Scholarly record

IMPACT OF HIGH-TEMPERATURE DRILLING FLUID DEGRADATION ON PDC AND DIAMOND BIT PERFORMANCE

Boranbay Ratov

Abstract

High-temperature drilling in deep HPHT and geothermal wells (>180–220 °C) causes thermal degradation of drilling fluids, which compromises hydraulic performance and accelerates wear of PDC and diamond-impregnated bits. This study evaluates three fluid systems – high-temperature oil-based mud (HT-OBM), thermally stabilized water-based mud (HT-WBM), and nanoparticle-enhanced synthetic-based mud (nano-SBM) – subjected to static aging in HPHT cells at 150–240 °C for 16–40 hours, followed by measurements of rheology, filtration, and thermal conductivity. Hydraulic efficiency was tested on a scaled PDC bit flow loop (nozzle pressure drop, jet velocity via PIV, hydraulic horsepower), while cutter durability was assessed through single-cutter scribing and full-bit drilling simulations, with wear quantified by microscopy and SEM. Results reveal severe degradation in HT-WBM (up to 75 % viscosity loss and 33 % conductivity reduction), moderate effects in HT-OBM, and superior stability in nano-SBM (conductivity loss limited to ~14 % at 240 °C). Degraded fluids reduced nozzle ?P by 18–42 %, jet velocity by 12–35 %, and hydraulic horsepower by 20–48 %, leading to cutter temperature increases of 60–130 °C, wear rates 2.1–4.5 times higher, wear flats enlarged 1.8–3.2 times, and ROP declines of 25–55 %. The work establishes a direct causal link: thermal fluid degradation impairs bit hydraulics, reduces cooling and cleaning, and accelerates thermal-mechanical wear of cutting elements, with nanoparticle-enhanced synthetics offering the best performance preservation for extreme-temperature drilling applications.

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