--> Abstract: Integration of Outcrop and Subsurface Fracture Data for Reservoir Modeling of the Natih Field, North Oman, by C. G. L. Mercadier and H. U. C. Milatz; #91004 (1991)

Datapages, Inc.Print this page

Integration of Outcrop and Subsurface Fracture Data for Reservoir Modeling of the Natih Field, North Oman

MERCADIER, C. G. L., and H. U. C. MILATZ, Petroleum Development Oman LLC., Muscat, Sultanate of Oman

The Natih field reservoir comprises several distinct fractured limestone intervals which contain some 500 * 10x6 cu m STOIIP. The field is being developed by gas-oil gravity drainage. Fracture orientations, dimensions, and spacings are critical to predict the effectiveness of this process. Statistically representative fracture data from Cretaceous Natih outcrop analogs in North Oman, core data, and electrical borehole imagery provided a realistic input for Natih field reservoir modeling and simulation.

In the outcrops the fractures trend both cross-axially and longitudinally with dimensions and spacings varying with lithology, bed thickness, and curvature. Dimensions of matrix blocks in clean thickly bedded limestones are an order of magnitude greater than in more argillaceous thinly bedded limestones.

Subsurface data from the Natih reservoirs indicate that open cross-axial subvertical northeast-southwest-trending fractures dominate and strongly influence the reservoir flow pattern, but longitudinal fractures could not be identified. This is in line with the orientation of the present day, principal horizontal in situ stress that preferentially keeps open the cross-axial fracture set. Fracture apertures from borehole imagery have a range of 0.1 to 0.3 mm which is consistent with that derived from reservoir pressure behavior.

Combining outcrop and well data results in a Natih reservoir fracture model with open cross-axial fractures that have a lithology dependent spacing of 0.1 to 2 m over the entire structure. From these data fracture porosities are calculated for each gridblock in the model. Longitudinal fractures probably exist in the vicinity of faults and in the northern part of the field where rapid down-warping occurs.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)