Abstract
Abstract
The steam-assisted gravity drainage (SAGD) process simulations described in this study have been optimized to have the lowest cumulative steam-oil ratio (CSOR), highest RF and highest CDOR in order to obtain optimal operation conditions. In addition, net present value (NPV) calculations were performed for each simulation case to take the time factor into account.
A simple thermal efficiency parameter (STEP), based on CSOR, CDOR and RF for the time corresponding to SOR = 4, was developed to evaluate the performance of a SAGD project under optimized conditions. A linear relationship was found to exist between STEP and NPV, with a correlation coefficient in excess of 0.96 for most of the cases studied. For each simulation case, highest values of NPV and STEP indicated optimum SAGD operating conditions.
Introduction
The steam-assisted gravity drainage (SAGD) process has been tested in the field and has proven to be an effective recovery method with more than 50% recovery efficiency in the Alberta oil sands (Athabasca, Cold Lake and Peace River deposits).
Before a SAGD project is implemented in the field, a sensitivity analysis is usually required for optimizing the SAGD operating conditions: pre-heating period, steam injection pressure, steam injection rate and injector to producer spacing (I/P spacing). The economics of a SAGD project are related to several production performance parameters.The most significant of those are steam-oil ratio (SOR), ultimate recovery (recovery factor RF), calendar day oil rate (CDOR), and project life. Our main goal is to maximize oil production with the least amount of steam and in the shortest time.
There is very little research regarding an economic indicator for thermal recovery. Kisman and Ruitenbeek1 introduced a performance indicator for thermal recovery. They developed a model for the economic and performance evaluation of thermal recovery projects including steam stimulation, steam drive and combustion processes.
In this research, a new simple economic parameter, named STEP (simple thermal efficiency parameter), was introduced to optimize SAGD operating conditions for Athabasca, Cold Lake, and Peace River type reservoirs. Four operating conditions were optimized for the SAGD process. They are:preheating period, I/P spacing, steam injection pressure, and steam injection rate.
The net present value (NPV) of each case is first calculated for optimized SAGD performance. Then, STEP is calculated from three performance parameters: CSOR, CDOR, and RF.Finally, STEP is correlated with NPV for each optimized case.
Development of new economic indicator
The SAGD simulations described in this study have been optimized to have the lowest cumulative steam-oil ratio (CSOR), highest RF and highest CDOR in order to obtain optimal operating conditions.If a case has the lowest CSOR and the highest CDOR and RF, this gives the optimal operating conditions. However, there are cases which have low CSOR and low RF or CDOR. In this case, it is difficult to optimize operating conditions without an economic parameter such as NPV or rate of return.
STEP was introduced and developed for being used as a simple economic indicator during the SAGD optimizing procedure instead of NPV.
In this study, the economic calculations assume that a project is cost-effective as long as the instantaneous SOR is below a value of 4.Capital costs have not been taken into account, assuming that these are similar for all the cases studied because the same well configurations and development plan are considered. NPV calculations only considered the cost of steam ($5/bbl) and price of bitumen ($20/bbl), at a 10% discount rate.