Calibration of Igneous Systems and Basin Prospectivity using 2D Seismic and Potential Field Interpretations

Krassay, Andrew; Connors, Karen; Pryer, Lynn; Jorand, Cedric
FrOG Tech, Canberra, ACT, Australia.

Exploration for unconventional and conventional hydrocarbons is experiencing a boom in older, onshore basins where seismic data is commonly sparse. In Australia, large onshore Proterozoic to Mesozoic basins host multiple working petroleum systems, potentially huge volumes of gas and oil, and have been affected by many igneous events. In onshore South America, the interior Paleozoic basins feature Triassic and younger igneous events that affected generation timing, reservoir quality, preservation potential and migration.

Regional 2D seismic is used to interpret the location, depth and thickness of igneous rocks that have intruded into source-reservoir systems. Seismic facies analysis is important for assessing lithofacies variations where interbedded volcanics are present. In the Jurassic-Cretaceous Otway Basin, seismic interpretation helps distinguish synrift flow-basalts from lacustrine shale source intervals.

In the greater McArthur Basin in northern Australia, dolerite sills have been intruded directly into the main marine source rock and above and beneath the main conventional reservoir. Similarly, in onshore South America (eg. Solimões, Amazonas basins) Mesozoic sills and dykes have been intruded directly into the Paleozoic petroleum systems elements and provide the critical moment for these systems.

Basalt flows and diabase sills are commonly able to be mapped on the seismic data but it is more difficult to interpret dykes on seismic data alone. Igneous units commonly exhibit high seismic reflection amplitudes compared to surrounding basin units. Seismic interpretation of the character and type of the igneous units is important for identifying the likely location of igneous feeder systems and the possible extent of the igneous systems.

Combining seismic and potential field interpretations provides many benefits. Firstly, potential field data commonly cover a greater area than seismic grids and allow an interpretation to be expanded across an entire basin to rapidly assess prospectivity and volcanic risk. Secondly, high resolution magnetic and gravity data can help distinguish subtle igneous features such as dyke trends and igneous centres (igneous complexes, feeder systems) that may be obscured on seismic. Thirdly, the correlation of seismic and wells to potential field data is critical for mapping basement depth, and composition and interpreting deep-seated fault control on igneous bodies and the role of basement heat flow for basin modeling.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012