Thermodynamic Characterization of a PVT of Foamy Oil

Abstract

Abstract This work is based on theoretical studies and/or experimental observations carried out diverse authors whom have investigated on the "foamy oil phenomenon" developing a methodology to characterize these crude oils thermodynamically, taking as bases nonconventional PVT analysis and using as research tool the application of equations of state and methods known for the determination of the equilibrium constants liquid-gas. It is presented two new correlations developed in this work for the calculation of the viscosity of heavy crude oils, which are based on values of molar fractions of liquid and gas in equilibrium. The proposed methodology was validated using conventional and nonconventional PVT data of wells located in the Orinoco Belt, Jobo Field, Morichal Area obtaining excellent results and showing that the proposed methodology is applicable to conventional and nonconventional heavy crude oils in all the possible scenes, that is to say, whether necessary information is available. Introduction When we analyse foamy crude oils under the optics of primary production mechanisms known traditionally, have not been able to explain with exactitude the production behavior in these reservoirs1; this has given basis to many people to do research with the objective of explainning the origin of this atypical behavior. To such extreme to establishment the theory of "foamy oil phenomenon", which considers a transient state or supersaturation condition, in which take place the characteristics named "atypical" that identify to this type of heavy crude oils. It's of extreme importance for the petroleum industry to model the thermodynamic behavior of foamy oils reservoirs, since a good characterization fluid increases the probabilities to obtain better numerical reservoir simulations of and thus to be able to consider with most exactitude the total recovery. Characterization of Foamy Oils The foamy oil phenomenon has appeared only in heavy and extra-heavy crude oils, since in these crudes the viscous forces surpass to the gravitational forces on the productive life of reservoirs, reason why this phenomenon goberns the production behavior of these reservoirs. This phenomenon to appear after that reservoir pressure reaches the bubble point pressure, from this pressure the petroleum production increases, the gas bubbles expand to displace petroleum towards wells quickly. Depending of pressure and extraction rate of wells placed in the reservoir is possible that gas bubbles be produced with the oil. With the purpose to characterize the ability that have some heavy crudes to show the foamy oil behavior and entrap gas that is released by each decrease of pressure. Nonconventional PVT analysis were developed which defer from the method used traditionally. The conceptual difference between this analysis and the method used conventionally, is that the flash and differential liberation tests are carried out without agitation of the cell2. Generally, the results obtained by means of conventional and nonconventional PVT analysis differ remarkably mainly in the values of bubble point pressure obtained by both methods for foamy oils. Frequently values of bubble point pressure smaller are obtained in nonconventional PVT analysis because occurs entrapping of gas within the oleic phase of the crude reason why it's deduced that supersaturation phenomenon occurs, the gas bubbles released to pressure far below the bubble point pressure are dissolved and/or dispersed within the phase of petroleum in a perfect hydrodynamic equilibrium. It later on that such hydrodynamic equilibrium should be broken to obtain free gas. It had been determinate by laboratory experiences that viscosity of foamy crude oils obtained using capillary viscometers are more suitable to make reservoir numerical simulations than those obtained with rotational viscometers, in this case, strench caused by shaking the crude sample breaks the dispersion gas/oil and release bubble gas to build a free gas cap separated of the crude oil.