Page 159 - Fundamentals of Enhanced Oil and Gas Recovery

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Thermal Recovery Processes

This would affect oil mobilization and steam distribution. The rock should be of
moderate strength with low content of clay. The oil with API gravity more than 10
and viscosity within the range of 1000 4000 cP is favorable. The permeability of the
reservoir should be more than 100 mD [13,19].

5.2.2.2 Reservoir Properties Changes With CSI
It is important to study the effects of EOR techniques on reservoir properties. For
instance, the induced heat in CSI technique leads to creating tension and changing
the structure of formations. This may lead to alteration in reservoir permeability and
mobility of water [24]. The change in pore volume and permeability is a function of
three parameters: (1) change in mean effective stress, (2) change in temperature, and
(3) shear stress alterations. As temperature increases, the sand structure is expanded.
The latter parameter was studied in Cold Lake field in Canada which revealed that as
steam is injected into the reservoir and the pores are pressurized, the effective stress
would be decreased [24].
In another study, for Clearwater formation in Canada, the expansion effect of
CSI process was transferred to the surface and different areas in the reservoir [25].
This is reflected by changing the level of the well which is mostly observed in
shallow reservoirs. Walters [26] also studied changing the pressure in the isolated
aquifer which has sealed the Clearwater formation as an outcome of poroelastic
effect. On the other hand, sand deformation and geomechanical changes would
lead to initial injectivity of formation, supplying the driving energy for production
[27]. The shear may be enlarged due to hot fluid injection in CSI [28].
Permeability changes as a function of shear dilation were reported by Wong et al.
[28].Yaleet al. [29] confirmed that the most sensible changes occur in relative
water permeability. On the other hand, as water is condensed by moving in the
frontofthe hotsteam,the pressure of the reservoir increases. This mechanism
leads to saving the driving energy of the reservoir and supplying it by dilation.
Gronseth [30] studied on streamline distribution during the fluid injection into
Clearwater formation and confirmed that as injection rate of the fluid is more
than its diffusion into matrix, the reservoir volume is justified by that of injected
fluid. Increase in volume would lead to pressure increase. As the production initi-
ates, the effective stress increases and pressure would reduce. This leads to contrac-
tion of the reservoir whereby a portion of increase in the initial steps of the
process is compensated [30]. The reservoir deformation is studied using various
techniques. The results of these studies are applied for optimization of production
parameters including injection rate, well length, and well spacing. Migration of
the steam and changes in the formation are recorded using tilt-meter and incli-
nometer [31]. The accuracy of tilt-meters is also greater one order of magnitude in
comparison to inclinometer [32].