Analytical Modeling of Cyclic Steam Stimulation Process for a Horizontal Well Configuration
Date
2013-12-04
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Abstract
Cyclic steam stimulation is one of the most widely used heavy oil recovery methods. Steam is injected into a formation at high rates for several weeks through a vertical well. The well is then shut-in for a certain period of time, which is called “soak” period. Steam condenses in the formation, thus heating the reservoir rock and fluids around the wellbore. During this period the oil viscosity is reduced by many times. The heated sand contains mobile oil, steam and water. The oil and other fluids are expelled out as the sand face pressure is lowered when the well is put on production. Oil is produced until the oil rate reaches an economic limit and the cycle is repeated again.
There are many analytical models that predict the performance of a conventional Cyclic Steam Stimulation process for vertical wells. However, there are only very few models that are applicable to a horizontal well configuration. The objective of this study is to model heavy oil production using cyclic steam stimulation with a horizontal well configuration. Reasonable assumptions were made to simplify the problems to an extent that they can be solved using analytical or semi-analytical methods. Such analytical or semi-analytical solutions are required for more advanced understanding of the physical problem under investigation and validation of more sophisticated numerical models. The practical value of these solutions lies in the fact that they aid to improve interpretations and conduct fast sensitivity analysis and fast computations.
In order to predict oil production the governing equations of heat and fluid flow in cylindrical coordinate need to be solved. Average temperatures in the formation during the steam injection process are calculated by solving the transient heat transfer equations. The heat transfer model is then coupled to a fluid in flow model to predict the fluid rates. The fluid inflow model is a two phase model that takes into account the relative permeability of oil and water. The developed model is validated with the fine grid numerical simulation of the problem using STARS® numerical simulator from CMG. Since, a lot of simplifying assumptions are involved modifications, such as a correction for the pressure drawn-down and water relative permeability, were made during the history matching with STARS in order to get a good match for the fluid rates. These modifications include altering the relative permeability of water and making an initial guess of the pressure draw-down based on the results from the simulator. The robustness of the model was tested by comparing the model results with the results from the numerical simulator by changing various parameters such as: steam injection rates, reservoir permeability, relative permeability, oil viscosity and reservoir diffusivity.
With some reasonable assumptions, it is seen that the results from the developed model are very close to the results obtained using STARS numerical simulator from CMG and it can be concluded that the proposed model captures the essential mechanism of the process. The model is relatively simple and all the calculations can be performed using a user friendly spreadsheet in just a few minutes. Currently, the proposed model can be used to optimize production from a single well. The model can be coupled with an economic model to optimize steam injection rates and production rates based on the reservoir properties.
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Engineering--Petroleum
Citation
Saripalli, H. (2013). Analytical Modeling of Cyclic Steam Stimulation Process for a Horizontal Well Configuration (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/24826