Expulsion efficiency

After primary migration has taken place, a certain proportion of the generated hydrocarbons remains in the pore system of the source rock (Hunt, 1979). The oil fraction that remains in the source rock will be cracked to gas as the source rock is buried to greater depths and temperatures (Section 3.1.5). The effect of primary migration of hydrocarbons can be indicated by the expulsion efficiency. The petroleum expulsion efficiency is the ratio of the expelled petroleum and the sum of the generated and initial petroleum and can vary from zero (no expulsion) to 1.0 (complete expulsion) (Cooles et al., 1986). The expulsion efficiencies are not uniform in time and space (Leythaeuser et al. 1987b). They depend on the tsrpe of source rock, its richness and thermal maturity and the primary migration mechanism. 

The expulsion of gas is probably very efficient. Altebdumer (1982, in Cooles et al., 1986), for instance, showed that gas expulsion from the gas-prone Lias 5 shales, N.W. Germany, is very efficient with up to 95% of generated gas being expelled from the source rock. As outlined in Section 3.2.2.1, gas generation 

PGI = Petroleum Generation Index PEE = Petroleum Expulsion Efficiency 

The rate of hydrocarbon expulsion from mature rich oil-prone source rocks is about 8 x l( -i to 8 x 10- m m- s-, according to a rough estimate made by England et al. (1987). England et al. s calculations are based on the subsurface conditions given in Table 3.4. 

Assumed average subsurface conditions for rich oil-prone source rocks 

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Figure 3.14 Variation of average bulk oil expulsion efficiency with average initial hydrocarbon potential (after Cooles et al., 1986. Reprinted with permission from Organic Geochemistry, Vol. 10, Copyright 1990, Pergamon Press Ltd.).

For a certain geological heating rate, the petroleum expulsion efficiency, in combination with the type and richness of a source rock, determine whether oil, gas condensate or gas will be expelled over a certain temperature range (Mackenzie and Quigley, 1988 Figure 3.15). 

Hydrogen index Petroleum generated Expulsion efficiency... 

Source rock gas content This property essentially defines the quantity of gas remaining in the source rock at current conditions. It is estimated from gas desorption tests. Conversely, this measurement can also help estimate the gas expulsion efficiency. 

Note that the source rock s gas expulsion efficiency is very difficult to quantify directly from source rock measurements. However, this parameter may be estimated from a mass balance calculation on the source rock. The gas volume remaining in the source rock or shale at present-day conditions may be estimated using... 

The gas volume remaining in the source rock can be related mathematically to the generated gas volume and source rock expulsion efficiency by combining equations (2) and (8) as follows ... 

Further, combining equations (7) and (9) yields an equation to compute gas generated from the source rock in terms of the gas desorption parameters and expulsion efficiency as... 

Finally, equating equations (3) and (10) yields an equation to calculate the gas expulsion efficiency directly as... 

Rather than estimating reservoir trapping efficiency from seal capacity measurements, gas volumes expelled from the source rock (equation (13)) were compared with gas volumes computed from conventional reservoir engineering approach (equation (14)). These comparisons provide an indication of the range of possible trapping efficiencies in each prospect area. Additionally, the distribution of source rock expulsion efficiency was computed using a Monte Carlo simulation technique and equation... 

PMDs come in numerous styles and designs, each with its own specific purpose. Multiple PMDs are often required to meet the demands of a particular mission, whether using storahle or cryogenic propellants. PMDs have been used extensively in chemical storable propulsion systems and can even be implemented in electric propulsion systems (Polzin et al., 2007). PMD performance is determined by three primary characteristics PMD system mass, demand mass flow rate, and expulsion efficiency (EE), which is defined as... 

Historically, there are two space experiments which employed a vane type PMD. The Fluid Acquisition Resupply Experiment-II (FARE-II) tested a vane type LAD using a simulant fluid onboard of the Shuttle mission STS-57 as its primary PMD (Dominick and Tegart, 1994 Dominick et al., 2011). The secondary PMD resembled that of a sponge. The purpose of the experiment was to establish vane performance limits in terms of maximum achievable expulsion efficiencies under adverse acceleration levels. A snapshot of the FARE-II experiment is shown in Eigure 2.10 (Dominick et al., 2011). This was a very successful mission which generated useful low-g data. 

Trends in room temperature reseal pressure data mirrors trends in bubble point pressure data. All reseal pressures collected here are about 90% of the corresponding bubble point values. Operationally, this implies that only a ->10% reduction in differential pressure across the screen is required to reseal the screen and prolong the point of total LAD failure to yield a higher overall expulsion efficiency. Wicking rate test results performed in IPA align nicely with historical trends as coarser meshes outperform finer meshes. 

As will be shown later, warm pressnrant will always decrease the surface tension of the cryogen, consequently, degrading the LAD performance. Clearly an optimal design point between the pressurization and LAD subsystems exists for each mission. Ln low gravity, warm gas will not impinge on the LAD screen imtil low tank fill levels, but tests are warranted to quantify the effect of heat absorption into the liquid on the LAD performance because warm gas will adversely affect the expulsion efficiency of the LAD. 

Equation (14.15) is then numerically integrated to determine R x] and subsequently Ru, which is the final value of R x). To calculate the expulsion efficiency at EOL, A x) is used to calculate the residual filet volume ... 

For the vanes, tank drain simulation was not required since the model already considers an EOL configuration. To size the vanes, the height and number of vanes were varied to submerge the sump fully, the liquid filet volume was calculated (following the method outlined in Section 14.3), and expulsion efficiency and PMD mass were obtained. Vanes were also sized to maximize expulsion efficiency at a given demand flow rate. If multiple vane systems could achieve the same expulsion efficiency, the system with the lowest mass was chosen. 

Results show that expulsion efficiency is not as sensitive to changes in some of these variables. For example, increasing the tank pressure causes a small increase (<0.5%) in the... 

Table 14.2 Screen Channel Liquid Acquisition Device Expulsion Efficiencies for Variable Thermodynamic Conditions, Demand Flow Rates, and Screen Types...

Screen/Fluid 7- K) Tgas (K) P(kPa) Mass Flow Rate (kg/s) Expulsion Efficiency ... 

To determine how the IADs scale with flow rates, in order to compare performance with the vane PMD, simulations were also run at multiple flow rates between 1 x 10 and 2.76 x 10 kg/s for a 325 x 2300 screen in LH2 at a fixed liquid and pressurant gas temperature of 20.3 K each and a tank pressure of 101 kPa. Table 14.4 presents the resultant expulsion efficiencies and PMD mass for the screen channel LAD cases at different demand flow rates. The results show that up to a mass flow rate of 0.0049 kg/s, the LAD can achieve a maximum expulsion efficiency of 98.1% of the small-scale LH2 tank. This upper limit is due to the fact that the gallery arm cannot access the small residual propellant pool in between consecutive arms at very low fill levels due to the closed flow... 

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