20th October 2020
Speaker: Stuart Harker
Topic: Onshore Petroleum Geology of Morocco, Underexplored or Underperformance?
Examples are given of several areas in onshore Morocco that have proven petroleum systems. However, the volumes found and produced are very low in comparison to the aerial extent of the basins. This may be the result of underexplored stratigraphy and trap types or possibly due to underperformance of the petroleum systems. The presentation is a personal view based on eight years’ experience of the author working on Moroccan exploration and production projects. The one really successful venture has been for shallow gas in the Rharb basin and most detail is presented on this region.
The Rharb Basin lies onshore to north of the Moroccan capital of Rabat and south of Tangier, situated between the Atlantic coast and the Rif Mountains and contains a thick succession of Late Tertiary sediments. Oil exploration in this foreland basin started with the first well in 1890, based on the location of surface oil seeps. Field mapping of surface structures and later magneto-telluric surveys continued through to the 1950’s with the discovery of some small shallow oilfields (Tselfat, Ain Hamra and Bou Draa) and a series of small gas fields on the Sidi Fili trend. Petrofina started using multitrace seismic in the 1960’s leading to several small gas discoveries. In the 1970’s with the advent of bright spot technology, additional gas discoveries were made, though several dry holes were also drilled.
2D seismic was the “norm” in the Rharb until the winter of 2007-2008, when Circle Oil acquired a 3D seismic survey over after the Sebou concession, which had been granted in 2006. The initial drilling programme started in September 2008 following interpretation of the 3D and the first well was successfully tested as a gas discovery and the well was tied into the existing small capacity pipeline to the local industry in the coastal town of Kenitra. First gas was produced in November 2008. Several wells have been drilled since that with considerable success.
A sequence stratigraphic subdivision of the mudrock dominated Mio-Pliocene “Productive Series” has been used to distinguish and map eight units for the central part of the Rharb Basin. The gas-bearing sands are of good reservoir quality, but usually thinly bedded. Where gas bearing, the seismic response of the sands shows up as bright negative amplitudes, due to the lower density and slower seismic velocity compared to the water-bearing sands and the encasing mudrocks. Modern 3D seismic makes the location and geometry of these anomalies stand out as clear drillable targets. The gas is contained in combination structural-stratigraphic pinchout traps, with top, bottom and lateral seals provided by coeval marls and shales.