Economic Optimization and Uncertainty Assessment of Commercial SAGD Operations

摘要

As SAGD is being increasingly used as a commercial technology to recover heavy oil and bitumen,it is essential to determine the most economical operating conditions for a SAGD operation by reservoir simulation.Furthermore,to support the decision-making process of a SAGD project,it is also important to quantitatively assess the uncertainty of its economic forecast.In this paper,application of experimental design,response surface generation,and Monte Carlo simulation techniques in the workflow of SAGD simulation studies was demonstrated with a real field case example.The field case is an infill SAGD project with two planned SAGD well pairs and eight existing primary production wells which have 5-years of primary production.A bottom water zone is also present.Three major steps of the workflow are (1) history matching primary production data,(2) optimizing SAGD performance,and (3) quantifying uncertainty of the SAGD forecast.Firstly,experimental design and response surface generation techniques were used to achieve a faster and better history match than the traditional manual history match.Secondly,SAGD performance was optimized by adjusting steam injection rate and producer liquid withdrawal rate during different SAGD operation periods.Finally,experimental design and response surface generation techniques were applied to build a polynomial response surface through which the net present value (NPV) of the SAGD project is correlated with uncertain parameters and a SAGD design parameter.Monte Carlo simulation was then performed to quantify the uncertainty of SAGD forecast in terms of cumulative probability distribution of the NPV at different values of the SAGD design parameter.The results show that the economics of this project are improved considerably through optimization.The optimum operating conditions obtained use a high initial steam rate and high production rate to develop the steam chamber.After the instantaneous steam-oil ratio reaches a certain value,both steam rate and production rate are lowered to prevent steam breakthrough to the bottom water.The uncertainty of the project NPV was assessed,taking into considerations the uncertainties in high-temperature relative permeability endpoints and the variation of the SAGD design parameter.