A comparative analysis of numerical simulation and analytical modeling of horizontal well cyclic steam injection

摘要

The main objective of this research is to compare the performance of cyclic steam injection using horizontal wells based on the analytical model developed by Gunadi against that based on numerical simulation. For comparison, a common reservoir model was used. The reservoir model measured 330 ft long by 330 ft wide by 120 ft thick, representing half of a 5-acre drainage area, and contained oil based on the properties of the Bachaquero-01 reservoir (Venezuela). Three steam injection cycles were assumed, consisting of a 20-day injection period at 1500 BPDCWE (half-well), followed by a 10-day soak period, and a 180-day production period. Comparisons were made for two cases of the position of the horizontal well located on one side of the reservoir model: at mid-reservoir height and at reservoir base. The analytical model of Gunadi had to be modified before a reasonable agreement with simulation results could be obtained. Main modifications were as follows. First, the cold horizontal well productivity index was modified to that based on the Economides-Joshi model instead of that for a vertical well. Second, in calculating the growth of the steam zone, the end-point relative permeability??s of steam and oil were taken into consideration, instead of assuming them to be the same (as in the original model of Gunadi). Main results of the comparative analysis for both cases of horizontal well positions are as follows. First, the water production rates are in very close agreement with results obtained from simulation. Second, the oil production rates based on the analytical model (averaging 46,000 STB), however, are lower than values obtained from simulation (64,000 STB). This discrepancy is most likely due to the fact that the analytical model assumes residual oil saturation in the steam zone, while there is moveable oil based on the simulation model. Nevertheless, the analytical model may be used to give a first-pass estimate of the performance of cyclic steam injection in horizontal wells, prior to conducting more detailed thermal reservoir simulation.