S.A. Mehta

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.

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.

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.

In Situ Upgrading of Llancanelo Heavy Oil Using In Situ Combustion and a Downhole Catalyst Bed

There are vast heavy crude oil resources worldwide that are relatively uneconomical to produce and upgrade. However, there are novel processes available that can be employed in a downhole environment to upgrade these oils, resulting in significantly less sulphur content, and lowered densities and viscosities. A process that is especially favourable for downhole implementation is the use of in situ combustion to generate reactive upgrading gases, such as CO, and possibly H 2 , to drive oil over a near-well-bore heated bed of catalyst. Two laboratory combustion tube tests were completed to validate this concept. The first test used conventional in situ combustion tube packing and testing techniques, while the second test employed a heated catalyst bed in the downstream region of the combustion tube. A heavy crude oil from the Llancanelo field in Argentina was used for the testing. During the first test, this oil was found to be amenable to the in situ combustion process and exhibited stable combustion performance. Passing mobilized oil and combustion gases over the catalyst bed prior to production in the second test resulted in significant upgrading of the produced oil, including substantial decreases in oil density and viscosity. It is believed that the catalyst efficiently used CO, generated at the combustion front, via the water gas shift reaction to generate H 2 , which then reacted with the oil to effect upgrading. However, it was found that the presence of a large amount of coke on the post-test catalyst probably indicates the need for periodic regeneration. The presence of a heated production-end catalyst zone did not significantly affect the in situ combustion performance during the second test.

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.