Economic Evaluation of Steam and Nitrogen Injection on SAGD Process

Abstract

Abstract Thermal recovery methods made possible the production of heavy oil fields considered non-commercial with conventional methods of recovery. In this context, steam injection has proved to be a major cost-effective alternative for increasing the heavy oil recovery. Steam Assisted Gravity Drainage (SAGD) is one of the field proven improvements. It uses two horizontal wells with the steam injector above the producer, which stays at the base of the reservoir. Sweeping the reservoir with the growth of a steam chamber. The variations on conventional SAGD involving non-condensable gases show a new trend. Numerical results suggest that after a certain period of time operating only with steam is effective to inject only inert gas. In this process the steam chamber keeps growing even after the steamflood is stopped. The purpose of the gas injection is to maintain the reservoir pressure elevated to keep the oil production. The cumulative steam oil ratio has a downward trend, yielding a reduction in the project costs. In this paper, a numerical study of the SAGD method in field scale is conducted. The reservoir model is simulated with properties obtained from a Brazilian onshore field. The methodology used involves an investigation of the main parameters that influence the application of the method and, according to a sensitivity analysis. The aim is to determine the best time to start gas injection looking to maximize NPV. A commercial software is used to simulate the injection of nitrogen after steamflooding the reservoir in order to obtain the results that are used to perform the sensitivity analysis. It was verified that the steam injection rate and the bottom hole pressure are decisive parameters to be considered. The simulations show that the nitrogen injection after a determined period of time of continuous steam injection reflects in a reduction in the order of 40% of the steam oil ratio. However, the cumulative oil production is almost the same when compared with the conventional SAGD.