Best laboratory practices for reducing uncertainty in the pressure differential (ΔP) measurements in core-flooding tests for the petrophysical characterization of reservoirs

Abstract

Special Core Analysis (SCAL) as a tool for characterization of conventional reservoirs in the laboratory reduces the petrophysical uncertainty and optimizes the resolution and precision of rock-fluid petrophysical models to refine reserve estimates, calculate oil in place, and select the best oil-field development mode. Within the SCAL program, measurements of fluid flow capacity through porous media (permeability [Darcy]) are used to characterize geological formations of interest, with the fluctuation of “pressure differential” values being decisive in the calculation of this property. This research focuses on determining the sources that generate these fluctuations and implements a significant reduction by varying certain parameters in the laboratory. Through detailed analysis of the experimental procedure and equipment operation, as well as a statistical analysis, the sources impacting the quality of the measurements were identified. It was found that the precision and accuracy of pressure differential values were considerably low and directly related to: (1) the pressure pulses created in the backpressure system; (2) the high dead volume in the signal conduction lines (piping); and (3) the influence of temperature variation of the measurement environment. Modifications were implemented both in the experimental protocol and the core-flooding equipment, and tests were conducted under the same conditions to observe the changes produced. It was possible to significantly reduce the standard deviation in the measurements of the pressure differential value from 7.08% to 1.45% with respect to the mean. Consequently, these modifications reduced data dispersion, obtaining more-accurate readings of the stability behaviour of the pressure differential value and, thus, generating more-reliable results. The relevance of this work is demonstrated by the improvement in quality and reliability of petrophysical measurements, in addition to the optimization of turnaround times considering that, by reducing dispersion of pressure differentials values, flow stability state in the porous medium is reached in less time, which is a critical condition for permeability evaluations.