--> Abstract: Geological and Geometrical Characteristics of Reservoir Fracturing Throughout the Middle East, by R. Nurmi, M. Akbar, and E. Standen; #90990 (1993).

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NURMI, ROY, and MAHMOOD AKBAR, Schlumberger Technical Services, Abu Dhabi, U.A.E.; and ERIC STANDEN, Schlumberger Technical Services, Cairo, Egypt

ABSTRACT: Geological and Geometrical Characteristics of Reservoir Fracturing Throughout the Middle East

The geometry and basic characteristics (length, density/intensity, aperture, and porosity) of fractures (joints) have been defined recently for a number of Middle East reservoirs. The factors that determine the occurrence of natural, open, permeable fractures within Middle East reservoirs are nature and degree of folding and/or faulting, in-situ stresses, and changes in rock properties such as porosity, lithology, and especially shaliness.

Fracture distribution and orientation within Mesozoic Arabian/Persian Gulf halo-kinetic structures is important to reservoir development and modeling, although the fractures generally only assist productivity. The reservoir importance of fractures becomes increasingly important in the deeper Paleozoic reservoirs. These fractures are best developed in relatively anhydrite free, low porosity, dolomite facies, and with few exceptions their orientation is related to regional trends, only slightly modified by local tectonic features. Exploration for deep-fracture reservoirs needs to consider that the probability of uncemented fractures will be present only where the timing of hydrocarbon migration was close in timing to fracturing.

Examination of fractured reservoirs in the Zagros-Bitlis orogenic belt from Turkey through Syria, Iraq, Iran, and the northern Emirates demonstrates that the fracturing is dominantly related to folding, with only minor karst fracturing or fault-related fracturing, whereas the fractures in the Gulf of Suez are closely related to the faulting history, with some of the most intense fracturing of the low-porosity Eocene limestones forming a fracture reservoir near fault zones. Careful studies of the basement fracturing reveals that decrease in fracture apertures generally accompanies an increase in fracture density. The fracture distribution of fractures within the northern Sinai closely fit a wrench-tectonic model, where the greatest density and largest apertures occur in

the dolomitic facies and have an orientation parallel to synthetic faulting of the wrench system.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.