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A Virtual Ride through a Fractured Microbialite Carbonate: 3D Digital Reservoir Model of a Microbialite Reef in the Neoproterozoic Nama Group in Namibia

Winterleitner, Gerd *1; McCaffrey, Ken 2; Mapani, Benjamin 3; Vining, Bernard A.4; Le Heron, Daniel P.1; Figueiredo, Carlos 5; Kandjoze, Obeth Mbui 6
(1) Earth Sciences, Royal Holloway, University of London, Egham, United Kingdom.
(2) Earth Sciences - Reactivation Research Group, University of Durham, Durham, United Kingdom.
(3) Department of Geology, University of Namibia, Faculty of Science, Windhoek, Namibia.
(4) Baker Hughes, London, United Kingdom.
(5) Sonangol Gas Natural, Luanda, Angola.
(6) Namcor, Windhoek, Namibia.

In this study, we describe and interpret a reservoir model constructed from a Neoproterozoic fractured thrombolite-stromatolite reef system. Due to the increasing significance of these systems as possible hydrocarbon reservoirs, a better understanding of their internal structure is required.

A new frontier in approaching this problem is the development of digital outcrop models (DOMs). These are highly valued datasets in petroleum geoscience because they allow all elements of a petroleum system to be imaged in detail. Light detection and ranging (LiDAR) is a technique that has come to the forefront of creating DOMs in the last decade. This laser-based measurement system allows the rapid acquisition of detailed point data describing an outcrop in 3D with high precision of a few centimeters. In conjunction with traditional mapping methods, these 3D photorealistic DOMs are used for the development of static and dynamic reservoir models. Field geologists can bring the outcrop virtually to the office.

As a potential reservoir analogue, outcrops of the Omkyk Member in the Neoproterozoic Nama Basin of Namibia were chosen for the development of a DOM. The exceptional quality of the outcrops provides an excellent opportunity to study a microbial dominated reef system as a potential reservoir. This reef complex developed in a wave-dominated inner carbonate-ramp setting and it is characterized by the evolution of individual thrombolite-stromatolite build-ups. Previous studies have shown that the spatial distribution of the reefal build-ups is the major constraint on the reservoir quality and connectivity. However, these studies have not investigated the fracture and fault network, which has a major impact on the connectivity between the individual build-ups and consequently on the reservoir quality. We scanned and digitized an area of approximately 3 km2 and evaluated the contribution of the fracture patterns to the enhancement of the reservoir quality. We developed a reservoir model with the modeling software JewelSuiteTM to simulate the interplay between vertical and lateral facies changes and fracture sets. In this paper, we show how LiDAR based mapping and the quantitative acquisition of fracture and fault patterns improve our understanding of fractured carbonate reservoirs.

Furthermore, this reservoir model can be used as a base model for microbialite reservoirs, such as the reservoirs in the recent giant discoveries in the Cretaceous pre-salt, offshore Brazil.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California