Reserves Estimation Using Production Rate Decline Trend Analyses

Abstract

A constant production rate decline was simulated for reserves estimation, using flow regimes in oil and gas reservoirs. The problem of estimating oil reserves in place or cumulative recovery factor in a dynamic state calls for research. The problem has been so because no researcher has estimated accurate decline constant which can predict an accurate recovery factor or estimate accurate reserves initially in place. Flow regimes in reservoirs were established as a field of study using equations of fluid flow in porous media. The fluid flow equations were used to establish the decline trend, and the estimated production rate decline constant was also used to model the decline. The decline rate constants were subsequently used to build models to predict yearly production data for any given period. These were used to generate models for projecting oil and gas cumulative production and reserves in place. The results obtained were validated using actual yearly production field data from the original data source. The evaluation models were subsequently built using the predicted yearly data. The models were then used to estimate cumulative reserves recovery in any given period and reserves initially in place. The values obtained compared favourably with the respective tank values. The percentage accuracy for gas fields ranged from 99.86% and above, while the percentage accuracy for oil ranged from 98.64% to 99.98%. The models reduce the complexity and time used in reservoir simulation. They are very flexible and can be applied with high accuracy from the reservoir decline stage to abandonment. They are equally used for the establishment of production and for making economic decisions.