"Old" (Pre-1958) Electric Logs: A Quick Review

Hilchie (1979) reported that in North America alone there are approximately 1 million wells that were logged with "old" logs. In many of our fields that we are studying "old" logs make up 50% or more of our well log data. This amount of well control can not be ignored. This one day course is designed to illustrate how these logs work, and how to interpret them for your log analysis and field studies.

Fresh mud (Rmf >> Rw) surveys from 1932 to 1958 consisted of the following logs in order of their depth of investigation: 1.) 18'8" LATERAL (deep), 2.) 64" NORMAL (intermediate), and 3.) 16" NORMAL (shallow). All of these logs were non-focused resistivity tools that required a set of rules to properly interpret the results. These rules were based on the ratio of bed thickness to tool electrode spacing, and whether the bed had greater or less resistivity than the adjacent beds. In 1945 the 32" LIMESTONE LATERAL log was introduced as a porosity tool that was run only in western Canada and the Permian Basin. In 1948 the MICROLOG was added as an Rxo device, and was also used as an indicator of permeability. During this time period porosity was mainly determined from the 16" NORMAL log.

Logging tools suitable for running in salt mud (Rmf = Rw) were available after 1952. The following are salt mud resistivity logs in order of their depth of investigation: 1.) LATEROLOG-3 or LATEROLOG-7 (intermediate), and 2.) MICROLATEROLOG (flushed zone –Rxo). All of these logs were focused resistivity tools that could be analyzed much like modern logs.

The only non-electrical logs available during this period were the "old" GAMMA RAY – NEUTRON logs. The "old" gamma ray logs were recorded in counts and not in porosity units like modern neutron logs. Therefore, the "old" gamma ray–neutron logs MUST be normalized to modern gamma ray–neutron logs before they can be applied to any quantitative log analysis.

Numerous examples of how to analyze "old" logs will be presented during the course. In addition eight examples will be provided for the class to analyze. various units (i.e. micrograms Radium equivalent/ton) and not standardized in API units like modern gamma ray logs. The "old" neutron logs were recorded in neutron

George Asquith, Ph.D.
Pevehouse Chair of Petroleum Geology. He is a Professor of Geosciences and co-director of the Center for Applied Petrophysical Studies at Texas Tech University. Twenty- five years of petroleum industry experience that included research geologist Atlantic-Richfield Co., staff geologist ALPAR Resources, chief geologist Search Drilling Co., district geologist Pioneer Production Corp., and project leader Mesa Limited Partnerships. He has published one hundred and twenty publications, including 5 books in the fields of petrophysics, carbonate and clastic sedimentation/petrology, and computer geology.

Dr. Asquith received the Distinguished Service Award from the WTGS 1999, and the Distinguished Lecturer for the Society of Professional Well Log Analysts (1991-1992 and 1994-1995). He was a lecturer for the AAPG Subsurface Carbonate Depositional Modeling School (1980-1986) and received the Monroe Cheney Science Award from the Southwest AAPG 2001.

G131133Q May 28 8:00 am - 5:00 pm
Wed  $375.00
($400.00 out-of-state)
Midland College PPDC Building
Registered: 4 8.0 Hours

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