--> ABSTRACT: The Perla World-Class Giant Gas Field, Gulf of Venezuela: Depositional and Diagenetic Controls on Reservoir Quality in Early Miocene Carbonates, by Borromeo, Ornella; Miraglia, Salvatore; Sartorio, Dario; Bolla, Eleonora M.; Andrea, Ortenzi; Reali, Sandro; Castellanos, Carlos; Villalobos, Rosemary; #90135 (2011)

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The Perla World-Class Giant Gas Field, Gulf of Venezuela: Depositional and Diagenetic Controls on Reservoir Quality in Early Miocene Carbonates

Borromeo, Ornella 1; Miraglia, Salvatore 1; Sartorio, Dario 1; Bolla, Eleonora M.1; Andrea, Ortenzi 1; Reali, Sandro 2; Castellanos, Carlos 3; Villalobos, Rosemary 3
(1)Eni E&P, San Donato Milanese, Italy. (2) Cardon IV, Caracas, Venezuela. (3) MENPET, Caracas, Venezuela.

The recently discovered PERLA Field is a massive natural gas accumulation found offshore Gulf of Venezuela. The reservoir is interpreted as an early Miocene carbonate bank developed upon a basement high. The integration of available data, 3D seismic and three wells, two of them with consistent cored intervals, allowed the definition of a preliminary geological model and the identification of the major depositional and diagenetic controls on the reservoir quality.

The reservoir consists mainly of limestones with minor sandstones and dolomitic and silty limestones in the lower part. Dominant components are branching red algae, rhodoliths and larger foraminifera, with lesser amounts of finger corals, mollusks, barnacles, green algae, bryozoans and planktonic forms. Rhodalgal carbonate systems are common from Miocene to Recent and usually form coarse, grain-supported bodies whose texture and geometry are strongly controlled by depositional physico-chemical processes.

Cores recovered from a well drilled in the western margin of the bank, suggest a ~200 m-thick succession of rhodalgal carbonates with an overall deepening-upward stacking pattern. In general, from base to top, the section changes from relatively shallower middle ramp facies, composed of grainstones with larger foraminifera and branching red algae debris, to deeper outer ramp facies dominated by rhodolith floatstones/rudstones and planktonic foram-bearing grainstones, ending with a drowning unconformity.

Although cementation is significant in the middle ramp facies, the primary interparticle porosity was enhanced during marine phreatic to shallow burial diagenesis by dissolution of unstable grains (probably made of aragonite and/or high Mg-calcite); this process produced biomoldic porosity partially cemented later by equant calcite. The pore system is dominated by micropores (<50 µm) and the facies are characterized by high porosity and low permeability. In the uppermost and coarsest outer ramp facies, the unstable components were relatively less important and cementation in the marine phreatic to shallow burial realm was less effective. This favored the preservation of primary inter- and intraparticle porosity and resulted in a pore system with moderate to high porosity and high permeability.

 

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