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TIHAMAH BASIN THE FUTURE HYDROCARBON PROVINCE IN YEMEN.

INTRODUCTION.

The Red Sea basin originated as an Oligocene cratonic rift between the northeastern part of the African continent and Saudi Arabian peninsula. It has the undergoing sea floor spreading for the last 5 m.y. Countries located in the Red Sea are : Yemen, Saudi Arabia, Eritrea, Sudan and Egypt(Fig-1).

The Tihamah basin offers an attractive exploration opportunities in the whole thick sedimentary succession(Figs-2,3). The Pre-Rift sediments range in age from Upper Jurassic to Lower Eocene. Deep drilled exploratory wells did not reach the Syn-Rift unconformity. Syn-Rift sediments comprise evaporite-carbonate succession with clastic input in the lower part and salt in the upper part. Post-Rift sediments consist of clastics and carbonates (organic reef growth ) of Late Miocene/ Pleistocene.

Presence of oil, gas and condensate discoveries in the Gulf of Suez, Sudan and Saudi Arabia and also presence of numerous oil and gas seeps in the Red Sea offshore region prove that the source rocks are available and are mature. These seeps are also plenty in the Yemeni part of the Red Sea ( Tihamah Basin ).

Presence of Maqna Play in the above mentioned hydrocarbon discoveries, including  Tihamah Basin, leads to future higher hydrocarbon potentiality of this basin.

MAQNA Formation.

Age: Lower-Middle Miocene.

Authors: Hughes and Filatoff ( 1994 ) as Maqna Group in the Red Sea ( Subsurface ) area of Saudi Arabia, divisible into two formations each with lateral variations in facies. Emend. to Maqna Formation by Yemen Stratigraphic Commission for application to the subsurface succession in the Red Sea of Yemen(Fig-4).

Synonymy: Carbonate-Evaporate Group ( part), used by some of the operating oil companies; Zeidiye(part) as suggested by Hughes and Beydoun ( 1992), Karim and Belayim Formation of the Gulf of Suez region.

Reference(Subsurface) Section in Yemen. The Zeidiye-1 well  serves as the principal subsurface section, with Abbas-1 and Al- Auch-1 serving as additional sections where halites are present, while Hodeida-2 exhibits a non-evaporatic facies. Zeidiye –1(Fig-5) has about 390m of Belayim-Kareem ( Gulf of Suez ) equivalent succession consisting of shales-mudstones-siltstones in the upper part and carbonate-anhydrite-shale-thin sand  interbedding   in the lower part; Abbas-1 and Al-Auch-1 exhibit an interbedding of shale-mudstone with halite ( Belayim equivalent only ) with over 470m present in the first well and over 290m in the second well with the base of the Maqna not reached. Hodeida-2 exhibits over ? 570m of Belayim equivalent in a facies of alternations, limestones and claystones-mudstones(Hughes and Beydoun, 1992;SPT, 1994;

Doornenbal et al.1991). These are the only four Yemeni Tihamah Red Sea wells to operate the pre-evporite syn-rift sequence. No surface exposures of any “ pre evaporites “ are recorded from the area.

Foraminiferal assemblages from these sediments include: Orbulina universa, Praeorbulina glomerosa circularis, P. transitoria suggesting an age close to the Early-Middle Miocene boundary.

MAQNA  Play

Source Rocks: Miocene ( and some Pliocene ) oil and gas prone Syn-Rift and Post-Rift shales from variety of laterally limited depositional settings ranging from marine to terrigenous. They typically average 1 to 4% TOC, ( maximum 30% ) with variable thicknesses.

Maturation: Dominantly Late Miocene to Recent, 10 to 0 Ma. Thermal gradients are high, good for the above mentioned ages.

Migration: Migration paths are expected to be simple and short in distance.

Reservoir Rocks: Miocene and younger sandstones and carbonates from depositional environments ranging from deep marine to deltaic, coastal and sub-aerial. Average porosity is about 22% and permeability of about 1darcy. 

Seals: The regional seal is extensive Upper Miocene and Pliocene salts, evaporites and shales reaching hundreds of meters in thickness.

Traps: Traps are expected to be both stratigraphic and structural. Halokinesis had played a big role in the formation of different types of salt related structures.

Remarks: The Maqna Formation constitutes the upper part of the early Syn-Rift succession ( Lower-Middle Miocene ) of the Yemeni Red Sea area and is equivalent to the Maqna Group of Saudi Arabian sector of the Red Sea and the Kareem-Belayim Formations of the Gulf of Suez, Egyptian sector of the Red Sea. Oil,gas and condensate have been discovered in commercial quantities in these sediments in the Midyan area of Saudi Arabia both onshore and offshore ( Barqan offshore structure ) and Midyan onshore structure. Commercial oil production from these formations in the Gulf of Suez area in Egypt has long been established and sandstone reservoirs of the Kareem Formation ( and underlyimg Rudeis and Nukhul Formations ) and in the Belayim Formation ( and part of the overlying South Gharib Formation) constitute the main Tertiary oil bearing levels ( Ayouti, 1990; Beydoun,1995). These formations contain source, reservoir and seal levels; the source levels can reach exceptional quality locally and in general are good to excellent.

In the southern sector of the Red Sea in Yemen, higher geothermal gradients during rifting make the top of the oil window shallower and variable, even Salif Formation source levels ( within the evaporites and in the Ghawwas Member )can be late to post-mature at about 1,800m and below in the offshore region of Yemen, close to the axial of Red Sea rift.

In the adjacent Jizan area of Saudi Arabia Red Sea and only some 30km north of the land border with Yemen, three wells recently drilled onshore ( centered on about lat.16deg 47min  long.42deg 44min, about 26km SE of Jizan Dome), tested 42 API gravity, waxy paraffinic crude oil and dry gas ( Cole et al., 1994, 1995 ) from a Maqna sandstone reservoir ; here the oils were conclusively correlated with the thin Maqna organic-rich mixed oil/gas to oil prone source rock unit immediately below the Maqna sand reservoir in the Jizan North-1 and 3 wells ( Cole et al., 1995 ). The Maqna shales have the TOC which  reaches up to7.48%, and thickens towards the “ Kitchen “ area.

CONCLUSION.

1-Presence of Maqna  Play in the adjacent hydrocarbon discoveries of Saudi Arabia and the Tihamah basin leads to future hydrocarbon province in the Yemeni part of the Red Sea.

2- Higher geothermal gradients during the rifting make the top of the oil window shallower and variable, even for Salif Formation source levels at 1800m and below in the offshore region of Yemen, close to the axial of Red Sea rift.

REFERENCES:

 * A.S.O.NANI, Relation Between Halokinesis and Hydrocarbon Accumulation in Sabatayn and Possible Tihamah Basins of Yemen. 2^nd  International Yemen Oil & Gas Conference, 24^th –25^th  june 2002, Sana’a Yemen.

 * A.A.Abdillah, M.As-Saruri, A.Al-Malasi, Tihamah         basin Yemen Red Sea: Geological Setting and Exploration Potential. 2^nd Yemen Oil & Gas Conference, 24-25^th   June 2002. Sana’a, Yemen.

*S.J. Lindquist, 1998, The Red Sea basin province- Sudr-Nubia and Maqna Petroleum Systems: U.S. geological Survey Open File Report.

*Ziad R. Beydoun, Mustafa A.L.As-Saruri, Hamed El- Nakhal, Ismail N. Al-Ganad, Rasheed S. Baraba, Abdul Sattar O. Nani and Mohamed H. Al- Aawah. International Lexicon of Stratigraphy, Volume III, republic Of Yemen, IUGS Publication No. 34.

1998,

* PEPA Publications, brochure No.5-Sana’a-April 2002.