In Kazakhstan an operator completing multi-stage, horizontal wells has historically accomplished this using drop balls and baffles which were subsequently milled out afterwards with Coiled Tubing (CT).

However, several unavoidable drawbacks from this approach were encountered: introduction of additional fluids by the CT; formation damage from the water based milling fluids; lifting of the well afterwards and longer cleanup times.

Further, the completion sleeves can become damaged as well as accidentally shifted close from the tripping CT BHA. A new approach was field trialed using electric line (e-line) milling tools. Since then, improvements to the milling tool configuration, as well as to the baffles, have resulted in this technology becoming the operator’s preferred method for ball and ball seat removal.

Following several surface tests of the Well Miller® combined with the Well Tractor®, several important modifications were fine-tuned and implemented. First, a customized bit was designed and manufactured. Then the amount of Weight on Bit (WOB) provided by the Well Tractor was determined, tested and proven effective with the new bit during the first field trials.

During the first three field trials, a challenge was also encountered from the debris of previously milled balls which would ‘spin’ on the end of the bit between it and the next ball. To mitigate this, a Well Stroker® was incorporated into the tool string to provide an increased WOB, above and beyond what a tractor could provide.

With the new tool string configuration of Well Tractor and Well Stroker providing an optimized WOB, and the Well Miller equipped with a new bit, the next eleven wells (each with 5 – 9 ball/baffle sleeves) were all successfully milled on e-line.

This performance delivered an estimated 24 day gain in production.