Enhanced oil recovery is oil recovery by the injection of stuffs non usually present in the reservoir. In situ Combustion ( ISC ) is the procedure of an enhanced oil recovery procedure to better the recovery of heavy petroleum oil. As it is the oldest thermic recovery technique, it has been used for over nine decennaries with many economically successful undertakings. However, it is regarded as a bad procedure by many, chiefly because of many failures of early field trials. Most of those failures came from application of a good procedure ( ISC ) to the incorrect reservoirs or to the poorest chances. This paper contains a description of ISC, a treatment of research lab testing techniques, an illustration of how to use laboratory consequences to field design, a treatment of operational patterns and jobs, and an analysis of field consequences. For complete reappraisal, the instance survey is done on Balol and Santhal Fieldss in Mehsana.
In-situ burning has been known since 1888. Mendeleev was the first scientist to propose the unmoved transition of coal into combustible gases. Based on the earlier laboratory consequences, Sheinman and Dubrovai in 1934 proposed the processed the procedure of oil supplanting by agencies of a traveling belowground fire-front. A figure of field trials, were performed in assorted parts in the late 1940 ‘s and early 1950 ‘s. The consequences from these trials indicated that the heat losingss were big, hence the injected hot gases reached the formation zone with nothing thermic energy. These surveies nevertheless were followed by laboratory research field trials and development of mathematical theoretical accounts to imitate unmoved burning as a consequence of which this procedure has been recognized and can be used as a promising method of retrieving heavy oil from crude oil reservoirs.
The rule of unmoved burning is to accomplish burning within the pores of hydrocarbon-bearing reservoir, firing portion of the oil in topographic point in order to better the flow of the unburned portion. Combustion is supported by the injection of air into the reservoir at one or more Wellss. The heat generated during burning is sufficient to raise the stone to a high adequate temperature to enable the burning forepart to self propagate after initial ignition by increasing mobility of the fluid.
Methodology
The unmoved burning procedure was applied to petroleum reservoirs depending on broad scope of features like Nature of formation, deepness, temperature, reservoir thickness, permeableness, porousness and oil impregnation in order to retrieve oil. Pressure is besides a factor but non much critical.
The procedure was applied in reservoirs with mean permeableness runing from 40 to 8000mD, whereas the oil impregnation varied from 25 to 95 % . In add-on fuel content is one of the most of import factors act uponing the success of a fireflood procedure. The fuel content of the reservoir is the sum of coke available for burning that is deposited on reservoir stone as a consequence of distillment and thermic snap. If the fuel content is excessively low, the burning procedure in the reservoir can non be self sustained. Furthermore, a high fuel content requires a big sum of air and high power cost which means low oil production. Gates and Ramey ( 1980 ) compared the estimated fuel content by assorted methods including laboratory consequences with that of field undertaking informations. It has been shown that fuel content determined by experimentation in the research lab by tubing -run method can supply a moderately good appraisal of the fuel content obtained in the field.
In situ burning is fundamentally injection of an oxidising gas ( air or oxygen-enriched air ) to bring forth heat by firing a part of the resident oil. Most of the oil is driven towards the manufacturers by a combination of gas thrust ( from the burning gases ) , steam and H2O thrust. This procedure is besides called fire implosion therapy to depict the motion of a combustion forepart inside the reservoir. Based on the several waies of front extension and air flow, the procedure can be frontward, when the burning forepart progresss in the same way as the air flow, or contrary, when the forepart moves against the air flow.
Rearward Combustion
This procedure has been studied extensively in research labs and has been field tested. In brief, it has non been successful economically for two major grounds. First, burning started at the manufacturer consequences in hot produced fluids that frequently contain unreacted O. These conditions require particular, high-cost tubular to protect against high temperatures and corrosion. More O is required to propagate the forepart compared to send on burning, therefore increasing the major cost of runing an in situ burning undertaking. Second, unreacted, coke-like heavy terminals will stay in the burnt part of the reservoir. At some clip in the procedure the coke will get down to fire and the procedure will return to send on burning with considerable heat coevals but small oil production. This has occurred even in carefully controlled research lab experiments. In drumhead contrary burning has been found hard to use and economically unattractive.
Forward Combustion
Forward burning can be farther characterized as “ dry ” when merely air or enriched air are injected or “ wet ” when air and H2O are co-injected.
Dry Forward Combustion
The first measure in dry forward ISC is to light the oil. In some instances auto-ignition occurs when air injection begins if the reservoir temperature is reasonably high and the oil moderately reactive. Artificial Ignition has been induced utilizing down hole gas burners, electrical warmers, and/or injection of pyrophoric agents or steam injection.
Figure: conventional illustration of the unmoved burning procedure ( Source )
After ignition the burning forepart is propagated by a uninterrupted flow of air. As the forepart progresses into the reservoir, several zones exist between injector and manufacturer as a consequence of heat and mass conveyance and the chemical reactions. The above figure is an idealised representation of the assorted zones and the resulting temperature and unstable impregnation distributions. In the field there are passages between zones.
A. The burnt zone is the volume already burned. This zone is filled with air and may incorporate little sums of residuary unburned organic solids. As it has been subjected to high temperatures, mineral changes are possible. Because of the uninterrupted air flow from the injector, the burned zone temperature increases from injected air temperature at the injector to combustion front temperature at the burning forepart.
B. The burning forepart is the highest temperature zone. It is really thin, frequently no more than several inches thick. It is in this part that O combines with the fuel and high temperature oxidization occurs. The merchandises of the combustion reactions are H2O and C oxides. The fuel is frequently misnamed coke. In fact it is non pure C but a hydrocarbon with H/C atomic ratios runing from about 0.6 to 2.0. This fuel is formed in the thermic checking zone merely in front of the forepart and is the merchandise of checking and pyrolisis which is deposited on the stone matrix. The sum of fuel burned is an of import parametric quantity because it determines how much air must be injected to fire a certain volume of reservoir.
C/D. The cracking/vaporization zone is downstream of the forepart. The petroleum is modified in this zone by the high temperature of the burning procedure. The light terminals vaporize and are transported downstream where they condense and mix with the original petroleum. The heavy terminals pyrolize, ensuing in CO2, CO, hydrocarbon gases and solid organic fuel deposited on the stone.
E. The steam tableland. This is the zone where some of the hydrocarbon bluess condense. Most of those condense farther downstream as the steam condenses. The steam tableland temperature depends on the partial force per unit area of the H2O in the gas stage. Depending on the temperature the original oil may undergo a mild thermic snap, frequently named visbreaking that normally reduces oil viscousness.
F. A H2O bank exists at the taking border of the steam tableland where the temperature is less than steam impregnation temperature. This H2O bank decreases in temperature and impregnation downstream, with a ensuing addition in oil impregnation.
G. The oil bank. This zone contains most of the displaced oil including most of the light ends that consequence from thermic snap.
H. Beyond these affected countries is the undisturbed original reservoir. Gas impregnation will increase merely somewhat in this country because of the high mobility of burning gases.
Wet Forward Combustion
A big sum of heat is stored in the burnt zone during dry forward in situ burning, because the low heat capacity of air can non reassign that heat expeditiously. Water injected with the air can capture and progress more heat stored in the burnt zone. During wet burning injected H2O absorbs the heat from the burned zone, vaporizes, moves through the combustion forepart and condenses, spread outing the steam tableland. This consequences in faster heat motion and oil supplanting. Depending on the water/air ratio, wet burning is classified as: ( 1 ) incomplete when the H2O is converted into superheated steam and recovers merely portion of the heat from the burned zone, ( 2 ) normal when all the heat from the burned zone is recovered, and ( 3 ) quenched or ace moisture when the forepart temperature declines as a consequence of the injected H2O.
ISC requires peculiar attending to air compaction, ignition, good design, completion, and production patterns. Air compaction causes high temperatures because of the high degree Celsius P / curriculum vitae ratio of air. Compressor design must see these high temperatures to guarantee uninterrupted, sustained operations free from the caustic effects of air and the detonation jeopardies of some lubricating fluids. Mineral oils are non recommended. Man-made lubricators withstand the higher temperatures and offer lower volatility and flammability than conventional lubricators.
In order to accomplish the burning in the crude oil reservoir, chiefly Spontaneous ignition and Artificial ignition are the two methods that are used for heavy oil recovery. Ignition can happen spontaneously if the oil is reactive, the reservoir temperature high plenty, and the reservoir is moderately thick. Down hole gas-fired burners allow good control of the temperature of injected gases and may be operated at a greater deepness than other methods. The disadvantages include the demand to run multiple tubing strings in the injection Wellss. Catalytic warmers run at lower temperatures but are expensive. Electrical warmers can be lowered with a individual overseas telegram, and can supply first-class temperature control. They can be reused repeatedly. There is, nevertheless, a deepness restriction because of electrical power losingss in the overseas telegram. Chemically enhanced ignition may necessitate handling and storage of unsafe stuffs. Steam may be used to locally increase reservoir temperature and facilitate car ignition. It suffers from deepness restriction because of wellbore heat losingss, but when the conditions are right it can be a really simple and effectual method for ignition. Combustion procedure was besides employed as primary and third recovery procedures.
Applications
In situ burning can be applied to many different reservoirs. Some suggested screening guidelines are:
Nature of the Formation: The stone type is non of import provided that the matrix/oil system is reactive plenty to prolong burning. As in any thrust procedure, high permeableness runs are damaging. Swelling clays may be a job in the steam tableland country.
Depth: Depth should be big plenty to guarantee containment of the injected air in the reservoir. There is no depth bound, except that this may impact the injection force per unit area.
Pressure: Pressure will impact the economic sciences of the procedure, but does non impact the proficient facets of burning.
Temperature: Temperature will impact car ignition but is otherwise non critical.
Reservoir Thickness: Thickness should be greater than approximately 4m ( 15 foot ) 2,3 to avoid inordinate heat losingss to environing formations. Very thick formations may show sweep efficiency jobs because of gravitation override.
Permeability: This has to be sufficient to let injection of air at the designed air flux. The air injectivity is particularly of import for heavy oil reservoirs. Conditionss are favourable when kh /I? is greater than approximately 5md m/cp.3
Porosity and Oil Saturation: These have to be big plenty to let economic oil recovery. The merchandise, I† So, needs to be greater than 0.08 for burning to be economically successful.
Oil Gravity: This parametric quantity is non critical. Insitu viscousness has to be low plenty to let air injection and resulting oil production at the design rate.
Oil Nature: In heavy oil undertakings the oil should be readily oxidizable at reservoir and stone matrix conditions. The research lab experiments can besides find the sum of air needed to fire a given reservoir volume. This is cardinal to the profitableness of the procedure.
Current Status of In-Situ Combustion
The unmoved burning procedure is attractive economically, provided it is applied to petroleum reservoirs incorporating about 50 % oil impregnation. The fuel content is one of the of import parametric quantities for burning support at a comparatively low air/oil ratio. Although laboratory experiments can supply some basic apprehension of the procedure, the primary rating factor is a field application before the procedure is employed on a big graduated table.
The present position of oil production by unmoved burning in the United States is about 11,000 bbl/day. The commercial dry ISC undertaking at Romania is the largest undertaking of its sort and it has been in operation for more than 34 old ages. The Balol and Santhal undertakings in India have been in operation for more than seven old ages and have been applied in a wet manner. Currently, combined all these three undertakings produce about 2300m3 /day. It is likely that really small laboratory research can be performed to better the displacement efficiency of this procedure. With continued betterment of the unmoved burning engineering, it is about certain that some signifier of this procedure, such as dry, wet, and partly satisfied burning, will happen greater application in the coming old ages.
Presently, commercial In situ burning undertakings are
Economic Evaluation
It is recognized that the success or failure of an enhanced oil recovery procedure depends on the economic rating. An economic survey completed by Wilson and Root ( 1966 ) , which is based on a modified signifier of planar theoretical account presented by Chu, compares the cost of heating a reservoir. The cost comparing was studied for a reservoir either in the presence of steam injection or forward burning without oil production. The chief consideration was to find heating cost of the same dimensions of a reservoir by either steam injection or by forward burning. The undermentioned decisions were drawn from this survey ;
( 1 ) Combustion is favored over steam injection as the sand thickness decreases the force per unit area addition.
( 2 ) As the coke deposition additions, steam injection is favored over the burning procedure.
( 3 ) As the het distance in the reservoir additions, reservoir warming by burning is more favourable as compared to steam injection.
( 4 ) Decreased injection rated favours the cost of steam injection relation to air.
( 5 ) Increased wellbore losingss with increasing deepness favour burning.
Decisions
It has been shown that unmoved burning procedure is suited to displace oils of gravitations greater than 10 degree API. The mean oil recovery by using unmoved burning is 50 % . The major sum of oil is recovered before discovery of the burning zone. For heavy oils, approximately 50 % petroleum oil recovery occurs after discovery, whereas low-viscosity oil production declines really quickly following discovery. The discovery of burning zone can be recognized by an addition in gas production and its O content. This is followed by a crisp addition runing from 100 grade to 200 grade Fahrenheit in bottom hole temperature. In add-on, the addition in H2O cut of the produced oil besides indicates the discovery of the burning zone. At the same clip, pH of the produced H2O lessenings, which is normally due to increase in the content of ions such as Fe and sulfate.
CASE STUDY
In-situ COMBUSTION AT MEHSANA, GUJARAT.
Mehsana plus, located in the northern portion of Gujarat province in India is the highest oil bring forthing onshore plus of ONGC with one-year petroleum oil production of 2.35 MMT. Its holding oil Fieldss bring forthing both heaviest petroleum and the lightest petroleum in India with API gravitation runing from 13Es – 42Es . Balol and Santhal Fieldss form a portion of this heavy oil belt with a API gravitation 15Es-18Es . Balol and Santhal field encompass 22.17 MMT and 53.56 MMT of oil in topographic point severally. The petroleum is asphaltic in nature incorporating 6-8 % asphaltene and the oil viscousness ranges from 50-450 hertz at reservoir force per unit area of 100 kg/cmA? and 70Es C temperature. Reservoirs have the permeableness of the order of 3-8 darcies and are runing under active H2O thrust. Subsequent Artificial lift methods resulted into high H2O production than oil. In many Wellss it became 95-100 % and some Wellss had to be closed due to high H2O cut. The hapless primary and secondary necessitated for In-Situ burning technique in these Fieldss.
Exploitation of heavy oil from these heavy oil Fieldss was a challenge for Mehsana plus. Based on consequences of laboratory surveies, the In-situ burning procedure was identified as the most suited technique for heightening the recovery from these Fieldss.
PILOT SCHEME
A pilot trial was designed and initiated in 5.5 acre country of southern portion of Balol field in 1990-91. The first good CP # 10 and thenceforth Balol # 171 were ignited with the aid of foreign experts. The sustained burning and production addition from nearby manufacturers lead to conceptualisation of the commercialisation strategies in full Balol field.
In another effort, a pilot strategy was besides designed for Lanwa oil field and an upside-down five slot form with four manufacturer Wellss had been ignited in 1992. At present the commercialisation of the strategy is in advancement to heighten the production from the field. A pilot strategy is besides running since 2002 in Bechraji field with four EOR injectors.
COMMERCIAL SCHEMES
Based on the techno-economic success of Balol Pilot undertaking, commercial strategies were designed for full Balol field for development of heavy oil. Sing the similarities between the Balol and Santhal oil Fieldss, this EOR technique has been implemented on a commercial graduated table in 1997 both at Balol and Santhal Fieldss. Soon four commercial strategies viz. Balol Ph-1, Santhal Ph-1, Balol Main and Santhal Main are running successfully. Till day of the month entire 61 Wellss have been ignited in Balol and Santhal under these commercial strategies. More Wellss are in line for transition into EOR injectors.
For commercial development of Balol and Santhal Fieldss utilizing In-situ burning technique, four major air compressor workss, two, each in Balol and Santhal Fieldss were set up. These workss supply compressed air to injector Wellss at reservoir conditions. Compressors except exigency air compressors at all the workss run on electricity. Combined installed capacity of these four workss is of compacting 4.9 NMm3/day air at maximal force per unit area of 123 Kg/cm2. Since H2O is required to be injected later during wet stage, installations for H2O intervention and injection are besides installed in the several workss. All these four workss are connected to each other with an integrated air grid web for better use of resources. A nomadic unit called Ignition dawdler is being used to originate ignition procedure. Gas burners are used for unreal ignition in Mehsana.
Consequence
After execution of the technique, diminution in production from Balol and Santhal Fieldss was arrested. A figure of Wellss have started fluxing on ego which were in unreal manner prior to unmoved burning procedure. Production proving informations of affected Wellss show the gradual addition in liquid production and lessening in H2O cut ensuing addition in net oil production. Presently EOR addition from both the Fieldss in the melody of 1200 TPD and air injection is in melody of 1.4MM Nm3/d. Production public presentation of these Fieldss shows the gradual addition in oil production and lessening in W/C % with increasing figure of injectors/air injection rate. It has non merely given a new rental of life to Balol and Santhal Fieldss but has besides increased the oil recovery factor by 2-3 creases from 6-13 % to 39-45 % .
OTHER HIGHLIGHTS OF THE PROJECT
ONGC is one of the few organisations in the universe, which has taken up In-situ burning procedure on such a big graduated table.
Entire 68 Wellss have been converted in EOR injectors at Mehsana Asset so far.
Most of the EOR injectors are old manufacturer Wellss. They have been converted to injector Wellss after proper lavation and cleansing of Wellss.
Ignition is being done in the reservoir at an mean deepness of 990 metres, holding 100 Kg/cm2 force per unit area and 70 degree Celsius temperature.
Present Air-Oil ratio in these Fieldss is about 1160 Nm3/m3 and Air-Oil ratio on cumulative footing it stands at 985 Nm3/m3, which indicates rather good efficiency of ISC procedure.
Figure: Production profiles of Santhal and Balol Fieldss ( Source )
MAJOR ISSUES
Happening of Auto-Ignition:
In Mehsana Gas burner is being used for unreal ignition. In this method air is injected through the ring and natural gas through tubing. An aluminium stopper fitted at the tip of burner prevents air and gas to blend. The stopper pops out when gas injection force per unit area is more than air injection force per unit area and signifiers gas-air mixture at the underside. A pyrophoric chemical is being used to originate the fire. At good no. Balol # A on 1998 the burner caught fire without take downing pyrophoric liquid. Burner temperature shot up to 910 grade Celsius and was shortly controlled by ignition tem members. There was no harm to thermocouple and down-hole assembly in this well. After this incidence car ignition occurred in turn in another three Wellss. In last two Wellss Santhal # B and Balol # C, thermocouple got damaged. Ignition experts were unable to set up the ground and redress for car ignition. Due to this failure, ONGC had wholly suspended all the ignition operations fearing farther car ignition and harm to thermocouple.
A close survey of all four instances of car ignition revealed that gas injection was used to be done at full discharge rate of gas compressor. Due to this sudden release of immense sum of gas, a really rich mixture of air and gas signifiers doing state of affairs vulnerable for car ignition. To get the better of this job, ignition squad came up with an thought to set a shock absorber of an inert gas in the tube before get downing gas injection. At the clip of stopper dad up, now this inert gas release foremost afterwards natural gas comes in contact with air. This shock absorber supply ample clip between stoppers pop up and release of natural gas which facilitate in modulating the gas injection rate to forestall formation of unwanted combustible mixture. The whole thought was put up before the direction which was quickly agreed and broke the dead lock of suspended ignitions. After acceptance of this technique boulder clay day of the month no instance of car ignition encountered.
EFFECTIVE UTILIZATION OF AIR COMPRESSOR
Compaction of air at high force per unit area is a dearly-won matter because of immense ingestion of electricity. To minimise this wastage of energy and for optimise the use of air compressors, it was thought to link all the four workss with a common air grid. Subsequently the air grid was constructed utilizing 6 ” and 4 ” Defense Intelligence Agency grapevines as required. Now compressors are being run as per the entire air demand. By utilizing this grid, on an mean INR 2.0 Crores per month ( USD 5.3 million per annum ) are being saved as electricity charges.
Failure OF AFTER COOLER OF AIR COMPRESSOR
Runing of big air compressor is hard in India particularly during summer due to high temperature. It may take to explosion at tight air shrieking due to accretion of carryover lubricators and high discharge temperature. Two incidents of bursting of 3rd phase ( Final phase ) after ice chests of HP compressor had taken topographic point at a compressor works of Santhal field. As a redress man-made lubricator has been introduced. Further regular chemical cleansing of the lines is being carried-out and monitoring of operational parametric quantities has been intensified.
Seepage OF AIR/FLUE GASES
In Mehsana, largely old Wellss were used for injection every bit good as for production. In some instances failure of shell or cementation have observed and has caused force per unit area built-up in outer shell and even in some instances seeping of gases/air from good site has besides been observed. The redresss are
1 ) New additives for cementation ( like thermal cements and Ca aluminates ) have been introduced which help to defy higher temperatures.
2 ) It is recommended to cement the shell to the full deepness in instance of new injector Wellss to forestall the hazard of coming out of gas into overlying permeable beds.
3 ) It is suggested by IEOT ( ONGC Institute ) to hold shell of API 5CT L-80 13 Cr steel in new injector Wellss and tubing in all Wellss.
4 ) New injector Wellss are being drilled to accommodate specially for unmoved burning.
5 ) Regular monitoring of injection force per unit area, annulus force per unit area and outer shell force per unit area.
Research Work
Figure: demoing the working theoretical account made in the research lab
The working theoretical account for the In situ burning was made in research lab. In this theoretical account Injection good and the production good is present on the left and right side severally, gas injection at high force per unit area, ignitor is taken as the kitchen igniter, trial tubing is made as an unreal reservoir and ignition zone near the unreal reservoir and besides the temperature demoing device at the underside of the production good. This theoretical account can be compared to the existent conditions with the aid of the undermentioned diagram.
Figure: In situ burning procedure ( beginning )
There were many challenges during the mold. These challenges were faced harmonizing to the demand, economic system and the factors available. For illustration reservoir simulation was non perfect, burning zone was non able to be built precisely in the pores due to miss of O supply. Hence I discover that this procedure is really economical as compared to other EOR procedures but it is really hazardous as injection of gas should be done at right topographic point and ignition should be controlled so this procedure acts as thaumaturgy recover the oil to 65 % . I was successful in retrieving the oil but the simulation job was a chief restraint of this working theoretical account as that requires a whole research lab for its working. Hence harmonizing to my research heat loss should be minimal, burning should be in controlled mode are the major challenges that should be overcome.
And these can be overcome by ciphering the country in which injection is to be done and what should be the ignition system usage for ignition ( whether a chemical can be used, unreal ignitor at the burning can be used or if the temperature of the underside of the hole is really high that can give self-generated ignition ) should be preplanned harmonizing to the status.
The latest and of import factor is the chemical injection to light the heavy petroleum oil, allow us say the oil nowadays there is really heavy oil that can non be straight ignited ; for that state of affairs a chemical can be injected inside which will fire foremost and so increases the temperature of the several zone to such an extent that the oil nowadays at that place will light and the farther procedure should get down.
