AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Detection of Fractures with Dual Oil Base Mud Imager in Jurassic Carbonate Reservoirs, North Kuwait - A Case Study
(1) Exploration Group, Kuwait Oil Company, Ahmadi, Kuwait.
(2) Schlumberger, Ahmadi, Kuwait.
Najmah, Sargelu and Marrat Formations of Middle to Upper Jurassic age are the prime targets for hydrocarbon exploration in North Kuwait. These Jurassic carbonate reservoirs, particularly Najmah and Sargelu, are in general tight. Despite low matrix permeabilities, presence of natural open fractures in these reservoirs is believed to have enhanced the permeability by several folds, as is evident by production rates as high as tens mmscf of gas and several thousand barrels of condensate/oil per day. As such, proper evaluation of fractures is key to exploration and exploitation of these tight carbonate reservoirs. Image log is one of the key tools used for fracture characterization in the Jurassic reservoirs. Oil Base Mud Imager, OBMI, which is the tool used for resistivity imaging has the disadvantage of limited borehole coverage. This limitation was successfully overcome by using Dual OBMI in one of the recent wells. The aim of this paper is to demonstrate the innovative technique in Dual OBMI tool and to highlight its advantages over the conventional OBMI tool even with two passes. In Dual OBMI two OBMI tools are stacked one over another at an angle of 45 degree. Thus there are 8 pads in dual OBMI as compared to 4 pads in conventional OBMI tool. Each pad acquires five measurements and the data is displayed as a color image oriented with respect to the geometry of the tool and borehole. With dual OBMI the borehole coverage area is increased by 100%. In 8” hole the borehole coverage with conventional OBMI is 32%, whereas, it increases to 64% with Dual OBMI. Increased borehole coverage allows more complex features, both large and small to be properly identified and described. Structural and stratigraphic features as small as 1cm can be seen, yielding a wealth of high resolution, azimuthal information. This results in enhancement of the interpretation of the borehole and the regional geology as well. It has application in structural and stratigraphic analysis and high resolution net pay count. The following fracture types were determined Using Dual OBMI : (1) open or closed fractures (2) resistive fractures (3) continuous or discontinuous fractures based and (4) possible fractures. Dual OBMI also saves rig time as it obviates the practice of two passes with conventional OBMI to increase the borehole coverage. This technique, not only provides double borehole coverage, higher resolution but also saves valuable rig time.