1965 Paper I-B

AUTOMATIC LOG COMPUTATION AT WELL-SITE: FORMATION ANALYSIS LOGS

By:

M. P. Tixier, F. M. Eaton, D. R. Tanguy, and W. P. Biggs Schlumberger Well Surveying Corporation - Houston, Texas

ABSTRACT

New logs and greater flexibility in electrical well logging applications are now provided by truck-mounted computer systems. These special computers digitize and record on tape the data from well surveys. Simultaneously with the recording of a subsequent log, the computers merge taped data and perform continuous log analysis computation. The optical recordings of these computations provide a rapid means of formation evaluation in the field.

Two computer systems have been developed. In one the data is recorded digitally on punched paper tape. The second system records the data digitally on magnetic tape using a format compatible with most digital computers.

A major application of the truck-mounted computer systems has been the merging of data from an Induction-Electrical Survey with that from either a Sonic or a Formation Density Log. The resulting Formation Analysis Log consists of continuous curves of Rwa, FR/FS (or FR/FD), and apparent porosity. The location of potential pay zones is more easily and quickly accomplished by scanning these computed logs than by manually performing the many computations required for a similar study. Since computations are automatically performed on all zones, it is unlikely that productive zones will be overlooked.

Other combinations of log data are also possible. For example, the merging and computation of data from a Sonic log and a Formation Density Log provides a log of the relative clay content of shaly sand formations. For a sand containing dispersed clay these data correlate with permeability, and, thus, permit reasonable predictions of the ability of the sand to produce. This combination is particularly appropriate for wells drilled with oil-base muds.