The Mukhaizna heavy oil field in the Sultanate of Oman has three distinct zones that need steam injection to enhance oil recovery. A new geocellular based reservoir description was prepared as the starting point to evaluate the performance of these three zones; UG2A, UG2B, and MG to different injector and producer configurations. The major challenge was to ensure good production rates without compromising recovery efficiency. The three zones are separated from each other except in a few places where the two zones UG2A and 2B communicate.
During the flood design, producers with horizontal laterals were considered for each of the three zones. However, determining a method for steam injection that delivered recoveries similar to steam assisted gravity drainage (SAGD) was a challenge. A thermal reservoir simulation model was used to evaluate various configurations including horizontal and vertical injectors.
The final design called for commingled vertical injectors positioned between offset horizontal producers with three laterals stacked vertically. This design created a new modified SAGD recovery process for the reservoir. A steam chamber is created above each horizontal lateral, but the steam arrives from the side. One advantage of this design is the ability to control steam in each vertical injector. With advanced surveillance techniques to determine locations of early steam breakthrough, vertical injectors can be controlled to optimize recovery.
This paper will show the design options considered and their estimated recovery. Then the modified SAGD design, implemented at Mukhaizna, will be compared to current production performance in a selected area of the field which has been under injection for around 2 years. Field performance, which will be presented as rate versus time, and, also using dimensionless plots is tracking the thermal model based design quite nicely. The use of surveillance methods to control injection is also discussed.