In-situ Combustion Research Articles

Catalytic capacity evolution of montmorillonite in in-situ combustion of heavy oil

Clay minerals such as montmorillonite are significant in petroleum storage and recovery. Montmorillonite (Mt) is a natural solid acid catalyst containing Brønsted and Lewis acid sites and can catalyze heavy oil oxidation (HOO) during in-situ combustion (ISC). However, its catalytic activity largely depends on the heating process of heavy oil. In the study, the catalytic capacity evolution of Mt in ISC of heavy oil was explored with the isoconversional method and thermal analysis. In low-temperature oxidation (LTO) and high-temperature oxidation (HTO) stages, the addition of Mt largely reduced the peak temperatures (Tpeak) of DTA and DTG and the Tpeak of H2O (LTO and HTO stages) and CO2 (HTO stage) in HOO. Notably, Mt did not always show the positive catalytic effect. In LTO stage, the thermal transformation process had a small effect on DTA Tpeak, Tpeak of H2O and CO2, and the reaction activation energy (Eα) of HOO. In HTO stage, the catalytic effect of Mt on HOO was related to its thermal transformation process, especially interlayer water (IW) dehydration and dehydroxylation. In HTO stage, the IW dehydration process of Mt showed the strongest catalytic effect on HOO, significantly reduced DTA Tpeak and Eα, and resulted in the lowest Tpeak of H2O and CO2. The dehydroxylation process of Mt also showed a certain effect, whereas the overlapping process between the dehydration (IW) reaction and partial dehydroxylation reaction of Mt had no positive catalytic effect on HOO. DTA, TG-FTIR, and non-isothermal kinetic analysis further confirmed that the catalytic capacity of Mt in HTO stage was improved by IW dehydration process of Mt and weakened by the dehydroxylation process of Mt.

A Novel Approach in Understanding the Role of Water in Oxidation and Upgrading Reactions during In-Situ Combustion Oil Recovery, Part B: Interpretations

Summary To understand the role of connate water as a source of hydrogen in oxidation and upgrading of bituminous oil at high temperature, heavy water (D2O) and O-18 enriched water (H2O18) were used as connate water in two different in-situ combustion experiments using a conical tube. Aside from a fundamental understanding of the role of such reactions in in-situ combustion, the results could also potentially help in optimizing in-situ hydrogen generation and upgrading of heavy and bituminous oil. The conical tube had previously been used for understanding the impact of air flux in sustaining the combustion front (please see Alamatsaz et al. 2011Alamatsaz et al. 2012,2). Significant upgrading was observed in these tests with a produced API gravity of 35 °API compared to the original bitumen gravity of 9 °API. The produced fluids (gases and water) were analyzed with a mass spectrometer to demonstrate the effectiveness of using D2O and H2O18 as tracers in bitumen upgrading reactions and specifically to determine whether the H2O18 would be more effective than D2O in understanding the role of connate water. It was found that heavy water exchanges too readily with hydrogen atoms in the bitumen when the two are mixed. As a result, it could not be reliably used as an indicator for identifying the role of water. The run with O-18 enriched water, however, provided a better indication of water participation in the oxidation reactions. The results obtained from the mass spectrometry analysis of evolved gases and water samples collected in the second test showed that water does split during the reaction and O atoms of indigenous water molecules do combine with C atoms (from the hydrocarbon) to form CO2. These findings open the path for mechanistic considerations around the processes taking place during in-situ combustion and in-situ upgrading reactions.

A Novel Approach in Understanding the Role of Water in Oxidation and Upgrading Reactions during In-Situ Combustion Oil Recovery, Part A: Experimental Observations

Summary To understand the role of connate water as a source of hydrogen in oxidation and upgrading of bituminous oil at high temperature, heavy water (D2O) and O-18 enriched water (H2O18) were used as connate water in two different in-situ combustion experiments using a conical tube. Aside from fundamental understanding of the role of such reactions in in-situ combustion, the results could also potentially help in optimizing in-situ hydrogen generation and upgrading of heavy and bituminous oil. The conical tube had previously been used for understanding the impact of air flux (AF) in sustaining the combustion front (Alamatsaz et al. 2011). Significant upgrading was observed in these tests with a produced API gravity of 35 ° compared to the original bitumen gravity of 9 °API. This paper (Part A) deals with the experimental results including a comparison between conical tube and a combustion tube (CT) results. A subsequent paper (Part B) will discuss the upgrading aspects and the mass spectrometry results.

Reservoir Properties Alteration in Carbonate Rocks after In-Situ Combustion

Summary This study summarizes the work conducted as a part of laboratory modeling of in-situ combustion (ISC) experiments on cores from carbonate heavy oil fields. Porosity, permeability, fluid saturation, thermal, and geochemical properties are crucial characteristics of the target field defining the performance of the combustion technology. Here, we report the changes in reservoir properties, porous structure, and mineral composition of the rock samples induced by the thermal exposure and registered by a set of standard and advanced experimental techniques. Most combustion tests are conducted on the crushed core pack, which does not accurately represent the reservoir properties. In this paper, we present the results of three combustion tube tests (classic ISC and consecutive hot-water treatment ISC) involving actual field core samples. Gas porosimetry, nuclear magnetic resonance (NMR), and microcomputed tomography (μCT) revealed an increase in total porosity and pore size distribution and enabled visualizing the changes in the porous core structure at nano- and microlevels. X-ray diffraction (XRD) and scanning electron microscopy (SEM) demonstrated the change in mineral composition and lithological texture as a result of dolomite decomposition; Rock-Eval pyrolysis and elemental analysis were utilized to confirm the changes in the rock matrix. Optical scanning registered the changes in thermal conductivity (TC) of samples, which is important for numerical modeling of the combustion process. The proposed core analysis has proved its efficiency in providing a complete petrophysical description of the core of a heavy oil carbonate reservoir in the framework of evaluation of the ISC application for dolomite-rich carbonates and demonstrated the different responses of rock to the ISC technology.

Simulation of stability or failure of a combustion front during in-situ combustion in a Post-SAGD process

The highly viscous nature of heavy oil/bitumen in the Lloydminster area leads to difficulty for oil recovery and production. In-situ combustion (ISC) is an attractive candidate as a post-SAGD (steam assisted gravity drainage) operation to improve oil mobilization and maximize oil production. The objective of the study was to demonstrate that the stability or failure of a combustion front when in-situ combustion is implemented in a post-SAGD reservoir can be realistically simulated on the basis of a sound understanding of the underlying chemical reactions, whose rates and stoichiometry have been determined from laboratory measurements. This accomplishment represents a significant step towards an improved application of the in-situ combustion processes.The simulations were performed with the Computer Modelling Group's (CMG) commercial simulator STARS. Four dominant ISC chemical reactions (i.e., pyrolysis of non-volatile oil, low-temperature oxidation, pyrolysis of partially oxidized oil, and combustion) were developed on the basis of available experimental data. Material and energy balances were applied. A representative fluid properties package was obtained by tuning components' parameters to match with available vapor-liquid equilibrium data. ISC was initiated after the steam-assisted gravity drainage stage had been simulated. By successively reducing the simulated initial (pre-SAGD) oil saturation in steps, it was shown that the combustion front changed from stable propagation to being extinguished at a low initial oil saturation around 0.06, for which a combustion-front temperature of 400 °C was maintained. The residual oil saturation approached zero after combustion.

The Geoscience of In-Situ Combustion and High-Pressure Air Injection

Considering the global drive toward net-zero carbon emissions in the near future, the need to find clean sources of energy has never been more important. It is estimated that globally there are tens of thousands of depleted and abandoned oil fields that may be adapted to produce green energy. These may be re-cycled with the help of air injection, either from the production of hydrogen, as a direct result of oxidation of oil, or the exploitation of the inherent increase in heat flow and pressure via enhanced geothermal systems. In the past, the use of in-situ combustion (ISC) and high-pressure air injection (HPAI) have experienced many failures, largely due to poor project design and inappropriate reservoir selection. Here, we review data from field applications, experimental studies, and numerical modelling to define the roles of sub-surface sedimentology and petrophysics, structural geology, geomechanics, mineralogy, diagenesis, and petroleum geology on the success of ISC and HPAI. We show how current knowledge can help mitigate project failure via improved project design and initial reservoir selection. Improvements to the design and implementation of ISC and HPAI projects promise to allow the utilisation of the many abandoned oil fields, to produce green energy with the added benefit of the cost-effective, and materials and energy efficient, re-use of existing oil field infrastructure. We conclude that the integration of field data, laboratory experiments, and numerical modelling methods previously studied can be used to help develop ISC and minimize risk of failure.

Comparative Study of In-Situ Combustion Tests on Consolidated and Crushed Cores

Summary A significant amount of oil is contained in carbonate reservoirs, but only half of that oil can be produced by secondary enhanced oil recovery (EOR) methods. However, substantial improvements were made in EOR techniques and the prediction of carbonate reservoir performance within the last decades. Nevertheless, existing flow-simulation computer programs failed to provide a reliable prediction of such reservoirs due to their high heterogeneity and the reactivity of the rock. Potentially, in-situ combustion (ISC) is considered effective in developing heavy oils in carbonate reservoirs. The combustion reactions between crude oil and heterogeneous rock matrices introduce additional complexity to the simulation process. Also, most of the laboratory experiments studying the reaction kinetics of the ISC process are performed on the crushed core. However, to minimize the risks, improve the control of the process, and overcome upscaling issues, physical simulation must be carried out under conditions as close to the reservoir as possible. Consolidated core material in combustion tube (CT) experiments is desirable for better simulating some reservoir conditions with synthetic packs and for the cases when actual preserved reservoir core material may be available. Studying the relative effects of porosity and packing properties (specific surface area, sand grain distribution, and cementation) on the fuel is essential to evaluating the process under actual field conditions. This work presents a set of medium-pressure CT (MPCT) tests on crushed and consolidated cores and analyzes the differences, limitations, and performances of both approaches. Two MPCT tests were performed to evaluate the ISC feasibility on the heavy-oil carbonate reservoir with an initial oil saturation level of 0.38 to 0.50. According to previously published experimental results, such oil saturation levels can help avoid oil banking. Both experiments were conducted at reservoir conditions to consider the phase behavior at elevated pressures and temperatures. The method used in this research allows approbation of the methodology of ISC tests using consolidated core at high pressure, ensuring pack and process integrity during the experiment. The influence of consolidated core caused by significantly lower porosity and more uniform porous media elements than those made with unconsolidated material on combustion performance was assessed. Valuable data for different variations of combustion experiments were generated. This work compared two tests and presented the combustion parameters for a stabilized combustion period, such as fuel and air requirements, recovery efficiency, front velocity, and composition of produced gases. The research intends to demonstrate the potential application problems and address issues that might arise during ISC application on target reservoirs, including the higher air flux required for lower porosity of consolidated core samples. The experimental results performed under conditions closest to reservoir conditions are essential for further predictions and affect the ISC performance during pilot tests.

Athabasca Toe-to-Heel Air Injection Pilot: Evaluation of the Spontaneous Ignition Based on Apparent Atomic Hydrogen-Carbon Ratio Variation

Summary An in-depth analysis was performed to determine the ignition delay via the enhanced spontaneous ignition (ESI) method on three well pairs (each pair constituted by one vertical injector and one horizontal producer) belonging to the Toe-To-Heel Air Injection (THAI) pilot in Athabasca. ESI consisted of preheating of the surroundings of injection wells by injecting a steam slug for 3 to 4 months just before starting air injection. At first, the ignition delay had been determined based on both the oil production and on the bottomhole temperatures (BHTs) recorded in the observation wells as well as at the toe of the horizontal producer. For the purposes of this paper, a more rigorous evaluation was carried out based on the variation in time of the apparent atomic hydrogen-carbon ratio (AAHCR) calculated from detailed gas analyses for a long period of time. AAHCR is a very strong synthetic parameter giving a direct indication of the peak temperature value before, during, and after the in-situ combustion (ISC) front is generated. Therefore, it provides complete information on the occurrence of high-temperature oxidation and low-temperature oxidation (LTO) reactions. Using the variation of the AAHCR, it was found that the ignition time was shorter than those determined by the previously mentioned methods. In the case of first well pair, ignition took 3 weeks as compared to the 1 month determined by the previous methods. The second well pair ignited in 1 month as compared to the previously calculated 2 months, and for the third well pair, ignition time was approximately 2 months in both cases. As an additional and complementary approach, estimation of the ignition time was also based on the variation of individual components of the produced gas. This allowed for the discovery of a new method for ignition time determination. This was possible in the THAI process, unlike conventional ISC processes, significant concentrations of hydrogen (H2) are produced, and the interpretation of its variation can give an indication of the ignition time. The new method is very simple to use, as the percentage of hydrogen in the produced gas starts to take off only after the full establishment of an ISC front, as hydrogen production is associated with high-temperature bond scission reactions in the ISC front. In general, the ignition delay is overestimated to some degree when using this method.

New Insights into the Understanding of In-Situ Combustion: Important Considerations When Modeling the Process

Summary Air-injection-based enhanced oil recovery (EOR) processes have historically been of great interest due to their high recovery potential and applicability to a wide range of reservoirs where other processes are not effective or economical. However, most operators require a certain level of confidence in the potential recovery from these (or any) process before committing resources; this is commonly achieved with the support of laboratory and reservoir simulation studies. Laboratory testing, including combustion tube, ramped temperature oxidation (RTO), and accelerating rate calorimeter (ARC) tests, can supply data for simple analytical models. It can also provide important insights into potential oxidation behaviors and oil recovery mechanisms. Similarly, reservoir simulation of some of those experiments can assist in the understanding of the process and may allow for the development of kinetic models that can be used for further reservoir modeling. However, due to sample size limitation and the unscaled nature of the experiments, these tests are not ideally suited to provide detailed or unique kinetic data for direct use in numerical simulators. In fact, the oxidation reactions are sufficiently complex that, regardless of how robust a thermal reservoir simulator may be, its predictive capability strongly depends on the engineer’s understanding of the process and ability to model the most relevant oxidation behaviors of the particular hydrocarbon reservoir under study. Over the past 50 years, the In-Situ Combustion Research Group (ISCRG) at the University of Calgary has dedicated its efforts toward the advancement of this technology. Under the leadership of Professor Gordon Moore, the ISCRG has performed a large number of combustion tests, designed and carried out many novel oxidation experiments, and also made important contributions to the numerical modeling of air-injection-based processes. Nevertheless, in spite of its long research history, the group acknowledges that there is still much that needs to be learned about the process. For example, two oils with the same physical properties such as viscosity and density can have significantly different oxidation behaviors, which are difficult to predict; this is one of the reasons the group continues to perform laboratory experiments and conduct research in this area. This paper describes some of the most important conceptual contributions made by the ISCRG based on their experimental results and how they have enhanced our understanding of the process. These continue to be an important source of knowledge toward the development of predictive reservoir simulation models, as it is very difficult, if not impossible, to properly model a physical problem one does not understand well. For instance, the fundamental equations used for mathematical modeling depend on selecting of the relevant physical mechanisms and assumptions made, and these are derived from experimental work. Similarly, when using a commercial numerical simulator, the selection of fluid pseudocomponents as well as their physical properties and chemical reactions, as well as their kinetic parameters, also depend on an understanding of the process. This paper provides a summary of the relevant physical aspects to consider when modeling the in-situ combustion (ISC) process as well as new insights on its dynamics based on the laboratory experiments performed by the ISCRG.

Insights into in-situ upgrading of bitumen in the hybrid of steam and combustion process: From experimental analysis aspects

In situ combustion (ISC) has been evaluated as a follow up process in the steam injection process for heavy oil and bitumen recovery. Except for providing energy or heat to reduce bitumen viscosity, in situ upgrading of bitumen is another advantage of ISC process. In situ upgrading of bitumen through co-injection of steam and oxygen is evaluated in this work. Three different types of laboratory experiments, including one static thermal cracking experiment, one ramped temperature oxidation (RTO) experiment, and one combustion tube test, were performed to examine the produced oil properties and the potential of bitumen in situ upgrading. A comprehensive analysis of produced oil properties and gas composition was performed. Bitumen was significantly upgraded in the thermal cracking experiment at a temperature of 430 °C, in which Saturates fraction increased to 56%, while Resin and Asphaltene fractions reduced to 6.7% and 6.8%, respectively. The thermal cracking of Resin and Asphaltene contribute to the production of the light oil and gases, leading to the upgrading of the bitumen. Dynamic properties of produced oil were measured in the RTO and combustion tube test in terms of produced oil viscosity, density, boiling point temperature distribution, and produced oil compositions, etc. In the RTO test, the extent of bitumen upgrading is greater with the increase of temperature, further proving that the high temperature generated by the combustion front is able to effectively crack the bitumen. Furthermore, the lack of light hydrocarbon in the produced oil indicates light hydrocarbon participates in the high temperature oxidation reactions. Different from thermal cracking experiment and RTO test results, combustion tube test results indicated that the bitumen was slightly upgraded in late stage of the combustion tube test and most produced bitumen are similar with original bitumen. By examining the temperature distribution along the combustion tube, it is found that upgraded bitumen cannot be effectively displaced to the producer. This implies the limitation of in situ upgrading in the conventional in situ combustion process. Proper well configuration was recommended for the future field application of the hybrid steam and combustion process to achieve the high oil recovery factor and partial in situ upgrading of bitumen.

Methods to Enhance Success of Field Application of In-Situ Combustion for Heavy Oil Recovery

Summary While much has been learned in the laboratory over the past four decades about the in-situ combustion (ISC) process, especially through carefully conducted physical model experiments, and many advancements in numerical simulation capability have been achieved, successful field application of ISC remains a rarity. This paper discusses challenges that have been faced in moving from laboratory to field and some strategies that may be used for improving the success rate. There is a brief discussion of the advantages and disadvantages of ISC as a recovery method and comparisons with steam injection, which is the dominant thermal recovery method used in the field. A discussion of the challenges and progress made in numerical simulation is provided with the suggestion that such mathematical modeling can now be a useful tool in designing field projects and can increase the probability of success. The needs of industry to operate safe, simple, and economically and environmentally sustainable projects are discussed along with the currently negative perception of the ISC process in industry. The paper makes some suggestions regarding how to address these issues. The main thesis of this paper is that air injection into a reservoir introduces a large amount of nitrogen that is detrimental to the displacement of oil, and oil recovery yet offers few, if any, advantages. Reducing the amount of noncondensable gas (NCG) associated with the process can be done mainly in two ways—by using oxygen-enriched air injection and furthermore by injecting a mixture of steam and oxygen-enriched air. The paper does not make a comprehensive review of past field projects but does include a summary of promising areas for future application of the ISC combustion recovery process.

Simulation tool for the analysis of in-situ combustion experiments that considers complex kinetic schemes and detailed mass transfer- theoretical analysis of the gas phase CO oxidation reaction

A simulation tool was designed for analyzing various experimental setups that include the ability to model detailed chemical reaction schemes for in-situ combustion (ISC) analysis.,. The simulation tool was illustrated with a theoretical example to the extent of CO oxidation in a gaseous phase takes place during ISC. The models in the simulation tool are based on fundamental conservation laws, physical correlations for porous media properties, and property databases available in literature. Emphasis is made on the analysis of chemical reactions in the gas phase, a characteristic that may be useful when temperatures are above 700°C and oxygen, unburned hydrocarbons, and CO coexist. The three modules of the simulation tool: (i) Kinetic cell, (ii) One-dimensional reactor, and (iii) Combustion tube, can be used to represent in detail the processes taking place in the typical laboratory-scale equipment used to characterize ISC. Tools for the analysis of transport phenomena and multiphase reactions, present in all three models, can support the process of finding chemical kinetic parameters for an easier calculation of device-independent kinetic constants. Four applications have the simulator scope: (i) Analysis of reactions in the gas phase, (ii) Axial gradients in a kinetic cell, (iii) Pressure build-up in a combustion tube, and (iv) Ignition in a combustion tube. These examples highlight the importance that homogeneous reactions may have in these systems and the existence, under certain conditions, of concentration gradients that are normally neglected, and can affect the interpretation of ISC experiments.

New Insights into the Understanding of In-Situ Combustion: The Nature of the Fuel and the Role of Operating Pressure

Summary Historically, the air injection literature has stated that the fuel for the in-situ combustion (ISC) process is the carbon-rich, solid-like residue resulting from distillation, oxidation, and thermal cracking of the residual oil near the combustion front, commonly referred to as “coke.” At first glance, that assumption appears sound, because many combustion tube (CT) tests reveal a “coke bank” at the point of termination of the combustion front. However, when one examines both the laboratory results from tests conducted on various oils at reservoir conditions and historical field data from different sources, the conclusion may be different from what has been assumed. For instance, CT tests performed on light oils, at elevated pressures, rarely display any significant sign of coke deposition, which would make them poor candidates for air injection; nevertheless, they have been some of the most successful ISC projects. An analysis of different ramped temperature cracking (RTC) and ramped temperature oxidation (RTO) experiments performed on oil samples ranging from 6.5 to 38.8 °API, at reservoir pressures, indicates that thermal cracking and oxidation do not tend to generate enough coke to sustain the ISC process in light oil reservoirs. Similarly, peak temperatures observed during RTO and CT tests performed on lighter oils, at high pressures, were below the levels required to be associated with the combustion of coke. Instead, RTC and RTO experiments indicate that flammable vapors are also generated and can be consumed as fuel, in a behavior that is consistent across the entire oil density spectrum. Such vapor fuel appears to be the result of oxidative and thermal cracking of original and oxidized oil fractions. Therefore, while coke may form as a result of low-temperature oxidation of heavy oil fractions, and while thermal cracking of those fractions on the pathway to coke may produce vapor components that may themselves burn, the coke itself is not necessarily the main fuel for the process, particularly for lighter oils. This paper presents new insights regarding the nature of the fuel utilized by the ISC process and the role played by the different hydrocarbon phases present. It discusses the fundamental aspects associated with the proposed theory, and it summarizes the laboratory evidence and the field evidence which support the concept. This new theory does still share much common ground with the current understanding of the ISC process, but with a twist. The new insights result from the analysis of laboratory tests performed on lighter oils at reservoir pressures; data that were not available at the time the original ISC concepts were developed. This material suggests a change to one of the most important paradigms related to the ISC process, which is the nature of the fuel. This affects the way we understand the process but provides a unified theory, which is important for the modeling efforts and overall development of the technology.

Superior Creep Resistance and Remnant Strength of Novel Tempered Ferritic-Martensitic Steels Designed by Element Addition.

The in situ combustion (ISC) technique is promisingly applied in heavy oil recovery, whereas the operation inevitably causes high temperature and high pressure for a long duration in the thermal recovery well. As a critical component, oil casing, traditionally made of plain carbon steel in China, generally suffers from poor creep resistance and degraded remnant strength under such a harsh environment, which leads to frequent casing damage and inferior recovery efficiency. In this study, a strategy was adopted to tackle the issue by adding chromium (Cr) element into the plain carbon steel. We designed two types of novel steel with the respective addition of 1 wt.% and 13 wt.% Cr element into plain carbon steel for oil casing. Surprisingly, the trace addition of Cr element with 1 wt.% effectively lowered the creep rate in a creep test at 600 °C and 400 MPa and maintained high remnant tensile strength after creep. More significantly, prior creep history dramatically enhanced remnant strength when Cr element was added up to 13 wt.%. After a long-term creep time of 96 h, the samples were conferred by a stress increment of ~92.5 MPa (~11.0%) relative to the creep-free counterparts, whereas the value was reduced by ~158.4 MPa (~17.8%) for plain carbon steel under the same deformation conditions. Such superior mechanical performances in the Cr-doped steels are mainly ascribed to precipitation retardation of carbides and sluggish precipitate coarsening, which continuously favors a precipitation–strengthening effect in steel. These findings provide a fundamental understanding of precipitation response and creep behaviors and, more importantly, enable the development of high-performance steels used in the field of unconventional petroleum and gas resources.

Optimization and uncertainty quantification of in situ combustion chemical reaction models

Heavy oil, deep, and waterflooded reservoirs contain significant petroleum resources but present many unique challenges for oil recovery. In situ combustion (ISC) is a thermal enhanced oil recovery method that has been proposed for such reservoirs. A persistent challenge in understanding ISC is modeling the underlying chemical reactions. While many different reaction models have been proposed, these models are typically developed on an ad-hoc basis for individual crude oil samples and manually calibrated to experimental data. While some work exists on applying optimization-based approaches to reaction calibration, existing approaches are not fully-generalized nor do they quantify uncertainty in the estimated parameters. Here we present such an approach for calibrating and quantifying uncertainty in ISC chemical reaction parameters. The workflow presented is generalized to any hydrocarbon pseudocomponent-based reaction model of ISC, provides a framework for quantification of uncertainty in estimated parameters, and is fully automated. Thus, no parameter initialization or manual calibration is needed. We apply this workflow to characterization of a heavy crude oil sample and demonstrate the capability of this workflow to predict ISC oxidation kinetics and upscale to a combustion tube simulation. Overall, this work provides an algorithmic approach to calibrating ISC kinetics that enables quantitative analysis and comparison of oil types, reaction models, and reservoir conditions for ISC.

Cyclic In-Situ Combustion Process for Improved Heavy Oil Recovery after Cyclic Steam Stimulation

Summary Cyclic in-situ combustion (ISC) is a novel process with great potential for thermal enhanced oil recovery (EOR). In this study, a 3D physical simulation experiment of cyclic ISC after cyclic steam stimulation (CSS) was carried out for the first time. The mass loss during heavy oil oxidation was studied by thermogravimetry (TG) and the preheating temperature of sandpack was determined by differential scanning calorimeter (DSC). The oxidation process of heavy oil in a porous medium was investigated by a heavy oil static oxidation experiment. The development characteristics and EOR mechanism of cyclic ISC after CSS were studied through 3D physical simulation experiments and the characteristics of the coking zone was studied by scanning electron microscope (SEM) and computed tomography (CT). The results of the thermal analysis indicate that three different regions were observed with increasing temperature: low-temperature oxidation zone (LTO), fuel deposition zone (FD), and high-temperature oxidation zone (HTO). When the temperature reaches 480°C, the mixed oil sand has the most exothermic effect and the high-temperature oxidation reaction is the most vigorous. The results of the 3D physical simulation show that steam channeling and steam overlay in CSS reduced the swept volume of steam and heat usage rate. During the cyclic ISC, the oil bank can overcome the heterogeneity of the oil reservoir caused by steam channeling and steam overlay, which makes the combustion front move forward smoothly. Cyclic ISC can greatly increase the temperature of the zone near the well, and upgrade the crude oil through cracking to reduce the viscosity of heavy oil. The foaming oil formed by the dissolution of flue gas improves the fluidity of the crude oil. The oil recovery of CSS is 19.3%, and the oil recovery of cyclic ISC increased by 13.2%. SEM and CT show that flake black solid coke was attached to the surface of the sand at the coking zone. The coking zone is a porous medium structure with a porosity of 35.14%, which has little effect on the oil recovery in the process of cyclic ISC.

Effect of secondary water body on the in-situ combustion behaviors

In-situ combustion (ISC) is an effective alternative method for the development of heavy oil reservoirs, especially in the later stage of steam injection and a large majority of high water-saturated channels have been formed during this phase. The water-saturated channels, also known as secondary water body (SWB), is regarded as a sensitive factor to the ISC performance. The effect of the SWB with different scales and locations was investigated by using combustion tube experiments. Results show that the existence of SWB is conducive to improving the propagation speed of combustion front combined with the reduction of combustion stability during the ISC process. As combustion front propagates to the SWB, the temperature is quickly decreased accompanied by an unstable propagation process, which inevitably induces the significant reduction of the O2 availability and COx emission concentration. Additionally, oversized SWB would lead to a worse combustion process with much lower COx concentration and O2 availability or even fall into an extinguishment process. Better combustion performance and oil recovery factor are obtained when SWB has large spacing to the gas injection well or exists in the lower layer. Whereas the premature O2 breakthrough and unstable fire front propagation are generated if the SWB is close to the gas injection well or forms in the upper layer. The findings of this study are significant for better understanding the ISC performance with the consideration of SWB in heavy oil reservoirs.

Study on the technique of flue-gas detection and combustion state identification of in-situ combustion process

In this study, the relationship between the flue gases and combustion state of In-Situ Combustion(ISC) were systemically studied by analysis of combustion mechanism, simulate static and dynamic oil flooding experiments. On-site detection gas method was established and used for the detection the content of O2, CO2, H2S, CO, CH4 in the flue gases. The results showed that the CO2 content was higher than 10%, the O2 content was lower than 3%, and the range from 70-85% of N2 in the flue gases, it can be evaluated as high temperature burning state. The CH4 content in the flue gases was higher than 30%, the heavy oil reservoir would undergo hydro-thermal cracking reaction and the corresponding wells were in the combustion preheating stage. The gases content was conducted to evaluated the combustion state and ensure the safety of underground production Well. Based on that, the identification of combustion state and application in the fire flooding industrial pilot area of Hongqian-1 Wellblock was further explained. The results showed that 67% of ignition wells were in high temperature combustion state, and other 25% wells were evaluated as stalled. This study provided technique support for scheme formulation and production dynamic control.

Molecular composition of low-temperature oxidation products in a simulated crude oil In-situ combustion

In-situ combustion (ISC) is a thermal enhanced oil recovery process in which energy is generated by the combustion of a portion of the oil within the reservoir. Low temperature oxidation (LTO) is one of the dominant mechanisms controlling fuel availability in ISC and affects the physical properties of the crude oil, thus the characterization of the crude oil and its LTO products are essential for a better understanding of the ISC process. In this study, a thermal oxidation experiment of a heavy crude oil was carried out to investigate the molecular changes associated to coke formation during ISC. More than half of the component was depleted by combustion or thermal pyrolyzed out, leaving a coke-like solid in the reactor with a yield of a quarter by weight of the crude oil. More than 90% of the coke-like solid is toluene soluble. Condensate oil expelled from the reactor was collected with a yield of about 15 wt% of the crude oil. Small-molecule oxidation products, such as ketones, fatty acids, phenolic compounds were identified in the condensate by GC–MS. High-resolution mass spectrometry results showed that the molecular composition of oxygen- and sulfur-containing compounds changed largely, with the generation of highly oxygenated compounds and sulfoxides. A substantial portion of large-molecule hydrocarbons were survived and enriched in the residue. The main components in the toluene insoluble substance, namely oxidation coke, are methanol soluble and composed of highly oxygenated compounds. The results indicate that oxidation and thermal cracking are both the important reaction in the simulated ISC, the molecular composition is instructive for the understanding of pyrolysis and oxidation behavior of coke formation from the crude oil.

Experiments and simulations on factors affecting the stereoscopic fire flooding in heavy oil reservoirs

In-situ combustion (ISC) or fire flooding (FF) technology had been widely applicated in developing heavy oil reservoirs. Due to the complex physical and chemical processes, it is not easy to guarantee the high oil recovery. For thin layer reservoirs, vertical well mode of FF can achieve good results, but for thick layer reservoirs, the vertical producing degree of FF under vertical well pattern is low. Therefore, it is necessary to deepen the basic understanding of fire flooding under different well patterns and study the influencing factors for thick heavy oil reservoir. Stereoscopic fire flooding (SFF) mode is proposed in this paper, and the one-dimensional combustion tube and differential scanning calorimetry (DSC) experiments were introduced and designed. The heavy oil samples of G block in Liaohe oilfield in China were studied and the oxidation kinetic parameters were obtained by experiments. The applicability of oil samples for fire flooding was tested. The different fire flooding modes was compared and the influencing factors of SFF were analyzed through simulations. The results indicated that the temperature of high temperature oxidation (HTO) was above 450 °C. The CO2 content of the produced gas was more than 13% and the apparent HC atomic ratio was 1.28. DSC experiments showed the activation energy of HTO stage was 1.40 × 105 J/mol. The results indicated that the heavy oil samples can reach a high temperature combustion state. The SFF mode was simulated by CMG-STARS module based on the experimental results. The simulation results showed that SFF had better performance than FF of only vertical wells in oil recovery. The important factors of SFF, such as gas-injection rate, reservoir thickness, transverse permeability, vertical permeability, crude oil viscosity, formation dip angle and relative position of horizontal wells and the applicable conditions of SFF mode were analyzed and the optimum condition for SFF mode for each influencing factor was analyzed, and the conclusions were obtained.