The geothermal drilling environment presents many obstacles that limit the use of directional-drilling and logging-while-drilling (LWD) technologies, such as borehole washout, mud losses, severe vibration, and high temperature. The case study presented in this paper demonstrates a novel practice to enhance data logging in geothermal drilling by deploying advanced telemetry and LWD technologies. This operation aims for continuous improvement in geothermal drilling operations.
The case study covers the 12.25-in. hole section of well XXE-05 in the Sorik Marapi Geothermal Field. The LWD string consisted of electromagnetic (EM) telemetry, pressure while drilling (PWD), vibration (DDSr), and acoustic caliper (ACAL). Through this tool configuration, the operator acquired drilling mechanics and caliper logs in real-time and recorded mode, enabling effective monitoring and evaluation of wellbore stability.
Throughout the real-time acquisition, EM telemetry provided a data rate to the surface unit three times faster than conventional tools. Furthermore, with the integration of caliper and drilling mechanics data (vibration and equivalent circulating density), the borehole conditions became more visible to the directional driller, allowing better control of drilling parameters to minimize vibration and achieve optimum hole cleaning in washed-out or tight formation sequences. The recorded data from the caliper sensor indicated an average of 8.6% washout for the entire 12.25-in. interval. Washout intervals were compared with loss occurrence during drilling and the presence of smectite-bearing paleosols, showing that the washout zones associate with the latter, supporting the smectite-bearing paleosol model in explaining the cause of stuck pipe incidents in the Sorik Marapi field. In addition, measurements of hole ovality were compared with the interpreted fault trend, providing further insight into the existing model. In general, this LWD case study has given added value through geothermal borehole characterization, from drilling hazard identification to subsurface analysis.
Identified challenges while running LWD in this geothermal environment were addressed for future improvements, such as the effect of tool eccentricity and the impact of vibration. Perusal of both real-time and recorded caliper and drilling-mechanics data has opened various possibilities for maximizing the sensor usage in future wells.