Prospect Risking for Stratigraphic Traps

James G. McIlroy
PDO
[email protected]

The South Oman Salt Basin, a prolific source of oil from carbonate stringers of Neoproterozoic-Early Cambrian age, contains many prospects. The stringers are unique in that they represent a self-contained petroleum system such that each stringer includes source and reservoir units within an insulated system. Early discoveries were based on structural traps but it became clear that the trapping mechanism is the Ara Salt, within which they are encased, and that any stringer is a potential stratigraphic trap. Risking new prospects requires a unique approach that must be updated as the prospect inventory is drilled. Existing risking methods include reviewing the five factors for hydrocarbon entrapment from traditional standpoints where each parameter is risked independently. The stringer play, dominated by stratigraphically trapped reservoirs, benefits from a statistical approach to risking. Compiling a database of stringer wells and conducting post-mortems is the most acceptable base from which to risk new prospects. Examples include stringers sealed up-dip by salt, with base-seal risks and where internal compartmentalisation is required to make an effective trap. Methods used to assist de-risking include analogy, seismic attribute displays and statistical analysis. The South Oman Salt Basin stringer play has benefited from traditional interpretation; however to improve the success rate a more detailed results-based analysis is used to focus the risking. More recent results indicated that this process demonstrates that the risking of prospects is improving which benefits the whole exploration process.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain