Operational Improvements Using a Coiled Tubing Telemetry System for a Complex Milling Operation in Shut-in Conditions
Authors: Kubeisinova A. , Tankiyev T. , Izbassov A. , McGachy D. , Viti M. , Pitoni E. , Correa P. , Parra D. , Craig S. , Livescu S. , Yeginbayev A. , Nadirov Z. 
Published: March 2018

A new horizontal well in Asia was not capable of unassisted flow due to low gas production rates and a wellhead pressure below that required to enter the production gathering system. Two zones were identified at the heel that could increase the gas/oil ratio (GOR). Because these two zones had deviations greater than 80 degrees, coiled tubing (CT) was selected for the perforation and stimulation intervention. In addition, mechanical isolation was required to ensure the stimulation fluids entered only the new zones. Accurate depth control was required for three runs: setting two composite bridge plugs (CBPs); deploying CT-conveyed perforating (TCP) guns for opening two intervals; and milling out the two CBPs without taking returns to surface. All these runs were performed with a 2.875-in. tube wire-enabled CT telemetry (CTT) system. For the first time, a tension, compression and torque (TCT) subassembly was used to improve the milling operation.

The CTT system consists of a customized bottomhole assembly (BHA) that instantaneously transmits internal (i.e., inside the BHA) and external (i.e., outside the BHA) pressure and temperature, and casing collar locator (CCL) data to surface through a non-intrusive tube wire installed inside the CT. Monitoring the BHA force and torque data in real time helped improve the motor and mill performance and life because the weight on bit (WOB) could be adjusted to the recommended values. For instance, based on the optimum working ranges for the motor used, the operator decided how and when to modify the working variables to achieve a reliable and efficient milling process.

The CTT system alone helped set the first CBP at 5363 m measured depth (MD), set the second CBP at 5281 m MD, and perforate the intervals between 5297 and 5306 m MD and between 5152 and 5164 m MD. In addition, the CTT system with the TCT subassembly was used to mill the two CBPs in shut-in conditions, without any stalls. This created a continuous milling operation, reducing the job time and the working fluid volume compared to similar milling jobs using CTT system alone. Comparing this CBP milling job performance with a previous operation in another well with similar conditions (depth, deviation, etc.) using the CTT system alone reduced the milling time for one CBP by 22%. Although the overall job performance exceeded the operator's expectations, the working parameters used during the CTT system with the TCT sub-assembly job were not constant, leaving a few areas of improvement for the upcoming milling operations. For instance, the constant differential pressure and WOB were not used on every milling pass down.

The novelty of using the CTT system and TCT subassembly consists of real-time monitoring of BHA data for positioning two CBPs and opening new intervals exactly at the required depths. In addition, this approach enables removal of two CBPs by adjusting the milling parameters to achieve the optimum working parameters for the motor and mill, providing direct and positive financial impact for the operator.