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Qualifying real time bit wear through innovative monitoring of alkenes - part two

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Oilfield Technology,

This is part two of a two-part article. Part one is available here.

Economics-based decision making

Even with alkene detection providing a definitive indicator of when a bit is prematurely nearing the end of its workable life through wear, operational decision-makers still need to balance the economics of continuing to drill slowly with an increasingly dulled bit versus the cumulative NPT cost of POOH, changing bit, and RIH in order to then drill ahead faster with a fresh bit.

A prototype software application has been designed to help remove subjectivity and potential procrastination in making this decision by calculating in real time the operating time, and therefore costs, of both options concurrently. The system determines a rate of dulling based on the drilling parameter and alkene trends so as to determine the rate at which ROP is expected to continue to decline; this gives the time and cost for the ‘as-is’ scenario of drilling ahead. In parallel, the previous tripping in/out speeds are used as a basis to extrapolate an expected time for a potential round trip for bit change if started from the current bit depth. In addition, the system uses the ROP recorded at the start of the current bit run, when the bit is assumed to have been fresh, as reference for the expected ROP post-trip; these give the time and costs for the ‘what-if’ scenario of changing the bit. All operating intervals used by the application in determining the averaged reference values (slow ROP with dull bit, fast ROP with fresh bit, trip out and trip in) can be user-selected.

The continuous comparison of simplified ‘as-is’ versus ‘what-if’ predictions within a basic software tool thus allows the decision-maker to objectively realise the cost-driven tipping point and act accordingly.

Example case history

Alkene detection has been used worldwide, from US land to deepwater Africa. In this example a Middle East NOC drilling onshore exploratory deep HPHT wells was concerned about excessive bit wear in order to avoid potential loss of the bit in whole or part, and to avoid drilling undergauge hole in order to ensure smooth casing runs. The alkene detection service was provided in the 22 in. hole section while drilling carbonates with water-based drilling fluid with diesel additive, and again in the 16 in. hole section drilling predominantly sandstones with oil-based fluid.

In the higher section the bit had been efficiently drilling thickly interbedded carbonates and shales, and as the bit passed into a sandstone the ROP increased noticeably with no alkenes detected, showing the bit retained an efficient cutting action. However, after a further ~250 ft the ROP began to decrease with increasingly erratic torque accompanied by a substantial increase in measured alkenes, leading to the decision to POOH suspecting terminal bit wear. On surface the bit was notably undergauge and showed clear indication of wear with chipped teeth on the nose, face and gauge cutters, validating the decision to POOH (Figure 2).

Figure 2. 22 in. PDC bit shows clear chipped cutters and undergauge, validating the decision to POOH. 

The subsequent 16 in. section was drilled with oil-based fluid, and again alkene monitoring provided an invaluable contribution to diagnosing and qualifying degree of bit wear. In this example, while drilling a homogenous carbonate formation the ROP started to decrease; despite applying additional WOB no incremental torque was observed, implying loss of cutting action through bit wear, a conclusion supported by the increase in alkenes observed in parallel. On surface the bit showed clear signs of wear, with numerous chipped and lost cutters and damaged matrix, confirming the timeliness of the bit trip (Figure 3).

Figure 3. 16 in. PDC bit shows clear chipped and lost cutters, worn matrix and undergauge, again validating the decision to POOH.  


Alkene detection demonstrably provides a valuable tool in diagnosing the occurrence, character and severity of bit wear in real time. When used as an integral part of a rigsite drilling optimisation solution, it drives appropriate remedial action and informs critical operational decisions, eliminating potentially substantial NPT that can arise from prolonged drilling with a worn bit, such as undergauge hole and/or junk in hole, and avoidable cost such as untimely trips or bit DBR. Qualitative measurement and monitoring of alkene trends is cost-effective and is being used increasingly in a wide range of drilling and geological conditions, both standalone and as part of sophisticated integrated drilling analytics.


  1. M. Regan, E. Carcione, A. Martocchia, Near Real-time Monitoring of PDC Bit Condition and Associated NPT Mitigation Using Online Alkene Detection, IADC/SPE Asia Pacific Drilling Technology Conference, Bangkok, Thailand, 27 - 29 August, 2018, IADC/SPE 190997.
  2. Carcione, E., Easow, I., and Chiniwala, B. Alkenes Detection from Drill Bit Metamorphism and Real-Time Geochemical Elemental Analysis on Drill Cuttings Aids Drilling Optimization and Geo-Steering in Tight Unconventional Laterals, Unconventional Resources Technology Conference, Austin, Texas, USA, 24 - 26 July, 2017 URTeC 2697162.

This is part two of a two-part article. Part one is available here.

Written by Matt Regan, GEOLOG International, UAE.

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