Identifying Source Rocks in Frontier Basins on Seismic Data, Evidence from West Africa and Implications in the Eastern Mediterranean

Spectrum’s David Eastwell, Karyna Rodriguez and Neil Hodgson produced this abstract for PETEX 2018.

The most important component to a working petroleum system is the presence of a hydrocarbon producing source rock. When operating in frontier or immature basins, identifying potential source rocks can be difficult in the absence of well data or onshore outcrop analogues. Until recently the interpretation approach to identifying source rocks on seismic data would require either a tie to a pre-existing well, or a holistic approach based on a geological model and experienced “eye” of the interpreter.

In 2011 Løseth et.al published a set of four criteria which can be used by interpreters to constrain the horizon picks for a candidate source rock as well as provide quantitative evidence as to its presence. The Løseth et.al 2011 Criteria are as follows:

  1. The top and base of thick (>20m) organic-rich claystones are expressed by a significant reduction and increase in AI respectively.
  2. The top of an organic-rich claystone will show a reduction in amplitude with increasing reflection angle at the top of the unit (AVO class4).
  3. Assuming otherwise constant rock composition and consistent embedding rock properties, the amplitude at the top and base of the source unit will vary laterally, rising with increasing TOC%.
  4. The seismic amplitude response vertical profile should reflect the vertical TOC%profile over the source unit.

Spectrum has developed an integrated process for the identification of source rocks on seismic data utilizing a three step methodology. First step is the traditional process of establishing a geological model and rationale for the deposition and preservation of a source rock. Secondly a modified Løseth 2011 characterization is undertaken including frequency analysis and finally these steps are integrated with non-seismic based DHI’s such as satellite derived seep studies.

Presented in this paper are two example case studies demonstrating this methodology. Firstly using a known and proven oil producing marine shale source rock, the “Kudu” Barremian-Aptian shale in Namibia. Secondly using the same process to identify and de-risk a previously a proposed but unproven Paleocene-Eocene source rock in the Eastern Mediterranean.

 

Click to read the full abstract here:
Identifying source rocks in frontier basins on seismic data,
evidence from West Africa and implications in the Eastern Mediterranean