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An unconsolidated clastic reservoir of Middle Miocene age is under full field development plan in the State of Kuwait. Underlying the shale cap rock, main hydrocarbon bearing reservoir consists of two sand bodies separated by predominantly shale interval present throughout the field. To determine the role of facies and depositional environment in controlling the orientation and quality of the reservoir, an integrated analysis of borehole images, open hole logs and core data from wells spread across the field was successfully attempted. Fifteen identified generic image facies principally based on lithology and reservoir quality with core data validation were grouped into six genetically related associations. Facies recognition used criteria of image textural variations, dip patterns, direct recognition of features and relationships of cementation, bioturbation and sediment deformation. Statistical analysis of the identified sandy facies of upper reservoir unit indicated high abundance ratio and preferred distribution trend while no significant distribution trend observed for the lower reservoir unit. Observations from the image and core data helped to define depositional environment and sub-environments. Results indicate that depositional setting was created by succession of several depositional environments such as shore face, coastal plain of fluvial & distributary channels and lagoon. The high angle cross-bed features distinctly noticed are interpreted to be deposited in confined depositional environment of channel sand bodies, suggesting a major paleo sediment transport orientation. The marine shale deposited during a major flooding event on top part of the hydrocarbon bearing reservoir acts as cap rock. Tight carbonate cemented sandstone intervals also identified at various levels within the reservoir. In general, the formations exhibit distinct episodes of regression and transgression events marked by erosive and flooding surfaces. The identified rock facies relationship and depositional environment provided significant lead in formulation of full field geological model.

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Continued technological advances have made logging-while-drilling (LWD) technologies a reliable and widely used class of tools to evaluate and describe the reservoir. High-resolution imaging-while-drilling, in particular, offers a detailed view of fractures, vugs, faults, bedding planes, and other borehole features in deviated and horizontal wells. One benefit of imaging-while-drilling is the ability to evaluate the formation in real time. This can provide better well placement in the target formation. However, unlike many conventional logging tools that can be used in a wide range of conductive and non-conductive mud environments, resistivity imaging tools require special considerations to obtain high-quality data. Drilling fluid resistivity is one of the important considerations to be verified when a micro-imaging log is planned. In the Arabian Gulf, the most common muds used for drilling horizontal wells are non-damaging fluid (NDF) systems that use calcium chloride to weight the mud. This brine mud is highly conductive, which can cause the emitted current of a micro-imager to flow into the mud instead of the formation, which results in poor image data quality. If a highly conductive mud is combined with a moderate- to high-resistive formation, the image quality can further deteriorate. While a mud system with lower conductivity (such as barite-based mud) is preferred when imaging high resistivity formations, the use of such a mud system may not be possible. Several ADCO wells with various mud and formation conditions were drilled with a new micro-imaging tool. This tool features a unique button design that creates multiple image resolutions and depths of investigation, which improves the chances of obtaining a high-quality image in various drilling conditions. While the resulting images from these wells varied, the tool enabled the development of a logging and integrated geoscience solution to overcome the mud and formation challenges and provide better reservoir characterization. This extended abstract reviews the micro-imager's deployment, the considerations that need to be reviewed before a micro-imaging job commences, and the integrated solution that was developed for imaging highly resistive formations.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractWell bore images become increasingly important in identifying formation features and their possible extent. There are two different tools that acquire image data, acoustic and micro-resistivity. Both tools faced difficulties and challenges in acquiring quality data over the deviated and horizontal section of a well.To perform quality image data in deviated and horizontal section of a well is difficult because of; firstly, drilling rogues, deviated and horizontal section, and these results in poor padwall contacts. Therefore, the quality of the resistivity image data is highly affected by the drilling fluid, along with the acoustic data. Secondly, poor mud properties that behaves as a blocking medium to acquire quality data.A new technique requires modifying in both drilling and mud properties has been applied in different fields with high success. This new technique requires certain bottom hole assembly and drilling parameters, along with drilling fluid properties to better drill smooth holes.The new technique resulted in smooth horizontal section and better in the deviated section, therefore, better pad-wall contact. Images from both; resitivity and acoustic modes provided high quality data acquisition. As a result, geological features were very clear by the image logs after the implementation of this new technique.In this paper, the new technique is explained along with case histories from three different fields of the image logs are presented and compared to previous poor quality logs.