Source rock characteristics and compositional kinetic models of Cretaceous organic rich black shales offshore southwestern Africa

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doi: 10.1016/j.orggeochem.2012.07.008
Author(s): Hartwig, Alexander; di Primio, Rolando; Anka, Zahie; Horsfield, Brian
Author Affiliation(s): Primary:
German Research Center for Geosciences, Potsdam, Germany
Volume Title: Organic Geochemistry
Source: Organic Geochemistry, Vol.51, p.17-34. Publisher: Elsevier, International. ISSN: 0146-6380
Note: In English. 75 refs.; illus., incl. 4 tables, sketch map
Summary: The source rock potential of Cretaceous organic rich whole rock samples from deep sea drilling project (DSDP) wells offshore southwestern Africa was investigated using bulk and quantitative pyrolysis techniques. The sample material was taken from organic rich intervals of Aptian, Albian and Turonian aged core samples from DSDP site 364 offshore Angola, DSDP well 530A north of the Walvis Ridge offshore Namibia, and DSDP well 361 offshore South Africa. The analytical program included TOC, Rock-Eval, pyrolysis GC, bulk kinetics and micro-scale sealed vessel pyrolysis (MSSV) experiments. The results were used to determine differences in the source rock petroleum type organofacies, petroleum composition, gas/oil ratio (GOR) and pressure-volume-temperature (PVT) behavior of hydrocarbons generated from these black shales for petroleum system modeling purposes. The investigated Aptian and Albian organic rich shales proved to contain excellent quality marine kerogens. The highest source rock potential was identified in sapropelic shales in DSDP well 364, containing very homogeneous Type II and organic sulfur rich Type IIS kerogen. They generate P-N-A low wax oils and low GOR sulfur rich oils, whereas Type III kerogen rich silty sandstones of DSDP well 361 show a potential for gas/condensate generation. Bulk kinetic experiments on these samples indicate that the organic sulfur contents influence kerogen transformation rates, Type IIS kerogen being the least stable. South of the Walvis Ridge, the Turonian contains predominantly a Type III kerogen. North of the Walvis Ridge, the Turonian black shales contain Type II kerogen and have the potential to generate P-N-A low and high wax oils, the latter with a high GOR at high maturity. Our results provide the first compositional kinetic description of Cretaceous organic rich black shales, and demonstrate the excellent source rock potential, especially of the Aptian-aged source rock, that has been recognized in a number of the South Atlantic offshore basins. Abstract Copyright (2012) Elsevier, B.V.
Year of Publication: 2012
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
Key Words: 02 Geochemistry; 06 Petrology, Sedimentary; Africa; Albian; Angola Basin; Aptian; Atlantic Ocean; Basins; Black shale; Clastic rocks; Condensates; Cores; Cretaceous; Crude oil; DSDP Site 361; DSDP Site 364; DSDP Site 530; Deep Sea Drilling Project; Hydrocarbons; IPOD; Kerogen; Kinetics; Leg 40; Leg 75; Lower Cretaceous; Mesozoic; Namibia; Natural gas; Offshore; Organic compounds; Organic sulfur; P-T conditions; Petroleum; Pyrolysis; Sedimentary basins; Sedimentary rocks; Source rocks; South Africa; South Atlantic; Southern Africa; Sulfur; Thermal maturity; Turonian; Upper Cretaceous; Walvis Ridge; Waxes
Record ID: 2012088760
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands

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