Page 42 - Reservoir Formation Damage

26 Reservoir Formation Damage

Montmorillonite, NaCl/KCl mixed

o.: Crystalline Swelling

o.oi

Formation Damage Zone
0.0010

o.ooi 0.01

NaCl(N)

Figure 2-16. Swelling chart for montmorillonite exposed to sodium and po-
tassium chloride brines (after Zhou et al., ©1996; reprinted by permission of
the Canadian Institute of Mining, Metallurgy and Petroleum).

properties of reservoir formations containing swelling clays and for rep-
resenting these properties in the prediction and simulation of reservoir
formation damage and in well-log interpretation.
The laboratory studies by many researchers, including the ones by
Zhou et al. (1997) and Mohan and Fogler (1997), have concluded that
clay swelling primarily occurs by crystalline and osmotic swelling mecha-
nisms. Civan and Knapp (1987) and Civan et al. (1989) recognized that
water transfer through clayey porous media occurs by diffusion and de-
veloped the phenomenological models for permeability and porosity re-
duction by swelling by absorption of water via the diffusion process. Ohen
and Civan (1990, 1993) and Chang and Civan (1997) incorporated these
models into the simulation of formation damage in petroleum reservoirs.
Ballard et al. (1994) experimentally studied the transfer of water and
ions through shales. They determined that diffusion controls the transfer
process and osmosis does not have any apparent effect when pressure is
not applied. Their findings reconfirms the mechanism proposed by Civan