Facies Architecture in Outcropping Analogues for the TAGI Reservoir. Exploratory Interest

Viseras, César ¹; Fernández, Juan ¹; Henares, Saturnina ¹; Cuéllar, Nathanael ²
(1) Stratigraphy and Paleontology, Sedimentary Reservoirs Workgroup (SEDREGROUP), University of Granada, Granada, Spain. (2) Crimidesa Maroc S.A., Taroudant, Morocco.

The pattern of stratigraphic architecture in red beds successions developed in a continental rift context shows important similarities in both the general features of the stratigraphic succesion and the development of meso-scale architectural elements.

We study two examples of Spain and Morocco, in which we differentiate 12 sandy architectural elements that are resembled the productive beds of the TAGI (Algeria). The Spanish example corresponds to the Triassic Red Beds that are part of the Tabular Cover of the Iberian Meseta (TIBEM). In Morocco we have analyzed the thick Permian-Triassic successions that crop out in the western extreme of the High Atlas (THATLAS).

With a low interest are the crevasse complex, levee and sheet flood deposits, among others, characterized by small thickness and frequent interbedded fine sediments.

Intermediate interest have the high sinuosity and straight channels, leading to sandy ribbon-type bodies of intermediate thickness and lateral continuity. These bodies are vertically and laterally well sealed by fine sediments, but sometimes appear highly compartmentalized.

The deposits of braided and anastomosed channels have a high interest. The first ones form elements of up to 40 m thick and 300 m of lateral continuity, and we find large differences in porosity and permeability depending on if it is channel or bar facies. The anastomosed system gives rise to a body of up to 15 km of lateral continuity and about 20 m thick. In this case the island facies, dominated by clayey sediments, act as a barrier to lateral movement of fluids, so that the degree of impregnation will depend greatly on the direction in which the secondary migration has occurred.

The best reservoir rock is represented by braidplain deposits, which form beds 15-20 m thick, with kilometric lateral continuity and well defined top and bottom. This architectural element is characterized by high values of porosity and permeability and low internal lateral or vertical barriers that impede the movement of fluids. Given the geometry and the texture of this braidplain architectural element, discoveries in this type of sedimentary body allow extrapolation to an extension of many km². Also, a very accurate reserve estimation can be performed.

The identification of these different architectural elements in cores of the TAGI can have a high interest with regard to the planning of its exploitation.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.