THE EFFECT OF THE RESERVOIR FLUID PHASE BEHAVIOR TREATMENT ON THE RESERVOIR SIMULATION PREDICTIONS OUTPUT
Abstract
Two different methods are used for solving the phase behavior problem during reservoir simulation applied to hydrocarbon reservoirs; the black oil Tables and the compositional approaches. The black oil Tables simulators use Tables of volumetric factors (solution gas-oil ratio, oil formation volume factor, gas formation volume factor, oil content) versus pressure and by performing interpolation at each pressure step the produced volumes are calculated. On the other hand, the compositional simulators, perform the phase behavior calculations by using an equation of state so as to calculate the equilibrium phases and their properties at different operating conditions.
The main advantages of the black-oil Tables simulators are that they require low calculation (CPU) time low computer memory. On the other hand, compositional simulators are more accurate and can perform better with volatile oils and gas condensates. Nevertheless, operators still use black-oil simulators to simulate volatile oils and gas condensates, valuing thus more the speed of calculations as the expense of accuracy. The question is how much information is lost with respect to the compositional approach and how much off the black oil tables approach reservoir simulation predictions can be.
For this thesis, the commercial software IMEX and GEM of Computer Modeling Group has been used. These models are presented in detail and the different options that they offer are discussed. The objective of this work was to discuss to present the available models of the black oil tables and compositional simulators as well as their difference in predictions and to assess their differences in predicting the reservoir production performance. A simple reservoir containing volatile oil was modeled and its depletion was simulated using both simulators and their results were compared.
The two simulators exhibited a small divergence between their predictions for the initial volumes in place and the simulation runs. However, the compositional simulator is thought to be more accurate than the black oil simulator in its predictions as it is a compositional simulator. Moreover, it was found that the black oil simulator calculated almost the same amount of initial volumes in place, whereas it over-predicted the oil recovery and the oil cumulative production.
