SAGD Wind-Down: Lab Test and Simulation

Abstract

As SAGD moves from pilot test to commercial operation, a number of issues need to be dealt with. These include diagnosing and solving operational problems and improving energy efficiency. One of the methods of improving energy efficiency is to prolong oil production after steam injection stops by using the energy remaining in place. The results of a laboratory experiment and corresponding numerical history matching are reported in this paper. The study showed that the hot chamber continued its expansion after steam injection was stopped and a gas injection was initiated. The continuous expanding period represented the most productive period in the gas injection wind-down process. A total of 12.5% of OOIP was recovered during wind-down. Successful history matching of both the oil production curve and temperature profiles at different times demonstrated that the numerical simulation could handle the gas/steam mixing phenomena. Gas concentration profiles from numerical simulation indicated that gas was concentrated at the region where oil saturation was experiencing big changes. Introduction The successful tests of the SAGD process at UTF(1, 2) and other pilot projects(3, 4) have established SAGD as a viable technology for in situ recovery of the huge heavy oil and bitumen resources in western Canada. A number of commercial SAGD projects in western Canada are in the operation, construction, or planning stages(5). However, the SAGD technology is still in a transition from pilot to commercial operation. Development of the technology is currently focusing on two areas. The first is to diagnose and solve operational problems. In field operations, many projects have encountered difficulties, such as lower than expected oil production rate, higher than expected steam-oil ratio (SOR), or premature production rate decline. In each case, the cause of the problem needs to be identified in order to develop methods to deal with the problem and avoid the problem in the future. The second area of SAGD development is to improve energy efficiency as the costs of fuel and associated water treatment account for a large portion of the oil production cost. These developments include hybrid processes using co-injection of steam and solvent(6 – 10), or steam and non-condensable gas(11). The hybrid processes take advantage of both heating by steam and dilution by solvent. The injection of non-condensable gas is intended to reduce heat loss to the overburden, and therefore, improve SOR. With this idea in mind, efforts have been directed to developing SAGD wind-down methods. At a certain stage of the SAGD operation, as instantaneous SOR increases, there is no economic benefit to continue pure steam injection. At this stage, a wind-down process can be started to utilize energy in place and continue oil production. A numerical simulation and economic evaluation study(12) showed that a co-injection of steam and non-condensable gas gave the best result. Recently, the results of co-injection of steam with flue gas into UTF Phase B as a wind-down process was reported(13). The key to achieve the best economics for a SAGD wind-down process is optimization.

A Critical Review of Reservoir Simulation Applications in Key Thermal Recovery Processes: Lessons, Opportunities, and Challenges

“…Zhao et al (2005) experimentally investigated a SAGP application during a wind down process, which indicated that 12.5% more original oil in place could be produced compared with SAGD. 222 All these results demonstrated that SAGP was a good modification to SAGD. NCG coinjection with steam could reduce heat loss after a chamber contacts with overburden.…”

“…In SAGD, a steam chamber cannot penetrate a low permeability layer until the temperature in this layer reached steam temperature, while in SAGP gas fingers were easier to penetrate this layer, which demonstrated that SAGP could have a better performance in a reservoir with low perm layers than SAGD. Zhao et al (2005) experimentally investigated a SAGP application during a wind down process, which indicated that 12.5% more original oil in place could be produced compared with SAGD . All these results demonstrated that SAGP was a good modification to SAGD.…”

Machine-Learning Approach for Forecasting Steam-Assisted Gravity-Drainage Performance in the Presence of Noncondensable Gases

“…Other sets of experiments to evaluate the wind-down process by injecting NCG after SAGD resulted in a recovery of 12.5%. 6 The temperature profile demonstrated that the hot chamber continued growing when the steam injection stopped due to the expansion/pressurization with NCG addition. In another study, two sets of experiments were conducted to evaluate the NCG distribution in the SAGD chamber when there was initial gas saturation: one at low pressure and one at high pressure.…”

Relative Permeability Estimation in Steam Assisted Gravity Drainage (SAGD) Using a Fractional Flow Model

“…This discrepancy in the literature is due to unknowns associated with reservoir rock and reservoir fluid interaction and high asphaltenic content of reservoir fluids (Kar et al, 2016). Both the liquid-gas relative permeabilities and relative permeability end point as a function of temperature are important simulation parameters for performance estimation of hot-water and steam injection processes, but most simulation studies ignore their importance and do not introduce those parameters into the model by assuming two-phase flow (Li and Horne, 2003;Zhao et al, 2005;Hascakir and Kovscek, 2010 ).…”