Significance of the Critical Phenomena in Oil and Gas Production

Abstract

The critical phenomena have been studied during the past century but ourknowledge of the critical temperatures and pressures of complex hydrocarbonmixtures still is very limited. The critical temperatures and pressures of puresubstances have been examined in large numbers, and in great detail. Noexperimental determinations of the critical phenomena have been reported onsuch complex hydrocarbon systems as a reservoir fluid. The critical temperature is defined by Taylor as follows: "there is sometemperature for each gas above which the gas cannot be liquefied. Thistemperature is called the critical temperature." The critical pressure of apure substance is the vapor pressure at the critical temperature. It should benoted that these definitions refer to a given substance in the pure state anddo not mean that the pure substance cannot be liquefied in the presence of asecond constituent. The normal procedure for obtaining the critical temperature of a substance isto heat it in a glass tube 1.20 under pressure until the meniscus between theliquid and vapor phase disappears, although other methods, especially formixtures, have been used. However, when considering oil and gas reservoirs, itis more enlightening to. consider a critical phenomenon that occurs when amixture of oil and gas are compressed at a reservoir temperature until themeniscus disappears because the two phases become equal in composition. Thisconception, along with erroneous applications of the definition of the criticalphenomena of a pure substance to that pure substance when it is part of acomplex mixture, has caused confusion even among persons familiar with theclassical theories. T.P. 971