Abstract
During fluid production in carbonate reservoir rock under high Pressure and Temperature conditions, the production-enhanced shear-heating of a creeping fault can lead to a thermal run-away. The reactivation of the fault is then accompanied with a large increase of permeability (by orders of magnitude) due to the dissolution of the rock. As a detrimental consequence for the industry, pressure equilibrates between the two compartments of the reservoir delimited by an initially sealing fault. To model such behavior, we present a three-scale framework implementing a THMC fault reactivation model. The framework links the three different scales of the problem: (a) the poro-elastic reservoir (km) scale, where faults are treated as frictional interfaces with the equivalent friction law being determined from the meso-scale; (b) the thermo-poro-chemo-visco-elasto-plastic fault at the meso-scale (m), encompassing all the physics at hand; and (c) its chemo-mechanically altered pore structure at the micro-scale (μm), where meso-scale properties (like permeability) are upscaled. In the present approach, the multiscaling approach allows us to replace the common use of empirical laws to the profit of upscaled physical laws. The framework is used to simulate the fault valve behavior appearing during induced reactivation coming from the production scenario next to a sealing fault.
Highlights
Faults are critical features of many reservoirs because their potential lower permeability may induce reservoir compartmentalization
With more than half of global gas reserves held in carbonate reservoirs, chemical fault reactivation represents a major case study that will only become more relevant as reservoir operations are getting increasingly deeper
The chemical shear zone model incorporated in our multiscale framework showcases the possibility of fluid invasion across a reactivated fault that could happen during production of deep carbonate rocks
Summary
Faults are critical features of many reservoirs because their potential lower permeability may induce reservoir compartmentalization. A sealing fault becomes a flow path, which can provoke leakage of the reservoir into the adjacent compartment (Wiprut, 2000) or fluid invasion leading to early water breakthrough (Dos Santos, 2014) Both cases are extremely detrimental and can render a reservoir completely non-operable at engineering time-scales, irrespective of the type of application. We illustrate this general behavior with a case study on carbonate rocks, as a typical example of deep reservoirs in Brazil Fault reactivation in this context can provoke an increase of permeability high enough to break the seal integrity of a reservoir. The same model can lead to one-off events much more in environments with much lower forces involved (Poulet et al, 2014b) Considering this type of reactivation, a substantial permeability increase can get generated during fault slip by chemical dissolution
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