Claude G. Abry¹

(1) Phillips Petroleum Company, Bartlesville, OK

ABSTRACT: Quantitative Estimation of Fracture Intensity and Fault Zone Deformation in a Carbonate Reservoir, Ambrosio Field, Venezuela

The Ambrosio field is located offshore on the NW side of Lake Maracaibo, Venezuela. The lower Cretaceous Cogollo group forms the reservoir, which consists of carbonates deposited over a broad shelf. High-energy grainstones and packstones alternate with low-energy tidal-flat and lagoonal sediments.

Because of low matrix porosity and permeability in the carbonates, fractures play a major role in augmenting well productivity. Susceptibility to fracturing increases from marls to ductile clayey carbonates to brittle clean carbonate.

The procedure to evaluate fracture intensity in the reservoir combines two techniques: (1) Gaussian Curvature analysis which calculates the extent to which a layer has been stretched or compressed to form a non-cylindrical fold, and (2) Fault Zone Deformation analysis which calculates the width and intensity of deformation due to throw in bands centered on fault traces.

Both techniques were first calibrated against well productivity, then combined using cross plots and linear regression. The resulting porosity modifier was applied to selectively enhance matrix porosity in a 3D model of the reservoir volume.

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