Overview

The onshore Gharb basin is located in the external zones of the Rif foldbelt. This basin, covering an approximate area of about 7 394 Km², extends from the city of Sidi Kacem to the South East to Moulay Bousselham village to the North West. To the West, the Atlantic Coastline between Moulay Bousselham and Kenitra cities limits the basin.

Data base

  • Seismic data:In the Gharb basin, many seismic campaigns have been acquired so far. The existing seismic data includes 5 877 Km of 2D and 798 Km² of 3D seismic are being acquired.
  • Wells data:Over eighty exploratory wells have been drilled out of which some have produced biogenic gas and/or being produced.

Basin fill and geometry

The Gharb basin is a foreland to fore deep basin type developed at the front of the Rifain Chain. Sedimentary evolution led to the deposit of more than 3000 m of Upper Miocene clastic sediments above the complex of nappes. A very thick series of Eocene and Oligocene turbidites and Early to Middle Miocene continental molassic sediments are developed within the infranappe sequence overlying the Mesozoic carbonates and clastics.

Petroleum system

Source rock

The Gharb is a biogenic gas producing basin. Methane is early expelled from Upper Miocene type III or I source rocks (mainly shale and marls) and trapped within surrounding sand lenses. In the central part of the basin, at depths greater than 1600 m, Cretaceous source rock, located within the complex of nappes would be mature and would generate oil or cathagenic gas.

Reservoir Rocks

Reservoir rocks have been deposited during Tortonian and Messinian times, series with turbiditic sandy lenses were developed under fall of sea level conditions. Recorded porosities are very high and could reach 33% in some cases with an average of 25 to 30%. Permeabilities are also good to very good permitting a very good productivity such as the case of OLB-1 well (calculated permeability = 400 mD).

Seals

The seal is provided by the marls deposited during an increase in sea levels during both the Tortonian and the Messinian times. This marls called “blue marls” present very good characteristics of selling. A thin layer would be sufficient to completely isolate the reservoirs.

Traps

In the Gharb basin, objectives are presents in combined stratigraphic (sand lenses) and structural traps (faulted and folded blocs).

Play Concepts

The developed play concepts lie to the presence of amplitude anomalies within the supra-nappe sequence in the central and southern parts of the basin. Many amplitude anomalies have been identified, drilled anomalies have produced or being produced from objectives located at shallow depths (700 to 1300 m).

In the central part of the basin, at depths greater than 1600 m, Type II and I source rocks would be mature and would generate oil. This increases also the probability of generation from the complex of nappes. As far as liquid hydrocarbons are concerned, the deeper parts of the basin, which are practically unexplored, may contain potential objectives.

In the north and the north-eastern parts of the basin, recent studies have shown the presence of various zones of interest within the supra-nappe sequence. Objectives are shallow (between 100 and 700m) and are visible on seismic as amplitude anomalies related to gas caps over oil accumulations. In this area, the nappes complex (Ouezzane and Prerif nappes) may also provide good reservoirs within Eocene, Oligocene and Lower Miocene sandstone and conglomerate.

Prospects and leads

Exploration conducted so far in the Gharb basin has demonstrated the presence of important hydrocarbon potential within the Tertiary depositional system. Defined prospects are small in size but they are economically interesting for the following reasons:

  • They are located at depths less than 1500m;
  • The presence of a gas pipe network and a market for any gas that will be generated within the area.

Production history

The Gharb basin has produced oil in the Ain Hamra and biogenic gas from many small fields located within the central and southern parts of the basin. The total production of oil reached 0.1 MMbbls. The cumulative gas production is around 35 Bcf.

Basin

Gharb

Basin type

Foreland basin

Area

7 394 Km²

Exploratory wells

82

Gas discoveries

Biogenic gas

2D Seismic/3D Seismic

5 876.91 Km of 2D / 797.87 Km² of 3D

Source Rocks

Upper Miocene (III or I); Cretaceous

Reservoir Rocks

Turbiditic sandy lenses from Tortonian and Messinian times

Seal Rocks

Marls from the Tortonian and the Messinian times

Hydrocarbon type

Biogenic Gas