Phil C. deGruyter¹

(1) Repsol-YPF, Englewood, CO

ABSTRACT: Reserve-Scale in Thrust Fronts

One of the most significant trends in the oil industry over the past ~15 years is a series of discoveries and "re-discoveries" in thrust-front settings. By far, these represent the largest contribution of new reserves for South America - on the order of 12-15 Billion BOE. The focus here is to show how thrust-fronts are often confused with high-risk "thrustbelt" settings and how their characterization can help the scale-conscious explorer.

The relationship between thrust-fronts and big reserves is not a coincidence. It is the result of the efficient interaction of the "structure-prone" deformational front and the "kitchen-prone" foredeep or buried imbricate stacks with source rock units.

Thrust-fronts can be divided into ~6 types in which the most HC-prone tend to be buried thrust-fronts with 1) low-angle thrusting, 2) at least one prolific source rock and 3) a multi-cyclic structural history of repeated subsidence and uplift cycles. These ingredients tend to create multiple large prospects with repeated and/or thickened reservoir, source rock and seal units.

Thrust-fronts have notorious "finding lags" of 10-30+ years due to poor initial understanding and lack of project confidence, but once "on track," trend statistics demonstrate excellent finding rates with large field size distributions. To avoid the "learning dilemma" facing many companies in compressional trends, there is a need to precisely capture the characteristics of these trends and fields and organize the prospect criteria and methodology in order to perform the predictive work necessary for finding the next discoveries and for extending the known trends.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado