Al-Khatib Mohammad Hanai. N.R. Kazurova

Schlumberger Inc. Moscow. Russia

The advent of a new generation of imaging tools has brought new insights into reservoir characterization (Taha, 1997; Bell and Osorio, 1997; Slatt et al., 1998). 

High-resolution borehole electrical imagery is regarded as a powerful tool to improve sedimentological and structural models, as well as determination of natural fracture orientations in fractured reservoirs and minimum and maximum stress orientations. Borehole images are used to identify sedimentary, biogenic and diagenetic structures as well as sand body orientations within a facies succession, which is of great value in interpreting depositional environments for reservoir characterization and optimum field development. Borehole images, when calibrated to core, can be useful for identifying image log criteria that can be used for interpreting facies and facies associations. By comparing the borehole images to the cores it is possible to develop borehole-image criteria for a variety of sedimentary structures and stratification styles, and from these, to identify depositional facies.

Borehole images demonstrate their value for interpreting individual sedimentologic features, facies, and attributes away from the wellbore. It is important to highlight that borehole images provide paleocurrent determinations and sand orientations that complement the sedimentological interpretation from conventional core. Borehole electrical imagery, integrated with selective conventional core data, thus constitutes a very powerful and effective technique for use in detailed reservoir characterization and further field development.

Reservoir architecture, continuity and connectivity are primary concerns in development of clastic and carbonate reservoirs. Smaller-scale features of continuity and connectivity of individual beds or packages of beds also control performance, but they cannot be interpreted from seismic, or in many cases even from conventional well logs because they are beneath resolution limits. Borehole images logs are of sufficiently good resolution and quality to allow identification of individual sedimentary features, as well as vertical stratification styles. Features observed in the core, such as thinly laminated shales, massive sandstones, bioturbated sandstones, presence of roots, high-angle cross stratificacion. were identified on the borehole images. The comparison provided improved interpretation of borehole electrical images FMI/FMS of the oil and gas fields.

This paper focuses on the application of borehole electrical images to improve the sedimentological models developed for each reservoirs for further field development and optimum well locations. Additionally, it demonstrates the application of core-image characterization for improved understanding of clastic and carbonate fades in analog ancient reservoirs provided with an illustrations and examples of these application.

The images provide detailed sedimentary and structural information for clastic rocks. which is of great value for geological and reservoir modeling. The interactive analyses on the Image Examiner Workstation have further enhanced our capabilities toward extracting a wealth of information. The interactive dips picked can be regarded as having the highest possible accuracy, since they are manually selected from the images and categorized by bedding type (Taha. 1997). High-resolution electrical borehole images are obtained from the fullbore formation microimager tool (FMI) by scanning the borehole wall with arrays of small electrodes (192) pressed against the borehole surface. These buttons examine successive small vertical increments of the formation (every 0.1 inch).

Also, the tool provides a better borehole coverage (80% in the case of the SW boreholes). A tri-axial accelerometer permits determination of tool position and three magnetometers allow determination of tool orientation. The primary purpose of computer processing of raw FMITM data is to convert the raw acquisition data into the best visual representation. A histogram of the data is computed and the total range is partitioned into 64 classes, each with the same data count. By default, the 64 colors range from white (resistive) through orange to black (conductive). With DYNAMIC normalization technique, called image enhancement- may be used to bring out details.

This presentation proves how the interpretation of high-resolution borehole electrical images improved the structural, petrophysical and sedimentological models for both clastic and carbonate reservoirs in terms of depositional environments. The field geological models are updated and adjusted with every new well drilled. The presentation demonstrates the application of core-image characterization for improved understanding of carbonate and clastic reservoirs fades that help for further reservoir development, production enhancement and stimulation.

REFERENCES

1. Taha, M., 1997, Borehole Electrical Imagery, The Search for Oil and Gas in Latin America & the Caribbean. Number 5, pp. 8-27.
2. Bell, J. and Osorio, M., 1997. Hi-Res logs as reservoir characterization tools. The Search for Oil and Gas in Latin America & the Caribbean, Number 5, p: 43-59.
3. Slatt, R. M., Browne, G. H., Lower Hutt, Davis, R. J., Clemenceau, G. R, Colbert, J. R.3 Young, R. A., Anxionnaz, Н. and Spang, R. J., 1998, Outcrop-Behind Outcrop Characterization of Thin-bedded Turbidites for Improved Understanding of Analog Reservoirs: New Zealand and Gulf of Mexico, SPE 49563, p. 845-853.

ARCTIC SHELF OIL AND GAS CONFERENCE 2004