Rheology of Petroleum Fluids
ANNUAL TRANSACTIONS OF THE NORDIC RHEOLOGY SOCIETY, VOL. 20, 2012
Rheology of Petroleum Fluids
Hans Petter Rønningsen, Statoil, Norway
ABSTRACT NEWTONIAN FLUIDS Among the areas where rheology plays In gas reservoirs, the flow properties of an important role in the oil and gas industry, the simplest petroleum fluids, i.e. the focus of this paper is on crude oil hydrocarbons with less than five carbon rheology related to production. The paper atoms, play an essential role in production. gives an overview of the broad variety of It directly impacts the productivity. The rheological behaviour, and corresponding viscosity of single compounds are well techniques for investigation, encountered defined and mixture viscosity can relatively among petroleum fluids. easily be calculated. Most often reservoir gas viscosity is though measured at reservoir INTRODUCTION conditions as part of reservoir fluid studies. Rheology plays a very important role in The behaviour is always Newtonian. The the petroleum industry, in drilling as well as main challenge in terms of measurement and production. The focus of this paper is on modelling, is related to very high pressures crude oil rheology related to production. (>1000 bar) and/or high temperatures (170- Drilling and completion fluids are not 200°C) which is encountered both in the covered. North Sea and Gulf of Mexico. Petroleum fluids are immensely complex Hydrocarbon gases also exist dissolved mixtures of hydrocarbon compounds, in liquid reservoir oils and thereby impact ranging from the simplest gases, like the fluid viscosity and productivity of these methane, to large asphaltenic molecules reservoirs. Reservoir oils are also normally with molecular weights of thousands. This Newtonian fluids, but the variation in chemical variation is reflected in a large viscosity can be extremely large, both as a variation in viscosities, ranging from result of chemical variation, ranging from fractions of a centipoise to millions of light, low-viscous gas condensates to highly centipoise, and rheological behaviour, from viscous heavy oils, and temperature perfectly Newtonian to highly non- variation, which always has a large, and Newtonian, visco-elastic and nearly solid- fairly predictable impact on the Newtonian like. Description and rheological viscosity. Fig. 1 shows an example of a characterization of petroleum fluids thus rather heavy North Sea oil with nearly requires a broad variety of experimental perfectly Newtonian behaviour, even at a techniques and modelling approaches. low temperature. This is quite typical also of much heavier oils. The mentioned temperature variation of the viscosity of
11 these Newtonian fluids, is most often very representative of the fluid at real field well described by a so-called Arrhenius conditions. relation, i.e. a linear relationship between the logarithm of the viscosity and the 25 inverse temperature1: 30°C 20 40°C s) 50°C 15 60°C