Estimation of Developed Reserves in Gas Lifted wells.

Abstract

Reliable estimates of petroleum reserves are

invaluable in reservoir management decisions and

economic evaluation. Classical decline curve

analysis techniques have been routinely used and

are generally accepted in the industry to reliably

estimate developed reserves up to a

predetermined economic limit qec in oil wells.

However Decline curve analysis techniques are

based on the assumption that past production

trends and their controlling factors will continue in

the future and therefore can be extrapolated for

predictions.

During gas lifting, production trends could be

distorted hence there is need to modify the

classical decline curve analysis equation.

In this study, the principle of superposition has

been applied to the entire duration of production

(t) of wells producing under gas lift This resulted

in the so called Double Semi log equation for well

decline analysis. Model validation with two fields

in the Niger Delta area show excellent results and

the economic advantage of gas lifting. The Models

showed excellent correlation coefficients with

available field data.

It is concluded that gas lift could increase the

reserves in some wells. Furthermore the Double

Semi log technique provides a better and more

reliable theoretical foundation, easier and more

reliable technique for decline analysis in gas lifted

wells.