A novel method to improve mud pulse telemetry performance during gaseated underbalanced drilling

Abstract

Gaseated underbalanced drilling is an attractive choice for horizontal drilling in unconventional reservoirs. However, mud pulse telemetry usually fails in gaseated systems. In this study, an overview of mud pulse telemetry in gaseated drilling was first given for better understanding the current state of the art. Then, factors influencing pulse attenuation in compressible drilling fluids were discussed. Subsequently, a novel method to improve mud pulse telemetry in gaseated drilling were developed. Intermittent gas injection was first developed as a main solution, which refers to pumping only drilling fluids for a while when taking surveys. A model for determining the optimal duration for stopping the gas injection was also proposed, which is critical and must be optimized to allow both telemetry use and underbalance. As another sub method, a gas–liquid mixer was designed to overcome the nonuniform mixing phenomenon in the standpipe, which is also a potential factor in telemetry failure. Flow restrictor and lowering operating frequencies as the other two sub methods were also recommended. Finally, case studies and efficacy analysis were conducted to evaluate these sub–methods. The method of intermittent gas injection was applied in one case. The maximum gas injection rate allowed by acceptable telemetry was raised from 6 m3 min−1 to 12 m3 min−1, which demonstrates the feasibility of the method. Another case showed that the gas–liquid mixer enhanced the detected signal amplitude from 0.0033 MPa to 0.01 MPa, which obtained successful decoding. The results also show that the continuous wave mud pulse telemetry tool has more advantages than the positive pulse systems for mud telemetry in gaseated drilling. The results of efficacy analysis show that flow restrictor and lowering operating frequencies also can enhance mud pulse telemetry performance in gaseated drilling.