Enhanced oil recovery is oil restoration by the injection of materials not normally within the reservoir. In situ Combustion (ISC) is the process of an increased oil recovery process to enhance the recovery of heavy crude essential oil. As it is the oldest thermal recovery technique, it's been used for over nine generations with many economically successful assignments. Nevertheless, it is regarded as a high-risk process by many, primarily because of many failures of early field tests. The majority of those failures came from program of a good process (ISC) to the incorrect reservoirs or to the poorest potential clients. This paper consists of a information of ISC, a discussion of laboratory verification techniques, an illustration of how to use laboratory leads to field design, a discourse of operational routines and problems, and an research of field results. For complete review, the research study is done on Balol and Santhal domains in Mehsana.
In-situ combustion has been known since 1888. Mendeleev was the first scientist to suggest the in-situ conversion of coal into combustible gases. Predicated on the earlier laboratory results, Sheinman and Dubrovai in 1934 suggested the processed the process of oil displacement by means of a moving underground fire-front. Several field assessments, were performed in various regions in the past due 1940's and early on 1950's. The results from these exams indicated that the heat losses were large, which means injected hot gases come to the formation area with zero thermal energy. These studies however were followed by laboratory research field exams and development of mathematical models to simulate in-situ combustion therefore of which this technique has been recognized and can be used as a encouraging method of recovering heavy olive oil from petroleum reservoirs.
The basic principle of in-situ combustion is to attain combustion within the skin pores of hydrocarbon-bearing reservoir, getting rid of part of the oil set up to be able to enhance the movement of the unburned part. Combustion is reinforced by the injection of air into the reservoir at a number of wells. The heat produced during combustion is enough to raise the rock and roll to a high enough heat range to enable the combustion entry to self propagate after first ignition by increasing ability to move of the liquid.
Methodology
The in-situ combustion process was applied to petroleum reservoirs depending on huge selection of characteristics like Characteristics of development, depth, heat, reservoir thickness, permeability, porosity and petrol saturation in order to recover olive oil. Pressure is also one factor however, not much critical.
The process was applied in reservoirs with average permeability ranging from 40 to 8000mD, whereas the oil saturation varied from 25 to 95%. Furthermore fuel content is one of the most important factors influencing the success of a fireflood process. The fuel content of the reservoir is the amount of coke designed for combustion that is transferred on reservoir rock consequently of distillation and thermal cracking. If the energy content is too low, the combustion process in the reservoir can't be self sustained. Furthermore, a high fuel content requires a sizable amount of air and high power cost which means low oil development. Gates and Ramey (1980) compared the estimated fuel content by various methods including laboratory results get back of field job data. It's been shown that gas content established experimentally in the laboratory by pipe -run method provides a fairly good estimation of the petrol content obtained in the field.
In situ combustion is actually injection of the oxidizing gas (air or oxygen-enriched air) to create heat by burning up a portion of the resident essential oil. Most of the oil is motivated towards the providers by a combination of gas drive (from the combustion gases), heavy steam and normal water drive. This process is also known as fire flooding to spell it out the movement of any burning front inside the reservoir. Predicated on the respective directions of prominent propagation and air flow, the process can be frontward, when the combustion leading innovations in the same path as the air flow, or invert, when the front moves up against the air flow.
Reverse Combustion
This process has been studied thoroughly in laboratories and has been field analyzed. In quick, it has not been successful economically for just two major reasons. First, combustion started out at the manufacturer results hot produced liquids that often contain unreacted oxygen. These conditions require special, high-cost tubular to protect against high temperature ranges and corrosion. More air is required to propagate leading compared to forwards combustion, thus increasing the major cost of operating an in situ combustion job. Second, unreacted, coke-like heavy ends will remain in the burned portion of the reservoir. Sometime in the process the coke will start to burn and the process will revert to forward combustion with sizeable heat technology but little engine oil production. This has happened even in carefully manipulated laboratory experiments. In summary change combustion has been found difficult to apply and financially unattractive.
Forward Combustion
Forward combustion can be further characterized as "dry" when only air or enriched air are injected or "damp" when air and drinking water are co-injected.
Dry In front Combustion
The first step in dry ahead ISC is to ignite the essential oil. In some cases auto-ignition occurs when air injection begins if the reservoir temperatures is rather high and the petrol reasonably reactive. Man-made Ignition has been induced using down hole gas burners, electrical heaters, and/or injection of pyrophoric agencies or heavy steam injection.
Figure : schematic illustration of the in-situ combustion process (Source)
After ignition the combustion front side is propagated by a continuing move of air. As the front progresses into the reservoir, several areas can be found between injector and designer as a result of high temperature and mass travel and the chemical substance reactions. These figure can be an idealized representation of the various areas and the causing temperature and smooth saturation distributions. In the field there are transitions between zones.
A. The burnt zone is the quantity already used up. This zone is filled up with air and may contain smaller amounts of residual unburned organic and natural solids. As it has been put through high temperatures, nutrient alterations are possible. Due to the continuous air flow from the injector, the used up zone temperature rises from injected air temperatures at the injector to combustion forward heat range at the combustion entry.
B. The combustion leading is the best temperature zone. It's very thin, often no more than several in. thick. It is in this area that oxygen combines with the fuel and high temperature oxidation occurs. The merchandise of the burning up reactions are water and carbon oxides. The petrol is often misnamed coke. Plus its not 100 % pure carbon but a hydrocarbon with H/C atomic ratios ranging from about 0. 6 to 2. 0. This fuel is developed in the thermal cracking area just prior to the front and is also the product of cracking and pyrolisis which is transferred on the rock matrix. The amount of fuel burned is an important parameter since it establishes how much air must be injected to lose a certain level of reservoir.
C/D. The cracking/vaporization zone is downstream of leading. The crude is altered in this area by the high temperature of the combustion process. The light ends vaporize and are carried downstream where they condense and mixture with the initial crude. The heavy ends pyrolize, leading to CO2, CO, hydrocarbon gases and stable organic fuel deposited on the rock and roll.
E. The vapor plateau. This is the zone where a few of the hydrocarbon vapors condense. Most of those condense further downstream as the steam condenses. The heavy steam plateau temperature depends on the partial pressure of the in the gas period. Depending on the temperature the initial oil may experience a moderate thermal breaking, often called visbreaking that always reduces petrol viscosity.
F. A normal water bank is available at the leading edge of the heavy steam plateau where the temperature is less than steam saturation temperature. This water bank or investment company decreases in temps and saturation downstream, with a ensuing increase in engine oil saturation.
G. The engine oil bank. This zone contains the majority of the displaced essential oil including most of the light ends that derive from thermal cracking.
H. Beyond these damaged areas is the undisturbed original reservoir. Gas saturation increase only slightly in this field as a result of high range of motion of combustion gases.
Wet In front Combustion
A large amount of warmth is stored in the burnt zone during dried up ahead in situ combustion, because the low temperature capacity of air cannot copy that heat efficiently. Water injected with mid-air can capture and improve more high temperature stored in the burnt zone. During moist combustion injected drinking water absorbs heat from the burned zone, vaporizes, moves through the burning up front and condenses, widening the steam plateau. This brings about faster heat motion and oil displacement. With regards to the water/air ratio, wet combustion is categorised as: (1) imperfect when this is converted into superheated steam and recovers only part of the heat from the burnt zone, (2) normal when all the heat from the used up zone is recovered, and (3) quenched or very wet when the front temperature declines consequently of the injected water.
ISC requires particular focus on air compression, ignition, well design, conclusion, and production methods. Air compression triggers high temperatures because of the high c p / cv percentage of air. Compressor design must consider these high temperature ranges to ensure ongoing, sustained operations clear of the corrosive effects of air and the explosion dangers of some lubricating liquids. Mineral oils are not recommended. Man-made lubricants withstand the bigger temperatures and provide lower volatility and flammability than classic lubricants.
In order to achieve the combustion in the petroleum tank, mainly Spontaneous ignition and Artificial ignition will be the two methods that are used for heavy olive oil recovery. Ignition may appear spontaneously if the oil is reactive, the reservoir temps high enough, and the reservoir is reasonably dense. Down opening gas-fired burners allow good control of the temperatures of injected gases and may be controlled at a greater depth than other methods. The drawbacks are the need to perform multiple tubing strings in the treatment wells. Catalytic heaters run at lower temperature but are expensive. Electrical heaters can be lowered with an individual cable, and provides excellent heat control. They could be reused repeatedly. You can find, however, a depth restriction because of electrical power losses in the cable television. Chemically improved ignition may necessitate handling and safe-keeping of dangerous materials. Vapor enable you to locally increase reservoir heat and facilitate car ignition. It is suffering from depth limitation because of wellbore heat losses, however when the conditions are right it's rather a very simple and effective way for ignition. Combustion process was also utilized as primary and tertiary restoration processes.
Applications
In situ combustion can be employed to many different reservoirs. Some recommended screening guidelines are:
Nature of the Development : The rock type is not important provided that the matrix/petrol system is reactive enough to support combustion. As in any drive process, high permeability streaks are detrimental. Swelling clays may be a problem in the heavy steam plateau area.
Depth: Depth should be large enough to ensure containment of the injected air in the tank. There is absolutely no depth limit, except that this may influence the shot pressure.
Pressure: Pressure will have an effect on the economics of the procedure, but will not affect the complex aspects of combustion.
Temperature: Heat range will affect auto ignition but is otherwise not critical.
Reservoir Thickness: Width should be greater than about 4m (15 ft) 2, 3 to avoid excessive heat loss to encircling formations. Very dense formations may present sweep efficiency problems because of gravity override.
Permeability: This must be sufficient to permit shot of air at the designed air flux. The environment injectivity is especially very important to heavy olive oil reservoirs. Conditions are favorable when kh / is higher than about 5md m/cp. 3
Porosity and Petrol Saturation: These need to be large enough to permit economic oil recovery. The merchandise, So, must be higher than 0. 08 for combustion to be financially successful.
Oil Gravity: This parameter is not critical. Insitu viscosity must be low enough to allow air shot and resulting oil production at the look rate.
Oil Mother nature: In heavy olive oil projects the petrol should be easily oxidizable at reservoir and rock and roll matrix conditions. The lab experiments can also determine the amount of air had a need to burn confirmed reservoir volume. That is key to the profitability of the procedure.
Current Status of In-Situ Combustion
The in-situ combustion process is of interest financially, provided it is put on petroleum reservoirs made up of approximately 50% oil saturation. The gasoline content is one of the key parameters for combustion support at a comparatively low air/oil proportion. Although laboratory experiments can provide some basic understanding of the process, the principal analysis factor is a field program before the process is utilized on a large scale.
The present position of oil development by in-situ combustion in america is almost 11, 000 bbl/day. The commercial dried ISC project at Romania is the largest task of its kind and it has been in operation for more than 34 years. The Balol and Santhal jobs in India have been in operation for more than seven years and have been applied in a damp mode. Currently, mixed all these three jobs produce about 2300m3 /day. Chances are that very little laboratory research can be performed to enhance the displacement efficiency of the process. With continuing improvement of the in-situ combustion technology, it is nearly certain that some type of this process, such as dry, wet, and partially quenched combustion, will see greater software in the coming years.
Currently, commercial In situ combustion jobs are
Economic Evaluation
It is accepted that the success or failing of an increased oil healing process is determined by the economic analysis. An economic study completed by Wilson and Main (1966), which is dependant on a altered form of two-dimensional model provided by Chu, compares the cost of heating a reservoir. The cost evaluation was studied for a tank either in the presence of steam treatment or forwards combustion without olive oil production. The main factor was to determine home heating cost of the same measurements of a reservoir by either heavy steam treatment or by frontward combustion. The next conclusions were drawn from this research;
(1) Combustion is favored over steam treatment as the sand thickness reduces the pressure increase.
(2) As the coke deposition rises, steam injections is favored in the combustion process.
(3) As the warmed distance in the tank increases, reservoir warming by combustion is more beneficial when compared with steam shot.
(4) Decreased injection rated favors the price tag on steam injection in accordance with air.
(5) Increased wellbore deficits with increasing depth favour combustion.
Conclusions
It has been shown that in-situ combustion process would work to displace natural oils of gravities higher than 10 level API. The common oil recovery by employing in-situ combustion is 50%. The major amount of engine oil is recovered before breakthrough of the combustion area. For heavy oils, about 50% crude essential oil restoration occurs after breakthrough, whereas low-viscosity olive oil development declines very rapidly following discovery. The discovery of combustion zone can be acknowledged by an increase in gas development and its oxygen content. That is followed by a distinct increase ranging from 100 level to 200 degree Fahrenheit in underlying part hole temperature. Furthermore, the upsurge in water chop of the produced essential oil also suggests the discovery of the combustion area. At the same time, pH of the produced drinking water decreases, which is usually credited to increase in this content of ions such as flat iron and sulphate.
CASE STUDY
IN-SITU COMBUSTION AT MEHSANA, GUJARAT.
Mehsana asset, situated in the northern part of Gujarat point out in India is the highest engine oil producing onshore advantage of ONGC with annual crude oil development of 2. 35 MMT. Its having engine oil fields producing both heaviest crude and the lightest crude in India with API gravity ranging from 13 - 42. Balol and Santhal areas form an integral part of this heavy petrol belt with a API gravity 15-18. Balol and Santhal field encompass 22. 17 MMT and 53. 56 MMT of olive oil in place respectively. The crude is asphaltic in aspect filled with 6-8% asphaltene and the petrol viscosity runs from 50-450 cps at reservoir pressure of 100 kg/cm† and 70 C temperature. Reservoirs hold the permeability of the order of 3-8 darcies and are working under active normal water drive. Following Artificial lift methods resulted into high normal water production than petrol. In many wells it became 95-100% plus some wells had to be closed credited to high normal water cut. The indegent primary and extra necessitated for In-Situ combustion approach in these domains.
Exploitation of heavy essential oil from these heavy engine oil fields was a concern for Mehsana asset. Predicated on results of laboratory studies, the In-situ combustion process was recognized as the most suitable technique for enhancing the recovery from these fields.
PILOT SCHEME
A pilot test was designed and initiated in 5. 5 acre part of southern part of Balol field in 1990-91. The first well CP#10 and thereafter Balol#171 were ignited with the aid of foreign experts. The suffered combustion and development gain from close by makers lead to conceptualization of the commercialization techniques in entire Balol field.
In another try out, a pilot design was also designed for Lanwa engine oil field and an inverted five slot machine game routine with four maker wells had been ignited in 1992. At the moment the commercialization of the program is in progress to improve the creation from the field. A pilot plan is also operating since 2002 in Bechraji field with four EOR injectors.
COMMERCIAL SCHEMES
Based on the techno-economic success of Balol Pilot project, commercial plans were suitable for complete Balol field for exploitation of heavy essential oil. Considering the similarities between the Balol and Santhal olive oil domains, this EOR approach has been applied over a commercial size in 1997 both at Balol and Santhal areas. Presently four commercial strategies viz. Balol Ph-1, Santhal Ph-1, Balol Main and Santhal Main are working successfully. Till time total 61 wells have been ignited in Balol and Santhal under these commercial plans. More wells are in-line for change into EOR injectors.
For commercial exploitation of Balol and Santhal domains using In-situ combustion approach, four major air compressor vegetation, two, each in Balol and Santhal domains were create. These plants supply compressed air to injector wells at tank conditions. Compressors except emergency air compressors at the plants run on electricity. Put together installed capacity of the four vegetation is of compressing 4. 9 NMm3/day air at maximum pressure of 123 Kg/cm2. Since drinking water is required to be injected consequently during wet period, facilities for normal water treatment and injection are also installed in the respected plants. Each one of these four crops are linked to one another with a air grid network for better utilization of resources. A mobile unit called Ignition trailer has been used to start ignition process. Gas burners are being used for unnatural ignition in Mehsana.
RESULTS
After implementation of the approach, decline in development from Balol and Santhal areas was arrested. A number of wells have started out flowing on self which were in artificial setting prior to in-situ combustion process. Production screening data of damaged wells show the progressive increase in liquid production and decrease in water cut causing increase in online oil production. Currently EOR gain from both domains in the tune of 1200 TPD and air injection is at tune of just one 1. 4MM Nm3/d. Creation performance of these domains shows the continuous increase in olive oil production and decrease in W/C% with increasing range of injectors/air injection rate. It hasn't only given a fresh lease of life to Balol and Santhal fields but has also increased the essential oil restoration factor by 2-3 folds from 6-13% to 39-45%.
OTHER HIGHLIGHTS WITH THE PROJECT
ONGC is mostly of the organizations on the planet, which has adopted In-situ combustion process on such a big scale.
Total 68 wells have been changed in EOR injectors at Mehsana Property up to now.
Most of the EOR injectors are old producer wells. They have been changed into injector wells after proper washing and cleaning of wells.
Ignition is being done in the tank at an average depth of 990 meters, having 100 Kg/cm2 pressure and 70 level Celsius temps.
Present Air-Oil proportion in these areas is approximately 1160 Nm3/m3 and Air-Oil proportion on cumulative basis it stands at 985 Nm3/m3, which signifies quite good efficiency of ISC process.
Figure : Development information of Santhal and Balol fields (Source)
MAJOR ISSUES
Occurrence of Auto-Ignition:
In Mehsana Gas burner has been used for man-made ignition. In this technique air is injected through the annulus and gas through tubes. An aluminium plug fitted at the tip of burner helps prevent air and gas to mix. The plug pops out when gas injection pressure is more than air injection pressure and varieties gas-air mixture in the bottom. A pyrophoric substance has been used to start the fire. At well no. Balol # A on 1998 the burner caught fireplace without decreasing pyrophoric water. Burner temperature shot up to 910 degree Celsius and was soon manipulated by ignition tem members. There is no damage to thermocouple and down-hole assembly in this well. Following this incidence auto ignition occurred successively in another three wells. In last two wells Santhal #B and Balol # C, thermocouple received destroyed. Ignition experts were not able to establish the reason and solution for car ignition. Due to this failure, ONGC possessed completely suspended all the ignition procedures fearing further car ignition and harm to thermocouple.
A close review of all four situations of auto ignition discovered that gas injection was used to be done at full discharge rate of gas compressor. Because of this sudden release of huge amount of gas, an extremely rich combination of air and gas forms making situation susceptible for car ignition. To triumph over this issue, ignition team developed an idea to place a cushion of an inert gas in the tubing before starting gas injection. At the time of plug pop up, now this inert gas release first later natural gas touches air. This cushion provide ample time between plug pop-up and release of gas which facilitate in regulating the gas injection rate to avoid creation of unwanted combustible combination. The whole idea was set up before the management which was promptly arranged and broke the inactive lock of suspended ignitions. After adoption of the technique till date no circumstance of auto ignition came across.
EFFECTIVE USAGE OF AIR COMPRESSOR
Compression of air at ruthless is a costly affair because of huge intake of electricity. To minimize this wastage of energy and then for optimize the utilization of air compressors, it was considered to connect all the four crops with one common air grid. Subsequently the air grid was produced using 6" and 4" dia pipelines as required. Now compressors are being run according to the full total air requirement. By using this grid, on an average INR 2. 0 Crores monthly (USD 5. 3 million per annum) are being saved as electricity charges.
FAILURE OF AFTER Chiller OF AIR COMPRESSOR
Running of large air compressor is difficult in India especially during summer due to temperature. It could lead to explosion at compressed air piping anticipated to deposition of carryover lubricants and high discharge temperature. Two situations of bursting of 3rd stage (Final stage) after coolers of HP compressor had occurred at a compressor seed of Santhal field. Like a remedy man made lubricant has been released. Further regular chemical cleaning of the lines has been carried-out and monitoring of operational guidelines has been intensified.
OOZING OF AIR/FLUE GASES
In Mehsana, usually old wells were used for injection as well for production. In some instances inability of casing or cementation have observed and has triggered pressure built-up in exterior casing and even sometimes oozing of gases/air from well site has also been seen. The remedies are
1) New additives for cementation (like thermal cements and calcium aluminates) have been presented which help to withstand higher heat.
2) It is recommended to cement the casing fully depth in case of new injector wells to avoid the chance of coming out of gas into overlying permeable layers.
3) It is suggested by IEOT (ONGC Institute) to acquire casing of API 5CT L-80 13 Cr metallic in new injector wells and tubing in all wells.
4) New injector wells are being drilled to match specially for in-situ combustion.
5) Regular monitoring of injection pressure, annulus pressure and outside casing pressure.
Research Work
Figure : showing the working model manufactured in the laboratory
The working model for the In situ combustion was made in laboratory. In this particular model Injection well and the development well is present on the departed and right area respectively, gas injection at ruthless, igniter is used as your kitchen lighter, test tube is made as an man-made reservoir and ignition zone near the man-made reservoir as well as the temperature showing device in the bottom of the production well. This model can be set alongside the real conditions by using the next diagram.
Figure : In situ combustion process (source)
There were many issues during the modeling. These difficulties were faced according to the need, overall economy and the factors available. For instance reservoir simulation had not been perfect, combustion zone was not able to be built exactly in the pores due to insufficient oxygen resource. Hence I discover that this technique is very economical when compared with other EOR procedures but it is very high-risk as injection of gas should be done at correct place and ignition should be controlled then this process serves as magic recover the olive oil to 65%. I got successful in recovering the oil but the simulation problem was a primary constraint of the working model as that will require a whole lab because of its working. Hence according to my research heat loss should be least, combustion should be in controlled manner will be the major challenges that needs to be overcome.
And these can be beat by calculating the region where injection is to be done and what ought to be the ignition system use for ignition (whether a chemical can be used, man-made igniter at the combustion can be used or if the temp of the bottom of the hole is high that can give spontaneous ignition) should be preplanned based on the condition.
The latest and important factor is the chemical substance injection to ignite the heavy crude oil, let us suppose the essential oil present there is certainly very heavy petrol that can't be directly ignited; for this situation a substance can be injected inside which will melt away first and then increases the temperature of the particular zone to this degree that the petrol present there will ignite and the further process should start.
