Mathematical modeling of phase behavior of multicomponent hydrocarbon mixtures is an essential part of up-to-date practices in petroleum reservoir engineering. Phase behavior calculations form the basis of the PVT software, as well as the 'flash' procedures for determination of phase state and compositions within compositional flow simulators. Adequate description of phase behavior is important for simulation of petroleum production with intensive phase transitions in the reservoir, wells and surface facilities.
One of the key assumptions of industry adopted models is that phase state of the hydrocarbon mixture and phase compositions correspond to the condition of thermodynamic equilibrium. However, there are typical cases for oil and gas-condensate reservoirs when field data are principally inconsistent with equilibrium models. Some examples to give are data of well operation at Novogodneye, Vuktylskoye, Krasnoleninskoye, Kamennoye and many other fields.
In hydrocarbon production, non-equilibrium effects are evident in the following cases:
1) pressure increase in a reservoir (by water or gas injection) following previous pressure depletion with evaluation of the second hydrocarbon phase (liberation of dissolved gas from oil or retrograde condensation in a gas-condensate system) – so-called gas dissolution / condensate evaporation hysteresis;
2) pressure depletion in a gas-condensate reservoir below the maximum condensation pressure (transition from retrograde condensation to direct re-vaporization);
3) gas injection in oil or gas-condensate reservoir.
Similar processes may also take place during hydrocarbon flow in wellbores and surface facilities.
Non-equilibrium effects result in considerable (tens or hundreds percent) deviation of actual reservoir system parameters (saturation pressure, production composition) from their estimates by equilibrium models.
For practical needs, reservoir engineers are limited to either using equilibrium compositional models with no account for non-equilibrium effects, or black oil models with the option of limited gas dissolution /condensate vaporization/ This option is based on a simple technical relation and doesn't consider specific physics of non-equilibrium processes.
In the presentation, methods and algorithms are presented for non-equilibrium phase behavior simulations suitable for wide practical use. A relation is shown between non-equilibrium effects and simulation scale. As the applications, flow simulations with compositional and black oil formulations are considered. Phase behavior simulation cases are shown for real oil and gas-condensate mixtures, including matching of the non-equilibrium condensate recovery dynamics for the late stage of production at the Vuktylskoye field.
Author:
Ilya M. Indrupskiy
Chief researcher / head of Gas-, Oil- and Condensate Recovery Lab of the Oil and Gas Research Institute of the Russian Academy of Sciences (OGRI RAS). Professor of the Applied Mathematics and Computer Modeling Department of the Gubkin State University of Oil and Gas.
Graduated from the Gubkin University with an engineering degree in applied mathematics. Doctor of technical sciences in reservoir engineering. Professor of the Russian Academy of Sciences. Author of more than 150 journal and conference papers and more than 20 patents.
Research area includes improvement of integrated 3D reservoir modeling; forward and inverse problems of fluid flow and thermodynamics in oil and gas reservoirs; development of highly informative well testing and data interpretation methods; advancements in production techniques for hard-to-recover hydrocarbons.
Ilya has a considerable experience in research projects for the Russian Academy of Sciences, as well as for Gazprom Neft, TNK-BP, Rosneft, Lukoil, Gazprom and other companies.