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Abstract

The implementation of the Improved Oil Recovery (IOR) methods to increment the recovery factor in<br>naturally fractured reservoirs is often expensive and time-consuming; therefore, a detailed quality<br>reservoir assessment of key attributes of the fracture network in an analogue outcrop carbonate rocks<br>will help unravel its impact on the IOR pilot.<br>Detailed fracture analysis was conducted on collected data from the Eocene-Miocene outcrop exposure<br>of the fractured carbonate rocks in Jabal Hafit anticline/Abu Dhabi. This paper aims to assess the effect<br>of critical fracture parameters such as geometry, interconnectivity, density, aperture, size, mechanical<br>layering and ambient stress condition on fractures openness and reactivation mechanisms. It also<br>introduces a method to estimate the seal potential ratio based on aperture measurements of<br>representative fractures chosen over areas of different structural settings in Hafit structure.<br>Results indicate that there are two fracture systems; an older E-W trending and a younger N-S striking<br>system, which have been formed in at least two different tectonic settings from Cretaceous to present.<br>Each of these systems is divided into three vertical to sub-vertical fracture sets; an extensional (joints)<br>and two conjugate shear sets (faults). Some of these extensional fractures and faults are partially or<br>entirely sealed by calcite or clay gouge filling. Fracture density shows a log-normal relationship with<br>bed thickness, which increases in dolomitized limestone facies, in the crestal area and in the vicinity of<br>pre-existing faults and shear zones. Fracture size is inevitably constrained by the outcrops exposure.<br>Fractures aperture varied between 0.5 to more than 30 cm, depending on fracture geometries,<br>positions in the anticline and lithology, and calcite fillings.<br>We consider that only fractures of the second system is preferred for fluid flow along corridors that are<br>held opened by the current N-S to NE-SW ambient stresses unless locally sealed by clay or calcite<br>mineralization. However, at the vicinity of a fault, the estimation of fractures openness depends on the<br>fault geometry and the associated in-situ stress tensors around the fault. Fractures connectivity is<br>controlled by individual fracture set geometry together with the current in-situ stress. Riedle and<br>diffused fractures connect those opened fractures and faults of this system together with the bedding<br>planes giving rise to a dual permeability reservoir.

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/content/papers/10.3997/2214-4609-pdb.248.150
2010-03-07
2021-10-19
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