Use of Dipmeter Data in Clastic Sedimentological Studies (1)

Abstract

Resistivity curves from he eight measuring electrodes of Schlumberger's Stratigraphic High-Resolution Dipmeter Tool{TM} (SHDT) can be processed to give a detailed reservoir characteriation that includes electrofacies and sedimentary dip data. This conclusion is supported by evaluation of processed SHDT data compared with information from over 1,000 m (3,280 ft) of cores covering fluvial and eolian sedimentary environments. Based on three examples, we give general guidelines for processing of and noise removal from SHDT data to obtain satisfactory geological information. Foreset dips in sets as thin as 20 cm (8 in.) can be reliably calculated by using side-by-side processing options with a correlation interval of 10 cm (4 in.) and a step distance of 7.5 cm (3 in.). In many formations, spurious dip readings cause serious problems. These readings originate from irregularities in the formation or from processing artifacts, have no directional implication, and produce unsatisfactory signal-to-noise ratios. However, criteria have been defined to select relevant dips from such noisy data. Structural dips must be measured with a sufficient degree of confidence to accurately subtract them from sedimentary dips. Reliable data can be obtained by large-scale interval correlation, particularly when the interpretation is concentrated on suitable intervals (laminated shales and horizontally bedded heterolithic sequences). The SHDT tool also can provide detailed information on reservoir characteristics, particularly on small-scale heterogeneities that escape the resolution of conventional logs. Boreholewide resistivity displays from interpolation of SHDT traces enable the recognition of resistivity distribution patterns and may give a new scope to facies recognition from logs.