• Reservoir simulations integrated with geomechanics for West Sak Reservoir

      Chauhan, Nitesh; Khataniar, Santanu; Dandekar, Abhijit; Patil, Shirish (2014-07)
      Geomechanics is the study of the mechanical behavior of geologic formations. Geomechanics plays an important role in the life of a well. Without a proper understanding of the geomechanics of a reservoir, the projects associated with it may run into problems related to drilling, completion, and production. Geomechanics is important for issues such as wellbore integrity, sand production, and recovery in heavy oil reservoirs. While studying geomechanics, proper weight is given to mechanical properties such as effective mean stress, volumetric strain, etc., and the changes that these properties cause in other properties such as porosity, permeability, and yield state. The importance of analyzing geomechanics increases for complex reservoirs or reservoirs with heavy oil. This project is a case study of the West Sak reservoir in the North Slope of Alaska. Waterflooding has been implemented as enhanced oil recovery method in the reservoir. In this study, a reservoir model is built to understand the behavior and importance of geomechanics for the reservoir. First, a fluid model is built. After that, reservoir simulation is carried out by building two cases: one coupled with geomechanics and one without geomechanics. Coupling geomechanics to simulations led to the consideration of many important mechanical properties such as stress, strain, subsidence etc. Once the importance of considering geomechanical properties is established, different injection and production pressure ranges are used to understand how pressure ranges affect the geomechanical properties. The sensitivity analysis defines safer pressure ranges contingent on whether the formation is yielding or not. The yielding criterion is based on Mohr's Coulomb failure criteria. In the case of waterflooding, injection pressure should be maintained at 3800 psi or lower and production at 1600 psi or higher. And if injection rates are used as the operating parameter, it should be maintained below 1000 bbls/day. It is also observed that injection pressure dominates the geomechanics of the reservoir.
    • A study of waterflood sweep efficiency in a complex viscous oil reservoir

      Jensen, Marc Daniel; Khataniar, Santanu; Dandekar, Abhijit; Patil, Shirish (2014-12)
      West Sak is a multi-billion barrel viscous oil accumulation on the North Slope of Alaska. The unique geologic complexities and fluid properties of the West Sak reservoir make understanding ultimate sweep efficiency under waterflood a challenge. This project uses uncertainty modeling to evaluate the ultimate sweep efficiency in the West Sak reservoir and honors a rich dataset gathered from 30 years of development history. A sector model encompassing the area of the West Sak commercial pilot was developed and a sensitivity analysis conducted to determine the most important parameters affecting sweep efficiency. As part of this process unique constraints were incorporated into the model including measured saturations at the end of history, and observed completion performance. The workflow for this project was documented and can be adapted for use in larger scale models. The workflow includes the development of static cell properties which accurately represent field behavior, a preliminary history match using conventional methods and a sensitivity analysis employing a multi-run visualization tool to effectively navigate and process large amounts of data. The main contributions of this work include the identification of key parameters affecting sweep efficiency in the West Sak oil field, a documented workflow, and increased insight into observed production behavior.