Located in Iranian part of Persian Gulf, Foroozan field was discovered in 1961 and is among the crucial offshore hydrocarbon assets of Iran. This field is shared with Marjan field of Saudi Arabia. Foroozan contained over 5 billion barrels of original oil in place according to the latest estimates. Approximately 772 million barrels of oil have been extracted from different reservoirs of the field as of May 2015. An integrated reservoir study project was granted by Iranian Offshore Oil Company (IOOC) as the client to Dana Geophysics Company (DGC) as the contractor aimed at preparing Master Development Plan (MDP) for future development of the field. AGR TRACS Company acts as international partner of DGC in this project.
Complexities and Challenges
Foroozan Field is commonly known for its particular complexities, and, construction of reliable static and dynamic models for such a complex field is indeed challenging. Due to connection to Marjan field of Saudi Arabia and the fact that more than 80 percent of the total hydrocarbon volume lies in the Arabian side, prediction of field behavior is intricate since there are no official data about the production/injection history of the Arabian sector. Foroozan field by itself consists of 7 reservoirs divided by structural/stratigraphic barriers into 3 different zones (F2, F3, and F8). Therefore in the present project, 21 separate static models were constructed and 13 dynamic models were simulated for field development purposes. More than 80 well logs were interpreted (of which 15 wells belong to Marjan field) and many faults were included in the structural model. In general, the data from Foroozan field are abundant but misleading. For instance, the well data (logs, tests, cores, and fluid samples) belonging to initial conditions of the field are very old and have rather low quality. Therefore, it was very difficult to determine original state of many reservoirs including accurate fluid contact levels. Special core analysis data were not available for carbonate reservoirs, which added to the uncertainties. Heterogeneities in rock properties are observed in the entire field. Shale layers are present in 2 clastic reservoirs while the rest 5 carbonate formations are characterized by fractures and facies changes. Also, fluid properties vary versus depth in the main reservoir of the field (Burgan A&B). Most reservoirs in the field produce under a combination of natural drive mechanisms (aquifer influx, gas cap and solution gas drive). The field has more than 40 years of production history from nearly 60 producing wells, mainly deviated and horizontal. Insufficient number of reliable pressure measurements in Foroozan intensifies the ambiguities caused by Marjan field’s effect.
Despite all challenges and complexities, DGC and its international partner (AGR-TRACS) have accomplished their tasks in accordance with the contractual scope of work. All reliable field data were incorporated in the models to honor the field complexities. Up to this stage of the work, Dana Geophysics Company has managed to acquire a very high level of client’s satisfaction in official assessments. In technical terms, sophisticated fine-grid static and dynamic models were prepared to capture the impact of reservoir heterogeneities. The efforts in the activities carried out before and during Static Modeling phase of project led to revision of hydrocarbon reserves via improving accuracy of volumetric calculations. In Dynamic Modeling phase, following meticulous basic reservoir engineering studies, high-resolution dynamic models were built for the target reservoirs. The outcome of history matching is more favorable compared to the studies carried out by the previous contractors.
The remaining activities of the project include integrated assessment of numerous development scenarios (including infill drilling, gas lift operation, water flooding, and immiscible gas injection). According to the new amendment to the main contract, a development plan shall be also prepared for recovery of gas from gas cap of Burgan Reservoir in F3 zone of the field with minimal negative effect on oil recovery. The final intent of the project is to select the optimal scenario(s) of field development from technical, operational, and economical points of view.
Reservoir Geoscience & Engineering (RGE) Manager