Simultaneous correlation of multiple well logs

Well log correlation is an important step in geophysical interpretation, but as the number of wells increases, so does the complexity of the correlation process. We propose a new method for automatic and simultaneous well log correlation that provides a globally optimal alignment of all logs, and in addition, is relatively insensitive to large measurement errors common in well logs. First, for any number of well logs, we use a new variant of the dynamic warping method, requiring no prior geologic information, to find for each pair of logs a set of corresponding depths. Depths in one log may have one or more corresponding depths in another log, and many such pairs of corresponding depths can be found for any pair of well logs. Requiring consistency among all such pair-wise correlations gives rise to an overdetermined system of linear equations, with unknown depth shifts to be computed for each log sample. A least-squares solution of these equations, found using the conjugate gradient method, yields for every well log a sequence of depth shifts that optimally align all well logs.