Chemically Assisted Ignition Technologies for a Light Oil Air Injection Process

Abstract

A light oil (API 30 º) reservoir is an excellent candidate for high pressure air injection, but the oil is not believed to be capable of self-ignition at the reservoir temperature. Several chemical additives and catalysts are studied to evaluate their effectiveness of ignition improvement for this light oil sample. Pressurized Differential Scanning Calorimetry (PDSC) and Accelerating Rate Calorimetry (ARC) experiments are examined in this study. The oil sample, which is mixed with certain catalysts and chemical additives, is subjected to a controlled heating schedule under a constant flow rate of air at 4.14 MPa (600 psig) and 13.8 MPa (2,000 psig) pressure for the PDSC and ARC tests, respectively. The amount and rate of heat released by the oxidation reactions is analyzed for those tests. In the presence of a metallic catalyst and chemical initiators, oxidation behaviour of the oil tested is dramatically improved. Also observed are a significant reduction in the onset temperature of significant exotherm and an increased rate for the release of heat. Introduction Air injection has been proven as a viable process in improving oil recovery from light oil reservoirs, and as a result, it has received much interest in recent years(1, 2). The concept of recovery increment is when air is injected into a light oil reservoir and exothermic chemical reactions occur. The desired reactions result in heat generation and the production of carbon dioxide. Downstream of the reaction zone, the combustion produced gas sweeps oil toward the production wells, combining with light hydrocarbon fractions vapourized by heat released from oxidation reactions. Therefore, incremental oil production is achieved. However, air injection for a light oil reservoir is a complex process involving simultaneous heat and mass transfer in a multiphase environment coupled with oxidation chemical reactions. Ignition is the first phase of this process and a satisfactory ignition is of prime importance in initiating a successful air injection process(2). In high temperature reservoirs, the air injection process is initiated by injecting air, which may spontaneously ignite the oil-in-place(1). However, in some cases, spontaneous ignition of the reservoir oil is not likely to occur so that several artificial means have been implemented(3), including down hole electrical heaters, a gas burner or injection of steam, but it is highly desirable to avoid having to run heaters or burners when air injection is to be applied in deep, high pressure reservoirs. As a result, chemical ignition is proposed(2). The concept of chemical ignition is where a slug of chemicals with reactive oxidation characteristics is injected into an oil bearing zone prior to the injection of air from an injector. If heat released from an oxidation reaction is continually generated at a rate greater than it is dissipated, starting at the native reservoir temperature, oil can be spontaneously ignited without the application of artificial means. The reactive nature of the base oil present in the ignition zone can be enhanced or stimulated. A spontaneous ignition may occur within the formation. Bednarski(4) reported on a chemical ignition improvement experiment.

Characteristics and Properties of Coke Formed by Low-Temperature Oxidation and Thermal Pyrolysis during in Situ Combustion

“…To make investigation easier, Moore divided the oxidation of crude oil during the ISC process into three categories: low-temperature oxidation, fuel deposition, and high-temperature oxidation. − Coke forms in the low-temperature oxidation and fuel deposition regions. When oxygen makes contact with the crude oil in the reservoir in these regions, the oxygen dissolves into crude oil under high pressure.…”

Experimental Study on New Ignition Agents Used in Initiating in Situ Combustion

“…If spontaneous ignition fails or is not desirable, some artificial measures are necessary, including electrical heaters, hot-fluid injection, downhole burners, chemical methods, etc. However, in deep and high-pressure reservoirs, chemical ignition is a good choice, while heaters and burners should be avoided …”

“…Available autoignitable fluids are linseed oil, tung oil, a mixture of tung oil and tall oil, unsaturated aliphatic compounds, unsaturated nonhydrocarbon oils, and polymers with iodine numbers greater than 130. − Bandyopadhyay initiated a fireflood by using the water emulsion of a carbon black material to increase the fuel concentration around the ignition well. Last but not least, some oxidation catalysts, such as cobalt naphthenate, cobalt tallate, and cobalt octoate, are added to enhance the desired reaction. − Li et al used an iron-based catalyst to enhance ignition. In a patent issued to Ning et al, platinum and palladium are used as catalysts.…”

“…However, in deep and high-pressure reservoirs, chemical ignition is a good choice, while heaters and burners should be avoided. 4 Chemical methods include crude oil, which is ignited by injecting chemicals into the stratum compounds prior to air. The heat required for ignition is generated by chemical reactions completely within the ignition zone.…”

“…Last but not least, some oxidation catalysts, such as cobalt naphthenate, cobalt tallate, and cobalt octoate, are added to enhance the desired reaction. 10−12 Li et al 4 used an iron-based catalyst to enhance ignition. In a patent issued to Ning et al, 16 platinum and palladium are used as catalysts.…”