In the context of global warming, CO2 capture is one of the explored solutions for greenhouse gas emission mitigation. Its injection in oil fields is one of the EOR schemes adapted to the Middle East carbonate reservoirs. A very high ultimate oil recovery is expected with such a process. A proper design to develop full field EOR CO2 is yet to be found and may be fulfilled through the implementation of one or several pilots. This study of EOR CO2 pilot implementation required a geosciences, reservoir and surface integrated work in order to place it in some robust and promising locations. A static and dynamic synthesis was performed to understand and better capture the structural context of the field and its level of production maturity. The major risks were taken into account for the selection thanks to a complete synthesis of the available data from the core scale to the surface facilities. An adequate methodology was developed to narrow down the possible locations from the field extent (several hundred km2) to only a few squared kilometers of interest. The field was divided in 6 km2 squares (called "locators") for which a two step selection process was applied. In the first step, the geological typology of the reservoirs and their dynamic statuses at the locator level were defined. Then the risks associated to CO2 injection were assessed. At the end of this step, the selected locators were the less risky ones, representating each geological typology. In the second step, the locators were studied more thoroughly with the evaluation of the level of knowledge illustrating the amount and quality of data available; a geological variability study on permeability was also performed on each area. Finally the surface constraints were incorporated to prevent any incompatibilities with the current or future facilities. This second step provided another sub-selection of locators amongst the ones kept at the end of step 1. Overall, the methodology applied allowed to screen the whole field and its reservoirs, and to identify some promising pilot locations representative of the geology, for a given dynamic status, combining high level of knowledge and low risks related to CO2 injection.

OBAGI is an onshore oil field located on OML58, 85 km north-west of Port-Harcourt, Nigeria. It is composed of 26 stacked reservoir levels with an estimated total OOIP of 1.2 Gbbls. It was discovered in 1964 and has been producing since 1966 through 123 wells and 257 completions. 21 layers have been developed. With a global recovery to-date of 50% and an average producing water-cut of 75%, OBAGI can be considered as a mature oil field. Current activities are driven by two main objectives:to sustain short term production level, andto identify potential remaining resources for additional developments Appropriate monitoring and global static/dynamic review are the key factors to achieve these objectives. The short term objective is to maintain production by optimizing the injection capacity. Difficulties to model reservoir performance have resulted in implementation of an intensive monitoring program. This is to limit water production and to maintain/increase water injection capacity. For the long term, it is believed that potential resources not accessible with current wells could effectively double the remaining reserves. For this purpose, complementary developments have to be proposed to target clearly identified attic oil or by-passed regions. A pragmatic approach was adopted based on 2G model review, material balance study and fluid contact updates (with regular saturation survey campaigns) to identify additional reserves potential. The progress of the study is presented for one of the layers of the field. Introduction OBAGI is an oil field located onshore Nigeria (Figure 1) and discovered in 1964. The OOIP has been estimated to 1.2 Gbbls, split in 26 stacked reservoir levels (Figure 2). Oil production started in 1966 and the maximum of 70,000 bopd was reached in 1983. Both oil and gas productions are currently valorised thanks to Obite Gas Plant start-up in 1999 (also located on OML58). Therefore, although Obagi is mainly an oil field, 5 gas caps are also considered for future production. All produced water is reinjected into the field to minimise environmental impact and support the reservoir pressure.

Integrated Asset Modeling (IAM) has now become widely used for oil and gas production optimization. It has the advantage of integrating constraints from reservoir, well inflow and outflow, pipelines, compressors and processing facilities in one integrated simulation model. IAM is also a powerful tool for decision making and planning, it allows a quick and comprehensive assessment of geosciences uncertainties combined with different development strategies. This paper describes how IAM is a key for OML58 gas fields optimization and forecast. It has proven its ability to identify potential benefits of upgrading surface facilities to ensure sustainable gas supply to the Nigeria Liquefied Natural Gas Plant (NLNG) and the domestic market. The OML58 upgrade project comprised the increase of gas compression capacity and the construction of two major pipelines: The Obite-Ubeta-Rumji (OUR) pipeline and the Northern Option Pipeline (NOPL). The commissioning and start-up was completed in August 2016 and the first domestic gas supply to the Alaoji Power Plant was achieved in October 2016, marking an important milestone for Total E&P Nigeria Limited (TEPNG) and its joint venture partner NNPC. The paper also highlights the importance of OML58 IAM in addressing both short and long term challenges. The model is used to maximize condensate production using an algorithm that automatically prioritizes high condensate wells in forecast stage. It also guides the planning and the optimization of well intervention for both data acquisition and production enhancement. In long term perspective, the paper illustrates the flexibility to perform the screening of different infill/workover drilling options, the integration of undeveloped gas fields and the preliminary assessment of gas explorationprospects.