The Perla World-Class Giant Gas Field, Gulf of Venezuela Seismic Inversion and Integration of Geology and Geophysics as Keys for Success

Borromeo, Ornella ¹; Corrao, Antonio ¹; Marini, Alfonso Iunio ¹; Redaelli, Massimo ¹; Spadafora, Elena ¹
(1)eni E. & P. Division, San Donato Milanese, Italy.

The early integration of geological concepts and seismic interpretation enhances the probability of success of an appraisal campaign. The described workflow was applied in the Perla giant gas Field (Gulf of Venezuela), an Early Miocene carbonate reservoir.

The seismic shows an isolated bank developed upon a basement high; thickness decreases from the crestal zone toward the flanks. The discovery well Perla1X found about 200m of high porous, red algae and large benthic foram GRST/PKST.

In recent Mediterranean analogues, red algae occur from few to several tens of metres water depth. Red algae-dominated carbonate systems commonly form low angle ramps controlled by physical processes, instead of building up to sea level like classical flat-top platforms.

In such system, if diagenetic imprint is moderate or facies-selective, a stable acoustic/elastic properties vs depositional facies relationship can be established. It suggested to conjugate seismic geometries and signal attributes in terms of broad facies belts, to provide an initial frame to locate appraisal wells within defined G&G domains.

The input seismic angle-stack cubes were conditioned to improve imaging and to achieve an optimal frequency content. Subsequently, structural attributes, continuity/curvature, were computed to enhance tectonic lineaments.

AVO attributes, like Gradient, supported a detailed horizons interpretation, since interfaces respond mainly to elastic changes rather than acoustic contrasts. Quantitative use of seismic required a strict amplitude reliability assessment, adopted at a very early stage, upon the availability of petroelastic model.

Seismic inversion, was performed soon after the first well. An effort was devoted to build a realistic a-priori model, accounting for overburden and Carbonate sequences Vp fields. Results allowed to generate a Seismic Porosity Volume (SPV) which was one of the keys for success of the appraisal campaign. Appraisal wells confirmed the PHIE predictions and the approach robustness. This method was later strengthened by the availability of extensive core data.

The SPV and the preliminary sedimentary model were included into the static reservoir model, and integrated as spatial trend in the simulation process to reconstruct PHIE distribution at seismic scale.

Additionally, seismic facies cubes were generated using well-driven and non-supervised approaches, providing further input to refine the sed-model and drive Sw and K distribution.

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