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Reducing Frictional Heat in Hard/Abrasive Formations Improves Drilling Efficiency

Fig. 2—Typical dull condition of 6⅛-in. PDC bit run in Colony Wash horizontal play, western Oklahoma.

A fixed polycrystalline-diamond-compact (PDC) cutting element creates an inherent limitation because only a small portion of the diamond table contacts the formation; as the cutter wears or chips, drilling efficiency declines. A research initiative was launched to investigate different methods to enable a PDC shearing element to fully rotate while drilling to increase overall cutting efficiency and bit life. The recent introduction of a new rolling-cutter PDC bit that uses 360° of the diamond edge has delivered positive results in field trials.

Introduction

When drilling with a conventional PDC bit, the percentage of cutter that contacts the formation will vary depending on several factors. However, in most cases, only 10 to 40% of the cutter will be used to actually shear the formation. The remaining 60 to 90% of the cutter is locked into the bit body and remains unused during the run. The resulting wear generates a high degree of frictional heat, which breaks down the diamond bond; the increased temperature then induces more abrasive wear. The mechanical wear combined with the thermal effect damages the cutter’s edge. As wear progresses through the synthetic-diamond table into the tungsten carbide substrate, shearing efficiency is reduced dramatically, lowering the rate of penetration (ROP). A driller’s typical reaction to the reduction in ROP is to increase drilling parameters. This worsens cutter wear further until the ROP drops below an acceptable level, resulting in a short run and a premature trip for a new bit. An analysis of more than 45,000 worldwide bit runs with conventional fixed-cutter-only PDC bits indicated that worn and chipped cutters account for 60% of the dull-grade characteristics reported on bit records.

A finite-element-analysis (FEA) -based software system was used to study the effects of frictional heat at the cutter tip as it engaged and sheared the rock. The study clearly indicated concentrated heat buildup at the cutting edge. Comparing the modeled cutter with an actual dull cutter used in a hard/abrasive application verified the concept.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 166465, “Fully Rotating PDC Cutter Gaining Momentum: Conquering Frictional Heat in Hard/Abrasive Formations Improves Drilling Efficiency,” by Youhe Zang, Yuri Burhan, Chen Chen, Sandeep Tammineni, Bala Durairajan, Siva Mathanagopalan, and Robert Ford, Smith Bits, a Schlumberger Company, prepared for the 2013 SPE Annual Technical Conference and Exhibition, New Orleans, 30 September–2 October. The paper has not been peer reviewed.
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Reducing Frictional Heat in Hard/Abrasive Formations Improves Drilling Efficiency

01 December 2014

Volume: 66 | Issue: 12

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