Attenuation and noise in long laterals

Down a long lateral the mud pulse attenuates, the pulse shape spreads, and noise from the pumps and from drillstring vibration rises at the same time. Most lost data is not a tool failure; it is the decoder failing to keep up with a changing channel.

What makes long laterals hard

• Attenuation and dispersion — Pulse amplitude drops and the waveform spreads, so adjacent symbols overlap each other.
• Rising noise — Pump strokes, the mud motor and reflections off the surface manifold add up, and signal-to-noise ratio keeps falling.
• Lost sync is hard to spot — Once symbol sync is lost, every survey after it is wrong, while the pressure trace still looks perfectly normal.

What we do about it

• Adaptive noise cancellation keyed to the pump strokes.
• The surface software allows sync to be rebuilt by hand, without shutting the pumps down to re-establish it.
• Raw pressure data is kept for the whole run, so it can be re-decoded with an improved algorithm to recover surveys lost earlier.