As the drilling of deviated and horizontal well bores continues to rise, now well over 70% vs. vertical wells, operators are constantly dealing with Directional Surveys, new techniques for viewing well profiles, and some of the differences when looking at Measured Depth (MD) vs. True Vertical Depth (TVD).
As covered in a previous post, certain aspects remain the same when looking at MD vs. TVD, while others change drastically:
Logging Measurements remains
Depth measurements, no matter what well deviation, is key measurement and is typically displayed in both MD and TVD
If the depth of any data readings, cuttings, etc. are off it puts the entire well in jeopardy going forward
Operators Success changes
Success is now measured by Meters Drilled vs. Rig Count due to the extended reach HZ and $$’s spent on completions of these lengthy HZs rather than # of wells drilled
When comparing Measured Depth (MD) & True Vertical Depth (TVD) of a well, many different scenarios arise:
1. Increasing MD – Constant TVD:
Formation Temperatures remain stationary
Temperatures are relative to the temperature gradient
Formation Pressures can change
Requiring different completion strategies through different portions of the HZ well
Geological factors of a well can change slightly or even track outside the Zone of Interest (ZOI) completely
Making technologies such as directional drilling very important in the HZ
2. Increasing MD – Increasing/Decreasing TVD:
TVD adjustments while HZ drilling
Thin bed formations may require adjustments to stay in the ZOI
Toe Up/Down well design
Create a single liquid accumulation point at the Toe or Heel of a well
Determine thickness of the formation by touching into the adjacent bed at the end of the lateral
With these thin formations, and to gain some extra well information, to compare On-Site Geology cuttings, Cordax's Logging While Tripping system can go anywhere the drill bit can. Aspects such as tough-hole conditions and dogleg severity have no impact on data quality or well safety.
