Arches and Hydrocarbon Accumulations

M. El Hashami

Arching is a dynamic process that starts with part of the cratonic crust being folded. The fold continues to grow and may spread over hundreds of miles before its growth is terminated, usually by faulting. In many continents, arching was the dominant intracratonic structural style during the early Paleozoic. The paleogeographic effects of this evolutionary stage determine the nature, size, and trends of hydrocarbon traps in such regions.

The stage of arch growth defines the nature of future reservoirs. Pinchouts develop in a clastic sedimentary regime (e.g., Hassi Massoud, Algeria), whereas reefal belts are associated with a carbonate regime (e.g., Peace River arch, western Canada).

The stage of faulting determines the future setting of traps. The particular pattern of faults developed at the end of arch growth, and its response to later changes in stress and superposition by subsequent structural elements, define the closure, size, and distribution of hydrocarbon traps.

A model from western Europe illustrates the growth, faulting, and postfaulting stages of an arch. The duration of the growth stage in this model, from Early Devonian to Late Triassic, illustrates the role of this particular tectonic frame in the modality of sedimentation and the distribution of facies and unconformities. The faulting stage of this arch, during the Early Jurassic, was dominated by longitudinal, northwest-trending faults. These early developed faults played an important role during later tectonic events in the area.

This model and examples from North America provide clues for exploration strategy in regions that have undergone arching.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.