thicker section development to the north, outside of the Wafra field structural area. To the south these beds are missing in the great regional Aruma-Wasia unconformity. 103 UHCONFORMITY
MIDDLE CRETACEOUS
Ahmadi Formation:
The Ahmadi shale varies from zero thickness in the central parts of the field and in the locally high "Southeast Area", to 130 feet in R-No. l4-A on the northern edge of the field. It is a characteristic green to brown fissile shale with some pyrite. This is the "Caprock Shale" of field usage. Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021 Wara Formation:
The Wara, or "First Burgan Sand" is a sequence of sand and shales, with lignitic laminae. It appears to be deltaic in origin and varies from loose unconsolidated sand to fine, tight siltstone. Although some zonation can be made, the sands vary considerably from we1l to well. It s thickness averages 175 feet.
Mauddud Formation:
The Hauddud Formation occurs as a thin, hard, shaly limestone under lying the Wara Formation. It is greenish-grey, and generally its thinness, 10-20 feet, cause it to be poorly represented in samples but its character istic high resistive "spike" is distinctive on the electrical log.
Burgan Formation:
The Burgan Formation consists of 1,100 - 1,200 feet of generally clean, medium to coarse grained, well sorted sand, with some thin beds of grey to dark grey shales. They have been divided into a ''Third Burgan" and "Fourth Burgan" sand at a fairly constant band of shaly beds about 400 feet from the top, but the entire section is water bearing and the division has no utility, the entire section being considered as the Burgan Formation.
LOWER CRETACEOUS
Shuaiba Formation:
This dolomitic limestone, from 150 - 200 feet thick, is usually medium to coarsely crystalline, vugular to cavernous, and often breaks down to cause lost circulation. Cores and tests of this formation have never shown anything but water.
Zubair Formation:
The Zubair is a massive, clean, medium to coarse, unconsolidated sand with very little silty or shaly material. It is usually about 1,200 feet thick.
Ratawi Formation: The Ratawi Formation a. it now stands is classed as a formation;
1M with three members. It is felt that the members deserve formation rank, but a workable nomenclature and suitable definitions have not yet been devised.
The Ratawi Shale is about 250 feet thick and consists of a green to greenish grey, massive shale. It is calcareous and grades into the underlying Ratawi Limestone.
The Ratawi Limestone is interbedded with shales similar to the overlying shale and is usually fine grained to dense, grading to granular in part and often pelletal. It is often fossiliferous and at timesis a Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021 shale-limestone breccia. The section is normally 250 feet thick.
The Ratawi Oolitic Limestone section is gradational with the over lying beds but in its full development is a tan, fine to medium grained limestone, developing numerous beds of oolite. In the upper part there are many beds of "fossil hash", as well as oolitic development~ Cementa tion appear to increase in the basal part. The total thickness is 650-700 feet.
Lower Sulaiy Formation:
These beds are not well known, having been drilled in very f~wells. It is a light tan to white, fine crystalline limestone, somewhat siliceous and styolitic. Pyrite is present as an accessory. This interval is 200- 300 feet thick.
JURASSIC
Hi th Formation:
Below the Lower Ratawi Formation lies from 200 - 250 feet of anhy drite with stringers of anhydritic limestone. The limestone is sometimes granular enough to develop porosity and staining but generally too tight to have any permeability.
Arab Formation:
In the Wafra field about 1,000 feet of alternating anhydrite and anhydritic limestone occurs below the dominantly anhydritic Hith. The limestones are fine grained, anhydritic and generally hard and somewhat shaly, having thin laminations of shale in some beds. Some dolomitic beds are present. Attempts have been made to sub-divide the interval into the classic "A", "B", "c" and "D" zones of Saudi Arabia, but the correlations are very weak and require a great deal of arbitrary adjustment which make them extremely questionable. The present deep wells to the south of the Wafra field in the Neutral Zone and in Saudi Arabia have found the Arab Formation almost completely dolomitized, thus preventing the correlation to be carried into the area of certain knowledge. It is preferable to wait until such time as closer subsurface control will enable a better correla t ion to be made.
105 Jurassic. Undivided: Below the Arab Formation the deepest wells have penetrated nearly 900 feet of limestone and dolomites, generally dark colored, fine grained and siliceous in part. They are hard and tight with only very minor por osity in a few thin fine granular beds. They represent Jurassic beds, including the Jubaila, Hanifa, and Tuwaiq Mountain Formations, and perhaps part of the Dhruma Formation, but without better control they are grouped together as pre-Arab Formation Jurassic.
Fig. 2 is a graphic repres"entation of the stratigraphy of the field area. It should be noted the column "Field Term" indicates only common Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021 usage that has grown up in the field. These names do not have any formal stratigraphic standing.
STRUCTURE
At the "First Eocene" level, about -500 to -600 feet subsea and about 1,000-1,100 feet drilling depth, the Wafra structure is a gentle, elongate anticlinal fold about 10 miles long and four miles wide, with a closure of about 75 feet. (Fig. 3) A smaller fold, about three miles long and one and one half miles wide, lies to the southwest, and is separated from the main structure by a shallow saddle about 75 feet deep. This western area is associated with the strong linear Fuwaris fold which trends northwest southeast just west of the Wafra field. However, at the "First Eocene" level the crest of the small western fold appears to be a little east of the crest on the deeper beds, but control is sparse and the relationship is not clear. The seiamic data show a fault striking northwest-southeast in this area but it cannot be identified in the subsurface at this level, except by the "saddling" area between the main structure and the western minor feature.
To the southeast the structure at this level plunges flatly through the southeast Wafra area where there is minor closure and accumulation in the "Second Eocene", "Burgan" and Ratawi Oolitic Limestone. This area is not productive on the "First Eocene" and is not shown on the structure map.
The "Second Eocene" map (Fig. 4) shows much the same general con figuration, but with slightly more irregularity and also the delineation of the Southeast Wafra area which forms a separate reservoir with the aid of ~band of impermeable development between the main field area and the southeast area. The western area appears to be separated from the main area completely, since the same sequence of beds which produce in the main area are wet at a higher subsea elevation. The wells which are productive in the west area have a porous development higher in "Second Eocene" sec tion. In order to show the structural relationship, this part of the map is drawn on the beds correlative with the main area. A fault is shown, although an interpretation can be made without the fault, but the use of the fault indicated by seismic data, explains the reservoir condition more reasonably. The area of accumulation in the War a (First Burgan) is much more limited than that of the Eocene reservoir. The map on the top of the Wara Sand (Fig. 5) has been drawn using the Ratawi wells for control in the Southeast Wafra. area. The central high has split into tvo subsidiary highs
106 separated by a narrow low trending northwest-southeast in the same position on "the low area' seen on the "Second Eocene" map. The East Wafra nose appears on the Wara map, based on the production found in the EW-4 well shown isolated to the northeast. This bifurcation of structure appears to be a common trait of fields in this general area on the southwestern side of the Arabian Gulf. It seems possible that the north-south and northeast-southwest alignments are of Cretaceous age and the northwest trends of Tertiary age.
The structure on the top of the Ratawi Oolitic Limestone (Fig. 6) shows less irregularity, perhaps due to less control, and greater relief, having from 225-250 feet of structure. Control to the southwest is limited becauseofa tighter facies condition in wells R-ll and R-12 on the southwest Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021 side. This condition discourages any additional drilling on that flank even though the structural position of such wells would be above water in this reservoir.
Not enough wells have been drilled below the Ratawi to give control for a map on the Arab Formation, but the structure at that level will pro bably be much as shown on the Ratawi map.
RESERVOIRS AND PRODUCTION
"First Eocene"
The "First Eocene" pay zone lies in the upper part of the Radhuma Formation, at about 1,100 feet. It underlies the Rus Anhydrite but is usually separated from it by about thirty feet of dense, marly, non-porous limestone. The full pay zone measures from 200 - 230 feet in thickness and characteristically has abaut 120 feet in two upper porous beds of 40 - 50 feet in thickness divided by a slightly less porous bed of marly limestone. The third porous bed at the base is commonly 70 feet thick.
The limestone grades from crystalline to granular, more often granular, with a calcarenitic appearance. It tends to be marly and shaly and often has considerable amounts of anhydrite infilling the porosity and contaminating the limestone.
Porosity in the better pay zones is high, ranging from 30 to 351.. The development of the reservoir is very irregular, good wells being offset by very poor ones. Generally the porosity becomes poorer to the north and west, and it can be seen from the map (Fig. 3) that in the north extension and the west feature there are many dry locations higher than producing wells on the eastern flank of the field. All the wells produce brackish water in varying amounts and a very large number of the wells are on pumps.
The oil averages 190 API and contains 4.43% sulfur. The total possible productive acreage is approximately 23,000 acres and the accumulated production for this reservoir up to July 31, 1967 was l26,36l,39O barrels.
"Second Eocene"
About 1,000 feet below the "First Eocene" lies the "Second Eocene" pay, very similar to it and underlying another thickness of anhydrite beds. The so-called "Second Anhydrite" is much thinner than the "First Anhydrite", being only about 100 - 120 feet thick and containing some limestone interbeds
107 and sometimes enough porosity in the basal beds to carry Some oil. How ever the "Second Eocene" reservoir starts about 130 - 140 feet below the base of' the anhydrite in most of the field and is overlain by denser marly and shaly limestone which serves as a seal.
The lithology of the "Second Eocene" reservoir is much like the "First Eocene" and is generally tan, loosely aggregated, granular lime stone with varying amounts of marly limestone and gypsiferous limestone. It is commonly from 160 - 180 feet thick, having much the same appearance of the upper part of the "First Eocene" with an upper porous bed of 60 - 70 feet thick, a lower porous bed of about the same thickness and a less porous Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021 middle zone of some 30 feet thickness.
It has an erratic distributio,n of permeability but not as extre.ne as the "First Eocene" limestone reservoir. From an examination of the map (Fig. 4) it can be seen that there are four separate areas of production. The western area is separated from the main area, probably by a fault,since the pay in the western area is immediately below the "Second Anhydrite" and the underlying beds, correlative with the producing beds to the east, are wet.
The main central area is separated from the southeastern segment by a broad band of relatively impermeable, marly development in the pay zone and wells tested in this area have produced small amounts of oil and water. The main area produces some water, but much less than the "First Eocene", while in the southeastern segment large amounts of water are produced.
To the north a small area has been found to be productive economi cally, with a much larger area existing in which potentials are low, and water cuts are high. The total productive acreage is approximately 20,000 acres. The average porosity is from 25 to 30% and the gravity of the oil is 200 API with sulfur content of 4.43%. The total accumulated production for all the areas to July 31, 1967 was 145,381,076 barrels.
High on the structure in the northern part of the field there is a minor development of porosity in the very lowest Eocene, about 300 feet below the base of the "Second Eocene". One well has produced 505,527 bar rels from this zone but is now plugged back to the "Second Eocene".
''Maestrichtian''
In the top of the Cretaceous Tayarat a very erratic zone of porosity 1sdeveloped in brown, granular to dark brown crystalline limestone. This zone has been tested over the field in various places and has produced in two wells in the northern part of the main central area, and in four scattered wells in the southern part of the main area. The total accumulated production to July 31, 1967 was 4,241,562 barrels of oil.
"Burgan" (Wara)
The "Burgan" reservoir consists of that part of the original "Burgan" above the thin Mauddud Limestone, and is called "First Burgan" in field usage. Its proper stratigraphic name is Wara Formation. It consists of 160 - 200 feet of sand, siltstone and shale, with the main development of sand usually being found in the middle part of the section. In som~ parts of the field it can be divided into three members, with the upper member being quite thin, 10 -
108 IS feet thick. However, it is highly lenticular and in places merges into a massive single sand. It is highly laminated and lignitic in some parts and appears to be a deltaic deposit. The wells all produce Some water and there may be independent water levels in some sand lenses. The average porosity of the pay sand is 29% and the gravity of the oil is 240 API. Sulfur content is 3.0%. Productive acreage is estimated at 14,000 acres. Production to July 31, 1967 has been 137,283,238 barrels.
"Ratawi" The reserve in this reservoir is larger than any of the other
three main reservoirs, due mainly to its uniform development and fairly Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021 large areal extent, being larger than the Burgan but smaller than the Eocene reservoirs. The overall porous section approaches 700 feet in thickness and some of the highest wells have over 300 feet of pay thick ness. The average is about 200 feet. On the southwest flank of the struc ture two wells have encountered tight oolitic facies and are completed in the poorly developed, somewhat fractured Ratawi Limestone section, and several of the lower wells on the flanks have a small amount of lower Ratawi Limestone section open. It is thought that the facies change is regional, since the EW-S, an isolated well very low on structure at the north end of the East Wafra nose, recently found good oolite porosity, refuting the for mer idea that the entire flank area was tight.
The average porosity of the pay zone is 20 to 23%, and the gravity of the oil is 24.So API with a sulfur content of 3.6%.
Some of the wells are on the pump, although still producing a sub stantial volume of oil. Very little water is produced from this reservoir. The producitve area for this reservoir is estimated at 20,000 acres. The total production from this reservoir to July 31, 1967 was 170,481,074 barrels.
FUTURE DEVELOPMENT
Although the general limits of production are established, there are still some areas thinly developed, especially in the "Burgan" and "Ratawi" reservoirs, and the East Wafra sector can be developed for both "Ratawi" and "Burgan" and the southeast sector for "Burgan". The several wells drilled to the Jurassic have not been successful and it is not believed that those beds constitute a reservoir in the Wafra Field.
ACKNOWLEDGEMENT
The permission and encouragement of the management of the American Independent Oil Company to compile and present this paper is appreciated. A large debt is acknowledged to the previous geologists who have worked in the Neutral Zone and upon whose labors most of the data in this paper is dependent.
109 Illustrations
Figure 1: Index map of Kuwait-Saudi Arabia Neutral Zone.
Figure 2: Stratigraphic column of the Wafra Field.
Figure 3: S true ture map on top of "First Eocene" pay.
Figure 4: Structure map on top of "Second Eocene" pay.
Figure 5: Structure map on top of Wara (First Burgan) pay. Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021
Figure 6: Structure map on top of Ratawi Oolitic Limestone pay.
110 KiC \,..'(A. AM£RlCAN IMl£PEND£NT OIL CO. NEUTRAL ZONe: SCAlf:: I: 400,000 "---.
\ G",AYA _ I ~ Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021 "'DCJ~ I.e ...... ,""\ ......
95C OCO
N E U
~"'';t'C Z 0 N E LOC. ~~ ... - ,.J .sc.... ,·, o ..-J
Figure 1: Index map of Kuwait-Saudi Arabia Neutral Zone.
111 STRATIGRAPHIC COLUMN WAFRA EIELQ ~UWAIT - SAUDI ARABIA-NEUTRAL ZONE TIME DIVISIONS ROCK UNITS APPRO< AGE STAGE GROUP FORMtmON Aao TERti DEPTH THICKt6S DESCRIPTION KEY FOSSILS RECENT PLEISTOCENE SANO;CLAY. AND 'RESH W.TtR KUWAIT SURFACE BEDS 200- 250 FT. PLIOCENE KUWAIT LIMESTONE. MIOCENE UHC()tilfOtlll.. TY LIMESTONE. TAN TO WHITE. CRYSTALLINE TO FINE GRAfNLAIt. ... LUTETIAN DAMMAM UPPER f.OCEN£ LM!I 250 FT. eoO-700FT. CHERT LAYE* AT TOP, ...... 'Tt
-' Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021 g SH.u.E AT ,"SE NU ...... '1'!S OISCORBINUS I ST EOCENE ANHYDRITE; wITH M'NOR 'Z 790 FT. 250- 3eoFT. EOCENE RUS ANHYDRITE LIMESTONE ANO SHALE - HASA 1St EOC£N£ UoIS. 10110 FT. 700-750FT. i:::~~,;rc: ~~O~SARLY a: ... 11175 FT. 110-120 FT. ANHYORIT£" AND ANHYOfUTIC ~=Y~~:fiN~ LIM(5TO"£ ST'UNGEAS. I 0• -' 2 NO EOCENE I.MS. 2020 FT. ~-4eOFT. "- RADHUMA =~~~~~5:;~g:~ R.L. MARKER 2350 FT. 10- 20FT. LIM€STOHE".SHALY FOSSIL FLOOO AOTAC," SP, I..OCI
Figure 2: Stratigraphic column of the Wafra Fiel·d.
112 WAFRA FIELD Kuwalt- Saudi Arabia Neutral Zone Top of "First Eocene" Pay C.t.• 25'
o 5.000' IO,OIV' I. I I Iii I Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021 PH.N Oct. 1967
j-
-550
• . :0:-. .. : • . -425 . •'. .----.----'; .. _- • •
Figure 3: Structure map on top of "First Eocene" pay.
113 WAFRA FIELD KUWOlt- Saudi Aroboo-Neutral Zone Top of "Second Eocene" pay C.I .• 25' Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021
.!,V•• c.
§ .2
Figure 4: Structure map on top of "Second I:ocene" pay.
114 - WAFRA FIELD KuwaIt-Saudi Arabia Neutral Zone Top of Wara (First BurQan) Pay c.t. -50' Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021
Fi gure 5: Structure map on top of Wara (First Burgan) pay.
115 WAFRA FIELD Kuwait- Saudi Arabia Neutral Zone Top of Rotowi
Oolitic Limestone Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021 ') C.l. = 50'~.: ! ill! P Ii N. Oct. 1961 ')90,' l\,.
9At.C,tC,
96'-.0(,,(.
..) u u. 8 0" ~ .. "'I ..
Figure 6: Structure map on top of Ratawi Oolitic Limestone pay.
116 COMMENTARY
E.W. Patterson, Kuwait Oil Company, Ltd.
I have throughly enjoyed the privilege of reading the paper
"Wafra Field - Kuwait Saudi Arabia Neutral Zone", by Mr. Paul H. Nelson. Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021 I found this paper interesting and informative.
Being familiar with the situation just north of Wafra in Burgan field it has been very instructive to compare the two areas and to note the similarities and differences between the two areas.
In Burgan for example the Ahmadi shale is always present. The shale here has formerly been referred to as "Caprock Shale". We dropped the term and incidentally would suggest that at Wafra where it is missing in structurally high positions the term "Caprock Shale" seems to be even less appropriate.
A more interesting point brought up by Mr. Nelson is the matter of the unconformity at the top of the Sadi. In the north we have assumed that there is an uncoformity at the base of the formation but we have never seen proof of an unconformity at the top. Could Mr. Nelson elabo rate on this point and indicate what evidence there is at Wafra for this post Sadi unconformity.
Another minor point that might need clarification for some geologists not entirely familiar with the area; Mr. Nelson mentions the now obsolete term IIFirst Burgan Sand" and the terms IIThird and Forth Burgan Sandll still in use, but does not refer to the IISecond Burgan Sand". ll This of course is the sand now referred to asl~ower Wara Sand • Is this sand present at Wafra?
These are very minor points, and I agree entirely with the overall geological picture that has emerged from Mr. Nelsonls paper which I think is a most valuable contribution to the understanding of the geology not only in the Neutral zone but also north of there.
117 DISCUSSION
Question by E.W. Patterson of Kuwait Oil Company. Ltd.
What evidence is there at Wafra for a post Sadi unconformity?
Answer by P.R. Nelson
The evidence for an unconformity at the top of the Sadi consists in a very variable section although truncation cannot be clearly Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021 proven.
Question by E.W. Patterson of Kuwait Oil Company, Ltd.
Is the "Second Burgan Sand" now referred to as the "Lower Wara Sand" present at Wafra?
Answer by P.R. Nelson
The term "Second Burgan Sand" is not used at Wafra because the entire interval of "First" and "Second" Burgan Sand is now called Wara. The sand is not easily divisible although in some areas a thin (10-15) sand was formerly called "First Burgan" Sand. Due to the erratic nature of the deposit, it is not considered practical to subdivide it.
Answer by P.R. Nelson for comment made by E.W. Patterson
"Caprock Shale" is not used as a formational name but merely as a field term. The section where present on the flanks is called "Ahmadi Shale".
Question by R.R. Robie of Atlantic Exploration Company
It is noted that locations made on the early geophysical work appeared to be slightly off structure. Ras more recent digital, stacked seismic work managed to clarify the structure? There appears to be a real possibility that similar structures to Wafra could exist.
Answer by P.R. Nelson
Geophysical picture now conforms well with areas where well control is available.
Question by E.P. DuBois of Esso Exploration, Inc.
What is the source of the Eocene oil?
119 Answer by P.H. Nelson
We have no certain knowledge on this point. It is possibly from shaly beds to the north and northeast, or, since the beds are often quite marly the source may be local.
Question by E.P. DuBois of Esso Exploration, Inc.
Is there asphaltic staining in Burgan Sands?
Answer by P.H. Nelson Downloaded from http://onepetro.org/SPEMERM/proceedings-pdf/68SAM/All-68SAM/SPE-2371-MS/2063160/spe-2371-ms.pdf by guest on 27 September 2021
There is no appreciable asphaltic residue or tar in the Wara (First Burgan) sands in the Wafra field. However, in the higher areas to the southwest, South Fuwaris field and Humma prospect the Wara is heavily impregnated with tar.
120