Downhole Measurements of Synthetic-Based Drilling Fluid in Offshore Well Quantify Dynamic Pressure and Temperature Distributions

Abstract

Abstract Accurate downhole and surface measurements of a synthetic-based drilling fluid were taken in a Gulf of Mexico well to resolve variances between actual and calculated pump pressures, and to quantify equivalent circulating densities. Current API equations seriously underestimated drillstring losses, which accounted for the pump-pressure differences. Conversely, annular losses were much lower than predicted. Introduction The drilling industry cannot consistently match calculated and actual pump pressures and is uncertain with the reliability of equivalent-circulating-density (ECD) predictions when using oil-based muds. Sensitivity to temperature and pressure is the most often cited reason for the discrepancies. Attempts to compensate for these effects with oil-based muds have not met with widespread success. Similar difficulties are encountered with synthetic-based muds (SBMs); however, concerns are more acute. Pump-pressure calculations with SBMs can be off as much as 35%. The high unit cost per bbl of SBMs makes lost circulation a serious risk if ECD values are unreliable. Related problems which also are affected by hydraulics include surge/swab pressures while tripping, sizing of mud pumps, hydraulic optimization, well control, and general well planning.