Bit Depth - ProjectDataClarity/SurfaceDerivedData GitHub Wiki
Introduction
Bit depth is the distance between a reference point and the bit. It gives the position of the bit while drilling, off bottom, during a trip or during circulation relative to a datum reference. Typical unit for bit depth is feet for field unit or meter for SI unit. In our approach, bit depth is calculated by using block height data to estimate length of drill string within borehole, without taking into account of drill string elongation or other effect that could introduce depth errors. While drilling, bit depth will be the same as measured depth (hole depth).
Calculation Approaches
The first step to calculate bit depth is to obtain block height data. In this approach, bit depth is estimated by accumulate block height changes during different rig activities. In this approach, bit depth is calculated when rig state is drilling, reaming, tripping in or tripping out.
The equation for calculating bit depth is:
bitDepth_feet(i) = bitDepth_feet(i-1)+(blockHeight_feet(i-1)-blockHeight_feet(i));
where i is the number of data entry. Note bit depth could increase or decrease depending on the rig state. For example, bit depth will decrease during tripping out, and will increase during tripping in.
Metadata Required
• Block Height – depth change of drill strings with corresponding time of recording
• Rig State – calculation only performed in certain rig state activities
References
Poletto, F. B., and Francesco Miranda. Seismic while drilling: Fundamentals of drill-bit seismic for exploration. Vol. 35. 2004. Adam, T. B., et al. "Applied drilling engineering." SPE Textbook Series, Dallas, TX 2 (1991).