Black-oil reservoir simulation still has wide application in the petroleum
industry because it is far less demanding computationally than compositional
simulation. But a principal limitation of black-oil reservoir simulation is
that it does not provide the detailed compositional information necessary for
surface process modeling.
Black-oil delumping overcomes this limitation by converting a black-oil
wellstream into a compositional wellstream, enabling the composition and
component molar rates of a production well in a black-oil reservoir simulation
to be reconstituted.
We present a comprehensive black-oil delumping method based primarily on the
compositional information generated in the depletion process that is used
initially to provide data for the black-oil simulation in a typical workflow.
Examples presented in this paper show the accuracy of this method in different
depletion processes: natural depletion, water injection, and gas injection. The
paper also presents a technique for accurately applying the black-oil delumping
method to wells encountering crossflow.
With advances in computing speed, it is becoming more typical to use a fully
compositional fluid description in hydrocarbon reservoir simulation. However,
the faster computers become, the stronger the simulation engineer's tendency to
build more challenging (and thus more CPU intensive) models. Compositional
simulation in today's multi-million-cell models is still practically
Black-oil fluid representation is a proven technique that continues to find
wide application in reservoir simulation. However, an important limitation of
black-oil reservoir simulation is the lack of detailed compositional
information necessary for surface process modeling. The black-oil delumping
technique described in this paper provides the needed compositional
information, yet adds negligible computational time to the simulation.
Delumping a black-oil wellstream consists of retrieving the detailed
components' molar rates to convert the black-oil wellstream into a
compositional wellstream. It reconstitutes the composition and component molar
rates of the production stream.
Black-oil delumping can be achieved with differing degrees of accuracy by using
options ranging from setting a constant oil and gas composition for the whole
run to using the results of a depletion process: constant-volume depletion
(CVD), constant-composition expansion (CCE), and differential liberation
The simplest method is to assign a fixed composition (component mole
fraction) to stock-tank oil and gas. This could be applied over the whole
reservoir, or, if the hydrocarbon mixture properties vary across the reservoir,
different oil and gas compositions can be reassigned at any time during the
Some black-oil simulators have an API tracking feature that allows oils of
different properties to mix within the reservoir. The
pressure/volume/temperature (PVT) properties of the oil mixture are
parameterized with the oil surface density. To provide a delumping option
compatible with the API tracking, stock-tank oil and gas compositions may be
tabulated against the density of oil at surface conditions.
© 2007. Society of Petroleum Engineers
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- Original manuscript received:
30 June 2005
- Meeting paper published:
9 October 2005
- Revised manuscript received:
9 May 2007
- Manuscript approved:
9 June 2007
- Version of record:
20 October 2007