--> Abstract: New Concepts in Exploring Subsalt Hydrocarbon Systems in Mature and Near Producing Areas of Morocco, by H. Jabour and A. Demnati; #90933 (1998).

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Abstract: New Concepts in Exploring Subsalt Hydrocarbon Systems in Mature and Near Producing Areas of Morocco

Jabour, Haddou; and Demnati, Ahmed - ONAREP

The subsalt hydrocarbon systems are one of the areally largest and remain, paradoxically, the least drilled in Morocco. Although, worldwide, these systems contain the largest potential plays and better still the few wells drilled to test the system in Essaouira Basin are producing commercial wet gas, these systems have never been tested in any other basin in Morocco. Large exploration areas in the Atlantic deep-sea, shelf and in the onshore Prerif and lnteratlasic Basin containing these systems await to be tested.

Impediments to exploration in these areas focused on the inability to map beneath the "geophysical basement" to seismically image subsalt structures.

Experience in the Gulf of Mexico's subsalt exploration play shows that careful survey design, use of basic techniques where they are not normally applied, and rigorous quality control can improve accuracy of the ultimate salt imaging techniques such as 3D prestack depth migration (PSDM), 3D subsalt AVO, and coherence technology. Understanding of subsalt geology becomes much clearer after integration these various geophysical tools and research ideas.

In Morocco to date, no 3D seismic data is acquired. However, recent integrated study combining newly acquired deep targeted 2D seismic, gravity, magnetic, geochemical data and basin modeling technique, has permitted to decipher some of the pre-salt structure, interpret basin evolution and assess source rock potential. Two sets of sub-salt petroleum systems are identified: (1) Triassic purebred systems and (2) Paleozoic hybrid systems.

Triassic systems are comprised of postulated lacustrine deposits rich in type I kerogen similar to those recorded in the Coeval basins of Newark. This oil prone source can be expected to charge alluvial fan and fluvial clastic reservoirs in both the hanging wall and the footwall of the half graben. Thick upper Triassic-lower Jurassic salt provides adequate sealing for this system.

Paleozoic sub-salt systems in the onshore evolved in basically five stages: (1) simultaneous sediment accumulation and structural formation during the Paleozoic, (2) major tectonism and erosion in late Paleozoic (Hercynian), (3) Triassic- lower Jurassic deposition of a regional seal (salt and evaporites), (4) Mesozoic charging primarily from Silurian to Carboniferous sources, and (5) re-initiation of generation from Silurian source in uplifted blocks following atlasic (Neogene) compression. Large subsalt structures and prospective stratigraphic features exhibiting many similarities to the prolific Triassic objectives of neighboring Algeria are still untested in Moroccan onshore basins.

In addition to these mainly onshore-located systems, a variety of attractive salt-related play concepts exist in the offshore area. As a result of Alpine structural inversion, Triassic-Lower Jurassic salt was injected into younger sequence of Cretaceous/ Jurassic is present underneath the salt in offshore Essaouira Basin providing attractive sub-salt plays. In the offshore Tarfaya Basin, salt diapirism created numerous closures against salt walls and salt overhangs within Cretaceous and younger sequences especially in the deepwater.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil