Reservoir Performance Analysis of a Tight Fractured Carbonate Reservoir in Bahrain Field, Key to Future Development Opportunities

Aljawder, Abdulla (Tatweer petroleum) | Barni, Sajeda (Tatweer petroleum) | Tawash, Feras (Tatweer petroleum) | Aljanahi, Ahmed (Tatweer petroleum)

OnePetro 

Abstract

Ahmadi Reservoir is one of the Reservoirs producing in the Bahrain Field. It has been producing for more than eighty years. Ahmadi is a tight carbonate Reservoir that belongs to the Wasia Cretaceous group. It consists of two main limestone units which are AA and AB. Like most Carbonates in the Middle East, Ahmadi production is dominated by secondary permeability which means that the reservoir has a dual exponential type Curve. Dual exponential in Ahmadi means a high flush initial production period and then a longer period of stabilized production.

Because of this behaviour, using conventional methods to monitor reservoir performance could be misleading. Hence, a new parameter was created to make sure that reservoir performance monitoring accounts for production in a more representive way. This parameter was called Normalized Production Index.

Normalized Production Index has been used to analyse reservoir performance in Ahmadi Reservoir as it accounts for both the flush rate and the stabilized production rate of wells. This parameter helps monitor and observe reservoir performance as it effectively identifies low and high productive areas, and hence leads to better decisions during reservoir development planning.

In this study, a Normalized Production Index of more than 246 wells was considered. These wells vary in area, dip direction, trajectory, and Horizontal length. The objective was to determine the most effective way of these to maximise production in Ahmadi.

Based on the analysis done using Normalized Production Index, it was found that the average oil production for horizontal wells is more than double that of a vertical/directional well. It was also found that wells oriented in an up-dip direction of the structure are performing better than wells oriented in a down-dip direction of the structure in some areas. These conclusions were considered in managing the reservoir. Some actions were taken based on these conclusions and resulted in positive performance, which verified the effectiveness of the Normalized Production Index.