Fracture Detection In The Middle East
Authors: Minne J-C. , Gartner J. 
Published: December 2007

Numerous oil and gas fields in the Middle East produce from carbonate reservoirs, many of which are produce from carbonate reservoirs, many of which are fractured. For optimum production, accurate knowledge of reservoir parameters is required. Conventional wireline formation evaluation techniques provide the primary parameters, such as: porosity, provide the primary parameters, such as: porosity, matrix type, shale content, fluid content and type.

The presence of fractures adds to the productivity potential of the reservoir but at the same time adds potential of the reservoir but at the same time adds to the complexity of its behavior and to its understanding. Hence, there is great interest and value in fracture detection.

At the present time no wireline logging technique can unequivocally locate and determine the orientation of fractures. However, from the proper use of appropriate combinations of logs, the presence of fractures can be inferred and qualitatively evaluated.

In the paper, the application of various logging tools and techniques for detecting fractures are discussed and field examples illustrating their use are presented. presented

Introduction

Numerous oil fields in the Middle and Near East produce from carbonate reservoirs. Many of these produce from carbonate reservoirs. Many of these reservoirs, such as those found in Turkey, the eastern part of Syria and the northwest parts of Iraq and part of Syria and the northwest parts of Iraq and Iran are fractured as well. Since fractures add to the complexity of the reservoir behavior and to its understanding, and to the productivity potential of the reservoir, it is desirable that such zones be recognized and evaluated, at least qualitatively.

Wireline logging devices can be used to detect fractures, however it should be remembered that most of these devices are limited to investigating the formation, at best, only a few tens of centimeters from the borehole. Also, the vertical resolution of the logging devices, which may vary from a few centimeters to about a meter, determines to a large extent the fractures that can be "seen". In fact, none of the logging devices actually see fractures directly but infer them from the response of combinations of logs. For example, open fracture(s) may be indicated on the logs by anomalies such as: a change in temperature, a very localized lower density or a slight change in average density, a localized resisivity contrast, a variation in hole size and shape, anisotropic resistivity, sonic cycle skipping, secondary porosity, increase in mud cake thickness, etc.

Although these techniques are helpful for completion purposes and provide an insight into possible purposes and provide an insight into possible reservoir characteristics, they usually cannot be used to predict quantitatively reservoir performance.

The purpose of this paper is to discuss the main wireline logging techniques presently available commercially, for locating fractures. Field examples illustrating these techniques are shown.

EFFECT OF FRACTURES ON TOOL RESPONSE

Fractures or fracture systems by themselves do not normally constitute commercial reservoirs, they do however often provide the mechanism necessary for commercial production from tight, low porosity, and low permeability reservoir rock. As such, there is great interest and value in fracture detection and evaluation.

At the present time no wireline logging technique can unequivocally locate and determine the orientation of each fracture per se.