Fragmentation and fission of giant molecular clouds occasionally results in a pair of gravitationally bound star clusters that orbit their mutual centre of mass for some time, under the influence of internal and external perturbations. We investigate the evolution of binary star clusters with different orbital configurations, with a particular focus on the Galactic tidal field. We carry out N -body simulations of evolving binary star clusters and compare our results with estimates from our semi-analytic model. The latter accounts for mass loss due to stellar evolution and two-body relaxation, and for evolution due to external tides. Using the semi-analytic model we predict the longterm evolution for a wide range of initial conditions. It accurately describes the global evolution of such systems, until the moment when a cluster merger is imminent. Nbody simulations are used to test our semi-analytic model and also to study additional features of evolving binary clusters, such as the kinematics of stars, global cluster rotation, evaporation rates, and the cluster merger process. We find that the initial orientation of a binary star cluster with respect to the Galactic field, and also the initial orbital phase, are crucial for its fate. Depending on these properties, the binaries may experience orbital reversal, spiral-in, or vertical oscillation about the Galactic plane before they actually merge at t ≈ 100 Myr, and produce rotating star clusters with slightly higher evaporation rates. The merger process of a binary cluster induces an outburst that ejects ∼ 10% of the stellar members into the Galactic field.

The common method to prevent condensate from dropping out in gas-condensate reservoirs that are produced by pressure depletion is gas cycling: the produced by pressure depletion is gas cycling: the reinjection of produced dry gas. However, dry gas is expensive and is not always available. An alternative could be nitrogen, which is available everywhere, relatively cheap and has favourable injection characteristics (safe, non-corrosive, environment-friendly). The problem with nitrogen injection, however, is that it may lead to significant in-situ condensate drop-out due to the mixing of nitrogen and gas-condensate in the reservoir. The objective of the study reported in the paper is to investigate whether nitrogen injection can be applied as an alternative for gas cycling, with emphasis on the condensate drop-out problem. The investigation comprised three phases:Formulation of a rich gas-condensate, consisting of methane, n-butane, n-tetradecane and nitrogen, using an interactive PVT simulator.Calculation of liquid drop-out for both dry gas and nitrogen injection as a result of mixing, by varying injection gas concentration.Evaluation of displacement efficiency by using a compositional one-dimensional simulator for various Peclet numbers. The chosen gas has common field characteristics (Gas Liquid Ratio = 2300 V/V, API gravity = 58.6) and is rich (shown by the maximum liquid drop-out of 30%). Liquid drop-out as a result of mixing is much higher for nitrogen (max. 25 %) than for dry gas process (max. 2%). Displacement calculations show that, at low Peclet numbers, nitrogen injection results in much poorer displacement efficiencies than dry gas injection. However, the difference decreases significantly at increasing Peclet numbers. The main conclusion of the paper is that, under field conditions, nitrogen injection could be a viable alternative to dry gas cycling. Nitrogen injection may find application in the production of condensate reservoirs in areas with a well developed gas market where dry gas is not available for injection. The main contribution of the paper is that it highlights and provides information on a relatively new process for the exploitation of condensate fields. P. 281

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Based on previous studies, nitrogen injection could recover oil up to 45-90% of initial reserves. Although this method has a very good ability to produce oil, sometimes the operation pressure is higher than leak off formation pressure. In this study, operation pressure used a low pressure to solve this problem under immiscible process. Objective of this study is to determine the effect of injection pressure and displacement rate on oil recovery performance of continuous one dimensional nitrogen gas injection with a slim tube apparatus. The effect of nitrogen gas-oil contact on the gas composition was investigated using Gas Chromatograph Mass Spectrometer apparatus. In the experiments, nitrogen gas was injected into an oil sample of 38.5 o API gravity at various rates: 20 cc/hr, 30 cc/hr and 36.66/hr under 1500 psi pressure, and then at 20 cc/hr undr 2500 psi pressure. The results showed that an increase in injection rate increased oil recovery factor. The recovery factor lies between 40-54% of original oil in place. Gas analysis before injection and at the injection outlet showed a change of composition. when oil was contacted by nitrogen, indicating that some molecular mass transfer had taken place.

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