What is a CDP cable?

Abstract

Referring to the multiconductor cables used to connect the geophones to a seismograph, a really good geophysicist once asked me, “What's the difference between a CDP cable and a refraction cable?” Now this person was well-versed in a variety of geophysical methods; in fact, he is the author of books and teaches classes in geophysics. And he's a practitioner, not an academic. You would recognize his name. If this person didn't know the difference, perhaps many don't. It occurred to me that with the onset of 3D seismic, and the decline in geophysical companies, the people who know how a CDP cable works are retiring and even dying off. Recently, one of my customers purchased a new CDP cable that was wired incorrectly—almost half the conductors were missing. If a cable manufacturer doesn't know how to build a cable, we're on perilous ground. I assumed that something as thoroughly embedded into geophysical consciousness as CDP cables would have been thoroughly documented, but I could find no reference that explained CDP cables, (or the more politically correct term CMP cables) on the Internet or in the Digital Cumulative Index of SEG, EAGE, ASEG and CSEG publications, 1936-2003, available on the SEG Web site. Humbly, I leap into the breech. A geophone cable is of course a multiconductor cable with a connector on either end and with individual connectors or “takeouts” for the geophones at intervals along the cable. We informally classify them as either refraction cables or CDP …