油层物理学：1-2 Solution and separation process in a gas-oilsystem

1、Section 2 Solution and separation process in a gas-oil system,Rs=P,1、Solubility Of Gas In Oil,1.1 Henrys Law,RsSolubility of gas, the standard volume of gas dissolved in a unit volume(SC) of liquid at pressure p, (standard) m3/m3； PPressure, MPa； Solubility factor, (standard) m3/(m3MPa,Notice： Henry

2、s law is applicable to the gas-liquid systems where gas and liquid vary greatly in their properties,Fig. 1.2.1 Solutions of different gases in crude oil,Fig. 1.2.2 Solutions of pure hydrocarbons in crude oil,1.2 Solution Of Natural Gas In Oil And Its Influencing Factors,1)Solution Of Natural Gas In

3、Oil,The heavier hydrocarbons have higher solubilities than the lighter hydrocarbons,Charactristic of solution Of Natural Gas In Oil,is bigger at low pressure, and then decrease, at last =C as P increase,Rs=P,2)Factors Of affectting Gas Solubility in Oil,T=C， P,P=C, t,Rs,Rs,4,The solubility of natura

4、l gas in crude oil depends on the pressure, the temperature and the composition of the natural gas and the crude oil,The solubility of gas components grows with the molecular weight of gases. The natural gas has a greater solubility in lighter oils than in heavier ones. The quantity of solution gas

5、increases as the composition of the gas and crude oil approach each other,The composition of the natural gas and the crude oil,图 1.2.2,2. Equilibrium Relations(相态方程,2.1 Derivation of Equilibrium Relations,We take 1 mole of mixture of known composition,Usage: to calculation dew point, bubble point, t

6、he quantities and compositions of the gas and liquid at two-phase conditions,component,1 mole,At pressure p and temperature T, a balance is established between gas phase and liquid phase,P、t,Nl、Ng- the total number of moles of liquid and gas. ni- the mole fraction of the ith component in the total m

7、ixture, xi、yi- the mole fraction of the ith component in the liquid and gas,Material balance of ith component,1) The relationship of xi and NL,2) The relationship of yi and Ng,We have yi/xi=ki 。equilibrium ratio, equilibrium constant (平衡常数,Use “trial-and- error” method to solve above equations,1)Cal

8、culate the bubble point(泡点压力)： the point at which the first bubble of gas is formed. At this point, the quantity of gas is negligible,2.2 Calculation of the bubble-point and dew-point pressure,Ng=0, NL=1,or,2)Calculate the dew point(露点压力,Ng=1,NL=0,Pressure does not appears explicitly in these Equati

9、ons, pressure is represented in the equilibrium ratio. The Pb and Pd may be determined by trial-and-error method,The point of which the first drop of liquid is formed. At this point the quantity of liquid essentially is negligible,or,Example: calculate Pb,Equilibrium constant Ki is the distribution

10、ratio of component i in the gas phase and liquid phase when these two phases are at equilibrium at a given pressure and temperature,2.3Equilibrium constant(平衡常数,Ki is also called equilibrium ratio,No heating effect when the components are mixed; The volume of the ideal solution equals the sum of the

11、 volumes the components. the intermolecular forces of attraction and repulsion are the same between molecules,Raoults equation(拉乌尔,Daltons equation(道尔顿,1) Ideal solution,The partial pressure of component I in the gas,Pvi - vapor pressure,Pvi is solely a function of temperature. So if ideal solution

12、behavior exists, the equilibrium ratio of each component is simply depends on pressure and temperature. But in practice, the equilibrium ratio for a component of a real solution is dependent not only on the temperature and pressure, but also on the composition of the system,2)For real solution Ki-De

13、termined by experiment,ki=yi/xi,Fig. 1.2.6,Convergence pressure(收敛压力,Characteristic of ki,At low pressure, the slope of each curve is approximately 1.0. Each curve passes through a value of unity at a pressure very close to the vapor pressure of the component at the temperature of the graph,At high

14、pressures, the effects of nonideality are seen. The curves for the components tend to converge toward a value of 1.0. The value of pressure for which the equilibrium ratios appear to converge to unity is known as the convergence pressure,In one system，all the components have the same convergence pre

15、ssure. But different system has different convergence pressure; Fig 1.2.7,At low pressure(0.7MPa)，Ki of i component is the same for different system,If the mixture is at its true critical temperature, the convergence pressure is the critical pressure,convergence pressures are 4.2, 5.6, 7.0, 21.0, 28

16、.5, 35.0, 70.0 and 140.0MPa,The apparent convergence pressure is a function of the composition of the mixture,美国石油天然气公司（NGAA）发表了不同收敛压力下的天然气平衡常数图版,3. Separation Of Oil And Gas,The manner of separation: Flash vaporization(接触分离）， Stage Separation(多级分离)、 Differential Vaporization(微分分离,Pressure, temperat

17、ure and composition of the system affect the solubility of gas in the oil as well as the separation of gas from oil. The gaseous components which are ready to dissolve into the oil are hard to separate, while those difficult to dissolve are easy to separate. The amount of gas separated from the oil

18、is dependent on the temperature, pressure and the manner of separation,Flash vaporization is the process in which the pressure on a liquid is reduced suddenly, causing a flash separation of gas from oil and an equilibrium between oil and gas is established immediately,3.1 Flash vaporization(闪蒸脱气、一次脱

19、气、接触分离,In Figure 1.2.9. The pressure at which the slope changes is the bubble-point pressure of the mixture,At each step, pressure and total volume of the reservoir fluid are measured,1)More gas is obtained. The gas has a higher specific gravity, It contains a large amount of lighter oil components.

20、 (2)The overall system composition remains constant,Characteristic,A stage separation is a process in which gaseous and liquid hydrocarbons are separated into vapor and liquid phases by two or more equilibrium flashes at consecutively (连续地)lower pressures,3.2 Stage Separation,More oil is obtained. T

21、he oil contains a large amount of lighter oil components. The gas has a smaller specific gravity. The composition of the system is changed,Characteristic,多级脱气,In laboratory : one stage vaporization apparatus,In oil field: one stage vaporization,two stage separation,two stage separation,3.3 Different

22、ial Vaporization(微分脱气,Differential vaporization is a process in which the gas is removed from contact with the liquid as the gas is formed. It is similar to the stage separation. - 分离级数无限多的多级脱气,It is usually used to simulate the gas-oil separation when pressure below the bubble point pressure,Example