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Content archived on 2024-04-16

Secondary and Tertiary drainage of oil with immiscible gases


To improve the understanding of gravity drainage on the reservoir scale. This understanding will reduce the risk associated with developments where gravity drainage is important.

The drainage of oil within a porous rock under gravitational forces is potentially an important mechanism in the production of many oil fields. Recent studies have indicated that when a gas is present, gravity drainage of a light oil in a water wet rock can result in very low residual oil saturations. The process could have considerable importance in the following situations:

a) Oil recovery in thick or steeply dipping reservoirs using immiscible nitrogen or hydrocarbon gas injection in either secondary or tertiary modes:
b) Oil recovery from the matrix blocks in fissured reservoirs:
c) Recovery of retrograde condensate in high permeability gas condensate reservoirs.

The programme will consist of three modules as follows:

a) Module A will investigate the basic parameters controlling gravity drainage, and provide information, which will be used in Module C, for developing a model to evaluate the process in oil reservoirs and in high permeability gas condensate reservoirs. In particular, it is planned to measure oil drainage rates and to establish the influence of oil physical properties, gas flow rate and rock wettability on the recovery of oil.

b) Module B is designed to investigate the influence of capillary end effects on the drainage process when short core plugs are assembled to form a long core. The aim will be to develop procedures for assembling core plugs so that they behave as a long core during gravity drainage, without end effects at each plug interface.

c) Module C is designed to provide a consistent explanation of the experimental results obtained in Module A, and to develop a model that can translate these results to the reservoir scale. The model will include a Darcy representation of the drainage behaviour in the presence of gravity, together with gas-oil and water-oil capillary pressure behaviour. The model will then be used to investigate:

The effect of butting in the core when capillary contact is poor. Comparison will be made with the results of Module B.
The drainage efficiency on the reservoir scale where length scales are much larger than the capillary transition zones. The importance of rate will be deduced.
The effect of reservoir stratification on the drainage efficiency.

Experiments will be conducted in simple capillary geometries, in glass micromodels, in sand packs and in long consolidated core sections.


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United Kingdom Atomic Energy Authority (UKAEA)
EU contribution
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Winfrith Technology Centre
DT2 8DH Dorchester
United Kingdom

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Participants (3)