| dc.description.abstract | Primary and Secondary Recovery techniques together are able to recover only about 35-50% of oil from the reservoir. This leaves a significant amount of oil remaining in the reservoir. The residual oil left after the water flooding is either from water swept part or area by-passed by the water flooding. The by-passed residual oil has a high interfacial tension with the water. One way of recovering this capillary trapped oil is by flooding the reservoir with chemicals (surfactant, alkali-surfactant (AS), surfactant-polymer (SP), or alkaline-surfactant-polymer (ASP)).
The Norne field which is the base case for this study having approximately current recovery factor of 60% with water flooding is one of the best subsea fields in the world. The oil production has peaked in 2001 and is now declining. The pockets of residual oil saturation are still trapped in the reservoir especially in the Ile and Tofte formations. The water flooding alone cannot recover capillary trapped oil pockets efficiently, thus requires enhanced oil recovery techniques. The EOR screening criteria suggested by Taber et al. (1) was applied to Norne E-segment in order to come up with the right EOR method that would reduce residual oil saturation to the minimum. Five EOR scenarios such as surfactant flooding, alkaline-surfactant flooding, polymer flooding, surfactant-polymer flooding, and alkaline-surfactant-polymer flooding were simulated for the Norne E-segment.
The main objective of this study was to do a comparative simulation study to evaluate the effectiveness of these chemical methods (scenarios) compared to a conventional waterflooding in terms of incremental oil production. After this, one of the flooding methods was to be concluded for the Norne E-segment based on incremental net present value (NPV).
The injection well F-3H and producer E-2H were evaluated as the most promising wells for above scenarios. A series of cases were run to ascertain the injection length, appropriate surfactant quantity and concentration. Five scenarios with different combination and concentrations of chemicals (alkali, surfactant and polymer) were run using Eclipse 100. In addition, calculation of incremental NPV based on incremental oil production for all scenarios; single parameter sensitivity analysis (Spider plot) for low case, base case, and high case at different oil prices, chemicals prices, and discount rate were also performed. It was found that change in oil price has substantial effect on NPV compared to other parameters while surfactant price is the least sensitive parameter i.e very low affect on NPV for high/low case.
From simulation results and economics analysis, ASP flooding was found to be better than other chemical methods (scenarios) in terms of incremental NPV for the Norne E-segment. However, the 1.40 % incremental recovery factor by ASP flooding seems not so high and will have an incremental net present value of +123.53 million USD. It is noted that the additional costs regarding operations and installations were not included in the economics calculation. The recovery factor as well as NPV can be optimized with accurate chemical designing in laboratory and modeling of compositional model in Chemical Compositional Simulator. It is recommended that right alkali, surfactant and polymer structure that would be compatible with fluid and rock properties of Norne field E-segment, be developed in the laboratory. It is also important that up-scaling the appropriate laboratory identified chemicals to a field-scale usage be done correctly. The timing of ASP injection into Norne E-segment is also recommended to be early in the life of the field because injection of ASP at a later time might not lead to best possible oil recovery. | nb_NO |
