Insights #3 :Frac Plugs - What the STUMP!?!
Lately I have found myself looking back at mill out data. Operators keep saying ‘faster mill times’ required. Has the market been responding with improved technologies, whether on the plug or motor/bit side? We have studied the data from both thru-tubing applications and the frac plug geometry. Are we actually removing the plug faster, or just compromising it and pushing the remainder, commonly called the stump, downhole?
Most frac plug designs do not vary widely within the composite market. All share the same basic components. Slips, cones, element, mandrel. It is what those four parts consist of that varies. What I find interesting is how various designs maintain the plugs ability to hold their position in the casing during the milling process. Poor designs allow the plug to release its anchoring grip early in the milling process, thus creating a ‘stump’ to be pushed downhole. How big is this stump? It could be up to 60% of the original plug size. Other factors also play a role in the plug releasing during milling, such as motor stalls that will torque up the plug and break it free, possibly due to a large rubber element in its design.
Two things happen once the stump goes downhole;
1) The time taken to mill the plug is written down and used as gospel, although only a percentage of the plug been milled. (skewed data….)
2) The long journey begins. The stump is pushed downhole where it will tend to hang up before reaching the next plug. This hang-up may provide some resistance for the milling process to continue, but not as an effective milling condition when compared to milling in its original position. In the case of coil in long laterals this can add up to over 30 minutes trying to mill out the floating stump. (up goes the milling cost…)
To investigate further into this concept, we reached out to Stuart Mclaughlin, CEO of Magnolia Research & Development. Stuart is a wealth of knowledge with a deep history in coiled tubing applications. He was able to reinforce many our conclusions. Magnolia provided data displaying actual time taken to remove frac plugs as well as chasing the stump on various wellbores. Magnolia’s Master Coil downhole technology allows for 8 different measurements to be taken at the BHA. Among those, actual weight-on-bit during milling, plus weight during the ‘chasing of the stump’ operations are recorded. In many instances, reported mill times were short, but significantly longer when the time taken to ‘chase-mill’ the stump was added to the original time.
When Lateral Completions first set out to create the best frac plug on market, one of the action items on our list was to improve how much of the plug is milled out before becoming a stump. By keeping this goal in mind, we have built not only a plug that mills out in under 6minutes, but 90% of that plug is milled out in its initial location in that 6 minutes. Thus, adding true value to the operator.
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