R. Gordon Moore

In situ combustion in Canadian heavy oil reservoirs

This paper reviews the laboratory combustion performance of different heavy oil and oil sand reservoir samples, and discusses the field performance of some of the in situ combustion projects which have been or continue to be operated in Canada. Abnormal behaviour (deviation from classical concepts of combustion) encountered in the field and in the laboratory are interpreted in the light of the combustion kinetics developed by the In Situ Combustion Research Group at the University of Calgary. The results are used to suggest design considerations for successful field projects.

An Experimental Study of Controlled Gas-Phase Combustion in Porous Media for Enhanced Recovery of Oil and Gas

This paper describes an experimental study aimed at establishing fundamental information on the various processes and relevant controlling mechanisms associated with gas-phase combustion in porous media, especially at elevated pressures. A novel apparatus has been designed, constructed and commissioned in order to evaluate the effects of controlling parameters such as operating pressure, gas flow rate, type and size of porous media, and equivalence ratio on combustion characteristics. The results of this study, concerned with lean mixtures of natural gas and air and operational pressures from atmospheric (88.5 kPa or 12.8 psia) to 433. 0 kPa (62.8 psia), will be presented. It will be shown that the velocity of the combustion front decreases as the operating pressure of the system increases, and during some test operating conditions, the apparent burning velocities are over 40 times higher than the open flame laminar burning velocities.

A model for improved analysis of in-situ combustion tube tests

Abstract Laboratory combustion tubes have been extensively used to study in-situ combustion mechanisms. Many of these studies have recognized that radial heat transfers, induced by equipment operation, can significantly distort temperature levels recorded inside the sand pack. The fact that the design and operation of combustion tubes have not been standardized, indicates the difficulty of physically eliminating this heat transfer problem. If thermal reservoir simulators are to be reliably calibrated using data from such experiments, these heat transfers must be understood and accounted for in the history matching. A general-purpose numerical model for simulating laboratory combustion experiments is presented that rigorously accounts for the on-off operation of the adiabatic heaters as well as external thermal-energy storage and convective circulations—a deconvolution of the laboratory phenomena. Included in the paper are applications of the model which show that combustion tubes of different diameters, being subjected to the same operating conditions (air injection flux, heater operating strategy, saturations, etc.) can produce significantly different results. Smaller tubes will tend to produce lower combustion front velocities and peak temperatures, and higher fuel loads. These results demonstrate why caution is required when translating laboratory data to field project design. This paper offers considerable insights into the role of heat losses in the combustion process. It rationalizes the significant differences in experimental data derived from different equipment configurations, but for similar oils. It also shows the direction of change to be expected in the experimental results when different size tubes are used.

Feasibility of In-Situ Combustion in the SAGD Chamber

Steam-assisted gravity drainage (SAGD) is a commercially successful bitumen-recovery method that has transformed some of the vast Canadian oil-sand deposits into recoverable reserves. Several SAGD projects have been developed in northern Alberta in the past few years, and many more are in the planning stages. As the projects mature, new operational problems are revealed, demanding new solutions. Because of operational restrictions, it is almost impossible to have the same growth rate in all steam chambers in a SAGD pattern. Hence, interference between a mature chamber and an adjoining immature chamber can become a problem. Steam leakage from the immature chamber into the mature chamber reduces the thermal efficiency of the project and requires a solution to prevent the steam dissipation. Filling the mature chamber with combustion gases is a possible solution for this problem. Carrying out in-situ combustion (ISC) in the mature chamber not only would create the needed combustion gases in the chamber, but also could recover a substantial part of the residual oil in the mature chamber. It is also likely that the combustion would create a reduced-permeability coke (toluene insoluble fraction) zone around the mature chamber, thus isolating it from the rest of the reservoir. To evaluate the merit of this idea, an elevated-pressure experiment was conducted using a 2D physical model. The conventional SAGD process was conducted in the model to develop a steam chamber. Air was then injected through a horizontal well near the top of the model into the SAGD chamber, and a combustion front was established around the air-injection well. By operating combustion in the depleted chamber, residual oil was mobilized and produced. Additional oil recovery was attained by more than 20% over the SAGD operation as a bonus. Initiation and propagation of combustion were confirmed by a large increase in the temperature in the combustion zone. After unpacking the model, it was found that a coke layer formed around the perimeter of the chamber.

Effect of Initial Water Saturation on the Thermal Efficiency of the Steam-Assisted Gravity-Drainage Process

The commercial viability of the steam-assisted gravity-drainage (SAGD) process is affected negatively by several undesirable reservoir features, such as pronounced heterogeneity, low vertical permeability, thick and areally extensive shale barriers, and steam thief zones. The efficiency of SAGD projects is also affected by the presence of higher water saturation in the target zone. Although the presence of small mobile-water saturation is not considered harmful, reservoirs with high water saturation may be poorly suited for the SAGD process. Nonetheless, SAGD remains the only practical technology for in-situ extraction of oil from oil-sand reservoirs, even when mobile water is present. This raises the question of how much mobile water is prohibitive. To investigate the effect of water saturation on SAGD performance, high-pressure physical-model experiments were carried out. Different levels of water saturations were established in the model by modifying the packing and saturating techniques. SAGD experiments were carried out by injecting superheated steam at controlled rates and producing the oil from the production well at constant pressure. The injection rate was selected to keep the pressure difference between the injector and the producer at a low level. The oil-production behavior was analyzed to evaluate the effect of water saturation on the thermal efficiency of the process. On the basis of the results of low- (immobile) and high- (mobile) water-saturation experiments, it was observed that the oil-recovery factor dropped by 6.6% when the initial water saturation was increased from 14.7% to 31.8%.

The thermal behavior of vertically-operated near-adiabatic in-situ combustion tubes

Abstract A commonly used approach for studying in-situ combustion processes has employed vertically-operated adiabatic combustion tubes. The data obtained from such apparatus are sometimes subject to interpretation problems because of convective circulations in the annulus, which are induced by the operation of the guard heaters. The main objective of this study was to systematically investigate the operational domain and impact of these convective heat transfers, and, in general, to provide a comprehensive framework for interpreting such experimental data. A microcomputer-based system was developed to automate the operation of the guard heaters and to provide a record of the power outputs of each heater with time. The automated system was used to gather data from five combustion experiments in which operating pressure, injected oxygen concentrations, water/oxygen ratio, and the type of gas in the annulus were varied. The experimental results showed that thermal energy from the heaters, as they responded to the combustion front, was transported upward by convection in the annulus. This energy elevated temperatures in the core behind the front. The tendency for annular convection to occur was found to increase with operating pressure, the on-time of the heaters, and with the Rayleigh number of the gas used in the annulus. Also, as the severity of convection increased there was (a) a reduction in the thermal efficiency of the heaters, and (b) an overall increase in heat loss from the combustion zone which required higher oxygen fluxes in order to avoid declining peak temperatures and to improve oxygen utilization. An analysis of the thermophysical properties of the annulus gases used explained these experimental observations, and demonstrated that gases of lower thermal conductivity may not necessarily reduce heat loss from the combustion tube.

Oxidation Characteristics of Light Hydrocarbons for Underbalanced Drilling Applications

This investigation is directly relevant to various applications associated with the safety aspects of underbalanced drilling operations where de-oxygenated air may be co-injected with oil-based drilling fluid. However, de-oxygenated air often still contains up to 5% oxygen by volume. This residual oxygen can react with oil during the drilling process, thereby forming potentially hazardous oxidized hydrocarbons and compromising the safety of drilling operations. This article examines the conditions and processes by which oxidation reactions occur and may be helpful in reducing risk in drilling operations. This project characterizes the oxidation behavior of several oils and a typical oil-based drilling fluid at atmospheric and elevated pressures using thermogravimetry (TG) and pressurized differential scanning calorimetry (PDSC). Tests performed on mineral matrix (core) from the oil reservoirs showed no reactivity in both inert and oxidizing atmospheres. In an inert atmosphere, tests on all hydrocarbon samples showed only vaporization, no reactivity. In an oxidizing environment, the tests on hydrocarbons showed several oxidation regions. The presence of core had no effect on the behavior of the hydrocarbons tested in an inert atmosphere but accelerated the higher temperature oxidation reactions of the oil samples. The oil-based drilling fluid exhibited the opposite effect-the presence of core material retarded the oxidation reactions. This is perhaps due to the presence of an oxygen scavenger reacting with oxygen-containing clays present in the mineral matrix. In all tests performed on mixtures of hydrocarbon and core in oxidizing atmospheres, elevated pressures resulted in acceleration of the lower and higher temperature reaction regions.