Petroleum Geology Offshore Cabinda

An Overview of N’SANO Field

Technical Report 2012 22 Pages

Geography / Earth Science - Geology, Mineralogy, Soil Science


List of Contents


1. Introduction
1.1 Objectives

2. Regional Geology
2.1 Stratigraphy

3. Petroleum System - N’SANO Field
3.1 Source Rock
3.2 Migration
3.3 Reservoir rock
3.3.1 Upper Pinda Reservoir
3.3.2 Vermelha Reservoir
3.3.3 Likouala Reseroir
3.4 Seal
3.5 Trap

4. Prospectivity Impact on Block 0 - NSANO Field

5. Conclusion

6. References


Figure 1 – Location map of offshore Cabinda Block 0

Figure 2 – Generalized stratigraphic column for offshore Cabinda

Figure 3 – Main source rocks types and their origin

Figure 4 – Maturation process of organic matter

Figure 5 – Location map of Block 0 – N’SANO Field

Figure 6 – Geochemical log Bucomazi Megasystem

Figure 7 – Burial history

Figure 8 – Primary and Secondary migration

Figure 9 – Structural trap

Figure 10 – Stratigraphic traps

Figure 11 – Anticlinal trap

Figure 12 – Events chart for the Congo Delta Composite

Figure 13 – General conceptual model of a Petroleum System

List of Tables

Table 1 – Major tectonic phases and stratigraphic events

Table 2 – Block 0 N’SANO field petroleum system description

1. Introduction

The N’SANO field discovered in October 1992, is one the 21 fields owned by Chevron in Block 0 located offshore Cabinda in Angola. The Block 0 (Fig 1) has an extension from the coastline to about 200 m isobath and it is divided into three areas known as A, B, and C (Schoellkopf and Patterson 2000, p. 361). The N’SANO field located in offshore Cabinda province is at 75 meters of water in Area A of Block 0 (King et al., 1998, p. 317).

The generation of hydrocarbons in Block 0 comes from multiple sources. Three prolific source rock Megasystem have been identified, which are associated with three geologic packages, these are the lacustrine shales of Lower Cretaceous Bucomazi, the marine Upper Cretaceous Iabe and Lower Tertiary Landana shales and marls, and the Tertiary Malembo shales (Schoellkopf and Patterson 2000, p.362).

1.1 Objectives

The objective of this report is to develop an understanding of the petroleum system offshore Cabinda, specifically on N’SANO located in Block 0 Area A.

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Figure 1— Location map of offshore Cabinda showing areas A, B, and C of Block 0 (Schoellkopf and Patterson 2000).

2 Regional Geology

The offshore Angolan basins evolved from an active continental rift system during early cretaceous into a passive margin that culminated in the drift stage, which separated African from the South American plates (Machado, 2007).

The tectonic regime associated with the continental separation has been divided into four stages (Table 1), from oldest to youngest, (Cole et al., 2000, cited by Brice et al., 1982, p.326).

Firstly, a Prerift sequence occurred with the deposition of fluvial-lacustrine sands that is up to 1000 m in thickness (Cole et al., 2000, p.326). Secondly the Synrift stage characterized by graben development along the early rifted margin that formed the depocenters for organic-rich lacustrine shales. The lake systems created within the grabens were filled by lacustrine turbidites arranged laterally and upward into organic rich-shales; these are the shales of the Bucomazi Formation, the most active source rock for major oil accumulations in West African margin (Cole et al., 2000 cited by Burwood et al., 1995 and Burwood, 1999, p. 326). Thirdly, the Synrift II stage a period of regional subsidence has resulted in marine incursions, consisting of lacustrine carbonates and sandstones and alluvial clastics. At the end of this stage occurred the transitional sequence of the Aptian Loeme Salt formation, characterized by a widespread deposition of Evaporites. Finally the Post rift stage is characterized by an initial Albo-Cenomanian transgressive sequence as result from the thermal subsidence of the basins as the American and African plates separated.

2.1 Stratigraphy

Three distinct geologic packages are directly related with the stratigraphic section of Cabinda (Fig 2).

1) The Presalt nonmarine rift and sag section, 2) The salt and Postsalt marine Cretaceous–lower Tertiary drift and passive margin subsidence section, and 3) The Tertiary (Oligocene–Holocene) sedimentary wedge (Schoellkopf and Patterson 2000, p. 362).

The Neocomian to Barremian Bucomazi formation is divided into three parts; 1. The Lower Bucomazi consists of laminated shale, mudstones, calcareous shale, marl, and sandstone with thickness up to 1000 m, 2. The Middle Bucomazi consists of organic-rich shale, carbonate mudstone, and marl with thicknesses ranging up to 1000 m, and 3. The Upper Bucomazi consists of green to brown mudstone and gray shale with thickness up to 400 m (Brownfield and Charpentier 2006, p.20)

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Table 1 – Major tectonic phases, stratigraphic events, and depositional stratigraphy in the west African – represented by Lower Congo Basin (LIU et al., 2008)

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Figure 2 – Generalized stratigraphic column for offshore Cabinda. (Schoellkopf and Patterson 2000)



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ISBN (Book)
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Robert Gordon University Aberdeen
petroleum geology offshore cabinda overview n’sano field



Title: Petroleum Geology Offshore Cabinda