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Traditional EOR approaches intend to minimize the injected CO 2 to reduce the high cost of the purchased gas, while this approach does not satisfy the sequestration objective to maximize the CO 2 stored in the reservoir by the end of the flooding period. In this paper, a new approach is presented where, a methodology is developed to optimize both EOR and sequestration processes.CO 2 injection into a North Sea chalk field is studied using a compositional reservoir simulator. We have investigated the effect of six parameters including injection scheme, injector and producer well type, well control mode, slug size and the WAG ratio on the coupled CO 2 EOR and sequestration process. Three different injection strategies using either pure CO 2 or a mixture of CO 2 and hydrocarbon gas including WAG, continuous CO 2 injection and soak alternating CO 2 injection have been investigated.Three well configurations are considered. It includes a vertical and two horizontal well options completed in the third and fifth layer of the reservoir. We have considered BHP and rate control as effective well control modes.Experimental design is used to perform an efficient sensitivity analysis on the mentioned parameters. Two objective functions have been defined, aimed at co-optimization of EOR and sequestration processes while respecting the economy of the process through minimizing recycled CO 2 .In this work a methodology / approach has been developed, which could be applied to other fields. In the case studied here, the results show that the water alternating gas injection scheme using a mixture of CO 2 and hydrocarbon gas to be the optimum case (EOR and sequestration process).

Light oil fields in Lake Maracaibo have been produced for several decades under depletion and waterflooding. Due to reservoir heterogeneity and complexity the traditional waterflooding oil recovery is not expected to exceed 30% of initial oil in place. Potential Improved Oil Recovery (IOR) methods capable to boost production from the mature fields are now under investigation and testing by the State Venezuelan Oil Company PDVSA. PDVSA's main IOR technology strategy is based on Integrated Field Laboratory (IFL) philosophy. IFL allows concentrating resources on modern technology evaluation, design IOR processes to solve regional problems, reduce the gap between laboratory screening and the field application phase for most promising recovery methods. The Water Alternating Gas (WAG) pilot at VLE–305 area of Lagocinco field is one of such IOR laboratory fields with the first immiscible gas injection pilot in Lake Maracaibo started in May 2000. The WAG pilot encompasses five production wells, one dual completion injection well and one observation well. The producing reservoir C-23 is a stratified sandstone with areal and lateral heterogeneities. Separator hydrocarbon gas is injected in the dual completion injection well in the WAG mode. Different sensitivity simulations were performed to design and optimize WAG injection strategy. The WAG pilot is now in its second stage of implementation and evaluation. Simulations are focused on tracer modeling and interpretation of production wells response. Since available injection volumes of hydrocarbon gas for large scale WAG injection projects are not available in the area, other IOR alternatives are being considered. The VLE pilot is again used as a laboratory for screening other potential IOR technologies. Nitrogen injection in WAG and continuum mode, and cyclic water injection are strategies under consideration. Nitrogen injection facilities will not be operational in the near future, therefore cyclic water injection is considered as an alternative for short-term production improvement under waterflooding. Cyclic injection can accelerate oil production and reduce water cut making production more economic and not requiring significant additional investments in the field. The preliminary evaluation of cyclic injection in the pilot area gives oil production improvement by 2–3%, and expansion of the process over a larger field area could give additional sweep improvement. WAG injection is estimated to improve oil recovery by 10–12% of STOOIP. WAG with nitrogen as injection gas may give 4–6% of STOOIP in increased oil recovery in comparison with waterflooding. Introduction PDVSA s light oilfields in Lake Maracaibo have been under exploitation for more than four decades. As these resources approach maturity, it has been realized that improving recovery will demand efficient IOR processes considering specific regional conditions. The Integrated Field Laboratory (IFL) philosophy is one of PDVSA s main technology strategies since 1998 designed to accomplish these goals [1]. Several IOR processes are currently under field evaluation, among those, alkali-surfactant-polymer (ASP) and hydrocarbon gas WAG injection. Nitrogen injection, steamflooding, pulse water injection and air injection in mature light and medium oilfields are other IOR methods under scrutiny. During the last decade WAG injection has become an important IOR technique around the world [2], and has been focus of interest in recent years in Venezuela [3].

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