The Viscosity of Air, Water, Natural Gas, Crude Oil and Its Associated Gases at Oil Field Temperatures and Pressures

Abstract

Abstract This paper presents useful charts for conversion of various viscosimeter unitsinto centipoises and graphically summarizes published investigations of theviscosity of air, water and natural gas at high temperatures and pressures.Where possible, charts and correlations were constructed to cover a range oftemperature (60'F. to 300'F.) and pressure (14.7 lb. per sq. in. abs. to 8000lb. per sq. in. gauge) encountered in oil fields. Correlation charts, for the purpose of predicting crude oil viscosity andsolubility behavior at oil field temperatures and pressures, were constructedfrom an analysis and correlation of 1332 viscosity and solubility observationsfrom 953 crude oil samples taken from 747 oil fields. Of these fields, 501 arein the United States, including 75 in California. Of the 1332 observations,12I5 were viscosity values, including 786 of gas-free crude oil, 351 of oilsaturated with gas, and 78 undersaturated with gas at pressures above thebubble point. Results show that crude oil viscosity at various reservoir conditions can bepredicted with average deviations varying from 24.2 per cent for gas-free crudeoil to as little as 2.7 per cent for under saturated crude oil "above thebubble point." The solubility of crude oil may be predicted from oilgravity and saturation pressure with an average deviation of 22.0 per cent fromobserved values. In conclusion, it is shown that the viscosity of a gas andgas-saturated crude oil may be predicted within the accuracy of most reservoircomputations. Introduction Viscosity is a measure of flow resistance; common units are in centipoises(cp.). The object of this report is to present conversion charts and simplifiedcorrelation charts showing the viscosity behavior of air, water, gas and crudeoil and gas-saturated crude oil under oil field temperatures and pressures, which have been known to be as high as 300'F. and 8000 lb. per sq. in. gaugeunder subsurface conditions. The viscosity of a liquid or gas is important because it is a measure of itsfluidity, or its ability to flow through pipe lines or oil sands. Viscosity ofair has become important because it is being used in secondary recoveryprojects. The viscosity of natural gas and water at reservoir conditions isuseful because they are almost universally associated and produced with crudeoil. The viscosity of gas-saturated crude oil at reservoir pressures andtemperatures is of particular value in making estimates of oil reserves andrate of oil recovery from flush pools when production decline data arelimited. Instruments Used to Measure Viscosity There are many types of viscosimeters, and the instruments most commonly usedto measure the atmospheric viscosity of liquids at moderate temperatures andtheir practical working ranges have been described in detail.