This field case present a risk analysis on production, plateau duration and ultimate recovery factor performed on a fractured carbonate reservoir. The field has been under early production for more than 48 years, with less than 2% cumulative produced Oil. Historical data measurements on Well Production Oil Rate, Well Gas Oil Ratio (GOR), Well Static Pressure and Well Bottom Hole Flowing Pressure have been utilized in order to constrain uncertain parameters during historical period and then propagate into prediction. The risk analysis takes into account reservoir uncertainties and geological uncertainties on Discrete Fracture Network (DFN). Several surface/controllable parameters have been considered for the Risk analysis evaluation on Plateau Length hypothesis and Recovery Factor. The risk analysis accounts for two main recovery mechanisms: gas injection from the crest for Gas gravity drainage and periphery down dip water injection with imbibition. Several scenarios of DFN's and 43 uncertain reservoir parameters with probability distribution were considered. Experimental Design and Response Surface Methodology have been extensively applied to minimize the number of Reservoir simulation runs of the study. Plackett and Burman Experimental Design has been used for the Screening Phase. During the screening phase, it has been revealed that 7 uncertain parameters account for more than 80 % of the total variation of Cumulative Oil Production. A detailed Latin Hypercube has been performed with 3 discrete fracture network, controllable uncertain parameters and these 7 most relevant parameters. This risk analysis identified the best cases of each phase of the development, P10 and P90, and the major uncertainties impacting the field development plan. Mitigation, acquisition and monitoring plan have been defined accordingly to reduce the major impacting uncertainties.

Depositional setting, diagenetic processes, structural history, hydrocarbon charging and entrapment in multi petroleum systems carbonate reservoirs is a complex process, resulting in hydrocarbon accumulation in multiple reservoirs not only in a conventional structural trap but also in unconventional traps (stratigaphic traps, combined structural and stratigraphic, monoclonal, etc). Such traps are difficult to be located and evaluated and can easily be over looked and missed even in mature oil producing fields or provinces. This paper discusses the case history of oil discovery in Upper Jurassic section in a producing ADMA OPCO offshore oil field. The appraisal of the discovered hydrocarbon is a challenging task and innovative approach was required to appraise and delineate this discovery utilizing planned and approved new wells for other reservoirs.The collected data has improved the understanding of the reservoir properties and reduced uncertainties associated with the size, shape, fluid type and productivity of this discovery.