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Dhahirah - Block 43B

SUMMARY

Block 43B is an 11,967 km2 area located along the coastal area of Oman north of the Hajar Mountains. This is an unexplored region, both geographically and stratigraphically. Block 43B has time-equivalent formations with the interior of Oman but these have not been explored in any depth.

The known formations located in the block are well-displayed in outcrop. Those that are the most likely reservoirs are thick and comparable in rock properties to oil-bearing formations in the interior of Oman. In the subsurface within the block these potential reservoir rocks have had gas shows.

Conventional gas is the main play type across the block. Oil is also possible since this block’s burial was not as deep as those to its south. While there have been no discoveries (only two wells have been drilled here) there are several prospects mapped across the block.

BLOCK OWNERSHIP HISTORY

Over its history Block 43B has had several owners, the primary ones being Petroleum Development (Oman) and Amoco. Other companies which have owned this block are:

  • Hawasina, LLC
  • MOL

Only two wells have been drilled. The first was drilled in 1985 by Amoco: the Barka-1. The last well, the Hawasina-1, was drilled by MOL. The last owner of the block was MOL.

AVAILABLE DATA

  • 1,200 km of 2D seismic data
  • Block seismic base map, satellite image map and infrastructure map
  • Gravity data
  • Data for two wells

Seismic and well location base map

STRATIGRAPHY

Oman chronostratigraphic chart (GTS 2012 dates incorporated)

The stratigraphic section that occurs within this block is predominated by Tertiary age carbonates and clastics. The Eocene and Paleocene formations are the most significant potential reservoirs. The Miocene through Pleistocene section has a complex stratigraphic architecture. This section is potential reservoir. The Campanian age Al Khwad Formation is a possible reservoir.

From a chronostratigraphic point of view the section within Block 43B is equivalent to the post-Fars, Fars, Hadhramaut and Aruma groups.

Stratigraphic column for Block 43B

Stratigraphic relationships for Block 43B. The base of the Al Khwad Formation is an unconformity. In some areas this formation may sit directly upon ophiolites, as shown here.

Based on outcrop and seismic analyses the entire stratigraphic section from Campanian through Holocene is characterized by numerous unconformities. These are directly related to two controlling factors:

  • Post-Cretaceous structuring due to tectonic plate interactions.
  • Sea level variations due to Tertiary age glacial episodes.
In addition to the unconformities the block covers the northern platform edges for several thick intervals. Vertical build-ups and progradational clinoforms occur along these edges.



Platform-edge mounding and clinoforms within the Seeb Formation.

OUTCROP AND ANALOGS

The Maastrichtian through Holocene sedimentary section is accessible and well-exposed in the mountains around Muscat. These provide a clear representation of the overall lithologies and stratigraphic successions expected to occur within the block. The specific formations that outcrop around Muscat are:

  • Undifferentiated Holocene, Pleistocene and Pliocene sediments
  • Seeb Formation
  • Rusayl Formation
  • Jafnayn Formation
  • Al Khwad

The outcrop belts extend to Wadi Tiwi, westward along the coast from Muscat.

DISCOVERIES

There have been no discoveries within the block. Gas shows were encountered throughout the carbonate units in the Barka-1.

PROSPECTS

Several prospects have been mapped within the Seeb Formation. These occur along the coastal portion of the block.

TRAP

Predominantly 2-way dip-closed, fault-bounded anticlines. Stratigraphic traps associated with reefs have been identified in adjacent blocks and are expected to occur within this block. Platform-edge mounding and progradation are visible on seismic within the block (see previous figure). Elsewhere in Oman, such as in the Natih and Shuaiba formations, such geometries result in successful stratigraphic traps.

SW to NE seismic line (4BAR-06/08) illustrating structure. Evidence of thrusting visible as are antithetics which create fault-bounded closures.

RESERVOIR

Reservoirs include stable, shelf limestones in the Seeb and Jafnayn formations, sandstones and conglomerates in Pliocene through Holocene deposits and limestone-dominated clastics in the Pliocene and Pleistocene deposits. Clastics in the Al Khwad Formation may also be of reservoir quality. The Seeb and Jafnayn formations have good reservoir quality with high porosity as well as permeability.

SEAL

Locally seals within the limestone units are probably thin but continuous shales/marls. On a more regional scale shaly units within the Rusayl Formation, marls within the Jafnayn and Seeb formations and Batinah Group marls and shales could serve as effective seals. The potential sealing intervals are visible in outcrop and contribute to the overall flat-iron patterns in the mountains near Muscat.

SOURCE

The Early Eocene rocks are considered a primary source. Paleocene and Maastrichtian rocks may also contain source rocks. Numerous possible migration pathways exist along bedding and faults.



Page created at 20/09/2016
Last updated at 12 Sep