Acoustic Telemetry Can Deliver More Real-Time Downhole Data in Underbalanced Drilling Operations

Abstract

Abstract Underbalanced drilling (UBD) is known to be beneficial in hydrocarbon exploration and production: less formation damage, faster drilling, better control of lost circulation and stuck pipe situations, plus an enhanced ability to further develop depleted and marginal reservoirs and fields. However, UDB is inherently more complex than conventional drilling. Therefore it is essential that downhole tool and formation information be collected and delivered in real time to the driller during UBD. Achieving reasonable telemetry data rates for logging-while-drilling during UBD can be problematic with current telemetry techniques. Mud pulse telemetry may become ineffective when highly compressible UBD drilling fluid is used. Electromagnetic telemetry fails when the formation becomes too conductive. Acoustic telemetry, based on the propagation of stress waves through the drill string, is however particularly suited for operation in underbalanced drilling operations. It is relatively unaffected by the properties of the formation and operates even more efficiently in UBD with compressible low weight drilling fluids compared with conventional overbalanced drilling with heavy drilling fluids. This paper will discuss the drill string acoustic channel characteristics, with particular reference to signal attenuation and transmissibility. It will be shown that acoustic telemetry is potentially capable of transmitting 50 – 100 bits per second through the drill string channel while drilling. Finally, preliminary field test results will be presented as part of the goal of demonstrating the advantages of the acoustic telemetry over both mud pulse and EM telemetry.