The presence of fractured reservoir zones presents significant challenges for the modelling and optimisation of squeeze treatments. Fluid flow in fractured systems is relatively well understood, and the effect of fractures on the placement of chemical can be modelled. However, to model the quantitative effects of fractures on scale inhibitor returning from squeezed zones, it is necessary to also model the retention and release of inhibitor from a fractured zone. This involves modelling the flow of inhibitor between fracture and matrix, while modelling the retention and release of inhibitor by the rock matrix.
Using conventional near wellbore squeeze simulators (Place iT v5), artificially induced fractures have been simulated using a near wellbore dual permeability approach more commonly used to model wells with a skin factor. The method has been extended from single fractured intervals to dual intervals/zones and the competitive placement of chemical between the fractured zones has been modeled.
The work shows how the predicted chemical placement and the resulting inhibitor return lifetimes can be simulated in fractured wells and how the sizing of the overflush can be more significant than simply accounting for the fracture volume. The mathematical concepts and assumptions used in the model development are presented.
Naturally fractured reservoirs present a special challenge both from the practical scale-management and theoretical (predictive modelling) points of view. Whereas useful conclusions can be drawn using simplified models, more physically meaningful modeling of fracture/matrix interaction is required for the more challenging wells. Rock matrix – fracture interaction can be accounted for using analytical methods including important processes such as molecular diffusion i.e. to account for rock / chemical / fluid imbibition and diffusion. The development of modeling capabilities for such systems is outlined and results from simulations compared with those conducted using more conventional though less rigorous approaches.