Page 29 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

12 Bin Yuan and David A. Wood

shrinkage and connectivity loss caused by the decline of reservoir pressure
(Davudov et al., 2017; Dong et al., 2010). In addition, in shale reservoirs,
high capillary pressure tends to result in water trapping and significant
damage to the relative permeability of oil and gas (Zitha et al., 2013).
Formation damage issues in shale reservoirs require that field operators
pay close attention to the strategies capable of achieving sustainable
production. Formation damage effects can be mitigated by optimizing
fracturing design and operations, improving the choice of fracturing fluids
and proppants, optimizing the online production strategy and conditions,
and/or introducing chemical agents to remediate the damage caused to
near-fracture and near-wellbore regions.

1.9 COAL-BED METHANE (CBM)

CBM is a natural gas extracted from coal formations. Dewatering is
typically required to initiate CBM extraction, through which natural gas
is gradually liberated from the coal matrix and fractures with the
depletion of reservoir pressure (Bassett, 2009). However, various types of
formation damage can be induced during the development of CBM by
the physical-chemical-biological-thermal incompatibilities among clay
particles, fluids, and coals, including fines migration, phase trapping, wet-
tability alteration, and biological activities, and mechanical damage of the
coal formations can also occur (Huang et al., 2015). During drilling and
fracture stimulation of CBM wells, formation damage can be generated in
the form of water blockage, clay swelling, and solid particles invasion,
together with the leak-off of drilling and fracturing fluids (Lu et al.,
2015). During the CBM-production phase, the main formation damage
is the matrix shrinkage or swelling caused by gas desorption/adsorption,
leading to the change of cleat aperture (Harpalani and Chen, 1995). Clay
minerals in micropores can hydrate once in contact with water, leading to
the blockage of flow paths (Zhang et al., 2016). In addition, the fluctua-
tions or increase of production rates can lead to problems of fines migra-
tion and subsequent blockage of flow paths in coal seams (Han et al.,
2015; Paul et al., 2014). During enhanced CBM recovery, the injection
of CO 2 N 2 mixtures has been explored to diminish swelling-related for-
mation damage caused by CO 2 (Vishal et al., 2015).