A New Algorithm for Automatic Shoulder Bed Correction of Dual Laterolog Tools
K. Turner, D. Tones, and R. Chemalt
Halliburton Logging Services
ABSTRACT
A new automated technique has been developed which corrects the reading of the dual laterolog for shoulder bed effects. Implemented as a computer algorithm, this technique accounts for all bed sequences underlying and overlying a given formation. By comparison manual shoulder bed corrections based on average charts are only applicable to a formation surrounded by a pair of identical massive shoulder beds.
The newly developed algorithm has several salient features. All corrections are based on an exact computer modeling of the bedding sequence as seen on the log, Including borehole size, mud resistivity, and all individual beds located within a large window surrounding the formation of interest. Remote shoulder beds are also included in the model using a resistivity averaging rule based on theoretical considerations. The process runs continuously, with no operator intervention, by virtue of an automatic grid generator which directly combines tool characteristics and bed boundaries.
The algorithm is successfully applied to simulated logs and to actual field data. In the case of simulated logs, both the deep and shallow measurements are corrected to the original resistivity value, demonstrating the accuracy of the technique. Equally sound results are obtained when the method is applied to a variety of field logs.