A client needed to install a ceramic screen system on packers with a 3.6″ running OD in a Trinidad gas well. However, the nipple in the well was 3.437″. The client contacted Welltec® to mill out the nipple to 3.7″ ID.

The client’s ultimate objective was to avoid pulling the upper completion by safely and efficiently milling out the ID of the 3.437” ID nipple at 9,388 ft to 3.7” using electric wireline (E-line) tools. Welltec proposed running the Well Tractor®, the Well Stroker®, and the Well Miller® for Scale Removal to achieve the objective.

Welltec’s plan was to use the Well Miller for Scale Removal to mill the nipple and recover the milled cuttings into the vacuum bailers. The Well Tractor was included to convey the tool string the final distance in the well to the nipple, and the Well Stroker was included in case the Well Miller became stuck while milling.

After performing a Systems Integration Test (SIT) including thorough checking of all tools in the Trinidad base, Welltec arrived on the platform, checked all tools again according to standard operating procedures and rigged up to run in hole. The nipple was tagged and the positioning was correlated prior to milling. Surface readout of the downhole power baseline was recorded and milling commenced in low speed mode.

Milling lasted three hours and 45 minutes. One stall occurred as milling was completed, an indication that the tool had milled out the end of the nipple. The Well Stroker was then engaged using a minimal overpull to free it. To ensure a smooth profile, the Well Miller was activated and drifted four times through the nipple.

The Well Miller effectively milled the nipple profile from 3.437” to 3.72” in one run while catching the milled cuttings to prevent future sticking problems in the well. A post-mill caliper confirmed that the milled nipple measured 3.72” ID. The client was then able to successfully install the ceramic sand screens.

Milling took only three hours and 45 minutes, a record for the amount of material removed. This time also represents a significant improvement over the eight hours required during the SIT. Additional weight from the entire tool string can improve drilling times in vertical vs high hole angles. Post-mill analysis also showed minimal wear to the tip of the mill bit.

Milling at 9,000-plus ft can make precision difficult. Welltec used a number of methods to confirm and ensure the milling was complete and the objective achieved. Upon pulling out of hole, the bit was inspected, and it clearly demonstrated that the tool is capable of milling a much larger volume. The bit showed little wear after milling the 18.25” length of the nipple; a total of approximately 29 cubic inches of material.