A Novel Analytical Curve for Forecasting and Monitoring Gasflood Performance

ABSTRACT

With the increasing proportion of gas cap & artificial gas injection reservoirs, production performance monitoring and evaluation of gas-drive reservoir are becoming more and more important. However, there is no efficient method to forecast the production performance of gas-drive reservoir. In this paper, the analysis starts from the statistics of oil/gas relative permeability data of cores experiments. Based on fundamental principles of segregated flow and material balance, a new analytical curve of gasflood was developed to analyze the production performance. We applied the novel analytical curve to the production data from 23 gas-drive reservoirs at home and abroad and found a better power function relationship between dynamic reserves (N_d) and the slope (B) as foreseen by the analytical curve. It has been shown that the slope of the new curve represents dynamic reserves value; the smaller the slope value is, the more dynamic reserves are. Furthermore, by introducing the economic limit gas-oil ratio and control conditions which include initial and boundary conditions, a chart of dimensionless fractional flow of gas vs. recovery percent of OOIP is established to evaluate oilfield development rapidly and intuitively. Finally, many examples of application confirmed strongly that the new analytical curve used in gas-drive reservoirs is practical and effective, which broadens the scope of gas-drive oilfield research.

Keywords:

Dynamic reserves evaluating, gasflood characteristic curve, gas-drive reservoir, recoverable oil reserves, recoverable oil reserves, relative permeability theory.