Abstract
Effective chemical deployment is an important factor in the efficient management of a producing field. Ideally, chemical addition should be as far upstream as possible in order 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 a producing 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 the rate of inhibitor return in the produced fluids. Moreover, since the chemical is immobilized in the near well-bore region, the immobilisation process must itself be controlled in order to govern the subsequent rate of chemical release.
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 treatments on the Magnus field, problems with post squeeze oil productivity have been identified. These have been attributed to changes in the near well-bore relative permeability arising from the influence of the injected fluids. The squeeze treatments, moreover, often have short return lifetimes. Both of these effects can arise as a result of injecting purely aqueous solutions into the near well-bore region. First, if injected water enters an oil bearing zone, the water can become trapped reducing permeability to oil. Secondly, the water-wet nature of the sandstone reservoir means that the penetration depth of the scale inhibitor solution is low (in addition, placement of the inhibitor is retarded by adsorption of the chemical too close to the well-bore).
A range of emulsion-based packages containing oilfield scale inhibitor squeeze chemicals have been developed. These have been evaluated as deployment systems designed to both overcome the problems described above and to reduce posttreatment well clean up times. It is envisaged that such an approach will have a significant impact on well productivity.
