Abstract: Reservoir Characterization and Sequence Analysis Using Borehole Images

BUCK, STUART

Micro-resistivity borehole images acquired in Triassic strata from the UK continental shelf were used for a detailed characterization of reservoir intervals and the analysis of sedimentary sequences. Such images are ideally suited for this work as they provide a continuous and oriented high resolution record of the sedimentary succession. The strata investigated comprise a mixed fluvial and eolian siliciclastic sequence. Detailed reservoir characterization was important for the evaluation of reservoir performance while sequence analysis assisted stratigraphic correlation of these unfossiliferous sediments. The data was analyzed systematically using UNIX workstation to record depth and orientation of bed boundaries, facies types and facies surfaces. Such systematic recording of image data has not previously been reported for reservoir characterization. This data was then output as ASCII files for inclusion into spreadsheets for statistical analysis and to automatically generate graphic sedimentological logs using a computer drawing package. Dip data was investigated to characterize the geological structure, especially the identification of key stratal surfaces and to define sandbody orientation and paleotransport direction. Azimuth and dip walkout plots proved extremely useful in identifying subtle unconformity surfaces. Statistical analysis of the data enabled the reservoir to be characterized in terms of net proportion, thickness, orientation and distribution of facies types. In addition, the sequence of occurrence of facies was investigated using embedded Markov chain analysis. This revealed the occurrence of distinct facies successions related to upward-drying and upward-wetting climatic sequences. The climatic sequences are considered to be related to the effects astronomical Milankovitch cycles and therefore highly correlatable within the basin.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria