Simulation is one of the most important and powerful reservoir engineering tools for understanding reservoir performance, devising operating strategies, and solving production problems. Simple homogeneous models are suitable for understanding basic reservoir engineering parameters and for simple sensitivity analyses. However in real reservoirs with heterogeneities such as at Nexen Long Lake, a comprehensive geomodel which includes all the available geology and geophysics knowledge is necessary in order to extract the greatest value from the simulation efforts.
A geomodel is representative of the real reservoir if simulation of the geomodel is able to reproduce the production history of the reservoir (history matching). For a typical SAGD pad, the parameters to be matched include the injection and production rates, downhole injection pressures, and pressure and temperature of observation wells.
Based on our experience, for this process to be effective and reasonably timely a team consisting of the geologist, geophysicist, geomodeler, production and reservoir / simulation engineer must work interactively and in an iterative, "trial and error" fashion.
The geomodelling part is presented in Part 1(10), of this paper and in Part 2 the simulation results are reviewed. The simulation process can be divided into three main parts - history matching, sensitivity analysis and forecasting. Once the history matching part is done, the geomodel is ready to be used for the other two parts.
High water saturation zones, also referred to as lean zones and top water, play an important role in different stages of a SAGD project. A detailed strategy is necessary to deal with them and to optimize the production. Simulation results show that one needs to be able to increase the total fluid rate and solve the sub-cool limitations at the time of contact with these lean zones.
The STARS thermal simulator from Computer Modeling Group (CMG) was used to do all the reservoir simulations in this paper.