3-D Numerical Modelling of Hydrocarbon Generation From the Barremian-Aptian Source Rock Unit of the Northern Orange Basin, South Africa

Abstract

A 3D Numerical modelling of hydrocarbon-generation from the Barremian/Aptian source rock intervals encountered in the northern part of the Orange Basin was done using the Basin boundary conditions of Heat flow (HF), Sediment Water Interface Temperature (SWIT), and Paleo-Water Depth (PWD) . The model results shows source rock reached a sufficiently mature stage around 108 Ma (Late Albian/Cenomanian), with VR values ranging from 0.64 to 0.72 in the northeastern to southwestern section of the study area respectively. The model reveals transformation of organic matter began from the centre of the study area (graben-filled depocentre) and increases towards the fringes. Hydrocarbon-generation reached its peak during the late Cretaceous, which coincides to the period of uplift of the entire Africa margin. At present day (0.0Ma), 100% transformation of organic matter into hydrocarbon has occurred at central section of the study area, while transformation into hydrocarbon has not occurred in extreme northeastern section. Consequently, good potential for future source rock transformation into hydrocarbon in the northern part of the area may be expected. Additionally, the 3D model precision was tested using 1D calibration data from wells AO-1, AE-1 and AF-1 spaced along the North-South trend in the study area. The calibrated temperature data from the three wells agrees well with the modelled temperature, while there are slight variations in modelled Vitrinite data and the calibrated Vitrinite data in the three wells, especially during the Cenomanian-Turonian and late Maastrichtian. These variations suggest the influence of additional regional or localized heat flow during these periods. However, 1D temperature and maturity calibration data for well AO-1(northern part) also indicates that the source rock is not yet thermally matured, which agrees well with the 3D model which indicates source unit in the northern part has not reached a maturity stage. The bulk generation and expulsion statistics shows that, at present day, 43070.94Mtons of gas and 3839.53Mtons of oil had been generated by both primary and secondary cracking processes, representing 91.81% and 8.19% of organic matter transformed into gas and oil respectively. The source rock has an expulsion efficiency of 0.77 on a scale of 1, which suggests good efficiency.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018