Coalbed methane (CBM) simulators

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Coalbed methane (CBM) simulators also model physical mechanisms thought to be
important in CBE recovery and CO2 storage processes: the dual porosity structure of the
coal bed, adsorption/desorption of CH4 at the coal surface, coal matrix shrinkage due to
CH4 desorption, and diffusion of gas from the matrix to the fracture system. Additional
physical mechanisms that may play a role in CO2 storage on coalbeds include: coal
matrix swelling due to CO2 adsorption onto the coal surface, mixed gas adsorption, and
diffusion of multiple gas components.
    Enhanced CBM simulators that are applicable to CO2 storage can be divided into two
groups: those that use a compositional framework and those that adopt a black oil
framework. In the compositional framework, fluid properties are rigorously modeled
based on an equation of state. In the black oil framework, fluid properties are supplied by
lookup tables, obtained through laboratory work or correlations.

    2.2.1 PSU-COALCOMP
    PSU-COALCOMP [85] is a compositional, dual porosity coal bed methane simulator
that accounts for multi-component sorption and transport phenomena. Multicomponent
sorption is modeled via an ideal adsorbed solution theory and the Peng-Robinson
equation of state. Mass transfer between the matrix and fracture system is defined via a
sorption time constant, a lumped parameter that incorporates diffusion time, rate or
sorption/desorption and cleat spacing of the coal. GCOMP a simulator that assumes
instantaneous diffusion between the matrix and the fracture systems, allowing reduction
of the system to a single porosity system [90]. Mixed gas adsorption is modeled via an
extended Langmuir model. In this approach, the concentration of each gas component is
a function of its partial pressure. Geomechanical effects on permeability and porosity are
modeled, as are coal matrix shrinkage and swelling due to adsorption/desorption of gases
on the coal surface.
    2.2.2 SIMED
    SIMED II is a two phase multicomponent single or dual porosity coal bed reservoir
simulator [100]. The Peng-Robinson equation of state is used to calculate fluid
properties. Water phase properties are evaluated internally. Multiphase gas adsorption
can be modeled via an extended Langmuir isotherm or an ideal adsorbed solution model.
Stress dependent permeability and porosity can be accounted for through a choice of one
of five models. SIMED II also accounts for geomechanical effects associated with
injection. A dynamic fracture model represents the initiation and growth of injection
induced hydraulic fractures.
    2.2.3 CMG-GEM
    CMG-GEM [12] is another multiphase, multicomponent single of dual porosity coal
bed reservoir simulator. Phase behavior can be described by either the Peng-Robinson or
Soave-Redlich-Kwong equation of state. Shape factors can be used to account for flow
between porosities and additional transfer enhancements can be used to account for fluid
placement in the fractures. Mixed gas adsorption is modeled via an extended Langmuir
isotherm, and the corresponding diffusion model can be selected base on either
concentrations calculated from adsorption characteristics or based on free gas properties.
Stress dependent relative permeability changes and matrix swelling and shrinkage can be
included.
     2.2.4 METSIM2
     METSIM2 [88, 89] is a 3D multicomponent, triple porosity coal bed reservoir
simulator. This formulation assumes that there is no water present in macropore system,
only free gas exists, and its transport is diffusion controlled. This formulation allows for
the competitive desporption in coal by specifying different diffusion time constants for
the macropore and the micropore systems. Gas properties are calculated using an
equation of state. Multicomponent adsorption is described using an extended Langmuir
model. METSIM2 is also coupled to a wellbore and rock mechanics simulator, allowing
pore pressure dependent permeability functionality.
      2.2.5 COMET3
     COMET3 is an extension of COMET and COMET2, developed to model low-rank
coal and water saturated gas-shale reservoirs [78]. It can model single, dual and triple
porosity approximation of the coal bed system. In the triple porosity system, gas desorbs
from the internal matrix, and migrates to the micropermeability matrix and finally to the
cleat system where it flows to the wellbore. In this formulation, the micropermeability
matrix system also models multiphase effects. This accounts for the establishment of a
critical gas saturation in the matrix, which may be responsible for a delay in early time
gas production observed in some fields. Desorption and diffusion are explicitly modeled.
COMET3 can model multiple gas components, and accounts for different diffusion rates
of the components. An extended Langmuir isotherm is used to model mixed gas
adsorption. Pore volume compressibility accounts for stress dependent porosity and
permeability changes. A differential swelling model based on laboratory experiments
accounts for swelling attributed to non-CH4 components of the gas.
      2.2.6 ECLIPSE-100
     ECLIPSE-100 [86] is a black oil simulator with additional features for modeling
CBM. A dual porosity system is used to model the coal bed system. This simulator is
only able to handle two gas components, and therefore it is not able to model an ECBM
process with flue gas injection. Compositional effects between CO2 and CH4 are handled
by introducing a “solvent” phase. Adsorption is described by the Langmuir isotherm.
Eclipse-100 can account for coal shrinkage and compaction effects.
     2.3 Summary: Simulation technology
        The simulators currently available for aquifer and coalbed storage of CO2 are very
capable, with many physical mechanisms represented. They will continue to be very
useful for exploring the interplay of physical mechanisms for computational grids of
limited size, but they are subject to significant limitations for application at field scale.
Conventional finite-difference compositional simulations, even with relatively small
numbers of components, are too slow to handle high resolution representation of thespatial distribution of permeability at field scale, and when coarse computational grids
are used instead, they are badly affected by numerical diffusion, which can alter
calculated composition paths in a way that affects calculated performance significantly.
Hence, they are probably not suitable for routine simulation of field-scale flows at grid
resolutions sufficient to capture the effects of preferential flow paths created by reservoir
heterogeneity, especially if the impact of variability in the permeability distribution is to
be assessed. For screening of sites, assessment of areas invaded by CO2, or rapid
exploration of the impact of injection well placement, simulation tools that are
significantly more efficient, but necessarily more limited in the mechanisms represented,
are appropriate. One approach, the use of streamline methods, is demonstrated in the
following sections for two of the geologic settings, gas reservoirs and aquifers.

justbetoo

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wwyy

Eclipse has a option about CBM simulation

aspire880

学习下。

rogue

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suihg

是论文么，下文呢？

happyzhc

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