Borehole images constitute a rich source of high-resolution geological data about various formations penetrated by oil and gas wells. Interpretation techniques of these images have progressively improved over the years and provide detailed information about formation dips, structure, rock fabric, fractures, and drilling-induced borehole damage. Wireline tools have the flexibility to be used in a wide variety of borehole sizes. In contrast, logging-while-drilling(LWD) tools are designed for particular borehole sizes. A new high-resolution LWD imaging tool has been built for 8.5-in. boreholes. This paper presents the results from two logging runs located in offshore United Arab Emiratescarbonate fields, including the first worldwide logging run of the tool.
Measurements made by this new high-resolution imaging tool are based on laterolog principles for the measurement of resistivity. The tool performs two main types of measurements, including an array of focused resistivity measurements with an axial resolution near 1 in., and an ultrahigh-resolution resistivity imaging pad consisting of an array of eight buttons. This paper focuses on the LWD tool’s imaging section, designed to provide the same volume ofinvestigation as one of the focused resistivity measurements. This design featureresults in measurement calibration confidence with respect to the formation resistivity, allowing for quantifiable analysis of the formation properties using the image data. The data for this first run were acquired during a washdown through a carbonate-evaporite sequence. Borehole deviation was approximately 60° and the mud was a typical high-salinity water-base mud. A suite of wireline data, acquired after the LWD washdown run, includes a pad-based resistivity imaging tool, which allows comparison of thetwo sets of acquired data.
Data from both the wireline and new high-resolution imaging LWD tools were processed and interpreted. Structural and cross-bedded layers were clearly visible on both imaging-type tools. Borehole crossing and layer-bound fractures were also observed and could be quantified from both tools.
Examples show how identifying some featuresis made easier on the full borehole coverage of the LWD images; however, the higher resolution of the wireline tool is beneficial for identifying some textural features. Results from both types of logging tools are presented and the similarities and differences are summarized. Advances in borehole image visualization are also presented as 3D views in addition to cross-sectional views across the borehole, which make visualization of features more user friendly for those not familiar with borehole image interpretation.