--> Abstract: Indirect Fracture Delineation in a Carbonate Reservoir: The Upper Jurassic Hanifa of Abqaiq Field, Saudi Arabia, by D. L. Bailey; #91004 (1991)

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Indirect Fracture Delineation in a Carbonate Reservoir: The Upper Jurassic Hanifa of Abqaiq Field, Saudi Arabia

BAILEY, DONALD L., Saudi Aramco, Dhahran, Saudi Arabia

Abqaiq field is a northeast-trending anticline approximately 60 km long and 12 km wide and contains several reservoirs. The Hanifa Reservoir is approximately 100 m thick and consists of fine-grained, muddy limestone with subordinate dolomite and anhydrite. Since discovery of the Hanifa oil pool in 1947, pressure fluctuations have indicated communication with the overlying Arab-D Reservoir. Welltest permeability measurements are approximately 40 times higher than core permeability measurements for the Hanifa. This divergence of Hanifa permeability measurements combined with the indicated Arab-D communication suggests the presence of a natural fracture network. Direct observations of Hanifa cores reveal common, sub-vertical fractures with average apertures <200 microns. With limited ore coverage and no oriented cores, a new technique was needed to delineate the areas affected by fractures. A technique combining indirect fracture indicators was devised for Abqaiq field and can be applied to other, similar fields.

Four indirect fracture indicators were evaluated for Abqaiq: (1) welltest and core permeability comparison, (2) flowmeter indications of abnormal flow, (3) lost circulation while drilling, and (4) percentage of lost core intervals. Considered alone, each of these factors has limitations; but combined, the individual limitations are minimized. Using standard computer mapping packages, all four indicators were individually gridded and then combined to produce an AREA OF COMMUNICATION MAP that areally delineates the open, natural fracture network. This map is being used in reservoir simulation studies to define the area of Hanifa/Arab-D communication and to explain several local water influx anomalies in both the Hanifa and Arab-D reservoirs. The actual flow system of the Abqaiq Hanifa i a complex interaction between matrix porosity/permeability and fracture permeability or "enhanced permeability." Future development plans allow for low matrix permeability access to much of the Hanifa storage space and high fracture permeability both within the Hanifa and connecting to the Arab-D Reservoir.

 

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