The effect of cross-bedding laminations on the efficiency of gas/oil multi-contact miscible displacements

Many oil fields produce from fluvial sands where cross bedding lamination is one of the most common type of small-scale heterogeneity. To our knowledge, there are no published studies on the effects of cross-bedding laminations on multi-contact miscible (MCM) displacement processes and how they might alter the development of miscibility during oil recovery by gas displacement. This work aims to remedy this deficiency. A particular objective was to quantify the accuracy of compositional simulation when modelling sub-miscible displacements in these systems. A series of well-characterized laboratory experiments in a two-dimensional, cross-bedded beadpack were carried out. A two-phase three-component (IPA/water/cyclohexene) liquid system, that exhibits an upper critical point at ambient conditions, was used as the fluid model. First contact miscible (FCM), immiscible and MCM displacement experiments were performed in the model laminated media. They were then simulated using a commercial compositional simulator with a single set of EOS parameters and without using history matching (the relative permeabilities as a function of IFT were obtained independently from displacement experiments in homogeneous packs). The produced oil and gas in the experiments were found not to be in compositional equilibrium. This was observed both in homogeneous and heterogeneous packs. As a result the oil recoveries and gas cut predicted by compositional simulation for MCM displacements in laminated media differed significantly from the experimental results, although an excellent match was obtained for the FCM and immiscible displacements. The use of alpha factors, derived from MCM experiments in a homogeneous pack gave a much-improved prediction of experimental results for both condensing and vaporizing gas drives in both homogeneous and cross-bedded porous media.