Integrated phase behaviour modelling of fluids in reservoir-surface processes using equation of state

摘要

Compositional reservoir simulation is widely used in the design of improved oil recovery (IOR) schemes, in particular for gas injectionand gas cycling studies. An integrated modelling approach, using a single equation of state (EOS), to describe fluid phase behaviour and properties within the reservoir, flow lines and process facilities is an attractive option for reservoir management. Low computational times for flash calculations is an improtant element in compositional reservoir simulation. Grouping of fluid components reduces the computational time, but the approach is not suitable for the integrated modelling, where detailed compositional information on produced reservoir fluids may be required in the design and operation of fluid processes at the surface. If binary interaction parameters (BIP's) are not used in an equation of state, the number of equations in phase equilibrium calculations will reduce to three, regardless of the number of components. This will reduce the computational time markedly. However, the current practice in the industry is to calibrate, or tune, EOS models against experimental data by mainly adjusting BIP's. In this paper, based on the approach which avoids using BIP's, a rapid flash calculation method has been evaluated and its convergence has been imporved for gas condensate reservoirs. To imprve the EOS prediction within a wide range of temperature, the temperature dependency function of the attraction term (#alpha#) was also modified. A practical tuning method has been develped which is consistent with the proposed #alpha# function. The presented integrated tuning method can be applied to match the experimental data of different types of fluids within wide ranges of temperature and compositional changes using any EOS. The reliability of the proposed method and the associated saving in computing time, in comparison with conventional methods, are demonstrated in this work for a variety of fluids.