Palabras De Despedida

Conventional water/oil displacement process is almost always studied with black-oil simulators. Is solution-gas-drive, gas-cap-expansion, or gas-injection studies, black-oil simulators are commonly used if the oil formation factor is less than2.

When the oil formation factor is greater than 2. Black-oil simulation may still be used if oil and gas formation factors, gas are solution, and oil and gas viscosities as functions of pressure can be determined accurately by calculation of experiment. However, if the oil formation factor is greater than 2, compositional models (more than two hydrocarbon components) should normally be used, because they can predict changes in produced fluid properties that can occur as depletion proceeds. If reservoir pressure declines significantly, recovery may not be predicted realistically unless compositional models are used.

Compositional methods are usually needed in studies of gas reservoirs that drop below their dewpoints during depletion. Dry gas injection to cycle such reservoirs after liquid dropout has occurred also fails into this category.

Compositional simulation is also needed to account for intermediates picked up by gas during oil displacement by dry gas injection, particularly in volatile oil reservoirs.

More- complex processes may require the use of compositional, miscible, or thermal simulation. Some of these processes are enriched gas drive, high-pressure gas injection, surfactant/polymer processes, and steamdrive. (See champ.11)

Pressure in reservoir will sometimes fall below the bubblepoint and then later increase, creating an opportunity for free gas to redissolve. If all gas released from which it came, no special simulation treatment is necessary to model re-solution. The gas should dissolve to an extent consistent with the relationship between solution GRO and pressure. If gas segregation has occurred, however, special treatment is necessary to estimate what fraction of oil in a gridblock is in contact with free gas, recognize when the single-phase condition is reached, and to define the oil –property curves applicable above the new bubblepoint.

Steffensen and Sheffield and straight et al. discuss treatment of gas that is assumed to be able to dissolve in all the oil in a block. This assumption is valid for cross-sectional models or 3D model whit sufficient vertical detail. It may be a poor assumption, however, for areal models or for coarsely gridded cross-sectional or 3D models that cannot model segregation of gas adequately. These types of models will yield optimistic results if, for example, they are used to study injection of gas into an under-saturated oil zone.

3.4.3 Variable fluid properties. Fluid properties vary vertically and areally in some reservoirs at discovery, pronounced variation can be represented by assigning different fluid properties to different regions of the model. In black-oil simulation, it is important to

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