Feasibility of High Pressure Air Injection in Heterogeneous Light Oil Reservoir by Thermal Simulation Aarshavi Shah, PDPU Kaushal Modi, PDPU

Transcription

1 SPE Feasibility of High Pressure Air Injection in Heterogeneous Light Oil Reservoir by Thermal Simulation Aarshavi Shah, PDPU Kaushal Modi, PDPU Copyright 2012, Society of Petroleum Engineers This paper was prepared for presentation at the SPE EOR Conference at Oil and Gas West Asia held in Muscat, Oman, April This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract HPAI in Light oil reservoirs have gained a success nowadays in the field. Air injection in light oil is decided on the basis of in which phase of the life reservoir stands. The main aim of this EOR method is to strip out the Lighter Hydrocarbons from the residual Heavy Fractions and also to act as a pressurizing agent as from conventional heavy oil reservoirs to reduce the viscosity and removing the residual oil saturation.the factors affecting the HPAI are Geology and the Geological structure and the reaction kinetics parameters like reaction frequency, enthalpy, activation energy and the mode of reaction i.e. Low Temperature Oxidation (LTO) and High Temperature Oxidation (HTO). In this paper, the laboratory procedures, for the Air injections have been calculated i.e. the velocity of the combustion front, temperature profiles and the ignition time of the initiation of reaction. Simulation of combustion tube experiment has been carried out and expanded to the block model in CMG STARS. The tuning of the reaction parameters is to generate the temperature profile of the twelve zones of the combustion tube experiment. History matching with the data generated in simulation and the outcomes of the laboratory experiment is performed. The block model with five spot inverted pattern predicts the variation of oil saturation, temperature, oil cut, water cut, cumulative fluid rates with time. The conclusion from this simulation is the feasibility of High Pressure Air injection processes in Light Oil Reservoir and predicting the future performance in the reservoir.the results from this simulation were that the clay particles affect the reaction kinetics in the Light Oil and the increment in the recovery is about 20 % because of HPAI.

2 2 SPE Introduction Air injection has been introduced as an improved oil recovery technique. Air was used as a pressurizing agent, but it was discovered that oxidation reactions occurred at the reservoir temperature, resulting in the development of high temperature reaction zone which could be sustained and displaced away from the injection well. High Pressure Air Injection processes are based on the in-situ generation of a flue gas; this concept is usually based on the mobile light oil reservoir. When air is injected into the reservoir two main processes take into place 1. Oxidation 2. Displacement The important factor determining the success of an air injection project is the oxidation kinetics of the reactions taking place because of the oxidation reactions. The air-injection capacity must be sufficient to deliver the required flow rate of oxygen to the oxidation reaction region. It is simple to develop a good estimate of the injected air/produced oil-ration based on the simple material based calculation. In the case of Light Oils, HPAI process has been implemented successfully in many fields. Light Oils are characterized by low viscosity, low specific gravity, and high API gravity from 32ºAPI to 42ºAPI. They are governed by a very low wax content.these type of characteristic oils are found at higher depths. There are many advantages: 1. Higher temperature 2. Low viscosity 3. The heat loss is reduced and solubility of the gases is higher at high pressures 4. The differential temperature between the reservoir and the heated air will be less so less heat loss. 5. As the solubility increases, the viscosity of Hydrocarbon gas and CO 2 will decrease and swelling increases. 6. Mobility and displacement efficiencies increase with the increase in solubility. The classification is based on the differences in the oxygen uptake V/s temperature behavior of oil. There are mainly two types of reactions taking place: 1. High Temperature Oxidation 2. Low temperature Oxidation In the case of Light oil, the air injection is operated in Low Temperature Oxidation. The range of oxidation reaction is from C and is an exothermic reaction into the range where oxygenaddition reactions dominate.

3 SPE Oxygen- Addition Reactions: Hydrocarbon + Oxygen Oxygen-Addition products where the oxygen-addition products consists of organic acids, aldehydes, alkylhydroperoxides. Low temperature oxidation of crude oil is characterized by either little or no carbon oxides being produced by the reaction.certain soils and metallic derivatives have a catalytic effect on LTO. There is an apparent increase in hydrogen-carbon ratio at low temperature which is due to the fact that oxygen is consumed in the reactions which do not produce carbon oxides. Decreasing the heating schedule rate increases the amount of fuel deposited due to LTO reactions.it is also found that LTO reactions increase the viscosity and boiling range of the oil. Light Oils are more susceptible to Low Temperature Oxidation. Because this process is generally considered for deep reservoirs where the native reservoir temperature is high, the reactivity of oxygen with the oil at the reservoir temperature will generally be sufficient to remove oxygen from the air stream.this means that oxygen reactions can be ignited spontaneously, and that the air flux can be operated at lower levels.the major concern with spontaneous ignition and low air flux operation is the formation of hydrogen peroxides in the region of the injection well. Light oils generally have good mobility in cold portion of the reservoir; thus the combination of the cold zone mobility and capability of effective displacement at low fluxes than a single reservoir can service a much greater volume of light oil reservoir than is possible in a heavy-oil reservoir. There are many geological concerns with the light oil reservoir. In a light oil reservoir that produces lowviscosity crude from wells that had good productivity, the following reservoir features would be desirable.generally the production wells will produce at a higher rate even at a reservoir temperature, if an effective drive-mechanism is used. A homogeneous permeability profile can be used in this type of secondary recovery project to obtain a high specific displacement and volumetric sweep. An early heat front arrival at the producing well is not desirable because these wells will produce oil adequately at reservoir temperature, provided sufficient differential pressure is available. A homogeneous permeability profile will enhance the possibilities of high vertical sweep. If the air-injection rate is increased slowly in the pattern, the tendency of the burning front to channel will be reduced, resulting in a high vertical sweep. A reservoir with little or no dip is preferred for oil characteristics of this type. Directional control of the burning front is easier in a flat reservoir because that injected air will not move up-dip. In this case uniform patterns with central injection wells are used. If the oil is highly mobile when the combustion drive begins, other structural features can increase oil recovery. Frontal Displacement characteristics of the gas drive are more efficient when the gas is injected high structurally, and gas and oil displacements are down dip. Most reservoirs, however, do not produce at a sufficient oil rates to

4 4 SPE support this displacement scheme. These reservoir features combine to give high vertical and areal sweep efficiency. Oil is produced from the cold wellbore at or a rate above the rate that is being displaced by the burning front. For various air injection projects it has been seen that the structure, lateral continuity and physical characteristics of the individual sand layers within the reservoir as well as the reservoir heterogeneities play an important role. Lack of good sand continuity and channeling can lead to failure of the project. Since HPAI is inter-well drive process good horizontal continuity is critical to the process. Gaps in the formation, overburden or leaky inter-zonal seals in stratified reservoirs can allow fluid to leak into overlying strata and reduce the effectiveness of the injectant. The key geological parameters to be considered when selecting a site for a HPAI are: 1. The degree and extent of lateral and vertical continuity 2. Depth 3. Thickness 4. Structural attitude and dip: Dip and resulting gravity dominance play an important role in economic success of HPAI injection.the reason behind the location of HPAI pilot at the uppermost part of the structure is that the burned volume of the pilot located at the upper part of the reservoir can be accurately be determined and both the air-oil ratio (AOR) and the incremental oil recovery due to combustion can be estimated more reliably. Also by locating the pilot up-dip, re-saturation of the burned zone can be avoided in case air injection is terminated due to compressor failure. 5. Overburden Competence 6. Reservoir Heterogeneities: Reservoir heterogeneities impacting in-situ combustion recovery performance include permeability barriers to lateral and vertical flow, natural fractures, high permeability thief zones, directional permeability, presence of gas cap and aquifers. Permeability barriers can have both positive and negative effect upon the HPAI process. As a positive effect, vertical barriers can divide a thick reservoir into small units, which can be more compatible with in-situ combustion process. Vertical barriers can act as a seal to upward migration of air injected and may result in uniform burning in relatively thick reservoir. As a negative effect, horizontal permeability barriers can reduce the reservoir continuity and recovery. Fracture and joints are secondary properties that may create preferential flow channels and influence the recovery. 7. Presence of gas cap and aquifier 8. Composition of reservoir matrix: The economic and applicability of air injection in a reservoir is dictated to a large extent by the nature and amount of fuel formed in the reservoir. If sufficient fuel is not deposited the combustion front will not be sustaining.considerable laboratory and

5 SPE some field evidence indicates that the mineralogical composition of the reservoir rock and chemical composition of the crude oil can affect the amount of fuel available to sustain combustion.rock type is probably more important in Light Oil reservoirs in determining the amount of fuel deposition in the reservoir.the clay and metallic content of the rock, as well its surface area has a profound influence on fuel deposition rate and its oxidation. Presence of clays and fine sands in the matrix favor increased rates of fuel formation. Increased clay content kaolinite and illite favor increased rates of fuel formation by favoring low temperature oxidation reactions. Rock minerals such as a pyrite, calcite, and siderite also favor fuel-forming reactions. Low air fluxes resulting from reservoir heterogeneities and oxygen channeling also promotes low temperature oxidation and fuel formation reaction. Fuel deposition varies with the lithologic characteristics of the rock. It has been seen that fine to very fine grained sandstone containing significant amount of siderite and pyrite deposited a greater amount of the fuel than medium grained sandstone containing similar amount of pyrite. Similarly medium grained sandstone containing large amount of clay material yielded large amount of fuel 9. Effect of well spacing: Problems may arise in two ways when determining the well-spacing.if the well-spacing is too close, the combustion front may experience early break through, while if the well-spacing is too large, the oil production rate will be slow, thus prolonging the life of the project and making economics unattractive. Hence well-spacing should be in the optimum range to maximize oil recovery. Geological considerations are quite important in determining the optimum flood pattern and well spacing. The wells should be spaced to fit the geological pattern of the sand. Many sand bodies where air injection projects have been implemented are not continuous sheets of sand, but are lenticular in shape.these sand bodies frequently exhibit anisotropy parallel to the bedding. The permeability of the sand in one direction therefore is greater than in other. In such anisotropic, lenticular reservoir, it is advisable from a stratigraphic standpoint to drill injection wells at right angle to the direction of high permeability trend at a closer well spacing. The production wells can be drilled along the trend on a wider spacing ( 600 ft or greater) Lab Data and Calculations for the experiment performed on HPAI of a G-field Core: Experiments are performed in the laboratory like Differential Scanning Calorimeter (DSC), Thermo Gravimetric Analyzer (TGA), and Combustion Tube. DSC is used to measure heat flow into or out of a sample as it is exposed to a controlled thermal profile.it provides both qualitative and quantitative information about material transition and also provides the temperature at which the transition occurred. It also indicates the heat involved in the reaction kinetics.

6 6 SPE Kinetics provides vital information like rapid automatic calculation of reaction order, activation energy, pre exponential factor and rate constant. By DSC we can investigate the feasibility of application of air injection, monitoring of ongoing combustion process, thermal behavior, oxidative stability of oil, determination of crackable part of crude oil, input parameter for starting a simulator. TGA measures the amount and rate of weight change in a material either as a function of increasing temperature, or isothermally as a function in a controlled atmosphere. Combustion Tube Experiment is performed to determine air and fuel requirements, which affect the economic viability of a field process, and can aid in preliminary design of compressors or other field elements, produced gas compostion, particularly the level of carbon dioxide, which act as a thermometer in a field setting, temperature, produced fluid rates for history matching and tuning of numerical simulators, effects of the process on produced fluid properties such as water ph (indicator for potential corrosion problems) and oil upgrading potential as production of H 2 S or other safety concerns. Following are the lab experiments output of Light Oil G-Reservoir, the air-fuel calculation, produced gas composition, time of ignition, etc. Fig 1: Chart of produced gas composition after air injection in combustion tube experiment. Fig 2: Cumulative production of oil and water after air injection in combustion tube experiment. Table 1: Normalized gas composition take into affect C1 component

7 SPE Calculations on Air/Fuel consumption based on the composition of the liberated gases: The basic chemical expression that describes the combustion of coke can be written as: C X H Y +ao 2 +RaN 2 = bco 2 +dco+ fo 2 +jh 2 O+RaN 2 R = y N2 /y O2 where R is the ratio of mole fraction of nitrogen to oxygen in the feed gas. (a, b, d, f, j are stoichiometric Coefficients). Calculation of the G-Data s Air-Fuel Consumption by the data given of the produced gases and injected air: Table 2: Stoichiometric calculations for the combustion reaction for the lab combustion tube experiment

8 8 SPE Calculation of the ignition time: An Arrhenius equation describes the reaction of air (oxygen) with oil or with the coke like-fuel. Most laboratory experiments, to determine the reaction rate, are conducted at low temperatures more representative of steam plateau than of the burning front. Several studies speculate the reaction shifts to one of diffusion controlled at high temperature zone. Calculation of the ignition time of the experiment performed of the G-field: Table 3: Calculation of ignition time after Air Injection in Combustion tube experiment

9 SPE Variation of temperature in 12 zones with the run time of the lab experiment: Fig 3: Variation of temperature in 12 different zones of Fig 4: Peak Temperature Profile of 12 zones of combustion tube combustion tube with respect to run time Here we can see that the peak temperature is decreasing from 4th to 9th zone, it is because of the breakthrough of the fluids. Here the oxygen utilization rate is taken from the GC mass data and the peaks of both the graph are matched to know the movement of the combustion front. Calculation of the velocity of combustion front: Velocity of combustion front at 300 C= slope of displacement Vs time at 300 C = m/hr Fig 5: Plot of position of combustion front in the combustion tube at 300 ºC Fig 6: Plot of position of combustion front in the combustion tube at 400 ºC Velocity of combustion front at 400 C= slope of displacement Vs time at 400 C = m/hr Fig 7: Concentration profile of variation of calcium and magnesium salts from the produced water data

10 10 SPE Change in the composition of various ions in water due to in-situ combustion: From above plot, we can say that from time 2 to 3 we can see that there is a decrease in the concentration of Ca ++, it is because of Dolomitization reaction, leading to increase in the magnesium ion concentration in that time period. At high temperatures, leaching process takes place leading to increase of Calcium ion process. At 350 C leaching of iron takes place on the surface. 1. The concentration of sulfate increases. 2. Pyrites will decompose to H 2 S leading to decrease of ph and increase in acidity. 3. Maltenes, Ketones, peroxides are produced in the oxidation reactions leading to decrease in ph. 4. Interstitial water will pushout the oil. Fig 8: Variation of ph of produced water Fig 9: Variation of Salinity and Total Dissolved Solids (TDS) of produced water Fig 10: Variation of sodium and chlorine ions in produced water in CT The clay and metallic content of the rock, as well as its surface area has a profound influence on fuel deposition rate and its oxidation. Clay and fine sand have very high specific surface area hence presence of clays and fine sands in the Matrix favor increased rate of coke formation. Clays are solid acid catalysts and their catalytic activities are related to their acid site density and acid strength. Increased clay content increases the acid site density and acid strength. Literature on catalytic cracking process reveals that increased acid site density and acid strength lower activation energy (smaller Arrhenius constant), and promote low temperature oxidation and coke formation reactions. This is particularly advantageous in light oil reservoirs, where fuel deposition can be less than that needed to sustain combustion. Metals and metallic additives also known to affect the nature and the amount of fuel formed. Metals are used as catalysts in the petroleum refining and chemical process industries to accelerate the hydrocarbon oxidation and cracking reactions. In studies undertaken to investigate the effect of metal contamination on hydrocarbon cracking reactions, it was found that various metals promote coke formation and the catalytic effect of these metals was found to be ordered as follows: Cu < V <Cr = Zn < Ni, with nickel

11 SPE about four to five times as active as vanadium. Studies on the effect of reservoir minerals on in-situ combustion indicate metals promote low temperature oxidation and increase fuel deposition. The combustion tube experiment model is simulated in CMG STARS and a 2-D Simultion is performed for the combustion tube. Here, the basic requirement to perform the simulation is the lab data requirement. The data generation from the given data is performed in Builder WIN Important parameters required in the simulation are Rock-Fluid Data, Reservoir parameters, Component, Initial condition, wells and recurrent data, I/O data.the model development is performed after the data generation. As we are performing the simulation of HPAI for light oils, the component selection is one of the important criteria as it governs the combustion process. The other important parameter is the reaction kinetics and its impact on the simulation. In this simulation, nine components have been taken into account Water', 'Dead_Oil', 'Soln_Gas', 'CO 2 ', 'HeavyOil','H 2 S', 'Oxygen', 'N 2 _CO','Coke'. Five reactions are generated according to the given input value of the rock-data, well data and reservoir parameter. In the reactions, Reaction frequency, Enthalpy, Activation Energy, Burning zone temperature upper limit are generated. Coefficient Unit Water Dead_Oil Soln_Gas CO2 Heavy Oil Aqueous Oleic Oleic Oleic Oleic Options KV1 kpa e KV2 1/kPa KV KV4 C KV5 C Table 4: K-Values of the five reactions generated in the Simulator for different components Item Options Units Water Dead_Oil Soln_Gas CO 2 HeavyOil Aqueous Oleic Oleic Oleic Oleic Phase Water and Oil Density Mass Kg/m Density Liquid Compressibility 1/kPa e e e e e st thermal expansion 1/ 0 C Table 5: Density, Liquid compressibility, thermal expansion values of different components

12 12 SPE Comp No. Component Oleic Gaseous Solid P crit T crit MW kpa C Kg/mol 1. Soln_Gas Reference K-Value p partial 2. CO 2 Reference K-Value P partial 3. Heavy Oil Reference P 4. H 2 S Reference P 5. Oxygen Reference P 6. N 2 _CO Reference P 7. Coke Reference P Table 6: Thermodynamical properties of different components From the lab data, the end point values of the saturation of the core are taken and according to the Stone s equation the relative permeability curves are constructed for oil-gas and oil-water. Fig 11: Oil-Water relative permeability curve Fig 12: Oil-Gas relative permeability curve Fig 13: Ternary Diagram for the three phases

13 SPE The following reactions are generated Sr. No Reaction Dead_Oil Soln_Gas CO HeavyOil H 2 S Coke Oxygen + 1Coke Water + 1CO Dead_Oil Oxygen HeavyOil Dead_Oil Oxygen 5.606Water CO N 2 _CO 5 1 Heavy Oil Dead_Oil Coke Table 7: The five reactions generated according to the input parameters given in the simulation Fig 14: Plot of Volume Balance (Prod/React of Equation) Vs. Pressure Fig 15: Plot of Arrhenius constant vs Temperature

14 14 SPE Well and recurrent data: In combustion tube experiment two injectors and one producer were taken Constraints Operate Operate Injector 1 Injector 2 Producer 1 Constraints Surface Gas 0.32 m3/hr Surface gas 0.32 Monitor Bottom Hole Rate(STG) Rate m3/hr Pressure(BHP) Bottom Hole 9492kPa Bottom 9492 Pressure(BHP) Hole kpa Pressure 9350 kpa Injected Fluid Composition N2 Purging 1.00% N2 O2 Options 0.78% 0.22% Status Open Status Shut-in hr Shut-In Open hrs Status Open Perforation Address Perforation address 100 Well-Index Tube-End Linear flow model Tube-End Flow Table 8: Properties of the wells placed in the 2-D CT Simulation model Well-Index Tube-End Flow After adding all the input parameters, the simulation is run and validated. The preceding profiles shows the variation of temperature and viscosity of oil phase at different time intervals At days Fig 16: Temperature profile at days Fig 17: Viscosity profile at days

15 SPE At days Fig 18: Temperature profile at days Fig 19: Viscosity profile at days At days Fig 20: Temperature profile at days Fig 21: Viscosity profile at days At days Fig 22: Temperature profile at days Fig 23: Viscosity profile at days

16 16 SPE Fig 24: Temperature profile generated after simulation of combustion tube experiment. The reaction parameters such as reaction frequency, enthalpy of reaction, activation energy are adjusted such that the temperature profile should be appropriate. The reaction frequency affects the temperature the most, higher the reaction frequency higher the temperature is achieved. History Matching: Here, the lab data and the results generated by the simulator are matched. The run time of the lab was from 12:00 AM to 10:48 PM. From this time, the gas rates were measures from the flow-meters and recorded in the computer. These rates corresponding to their respective time period were created in the excel sheet and then converter to ANSI file or.fhf file. Similarly, the temperature profiles, and cumulative gas, oil, water rates were taken from the combustion tube results.these files were opened in the RESULTS 3-D and this Field History file was matched with the output files generated by the simulator. Following are the matching plots: Fig 25: History Matching of Cumulative oil of Lab-data and the simulation generated data Fig 26: History Matching of Cumulative gas of lab-data and the simulation generated data

17 SPE The gas rates of the lab data and the simulated data are matching above 85%.So one can say that the data generated in the simulator are valid.the Cumulative oil rates are also matching above 50 %. Fig 27: History Matching plot of temperature profiles of lab data and simulation generated data Description: The temperature profiles of first five zones are matching with the temperature profile generated in the lab with respective run time.the temperature profile generated in the simulation in the last zones are remaining constant at a higher temperature while in the lab data the temperature profile is decreasing after attaining a peak temperature and attaining a equilibrium value. The reason behind this is that the composition of G reservoir rock consists of the clay minerals.thus, as we know that in Light Oil Reservoir, clay particles have a profound influence in the fuel deposition and indirectly the burning of combustion front as clay particles increases the rate of reaction and bring the reaction to the LTO mode. In the simulator, no parameter has been given as input for the presence of clay particles. The temperature of the simulated data operates in the HTO Mode and the temperature remains high of about 400 C. So, one can say that clay particles are an important parameter for governing the reactions behind the kinetics of the Light Oil. Block Model: After History Matching, a block model is created of one-layer, and five-spot inverted pattern is made i.e. one injector at the centre and four producers at the end of square. A Cartesian grid of 100*100*1 is created.

18 18 SPE The Grid Properties are as follows: Sr. No. Properties Value (%) 1 Porosity 28 2 Water saturation 50 3 Oil Saturation 30 4 Gas Saturation 20 Table 9: Rock and fluid properties of G-field The Block Model is made to run for 30 days.with same component history, reservoir parameters, only the well recurrent data is changed. The Surface Gas Rate is calculated on the basis of the air/fuel ratio and it is up-scaled on the basis of the rock volume of the reservoir.the air-fuel ratio was calculated kg/m 3 on the swept core volume is m 3, while the reservoir rock volume is 7200 m 3. And the calculated STG comes out to be 1, 87,000 m 3 /day. Following are the wells recurrent data added in the Builder: Injector 1 Producer 1,2,3,4 Constraints Constraints Operate STG Surface 2,00,000 Monitor Bottom Hole 9350 kpa Gas Rate m 3 /day Pressure(BHP) Operate BHP Bottom 9492 kpa Hole Pressure Options Injected Fluid Status Open Composition O 2 22% Perforation (1, 100, 1) Address N 2 78% (100, 1, 1) Options (100, 100, 1) (1, 100, 1) Status Open Status Open@350 0 C Open@76 0 C days Perforation Address (1,50, 1) Well index type Tube-end linear flow model Well Index type Tube-End Linear flow Table 10: Well properties placed in the 3-D reservoir block model

19 SPE The plots generated for seeing the variation of temperature on viscosity of oil at different days: At 2 nd day Fig 28: Temperature profile in 3-D block model in an inverted five-spot pattern at 2 nd day At 3 rd day Fig 29: Viscosity in oil phase(heavy Oil) in a 3-D block model in an inverted five-spot pattern at 2 nd day Fig 30: Temperature profile in 3-D block model in an inverted five-spot pattern at 3 rd day Fig 31: Viscosity in oil phase(heavy Oil) in a 3-D block model in an inverted five-spot pattern at 3 rd day At 9 th day Fig 32: Temperature profile in 3-D block model in an inverted five-spot pattern at 9 th day Fig 33: Viscosity in oil phase(heavy Oil) in a 3-D block model in an inverted five-spot pattern at 9 th day

20 20 SPE At 10 th day Fig 34: Temperature profile in 3-D block model in an inverted five-spot pattern at 10 th day Fig 35: Viscosity in oil phase(heavy Oil) in a 3-D block model in an inverted five-spot pattern at 10 th day At 28 th day Fig 36: Temperature profile in 3-D block model in an inverted five-spot pattern at 28 th day Fig 37: Viscosity in oil phase(heavy Oil) in a 3-D block model in an inverted five-spot pattern at 28 th day At 31 st day Fig 38: Temperature profile in 3-D block model in an inverted five-spot pattern at 31 st day Fig 39: Viscosity in oil phase(heavy Oil) in a 3-D block model in an inverted five-spot pattern at 31 st day

21 SPE Variation of Bubble point pressure of CO 2, Oil saturation, Gas saturation and water relative permeability: Fig 40: Variation of bubble point pressure (KPa) at 2 nd day Fig 41: Variation of bubble point pressure (KPa) at 10 th day. Fig 42: Variation of bubble point pressure (KPa) at 31 st day Fig 43: Variation of Water Saturation at 2 nd day. Fig 44: Variation of Water Saturation at 10 th day. Fig 45: Variation of Water Saturation at 31 st day. Fig 46: Variation of Gas Saturation showing the gas break through at the producer wells at 2 nd day. Fig 47: Variation of Gas Saturation showing the gas break through at the producer wells at 10 th day. Fig 48: Variation of Gas Saturation showing the gas break through at the producer wells at 31 st day. Fig 49: Variation of water relative permeability from injector to producer wells at 2 nd day. Fig 50: Variation of water relative permeability from injector to producer wells at 10 th day. Fig 51: Variation of water relative permeability from injector to producer wells at 31 st day.

22 22 SPE Future performance: Fig 52: Cumulative gas, oil and water SC(m 3 ) for 31 days of simulation run. Fig 53: Oil, Water, and Liquid Rate SC (m 3 /day), for 31 days of simulation run. Fig 54: Oil and water cut for 31 days of simulation run. Conclusions: Following interpretations were made after performing the simulation and matching it with the lab data: Fig 55: Plot depicting primary and tertiary production and showing the incremental recovery. 1) The above chart shows the primary and the tertiary production generated from the simulation of the G-Field. There is about an increment of 20% production of oil and a steady production, also we can see that an increase in the plateau time for the production due to this IOR method

23 SPE Thus, this HPAI project can be implemented in the field as we can see a better future forecast from the generated data. 2) From the temperature profiles, on can see that the reactions undergoing in the reservoir are in proper control and the burning front is sustained, thus the parameters like viscosity, oil saturations are also under control. 3) In 3-D image of the oil saturation of the block model, we can see early breakthroughs of the oil in the producer well. 4) The Gas saturation is varying with the injected air ratios, they are increasing at the burning front area and decreasing as the relative permeability to the air decreases and have a steep decreases as it approach the producer wells. 5) Even, from the Bubble point pressure 3-D images, we can see CO 2 in the dissolved state at the combustion front and increasing dissolution towards the producer well, which shows the swelling effect of the crude oil. 6) Now, the viscosity is a function of pressure and temperature, from the 3-D images that displays the rapid decrease in the viscosity of the dead oil in the reservoir along with the reduction of viscosity of heavy oil generated due to the LTO reaction of the Light Oil. 7) There is also a major disadvantage in this project, here due to high initial water saturation; one can see the early breakthroughs of the water. Even the water cut plot shows a high of 70 % because of the water generated due to the combustion reactions taking place inside the reservoir. Thus, the water production will be high along with the oil, so some facilities should be implemented at the surface for the oilwater separation. Water shut-off projects should be implemented at the early period of the production 8) The Heterogeneities in this model can be seen due to the presence of clay minerals in the G-field. The clay minerals here act as a catalyst for the kinetic reactions taking place in the reservoir. As we know the Light Oil have a significant effect of Clay minerals in the process of fuel deposition as they bring the reactions in the LTO mode and bring the down temperature by decreasing the activation energy and increasing the rate constant. 9) Thus, one can say that the HPAI projects can be implemented successfully in the reservoirs which have the impermeable streaks of shale in between the permeable sandstones.

24 24 SPE References Papers T.Onishi, SPE, and K. Otasu, SPE, Japan Oil, Gas and Metals National Corporation and T.Teramoto, SPE, Teikoku Oil Co. LTD. History matching with Combustion-Tube tests for Light Oil Air Injection Project,presented at 2006 SPE Oil and Gas Conference and Exhibition, Beijing, China, 5-7 December R Gordon Moore, S.A. Mehta, Matthew G. Ursenbach, Catherine J. Laureshen, Strategies for successful Air Injection based for IOR processes B.L. Hughes, H.K. Sarma, SPE, University of Adelaide, Burning reserves for Greater recovery? Air injection in potential in Australian Light Oil Reservoirs, presented at SPE Asia Pacific Oil and Gas conference and Exhibition, Adelaide, Australia, September 2006 A.T. Turta, SPE, and A.K. Singhal, SPE, Petroleum Recovery Inst. /Alberta Research Council, Reservoir Engineering Aspects of Light-Oil Recovery by Air Injection, SPE International Conference and Exhibition in China, Beijing, 2 6 November 2001 Thesis: Partha Sarthi, U.S. Department of Energy, Tulsa, Oklahoma, In-Situ Combustion Handbook and Practices, January 1999 Acknowledments: We will like to thanks Mr. P V Raju (Manager-Reservoir, Institute of Reservoir Studies (IRS), ONGC) to guide in running simulation on CMG STARS during summer internship.