Depth: A Love and Hate Story

Theys, Philippe


My affair with well depth started almost a half-century ago. In the early 1970s, wireline logging tools were not combined (e.g., separate logs were run with neutron, density and resistivity tools). As a logging engineer I was, in the jargon used in these distant years, cranking, that is manually adjusting the depth, of subsequent runs so that curves peaks and troughs would correlate. It was a challenge in laminated formations, as it was easy to mistake one bed with the previous one or the next one. The interpreter, most often performing interpretation with a pencil and a slide rule on paper or fi lm records, would handle possible mismatches with art. When digitally recorded data entered in the mid-seventies, 6-in. sampled data were much more difficult to correlate exactly. Logging companies developed many programs to achieve perfect correlations between concertina-like curves. The fact that few people remember the names of these programs confirms that they were not successful. At that time, aligning logging curves was the primary concern. Logger’s total depth needed to be close to driller’s total depth, as should logger’s casing shoe depth and driller’s casing shoe depth, but this could be easily arranged.