I have a question asked regarding what the differences between True Vertical Depth (TVD) and Measured Depth (MD). Today, I will describe both definitions and their importance for calculation in a drilling field.
True Vertical Depth (TVD) is measured vertically from the surface down to a certain target down hole.
Measured Depth (MD) is the total length of the wellbore measured along the actual well path.
See the following illustration for more understanding.