Navigating The Challenges of Buckling

“You can’t push a rope” tells us not to push flexible drill pipe (DP) with too much compression and expect great results. Yet, here we are drilling longer and longer laterals faster and faster.?

In 2009, an operator drilling extended-reach wells modeled friction factors of 0.20 when pulling out of hole, but 0.40 when drilling or tripping in the hole. ?Something didn’t make sense.? While a few things affect friction factor, the friction shouldn’t vary so much if the well conditions are constant: the same pipe is sliding on the same open hole in the same fluid.? Our understanding of what happens to pipe in compression needed to improve.

With an operator’s generous help, WWT built a buckling test fixture to confirm how real DP behaves in compression to better understand how to more efficiently drill horizontal and ERD wells. ?A full stand (three joints) plus end shafts of 2-7/8”, 3-1/2”, and 4” DP were compressed inside a 7” liner to directly measure friction due to compression or buckling.

Drag and friction from buckled drill pipe reduces weight on bit (WOB) and thus rate of penetration.? The more WOB attempted, the higher the drag.

?WWT’s buckling test fixture used a full stand of DP and 120 ft of casing and three cameras in viewing ports along the length.?

Sliding test (no rotation) showing drill pipe radially deflecting within the 7” casing.?

Test results indicate that Non-Rotating Protectors (NRPs) reduce drag by shortening the effective column length of the pipe such that 20% more weight can be applied for a given amount of drag.? In short, more weight is delivered to the bit using NRPs for a faster ROP, especially while slide drilling.? Further, by limiting radial displacement and having a soft rubber inner diameter, the NRPs damp vibration and smooth weight transfer to the bit and reduce torque while rotating.

The test results were used to modify the Dawson-Paslay buckling model and are included in TADPRO by Pegasus Vertex software.[RB1]?? The resulting “Semi-Empirical Buckling Model” more accurately captures the drag forces of compressed pipe and better aligns friction factors while drilling to the actual material coefficients of friction in a lab condition.? In short, around 0.3 open hole friction factor should apply regardless of pipe operation.? Previous modeling required a friction factor of 0.4 or greater to have confidence to reach TD because the pipe’s behavior was not well understood.? Full results are documented in SPE 144535 by WWT’s Sarah Mitchell Banks.?

Putting these findings to practical use, WWT’s Non-Rotating Protectors have been run in open hole to drill faster horizontally on thousands of wells since 2010.?

Non-Rotating Protectors installed mid-span along the DP joint for buckling mitigation also reduces pipe wear with visible results.? NRPs have been used to extend the life of DP as some formations can wear pipe and hardbanding on a single well.??

Drilling 40,000 ft wells with shallow TVD is possible and repeatable.? The challenge of completing and intervening in these wells follows shortly.? WWT’s FlexShoe and JetReam product lines can help deliver rigid casing to bottom by flexing through doglegs and washing settled cuttings beds to reduce drag. Using WWT’s powerful coiled tubing tractors can be used to clean out, log, and stimulate the full lateral for boosting production over the well’s life.?

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About the Author:

Eric Gollmyer , Engineering Manager, Drilling Tools, Anaheim, CA

Starting work with WWT International in 2008, the timing was lucky to catch this buckling testing.? The experience was valuable to understand how to put theory into action.? It started in the shop parking lot in Anaheim and now WWT helps drill ERD wells all over the world. ??With a team dispersed worldwide, we aim to find solutions for the next problems wherever they arise.

How it started, how it’s going.