The number of maturing reservoirs is increasing and the need to manage water production is becoming ever more pressing. As has been observed repeatedly it requires at least the same amount of energy to produce a barrel of water as it does to recover a barrel of oil. Water Shutoff Chemical Systems, especially the new generation of Relative Permeability Modifiers (RPM), offer a potential solution to the problems of excessive water production.

Polymers, in the form of weak solutions, are intended to control water production, especially when oil bearing and water zones cannot be isolated. These products, identified as Relative Permeability Modifiers, are introduced to the reservoir, typically by bullhead injection or as fracture additives, with the intention of reducing the relative permeability to water, while avoiding as much as possible any reduction in the relative permeability to oil. The phenomenon that the placement seeks to induce is disproportionate permeability reduction (DPR) and will, where successfully applied, significantly reduce production costs.

The claims made for the various RPM products in the technical and sales literature suggest that their applicability is essentially universal; being largely independent of such key parameters as wettability, pore throat size, clay content, saturation profile and temperature. If this were the case, RPMs would be employed on a routine basis, rather than infrequently, accompanied with a healthy level of scepticism. In reality each RPM treatment should be case specific, affording the client the opportunity to test the various products on offer. It also provides the suppliers with the opportunity to optimise the formulation of their particular Relative Permeability Modifier through the offices of an independent laboratory.

This screening process is achieved through the deployment of representative and fully characterised core material, prepared to preserve factors such as wettability and clay fraction integrity. The testing on this material, undertaken at reservoir conditions of temperature and pressure, yields, on a "before and after" treatment basis, effective permeability and saturation data sets. From these values (Residual) Resistance Factors for the two fluid phases are produced, to quantify the effectiveness of the impedance of water flow, without significantly reducing oil production.

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