A State-of-Art Approach to Apply Decline Curve Analysis on an Iranian Carbonate Reservoir

A State-of-Art Approach to Apply Decline Curve Analysis on an Iranian Carbonate Reservoir

An estimate of future performance has been made for one of Iranian carbonate fields using decline curve analysis. Certain conditions that must prevail for being able to analyze production decline curves, including the production and reservoir conditions being stable over the analysis period were very limiting in this field and considerable rate variations due to different well events and changes in the number of producing wells were seen in the field. Therefore, since the production trend was not smooth in the reservoir under study, the plot of production rate per well versus time was constructed and used to investigate the declining trend of production rate. This approach was able to demonstrate the declining trend of rate per well in the reservoir under study in the field. Sensitivity analyses on the minimum economic oil rate have been performed for the decline curve analysis. Furthermore, different recovery factors were applied in the analyses using type curves. Calculated values of Skin factor and permeabilities were consistent with those calculated in well testing when validated. Since in type curve analysis, the calculation of ultimate recoverable oil supposes the reservoir is being drained completely while in the conventional analysis, an economical limit rate is taken for the calculation which means the reservoir is drained only up to a certain rate and date, the calculated ultimate recoverable oil amount in type curve matching method is comparable and consistent with the final cumulative oil production values calculated in the conventional analyses. The original oil in place amounts concluded in the decline curve analysis have been compared with those of material balance and given the fact that in the decline curve analysis, average production rate per well has been taken into account, it turned out that the two methods were in agreement.