WAFRA FIELD Kuwait-Saudi Arabia Neutral Zone Top of Wara (First Burqan) Pay C.T
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sPc- d.37/ 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.