M.G. Ursenbach

The Challenge of Predicting Field Performance of Air Injection Projects Based on Laboratory and Numerical Modelling

Air injection-based enhanced oil recovery processes are receiving increased interest because of their high recovery potentials and applicability to a wide range of reservoirs. However, most operators require a certain level of confidence in the potential recoveries from these (or any) processes prior to committing resources. This paper addresses the challenges of predicting field performance of air injection projects using laboratory and numerical modelling. Laboratory testing, including combustion tube tests, ramped temperature oxidation and accelerating rate calorimeters can supply data for simple analytical models, as well as providing important insights into potential recovery-related behaviours. These tests are less suited to providing detailed kinetic data for direct and reliable use in numerical simulators. Indeed, the oxidation reactions are sufficiently complex that, regardless of how powerful the thermal reservoir simulator is, its predicting capability will strongly depend on the engineers understanding of the process and ability to model the most relevant oxidation behaviours of the particular oil reservoir under study. It is proposed that the optimum design cycle for air injection-based processes is to perform laboratory testing that would aid in the understanding of the process and in the design and monitoring of a pilot-scale field operation. Analytical models and simplified, semi-quantitative reservoir simulation models would be employed at this stage. If this evaluation stage is successful, a pilot operation would be initiated and the data gathered during the pilot, as well as laboratory oil property and compositional data, would then be used to history match and tune a model for predictions of the full field operation.

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.

Is High-Pressure Air Injection (HPAI) Simply a Flue-Gas Flood?

High-pressure air injection (HPAI) is an enhanced oil recovery (EOR) process in which compressed air is injected into a deep, light-oil reservoir, with the expectation that the oxygen in the injected air will react with a fraction of the reservoir oil at an elevated temperature to produce carbon dioxide. Over the years, HPAI has been considered a simple flue-gas flood, giving little credit to the thermal drive as a production mechanism. The truth is that, although early production during a HPAI process is mainly due to re-pressurization and gasflood effects, once a pore volume of air has been injected the combustion front becomes the main driving mechanism. This paper presents laboratory and field evidence of the presence of a thermal front during HPAI operations, and of its beneficial impact on oil production. Production and injection data from the Buffalo Field, which comprises the oldest HPAI projects currently in operation, were gathered and analyzed for this purpose. These HPAI projects definitely do not behave as simple immiscible gasfloods. This study shows that a HPAI project has the potential to yield higher recoveries than a simple immiscible gasflood. Furthermore, it gives recommendations about how to operate the process to take advantage of its full capabilities.

Air Injection in Heavy Oil Reservoirs - A Process Whose Time Has Come (Again)

Air injection in heavy oil and bitumen reservoirs, also known as in-situ combustion or fireflooding, is an enhanced recovery process that has been around for several decades. While on paper or in the laboratory this oil recovery process shows tremendous potential, its success in past field applications has been spotty at best. Times have changed, and so has our understanding of air injection-based oil recovery processes. Our available technologies for accessing and producing the reservoir and our emphasis on reducing environmental impacts have changed as well. In short, the industry is smarter, has better technology, and maintains a significant commitment to sustainable resource development. This paper reviews portions of the past history of air injection in Canadian heavy oil and bitumen reservoirs; discusses the significant advances in our understanding of the in-situ process; reviews currently successful air-injection projects; summarizes the keys to successful implementation of air-injection-based recovery processes; and proposes several novel applications of air injection, including hybrid processes with steam or vapour solvent, in-situ upgrading, in-situ steam generation, and in-situ gasification.

Investigation of the Oxidation Behaviour of Pure Hydrocarbon Components and Crude Oils Utilizing PDSC Thermal Technique

High Pressure Air Injection (HPAI) is an Improved Oil Recovery (lOR) technique in which compressed air is injected into light oil, high-pressure reservoirs. The objective of this process is the oxygen from the injected air reacts with a small fraction of the reservoir oil at an elevated temperature to produce a mixture of carbon dioxide and nitrogen. The produced gas flowing from the reaction region mobilizes the oil downstream of the reaction zone towards the production wells. Knowledge of the oils oxidation behaviour is a key to the successful implementation of this process. However, information on oxidation behaviour of oils based on their compositions is limited, especially for light oils. An experimental study was designed to examine the oxidation behaviour of three crude oils (a light oil, a medium oil, and an Athabasca bitumen) by using the Pressurized Differential Scanning Calorimeter (PDSC) at pressures from 110 to 6.894 kPa. Pure hydrocarbon aromatics and paraffin samples were also selected for the current study. The study shows an increase of pressure results in an increase in the rate of oxidation reactions and heat released from the oxidation reactions. The PDSC heat flow curves also clearly demonstrate the effect of chemical structure of the samples on their oxidation behaviour. The extent of oxidation of hydrocarbon samples is strongly dependent on the nature of the hydrocarbon.

Screening of Three Light-Oil Reservoirs for Application of Air Injection Process by Accelerating Rate Calorimetric and TG/PDSC Tests

Sarma, H.K., Yazawa, N., Moore, R.G., Mehta, S.A., Okazawa, N.E., Ferguson, H. and Ursenbach, M.G.

Numerical Simulation of In-Situ Combustion Experiments Operated Under Low Temperature Conditions

During in-situ combustion (ISC) processes, different chemical reactions occur depending on the temperature level. In heavy oils and bitumens, low temperature oxidation (LTO) reactions dominate below 300°C, increasing the density and viscosity and producing coke which could prevent the success of ISC. Above 350°C, combustion reactions dominate, known as high temperature oxidation (HTO), producing carbon oxides and water. Numerical models tend to include only thermal cracking and HTO reactions, as LTO reactions are not well understood. In the present work, ISC experiments operated under LTO were simulated, using Saturates, Aromatics, Resins and Asphaltenes (SARA) fractions to characterize the Athabasca bitumen. Concentration profiles and coke deposition for individual temperatures were matched for isothermal experiments from 60°C to 150°C. Based on these results, ramped temperature oxidation (RTO) experiments were then modelled, incorporating the heat of reaction at LTO. Different reaction models were studied to match temperature profiles along the reactor, oxygen consumption, coke formation and fluids production. This research will greatly increase the understanding of LTO reactions occurring in Athabasca bitumen during ISC and contribute to the creation of a reliable numerical model that predicts ISC performance under ideal (HTO) and, importantly, non-ideal (LTO) temperature conditions.

Oxidation and Ignition Behaviour of Saturated Hydrocarbon Samples With Crude Oils Using TG/DTG and DTA Thermal Analysis Techniques

This research is aimed at providing a better understanding of the oxidation behaviour of fractions of crude oil, and to then develop an approach to improve ignition for air injection processes. In this research, Thermogravimetric and Differential Thermal Analysis (TG/DTA) techniques were used to investigate oxidation behaviour using thermal fingerprinting effects on pure paraffin samples and mixtures of pure components with crude oil. The results demonstrated that each paraffin sample shows different oxidation behaviours at low temperatures and high temperatures. The fractions lighter than C16 distill before they reach a temperature where oxidation reactions are significant. Only low temperature exothermic activities are apparent for the fractions between C16 and C26. The heavier fractions show both low and high temperature exothermic activities. The lower molecular weight samples show lower onset temperatures for oxidation reactions. With increasing molecular weight, the exothermic peak temperatures both in the low and high temperature regions shift to higher temperatures and increased energy release. When low activity Oil B apd the more reactive Oil C were mixed with a small amount of paraffin sample heavier than C26, both crude oils showed intensified low temperature oxidation behaviour, with a greater magnitude of heat evolution. The addition of heavier paraffins offers the potential to accelerate reactions and improve ignition.

New Insights Into Enriched-Air In-Situ Combustion

This paper presents the results of 10 enriched-air in-situ combustion-tube tests performed on core from the Athabasca oil sands deposit. The tests show that at high pressures, the use of oxygen-enriched air results in increased low-temperature reactions between the oxygen and the oil, resulting in an increased fuel load and decreased burn stability. Although water injection may enhance the performance of oxygen combustion, it may also lead to increased oxygen storage in the swept zone.

New Insights Into Oxidation Behaviours of Crude Oils

Systematic studies are performed to investigate oxidation behaviour of three different types of crude oils (light oil, medium oil and Athabasca bitumen) by using two thermal analysis techniques: Thermogravimetry and Pressurized Differential Scanning Calorimetry. This study is also to look at the effect of pressure on energy generation associated with oxidation reactions in different temperature ranges. It is observed that oxidation behaviours for light and medium oils are substantially different from those of Athabasca bitumen. The difference is seen in the temperature ranges where signif- icant oxidation reactions occur. The experimental data in this work provide further evidence and addresses the difference in the oxidation behaviour of light oil and heavy oil.