In-situ Combustion Process Research Articles

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

Abstract 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 300ºC, increasing the density and viscosity and producing coke which could prevent the success of ISC. Above 350ºC, 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 60ºC to 150ºC. 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. Introduction ISC is a promising but complex oil recovery process in which thermal energy is generated inside the reservoir owing to combustion reactions between the heaviest fractions of the oil and an injected oxygen containing gas. For heavy oils and bitumens, ignition temperatures above 350°C are required to promote the combustion reactions (HTO). At lower temperatures, other types of reactions predominate, involving the addition of oxygen to the bitumen, producing heavier oxidized compounds. The LTO reactions are detrimental to oil production; hence, ISC processes are designed to operate under the high temperature combustion regime (HTO). However, LTO reactions occur if the air flux becomes too low to sustain the combustion reactions, leading to lower-than-estimated production yields. It has been proven in laboratory experiments that oil recovery is considerably reduced when LTO reactions occur to some extent, compromising the success of the ISC.

Isoconversional Kinetic Analysis of the Combustion of Heavy Hydrocarbons

One method to access unconventional, heavy-oil resources as well as waterflood residual oil is to apply in situ combustion (ISC) to oxidize in place a small fraction of the hydrocarbon, thereby providing heat to reduce oil viscosity and pressure that enhances recovery. Experimental analysis of crude-oil oxidation kinetics provides parameters, such as activation energy, for modeling and optimization of ISC processes. The complex nature of petroleum as a multicomponent mixture and multistep character of oxidation reactions substantially complicates the kinetic analysis of crude-oil oxidation. An isoconversional technique is reported to provide a model-free method for estimating activation energy. The technique naturally deconvolves multistep reactions, providing a useful diagnostic tool that characterizes the combustion qualities of different oils. The experimentally determined combustion kinetics of three crude oil samples, including Hamaca (Venezuela), are explored, adding to the knowledge base of crude-oil combustion. All samples exhibit fairly constant apparent activation energies of about 50 000 J/mol for so-called high-temperature oxidation reactions that occur in the range of 625−700 K. The so-called low-temperature oxidation reactions that occur in the vicinity of 500 K display significant variability and are difficult to group and characterize with a single activation energy. Synthetic examples augment the experimental program and document the diagnostic characteristics of the isoconversional technique applied to crude oil, thereby providing insight into the burning qualities of oil. Phenomena, such as “cool flames”, are identified and marked by negative apparent activiation energy.

Stability of THAI ™ Process-Theoretical And Experimental Observations

Abstract The performance of the THAI ™ process has been investigated in numerous 3D experiments, using heavy crudes and Athabasca oil sands bitumen. The stability of the process is demonstrated by high combustion zone temperatures, absence of gas channelling, insensitivity to large changes in air injection rate, tolerance of an overlying gas cap, increased combustion temperature and faster upgrading response with increasing oil layer thickness, 'controlled gas override', own 'front tracking' capability and steady oil production rate. The most important parameters for upscaling of (stable) experimental scale performance to (stable) field scale operation are combustion front temperature and combustion front velocity. Early stage results from the WHITESANDS THAI ™ field pilot at Christina Lake, confirm high combustion zone temperatures (700 – 800 °C), high fluids production of up to 2,000 barrels per day of gross fluids (50 – 55% bitumen cut) and signs of significant partial upgrading (up to 8.2 °API). These measures of field pilot performance are consistent with the experimental findings from 3D physical experiments. They are very encouraging indicators for the future development of THAI ™on a commercial scale. Introduction There is a long and tortuous history concerning the in situ combustion (ISC) process as applied to heavy crude and oil sands reservoirs. Some parts of it were tremendously innovative and successful, but there were also many failures, often due to poorly chosen reservoirs. One of the main reasons why projects failed was lack of control of propagation of the in situ combustion front. In many cases, there was a lack of understanding of the part played by gravity, and hence gravity segregation. Since the first field test of the ISC process in 1951, more than 160 field pilots have been conducted; most of them in the period 1970 – 1990. This led to the development of both the dry and wet ISC processes. They were tested for normal heavy oil and for oil sands using air and enriched air. However, the commercial application of ISC was attained only for heavy crude reservoirs around 1970, using air injection. At that time, most operators started to realize that ISC was actually a gas displacement process, benefiting from oil viscosity reduction due to heat generated by ISC reactions. Therefore, as in any gas displacement process, the injectors should be located at the most updip position. As of April 1992, according to an Oil & Gas Journal report, the incremental daily production from ISC was approximately 4,700 BOPD (from eight projects) in the USA, 8,000 BOPD (from ten projects) in the former Soviet Union, 7,300 BOPD (from three projects) in Canada and 12,000 BOPD (from five projects) in Romania. Thus, the 1992 world incremental daily oil production due to ISC was about 32,000 BOPD (from 26 reported projects)(1, 2). This included nineteen commercial operations and seven semi-industrial projects. Currently, only four commercial heavy oil projects are active: Suplacu de Barcau (Romania), Balol and Santhal projects (India) and Bayou State Oil Corp. (BSOC) in Bellevue, Louisiana, USA.

A Simple Kinetic Model for Coke Combustion During an In-Situ Combustion (ISC) Process

Abstract Although coke combustion studies have long been conducted, the literature is still lacking an accurate understanding of reaction kinetics. To this end, the thermo-oxidative behaviours of Neilburg oil and its asphaltene fraction were examined in the presence of core sand. Thermo gravimetric analysis (TGA) was performed in a flowing atmosphere at the heating rate of 10 °C/min up to 750 °C. Both nitrogen and air were used at a flow rate of 45 ml/min in the experiments. As earlier researchers have observed, at least two main regions of reactions were identified by the thermo gravimetric (TG) and derivative thermo gravimetric (DTG) thermo grams. Various effects, including distillation, low-temperature oxidation (LTO), thermal cracking, middle-temperature oxidation (MTO), high-temperature oxidation (HTO) or combustion, and even mineral decomposition, were observed. In this study, Neilburg oil and asphaltenes were completely cracked in a nitrogen atmosphere at 425 ° C to produce coke. Subsequently, the fresh coke was subjected to isothermal combustion at several temperatures from 374 °C to 519 °C. A two-step oxidation reaction model was applied to describe this combustion process. The chemical reactions were simplified into two oxidations occurring in series. In the first reaction, coke was partially oxidized to form an intermediate product, which was then burned in the second reaction. Based on the TGA data, kinetic parameters were estimated with the aid of custom written software. For comparison, the one-step oxidation reaction model was also employed to predict the combustion process. The two-step oxidation reaction model gave a better fit to the experimental data. It was also confirmed that the coke derived from the Neilburg asphaltenes is reasonably representative of the coke derived from the whole oil. Introduction It has long been recognized that in situ combustion (ISC) might be a potentially effective enhanced oil recovery (EOR) technique, particularly suitable for medium and heavy crude oil-bearing reservoirs, as well as for steam depleted reservoirs. However, the fact that the fundamental reaction mechanisms of the ISC process have not been completely understood makes its field performance prediction unreliable. It is generally believed that there are three major reactions during an ISC process: thermal cracking, low temperature oxidation (LTO) and high temperature oxidation (HTO). Thermal cracking of crude oil, including visbreaking and coking, produces a solid residue on the surface of the reservoir sand grains. The solid residue, or so-called coke, is consumed as the fuel for combustion. LTO reactions, which are typically heterogeneous reactions between the gas and condensed phases, involve the formation of oxygenated hydrocarbons. During an ISC process, LTO is possible if oxygen is present ahead of the combustion front, either due to the oxygen flux being relatively high or due to bypassing of the front by some of the injected oxygen(1). HTO is the heterogeneous (gas-solid) reactions that consume the coke deposited by thermal cracking to produce carbon oxides and water. Some efforts to investigate the oxidation reaction mechanisms during ISC can be found in the literature. An early extensive study was carried out by Dart et al.(2) who tested the combustion rate for oxidation of carbonaceous residues on clay catalyst pellets.

Modelización de procesos de combustión segregada in-situ mediante un modelo de desplazamiento vertical aplicado a un campo Colombiano.

Recently it has been proposed the incorporation of horizontal well technologies in thermal EOR processes like the in situ combustion process (ISC). This has taken to the conception of new recovery mechanisms named here as Segregated In-Situ Combustion processes which are conventional in-situ combustion process with a segregated flow component. Top/Down combustion, Combustion Override Splitproduction Horizontal-well and Toe-to-Heel Air Injection are three of these processes, which incorporate horizontal producers and gravity drainage phenomena. When applied to thick reservoirs a process of this nature could be reasonably modeled under concepts of conventional In-Situ Combustion and Crestal Gas Injection, especially for heavy oils mobile at reservoir conditions. A process of this nature has been studied through an analytic model conceived for the particular conditions of the Castilla Field, a homogeneous thick anticline structure containing high mobility heavy oil which seems to be an excellent candidate for the application of these technologies.

Main Mechanism for Stability of THAI-Toe-to-Heel Air Injection

Abstract THAI, or "Toe-to-Heel Air Injection," is an integrated horizontal well process for in situ recovery and upgrading of heavy oil and tar sands bitumen. During extensive studies of the process at the University of Bath, involving more than 50 three-dimensional combustion cell tests, the process has repeatedly demonstrated robust and stable operation. However, the answer to the question: "Why does oxygen breakthrough into the toe of the horizontal well not occur," has not been fully developed. This is now all the more important since the THAI process is about to be tested in the field. In order to maintain stable propagation of the combustion front, sufficient fuel needs to be available ahead of the front. This is fundamental to the in situ combustion (ISC) process, whether in its conventional form, or THAI. When the combustion front approaches close enough to the horizontal producer well, heavy residue can drain into the well. This residue, or coke material, provides a gas seal, preventing the injected air from channeling through to the well. This paper presents post-mortem results of two THAI experiments, in which the horizontal well was cut-open to reveal the extent of heavy oil residue/coke deposition. The visual evidence is supported also by a numerical simulation of the experiment, showing the distribution of coke and oxygen through the oil layer. Introduction In situ combustion (ISC) has, theoretically, always held the promise of high potential rewards for heavy oil recovery. This is basically because, if a stable combustion front at high temperature (500 - 600 ° C) can be propagated through the oil-bearing formation, virtually all of the heavy oil it contacts is displaced. The fundamental principle of ISC, as applied to heavy oil recovery, is well known, as described by Burger et al.(1). ISC is achieved by burning a small fraction of the oil in the reservoir, which releases sufficient reaction energy to create a large increase in reservoir temperature in the combustion front zone, thereby mobilizing and displacing the oil ahead of it. The chemical reactions between oxygen and crude oil are extremely complex, principally because there are a large number of components which can undergo thermal cracking reactions. The overall complexity of the ISC process is increased because of the interaction between chemical reaction and transport processes in reservoir porous media. Although considerable understanding of the ISC process has been gained in recent years, and new guidelines and strategies for field operations have been presented(2, 3), there are still a number of concerns about the process which need to be resolved if its full operational potential is to be realized. These include:Gravity segregation, or gas overriding;Oil banking in the cold region ahead of the combustion front; and,Permeability heterogeneity. Gas overriding, due to the buoyancy effect between the combustion gases and reservoir liquids, exacerbated by permeability contrasts in the reservoir porous media, can cause severe channeling of gas through to the producer well.

Downhole Catalytic Process for Upgrading Heavy Oil: Produced Oil Properties and Composition

Abstract The level of in situ upgrading of heavy Wolf Lake oil achieved by a downhole catalytic process, which is a catalytic variant of the THAI process-"Toe-to-Heel Air Injection"-has been investigated using various analytical methods. These included gas chromatography (GC), elemental analysis, simulated distillation (SIMDIS), micro-activity test (MAT), plus density and viscosity. The tests were performed on the oil produced from the downhole catalytic upgrading process, which was conducted in semi-scaled 3D combustion cells. The tests employed a standard hydrogen de-sulphurisation (HDS) catalyst, which was "gravel packed" around the horizontal producer well, forming an annular radial inflow type reactor. Although the analytical measurements made were necessarily selective in their scope, they nevertheless provide a good indication of what the potential may be for downhole upgrading in the field. Downhole catalytic upgrading produces a "light oil, " characterized by a low viscosity of around 60 mPas, or less. The produced oil is readily converted into gasoline and diesel fractions, with a higher conversion on an FCC basis than that obtained with normal virgin bitumen vacuum gas oil. Environmentally, there are also very significant potential benefits regarding in situ removal (and retention) of heavy metals, and reduction of sulphur in the oil. Introduction Fireflooding, in situ combustion (ISC), or heavy oil air injection (HOAI) is a process wherein a combustion front is propagated through the formation, vapourizing the oil and water ahead of it. Conventional forward combustion is a long-distance displacement process (Figure 1), so that vapourized oil and water are condensed in the cooler parts of the reservoir and are eventually produced from a producer well. Theoretically, forward combustion is intended to burn the least desirable fraction of the oil, leaving a clean formation behind. Its main drawback is that there must be sufficient mobility for the vapourized oil and water to be producedfter they have condensed ahead of the combustion front. This factor, frequently leading to loss of air injectivity and consequent inability to maintain the process in a high temperature oxidation (HTO) mode, has probably been responsible for the poor performance, or failure, of many field applications of the conventional ISC process. Short-distance displacement (Figure 1) is a concept that was made possible by the development of horizontal well technology. SAGD (steam-assisted gravity drainage) is the most well-known thermal process in this category. THAI-"Toe-to-Heel Air Injection," is an integrated horizontal wells-thermal process, also fitting into the short-distance displacement category (Figure 1), but with some unique features. Briefly, there is no necessity for communication into, or displacement through, the oil layer downstream of the combustion front. Rather, this is excluded by THAI, since the cold heavy oil region downstream of the combustion front provides a natural "barrier" by virtue of its very high viscosity, as well as providing a seal around the horizontal producer well. Figure 1 illustrates the "moving window" effect in THAI, due to the propagation of the combustion front.

Improvement of Medium And Light Oil Recovery With Thermocatalytic In Situ Combustion

Abstract The objective of this paper was to improve the understanding of the basic mechanisms responsible for fuel formation in in situ combustion (ISC) and to use that understanding to identify the conditions under which the ISC process can be applied to improve the recovery of heavy, medium and light oils. Using rocks of varying mineralogical composition and crude oils with different contents of asphalteoes and resins, pyrolysis and combustion tests were performed to examine the influence of thermocatalytic mocatalytic reactions on the amount and reactivity of fuel in an ISC process. From the results, it appears that the controlling mechanism of fuel formation is the conversion of crude oil components by radical polymerization. The conversion rate is influenced by many factors such as process condition and the nature of the crude oil and reservoir rock minerals. The formation of resins from lighter hydrocarbons and their polymerization into asphalrenes can be accelerated by clay minerals and metal components existing in the fuel formation zone. Therefore the importance of low tem-perature oxidation reactions is increasing in the thermocatalytic recovery process of even light and medium oils. Introduction The application of thermal energy to hydrocarbon reservoirs for increasing crude oil recovery has been given much attention. There are two main types of thermal recovery process, namely hot fluid injection and in situ combustion (ISC). ISC is thermal oil recovery method with a large theoretical potential but limited success in field application. This technique is also known to be the most complicated oil recovery method. It includes some aspects of nearly every oil recovery process. An important parameter to be considered in the design of an ISC project is the amount of fuel deposited ahead of the combustion front. Excessive fuel deposition causes a slow rate of advance of the burning front and large air compression costs and reduces the maximum oil recovery. On the other hand, if the fuel concentration is too low, the heat of combustion will not be sufficient to raise the temperature of the rock and the contained fluids to a level of self-sustained combustion. This leads to an unstable burning front and combustion failure. Thus, it is necessary to understand the reactions occurring at different temperatures as the combustion front moves in the reservoir. The most important controlling factors of the fuel formation are the nature of the crude oil and reservoir rock minerals and During this work, experiments were conducted to describe how the clay minerals and heavy metals derivatives, such as iron, affect the thermocatalytic conversion of crude oil compounds as well as the fuel formation and combustion. Thermocatalytic Oxidation of Crude Oil Compounds It has been confirmed by many authors, for example, Bousaid and Ramey(3), Dabous and Fulton(4) Burger and Sahuquet(5), that basically three major reactions occur at different temperature levels in an ISC process. These reactions are known as:Low temperature oxidation (LTO)Fuel deposition reactions (FDR)High temperature oxidation (HTO)

Influence of reservoir rock composition on crude oil pyrolysis and combustion

The principal objective of this study was to investigate the influence of reservoir rock composition on the pyrolysis and combustion behavior of crude oils in porous media in relation to in situ combustion (ISC) as a thermal oil recovery process. Using sand pack of varying mineralogical composition and different crude oils, pyrolysis and combustion tests were performed to examine how the clays affect the amount of fuel and its reactivity during the ISC process. From the experimental results, it appears that clay minerals present in the matrix enhance fuel deposition during the pyrolysis process and also catalyze the oxidation of fuel.

Evaluation of an In-Situ Combustion Process by Postburn Core and Log Analysis

Summary Evaluation of the performance of an in-situ combustion process applied by Cities Service Co. in the Bellevue field was made possible by analysis of postburn cores and logs from wells drilled within the flooded zone. postburn cores and logs from wells drilled within the flooded zone. Temperature-observation-well data and production performance were inadequate to describe the coverage and efficiency of the simultaneous air- and water-injection method applied. Introduction An attempt was made to monitor the coverage of the burn fronts generated by five injection wells in the Bellevue field using one temperature-observation well per injector. After 4 years' continuous injection, only one observation well ever had shown the high temperatures seen in laboratory combustion tube studies, and an accurate description of the burned zone could not be determined. After air injection was terminated, four wells were drilled within one pattern, obtaining openhole logs and cores of the producing formation. pattern, obtaining openhole logs and cores of the producing formation. Results from this postburn drilling program were used in constructing an approximate burned zone for the pattern, enabling better understanding of the combustion process and of the efficiency of the field project. Reservoir and Laboratory Data The combustion project is being conducted in the Bellevue field of northwestern Louisiana. This field, discovered in 1921, produces a 19API (0.9 g/cm3) crude from the Upper Cretaceous Nacatoch sand. Primary production from the field is estimated to have been less than 15% of the production from the field is estimated to have been less than 15% of the original oil in place (OOIP). The field is a 900-acre (4 × 10 6 m2) low-relief dome with pay thickness controlled by a water/oil transition at 212 ft. (64.6 m) subsea. The project area covered by this report is a 19-acre (77 × 10 3-m2) five-pattern demonstration conducted by Cities Service Co. under a cost-sharing contract with the U.S. DOE (Contract DE-AC03-76ET12057). In this area of the field the top of the Nacatoch is encountered between 109 and 174 ft (33.2 and 53.0 m) subsea, with dip to the northeast at 4.5 0. At this shallow depth, the Nacatoch is a highly unconsolidated sand with numerous thin, dense, fossiliferous limestone layers. These limestone layers are identified easily from bulk-density logs (Fig. 1) and essentially subdivide the pay section into four principal sand intervals (S1, S2, S3, and S4). The average porosity and permeability of the sand intervals are 33.9% and 700 md, with the sand having a 27.4% water saturation. Average reservoir pressure is only 40 psig (280 kPa). JPT p. 827

A Field Test of the In-Situ Combustion Process in a Near-Depleted Water Drive Reservoir

A Field Test of the In-Situ Combustion Process in a Near-Depleted Water Process in a Near-Depleted Water Drive Reservoir The recovery of additional oil from a watered-out reservoir has been found to be economically feasible using in-situ combustion techniques. Employing a single-point injection scheme, one company has recovered more than half a million barrels of oil, with few operating difficulties, from the North Government Wells field in South Texas. Introduction Most of the early in-situ combustion projects were conducted in shallow reservoirs containing relatively viscous crudes. Generally, the primary oil production from these reservoirs was very low. When Mobil Oil began in-situ combustion operations in the North Government Wans field in Sept., 1962, most of the basic guidelines of that time for successful thermal recovery operations were severely challenged. If this recovery technique were to become a strong tool in South Texas fields, its ability to overcome many conditions prevalent in the area, considered adverse to the success of the process, had first to be proven. It was with this goal in mind that Mobil chose a very demanding reservoir for their initial in-situ combustion operation in Texas (Fig. 1). The Government Wells reservoir underlying Mobil's Duval Ranch Section 208–09 lease contains approximately 13,100 acre-ft of net oil sand. The combination of a moderately strong water drive and a 10-cp crude had resulted in a very efficient sweepage of the reservoir. In mid-1962, the WOR had risen to 45:1 and the productive economic limit of the lease was rapidly being approached. Despite the fact that the primary oil recovery had been 40 percent of the original oil in place, some 800 bbl of oil per acre-ft still remained in the reservoir to be per acre-ft still remained in the reservoir to be recovered. The presence of this 10 million bbl of residual oil provided sufficiently strong incentive to embark on operations for determining the limits to which this process could be extended. The experience that was process could be extended. The experience that was to be acquired from the project would be adapted for future use in similar reservoirs. Geology The Government Wells sand is of the Jackson group of Eocene age and occurs at an average depth of 2,320 ft. The gross thickness of the sand underlying Mobil's DCRC Section 208–09 lease is approximately 60 ft, of which, in some instances, as much as the upper 30 ft is considered to be oil productive. Because of the early development of the field and a lack of electric logs, it is difficult to determine the effective sand thickness. The sand is quite heavily stratified with thin shale and bard lime streaks. The Government Wells reservoir is limited to the north and east of the lease by an oil-water contact originally located at - 1,790 ft. The aquifer has been fairly active throughout the life of the field, with encroachment predominantly from the east-northeast. This water influx gave initial indications of the anisotropy of the formation, which was later confirmed by gas movement through tile reservoir. Production characteristics and differential reservoir pressures indicate that an anomaly or permeability barrier exists in a north-south direction permeability barrier exists in a north-south direction across the middle of the lease in the immediate area of the project. JPT P. 153