Physical Properties of Petroleum Reservoir

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Reservoir having artesian water ().

Reservoir having bottom water and gas- cap

Reservoir with pinchout boundary (

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(4) Fundamentals of Enhanced Oil Recovery(Contences)(1)() Properties of reservoir Fluids(2) Properties of Reservoir Rocks(3) Properties of Porous Medium Containing Multiple Fluids

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(formation)

Reservoir is a porous and permeable subsurface formation containing reservoir fluids. It is bounded by a barrier() of impermeable rock and often by an aquifer barrier. It is characterized by one pressure system.

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(characteristic) (reservoir fluids)

Reservoir fluids refer to the crude oil, natural gas and water containing in the pores of the reservoir rocks. Physical properties of the reservoir fluids are different from those of the fluids at the surface.Characteristic() : Reservoir fluids are usually under high T and P, the crude oil contains a large amount of dissolved gas() ,reservoir water has much salts.

In this chapter, we will first discuss: (1) phase behavior of hydrocarbon system (2) Solution and separation process in a gas-oil system(3) Properties of gas, oil and water.

Section 1 Phase behavior of hydrocarbon systemThe hydrocarbons include alkanes(), cycloalkanes(), aromatic()At normal T and P:1. Chemical composition Commercial properties of petroleum and its classificationPetroleum is a mixture of naturally occurring hydrocarbons and nonhydrocarbons. 1.1 Chemical composition of petroleum

Nonhydrocarbons() are compounds of oxygen, sulfur, nitrogen of alkanes() 1.2 Commercial value of Petroleum:Commercial value of a petroleum liquid are specific gravity, viscosity, freezing point(), asphalt() content, sulfur content etc. Although the quantities of these nonhydrocarbons are very small, they exert great influences on some of the properties of petroleum, such as color, specific gravity, viscosity and interfacial tension.

When the reservoir is developed, the states of the hydrocarbon depends upon (1) the composition of the hydrocarbon fluid , (2)the pressure and temperature. 2. Basic concepts in study of phase behavior (1)System(): a amount of substances within given boundaries under specific conditions composed of a number of components.(2)Phase() is any homogeneous and physically distinct part of a system.There is a definite bounding surfaces between different phases. A phase can consist of several components.

(4) Composition() is the components and their relative quantities of a system.(5) p-T phase diagram() is the diagram which shows the conditions of temperature and pressure for which different phases exist . (3) Components() is the substance which consist of the system. such as the methane, ethane, propane, butane, etc in the petroleum.p-T diagram is the most often used one in petroleum industry.

3.1 phase behavior of one component system(1) The Characteristic of one component system 3. Phase Diagram of one-,two-,multi-component systemDew point() is the point at which only a small drop of liquid exist (or condensate) .

Bubble point( ) is the point at which the first few molecules leave the liquid and form a small bubble of gas.Characteristicbubble point()dew point()

(2) P-v diagram of one component system As temperature increases, the volume change from gas state to liquid state decreases. At Tc the length of horizontal line becomes a point C. If temperature >Tc, the gas can not be liquefied.Point C is called critical point. Pc --- The critical pressure Tc ---The critical temperature

(3)P-T diagram of one component system (1) It is a single linethe vapor pressure line, the locus of bubble points and dew points of the pure substance. (2)The critical point C is the highest pressure and highest temperature point at which gas and liquid can coexist. At point C, all the intensive ()properties of gas and liquid phases, such as viscosity, density etc. become identical.

(3)The phase diagram is divided into the gas region, liquid region and the two-phase region.liquid regiongas regiontwo-phase region

(4)With molecular increases the vapor pressure line move to the right side.

The use of phase diagramto determine the phase behavior of the component at different P and T.K:Initially entirely liquidI: Bubble point, Gas, liquid coexistI: Dew point, Gas, liquid coexistG: Entirely in gas stateExample: Constant temperature process KIG:

3.2 Phase Behavior Of Two-Component Systems (1) It is an envelope() line FC- bubble point line, line EC- dew point line. (2) The region bounded by Pb line and Pd line is the two-phase region. Above and to the left of the bubble point line, the mixture exists as a liquid. Below and to the right of the dew point line, the mixture exists as a gas. (3)The critical point C is the point at which the bubble point line and the dew point line join.

(1)The phase envelope for a mixture lie between the vapor pressure curves of the pure constituents. Fig. 1.1.6 P-T diagram for the ethane-n-heptane system.(2) As the composition of the mixture becomes more evenly distributed between the constituents, the two-phase region increases in size. P7The characteristic of two phase diagram

(3)As one constituent() becomes more predominant, the phase envelope tends to shift to the vapor-pressure curve of the major pure component. (4)The critical temperature Tc of the mixture lies between the critical temperatures of the two pure components. Pc is usually high then Pc of the two components.

Locus of critical points()(5)a larger difference in molecular size of the components causes the mixtures to have very large critical pressures. 6)a small difference in molecular size of the components causes the small critical pressures.

3.3 Phase behavior of multi-component system ()

The shape is an envelop.(1)Characteristic3.3 Phase behavior of multi-component system ()Fig. 1.1.8 Phase diagram of a multi-component system C Critical pointKC-Bubble point curve.OC-Dew point curve.

Liquid region --Above the bubble point line Gas region -Below and to the right of the dew point line Two phase region-- The region bounded the bubble point line and dew point line.Dotted lines --the iso vol lines (quality lines) -Liquid regionGas regionGas regionTwo phase region-

Cricondenbar P (the highest pressure on the saturation envelope.Cricondentherm T () the highest temperature on the saturation envelope.The shaded area--Retrograde region where condensation or vaporization occurs in reverse to the conventional behavior. --isothermal retrograde condensation--isobaric retrograde condensation

(2)Retrograde Condensation (Point A: entirely gasPoint B: Upper dew pointPoint D: maximum amount of liquid Point E :Lower dew pointPoint F: entirely gasAt normal condition, a decrease in pressure causes a change of phase from liquid to gas. But in condensate gas reservoir, the process is exactly the reverse of normal one, hence call it retrograde condensation.

the hydrocarbon system exists as a single liquid. It is an undersaturated oil reservoir (3)The use of phase diagram of multi-component systemTo determine classification of the hydrocarbon systemTo determine the phase behavior during production period.Example: point J

Point A a condensate gas The reservoir temperature lies between the critical temperature and the cricondentherm of the system. The reservoir condition is usually above the shade zone. Point Ithe initial reservoir conditions on the bubble point curve, the oil is said to be saturated. Gas cap may be exited in this situation.Point FGas reservoir

4 Phase Diagrams of Several Typical Oil/Gas ReservoirsConcepts:(1)Low-shrinkage crude oil is the oil with a low shrinkage in volume (2)high-shrinkage crude oil is the oil with a high shrinkage in volume A crude oil contains a certain amount of lighter hydrocarbons. When it is produced to the surface, the lighter hydrocarbons evolve from the oil and form gas. This will result in a shrinkage in oil volume. The larger amount of lighter hydrocarbons contained in the oil, the large shrinkage will occur in the oil volume when it is produced to the surface.

4.1 The low-shrinkage crude oil The phase diagram covers a wide temperature range. The iso-vol lines are near the dew point line. Fig. 1.1.10 low-shrinkage crude oil Line l23 ----phase behavior in reservoir . Sseparator conditionCharacteristic:contains large amounts of heavy constituents, the gas-oil ratio is small( 0.876). The stock-tank oil is very dark.

4.2 The high-shrinkage crude oilThe area of the diagram is smaller. Iso-vol lines are shifted upwards toward the bubble-point line.--- a small reduction in pressure below the bubble point 2, causes the release of a large amount of gas in the reservoir. Line l23 ----phase behavior in reservoir . Sseparator conditioncontains more lighter hydrocarbons, higher producing gas-oil ratio(901500m3/m3), the specific gravity less than 0.78. The stock-tank oil is colored .

The phase diagram is smaller than that of oils The reservoir temperature is higher than the critical temperature and lower than the cricondentherm.4.3 Phase Diagram For Retrograde GasFig. 1.1.12 retrograde gas Stock-tank liquid produced from retrograde gas reservoirs often is called condensate. The liquid can be lightly colored,

4.4 Phase Diagram For Wet GasThe area of phase diagram is small. No liquid is formed in the reservoir Separator conditions lie within the phase envelope. Stock-tank liquid --condensate. The liquid almost has no color, The type of reservoir is mainly determined by phase diagram.

4.5 Phase Diagram For Dry GasThe mixture is solely gas in the reservoir. Separator conditions fall outside the phase envelope. No liquid is formed either in the reservoir or at the surface.

low-shrinkage crude oil high-shrinkage crude oil retrograde gas wet gas dry gas

From the low-shrinkage crude oil to the dry gas, the phase diagrams have the following characteristics: (1) The critical points shift from right to left. (2) The phase envelopes become smaller. The oils have a broader two-phase region than the gases. (3) The iso-vols shift towards the bubble point lines.Conclusion to phase behavior