Abstract: Well Log Correlation, the Stratigraphic Framework, and the Computer Revolution

SWANSON, DONALD C.

Development of well logs established the discipline of subsurface geology as we know it today. Besides the petrophysical aspect of well logs, their most important use has been "correlation" between wells. Correlation or equivalency is a basic pan of subsurface geology and includes many differing techniques and uses. In fact "correlation" can have varying definitions and applications depending on the experience and goals of the user.

Well log correlation can be considered the identification and connection of equivalent patterns and/or values between log curves of adjacent wells. "Good' or "accurate" correlation can almost be viewed as an acquired art or craft hence there can often be much argument and dispute over the results. What characteristics of logs should be correlated and what do such connections mean?

If three or more wells have equivalent points, a surface is defined that should have stratigraphic meaning. The proper correlation of many characters or patterns on several or more well logs can provide surfaces that together develop the subsurface stratigraphic framework. The ordering of correlation derived surfaces display stratigraphic patterns such as onlap, truncation, thickness variations, facies, cycles and sequences

With the advent of computer technology and the resulting manipulation of digitized log curves and electronic databases, surfaces derived from the correlation of log equivalency become file "dividers". These surfaces critically define databases so there can be an efficient data flow to reservoir studies, prospecting, and modeling.

AAPG Search and Discovery Article #90936©1998 AAPG Southwest Section Meeting, Wichita Falls, Texas