EXPERIMENTAL EVALUATION OF THE INFLUENCE OF DRILLING FLUID COMPOSITION ON ANNULAR PRESSURE DROP AND EQUIVALENT CIRCULATING DENSITY USING THE HERSCHEL-BULKLEY MODEL

The influence of drilling fluid composition on annular pressure drop (ΔP) and equivalent circulating density (ECD) was quantified experimentally and numerically using the Herschel–Bulkley model. Water-based muds were formulated (350 mL water) varying bentonite (20–60 g), xanthan gum (0.5–2.5 g) and PAC-R (0.5–3.0 g); barite was held constant at 50 g. Rheological parameters (τy, K, n) were measured and implemented in a MATLAB routine to solve the concentric annulus Herschel–Bulkley problem. Results show that increasing bentonite from 20 g to 60 g (samples A → C) produced the largest increase in hydraulic loss: ΔP rose from 50.912 psi to 133.238 psi, with ECD increasing from 10.0816 ppg to 10.2135 ppg. Variations in xanthan gum (0.5 → 2.5 g, samples D → F) yielded moderate ΔP changes (65.023 → 73.326 psi) and small ECD changes (10.1042 → 10.1175 ppg). PAC-R showed a non-monotonic effect (ΔP: 91.696 → 72.882 → 57.750 psi for 0.5, 1.8, 3.0 g respectively), with ECD remaining in a narrow band (10.0925–10.1470 ppg). The Herschel–Bulkley numerical solution reproduced the observed trends and indicates that bentonite concentration is the dominant factor controlling annular pressure loss, while ECD variations are comparatively small for the tested formulations.