Casing-while-drilling (CWD) operations have become a well-known technology used to minimise drilling time and reduce AFE budget. PETRONAS has drilled several wells in Malaysia by using this technology, and it has proven to be a cost efficient strategy particularly in batch drilling process.
Past CWD operational experiences have demonstrated stark differences when compared to conventional drilling in terms of wellbore surveying and formation evaluation. Weak and noisy signals from mud pulse telemetry were primary issues that required a significant amount of rig time when acquiring measurement-while-drilling (MWD) and logging-while-drilling (LWD) data.
In fact, several significant challenges were encountered. First, the mud pulse signal which traverses from downhole (MWD) to the surface somehow dampened out. Although various types of mud pulse telemetry have been used, significant problems remain. In addition, the signal transmission worsened when seawater was used as the drilling fluid, resulting in nonproductive time due to provisioning ofchange out tools with different configurations for mitigation and trial-and-error purposes. Finally, overall drilling efficiency was reduced as a result of poor signal detection and capturing.
EM-MWD used in combination with gyro-while-drilling (GWD) was identified for implementation when drilling four wells using Tesco CWD technology in the Erb West field. The mud pulse and electromagnetic telemetry systems were executed asa pair to compare captured signal strengths in the same environment, i.e., directional CWD with seawater drilling fluid.
After drilling ceased, the generated results proved that EM-MWD is a viable technology that can be used to overcome signal attenuation issues in a CWD operation. It also minimise health, safety, and environment (HSE) risks as well as established a working model of EM-MWD-CWD. Most importantly, such application reduced rig time by 3.9 days which contributed to 26% of cost saving for the surface section drilling by having trouble free MWD signal detection and faster drilling operation.