Depth reference:

Alternatively, the depth reference is the point at which the depth is defined as being zero. it is typically the top of the kelly bushing or the level of the rig floor on the rig used to drill the well.

The depth measured from that point is the measured depth (md) for the well.

Even when the drilling rig has been removed, all subsequent measurements and operations in the well are still tied in to the same depth reference.

However, for multiwell studies, the depths are normally shifted to the permanent datum (generally mean sea level).

The depth reference and its elevation above the permanent datum are recorded on the log heading.

In some contexts, the term may refer to any point from which depth is measured.

Terms Related to Depth reference

• Driller’s depth

  The depth of a well or features within the wellbore as measured while drilling. The measured length of each joint of drillpipe or tubing is added ...

• Perforation depth control log (pdc log)

  A special type of nuclear log that measures the depth of each casing collar. Knowing the depth of the collars makes it easy to determine ...

• Depthometer

  A device used to measure the depth of a well or the depth at a specific point in a well (such as to the top ...

• Collar locator

  A logging device used to determine accurately the depth of a well; the log measures and records the depth of each casing collar, or coupling, ...

• True vertical depth

  The vertical depth (tvd) from the surface to the depth of interest. Used for formation comparison and calculation of hydraulic pressures.

• Pressure gradient

  1. A scale of pressure differences in which there is a uniform variation of pressure from point to point. For example, the pressure gradient of ...

• Caliper log

  1. A record showing variations in wellbore diameter by depth, indicating undue enlargement due to caving in, washing, or other causes. The caliper log also ...