Abstract: The traditional analysis method of the reservoir natural drive index can only be used in the judgment of reservoir natural energy scale prior to waterflooding. The theoretical study shows that the correlation curve of Δp and Npr assumes some kind of power relations, the bi-logarithmic curve assumes linear pattern; on the bi-logarithmic plot, the more dense the iso-time interval spots are, the more timely the energy feeding of bottom and edge water to the formation is, and the quicker the water influx rate is. The natural drive index can also be suitable for the analysis and evaluation of reservoir after waterflooding, and the variation of the curves is unchangeable, namely, the more tight the iso-time interval points are, the better the water flooding effectiveness. Also, the correlation of Δp and Npr is properly applied to prediction of oil recovery factor and hence to determination of rational accumulative and stage injection to production ratios integrated with waterflood characteristic curves of the reservoir. Finally, the case study shows good prediction of them.

Key words: natural drive index, natural energy, water injection, waterflooding, oil recovery, injection to production ratio, prediction, forecast