Full-Scale Implementation of Conformance Control by Nanospheres in Large Sandstone Oil Field

Abstract

The polymeric nanospheres (NS) is the conformance control agent significantly improving oil recovery through redistribution of water flows deep in reservoir. The operator took a decision to pilot nanospheres technology in their large sandstone Changqing oil field in China after the experimental program has been conducted proved its potential. The nanospheres pilot has been executed in the oil field, resulting in substantial oil recovery improvement and water-cut reversal. Full-field implementation began. Extensive experimental study was conducted to analyze the effect of nanospheres on oil displacement in the Changqing field. The focus of the program was on the impact of reservoir heterogeneity and effect of nanospheres on oil displacement at different permeability contrast. Coreflood experiments were conducted with dual-core set-up, where sand cores were mimicking permeability contrast of the target reservoir. The program resulted in selecting optimum injection concentration and volumes for the pilot. Nanospheres solution has been injected in the oil field, and dedicated surveillance program was executed. Water flooding is effective in heterogeneous reservoirs when the average permeability contrast is below 20. When the contrast is higher e.g. as in target reservoir with permeability ranging from 7 to 2900 mD, water flooding is less efficient, especially in low-permeability zones. Nanospheres can mitigate the negative impact of high permeability contrast by diverting flow into previously unswept reservoir layers. This improves oil recovery, chiefly from low-permeability areas. Coreflood experiments proved the feasibility – incremental oil recovery was observed at 34%. Optimum pilot injection strategy has been designed. The effectiveness of nanospheres with high permeability variation has been demonstrated in the field tests. The field results have confirmed the positive impact of nanospheres on water flooding. In one of the tests, an average oil production rate increased from 5.1 to 10.8 t/d while water-cut was reduced from 94% to 83%. Analysis confirmed that nanospheres provided efficient conformance control deep in reservoir and did not result in loss of injectivity. Chemical utilization factor achieved is more than 100 tons of oil produced per ton of chemicals injected. Treatment costs per pattern were significantly lower compared to other IOR/EOR techniques. The operator has decided to implement nanospheres for conformance control in all field. Dedicated experimental program to select and, more important, optimize conformance control in heterogeneous reservoirs will be presented. Further, the paper will describe the field trial conducted. Both experimental and field data demonstrate the relationship between the oil displacement efficiency and injection conditions for different permeability contrasts. Results of field implementation will be presented. The technology effectiveness has been confirmed and full-field implementation has started.