After a field has been put on production, it is very pertinent that the saturation and contact changes within the reservoir be monitored. This is difficult on a frequent basis considering the cost implications of the processes involved. Usually, the main two methods employed are the use of PNC/PNS (C/O and Sigma) logs, and the 4D-Seismic. The latter, though the more recent, has been gathering popularity especially in the Gulf of Mexico and North Sea, because of its relatively easier and seemingly more dependent concepts. However, the PNC/PNS logs remain the major method used for contact monitoring. Data generated from post-production saturation monitoring campaigns are used for proper reservoir management, generation of short-term oil gains, and reducing risks in planned new wells. Beyond these basic uses, the operation can also help to properly analyse the status of the wells, as well as redefine uncertainty level and reveal new information concerning the wells and reservoir conditions. In this work, a Niger Delta field that has been producing for about 20 years was analysed after the first post-production C/O log campaign was conducted. The logs were interpreted and the results were analysed. Apart from the observations common to the results of such operations, some other insights were revealed by this campaign, particularly in one of the wells producing from the field. The well was completed across two reservoirs, with the shallower completion put behind sleeves, while the deeper was put on production. A major boundary fault seals the reservoirs vertically, ensuring that no external communication was possible. From the production data corresponding to the producing deeper reservoir, it was expected that the logs would confirm that the reservoir was about to quit considering the fact that it had already exceeded its EUR (high). However, after the logs were double-checked for errors and analysed, it was discovered that the shallower reservoir, which has never been put on production, has been partially flushed, and the deeper reservoir, which was expected to be watered out, still had some reasonable amount of oil in place. With these striking discoveries, a full field analysis was done, the details of which was discussed in this paper. At the end of this work, some recommendations were made. This underlines the importance of frequent reservoir monitoring operations. This will help unravel and understand anomalous developments that could be occurring in the field/wells without the knowledge of the operators.

Gas condensate reservoirs usually exhibit reduced well productivity because of condensate dropout that occurs below the dew point pressure. Gas recycling has become one of the most favorable methods of improving recovery of condensed liquid. However, understanding the influence of different injection and reservoir parameters on productivity is of great importance when planning a gas recycling scheme. Traditional methods of sensitization during reservoir simulation for gas condensate fields creates the challenge of quick identification of the most critical properties for sensitization, and hence delay of overall simulation project delivery. This work aims at identifying the key variables that influence productivity of a gas condensate reservoir under a gas recycling scheme using the design of experiment approach (DOE). DOE represents a more effective method for computer-enhanced, systematic approach to experimentation, considering all the factors simultaneously. Identification of these parameters will help simulators achieve best optimization targets and also save time and resources during dynamic simulation projects. Furthermore, it will be shown that experimental design can be used to fit responses (condensate/gas production) to mathematical models that will be able to predict outputs for any given combination of variables.