A New Polymer Application for North Sea Reservoirs

Field trials have demonstrated increased oil recovery by injection of colloidal dispersion gels (CDG). Characteristics of these trials include reservoirs characterized by high permeability heterogeneity and low injection water salinities. The enhanced oil recovery (EOR) has been attributed to improved waterflood sweep in the rather heterogeneous reservoirs where this method has been applied. This study presents an investigation of the applicability of CDG at higher salinity, and particularly sandstone North Sea oil reservoir applications. Earlier laboratory work and field trials involving CDG have involved relatively low reservoir temperatures and low injection water salinity (approximate to 5000 mu g/g). This study involves experiments at high temperature (85 degrees C) and salinity (approximate to 35 000 mu/g). When crosslinking is complete, the CDG solutions have slightly lower viscosities than the corresponding polymer solutions, and they also appear to be more stable at high temperatures. In preparation for a field pilot, several coreflood experiments have been conducted. Significant increase in oil recovery resulting from CDG injection has increased the interest for a field trial in a North Sea oil field. On average, 40% of the remaining oil after waterflooding was produced by CDG injection in linear core-floods, and a mechanism of microscopic diversion is proposed to explain these results. Our hypothesis is that CDG injection can contribute as an EOR method, giving both a microscopic diversion and a macroscopic sweep.