Schlumberger

Basic Petroleum Engineering

FTC

FluidsFluids Fluids in a reservoir Description of the Hydrocarbon Reservoir Pressure Reservoir Temperature Hydrocarbon phases Fluid Production Formation Volume factors Surface tension forces Wettability Relative permeabilities

Notes

JJ Consulting 1997

1 1 1

Schlumberger

Basic Petroleum Engineering

FTC

DefinitionsFluid Contacts

Reservoir fluids need to be described in a different way from the rocks. The first definition is one of contacts, where the fluids would be in equilibrium. These are the gas-oil-contact, the oil-water-contact and the gas-water-contact. The latter is only possible in a well with gas and water (no oil). The second figure is the oil in place, the amount of hydrocarbon in the reservoir. The final figure is one of the hydrocarbon properties, the gas-oil-ratio; how much gas is in the oil. Due to the complexity of the hydrocarbons in the reservoir there are many other parameters which are needed to fully describe the fluids.

Oil in Place

OIP

The volume of oil in the reservoir in barrels or cubic metres.

Notes

Gas/Oil Ratio

GOR

The gas content of the oil.

API Gravity

API

Oil gravity.

2 2 2

Schlumberger

Basic Petroleum Engineering

FTC

Other gases can be found in wells, these include, helium, carbon dioxide and hydrogen sulphide. In most cases these occur as traces together with the hydrocarbon and water normally found. The formation water is uniquely described by its salinity. This varies from 500 ppm Chlorides to 250000ppm; a wide range. The major rock property involved in production is the permeability.

Fluids in a Reservoir

A reservoir normally contains either water or hydrocarbon or a mixture. The hydrocarbon may be in the form of oil or gas. The specific hydrocarbon produced depends on the reservoir pressure and temperature.Notes

The formation water may be fresh or salty. The amount and type of fluid produced depends on the initial reservoir pressure, rock properties and the drive mechanism.

3 3 3

Schlumberger

Basic Petroleum Engineering

FTC

Hydrocarbon Structure

Another way to describe the hydrocarbons is by the mixtures of the groups of hydrocarbon structure types. The three major groups are shown. The simplest and most abundant is the paraffin series, with the more complex structures in varying proportions.

The major constituent of hydrocarbons is paraffin.

Notes

4 4 4

Schlumberger

Basic Petroleum Engineering

FTC

Hydrocarbon CompositionTypical hydrocarbons have the following composition in Mol FractionHydrocarbon C1 Dry gas .88 C2 .045 .08 .08 .03 .03 C3 .045 .04 .05 .05 .01 C4 .01 .04 .04 .05 .01 C5 .01 .04 .03 .04 .04 C6+ .01 .08 .15-.2 .42 .8 1.0

Hydrocarbons vary widely in their properties. The first classification is by fraction of each component. This ranges from a dry gas which is mostly C1 (methane) to tar which is mostly the heavier fractions. The black oil normally found is between the two extremes, with some C1 and some heavier fractions. Every hydrocarbon extracted from a reservoir is of a different composition.

Condensate .72 Volatile oil .6-.65 Black oil Heavy oil .41 .11

Notes

Tar/bitumen

The 'C' numbers indicated the number of carbon atoms in the molecular chain.5 5 5

Schlumberger

Basic Petroleum Engineering

FTC

Hydrocarbon ClassificationHydrocarbons are also defined by their weight and the Gas/Oil ratio. The table gives some typical values:GOR API Gravity

Oil is more complex than gas and has to be defined in a more complete manner. The Gas-Oil Ratio, GOR (symbol Rs) is a measure of how much gas is in the oil and hence how light it is. This is measured at a specific pressure, for example the reservoir pressure. The API (American Petroleum Institute)gravity is a weight.

Wet gas Condensate Volatile oil Black oil Heavy oil

100mcf/b 5-100mcf/b 3000cf/b 100-2500cf/b 0

50-70 50-70 40-50 30-40 10-30

Notes

Tar/bitumen

0

C -> D) Reverse the process: force water into the core until the residual saturation is attained. (B) During the process, measure the relative permeabilities to water and oil.

Notes

44 44 44

Schlumberger

Basic Petroleum Engineering

FTC

Initially, the core permeability will be the absolute permeability as there is only one fluid at 100% saturation. The relative permeability of water will drop to zero when Swirr is reached because no more water will move. The relative permeability to oil will rise but never reach the absolute permeability because there is still water in the pores. When water is forced in, the relative permeability of water will rise but not reach the absolute value for the same reason.

Relative Permeability Experiment

Notes

45 45 45