# True Vertical Depth explanation?

So I figured out TVD does not mean The Vampire Diaries, means True Vertical Depth.  I see references to maybe 500 feet or 750 feet.  Is it better if they drill deeper or not?  And maybe some of it relates to whether its Haynesville or Bossier>  I don't know if it matters to me right now but it might in the near future.

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You are conflating different things, Iris.    First, the two "depths" that we see and discuss on Haynesville wells are "TVD" and "MD", True Vertical Depth and Measured Depth.  TVD is the depth from the Kelly Bushing (the floor of the drilling rig) to the deepest vertical depth drilled.  Measured Depth is the total length of the wellbore from the rig to the spot where the drilling bit is stopped and the hole ceases to be drilled, the length includingboth the vertical portion of the wellbore and the lateral which will be perforated to produce the natural gas.  TVD is the depth where the lateral portion of the well goes horizontal.  Since the drill bit can not make a 90 degree turn, there is a "curve" from the vertical portion of the wellbore to the horizontal portion.

The Mid-Bossier interval (usually referred to as just, Bossier) is not as deep as the Haynesville, both are shale intervals in the Haynesville Shale fairway.  The two intervals are generally 500' to 600' apart based on TVD.  How far apart depends on the specific location.

Okay, so thats part of what I’m asking. Understand generally about TVD and saw pictures. And you are explaining differences probably in Haynesville and Bossier depths. Of course I knew the vertical drill bit wouldnt curve, so now I know what MD means. Wasn’t what I thought I’d be interested un learning but I am.

The drill stem does in fact curve (bend).  The vertical portion of the wellbore is drilled with a drill bit that rotates with the drill stem but when it is time to "build the curve", the drill stem (pipe) is '''tripped" (retracted from the wellbore) and a "mud motor" assembly replaces it on the end of the drill pipe.  At this point the drill stem is not turning.  The mud motor bit turns by the drilling mud forced down the well casing and open borehole and through the mud motor assembly.  In driller speak, the drill stem is no longer turning, it is now "sliding" in the hole.  The mud motor is steerable and can be controlled to "build the curve" and drill the horizontal portion of the well.

Once again. the Bossier is 500' to 700' more shallow than the Haynesville.

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