A New Polymer Application for North Sea Reservoirs

Abstract 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. The present study presents an investigation of the applicability of colloidal dispersion gels at higher salinity, and in particular directed at North Sea oil reservoir applications. Earlier laboratory work and field trials involving CDG have involved rather low reservoir temperatures and low injection water salinity (~ 5000 μg/g). This study involves experiments at high temperature (85 0C) and salinity (~35 000 μg/g). When cross-linking 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 core flood experiments have been made. Significant increase in oil recovery due to CDG injection has increased the interest for a field trial in a North Sea oil field. On average, 40 percent 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 can contribute as an EOR method giving both a microscopic diversion and a macroscopic sweep.