The Wet Air Oxidation Boiler For Enhanced Oil Recovery

Abstract

Abstract Wet air oxidation is a proven commercial process in use on a worldwide scale for the treatment of aqueous wastes and sludges often in association with the recovery of by-product energy and chemicals. The basic elements and characteristics of the wet air oxidation system are described and previous industrial experience and applications are cited. The adaptation of the wet air oxidation process to enhanced recovery applications is described and a possible field deployment is presented. The operational advantages and disadvantages 0/ the wet air oxidation boiler in an oil-field enhanced recovery application are cited. Typical pilot-plant run are presented describing oxidation products and the results of materials corrosion tes ting. An investigative reservoir simulation study of steam and flue gas injection in a typical Cold Lake heavy oil reservoir established that the injection of 100% quality steam with 7% by volume CO2 increased calendar-day oil production by 35%. The injection of 100% quality steam simultaneously with 6% CO2 and 20% N2 was found to yield negative results compared to normal steam stimulation treatments. Various mechanisms contributing to the improved reservoir performance are proposed and the commercial feasibility of a typical wet air oxidation system is described. It is concluded that the wet air oxidation process is worthy 0f a detailed and intensive field test to assess the potential for thermal enhanced recovery operations. Introduction The process known as wet air oxidation or wet oxidation, often referred to as WAD, is in extensive commercial use. There are 200 installations worldwide for the treatment of aqueous wastes (Figure in full paper) and sludges, often with recovery of by-product energy and chemicals. More recently, the WAO process has been proposed for energy production as a primary objective(1)-(5). Environmental performance is an outstanding advantage, because the process, by its inherent nature, does not produce any S02, NOx or particulates in the off-gas. The process also has the ability to treat waste along with the production of energy. The WAO Process Wet oxidation, WAO, refers to the aqueous-phase oxidation of dissolved or suspended organic substances at pressures of 300–3,000 psi and temperatures of 300–700°F. Explanations of the process exist in extensive published literature(2)(3) (4). WAO can be demonstrated as follows: Place 100 grams of water and 3.5 grams of coal in an autoclave. Charge the autoclave with about 5 grams of oxygen. Heat the autoclave to 280°C (536°F) and hold for 60 minutes. The results of such a demonstration are shown in Table I. For WAO it is convenient to use chemical oxygen demand (COD) to measure the combustible content of fuel and oxidized products. It is clear that most of the combustible material in the coal has been converted to carbon dioxide and water. Results of a similar experiment using a typical petroleum coke, which seems to be a preferred fuel for EOR applications, are also shown in Table 1. A simple flow sheet, showing how wet oxidation is accomplished in a continuous system, is shown in Figure 1.