The Development and Application of a Novel Scale Inhibitor for Deployment in Low Water Cut, Water Sensitive or Low Pressure Reservoirs

Abstract

Abstract Water-in-oil emulsions have been developed which have been shown to be a credible means of deploying scale inhibitors in a non-aqueous medium. Furthermore, the use of slowly degrading emulsion systems provides a means of trapping scale inhibitor within porous media and allowing subsequent controlled release of the chemical. This has been demonstrated using sandpack and coreflood experiments where the lifetime of the inhibitor, as measured by pore volumes of brine eluted to a given inhibitor concentration, has been extended by up to (and possibly beyond) four times compared with the base case non-emulsified product. No permeability damage has been observed for the emulsion systems. The use of emulsion droplets to provide chemical reservoirs within the formation also considerably reduces the wastage of non-retained chemical observed with conventional squeeze treatments. The non-aqueous nature of the emulsion system potentially allows ingress of the scale inhibitor into parts of the reservoir normally denied access to an aqueous-based formulation and so can improve contact between the scale inhibitor and the reservoir fluids on production. Furthermore, the whole treatment can be non-aqueous allowing oil continuity to be maintained during the treatment affording rapid well clean up post treatment. Introduction The control of oilfield chemical deployment is an important factor in the effective management of a producing oil field. Ideally, chemical addition should be as far upstream as possible, to allow effective control of processes such as scale formation and corrosion. One approach to effecting control early in the production is through so-called squeeze treatments, during which inhibitor chemicals are squeezed under pressure into the near well-bore region of the producer well. Upon lifting the well, the inhibitor will be returned with the produced fluids. Clearly, the effectiveness of oilfield chemical squeeze treatments relies on the ability to control inhibitor return rates in the produced fluids. This, in turn, necessitates control over release rates of the active constituent as a result of immobilization mechanisms in the near well-bore region of the reservoir. Off-shore, the scale inhibitor is normally squeezed as an aqueous solution in sea water, the latter selected because of its obvious availability and also to reduce formation damage which may occur with lower ionic strength solutions. However, the effectiveness of this approach is not totally satisfactory for all reservoirs. For example, during scale inhibitor squeeze treatment on the Magnus field, problems of poor oil productivity have been identified and suggested as resulting from adverse relative permeability post treatment effects. The squeeze treatments have also been associated with short return lifetimes. These features have been interpreted in terms of near well-bore wettability and saturation effects1. The injected aqueous brine inhibitor solution will tend to be localized in the immediate vicinity of the well-bore, since its hydrophilic/aqueous nature will restrict ingress into more remote pore spaces in the reservoir. This also has the effect of reducing the return time as well as preventing oil flow through what will now have become a predominantly water saturated region.