Petroleum Fluid Characterization and PVT-Calibration in Basin Modeling

Armin Kauerauf¹ and Rolando di Primio^2
1IES GmbH, Ritterstr. 23, 52072 Aachen, Germany
²GeoForschungsZentrum Potsdam, Telegrafenberg, 14473 Potsdam, Germany

In order to model hydrocarbon migration under the changing pressure/temperature conditions of sedimentary basins, multi-component phase-predictive compositional models are required. It is well known that simple approaches such as black-oil models are incapable of correctly reproducing fluid phase behavior over the entire span of geological conditions due to the enormous ranges in pressure and temperature from source rock to trap. However, due to limited computer resources one is forced to restrict the compositional characterization to a relatively small number (usually <15) of components. Grouping and lumping of chemical species with similar properties to pseudo components with average properties cannot be avoided. Adapted sets of pure and pseudo components for a proper description of all relevant processes have to be created. This talk deals with the workflow of an accurate and consistent characterization of hydrocarbon fluids in basin modeling.

The description of petroleum fluids in basin modeling is primarily determined by two factors. Firstly, processes of generation and expulsion quantify the overall composition of the fluids. Secondly, PVT-behavior is responsible for the distribution of components to phases during secondary migration. Taking into account both aspects is a pre-requisite for phase property predictions such as gas to oil ratio (GOR), density or viscosity.

The PhaseKinetic approach (di Primio and Horsfield, 2006) offers the possibility of obtaining a compositional characterisation of generated fluids which is integrated with a bulk kinetic model and correctly reproduces hydrocarbon physical properties and phase behaviour as a function of increasing maturity. PhaseKinetics combines open and closed system pyrolysis as well as an empirical correction of generated gas compositions for the definition of the compositional kinetic models. The result of this procedure is a set of pure and lumped pseudo components to be used in simulations as descriptive of the fluid composition entering the carrier system.

For the calculation of the physical properties of migrating phases a precise definition of the pseudo compounds is required. The most sensitive variables for the correct reproduction of API gravity and viscosity are molecular weight, critical temperature and pressure as well as the acentric factor. Especially heavy end characterization of the fluids must be adapted. A calibration of these variables to those of natural fluids is required in order to obtain accurate basin wide predictions. Effects of fluid biodegradation can also be incorporated in this workflow with a satisfactory level of accuracy. In this presentation we will show examples of the calibration methodology applied.

References:
di Primio, R., and B. Horsfield, 2006, From petroleum type organofacies to hydrocarbon phase prediction: AAPG Bulletin, v. 90, p. 1031-1058.

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands