Oil recovery by cyclic steam stimulation.
Engineering Honours Degree 2009
University of Adelaide
This report is an extension on a past Enhanced Oil Recovery concept study recommending Cylic Steam Stimulation (CSS) for field “X”. This project is a preliminary simulation for a CSS process with limited data to determine key affecting parameters for a single well. The main aim of this project is to allow Origin to determine if CSS is a viable method and to determine the parameters affecting oil production.
Field “X” was recently acquired by Origin Energy in June 2008 with limited data. The field is a shallow Pliocene reservoir that produces heavy oil in the range of 13-18O API with an oil viscosity of approximately 40 to 150 cSt at 50O C. Cyclic steam stimulation is a thermal process applied to reduce the oil viscosity to improve oil mobility. The CSS method outlined in this study has three phases in each cycle: the injection, the soak and the production phase.
The model is created and simulated in CMG STARS. The model simulates CSS in the top layer of the field for a single well. The well selected for the CSS model is a potential good performer. The model applies assumed values and correlations to develop fluid properties, thermal rock properties and relative permeability curves. The created model applies typical industry values to create a base case. This is then varied to determine optimum CSS operational parameters and sensitivity.
The cumulative oil production during the CSS phase is 15238 m3 for the base case. The results show that a variation of 10% in the relative permeability’s correlation constants created a change of 8% in cumulative oil recovery. The results also show that removing skin can improve oil recovery by a factor of 1.46. The optimum CSS operational parameters are determined as:
• Injection pressure is 80% of break down pressure.
• Injection time is 7 days.
• Production time is 150 days.
• Soak time is 30 days.
It is recommended that critical relative permeability curve data are obtained for the field and more simulation study be conducted with more site specific data. Furthermore it is recommended that a stimulation program be investigated prior to the implementation of CSS based on an improvement in oil production with no skin.