Coke Zone Research Articles

A modified vertical-horizontal well pattern for enhancing in-situ combustion performance in extra-heavy oil reservoirs

A proper well pattern is critical for the efficient and economical exploitation of heavy oil and bitumen during the in-situ combustion (ISC). This paper brings a modified vertical-horizontal well pattern named the modified THAI process using additional injectors in staggered line drive with auxiliary gas producer wells and investigates its ISC performance using a 3D experimental simulation. The burning stability, spatial distribution of coke zone, pressure difference, and extension features of combustion chamber are studied and analyzed. Results show that a better burning state and stable propagation for the combustion front can be achieved in this modified well pattern. Spatial distribution of coke zone structure manifests a larger sweep volume of combustion chamber and a lower extent of combustion override. Combustion chamber extension characteristics are intuitively displayed by the variation of 350 °C isothermal surfaces, and its sweep volume finally enlarges to 53032.55 cm3 with a volumetric sweep coefficient of 47.95%. The production well intermittent shutdown (PWIS) method can improve unfavorable expansion behaviors of combustion chamber with little impact on the burning state and pressure difference. The oil displacement efficiency eventually reaches 85.6%. This well pattern exhibits significant potential for enhancing in-situ combustion performance, contributing to the economic and efficient exploitation of oil in commercial ISC application.

A dynamic control strategy for improving combustion chamber sweep efficiency during the in-situ combustion

Combustion chamber extension is closely associated with oil production efficiency and ultimate oil recovery during in-situ combustion (ISC) process. However, the effective method for controlling combustion chamber extension is is still being explored. This work proposes a novel measure to modify the unfavorable expansion behaviors of combustion chamber while minimizing the impact on variations in pressure difference and combustion stability, and it is implemented by the production well intermittent shutdown (PWIS) method in the heterogeneous porous medium. The variation of effluent gas compositions, spatial distribution of coke zone, swept area of combustion chamber, burning stability, and pressure difference are studied. The results show that the combustion chamber and coke zone develop uniformly and their expansion volume in low and medium permeability regions enlarge noticeably with the PWIS implementation. The PWIS method is able to modify the unfavorable expansion behaviors of combustion chamber with little influence on the burning state, especially as the combustion front propagated in the central section between the injector and producer. The final oil recovery factor can be enhanced by 73.8% after implementing the PWIS method. This work is of significance to the ISC field application and provides an approach to achieving a higher volumetric sweep efficiency of combustion chamber.

Applying dynamic mesh to examine evolution of effective thermal conductivity in porous medium undergoing macrostructure change

Heat transfer dynamics in packed bed appears to be vital, particularly with respect to thermochemical conversion of solid fuels. However, due to complex bed structure varying under high temperatures the prediction of its thermal behavior is very demanding. Heating of coke oven charge is one example, regarded as being considerably affected by radiation through fissures and cracks that cross cut coke zone as the carbonization proceeds. The investigation and quantification of such impact encounters difficulties due to irregularity of fissure network that depends on a parent coal type and the process temperature regimes. Unfortunately, the analyses of this issue are very limited, meanwhile an uncertainty in the assessment of radiation contribution might be a source of notable discrepancy in effective thermal conductivity of coal/coke bed reported to date in the literature. In this respect, the CFD simulations of heating of a coal/coke bed while taking into account the crack propagation were performed to estimate an influence of structure alteration on heat transfer process. The computations were carried out using Ansys Fluent package and the dynamic mesh was implemented to simulate the crack development. The numerically-derived temperature profile at the coke oven center plane is in good agreement with the experimental temperature history. The predicted thermal conductivity values in the near-wall zone are significantly higher than for the case excluding fissure presence, and achieved ∼6.2 W(m K)-1 at the end of process (for 1373 K), showing additionally a clear increase from 1.4 to 2.9 W(m K)-1 within 1070–1090 K. The computation results also revealed that slower developing cracks, contrary to faster propagating ones, lead to higher thermal conductivity.

Transformation of minerals at the boundary of magma-coal contact zone: case study from Wolonghu Coal Mine, Huaibei Coalfield, China

Mesozoic and Cenozoic magma activity in the Wolong Lake mining area of Huaibei is frequent, and the degree of magma intrusion into coal seams remarkable. On the one hand, magma intrusion affects the utilization of coal resources; on the other hand, the macro and trace elements in coal are redistributed to form new mineral types. This study uses the Wolong Lake magma intrusion coal seam as a research object. The mineral paragenesis for igneous rock, coke, and thermally-altered coal in an igneous intrusion zone is studied using SEM, XRD, and Raman spectroscopy. During igneous intrusion, the temperature and pressure of igneous rock metamorphose ambient low-rank coal to high-rank coal and coke. The response mechanism of minerals and trace elements to magmatic intrusion is discussed. The results are: ① SEM analysis shows that ankerite and pyrite are formed from magma intrusion. Both minerals are strongly developed in the magma-coal contact zone, and less well developed in thermally-altered coal. ② XRD analysis shows that igneous intrusion strongly influences the types and content of minerals in coke and thermally-altered coal. In addition to the increase amounts of ankerite and pyrite, chlorite, serpentine, and muscovite, and other secondary minerals, are generated following igneous intrusion. ③ Raman analysis suggests that thermally-altered coal possesses the characteristics of both pyrite and coke. Coke from the magma-coal boundary zone possesses the typical characteristics of pyrite. Igneous rock contains a mineral similar to pyrite, confirmed by both having similar Raman peaks. The scattering intensity of Ag indicates that the formation pressure of pyrite increases from thermally-altered coal via the boundary between the coke zone and the igneous rock.

Investigation on coke zone evolution behavior during a THAI process

A Toe-to-Heel Air Injection (abbreviated as THAI) process is regarded as a promising method in heavy oil and extra heavy oil recovery. Numerical simulations, together with laboratory experiments, were employed to investigate coke zone evolution. The time window of interest focuses on the interval from the commencement of oil production to that of air breakthrough. The simulation results show good history match in local temperature profile, cumulative oil production and produced gas concentration. For the purpose of quantitative assessment, new parameters named coke volumetric sweep efficiency (Esw) and volumetric expansion speed (Ssw) are proposed. Coke zone was first generated around the ignitor and then propagated forward and upward due to the effects of gravity drainage and displacement. The gravity effect makes a major contribution to sustaining a stable state especially in the early to middle term of the THAI process, which is also identified with the generation of a significant faster increase of Ssw. An evenly developed of coke zone with oval shape both in thickness and concentration is also accounted in this period (4 h ≤ t ≤ 9 h). Then changes occur in coke zone with stronger heterogeneity, and the peak value of Ssw occurring at the 9th hour generally infers the maximum oil drainage effect. When the Ssw decreases to around 0.02, an unstable combustion state happens. The characterization method of the coke zone construction proposed in this work and the combination of simulating tools such as CMG software can be beneficial in guiding the future work of ISC.

Analysis of a feasible field THAI pattern by the derivation of scaling criteria and combustion experiments

Abstarct Toe-to-heel air injection (THAI) process is considered as a potential enhanced oil recovery (EOR) method for heavy oil production. For physical simulation of THAI process in laboratory conditions, the simplified scaling criteria of THAI process were derived and a novel three-dimensional cylindrical apparatus was used to construct the new THAI pattern in this study. Equation analysis and dimensional analysis (Buckingham π-theorem) were applied to deduce the whole dimensionless groups, and sensitivity of the coefficients described with their distortion coefficients were used to obtain the influential weights and the simplified scaling criteria. STARS module in Computer Modeling Group (CMG) was used to verify the feasibility of the THAI pattern by two models, which represent the reservoir prototype and the 3D apparatus respectively. With an effective simulation of experimental results, a reasonable data set was obtained, and then those values were upscaled for simulation of field THAI process by the simplified scaling criteria. The experiment results showed that the horizontal well was well protected by a slant distribution of coke zone and the other parameters about oil production (such as the high temperature swept volume, oil production rate and recovery) were still satisfactory. The similarity of variation process of temperature field, oil saturation distribution and production performance between the laboratory results and THAI simulation in reservoir prototype showed the validity of the scaling criteria and indicated that a feasible field THAI process with a large combustion chamber upon horizontal well can be predicted to achieve.

Optimization of well spacing to achieve a stable combustion during the THAI process

Toe-to-Heel Air Injection (THAI) is a great potential in improving energy efficiency for heavy oil/bitumen recovery. A 3D cylindrical combustion model with large size is used to carry out several experiments using Xinjiang (China) crude oil. The evolution of the fire chamber, temperature variation rate, and mass of burned carbon were analyzed using temperature measurements and flue gas composition analysis. Coke zone was quantified in the variation of zone thickness and distribution characteristics. The results reveal that there is a prevailing stable propagation of the combustion front during the first one third of the process for varying injector to producer spacing. Oxygen breakthrough is more susceptible for smaller separations and the combustion zone is reduced in length. Larger combustion fronts with greater relative propagation in the horizontal direction occurs when the well spacing is larger. The distribution of coke is significantly influenced by the injector/producer spacing. For a THAI pattern with greater injector/producer spacing, a smaller inclination angle of the coke zone occurs and the likelihood of oxygen breakthrough to the horizontal production well is lessened. Hence, the injector to producer spacing needs to be considered in designing a safe THAI process for potentially larger efficiency and optimum economics.

Fire-flooding technologies in post-steam-injected heavy oil reservoirs

Abstract The mechanism and problems associated with development engineering of fire-flooding in post-steam-injected heavy oil reservoirs was studied using 1D & 3D physical simulation experiments and reservoir numerical simulation. The temperature of combustion zone decreased and high-temperature zone enlarged because there existed secondary water formed during steam injection, which could absorb and carry heat towards producers out of the combustion front during fire flooding, but high saturation of water in layers caused by secondary water had less influence on the quantity of fuel deposit and air consumption. In the process of 3D fire flooding experiment, air override was observed during the combustion front moving forward and resulted in a coke zone in the bottom of the layer, and the ultimate recovery factor reached 65% on fact that the remaining oil saturation within the coke zone was no more than 20%. The flooding model, well pattern, well spacing, and air injection rate were optimized according to the specific property and the existed well pattern in the post-steam-injected heavy oil reservoir, and the key techniques of ignition, lifting, and anticorrosion was also selected at the same time. The pilot of fire flooding in the H1 block in the Xinjiang Oilfield was carried out from 2009 based on these research works, and now begins to show better performance.

Feasibility of In-Situ Combustion in the SAGD Chamber

Summary Steam-assisted gravity drainage (SAGD) is a commercially successful bitumen-recovery method that has transformed some of the vast Canadian oil-sand deposits into recoverable reserves. Several SAGD projects have been developed in northern Alberta in the past few years, and many more are in the planning stages. As the projects mature, new operational problems are revealed, demanding new solutions. Because of operational restrictions, it is almost impossible to have the same growth rate in all steam chambers in a SAGD pattern. Hence, interference between a mature chamber and an adjoining immature chamber can become a problem. Steam leakage from the immature chamber into the mature chamber reduces the thermal efficiency of the project and requires a solution to prevent the steam dissipation. Filling the mature chamber with combustion gases is a possible solution for this problem. Carrying out in-situ combustion (ISC) in the mature chamber not only would create the needed combustion gases in the chamber, but also could recover a substantial part of the residual oil in the mature chamber. It is also likely that the combustion would create a reduced-permeability coke (toluene insoluble fraction) zone around the mature chamber, thus isolating it from the rest of the reservoir. To evaluate the merit of this idea, an elevated-pressure experiment was conducted using a 2D physical model. The conventional SAGD process was conducted in the model to develop a steam chamber. Air was then injected through a horizontal well near the top of the model into the SAGD chamber, and a combustion front was established around the air-injection well. By operating combustion in the depleted chamber, residual oil was mobilized and produced. Additional oil recovery was attained by more than 20% over the SAGD operation as a bonus. Initiation and propagation of combustion were confirmed by a large increase in the temperature in the combustion zone. After unpacking the model, it was found that a coke layer formed around the perimeter of the chamber.

Numerical prediction on the erosion in the hearth of a blast furnace during tapping process

The erosion caused by mass transfer in hearth is the most important factor for determining blast furnace campaign life. To support a helpful insight information of mass transfer for the hearth of the No. 2 blast furnace at CSC (China Steel Corporation), a numerical model including the mass transfer of carbon in thermal convective flow from a blast furnace hearth has been developed during the steady tapping process (based on a uninterrupted tapping process assumption). The three dimensional Navier–Stokes equation combined with the transport equations of energy and species with conjugate heat transfer and physical dissolution source is solved by the finite control volume scheme subjected to the segregated iterate under propriety boundary conditions. The results showed the concentration distribution of carbon expressed in terms of mass flux for analyzing the erosion of carbon brick in the blast furnace hearth with the different conditions including the status of dead-man, production of liquid iron, carbon concentration at the inlet, and porosity distribution in coke zone during tapping process at steady state. The result is useful to mitigate the erosion caused by mass transfer, and prolong the life span of the blast furnace.

Numerical prediction on the variation of temperature in the eroded blast furnace hearth with titanium dioxide in hot metal

This paper numerically predicts the decrease in temperature of the eroded hearth of the blast furnace with floating deadman (coke zone) case for Port Kembla no. 5 blast furnace (PKBF5) by solving the Navier–Stokes equation, the thermal-energy-balance equation with conjugated heat transfer, and the mass transfer equation with the effect of chemical reaction during tapping process at steady state. The chemical reaction is generated by titanium dioxide (TiO 2) reacting with saturated carbon in hot metal. The following calculations are done by using a commercial computational fluid dynamics (CFD) package, FLUENT (version 6.2), with a segregated model. As shown in the results, on the basis of the flow pattern of liquid iron, the inlet selection of adding TiO 2 may be far away from the taphole. The calculated temperature variation in the damaged hearth by reaction is significant, but that on the other side of the hearth without adding TiO 2 isn't influenced. Additionally, the numerical temperature data of different locations may be examined by the blast furnace operators to judge the effect of lowering temperature.

Reducing Ability of CO and H2 of Gases Formed in the Lower Part of the Blast Furnace by Gas and Oil Injection

Gases formed in the raceway by injection of reducing agents into the tuyere affect the blast furnace process in several ways. Energy set free by conversion in the raceway helps the melting of the burden and has beneficial effects on reaction kinetics. The formation of CO and H2 helps to save blast furnace coke. The aim of this work is to study effects of the gases formed after the injection of coke oven gas (COG) and heavy oil into the tuyere of a blast furnace and after conversion in the raceway when entering the active coke zone. For this reason a gas conversion simulation is developed including description of the zones of the lower blast furnace part. The cases studied have the same melting rate at which the injection of COG is accomplished with one and two lances while those of oil is studied with one lance. The simulation predicts that the available amount of species for the reduction of iron ore and the reduction potential is similar for the studied reducing agents COG and heavy oil. Evaluating the potential to save coke a theoretical exchange ratio of 0.84 can be determined for comparable cases in terms of the same reduction progress so that the same consumption of coke has to be expected if no difference between the agents exists.

Three dimensional iron flow and heat transfer in the hearth of a blast furnace during tapping process

The aim of this research is to numerically simulate iron flow and heat transfer in the hearth of a blast furnace by solving the three-dimensional turbulent Navier–Stokes equation coupled with the transport equation of energy at steady state. Under the effects of conjugate heat transfer and natural convection, a computational fluid dynamic calculation was performed to generate flow field in the hearth and the temperature distribution in the refractories during the tapping process. The accuracy and computation of the model is validated using operation data from BHP Steel's No. 5 blast furnace. The shear stress and heat flux on the wall were then predicted for the different vertical movements, shapes of the coke zone (dead-man), and the lengths of the tap-hole. As shown in the results, it is worth noticing that an increase in the tap-hole length causes the peak values of shear stress to shift in the increasing azimuthal direction at a particular plane, and the location of the peak value of shear stress coincides with the location of higher temperature actually measured on the hearth wall, signifying enhanced heat transfer to the wall at location of peak stress.

Simulation of Iron Flow and Heat Transfer in the Hearth of a Blast Furnace

The aim of this research is to numerically simulate iron flow and heat transfer in the hearth of a blast furnace by solving the three-dimensional turbulent Navier-Stokes equation coupled with the transport equation of energy at steady state. Under the effects of conjugate heat transfer and natural convection, a computational fluid dynamic (CFD) was performed to generate flow field in the hearth and temperature distribution in the refractories during the tapping process. The accuracy and computation of the model is validated using operation data from Bluescope Steel’s No. 5 blast furnace. The shear stress and heat flux on the wall were then predicted for the different vertical movements, shapes of the coke zone (deadman), and the lengths of the tap-hole. As shown in the results, it is worth noticed that an increase in the tap hole length causes the peak values of shear stress to shift in the increasing azimuthal direction at a particular plane, and the location of the peak value of shear stress coincides with the location of higher temperature actually measured on the hearth wall, signifying enhanced heat transfer to the wall at location of peak stress.

Influence of an igneous intrusion on the inorganic geochemistry of a bituminous coal from Pitkin County, Colorado

Although the effects of igneous dikes on the organic matter in coal have been observed at many localities there is virtually no information on the effects of the intrusions on the inorganic constituents in the coal. Such a study may help to elucidate the behavior of trace elements during in situ gasification of coal and may provide insights into the resource potential of coal and coke affected by the intrusion. To determine the effects of an igneous intrusion on the inorganic chemistry of a coal we used a series of 11 samples of coal and natural coke that had been collected at intervals from 3 to 106 cm from a dike that intruded the bituminous Dutch Creek coal in Pitkin, CO. The samples were chemically analyzed for 66 elements. SEM-EDX and X-ray diffraction analysis were performed on selected samples. Volatile elements such as F, Cl, Hg, and Se are not depleted in the samples (coke and coal) nearest the dike that were exposed to the highest temperatures. Their presence in these samples is likely due to secondary enrichment following volatilization of the elements inherent in the coal. Equilibration with ground water may account for the uniform distribution of Na, B, and Cl. High concentrations of Ca, Mg, Fe, Mn, Sr, and CO 2 in the coke region are attributed to the reaction of CO and CO 2 generated during the coking of the coal with fluids from the intrusion, resulting in the precipitation of carbonates. Similarly, precipitation of sulfide minerals in the coke zone may account for the relatively high concentrations of Ag, Hg, Cu, Zn, and Fe. Most elements are concentrated at the juncture of the fluidized coke and the thermally metamorphosed coal. Many of the elements enriched in this region (for example, Ga, Ge, Mo, Rb, U, La, Ce, Al, K, and Si) may have been adsorbed on either the clays or the organic matter or on both.

Organic Petrology and Elemental Distribution in Thermally Altered Coals from Telkwa, British Columbia

Abstract Thermal alteration of both organic and inorganic components of a coal seam from Telkwa, British Columbia, is examined, using reflected light microscopy, x-ray diffraction (XRD), and neutron activation analysis (INAA). The alteration resulted from intrusion of an alkali basaltic dike. The organic components of coal (macerals) at the contact with the intrusion are coked and developed strong anisotropy. The temperature of formation of this coke is estimated at >750°C and possibly >900°C with a fast rate of heating. However, coal at a distance of 120 cm from the dike is unaltered. Some liptinite macerals retained their original morphology in the altered residue but developed stronger anisotropy than the altered coal groundmass. Pseudovitrinite became reactive and developed fluidity in the altered coals. Original botanical morphology of pseudovitrinite superimposed by mosaic textures is still present in altered coal. Assimilation of less reactive components of coal by reactive components is observed in altered coal. Altered coal contained spherulitic and layered pyrolytic carbons that formed due to the thermal cracking of coal volatile matter, mainly tar. The variation of elements with increasing proximity to the dike is related to the organic and inorganic affinities of the elements; the elements with organic affinities, i.e., Cl, H, N, and O, are depleted in the coke zone of alteration, and only carbon becomes enriched in this zone. The enrichment index (El), which is an indication of input of elements from the -dike into the altered coal, is high for As, Ca, Cu, Mg, Mn, Sr, Th, and rare earths. The volatilization of elements in coals due to the thermal alteration, particularly in coke in contact with the dike, is high for Cl, H, Hf K, N, O, S, Sb, and Se.

Hot metal flow in a blast furnace hearth – model tests

Very recent operation measurements and test bore holes made in solidified blast furnace hearths indicate the presence of a downward‐arching, convex‐shaped coke zone in blast furnace hearths. By means of model tests using a two‐dimensional electric simulator that stands out against previously used models because of its easy handling, simulations were made of the effects of this convex‐shaped coke zone base on hot metal flows in blast furnace hearths. It was possible to detect a hot metal flow that has a different path to those known so far in the hearth bath and runs radially along the periphery of the hearth bottom to the tap hole. This flow path occurs when the coke zone rests partially on the hearth bottom centre. It causes increased stress on the refractory lining at the junction between the hearth bottom and hearth wall and in the long run can lead to extensive disintegration of the lining in these areas.When a coke zone with a convex base floats in the hearth bath, compared with a flat base, it produces no appreciable changes in the hot metal flows.As further tests showed, it is only possible to a limited extent to directly influence the hot metal flows by applying such operational measures as longer tap holes and a lower bath level.

石炭性状と乾留所要熱量の関係

Heat consumption for carbonization of coking coals is based on sensible heat for coking products and heat of reaction. The heat of reaction is calculated from the difference of heat of combustion between coal and its products. In commercial coke oven, heat for water gas reaction is also necessary to be added to heat consumption because water generated from coal contacts in coke zone during carbonization.In the present report, the total heat consumption described above (Net-HC) was investigated with 26 coking coals.The following results were found.(1) The values of Net-HC were in the range from 280 to 460 kcal/kg of dry coal.(2) Net-HC is decreased with developing coal rank and can be estimated efficiently from volatile matter, atomic ratio H/C and O/C of coal as described below.Net-HC (kcal/kg) =22.8 (VM)-548 (H/C) +320 (O/C) +808

高炉溶融帯・羽口間の動特性の理論解析

A mathematical model for analysing the dynamic characteristics of blast furnace in the region between melting zone and tuyere level are developed in this paper. On the basis of this model, the fundamental informations on the responses of both the location of melting zone and temperature of molten materials at the tuyere level to the step changes of blast temperature, steam ratio, blast volume and oil-injection rate have been obtained with the aid of digital computer.Three principal time constants, i. e., time constant concerning the accumulation of materials in melting zone, one related to the accumulation of heat in coke zone supposedly located below melting zone and one connected with the shifting process of melting zone, have been taken into account in the analysis. It has been found that the shifting process of melting zone affects severely on the dynamic behavior of blast furnace, since the time constant connected with this process becomes large value such as several hours.