Page 159 - Reservoir Formation Damage
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Paniculate Processes in Porous Media  141

             released  by  colloidal  forces  or  mobilized  by  hydrodynamic  shear  of  the
             fluid  flowing  through porous  media.  Fine  particles  can  also  be  generated
             by  deformation  of  rock  during  compression  and  dilatation.  This  is  due
             to  variation  of  the  net  overburden  stress  and  loss  of  the  integrity  of  rock
             grains.  Fine  particles  are unleashed and  liberated  because  of the integrity
             loss  of  rock  grains  by  chemical  dissolution  of  the  cementing  materials
             in  porous  rock,  such  as  by  acidizing  or  caustic  flooding.  These  are  the
             typical  internal  sources  of  indigenous fine  particles.
                Paniculate matter  can be produced  by  various  chemical  reactions  such
             as  the  salt  formation  reactions  that  occur when the  seawater  injected  for
             waterflooding  mixes with the  reservoir brine, and  formation of  elemental
             sulfur  during  corrosion.  Paniculate  matter  can  also  be  produced  by
             precipitation  due  to  the  change  of  the  thermodynamic  conditions  and  of
             the  composition  of  the  fluids  by  dissolution  or  liberation  of  light  gases
             (Amaefule  et  al.,  1988).  These  are  typical" mechanisms  of  particle pro-
             duction  in  porous  media.
                Once entrained by the fluids  flowing  through porous  media,  the various
             particles  migrate by  four  primary mechanisms (Wojtanowicz et  al.,  1987):
                1.  Diffusion
                2.  Adsorption
                3.  Sedimentation
                4.  Hydrodynamics
                The  transport of the  fine particles  are  affected  by  six factors (Wojtanowicz
             et  al.,  1987):
                1.  Molecular  forces
                2.  Electrokinetic  interactions
                3.  Surface  tension
                4.  Fluid  pressure
                5.  Friction
                6.  Gravity

                As  the  fine  particles  move  along  the  tortuous  flow  pathways  existing
             in  porous  media,  they  are  captured,  retained,  and  deposited  within  the
             porous matrix.  Consequently, the texture of  the matrix is adversely  altered
             to  reduce  its  porosity  and  permeability.  Frequently,  this  phenomena  is
             referred  to  as formation damage  measured  as the permeability  impairment.

                                  Particulate  Processes

                The  various  particulate  processes,  schematically  depicted  in  Figure  8-1,
             can  be  classified  in  two  groups  as  the  internal  and  external  processes.
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