Oil formation

As solution gas is liberated, the oil shrinks. A particularly important relationship exists between the volume of oil at a given pressure and temperature and the volume of the oil at stock tank conditions. This is the oil formation volume factor (B, measured in rb/stb or rm /stm ). 

The oil formation volume factor at initial reservoir conditions (B., rb/stb) is used to convert the volumes of oil calculated from the mapping and volumetries exercises to... 

Steam can also be injected into one or more weUs, with production coming from other weUs (steam drive). This technique is effective in heavy oil formations but has found Httle success during appHcation to tar sand deposits because of the difficulty in connecting injection and production weUs. However, once the flow path has been heated, the steam pressure is cycled, alternately moving steam up into the oil zone, then allowing oil to drain down into the heated flow channel to be swept to the production weUs. 

Laboratory analysis will indicate an initial oil formation volume factor of 2.0 res bbl/STB or less. Oil formation volume factor is the quantity of reservoir liquid in barrels required to produce one stock-tank barrel. Thus, the volume of oil at point 2 of Figure 5-1 shrinks by one-half or less on its trip to the stock tank. 

Laboratory observation of volatile oils will reveal an initial oil formation volume factor greater than 2.0 res bbl/STB. The oil produced at point 2 of Figure 5-2 will shrink by more than one-half, often three-quarters, on the trip to the stock tank. Volatile oils should be produced through three or more stages of surface separation to minimize this shrinkage. 

Also, the oil formation volume factor was measured as 2.504 res bbl/STB. Does this information confirm your previous analysis If so, in what ways ... 

The change in oil volume due to these three factors is expressed in terms of tins, formation volume factor of oil. Oil formation volume factor is defined as the volume of reservoir oil required to produce one barrel of oil in the stock tank. Since the reservoir oil includes dissolved gas,... 

EXAMPLE 8-2 A sample of reservoir liquid with volume of 400 cc under reservoir conditions was passed through a separator and into a stock tank at atmospheric pressure and 6CTF. The liquid volume in the stock tank was 274 cc. A total of 1.21 scf of gas was released. Calculate the oil formation volume factor. 

Pressure psig Oil formation volume gas-oil factor B0 res bbl/STB Solution gas-oi ratio R scf/STB Gas formation volume factor bbl/scf... 

Plot oil formation volume factor and solution gas oil ratio against pressure. Compare the shapes of your plots with Figures 8-1 and 8-2. Compare the shapes of the B0 graph and the Rs graph. Save your graphs you will need them in Exercise 8—17. 

Notice that the oil formation volume factor varies from 1.474 res bbl/STB to 1,495 res bbl/STB, Also, the solution gas oil ratio varies from 768 scf/STB (676 + 92) for a separator pressure of 100 psig to 795 scf/STB for a separator pressure of 300 psig. This is disturbing in that it... 

At pressures above bubble-point pressure, oil formation volume factors are calculated from a combination of flash vaporization data and separator test data. 

This chapter begins with bubble-point pressure and solution gas-oil ratio, and then explains methods of estimating the density of reservoir liquids. The results of the density calculations are used to estimate oil formation volume factors. A technique for adjusting the results of the correlations to fit field derived bubble-point pressure is presented. 

The results of the reservoir liquid density calculations can be used to calculate oil formation volume factors. 

When the composition of the reservoir liquid is known, oil formation volume factor can be calculated very accurately using the procedure given in Chapter 13. The other two situations will be discussed here. 

The oil formation factor can be calculated using the results of ideal-solution calculations of the liquid density at reservoir conditions. 

If the solution gas-oil ratio is known at some pressure below the bubble point, it can be used to enter Figure 11-9, and an accurate estimate of the oil formation volume factor at that reservoir pressure can be determined. Solution gas-oil ratio can be obtained from Figure 11-1. However, the accuracy of the final result is a combination of the 5 percent attributed to Figure 11-8 and the 15 percent attributed to Figure 11-1. 

EXAMPLE 11-11 Estimate values of oil formation volume factor at various pressures below bubble-point pressure for the reservoir oil of Example 11-1. 

The oil formation volume factor at pressures above the bubble-point pressure is less than the formation volume factor at bubble-point pressure because of the contraction of the oil as reservoir pressure is increased. This compression due to increased reservoir pressure is the only factor which affects formation volume factor at pressures above the bubble point. 

The accuracy of the results of the use of correlations to estimate oil formation volume factor and solution gas-oil ratio can be improved if an accurate value of bubble-point pressure is available. The method described in Chapter 9 can be used to get a reasonably accurate value of bubble-point pressure if reservoir pressure has been measured regularly during the life of the field. 

Tables of oil formation volume factor and solution gas-oil ratio tabulated against pressure are adjusted by changing the values of pressure. A delta pressure is calculated as the difference between field derived bubble-point pressure and bubble-point pressure from correlation.

A black oil has a bubble-point pressure of 4000 psia at 225°F. The oil formation volume factor at the bubble point is 1.519 res bbl/STB. Estimate the oil formation volume factor at initial reservoir pressure of 6250 psia. Use a value of 13 microsips for the coefficient of isothermal compressibility. 

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