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Geophysical well logs have been recorded in wells drilled for petroleum and natural gas since the early 1930s. These, largely hard-copy records, comprise the greatest pool of factual subsurface information on producing reservoirs and on new prospects that were either not economic or overlooked when the wells were drilled originally. As such, they are a valuable exploration tool but are difficult to use because of the incompatibility of recorded information both within and between wells.
Early well logs display a wide range of curve types with a
remarkable variety of calibration and depth scales. Visual analysis with well-to-well continuity is almost impossible with the logs in their original form. Fortunately, the hard-copy logs can be digitized and computer-processed to produce standardized logs that are amenable to accurate analysis for contained hydrocarbons and the spatial mapping of potential reservoirs.
The process does require the services of a petroleum geologist to determine the log response to clean formations within each well. However, once the individual curve parameters are determined, the computer can carry out the detailed computations for the display and isolation of all potential reservoirs. Examples of logs from New York state indicate that many gas-bearing reservoirs remain to be exploited.
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