**Tvd:**

## Terms Related to Tvd

### True vertical depth

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

### Normal pressure gradient

The normal pressure divided by true vertical depth.

### Equivalent circulating density (ecd)

The increase in bottomhole pressure expressed as an increase in pressure that occurs only when mud is being circulated. Because of friction in the annulus ...

### Deviation

Departure of the wellbore from the vertical, measured by the horizontal distance from the rotary table to the target. The amount of deviation is a ...

### 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 ...

### 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 isÂ added ...

### Depth reference

The point in a well from which depth is measured. Alternatively, the depth reference is the point at which the depth is defined as being ...

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