.1'!IS IS AN ORIGINAL KAWSCRIPT IT }(AY NOT BE COPIED WITHOUT TBE AUTiOR'S P~ISSIOi GEOLOGY OF SAUDI ARABIA Approved: ApDroved: Dean of the Graduate School GEOLOGY OF SAUDI ARABIA THESIS Presented to the Faculty of the Graduate School of The University of Texas in Partial Fulfillment of the Requirements For the Degree of ·MASTER OF ARTS :By Abdulla Homoud Tariki, B.S. Austin, Texas August, 1947 r-.. u.. - 0 rt:: o· :c ~-­ < ~ ....... ~ O' N r e; ::z: 11IE LIBRARY '.fHE UNIVERSITY OFTEXAs TABLE OF CONTENTS - Page Abstract • • 7 Intr oduction • 9 Location and General Features of Saudi Arabia • 10 Acknowledgement . 13 Genera.1 Discussion of Cretaceous and Tertiary Stratigr a.phy in Arabian Peninsula and Adjoining Areas Upper Cretaceous Aruma formation of Saudi Arabia . . . . 14 Equivalent strata in adjacent area • . 15 Eocene Eocene in Saudi Arabia • • • Eocene outside Saudi Arabia •• 18 • • 0 • • • • • • • • Oligocene •••• . . . . . . . . . • 19 Mari ne Neogene (Miocene and Pliocene) . • • 19 Hadruck Formation . . . 20 Dam Formation (Miocene) . . . . . . . 20 Hofuf Formation (Pliocene) • . . . . . • • • 21 Continental Neogene 21 ~uaternary ••••• • 22 Dibdiba gravels . . . • 23 Summan limestone • 23 • • • • • • • • 0 • • • • • • • • Geology of Saudi Arabia Historical review • . • • . . . . • . . • . • . • • • • • . . •• 26 Northwestern Saudi Arabia Physiographic features . . . . . . . . . . . . . 26 riiC. 624 3 TABLE .Q! CONTENTS, CONTINUED Pag e Northeast region . . . . . . . . . . 27 Southwest region • . . . . . . 27 Tubeiq Escarpment . . . . . . . . . . 27 Origin of Wadi Si rhan and Great Nufud . . 2S Oambro-Ordovician (?) (Uyu.m Formation) . . . . 29 Lower Jurassic (Mustawi Formation) •• 29 Jurassic-Cretaceous (Riyadh (7) Formation) .. . . .. . . . 30 Lower Cretaceous-(Wasia Formation) 30 Upper Cretaceous • • • 30 Eocene of Northwestern Saudi Arabi a 30 Contine.ntal Neogene 31 iocene (Sirhan For mation) . . . 31 Lower marl member . . . . . . . . . . . 31 Garaiyat l avas • • 32 Upper sandstone member 32 Quaternary (?) Harra Lava s • 33 Stratigraphic Sections of Upper Cretaceous , Eocene, Neogene, and Quaternary Strat a Along Wadi Al Batin and Wadi Aruma in Saudi Arabia Upper Cretaceous Section Eocene Section • Structure of the Ar ab ian Peni nsula . . . . Geological History • • • • • • • . •••• Oil Development Structural features of the Saudi Ar abian side of t he Persian Gulf • • • • • • • • • 0 • • • • • • • • • • • • • • • • 47 TABLE OF COlifTENTS, CONTINUED Dammam Dome • Abqai q Dome • J3ucaqa Dome • Q.atif Dome Ma1Aqala Structure Abu Had.riya Dome Structural Feature in lTorth Saudi Arabia El Jauf Structure • Reservoir Characteristics of the oil fields in the Persian Gulf region of Saudi Arabia Dammam Field Abu Had.riya Field • Abqaiq Field Q.atif Field • :Bibliography Vita Page 48 48 50 50 51 51 52 53 56 56 57 59 61 Figure l 2 3 4 5 6 7 g ILLUSTRATIONS Page Index map • • • • • • • • • • • • 12, Geological map of Saudi Arabia •••• 17 Composite columnar section of U_per Cretaceous • . . . . . . . ' . . . . . .. .. . 35 Ideal section. Profile across t wo drainage lines • • • . . . . . . . . . . . . . . 25 Geological map of ~orthwestern Saudi Arabia ~ ••• . . . . . . . . . . . Structural sketch of the Arabian Penin­sula and the surrounding countries • Structure locations in Eastern Saudi Arab ia . . . . . . . . . . . . . Diagram of well completion p~actices, Arab zone, Damm.am Dome 55 6 THE LIBRARY THE UNIVERSITY OF TEXAS .ABSTRACT Saudi Arabia is readily divisible into t wo geological provinces. The western area consists of crystalline i gneous and met amorphic rocks, of presumed Pr e-Cambrian age, topographically and structurally ' sloping to the northeast, east and southeast. The eastern area has ea sterly dJpping sedimentary rocks overlying t he basal i gneous and metamor-phic complex. These sediments consist of Paleozoic, Mesozoic (nearly complete section) ,--'lle.rtiary, and Recent de­posits. The area is subdivided into Nejd and Hassa (Persian Gulf) sub-provinces . The eastern parts of Nejd subprovince consist of sedimentary rocks, ranging in age from early Paleozoic to early Eocene. These sediments con­sist of alternating calcareous and elastic facies. Differences in the relative resistance of these rocks are responsible for smooth, gently di ping slopes to the east, on the one hand, and truncated west-facing escarpments on the other. Examples of these resistant rocks are found in the Jurassic strata of the Tuwaiq Mountai ns which extend in a north-south direction. Another example is the Aruma Plateau, capped by resistant limestone of Upper Cr etaceous age. There is an absence of marked alti­tudinal variations in the Nejd sedimentary rocks, and, hence, the rather uniform homoclinal dip has been preserved. In the Hassa subprovince the outcrop~ing rocks are limited to the Tertiary and later; these include the lower and middle Eocene, and Miocene to Pliocene. The Eocene rocks are al most entirely calcar eous, except ' One local anhydrite member on the coast of the Persian Gulf. The Miocene and -Pliocene strata are pri marily continental depo sits, except 7 g for some intercalated marine beds. The latter are composed of marls, clays, sands, and thin limestone, and they cover the Eocene sediments in most of the Hassa Province. INTRODUCTION The Department of Geology of the University of Texas suggested the research problem which is the subject of this paper. Little information dealing directly with the area in question has been found in t he few available sources. The writer communicated with Mr. James Terry Duce, Vice-President of the Arabian American Oil Company, Washington, D. c., who kindly fur­nished company reports and maps which have served as the chief sources of information. Consistency in using only one unit of measurement was not possible since the sources of information included both metric and English units. To insure as .much accuracy as possible the author felt it best to leave the units as stated in the sources. The writer regrets that he is unable to give a detailed description of the geology of Saudi Arabia; this part of the world has not been studied to any great extent. However, he has attempted to give as de­tailed a survey of the geology, structure and oil reservoirs of the region as available sources of information will permit . 9 LOCATION !fill GENEF..A.L FEATUF.ES fil: SAUDI .A.RA:BIA Saudi Arabia occupies most of the Arabian Peninsula. It has an area of about 865,000 SQuare miles. Saudi Arabia is bordered by the Red Sea on the wes t, Trans-Jordan and Iraq on the north, Kuwait Principality, Persian Gulf and Qatar Peninsula on the east, and on the south by Yemen Kingdom, Hadhramaut, and Oman Provinces . Saudi Arabia consists of five provinces. These are: Hejaz where Mecca and Medina, the Moslem's Holy Cities are located; Assir, south of Hejaz, a raised plateau concerning which little geological information is avail~i,ble; Nejd, the center of Arabia, a high, sandy plateau where most of the Arabian tribes live; and Hassa or Persian Gulf Province which has become t he most i mportant par t of Saudi Ar abia because of the discoveries of the huge oil reservoirs under its soil. Saudi Arabia generally is bar ren, a large port ion being covered by sand dunes and rocky regolith. The "backbone" of the Arabian Peninsula is the Tuwaiq Mountain chain, extending, in general, in a north-south direction. The.sand dunes of Dahna roughly parallel the mountains, and there culminate i n the great field of sand dunes of the north and south, I kno n as Great Nufud and Rub Al Khali, respect ively. Saudi Arabia is about seven hundred miles wide, measured from the Persian Gulf to the Red Sea. Extendi ng from the shore of the Persian Gulf westward for a distance of about 50 miles is the east-facing Oqair escarp­ment , exposing Neocene beds. One hundr ed miles farther west is the edge of the eastern margin of the Dahna sand ridges. Near this area most of the Eocene exposures are found. Another hundred miles ·:est wa.rd are the Dahna sand dunes and the great west-facing escarpment of the Aru1na (300 T"tl 10 meters high and Goo kilometers long) • Still another hundred miles to the west, the pre-Cambrian terrane occurs. (See figure 1.). 12 BEA NE N :lm1e A l f'IJO Figure 1 ACKNOWLEDGEMENTS The writer is deeply grateful to Dr. Hal P. Bybee, Dr. Don L. Frizzell, and Dr. R. H. Power who so kindly served as a thesis com­mittee and offered valuable criticisms and suggestions. Appreciation is also expressed to Mr. Arthur H. Deen for his gracious assistance a.nd guidance. Many of the maps and reports were furnished by the Arabian . I ~ Am~rican Oil Company for which the author wishes to express his sincere appreciation. 56b624 13 GEN.El.BAL DISCUSSION 0]' CRETACEOUS AND TERTIARY STRATIGRAPHY IN ~ ARABIAN PENINSULA !@. ADJOINING AREAS1 Up;eer Cr etaceous Arurna formation of Saudi Arabia: On the Arabian Peninsula the Upper Cretaceous.Aruma f ormation consists almost entirely of well-bedded, grey to greyish-tan, fine to medium grained fossiliferous limestones. The formation ext ends east of Laila in central Ar abia to the northern borders of Syria and Palestine. The northernmost point in Sauid Arabia at which this formation was measured is at Taisiya Plateau east of great Nufud. The thickness here is about 272 meters (See figure 2). In a southerly direction the thickness of the exposed section gradual ly decreases, and at a point east of Laila, just before this formation is overlapped by the Neocene Continental beds, it has thinned to about 22 meters. The Aruma formation is apparently ab sent in Hadhramaut in South Arabia, but the approximate equivalent of it is found in Dhufar and in the Oman range. (See figure 2) . A deep-well section of the coastal region also yielded evidence of a thinning of the Aruma formation in a north-south direction. For example, the thickness of the for mation in Dammam on the coast of the Persian Gulf is 261 meters, whereas, at Abu Hadriya to the north, it is 569 meters thi ck. (See fi gure 7). 1 . The material presented. in this part of the thesis was furni shed by the Arabian American Oil Company. (General Discussion on Cretaceous and Tertiary Stratigraphy on the Arabian Peninsula and Adjoining Ar eas.) 14 Eguivalent strata in adjacent areas: Lees and Bichardson2 reported that the Upper Cretaceous section in Western Iran consi sted of about 5,000 feet of normal marine sediments and over 10,000 f eet 1here the elastic facies is 'developed. Lees also reported the presence of the Upper Cretaceous in Oman3 and 4 Dhufar provinces in South Arabia. He did not give the exact thickness of the formation, but they are known to be less than those of Iran. Cretaceous5 sediments crop out i ntermittently along t he east coast of Africa from the Gulf of Aden to as f r south as Kenya. Upper Cretaceous limestones resting on ancient crystalline rocks are found on the island of Sokotra. Cretaceous beds also cro'P out in eastern British Somaliland; the thickness of those strata is ap roxi mately 1, 50 feet. In Palestine, Lower and Upper Cretaceous beds were found. The Lower Cretaceous, consist ing of about 300 feet of mostly sandstone, overlie a poorly reserved Upper Jurassic section. The upper portion of the Cretaceous (Cenomanian and higher) has a thickness of about 800 meters, ' and i t consists mainly of limestone. In Lebanon, Upper and Lower Crete.ceous strata have been identified. The Lo~ er Cretaceous, ( eocomian-Apt ian-Albian) has a thickness of about 600 meters. The Upper Cr etaceous, incl uding strata of Cenomanian and later age in the central Lebanon Mountains, consists of 4,000 feet or more of well-bedded limestone and chalk. These Cretaceous beds decrease 2t ees, G. M., and Richardson, F. D. s. Geol. Mag. No. 77 no. 7, p. 233. 3tees, G. M. Geol . and Tectonic of Oman and of parts of Southeastern Ar abia. ~uaternary Genl . Soc. 1928, p. 607. 4rtid, p. 605. 5Arabian Amer ican Oil Company report (general description of Creta ceous and Tertiary, p. 2). in thickness toward the east, where they are l ess than 1,000 feet thick in the Ruba district west of Iraq. The thi ckness and chara cter of the sec­tion in the Ruba district seems to be similar to the Upper Cretaceous sec­tion (Aruma formation) on the Tai siya Plateau, Saudi Arabia, where it measures 272 meters. As previously mentioned, the Upper Cretaceous reaches its maximum thickness in central and western Iran where the section consists of about 5,000 feet of marine deposits and 10,000 feet of elastics. The Lower Cretaceous in central Iran has a t hickness of about 3,0006 feet . Eocene Eocene in Saudi Arabia: The Eocene beds of Saudi Arabia consist predominantly of limestone, although more than 300 feet of anhydrite is known on the Persian Gulf Coast between the Abqaiq dome and the Kuwait Neutral Zone. In the interior, the Eocene consists almost entirely of light grey to light greyish-tan, fine to medium grained limestone. In many places a large portion of this formation is crystalline limestone. The section is rather diff icult to measure because of its massive character and very low dips. The total t hickness of a section in the Ma 1Aqala dis­trict is 715 meters. From Ma'Aqala southward the formation thins grad­ually. In Wadi Sahaba the thickness is 160 meters. South of Wadi Sahaba the Eocene strata are overlapped by the Neogene deposits. North of Ma'Aqala the thickness of the Eocene beds measured in Wadi El Eatin is 6 The Arabi an .American Oil Company report (general discussion of Cretaceous and Tertiary in Saudi Arabia and adjoining areas, p. 4.) . Goroivo\ • 3z• \ \ \ 31· 29• \ \ \ '...___ ......_ /-­-\---------~ \ (I -\ \ \ /I \ /(\\.,,\ \ \ \ "'"'"'*"''"''' I\ ~\\ \ \ ' \ G R N E A T E f u ' 31 • GEOLOGICAL MAP of NORTHWESTERN PART of SAUDI ARAE>\A m:J Con\inen\ol Neoge.ne From Arabi am Amen can 0 ii Company Terliory to RecQ,nt Volcanic& ITJ with change ~M1oc12ne Scale CTLl EocQ.nQ, Upper C re laceou5 (A rumo) Kilomele rs ~ 0 IO ZO 40 Lower C relac eou&(Wo'i'>io) ~ ,· ·, J'I •' I 0 10 1 ' ~'o L ov1 .•, Ca r:i b ro-0 rdovic ia n(Uy un) v lliJ · · . : Pre,-Carnbr'1on( lgne,ou5 Mefo morph;c) . t'" ~ O> . 0 <"i 0 c: 0 ~ 0 E o L E -o ;r;,.()' cU~t 1-~rn1 1:4 H) Figure 4 Northeast region: The drainage which extends from .Anaza southward divides this area into eastern and western regions. The eastern area is char acterized by the presence of numerous , intersecting wadis forming a dendritic pattern; the drainage is northeastward to the Tigris-Euphrates Valley . In the western region, the wadis are shorter and deeper, but out dendri tic pattern; these drain south ·estward to Vfadi Sirhan. The under­lying strata of the northeastern territory consisting of limestones, sand­stones and shales are of Eocene age; the dip is northeastward. Near Wadi Sirhan the sediments are covered with basaltic lava of probable Quaternary age . Southwest re~ion: The main topographic features of this region are due in large part to the erosion of low-dipping sediments ranging from Cambrian to Miocene in age.. Three prominent, southwest-facing erosional escarpments have been developed, namel y, the Sirhan, the Tubeiq, and the Tai ma. The Sirhan escarpment extends from near Q.asr Asaraci in Trans-Jordan to the vicinity of Jau Muraira in Saudi Arabia, a total distance of over uoo kilometers . The strike from the northernmost point , near l atitude 300 degrees north, is approximately 40 degrees west of north, South of this point, however, the strike changes abruptly to one almost due east. East of Jau :Muraira, a lower escarpment continues in a northwestern to southwestern direction, thereby forming the southwest facing cliffs which vary in hei ght from 200 to 250 meters. Tubeiq Esca:i;:Ement: It extends from the southern border of Trans­Jordan to the western margin of the Great Nefud, forming a conspicuous south-facing escarpment for a distance of almost 300 kilometers. There is reason to believe that this escar-oment continues under the Great Nefud Dunes, and is continuous ith one of the escar ments est of Dahna . The average height of the Tubeiq escarpment is about 200 meters. The third escarpment is kno'l'm as the Tai ma; it extends from the northern side of the town of Taima northwestward for a distance of about 250 kilometers. Like the Sirhan escarpment, it trends approximately 40 degrees west of north from Tai ma, but near Tai ma t he direction changes to an easterly one; the height is anout 225 meters. With the exception of the presence of several wadis which trend northeastward, the area between the Sirhan and the Tubeiq escarpments is a uniform, flat plain rising gradually to form with the Sirhan escarpment the Wadi Sirhan. Therefore, Wadi Sirhan is partly structural and partly erosional in origin. The surface between the Tubeiq and Taima escarpments i s quite dif­ferent from that previously described. It is dotted.with rounded hills and hillocks forming a conspicuous feature of this area. Some of these hills are brightly colored in shades of purple and red. South of the Taima escarpment, and extending eastward to Hail, the region is characterized by its high, flat-topped hills, such as Jebel -Arnan, and tortuous deep valleys. This ar ea is also distinguished by the presence of numerous rock pinnacles and spires, ranging from a few inches to 20 meters in height; these erosional remnants consist of bard, cross-bedded sandstones. The moving dunes kno'l'm as the Great Nufud, which occupy an area of about 50,000 square ki lometers, are notable because of their huge, conical shape. The dunes on the est and southern margins of this terrane range in color from light yello ,; to broi, n near the town of El Jauf, but south of the Tubeiq escarpments, the color becomes bright red, and east of Taima, the color again becomes li ght yellow to brown. Origin of Wadi Sirhan and Great Nufud: The orient ation and form of the sand dunes of the Great Nufud i ndi cate that the direction of the prevailing wind is from the west. The light yellow to brown colors of th ese dunes, near El Jauf, and Sak:aka., and t heir bright red color south of the Taima escarpment give reason to believe that the wind carries these sand grains from the weathering sediments of the Wadi Sirhan escarpment and from the Mustawi formation. Therefore, one can safely say that the Great Nufud and Wadi Sirhan which receive many streams but which have no outlet to the sea (See map), ar e due to the disintegration and erosion of the strata in Sirhan region and the concentration of the derived material in the great Nufud area. Cambre-Ordovician\?) (U;z:;.m Formation): A striking change in lithology appears near the l ower margin of Taima escarpment. The rocks in question consist of white and red cross-bedded sandstones intercalated with green and red, sandy clays. These beds are characterized by the presence of joints filled with iron oxide. In places at the surface, large irregul arly­shaped boulders of almost pure hematite can be found. No fossils have been obtained from the Uyum formation. The thickness of this sequence south of Taima is unknown, but the presence of similar lithologic materials in ex­cess of 300 meters in the nearby mountains is reason for assuming a thick­ness of a.t least this figure. Lower Jurassic (Mustawi Formation): A thick sequence of Lower Jurassic sediments (Mustawi Formation) was found in the lower margin of Jebel Tubeiq_. The sediments consist of dark red to purple, cross-bedded sandstones and shale. The contact with the overlying Eocene marls and limestones is un­conformable. The Eocene beds dip only slightly to the northeast, while t hese beds show a more pronounced dip in the sci.me direction. Similar beds are found all the way from the Tubeiq Escarpment to the Taima Escarpment, a distance of from 50 to 200 kilometer s . These 'beds are unfossiliferous, but their similarity in lithology to the strata of the Mustawi formation is cause for their being assigned to the Lower J urassic. Jurassic-Cretaceous (Riyadh (?) Formation) : Strata which might be re­ferred to the Jurassic-Cretaceous ma;y be found at the base of the cliff upon which stands t he Fort of Jauf . They consist of several meters of hard, white, siliceous limestone and gray shales. These beds are unfos­siliferous. Since they underlie the Wasia strata and are lithologically different, they might be considered. to be the equivalent of the Riyadh ' .. fo r mation. Lower Cretaceous-( fasia Formation): Between the towns of Jauf and Sakaka, a thickness of approximately 200 meters of white to red, coarse, cross-bedded sandstones and shales are known. With the exception of numerous fragments of silicified wood, these beds appear to be entirely unfossiliferous. They are probably of continental origin. Small, spheri­cal, iron oxide nodules occur abundantly in some parts of the formation. The reference of these beds to the Lower Cretaceous is based entirely on li thologic similarity to beds of known stratigraphic position in other areas. Upper Cretaceous: Near the northern rim of the ivadi Sirhan, north of t he town of Sakaka, a considerable thickness of rather massive clif.f­formi ng limestone is found. These bed.s are unfossiliferous, except for a few unidentified marine fossils. The fossils furnish no definite evidence as to the age, but from lithologic evidence this formation might be classi­fied as Upper Cretaceous (Aruma formation) . The Arum.a formation of the Wadi Hauran in quite similar structurally and lithologically to these strat a . Eocene of Northwestern Saudi Arabia: The northwestern part of Mejd province, which is considered geologically as a part of the Syrian Desert, is mostly underlain by limestone, of probable Eocene age. The exact thickness of these marine sediments is not known, but it is somewhat less than that of the Eocene known in the Persian Gulf province. In Wadi Mejinah (fossil locality s-75o)( See map) some poorly pre­ served specimens of Qperculina cf. complanata Defrance and Amphistegina (?) sp. were found. At J ebel Tubeiq, a thickness of approxi mately 100 meters of predominantly marl and silicified limestones was measured. A 1 small species of Nummulites was collected from the upper portion of the sili cified lil!lestone; Venericardia was found in the lower marly part of this sequence. These give little evidence regar ding the exact age of the strata, but are strongly indicative of the Eocene. 9ontinental Neo~ene: At J ebel Debusa, near the bou..~dary with Iraq, a considerable t hickness of continental deposits rest upon marine lime­ stone. Its age has been determined from fossil leaf impressions. On the basis of the probable occurrence of Schi zaster parkinsoni i n the Sirhan forma tion, the ne rest equivalent in the Persian Gulf region would be the Dam formation. Miocene (Sirhan Formation) : In the northern part of Wadi Sirhan, near Garaiyat, is a section of sedimentary rocks which gently dip toward the east. The formation, in its lower part, consists of sandstone over­ lain by basalt. The basalt is overlain by thin-bedded sandstone. On the eastern rim of Wadi Sirhan t he u per members ar e covered by the Harr a Lavas. The average thickness of this section is about 150 meters. The entire seauence is called the Sirhan formation. It has been divided into (a) lower marl member, (b) the Garaiyat lava, and (c) the sandstone member . Lower marl member: At the type locality, the base of this member is not expo sed. Here the strata consi st of from 10 to 30 meters of folded white, sandy marl. A short distance to the east , the upper sandstone member rests unconformably.upon this member. Similar beds can be traced south and ,rest of the type l ocality. The fossils found in this member consist mostly of echinoids. The following species have been identified: Scutella sp ., Schi zaster, pro­bably £arkinsoni Defrance, Agassizia near scrobiculata Valen., and Erissoides (?) sp . near E. meliteses Creq. Garaiyat lavas: The middle member of the Sirhan formation has been studied on the small hill near t he northern exposure of the Garaiyat out-. crop. At this locality a section of 35 meters in thickness highly weathered, olivine-bearing basalt, rests upon the lower marl member. Near the middle of · the sequence, these lavas are traversed by thin aplite dikes, and in some place an amygdaloidal phase can be f ound. The presence of basalt boulders in the conglomerate at the base of the upper sandstone member may indicate a considerable erosion 1 interval before the deposi­tion of the upper sandstone section. The Garaiyat basalt can be easily di stingui shed from the Harra ba salt, since the later is very resistant, while the Garaiyat is relatively soft. A few kilometers ~ est of the type locality the Garai yat the lavas are reduced to a meter in thickness and ul timately disappear. The north­south extent of these Miocene lavas is not known. Upper sandstone member: The upper member of the Sirhan formation consists of fine, light brown to white, calcareous sandstone, with a few meters of secondary gypsum near the top of the section. The thickness of this member i s about 65 meters. Northwest of Garai yat, brown argillaceous sandstone appears in the section. This member can be easily traced north and south of the Wadi Sirhan rim. The cap rocks of the higher margins of the western rim of Wadi Sirhan may be equival ent to this member. Quaternary (?) Harra l avas: Al ong the northeastern rim of Wadi Sirhan an extensive series of olivine-bearing basalts occurs. At Jebel Umm Wu'AL to the northwest, the 1ava cover has been removed and sediments of probable Eocene age are exposed. The thickness of the lava is about 100 meters; the flows are transversed by numerous, thin aplite dikes. Northeast of Garaiyat near the border of Tr ans-Jordan in the Jebel Misma region, the lava forms conspicuous pea...~s such as Jebel Abu Rasain. STRATIGBAPHIC SECTIONS Q! UPPER CRETACEOUS, EOCENE, NEOGENE, ~9VATERNARY STF.ATA ALONG WADI AL BATIN .AND WADI ARUM.A IN SAUDI ARABIA ll Upper Cretaceous Section The information available is shown in graphic form in figure 3. This section is 290 meters thick, divided into four different zones. The three lower zones are of limestone. The fourth and the upper one consists of shale. Eocene Section The Eocene section was measured along Wadi Al Batin between Themani and Hafer Al Batin. The lower zone consists of 172 meters of hard crys­talline limestone and grey to white, hard, silicified limestone with interbedded chert. In general, this zone contains more fossils than either of t he other two. In its upper part, Amphisorus remains were found. In the middle and the lowest portions Alveolina-bearing beds are known. The following is a detailed description of this section made by the Arabian American Oil Company. The middle zone of this section i s about 80 meters thick. It is similar in lithology t o the upper zone; more abundant but poorly preserved fossils such as various gastropods and cerithiids, with calcite repl acements occur. In the upper portion of llThese sections wer e measured by t he Arabian American Oil Company (measured stratigraphic sections at Upper Cretaceous, Eocene, and Q.uaternary along Wadi Aruma and Wadi Al Batin, Report) . 35 Ye.llou. to yello~i:.h bnow,.., si/t"5 a...... d clo.y!> 25 c:....-,fh compre$~Col ~o.~iropo4~; cc..o.J~ OJ"'d ru.distid~ . Gr~y "to Bu.ff lim«~tone. Cu '1th rou.9h c....> eoo.:fh~re d 100 I I I I I S u.rf:Ac.e _; foro..rn in'1ferc1l o..t -IJ..,c top~ ~c.h of I I I -0-,is ~t"le '10 coufered by J)a.hno.. .:;,o.nd:.. I I I I I I I I I I I I I I I, I I I I I I I I I l I I I I T~v., 6.,,c:h:Jcc::J lime:>lone. ~ith '1nter i:>edd'2d fo5sd1fe n:::>u.:> yelloc.o ma.rl~ a..V"lcl clca..y.s ~-.It preseroed _; diaql"'t 0$l1c. Upper Cr~ceou.5 -fo~si~ a.re a.loundarL lWo sepcua..t<2. horiz.ons a.re p r es......,t bo~ ca.rryi,...,9 n..o.dist.icb Cyc.lol•Te5 and o1her -form~. -~ --:­ .: :I .~ I ~~ -= 1 1 I I I I I I I I C o mpose d ch iefly ot qra.y 16 c:....> h1t12 ift\ pu.re Jo=i l1f£rou.~ Lirne.stone . th02 ba.sa.( s e c.t1on co.rricz~ 120 Ftm~onite~ a...,d £ch inoid~ . Loccdly d~udoped mca.rly zone:> bec:v CycJo/;tQ:;. a.nd t"u.d 1s-lids Total .zqo rrcter5 Figure 3 this zone the blue grey limestone commonly contains Mollusca. Most of the limestone cont ains calcite crystals . The uppermost zone of about 52 met ers consists of alternating strata of hard, soft, grey to white limestones and soft to hard chalky limestone . The uppermost part of this zone is largely unfossiliferous, although a few gastropods have been noted. Near the middle there are some traces of small fossils; in the lower portion these are fairly abundant but poorly preserved. A detailed stratigraphic section of Eocene strata along Wadi Al Batin, between The!Il8.mi and Hafer Al Batin follows. The thicknesses are in terms of meters. 4.o Hard, brown or yellow limestone. Bl ue­grey to grey, rubbly limestone or dolomite . 2 . 0 Partly covered, white, chalky, hard limestone. 2.1 Fine to medium-grained limestone. 3.5 Mostly ·1hite to grey, gastropods . hard limestone with 3.0 White, chal ky limestone. 1.8 Bl ocky weathering white to grey limestone. 5.0 Limestone stone. topped by blocky weathering lime­ 0.4 Hard, white, chalky limestone; finely porous, with traces of small f ossils. White, chalky limestone; soft, thin-be~ded. White, hard, chalky limestone ledge. 1.0 Mostly covered. 1.0 Hard, white, chalky limestone in massive ledges. 0 ~5 White, chalky limestone. 1.2 l.O Massive ledge of white, chalky limestone. 37 Alternating hard and soft, chalky limestone ; well bedded, with fairly abundant, poorly preserved fossils. 1.2 Hard,. white, chalky limestone. Elevation 422 m. 4.o Alternating hard and soft, chalky limestone. White, hard limestone, somewhat stained with manganese. o.lj. Hard limestone, locally recrystallized. 1.6 Partly covered, somewhat mottled limestones. o.6 White, hard limestone with calcite replace­ment of fossils. o.6 Somewhat soft, whitish-grey limestone. o.4 Top of ledge of blocky, hard, white to grey limestone with yellow stains; calcite lumps on surface. o.4 Shale and chalky limestone. 1.2 Chalky limestone with yellow streaks; mollusks r ather common. 1.0 Quite porous limeston~ with yellow streaks. o.s Ledge of chalky limestone. 0.8 Chalky limestone .with small cerithiid. o.6 Same as overlying. i.6 Rubbly weathering, chalky limestone with some soft members; gastropods pr esent. 2. 2 Covered. Blue-grey limestone with some yellow streaks, rubbly weathering with calcite crystals; forms a ledge; mollusks present . Covered. Base of zone of slumping. Very fine grained, somewhat porous limestone. Essentially slumped. 2.8 Alternating hard and soft chalky limestone; upper part contains gastropods. White, hard, chalky limestone with small poorly preserved, turreted gastropods. Covered. White, chalky limes tone traces; slightly porous. 0.3 Covered. l.O Massive ledge of white, geodal calcite present . i.6 White, chalky limestone, forms a prominent +edge. 1.4 White, chalky limestone, fith minute pi nk chalky limestone; nearly massive; some traces of yellow stain; upper o.4 m. contains fossils. 0.1 Softer material. White, chalky limestone with fossils. 1.2 Hard ledge of chalky l imestone. 1.0 Hard ledge of white limestone with some calcite lumps. 2 . 0 Hard, white limestone in beds roughly 0.33 m. t hick . Partly covered. Somewhat porous limestone with calcite repl acement of fossils. 1.4 Hard ledge of white limestone, with in­determinate f ossils. i.6 Hard limestone, in part porous, forming a ledge; with small and turreted gastropods. 1.5 Covered. Some~hat por ous hard limestone. 2 . 0 Hard, white bed of chalky limestone with f oraminifera.• 2.2 Massive, chalky limestone. o.8 Ha. r d ledge of chalky limestone. 2.0 Limestone, some hat porous, rubbly, capped by O.l m. of hard., yellow, massive limestone; top of def­nitely bard layers, softer and more easily eroded material above this interval; ~ith marbl e size concretions near top. 1.7 Mostly covered, but probably blue to white marly limestone. Limest'one grey to white, rubbly weathering, somewhat slumped; slightly silicilied on some surfaces; contains foraminifera. 1.5 Hard, white, crystalline limestone, with forami­nifera on weathered surface. · 3.5 Grey, crystalline limestone, rubbly weathering; coiled foraminifera in lower part of bed. 1.0 Covered. 4.o Massive, chalky limestone; top forms a bench. 3.0 Poorly exposed cream-colored limestone. o.4 Hard, cream-colored, crystalline limestone, locally replaced by l arge, ellipsoidal chert bodies. 2.0 Hard, white limestone, somewhat chalky; hill badly slumped. Alternating hard and soft, chalky limestone. 3.0 Soft, rubbly, white limestone, capped by a chert body . Hard, rubbly limestone, grey-colored; locally altered to chert. Porous, light grey limestone ith traces of small fossils. Grey, medium crystalline, hard limestone; upper portion laminated with traces of chert. 1.5 Grey, crystalline limestone with calcite lumps; local chert patches occur i n beds 0.2 m. thick, mostly confined to lo rer portion; Amphisorus present. 0.2 Grey crystalline. dolomite. 2.3 Covered. 12. 5 Grey limestone, somewhat recrystallized, rubbly weathering, with some chert in place; Alveolina beds 1 to 2 m. below top; uppermost bed partly replaced by brown chert . 4o 2.0 Cream­grey limestone, somewhat porous, with calcite lumps ; numerous poorly preserved fora.minifera present . 2 .0 Partly covered grey limestone. to yellow, porous , rubbly Grey, massive, rubbly limestone, preserved fossils . with poorly 1.2 Fine-grained, cream-colored limestone, in part replaced by chert ; in part foraminifera coquina; forming ledges . 1.6 Rubbly , mottled limestone, with rare Alveolina. 1.2 Recrystallized grey limestone. 2. 0 Limestone; mostly covered with chert, and regolith at top. pebbles, 2.0 Grey to brown, massive limestone, with some calcite stringers ; poorly preserved fossils present ; ledge forming . 2.1 Same as below; fera . ·ri t h poorly preserved foramini­ Fine-grained, white limestone with fora.minifera, forming a hard ledge; poorly preserved fossils include Alveolina. Fine-grained, white limestone, calcite crystals . with numerous 0.1 White, crystalline limestone . Ledge of grey, crystalline dolomite . Dolomite as above. 2.3 Covered. o.4 Fine-grained, dark grey, recrystallized dolo­mite; grey fine-6r ained limestone. 3.3 In part rubbly and in part blocky weathering; upper 0.5 m. a hard ledge of rhite, fine-grained limestone with manganese stains . Total 204 meters 12 STRUCTURE OF THE ARABIA1 PENINSULA The "Arabian Shield't consisting of old rocks, is a most significant factor in the genesis of the Arabian Peninsula. This, together with the Pre-Cambrian series of :Egyptian Sudan, which joined Arabia to the west, forms a more or less uniform Arabian-Nubian massif. This massif re­presents a...n uplift, sloping on the one hand to the west toward Nubia and on t he other hand towards Arabia in the east. Before the raising of this Arabian-Nubian mass it was probably covered in early Paleozoic times by the lo~er part of the terrestrial Nubian sandstone. After the upheaval the central part, which forms the highest point in this mass, was slowly eroded and Paleozoic-Mesozoic marine sediments were deposited on this shield. They can be recognized definitely on the northern borders of the shield in Egypt, Sinai, Trans-Jordan, and Great Nufud of northern Saudi Arabia. These sediments, little disturbed, ar e resting upon the Arabian shield. (See figure 6. Zone 11 211). This region is surrounded by a zone of folded rocks (fi gure 5, Zone "3"), which extends from the northern part of Egypt through Sinai,, Syria, and the Iraq Depression (syncline). It then passes through the Persian Gulf to Arabi a where it forms the Rub Al Khali depression (Zone "3a"). This zone of folding disappears at the foot of Sabea Plateau in the eastern part of Yemen territory. Picard13 believes that these folded strata f orm another synclinal 12The material preserved in this part of the thesis is a summary from L. Picard "on the Structure of the Arabian Peninsula, " The Geological De­partment, Hebrew University, Jerusalem Series 1, Bulletin 3, 1937. 13picard, L. The Geological Department, Hebrew University, Jerusalem Series 1, Bulletin 3, page 2. 41 trough around the south Mediterranean region (North Sinai and Palestine Coastal Zone) analogous to the Iraqian Depression which is largely ob­scured by the Quaternary faulting and Recent deposition of sediments. The next zone is one of severe folding. Zone 11411 passes through the western part of Iran, Northern Iraq, and Syria, and extends westward to Cypress Island in the Mediterranean. This zone crosses the Persian Gulf to form the Oman range of mountains on the Arabian Peninsula. These moun­tains, characterized by intense folding, obviously constitute a continua­tion of the Zindon Range of Iran. The ancient crystalline rocks of t he southern part of the Peninsula, the similar rocks on the Island of Sokotra, and those of Somaliland in east 14 Africa combine to form what Picardcal led the Arabo-Somali mass. This Arabo-Somali mass constitutes Zone "2a 11 , whi ch can be compared 11211 with Zone qf the Arabian-Nubian mass as regards their stratigr aphic and structural rel ationships • . The Arabian American Oil Company Report15 supports this assumption. The "Sabea Block" (or 11Block of Yemen-Abyssinia") includes the elevated major part of Yemen Province, Southwestern Area, where there is considerable evidence of volcanic activity. It extends across the Red Sea and has its greatest extent in Abyssinia. Thi s block is believed to have formed a continuous plateau that separated the Arabian-Nubian and Ar abo-Somal:l masses, and which must be considered as a separate structural element. The uplift of the Sabea block took place between the Eocene and eogene times. It is now crossed by three grabens, namely, the Rift Basin 14picard, L. The Geologi cal Department, Hebrew University, Jerusalem Series 1, Bulletin 3, page 2. 15Arabian American Report on general discussion of Cretaceous, Tertiary and ~uaternary of Saudi Arabia and adjoining lands, page 5. ~ "I. /onc"llll11tl.1ltt·' ~ :,!. t :1rnhO·!;om;:1li :I. /Ulh' or .., j111plc,:r ful1li11g ---3-­ 1.1ut••o..hth••ll•1u"') ;.1 Kh11h .ti h. ha li ,:. 1110.. \. of \ cmen-.\ 111•.,-.inia ("~.1l•1·a ) 1111111111111111111111 1111111111 111111111111 direction of ro1tli11f!: 1111)\'f!mc nl!'i dip o f :zone tabulnire N 1~ S\\' c111f _ t,,• . tl., I ~ ~~~·.·1 Ntll iia11 :Hlll•l"'t11t1t' ~J•;ilt·" , 1:ucc.·P1· {J;':~ !\letnm(1rphic" :'oh'...010i1 ) ::J:J:-J:. ju1·a..~ic (f1; , 1Plulunic-. t:rctac eon!> lTJ \'olcanic-. J·ig. ;! CrOS!I Sectio11 from ~ihl'~ (S\\) t•> tht' 1·er-.L111 1,ulf. (~I.I. IO million..; (Ill 111111 IOU l..m} Lengt h Height f,() t inu-... knKlh, ( 111 mm :! i..111) plane(.) on Llala on tie Btk kh, Lee~ & t !•tr...in ("El c:ru-..;.ing Lill· Aral•u-S11l11.111 suck, the Kctl Sc;1 Craheu and the 1\h'.SO!IO­t;l.mian geo~~ ndine. ,, NW . c ~ "' ·er. Mec.lit~r­ i-.:cdjd r:\tH!lll1 ~ " Hg. l)iagnuumal H' -.c:~tion frum the .\Tf"fliterranean (:-0:\\") to lladramoiul (')L) crol:t:.lng tht! Rif~ ~·alJe,--. uf llu:: th•atl St":t anc.I vf thC' \\ ad1 sirh:::n tht' Arabo-Nnhian m"if of old rod•.:. ,,ith j;., 1;11ilt· Jauit-.. tht• Khuh :11-Khall S)n­c:line, anll tla· .\ra ho-s.1111.di nn,.,i,· (South AralJian muginal c,,\\ell). /ont" •>f c onq.)•·x f ..-.,•rr 1.,J1hn).: ..--· • ', TaMC' la111!-. -:\fa-.si f (-..odd 'Xf:~o fuidini.: lllJ ~ l e of the Ar"lbian Pe'1insu a 11 , lj.r>o 1 . DPnt., µprrew Univ., JPrusalem, Snri ul". ~. pn. '" & 11. of East Africa, the Gulf of Aden, and the Red Sea. Assir province, which is located in the southwestern part of Saudi Arabia, is a higher block than the Sabea block, but the inadequacy of in­formation with reference to the extension 0£ the Arabian-Nubian massif, to the south, prevents the postufation of hypotheses concerning its origin. The tectonic movements responsible for the structure of the Arabian Peninsul a are believed to be as follows : (a) Movements in Paleozoic-Mesozoic mainly of epeirogenetic character (and still noticeable in the Cenozoic) . (b) Folding of Zone "3" (See figure 6) evidenced in the Upper Cretaceous of Oman, but, in the rest of the Peninsula strata from the Middle of Tertiary into the Q;uaternary. ( c) The most pronounced phases of' faulting (Zone 11 411) are ob­served in the Tertiary to Quaternary rocks, and at this time the most extensive vulcanism took place. GEOLOGICAL HIS':roRY During the Paleozoic era the Arabian Peninsula was connected with Africa by the Arabo-Nubian and the Arabo-Soma.li massifs (See figure 6). The Mesozoic seas also connected the Arabian lands with Africa. Arabia was connected with Asia during the Mesozoic. The Persian Gulf Seas ex­tended to cover the eastern and northern parts of Arabia. These seas advanced intermittently to meet the Mesozoic seas of the Mediterranean area. The Persian Gulf seas and the Mediterranean seas in their advance and retreat over the Arabic shield deposited strata of their respective ages, but the thickness of these strata show that the Arabic shield either stood most of time as an island or as a basin of a shallow sea. During Tertiary, especially, Eocene, the same conditions existed. The thickness (10,000 feet) of the Mesozoic and Tertiary strata in the Persian Gulf region indicate that this area was a site of much subsidence during the Mesozoic and the Tertiary. The thickness of these strata out­side the Persian Gulf during those ages were of less depth. During the Neogene, the Ara~ian Peninsula was high above the sea level and no marine sediments were found except in narrow strips on the Persian Gulf coast and the Red Sea. The marine Neogene sediments formed in the Persian Gulf Coast show that this part of Arabia was a huge terrace where the Neogene seas extended and retreated intermittently. The con­nection between the Mediterra...~ean and the Persian Gulf Sea during this time was north of the Arabian shield. All the known Neogene sediments of central and north Arabia have been identified as of continental origin. Sometime between Eocene and Q,U.aternary, the southern and western portions of Arabia became completely separated from Africa, due to the 45 development of the Gulf of Aden and the Red Sea. Since then, al l the sediments formed on the Arabian Peninsula seemed to be of continental origin. fil DEVELOPMENT STRUCTURAL FEATURES OF THE SAUDI ARABIAlif SIDE OF THE PERSIAN GULF16 The oil fields in Arabia, as well as those of Iran and Iraq, lie on the flanks of a deep, structural trough formed by t he southwestern thrust of the forces which formed the Alps-Himal aya System, culminating in the Pliocene epoch, against the thick series of sediments dipping gently away from the Arabian shield. This trough extends from a point on the Turkish-Iraq borders to the boundaries of southern .Arabia. It has an area approx­imately as great as that of the great plains in North America. The width of t his trough is about 500 miles. The axis of this trough lies in the Persian Gulf parallel to and near its eastern shore, and it appa.rently strikes northwest across Iraq to a point approximately midway between Mosul and Bagdad. The oil fields of Iran and Ira occur on the northeastern, steeply-folded flank of the trough; those of Arabia (Kuwait, Saudi Arabia, Bahrein, and Qatar) on the southwestern and gently-dipping flank of the Persian Gulf troue.,h. The reservoir rocks of the f ields of Iraq and Iran are limestones of Eocene to Miocene ages . Those of the f i elds on the Arabian flank are like~ ise of limestone, except for the immense Burgan field of Kuwait which is sa..~dstone, and t hese are of Jurassic and Cretaceous ages. Reservoir conditions on the Arabian side are due to the porosity of the limestone. 16The material presented in this part of the thesis was furnished by the Arabian American Oil Company (Structure in Saudi Arabia). Dammam Dome .............. The location of the Dammam Dome is latitude 26° 141 north and longi­tude 50° 08' east . (See figure 7). This conspicuous topographic feature has a maximum elevation of about 167 meters above sea level. The dome is oval-shaped; strata of middle Eocene age are exposed near the center of the structure, whereas on its perip~ery rocks of Miocene age are found. The intermediate slopes are clearly visible; they consist of gently dipping Eocene rocks . Four kilo­metArs westwaro f~om the apex there crops out a west-facing rim-rock of nummulitic limestone which rests on shaly marls known as the Shark Tooth Shale . The dip slope on the outer periphery of the structure is about 1/5 degree. The rim-rock and the outward dipping limestone beds clearly show the outline of this structure. The distance from the rim-rock in the north to the edge of the rim-rock in the south is about 14 kilometers, whereas the east-west or short axis width is about 10 kilometers. The numerous slump features due to solution of the Eocene and Upper Cretaceous rocks make it difficult to define the exact configuration of the ~pical area of this structure. Some of these solution features have a relief of 100 meters or more. Evidence from well records sho~rs that numerous faults are present, but their relationship to each other and to the dome are not as yet clearly understood. Abqaiq Dome The location of the Abqaiq Dome is l atitude 25° 651 north and longi­tude 49° 411 east. The Abqaiq Dome is located in the midst of large sand dunes, a north­ ward extension of the Jufura Nufud. 49 21• Buqaqo 26• SAUDI ARABIA 15° LEG ENO ' 'M;\e~ ~longe.r.. P: ~ PERSIAN G L F I RAN 2 • 21• :I"""• lft A .h1• ,,., Figure 7 The surface expression of this structure is extremely slight. De­tailed surface mapping was required to detect its existence. Miocene rocks with a dip of less than 1/4 degree were found to be outcropping in this area. The dip of the Eocene beds is less than 1/2 degree. Drilling re­vealed that the underlying Cretaceous rocks are dipping several degrees more than the Eocene and the Miocene strata. The shape may be described as that of a very long dome; its dimensions may be about 24 kilometers by 12 kilometers. The structure is quite symmetrical and no faults have been discovered. Eucaga~ The location of the Eucaqa Dome is latitude 260 141 north and longi­ tude 49° 48 1 east . This dome is located in the midst of a dune sand area where only oc­ casional outcrops of Eocene and do,,.m-dip Miocene rocks have been noted. Slumps of the earth, due to solution of some Eocene member, are common. ~he dips of these displaced solution members make it difficult to deter­ mine the exact configuration and dimension of the structure. Information gleaned from well records suggest t hat the structure is a broad, oval- shape dome with very gentle dips. Q,atif ~ The location of the ~atif Dome is latitude 260 321 north and longi­ tude 49° 59 ' east . This is an elongated dome located just west of the Q.atif gardens. Its exact configuration is not yet known. Surface mapping shows the structure to be an irregular one; numerous slumps caused by the solution of subsurface rocks have prevented its delineation. However, drilling has revealed some fe\ facts as regar ds its shape and magnitude. Ma 1Aoal a Structure 0 311 The location of this structure is latitude 26 north and longi­tude 47° 20 1 east. The ~.a 'Aqala structure is located on a barren, slightly dissected plateau-like area. Eocene rocks are exposed in the cent.er of the struc­ture and on the south end. Miocene rocks are found on its west, north and east sides. The dips of the central Eocene rocks are not deter­minable. The degree or amount of closure on the south side, if any, is not known. ~Hadriya Dome The location of this dome is l atitude 27° 22 ' north and l ongitude 49° 00 1 east. This is a large, broad dome of about 16 kilometers in diameter. The existence of this structure was revealed by surface mapping, but the exact limits have not been determined. Miocene rocks , exposed on the surface, consist of shaley sands, marls and chert. Definite surface dips have not been determined for these rocks. STRUCTURAL FEATURE IN ORTH SAUDI ARABIA fil:. ~St rue ture The location of this structure is l atitude 28° 07 1 north and lon.gi­ o 561 tua.e 47 east. Low-dipping Miocene rocks, consisting of rather soft sandstones and sandy shales, are found on the surface of this structure. The presence of these low-angle dips suggested the probability of the presence of a major structural feature. A seismographic survey revealed decided dips on t he flanks; these va:ry considerably, but, generally, they exceed 7 degrees. A wild cat well drilled in this area reached a depth of about 3, 658 meters. Oil showings were found at various horizons, but no oil zones of commercial importance were penetrated. 52 RESERVO IR CHARACTERISTICS OF THE OIL FIELDS IN THE PERSIAN GULF REGION OF SAUDI .ARABIA17 Dammam Field This field was the first to be discovered in Saudi Arabia. The first well was drilled with cable t ools to the Bahrein· zone of t he lower Upper Cretaceous, reached. at a depth of 3,203 feet. Several wells 1.ll'ere subsequently drilled to t hi s horizon with the hope of developing a supply of commercial i portance, but the Bahrein zone which is fairly productive in Bahrein Island (35 miles from Dammam) proved to contain only a relative­ly small quantity of oil in the Dammam field. Three of the wells which were drilled to the Bahrein zone are pro­ducing. Well Jfo . 1 produces approximately 500 BPD of 50° API crude, with a gas-oil ratio of B6q cubic feet per barrel. The gas obtained from well No. 1 does not contain hydrogen sul phide, and therefore can be used for domestic purposes. Containing only small quantities of oil in Dammam field, as well as in Q.atif and. Abqaiq_ fields, the Bahrein zone reservoir was not adequately tested and little is known about its characteristics. Fai lure to find large quantities of oil in the Bahrein zone in the first field drilled in Saudi Arabia led to deeper drilling in the same structure. ·{ell No. 7 was drilled to 4, 727 feet, with discovery of the Arab zone of upper Jurassic age, which is considered to be prolific in oil production. Dammam field now has more than thirty wells completed in the Arab zone. These wells, however, failed to give enough information 17Most of the material presented in t his part of the thesis is furnished by the Arabi an American Oil Company. (Reservoir char acteristic of the oil fields in eastern Saudi Arabia.) 53 from which to obtain a clear idea about the structure of this reservoir. One or more faults were encountered in 16 of the wells completed in the Arab zone. The Arab zone consists of four hyd.rocarbon-saturated limestone mem­bers, which are designated as the "A", "E", "C", and "D" members (See figure 8). The thickness of these members is 571, 251, 107' and 2291 , respectively. The porous limestone members are capped and separated from each other by an impermeable anhydrite. These members vary from extremely permeable and poorly cemented oolitic limestone to a dense, microcrystalline 11D11 limestone. While "A", 1'E 11 , and members are quite productive, the 11D11 member, which contains 30 per cent of the total volume of the reservoir rocks is low in productivity. All of the horizons contain oil of the same type. The gravity of the oil is approximately 35° API and each reservoir has a gas cap. This gas cap makes up about 15 per cent. of the total volume of the hydrocarbon­sat urated reservoir rock. The oil-water contact for the various members is at the same sub-sea dept h but the gas-oil contact varies because of the presence of the faults. The wells are spaced so as to produce a maximum of oil. They are located far from the gas-oil contacts so as to keep the producing gas-oil ratio almost the same as the ratio of the solution (gas-oil) . These wells are properly located above the oil-water contact. A packer is usually set above the iowest producing member in an.y well. The production from this lower member is obtained through the tubing, while the production from the other members is obtained through the casing-tubing annulus. Acid is used to clean the gun perforations, but it causes the mud to flocculate . Ho rever, it al so dissolves the limestone, causing the pores Oiagrom of we\!-comp letion practices . Arab zone, Dammom dome From 1hQ Oi and Gas Journal, Nov. 3, 1945 o.76 I Figure g to be freed of mud. Moreover, the acid washing alone sometimes improves the productivity of a well as much as 200 per cent. This field was discovered in 1936 ; by 1946 its daily pr oduction was about 100,000 barrels and its cummulative production was 95,000,000. The proven area of the field is about 9,000 acres. The reserves of the Dammam field are estimated to be between 600 and 615 million barrels. ig This is the second field to be discovered in Saudi Arabia. Oil was encountered in the Abu Hadriya zone, Upper Jurassic in age. This field i s a one-well field. The depth of the well is 10,220 feet. The gravity of the oil is 35.7° API and the oil-gas ratio is 230 cubic feet per barrel. At present there is no production from the field. However, the reserves of the area are estimated at 140 million barrels. This field, discovered in 1940, is the deepest producing field in Saudi Arabia. Abq,aiq, ~ 11 011 This field has seven wells. Oil was first found in the member 11B11 of the Arab zone. The upper members "A" and are known to be water­ 11D11 bearing. The lowermost member also contains oil and is nroductive. The oil from the 110" and 11D11 memoers is of different q_uality and gravity, whereas the oil produced f rom these zone mem ers in Dammam field was found 11 011 to be alike. In this field, oil within the member varies in gr avity, for eY..ample, from 190 API gr avity ?n the flank to 28° API gr avity on the 11 011 top of the structure. The oil reservoir, the member, is about ·80 feet 181947 World Atlas . _The .Q2l. Weekll, p. 327. TxU thick in Abqaiq, but the permeable portion is only 35 feet thick. Member 11 D11 is almost 232 feet thick and contains oil of 38° API gravity. The oil in the latter reservoir is undersaturated. The productivity indices of Abqaiq field wells exceed 150 BPD/PSI. Plans for producing this field in­ clude a limitation to 10,000 barrels per day for each well, thus keeping the gas-oil r atio to the desired minimum (about 900 cubic feet per barrel) . 11D11 The member reservoir is being developed according to a ring­spacing plan. Wells were drilled on a contour approximately one-third of the vertica,l distance between the top of the structure and the oil­water contact. It is thought that this reservoir will be exploited by means of a partial water-drive and a partial gas-drive. It is also pl anned to compensate the pressure by a secondary gas cap. This field, discovered in 1940, is the largest in Saudi Ar ab ia. The daily production of the seven wells is 112,000 barrels, and the est~mated reserves of Abqaiq field range from 3 to 5 billion barrels . The cun:ulative output in 1946 was 24,801,193· It is interesting to note that the oil column in well No. 10, completed in 1946, wa.s estimated to be 1,500 feet. Q,atif ~ This is the fourth and the last field to be discovered in Saudi Arabia (1945). It has a ma.rked similarity to the Abqaiq field. Oil is 11A11 produced from "C" and "D" members of the Arab zone, and the and "B" 11D11 members are wet . The gas-oil r atio of the member crude is about 560 cu.bi c feet per barrel. The producing limestone members of ~atif field are denser and more crystalline than those of Abqaiq_ or Dammam wells . The "D" member here has the same thickness a:;; tha.t found in the other field, but its lower portion is impermeable . This is also a one-well field. At the end of 1946 the well was flowing 2,675 barrels daily. The estimated reserve is thought to be about 50 million barrels. Its cummulative production through 1945-1946 was l,l4o,966 barrels. The gravity of the oil is 29-28 degrees (API) . The total proved reserves of the four fields described, namely, Dammam, Abqaiq, Abu Hadriya and Qatif have been estimated at 3,715 million barrels and their present daily production is about 250,000 barrels. IBLIOGBAPHY 1. ••••• "General Discussion on the Cretaceous and Tertiary Strati­ . graphy on the Arabian Peninsula and Adjoining Areas," Arabian American Oil Company (Report) . 2. •••··"A Geological Reconnaissance of Northern Nejd Province, North­eastern Saudi Arabia, 11 Arabian American Oil Company (Report). 3. ••••• "Structures in Saudi Arabia, 11 Arabian American Oil Company. 4. ·····"Measured Stratigraphic Section of the Upper Cr etaceous, Eocene, Neogene, and ~uaternary Along vadi Aruma and Wadi Al Batin, 11 Arabian American Oil Company. 5. ••••• "Reservoir Chara cteristi.cs of the Oil Fields in Eastern Saudi Arabia," Arabi an American Oil Company. 6. Dale, Nix. "Oil Development in Saudi Arabia, 11 ~Mines Magazine, November, 1946, p . 533. 7. De Golyer, E. "Oil Explora tion in the Middle Ea st, 11 ~Mines Magazine, November, 1946, p. 493. 8. Duce, J. T. "Foreign Oil Operations Marked by Uncertainties and Hidden Costs, 11 ~.Qi!~~J ournal, vol. 46 , No. 12, p . 160-161. 9. Lees, C. M. "The Geology of the Oil Fieids Belt of Iran and Iraq," ~Science.£! Petroleum, vol. 1, p. 140-148, Oxford University Press, 1938. 10. Miller, Robert P. "Drai nage Lines in Bas-relief. 11 Journal 2.! Geology, vol. 45, No. 4, p. 432-438, 6 figs., May-June, 1937· 11. Qll Weekl;i:;. 111947 World Oil Atlas". 12. Pic~rd, Leo. "On the Structure of the .Arabian Peninsula, 11 Hebrew 59 University, Jerusa.lem, Geology Department, S.I.E. 3, 12 PP• (Engl. Hebrew Summ.), l+ figures (incl. sk. map) F 137, 1937· Abdullah Homoud Tariki was born in Zelfi, Saudi Arabia , March 19, 1919. He attended Mohamadia Primary School in Cairo, Egypt, gr aduating in 1933· In 1934 he was a student at Khidivia Secondary School from which he was graduated in 1938. The following year he was enrolled in the Fouad University in Cairo where he was graduated in 1944 with the Bachelor of Science degree in chemistry and geology. In November, 1945, he enrolled in the Department of Geology; University of Tex.as, as a gradua te student. He spent two years there working towar ds the Master of Arts Degree with a major in geology. His permanent address i_s The Minister of Finance, Care,' Jedda, Saudi Arabia. This thesis was typed by J ayne Marliss Puls, B.B.A. 61