Application of Lorenz-curve model to stratified water injection evaluation

To evaluate the effect of stratified water injection accurately during different development stages, a Lorenz-curve model was constructed upon a modified four-parameter Sarabia-Lorenz-curve model with water injectivity test data over years, and the relationship between accumulative perforated sandstone thickness and injected water volume of single wells was described by the model. Three evaluation indexes, dimensionless water injectivity intensity, vertical sweep efficiency and water-injection non-balanced degree, and their calculation were presented. Dimensionless water injectivity intensity is used to evaluate the distribution and balanced degree of water injectivity intensity, vertical sweep efficiency is the proportion of oil layers that produce oil, and water-injection non-balanced degree illustrates the overall water-injection balanced condition, then the model is solved by particle swarm optimization algorithm. Thirty-eight stratified water injection wells were evaluated in the Daqing Xingshugang oilfield. And the factors influencing the effect of water injection in single wells were studied considering segments construction, water allocation projects and reservoir physical properties. Finally, technological limits of stratified water injection were proposed under extreme high water-cut and recovery.