Thin Bed Resolution Enhancement: Potential And Pitfalls

Thin bed analysis continues to be a crucial component of formation evaluation in complex reservoirs. Traditionally, thin bed information has been obtained through the use of fine resolution tools such as the minilog, and through deconvolution. Within the last few years a new technique has gained prominence. This technique combines measurements made by detectors or tools that have different effective depths of investigation and different vertical resolutions. While excellent results can often be obtained through the use of such methods, there are also significant dangers. For this reason, an understanding of the underlying assumptions and the expected results is necessary before successful use. This paper will address this understanding through the exploration of three different types of measurements: compensated neutron, compensated density, and resistivity. Two examples will be considered for each measurement: one in which the assumptions are valid, and one in which they are not. In this manner, an understanding of the inherent utility and limits of the method will be obtained. Finally formation conditions, borehole conditions, and formation measurement techniques will be discussed in light of how they facilitate or hinder the use of this method. This discussion will include both MWD and wireline measurements and will focus on how the measurements can best be used together to facilitate accurate thin bed analysis.