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RELATION BETWEEN HALOKINESIS AND   HYDROCARBON ACCUMULATION IN SABATAYN AND POSSIBLE TIHAMAH BASINS OF YEMEN.

2nd  International

Yemen Oil & Gas Conference

24-25 June ,2002

The Sharaton Hotel , Sana’a Yemen

RELATION BETWEEN HALOKINESIS AND   HYDROCARBON

ACCUMULATION IN SABATAYN AND POSSIBLE TIHAMAH BASINS OF YEMEN.

By: Dr.Abdul Sattar Othman Nani.

       Scientific Advisor to Chairman

       PEPA. MOM. YEMEN.

Introduction:

     Oil and gas fields have been discovered in the Sabatayn basin and oil seeps have been observed in the Tihamah basin, both of which are associated with halokinesis in different geological times. The salt in the Sabatayn basin is Jurassic ( Tithonian) in age and an initial phase of halokinesis began in very late Jurassic time. Features associated with halokinesis were detected during seismic interpretation and include: Listric- gaps, Rollover structures, Turtle backs, and Salt-Pillows.All these structural features are associated with listric faults, which played a positive role for the migration of hydrocarbons from Lam and Meem source rocks to the Alif reservoir rocks

.

The salt in the Tihamah basin is of Middle Miocene age and the initial phase of halokinesis began in very Late Miocene time.

     Features associated with the halokinesis were detected during seismic interpretation and include: Salt- Pillows, Stocks, Detached Stocks, Tongues, Canopies and Salt Cord Anticlines. A clear understanding of the implication of salt tectonics in the Tihamah basin will lead to oil and gas discoveries. Fig-1

JURASSIC SALT DOMES IN THE SABATAYN BASIN

SURFACE PIERCEMENT SALT DOMES:-

LOCATION                                 SALT DOME

1- Wadi Hajr                              a- Mintaq

                                                            b- Jubah

                                                            c- Siyal Al-Milh.

2- Ayad                                                 * Central Ayad.

3- Shabwa                                 a- Shabwa.

                                                            b- Maqah

                                                            * c- Milh Khirwa.

4- Bayhan                                              Al- Ayadim                                   

5- Safir                                                 Safir

Four Post-Rift Phases of Halokinesis

Salt in the Sabatayn basin is Upper Jurassic  (Tithonian )in age.Presence of Tintinids called Tintinopsella.

Four Post-Rift Phases of Halokinesis:-

            Phase-1:- In very late Tithonian ( U. Jurassic).

     Intra-Nayfa ( Azal ) units clearly thin onto many of the salt-domes in the Shabwa-Hajr sub-basins.

            Phase-2:- Mid-Cretaceous.

            Phase-3:- During Paleocene – Mid Eocene.

            Phase-4:- During Gulf of Aden and Red Sea  Rifting.

Relation Between Halokinesis and Hydrocarbon Accumulation

Relation Between Halokinesis and Hydrocarbon Accumulation.

Marib Sub-Basin:-

     In most of the area  salt is in layers and the halokinesis is passive due to the less thickness of the overburden and salt is in layers. The listric faults had formed Listric-Gaps.

     Therefore this had provided a good  Petroleum System for ( Lam-Alif ) to accumulate hydrocarbons in the Alif  clastic reservoir. Fig. 5

SALT-DOMES HAD NEGATIVE HALOKINESIS EFFECT

     Areas associated with salt-domes had negative halokinesis effect on the Petroleum System (Madbi-Supra salt- ).

Why????

     Huge thickness of salt about 800-1000m hampered the hydrocarbon migration from the excellent Madbi source rocks in the adjacent kitchens to the Supra-salt reservoirs.

Good examples are Ayadim, Amal and Central Ayad, etc.

Areas like West Ayad , East Ayad and Magraf; there the salt is in layers, it has a passive halokinetic effect. That made Petroleum System (Madbi-Sabatayn dolomites ) and (Madbi-Nayfa ) easier. Fig. 6

CONCLUSION

1-  In Marib Sub-basin halokinesis is passive due to less thickness of the overburden and salt is in layer. This in turn helped the accumulation of hydrocabons in the Alif sandstones.

2- a. In Shabwa-Hajr Sub-basins halokinesis had                             

          negative effect on the hydrocarbon accumu

          lation in the Salt- Dome areas.

     b. In Shabwa- Hajr Sub-basins halokinesis is passive due to the less    thickness of the overburden and salt is in layers (West Ayad field), this had provided a good hydrocarbon acuumulation in the supra-salt sediments.

TIHAMAH   BASIN

Tectonic Setting:-

 1-The Red Sea was initiated by a phase of rifting between African and Arabian Plates during the Oligocene, the area was considered to have been centred over the Afar triple junction. ( Menzies et al 1992 ).

 2- The early Syn-rift phase was in the Oligocene-Early  Miocene.

 3-The Syn-rift phase is followed in the Mid Miocene by a transitional phase represented by the main evaporite group.Fig-7,8. It is this unit which provides the mobile salt to form the wide variety of salt structures.

 4-The Post-rift phase begins somewhere in the Mid Miocene and continues until the present day, with a significant break at the end of the Miocene.When Africa and Arabia plates finally split apart in the southern Red Sea.

MIDDLE MIOCENE SALT DOMES IN THE TIHAMAH BASIN.

SURFACE PIERCEMENT SALT DOME.  

Location                                    Salt Dome

As-Salif Area                             As-Salif

Jabal Al-Milh Area                     Jabal Al-Milh Fig. 2,9

Subsurface Salt Features due to Halokinesis from the seismic lines.

The Roller Zone:-

Roller Anticlines.

·  The zone is entirely extensional. Fig-10.11,12.

2-The Canopy Zone:-

Characterised by Post-rift section.

· Present of salt-pillows, stocks, tonhues, canopies and anticlinal structures.

· Extensional and Compressional.

3-The Anticline Zone:-

Charactersied by sinnusoidal compressional anticlines.

·  The halokinesis in this zone is passive as the thickness of the overburden is less and the salt is not the driving mechanism in this formation.

HYDROCARBON PLAY OF TIHAMAH BASIN

4. The Outer Shelf Zone:-

* Extensional and halokinetic effects are minor.

Possible Relation Between Halokinesis and Hydrocarbon Accumulation.

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Presence oil seeps, hydrocarbon shows during deep exploration drilling, and presence source rocks within the Syn-rift and Post-rift sediments with TOC up to 4.2%. Fig-14.

-The sandstone horizons are are marine and westwards prograding alluvial fan of  Middle- Upper Miocene age. The porosity is about 20-25% and  permeability reaches up to 500 md.

-Salt is the best seal for the bedded sandstones.

-Salt features formed due to the halokinesis could serve as Traps for the hydrocarbon accumulation.

-Presence of faults could play role of hydrocarbon carriers from the kitchens to the adjacent reservoirs.

CONCLUSION:-

- The Anticline Z0ne is considered to be the most potential for the hydrocarbon discoveries due to the presence of compressional antoclines and the halokinesis is essentially passive, since the overburden thickness is less and although these anticlinal features are probably salt cored, the salt is not the driving mechanism in their formation.