Steamflood Performance In the Presence of Carbon Dioxide And Nitrogen
Authors: Harding T.G. , Ali S.M. Farouq , Flock D.L. 
Published: March 2010

The injection of mixtures of flue gas and Steam has been proposed in conjunction with the development of downhole Steam generators, the Vapor Therm process and the Wet Air Oxidation Boiler. The combined gas-steam injeclioll process may be superior to steam-only injection in terms of improved oil production performance and reduced levels of atmospheric pollution. This paper reviews previous experimental and numerical simulation work related to gas-steam injection and presents the results of an experimental study of steam-flooding with nitrogen Gild carbon dioxide additives. The experiments were conducted in linear porous media which were saturated with a moderately viscous refined oil and water. Several rests involved the injection of slugs of gas followed by steam but the majority used the simultaneous injection of The gases and Steam. It was found that for the systems studied, the addition of the gases to steam resulted in a slight improvement ill over-all recovery bill a marked improvement in the rate of production of oil.

Introduction

Much effort has recently been directed toward the development of downhole steam generators (DHSG) for use in thermal recovery of heavy oi1(1, 2, 3, 4). In the high pressure direct-fired DHSG, flue gases from combustion of the fuel are injected into the oil producing formation along with the steam. This type of DHSG has several advantages over conventional surface steam generation including 1) elimination of stack, surface line and wellbore heat losses during injection; 2) reduction of atmospheric pollution; and 3) potential for improved production performance due to the presence of gases which are soluble in reservoir fluids. The elimination of wellbore heat losses by placing the DHSG just above the producing interval extends the depth to which steam may be used to perhaps 1800 metres (6000 feet) from the current limit of 800 metres (2600 feet)HI, Recent field tests of DHSG have demonstrated certain beneficial effects of the reservoir on pollutants: the elimination of particulates, an order of magnitude reduction of NO2, substantial scrubbing of SO2 and a two-fold reduction of Co(2). A portion of the pollutants remain in solution in residual reservoir liquids and in gas which is trapped in the reservoir. Much of the pollutant material is also recovered in solution in the produced liquids(1), Soluble gas injection with steam may improve recovery and production performance due to a number of mechanisms including swelling, viscosity reduction, and solution gas drive(5). Meldau el al,(6)have used numerical simulation to identify the following mechanisms which assisted oil recovery in field experiments of cyclic air/steam stimulation:trapping of gas at saturations up to the critical;increased gas drive of heated oil near the wellbore;movement of heat into upper more viscous oil sands; andgreater drawdown due to higher reservoir pressures.

In addition to DHSG, two other processes have been proposed for enhanced oil recovery involving surface generation of mixtures of flue gases and steam: the Carmel Energy Vapor Therm Process(7,8) and the Zimpro-AEC Wet Air Oxidation (WAO) Boiler(9,10).