The most common method for preventing scale formation is by applying scale inhibitor squeeze treatments. In this process, a scale inhibitor solution is injected down a producer well and into the near wellbore formation. Generally, reservoir formations consist of a number of layers or zones of different permeability which may or may not be in pressure communication. When the zones are non-communicating within the reservoir, they are often at different pressures. When this is the case, then this can have a strong influence on the flow and placement of any injected fluids. Indeed, it can dominate the dynamics of the placement process and can also cause wellbore crossflow during the shut-in period following the squeeze treatment. In order to design a successful squeeze treatment, it is very important to know where the injected fluid goes; i.e. where the slug of scale inhibitor is placed in the formation. Therefore, our squeeze design and prediction models must incorporate these layer pressure effects along with the other models for the scale inhibitor transport and retention mechanisms.

In this paper, we develop the analytical expressions for calculating the flow partition in radial layered formations, where the layers are non-communicating. This is not in itself original and these equations are "well known". However, we have incorporated them into our multi-layer, two phase scale squeeze design software (SQUEEZE VI) to simulate situations where layers are at different pressures. We demonstrate that this has an important effect on the scale inhibitor slug placement in a heterogeneous system and it drives crossflow between layers at production or injection stages. Furthermore, we go on to show what the consequences of these placement effects on the squeeze lifetime are. We also present a wide sensitivity study of this effect showing how a number of ancillary parameters affect the squeeze lifetime e.g. the magnitude of the differential pressure between layers, the permeability contrast, the retention mechanism. Finally, we give some general field guidelines for various specific situations where formation zone pressures are not equal in terms of squeeze applications.

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