COMPARATIVE STUDY OF DRAINAGE CAPILLARY PRESSURE MEASUREMENTS USING DIFFERENT TECHNIQUES AND FOR DIFFERENT FLUID SYSTEMS

摘要

The determination of representative capillary pressures(PC)is needed for the forecast of the fluids distribution in the reservoir.The initial water saturation and the accumulation depend directly on this parameter.However variations between measurements obtained by various standard techniques(mercury injection,porous plate,centrifugation)or for different fluid systems have been often observed and reported in the literature.This study tries to establish relationships between drainage PC curves obtained from various techniques.With this goal,a series of drainage experiments was systematically achieved on samples from various lithological facies and with different core properties,with the samples having been made as water-wet as possible.The comparison of these measurements leads to the following observations:-for the air-brine system,both of the techniques(porous plate,centrifugation)fit accurately on the majority of the samples in spite of different cleaning procedures and sample sizes,with moreover a good agreement of the mercury injection PC curve using a suitable scaling factor,-the Pclo curves for the three pairs of fluids have the same relative position for each sample(where o is the interfacial tension of the fluid system),-the maximum gas saturation for an air-oil drainage is close,although always superior,to'the one for the air-brine system.On the contrary,a systematic 5 to 10 saturation unit difference is observed between the asymptotic limit of gas-liquid and oil-brine PC curves.With regard to a gas-liquid system and for fairly clay free samples,the three techniques appear to be valuable to describe the capillary balance.Oil reservoirs must be subject to particular measurements in order to estimate the oil-brine system behaviour.Drainage centrifuge experiments using pseudo reservoir fluids are then qualified to provide reliable data.