Azraq Basin Hydrocarbon Exploration Opportunities in Jordan

Azraq Basin

LOCATION AND GEOLOGICAL SETTING 

Azraq basin is a 1500 Sq.km. NW striking, structurally controlled Cretaceous basin. It is located in Amman / Azraq Block (11250 Sqkm.). It lays 120Km to the east of Amman; between the high central plateau in the west and the Basalt Plateau in the east. It is the only proven oil province in Jordan yet. It contains the small Hamza Oil Field, which was discovered after a successful completion of Hz-1 Well in 1984.

Stratigraphy

Rocks of Tertiary to Quaternary age with some basalt cover the studied area. It consists of limestone, silicified, marly in parts phosphatic argillaceous partly marly with nodules of chert and loose sand. The exposed thickness of these rocks is in order of 100 - 300m.On the other hand, the distribution of these rocks in the subsurface is rather complicated and associated with neo – tectonics. It varies from zero in the most eastern part to 850-1000 meters in the central part and to 600-800meter at the NW part of the basin. This complex pattern indicates a NW / SE faulting where Hamza Field is located in the deepest part of the basin.

The deposition of 150 m of Alb/Apt. Kurnub sandstones marked the beginning of the Cretaceous in Azraq Basin.  It consists of fluvial and deltaic sandstones intercalated with marl, black shale and rarely dolomitic limestone occurs at the base of this formation.

Transgression of the Tethys during the Upper Cretaceous, resulted in deposition of marine carbonate (Ajlun group). The Cenomanian carbonate and shale are divided into four formations ( Fuheis, Naur, Hummer and Shueib).  These formations are composed of   150m of thin hard, nodular limestone, alternating with soft weathered marly limestone, yellowish brown thinly bedded argillaceous limestone, and with hard dense fractured and dolomatic limestone pales chalky carbonates. Oil in Hamza Field is produced from these carbonates.

The Turonian rocks (Wadi Es Sir Formation) consist of 360 meters of white to light gray limestone microcrystalline and thinly bedded with very thin marl partings, fractured fossilifrous, and medium hard to hard limestone, interbedded with thin beds of anhydrite and medium beds of dolomite and dolomatic limestone.

The Camp / Santonian consist of two formations (Upper & Lower Amman)  , a 700m of brown finely crystalline, compact, silicified dolomite and limestone were deposited. The Santonian is marked by 500m of red clay and sandstones.

Finally, the Cretaceous was ended by the deposition of 700m of the Mastrichtian (Ghareb) argillaceous, marly and fossilifrous limestone and (Oil shale).

Both, Mastrichtian and Campanian / Santonian carbonates have heavy oil and asphalt especially when they are fractured.

The Jurassic rocks which was drilled by limited number of wells in Hamza oil field and Azraq Basin, are made up of colorless, friable well-sorted sandstone and dark gray thin beds of fissile, shale. The drilled thickness of the Jurassic rocks is 30 meters.

Triassic rocks in Azraq basin are composed of 300 meters of thin beds, well sorted bituminous in parts sandstone, and thin beds of fissile, dark gray shale interbedded with beds of brown, compact limestone and dense, buff, fine crystalline dolomites.

A major unconformity (Hercynian) separates the Paleozoic from the overlying Mesozoic in all Jordanian basins.  The unconformity cuts deeper following an east to west trend. Several other unconformities occurred during the Mesozoic. These are characterized by peneplanation surfaces and sands with good reservoir quality clastic driven from the Paleozoic and Precambrian basement rocks.

Most of the upper Ordovician (Dubaydib Formation) is eroded in Azraq Basin. The remainent section of Ordovician is composed of 300meters sandstones, colorless, siliceous cemented, hard, cemented sandstone interbedded with gray hard siltstone and thin beds of sandstone well sorted friable and ill cemented, with beds of weakly fissile calcareous shale. 

Stratigraphic Column of Azraq Basin

The Cambro/Ordovician rocks of Umm Sahem and Disi sandstone (1200m), consist of colorless, medium hard, fine to medium grained silty in parts, sub rounded sandstone, intercalated with thin beds of brown, soft, sandy silts, and streaks of medium hard compact weakly fissile shale. Wadi Ghadaf-2 well penetrated 500 meters of Cambrian rocks and was abandoned dry in Early Cambrian Salib sandstone formation. During Middle Cambrian (Burj formation) marine conditions were prevailing which resulted in deposition of 160 meters of Dolomite and siltstones of Burj formation.  

The Precambrian Saramuj (Basal) conglomerates were not penetrated completely or partially by any well in Azraq Basin.

To sum up, the lithological column of Azraq basin provide multiple chances to have source, reservoir and seal intervals.

Structural Framework of Azraq Basin

The Azraq Basin is bounded, by the high central plateau and the northern Highlands in the west and northwest, and by the Basalt Plateau in the east and northeast. It is flattened and covered by Paleogene and Neogene rocks. The elevation within the study area varies from 530m ASL to 650m ASL. This 1500 square km, asymmetrical half graben and structurally controlled Late Cretaceous basin is striking to NW/ SE direction. It is limited to the north and east by Fuluq fault and to the south by Siwaqa fault, to the west the strata rises gradually into the Northern Highlands. The basin is deepest in the east and northeastern parts, adjacent to the down thrown side of Fuluq fault.

Structural Framework of Azraq Basin

Surface geology, Landsat interpretation, well data and seismic interpretation indicated that, NNW/SSE, NW/SE and ENE/WSW trending faults characterize Azraq basin. It is widely believed that NW/SE sinistral faults such as, Fuluk, are related to the Najd Fault system. The Fuluk growth fault is the main structural element responsible for the development of a NW-SE trending asymmetrical graben with significant thickening of Cretaceous and Paleogene sediments. The sedimentary section reaches a maximum thickness of approximately 5500 meters in the vicinity of this fault, where as the vertical throw is more than 2500 meters (8ooo feet) to the southwest. In the Basalt Plateau, they are marked by some Basalt extrusions of younger age of the surrounding Basalt, indicating tensional tectonics rejuvenation along these faults. This trend may be, in part, associated with post Oligocene left lateral wrenching along The Dead Sea Transform (DST), it may also represent a rejuvenation of more ancient fracture associated with NW/SE strike slip faulting occurred in the Arabian Shield or Azraq Sirhan Basin during pre- Cambrian time.Siwaqa fault is an E/W striking dextral fault crossing the Jordan Platform for 200 km form the Dead Sea fault to Saudi Arabia. Siwaqa fault marked the southern limit of Azraq Basin.  As any other E/W fault in Jordan, Siwaqa fault shows strong structural deformation, associated with major right lateral strike slip and variable dip throw.  In the Pre – Cretaceous, the north of the Siwaqa fault was high block, where erosion cut deeply into the Paleozoic resulting in Ordovician underlying Cretaceous, however, the area was the site of thick sedimentation during the Cretaceous. This structural inversion resulted in separating the Azraq Basin from the Larger Sirhan Azraq basin.

Folds are the least impressive surface structural element in area Practically, they are absent; except for usually small compressional, sharp undulations, uplifted anticlinal blocks and arched sets of narrow blocks parallel and/or oblique to the major fault trends (WNW/ESE) associated with NNW/SSE. Neither type of fold is expected to be large.

Seismic coverage of Azraq Basin

Azraq Basin was subjected to intensive and multiple seismic programs between 1969 and 1988. A total of 7174 km of good to excellent seismic data are available at the NRA head office. The bulk of this data has 24 folds and 48 traces. Recent data have 48 and 60 folds with 96 and 120 traces.  All data were recorded using Vibroseis as the seismic source. About half of the data were recorded with 100-meter group intervals. The most recent data were recorded with 60-meter interval. When these data were redisplayed and interpreted, they show strong expression of wrench tectonics and structures. add to this 300Sqkm. of excellent quality seismic data was acquired in 2010.

Seismic Coverage Map  (Azraq Basin)

Structural Style and Trapping Mechanism

In spite of it’s diverse structural styles and long structural history, Azraq basin provides a vast range of potential hydrocarbon traps,. The traps in this basin are fault controlled structural features of relatively small size. Possible reservoirs are found in Lower Cretaceous Kurnub sandstone, Cambrian Sandstones and in Campanian Azraq sandstones. The proven oil bearing reservoirs are Cenomanian-Turonian fractured limestones and dolomites of the Shuieb and Hummar formations. Source rocks are interbedded Cenomanian and Turonian limestones and marls locally Wadi Essir Formation (WS2 member).

In addition to the proven oil accumulation in the down thrown side of the Fuluk fault, there are shallow prospects on the up thrown block to the east, where the structural style is one of rotated fault blocks controlled by antithetic fault trends associated with the major fault. A series of compressional anticlines is found on the down thrown side of the southern E-W boundary fault of the basin (Siwaqa Fault), these anticlines trend in an east-west direction. Several high-level closed anticlines have been mapped at the western up-dip margin of the Azraq Graben. They represent good targets at shallow depths, since they lie on possible migration pathways from deep basinal areas.

Drag Fold in the Upper thrown Faulted Trap

Based on the structural characteristics and history of the Basin, one can concluded that, two structural styles are dominating the study area, they are: -

1-      Normal faulting

2-      Wrenching

The following trap types are expected:

I) Normal Block Faulting

-          Horst Blocks

-          Tilted Faulted Blocks

-          Drag Folds

-          Graben Associated Structures

-          Graben Self Contained Traps

II) Compressional Wrenching

-          Rotated Fault Blocks

-          En Echelon Folds

-          Positive Flower Structures

Example of Tilted Horst Block Trap

Add to the above, faults in the basin are mostly sealing, thus preventing horizontal fluids migration out of the reservoirs. Fractures are playing a very important role in enhancing the reservoir quality and providing additional permeability to already low permeable Upper Cretaceous carbonates. On the other hand, the fractures are potentially important fluid migration pathways, thus greatly influences the hydrocarbon distribution in the basin.

 

 

Fault Related 2D  Structural Anomalies  

Oil Habitat and Hamza Oil Field

The Azraq basin has been the site of the early drilling activities undertaken by NRA at the beginning of the eighties. Following the oil discovery at Hamza-1 location seventeen (17) wells has been drilled, these included exploration delineation and production wells. More than 13 wells were drilled in other parts of the basin. Recent seismic interpretation indicated that most of the drilled wells were located of structures.

Hamza oil field is a narrow elongated E/W tilted horst block. The oil is produced from the Cenomanian Shueib and Hummer formations. By now only 826000 barrels of oil was produced. Geochemical studies indicate that 430 million barrels of oil was generated in Azraq Basin out of which 43 millions was trapped.

 

Geometry of Hamza Oil Field

a. Source Rocks and Maturation

The produced oil from Hamza oil field is genetically tied to the organic rich rocks of the lower part of Wadi Es Sir formation (Turonian). The oil generated from this interval is sweet (low sulfur), medium gravity (28 – 29 API). The initial oil generation triggered during the Eocene time. Significant generation and migration of the oil occurred in Miocene time. The oil window of this source rocks is 3000 meters. This depth equates to a temperature of 90 degrees C.  The area down dip of 3000m, such as the down thrown block of Fuluq Fault is considered of prime important for oil generation. An estimated 430 million barrels of oil was generated from this source rock only. Hamza oil field contains a small fraction of this oil approximately 1 million barrels. If only 10% of this amount is trapped then 43 million barrels would be available in other undiscovered structures in the basin.

A second type of oil was most likely generated indigenously in the Upper Cretaceous Ghareb and Amman formations. This sulfur rich oil formed at a relatively early stage of maturation.

Maturity Map of the Turonian Source

The middle Cambrian Burj group may provide possible oil source rock intervals, with varying richness and thickness. They are possibly within the oil window on some paleo-high or in shallow parts of the basin.

b. Reservoirs and Seals

Potential reservoir zones are distributed within most of rocks in the geological column of the Azraq Basin. Log interpretation, and core descriptions indicate that rocks with fair to good reservoir quality are available in the Paleozoic, Alb/Apt and the Campanian clastic, among these, the Alb/Apt.  Kurnub sandstone stands up with its excellent reservoir quality. A strong oil shows was reported in these sands in HZ-14 well.

 On the other hand, there are two proven carbonates reservoirs of Cenomanian age, in the basin; they are the Shueib and Hummer formations. Shueib is a dolomitized carbonate shelf deposit; sucrosic with abundant intercrystalline and moldic porosity enhanced by dolomitization and natural fractures. Both Wire line logs and core analysis showed that the porosity of Shueib formation ranges from 7 - 10 % with 1.3 and 22.8 md calculated arithmetic permeability’s respectively. The total thickness of this formation is 45 meters. By the same token, Hummer formation consists of 45 meters carbonates, somewhat dolomite towards the base. In general, due to the dense character of the Hummer formation, the porosity and permeability values are much lower than Shueib formation. Core analysis showed that an average porosity of 3.1% along with an average arithmetic permeability of 2.2 md. The argillaceous limestone and shale of Wadi Es Esir provide the seal.

Hz-12 Well, Global Interpretation of (DLL, MSFL, LDT, ISF, BHC, NGT) Logs

c. Trap

Hamza Oil field was discovered on top of an E/W tilted narrow horst block, with steep flanks. The field is located in Hamza graben, which is a principal sub-basin of the Azraq Graben.

X-Section Shows the Structural Configuration of Hz- Oil Field

Hamza graben is bounded by two NW/SE major faults, Fuluk left lateral fault and Rajil fault. Hamza structure is possibly an old uplifted positive flower structure. A later tensional tectonics phase may have formed the pronounced horst. Closure along the horst is provided either by a anticlinal flexure, or by narrowing of the horst block until the bounding faults join in the up dip direction.

Hamza Oil Field Play Summary

Seismic interpretation showed that there are grabens other than Hamza graben in the basin, such as Northern Hamza Graben to the north of Hamza Field. This could be an attractive structure for hydrocarbon exploration.

Fractures

Fractures are playing very important role in terms of productivity and migration pathways in Hamza oil field. Detailed micro tectonics study of 600 meter/cores showed that, the porosity and permeability of Cenomanian reservoirs are drastically enhanced by widespread fracture network. Three sets of fracture were recognized creating rubble zones and sweet spots. These fractures mostly open, wide angled and oil stained. Both reservoirs show strong fracture intensity ranges from 2 fractures to 20 fractures per meter. The density and distribution of these fractures are function of the structural attitude and history. 

  

  Part of Structural Log (Hz-4 Well)

East / West fractures provided migration pathways for the generated oil from the deeper part of the basin to Hamza structure, even in dry wells these fractures were open and oil stained. 

The Azraq Basin Block is now open for PSA

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