|Publisher||Society of Petroleum Engineers||Language||English|
|Content Type||Conference Paper|
|Title||Analysis of the Steam Assisted Gravity Drainage (SAGD) Process Using Experimental/Numerical Tools|
|Authors||Nasr, T.N., Golbeck, H., Alberta Research Council; Lorimer, S., Consultant|
International Conference on Horizontal Well Technology, 18-20 November 1996, Calgary, Alberta, Canada
|Copyright||Copyright 1996, Society of Petroleum Engineers, Inc.|
There has been a keen interest during the last decade in the application of the steam assisted gravity drainage (SAGD) process as a recovery strategy for oil sands and heavy oil reservoirs. The recent success of field pilot demonstrations in Alberta and Saskatchewan has further accentuated the need to understand process mechanisms and determine techniques to accelerate recovery rates for improving economics. This paper provides an in depth analysis of the SAGD process using numerical and experimental tools. Two-dimensional scaled gravity drainage experiments, designed to represent heavy/extra heavy oil reservoirs, were used to calibrate the thermal reservoir simulator STARS. Visual observations of the development of the steam chamber (gravity cell) were made during the experiments and compared to numerical model predictions. The results obtained provided insight into the effect of key parameters such as permeability, pressure difference between the wells, capillary pressures and heat losses on process performance. A detailed study on the effect of permeability on source/sink simulation of the SAGD process demonstrated the importance of the initialization or transient phase of the process. The duration of the initialization phase increased as the permeability decreased, indicating that this phase occupied an increasingly significant portion of the entire drainage process as permeability decreased. The sensitivity of the validated numerical model to a number of key parameters required for numerical simulation of the process are highlighted in the paper. The effort is intended as a precursor to modeling field scale gravity drainage processes. The ultimate application of the work is in thermal heavy oil recovery operations using steam assisted gravity drainage.
The steam assisted gravity drainage concept, developed by Butler, is a counter-current process driven by the buoyant forces created by density difference between steam and liquid phase. In the steam assisted gravity drainage (SAGD) field application, two horizontal wells are placed one above the other near the bottom of the formation. The top horizontal well is used to supply steam into a steam chamber that grows above it. The bottom well collects the produced liquids (formation water, condensate, and oil emulsions). The rising steam condenses on the boundary of the chamber heating the heavy oil which under gravity flows to the production well. Provided that fluid communication had been established between the injection and production wells for extra heavy oil, a continuous counter-current flow consisting of rising steam and down-flow of oil emulsions will rapidly advance and produce the immobile oil.
Successful application of the gravity drainage process for extra heavy oil has been demonstrated at the Underground Test Facility (UTF) field pilot. The UTF field pilot provided useful information regarding field implementation of gravity drainage concept and demonstrated that oil can be economically produced and a high reservoir depletion achieved.
Major advances which have been recently made in directional drilling and completion technology resulted in reduced drilling costs and provided new opportunity for application of gravity drainage and producing heavy oil reservoirs. However, further research and development is required to reduce the overall cost of oil produced through gravity drainage and enhance the robustness of the process for complex reservoirs.
The analytical model proposed by Butler provides a valuable reference and is a rapid method for estimating process effectiveness in homogeneous reservoirs using a simplified source-sink situation. However, for investigating various strategies for enhancing the effectiveness of gravity drainage, both experimental and numerical methods are used in this study to obtain detailed reservoir flow and pressure-temperature-saturation distribution inside and/or outside the gravity cell, as well as evaluating the role of capillary forces, including the countercurrent steam-emulsions flow in the near-wellbore region.
|File Size||1,104 KB||13|