On the significance of three-phase displacement mechanisms for the recovery efficiency in connection with planning and optimization of WAG/CGW-injection

The project consisted of two interdependent activites: a) experimental micromodel studies of mechanisms controlling three-phase transport in three-phase immiscible WAG injection; b) computer studies of three-phase transport and determination of three-phase relative permeabilities using a pore network simulator sequentially connected with a conventional, grid-based reservoir simulator; c) experimental determination of saturation trajectory using NMR and a model three-phase liquid mixture. The starting point of the project was an experimental micromodel study of pore-scale mechanisms controlling WAG injection. The experiments were aimed at investigations of interplay between pore-scale transport events, properties of reservoir fluids, and structure of the pore space. The micromodels were manufactured by applying techniques normally used in production of printed circuits by the microelectronic industry (lithography). The capillary tubings etched in silicon had two different depths. This particular feature of the micromodels ensured connectedness of wetting films considered as one of the most important mechanisms controlling three-phase transport. The GEUS micromodels with two etching depths were never before described in the open literature. The transport mechanisms observed during micromodel studies were stated as a set of rules and incorporated into a pore network simulator of three-phase transport. Among the mechanisms built into the network simulators are all six 'double' mechanisms which are unique for three-phase transport. Computer experiments aimed at the determination of three-phase relative permeabilities were performed using a hybrid reservoirsimulator consisting of a network simulator sequentially connected with a conventional, grid-based reservoir simulator. In particular, the relative permeabilities computed by the network simulator were transformed to the macroscale and used as ntut to a 1-D reservoir simulator. Relative permeability functions were determined in two cases. a) injection; b) water-alternating-gas injection. Only in the former case, the iterative procedure converged to a unique solution. For water-alternating-gas injection the iterative procedure collapsed because of the appearence of a discontinuous oil phase. A new experimental approach to determination of phase saturations in the case of three-phase transport involving Nonlinear Magnetic Resonanse (NMR) technique were developed and tested. This approach is based on the 'Chemical Shift Imaging' (CSI), which previously was implementet and tested for two-phase systems. The pilot study conducted in this project has shown that the same approach also is suitable for three-phase systems, for example in connection with experimental determination of three-phase relative permeabilities in water-alternating gas injection processes