(HP-97) IV True Stratigraphic & Vertical Thickness

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An extract from IV Finding True Stratigraphic Thickness and True Vertical Thickness of Dipping Beds Cut by Directional Wells, The Log Analyst, AMOCO, MAR-APR 1979, pgs. 3-6

ABSTRACT
… the thickness of a formation as measured from a log made in a deviated hole reflects neither its true stratigraphic thickness nor its true vertical thickness. The geologist who tries to trace a given bed across the field finds it difficult to deduce whether variations in bed thickness measured from logs are due to legitimate bed thickness variations or whether they are geometrical distortions due to hole deviation and bed dip effects. Likewise, the engineer trying to compute reserves is faced with the same type of problem. Measured bed thickness can be less than true vertical bed thickness in some cases and greater in other cases. A need for a quick and simple solution to the problem is evident, and a method of using a programmable pocket calculator (PPC) will be presented to satisfy the demands of both the explorationist and the engineer …
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 A simple PPC program to handle this computation is illustrated in the accompanying flowchart and program step listing suitable for an HP-97 calculator …
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CONCLUSION
 The PPC once again provides a simple and practical solution to a complex problem which to date has only been soluble via some rather questionable nomograms. While the program discussed is illustrated by use of an HP calculator, the authors find no reason why other similar makes and models of PPC should not be used provided the trigonometric functions behave in the same way that the HP functions do for limiting cases such as negative angles …

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