Mud Pulse Telemetry System
The mud pulse systems use valves to modulate the flow of drilling fluid in the bore of the drillstring, generating pressure pulses that propagate up the column of fluid inside the drillstring and then are detected by pressure transducers at the surface. The positive pulse system momentarily restricts mud flow through the downhole tool, resulting in a pressure increase, or positive pressure pulse, that propagates to the surface. With the annular venting system, mud is momentarily vented from the bore of the drill collar directly to the annulus, bypassing the bit jets and creating a brief pressure drop, or negative pressure pulse, inside the drillstring, which propagates to the surface. In both mud pulse systems, data from downhole sensors are encoded and transmitted by varying the time between consecutive pressure pulses.