High Pressure Air Injection Process Research Articles

A Comprehensive Approach to Modeling Air Injection-Based Enhanced Oil Recovery Processes

Summary Modeling of air-injection-based processes for enhanced oil recovery (EOR) is a challenging task, mostly due to the complexity of the chemical reactions taking place. Also, the applicability of currently available kinetic models is limited to the reservoir systems they were originally developed for. The objective of this study is to derive a general chemical reaction framework that could be used to develop a kinetic model for a variety of crude oils (i.e., light or heavy oils). The work is based on the modeling of high-pressure ramped temperature oxidation (HPRTO) experiments, and combustion tube (CT) tests, performed on two different oil systems: a volatile oil that is near critical at reservoir conditions (44 °API), and a bitumen sample (10 °API). The HPRTO test is a kinetic experiment that intends to mimic the flow conditions within the reservoir and allows the determination of kinetic parameters of the different reactions. On the other hand, the CT test is meant to provide quantitative information on the combustion performance that can be expected in the field. Therefore, a kinetic model was derived for each of the cases based on the history match of an HPRTO experiment. The resulting model was validated by history matching a CT test for each of the oils. An important feature of these experiments is that they were performed at representative reservoir pressure conditions. The modeling approach chosen is an extension of the methodology originally proposed by Belgrave et al. in 1993, which is arguably the most comprehensive kinetic model available in the air injection literature. However, their model was developed from experiments performed on Athabasca bitumen, and it fails to represent the high-pressure air injection process as it occurs in light oil reservoirs, which are typically encountered at higher pressure conditions. For example, Belgrave’s model is based on the deposition and combustion of semisolid residue commonly known as “coke,” which is rarely present during the combustion of light oils at high pressure. As in Belgrave’s model, this study also describes the original composition of the oil in terms of maltenes and asphaltenes. The main difference lies in the presence and importance of oxygen-induced cracking reactions, as well as the combustion of a liquid-vapor flammable hydrocarbon mixture that is generated by cracking and oxidation reactions, which take place in the gas phase. Also, a unique feature of these simulations is that, apart from history-matching traditional variables such as thermocouple temperatures, fluid recovery, and produced gas composition, they also capture changes in the physical properties of the produced oil, such as viscosity and density, as well as the amount of the residual phases in the post-test core. This enhancement to Belgrave’s reactions allows modeling the air injection process in cases where coke is not the main source of fuel, such as in high-pressure light oil reservoirs. This work changes a paradigm deeply rooted in the original in-situ combustion (ISC) theory, by deriving a general chemical reaction framework that is used to develop a kinetic model for two crude oils, which are at opposite ends of the density spectrum. This allows the consolidation of a new and comprehensive general theory for the description of the ISC process as applied to oil reservoirs. Moreover, as the pseudocomponents representing the fuel are not present in the original oil, the method is not limited to a fluid characterization in terms of maltenes and asphaltenes but could potentially be applied along with any type of characterization of the original oil.

Risk Assessment and Field Case Study on Oil/Natural Gas Explosion during High-Pressure Air Injection Process

Summary Air injection techniques have been widely applied in oil fields, but the associated safety issue of natural gas (NG) and oil explosion has been of great concern. In this study, explosion experiments of different NG compositions were conducted under high-pressure and high-temperature conditions (up to 15 MPa and 373 K) to reveal the necessary conditions for gas explosion in the air injection process. The experimental results indicate that the lower flammability limits (LFLs) and upper flammability limits (UFLs) of NGs change logarithmically with increasing pressure, which can significantly increase the explosion risk. The rise of temperature can also expand the flammability limit range. Based on the mechanisms and necessary conditions for NG and oil component explosion, fault tree analysis (FTA) models for explosion occurring during the air injection process were proposed that can provide valuable guidelines for designing anti-explosion procedures for field applications. Several explosion incidents that have occurred in air injection operations in different oil reservoirs are described, and the explosion mechanisms are analyzed. NG explosion can occur during air injection when NG is the main component present in the gas phase that can mix with air to form a combustible gas. For heavy oils with little NG, autoignited explosion of vaporized oil components can be the main reason for the incidents during the steam and air coinjection process because the autoignition temperature of heavy oil can be greatly reduced at high pressure.

Experimental assessment on the explosion pressure of CH4-Air mixtures at flammability limits under high pressure and temperature conditions

High-pressure air injection technique has been extensively used for enhanced oil recovery in oilfields. Yet, it is of great concern on the process safety in terms of the explosion of natural gas-air mixtures. To deeply understand the explosion characteristics in the air injection procedure, explosion experiments for methane (a main component of natural gas) and air mixture were conducted using a cylindrical vessel at elevated pressure and temperature situations. The explosion pressure, the pressure rise rate and deflagration index of CH4 and air mixtures in a closed chamber were investigated under pressure up to 15 MPa and temperature up to 100 °C, and the effect of CH4 concentration on explosion pressure was also examined. The results of this research can provide useful data to quantify the dependency of explosion risk parameters on pressure, temperature and gas concentration. The experimental results indicate that the explosion pressure at flammability limits of CH4 gradually increases with initial pressure, while it can be slightly declined at elevated temperatures. The pressure rise rate and deflagration index increase at high pressures, but these values become lower at higher temperatures. At lower flammability limits and upper flammability limits of CH4-air mixtures, the explosion pressure can be greatly reduced due to the presence of insufficient combustible gas or high content of inerting gas (N2). The explosion pressure data reported in this study can provide guidelines for the prevention and mitigation of explosion disasters in high-pressure air injection process.

High-pressure air injection laboratory-scale numerical models of oxidation experiments for Kirsanovskoye oil field

High-Pressure Air Injection (HPAI) as an enhanced oil recovery (EOR) method has a high potential and has already been effectively applied for carbonate reservoirs development. The target object of the current research is a Kirsanovskoe oil field confined to the North Kinelsky oil and gas region. Kirsanovskoye field is a carbonate reservoir with an average depth in the range of 1300–1350 m, average porosity of 11.5%, and average permeability of 70.6 mD.The HPAI process, which includes intensive oxidation and combustion reactions, phase transitions of components and change in the composition and properties of coexisting phases, is not fully explored yet. Its complexity and lack of reliable chemical and kinetic models both for light and heavy oils cause several limiting factors for the construction of a field numerical model with the high predicting level in the respect to the HPAI as the EOR method.The presented work is devoted to the construction and validation of laboratory-scale numerical models of oxidation experiments to provide proper HPAI kinetic model for oxidation and combustion reactions for the Kirsanovskoye oil field. For these purposes, high-pressure ramped temperature oxidation (HPRTO) and subsequent Medium pressure combustion tube (MPCT) experiments were conducted and analyzed. HPRTO test is used for the determination of the reaction kinetics together with such characteristics as a function of temperature, O2 uptake, CO2 generation, oxidation front velocity, peak temperatures, residual coke, and amount of burned and recovered oil. MPCT provides information on stoichiometry for the high-temperature process and optimal airflow rate. A significant part of the research is dedicated to the construction of 3D numerical models (multilayer design, proper heater regime, etc.) of HPRTO and MPCT experiments to avoid constructional uncertainties and their further validation against the experimental data. To describe the chemical behavior of hydrocarbons during the HPAI process we use the reaction scheme which includes polymerization of Malthenes and Asphaltenes in low-temperature oxidation region, thermal cracking and coke combustion in the high-temperature oxidation region.

High pressure air injection kinetic model for Bazhenov Shale Formation based on a set of oxidation studies

Modeling of high pressure air injection (HPAI) is a complicated process, where many parameters must be taken into account. One of the key aspects is to build a chemical reactions model for HPAI process, especially in oil shales, which is still under development. For successful HPAI implementation in the field, numerous laboratory and numerical studies must be done.The purpose of this study was to develop a HPAI kinetic model for Bazhenov Shale Formation by applying a complex approach including a set of oxidation experiments and complementary numerical simulation.Oxidation behavior of Bazhenov shales was studied by accelerating rate calorimetry (ARC), ramped-temperature oxidation (RTO) and pressurized differential scanning calorimetry (PDSC). Based on obtained data and experimental observations, the basic set of chemical reactions was proposed. It can represent an oxidation behavior and chemical changes of both oil and kerogen, occurring in HPAI process in Bazhenov Formation. Moreover, reactions kinetic model was developed. During validation of the numerical model with the experimental results, it was revealed that kerogen or its derivatives undergo oxidation in several temperature regions. Therefore, it should be represented by individual pseudo-components, which reflect their different physical-chemical properties. As a result, a minimum set of kerogen pseudo-components in solid phase that are necessary for describing oxidation reactions in low temperature region (LTR) and high temperature region (HTR) and pyrolysis reaction was determined.The application of experimental results has made it possible to substantially reduce the uncertainties revealed in air injection modeling in oil shales. Proposed chemical reactions and their kinetics were validated by experimental data and thus can be used as a start model for high-pressure air injection modeling in oil shales.

The influence factors analysis of the light crude oil oxidation reaction process

ABSTRACTDuring the high pressure air injection process, there are different types of oxidation reactions, which do not exist, and the predominant reaction type of is dependent on the specific conditions. In this study the influences of formation temperature, pressure, and oxidation time on light crude oxidation have been studied via oxidation experiments. And it is shown that the reaction types could be effectively improved by the temperature increment, which decreases the oil viscosity. As well, the pressure and oxidation time have obvious effects that were mainly present in oxygen addition reactions and the viscosity increase.

Sensitivity study on thermal behavior and kinetics of crude oil using thermal analysis techniques

ABSTRACTIn this study, the effect of heating rate, oil chemical composition, and clay mineral type on thermokinetic behaviors of oil oxidation was investigated by TG and DTA tests. The results show that temperature intervals of reactions are extended and peak and burnout temperatures are shifted to higher values when increasing the heating rate. Heavier oil with more heavy components exhibits faster reaction rate and higher energy requirement in the low-temperature oxidation stage, and releases more heat in the high-temperature oxidation stage. The catalytic properties and surface area effect of clays can positively influence the high-pressure air injection process through forming more carbonaceous deposits and lowering the activation energy of reactions.

Variation of reservoir fluid property during the high pressure air injection process

ABSTRACTThis research aimed at determining the variation of reservoir fluid property during the high-pressure air injection process. For this purpose, the forward multiple contact experiment was employed by pressure–volume–temperature (PVT) system to investigate the physical property variation of the crude oil and the complex oxidation reactions. The results show: under the relative low temperature and pressure condition, instead of carbon dioxide, carbon monoxide dominates the products in the air phase. The gas/oil ratio and volume ratio increased due to the generated gas while the viscosity and density achieved a descending trend. The colloid and bitumen in the oil phase reduced by half but the amount of wax achieved a small increase. The low-temperature oxidation and pyrolysis reactions caused the fluctuated change of the different compounds. The amount of light compounds decreased at the beginning and then increased while that of heavy compounds showed the opposite trend. But at last, due to the H/C ratio, the light compounds increased to more than their initial value.

The Kinetic Analysis of Coke Formation Under Differential Air-oil Ratio During High Pressure Air Injection

For studying the heavy oil property change during high pressure air injection process, constant temperature oxidation tube experiments have been finished to study the influence of air-oil ratio on the oxidation process with thermoanalysis methods. The results presented an increasing amount of formation coke was contained with the air-oil ratio increment. When the air-oil ratio reached 200:1, the oxidation process was promoted and the oxide was identified as “coke” with smell. Based on the Arrhenius method, it indicated the air concentration has positive influences on the coke deposition conducive to form and sustain stable combustion front.

Numerical simulation of mechanism of high-pressure air injection (HPAI) in light oil reservoirs

Abstract Based on the research progress of the crude oil oxidation-combustion model proposed by predecessors, this paper established a new multi-reaction model for high-pressure air injection (HPAI) process to compare the HPAI performance in reservoirs without water injection and high water cut reservoirs by numerical simulation. Results show that gas override is universal in air injection in light oil reservoirs before and after waterflooding, and is more apparent in strongly heterogeneous reservoirs. However, the produced oxygen concentration is very low all the time. For reservoirs that haven't gone through water injection, at high air injection rate oil is very likely to auto-ignite and keep high peak temperature and long time stable combustion front. However, there exists a critical value for the influence of air injection rate on the combustion front moving speed, above the critical value, oil recover factor increment is not obvious with the increase of air injection rate. At the same air injection rate, high water cut reservoirs are 6.3% lower in recovery factor than reservoirs without water injection, With high increase in GOR and high water recovery degree during HPAI process. It is suggested that polymer gel/ and or foam assisted air injection be taken to reduce GOR/ and or water cut in production wells.

A method based on the Harcourt and Esson equation to estimate the catalytic effect of metallic additives on light crude oil

Abstract This paper provides the research on four different metallic additives during the combustion process and kinetic behavior of crude oil based on the Harcourt and Esson equation. The oil-only sample and oil-metal additive mixtures were studied by TG/DTG and DSC. The results indicate that Dagang crude oil exhibites three regions low temperature oxidation (LTO), fuel deposition and high temperature oxidation (HTO) during the heating process. The metal additives show obvious catalytic effects on the oil and ZnSO 4 . The exotherm increment benefits the high pressure air injection (HPAI) process. Based on the Harcourt and Esson equation, the activity energy requirement presents different values and trends in the LTO and HTO processes. Compared with the TG/DSC profile and activity energy, ZnSO 4 shows a positive effect on Dagang light crude oil during the HPAI process.

Catalytic effect analysis of metallic additives on light crude oil by TG and DSC tests

This research aimed at the investigation of the effect of different metallic additive on the combustion and kinetic behavior of crude oil. For this purpose, the thermal behavior of the oil-only and oil–metallic salts mixtures were studies by the thermogravimetry (TG)/derivative thermogravimetry and differential scanning calorimetry (DSC) on heating rate at 10 °C min−1. The result shows that Dagang crude oil exhibited apparent low temperature oxidation (LTO), fuel deposition, and high temperature oxidation processes. With the addition of metallic salts, the LTO process has been shortened and samples added CuSO4, CrCl3·6H2O, and AlCl3·6H2O achieved a much lower peak temperature than that of oil. Based on the Arrhenius model, metallic additives were proven to have obvious influence on the combustion activation energy. And, by comprehensive analysis of TG/DSC profile and activation energy, ZnSO4 exhibited a positive influence on light crude oil combustion during the high pressure air injection process.

Buffalo Field High-Pressure-Air-Injection Projects: Technical Performance and Operational Challenges

Summary The Buffalo field air-injection units, located in northwest South Dakota, are the oldest high-pressure-air-injection (HPAI) projects currently in operation. Air injection began in January 1979, and as of December 2007, approximately 240 Bscf of air has been injected into the field. A total of 17.2 million bbl of incremental oil has been produced by the HPAI process, which is equivalent to 9.4% of the original oil in place (OOIP). The cumulative air/oil ratio (AOR) after 29 years of air injection is approximately 14 Mscf of air/bbl of incremental oil. This paper summarizes the performance of the projects and the overall experience gained by the operators after nearly 30 years of air injection. It covers almost every aspect of the entire operation since its inception; it discusses general management practices, technical and operational challenges encountered, injection and production facilities, and drilling and well-completion practices. It also includes estimates of incremental oil recovery caused by air injection and discusses how the air use has changed over time To date, the three HPAI projects in the Buffalo field continue to be a commercial success. In the last 3 years, horizontal laterals have been drilled out of more than 40 old vertical wells to enhance production, to take advantage of accumulated reservoir energy, and to improve sweep efficiency. Drilling injection wells out of old vertical wells was not possible because the openhole laterals cross a porosity zone that would have taken away some of the injection into nonproductive reservoir.

空気圧入法による軽質油の増進回収

In recent years, high pressure air injection (HPAI) into a light oil reservoir has been proven as one of valuable EOR technologies. HPAI is applied for light oil reservoirs where reduction of viscosity by thermal effect is not so important, because the original viscosity of light oil is not as high as heavy oil. As one of the most important recovery mechanisms of HPAI is immiscible flue gas flooding, HPAI process has sometimes been comparable to flue gas or nitrogen injection in general. But this is true only when the oil saturation of the reservoir is high enough and if the reservoir is waterflooded, distillation process by its thermal effect at combustion front is a critical factor for improved oil recovery. This paper discusses the applicability of HPAI for highly water saturated light oil reservoirs, by combustion tube tests (CT tests) and numerical simulation studies. One CT test was conducted with waterflooded core. Additional oil recovery was confirmed in this test, which implies the successful oil recovery from highly water saturated light oil reservoirs. To investigate oil recovery mechanism, a series of simulation studies of CT test was conducted. Through these studies it was clarified that the important oil recovery mechanism for high water saturation reservoir is the distillation process. By this mechanism oil bank was created at the combustion front and significant oil production was observed after some amount of water production in both CT test and its simulation.