Simulation research on carbon dioxide as cushion gas in gas underground reservoirs Simulation research on carbon dioxide as cushion gas in gas underground reservoirs

Simulation research on carbon dioxide as cushion gas in gas underground reservoirs

  • 期刊名字:哈尔滨工业大学学报(英文版)
  • 文件大小:853kb
  • 论文作者:TAN Yu-fei,LIN Tao
  • 作者单位:School of Municipal and Environmental Engineering
  • 更新时间:2020-09-13
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论文简介

Journal of Harbin Institute of Technology( New Series, Vol 16, No. 1, 2009Simulation research on carbon dioxide as cushiongas in gas underground reservoirsTAN Yu-fei, LIN Tao谭羽非,林涛School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, China)Abstract: Aimed at the problem of mixing working gas and cushion gas in carbon sequestration technology, thefeasibility of using carbon dioxide as the cushion gas in reservoirs is discussed firstly. At the usual condition ofservoir, carbon dioxide is a kind of supercritical fluid with high condensability, high viscosity and high den-sity. Secondly, this article studies the laws of formation and development of mixing zone by numerical simula-tion and analyses the impact on mixing zone brought by different injection modes and rational ratios of cushionrs. It is proposed that the appropriate injection ratio of cushion gas is 20%-30%0. Using carbondioxide as cushion gas in gas reservoirs is able to make the running of natural gas reservoirs economical and effi-Key words: carbon dioxide; gas reservoir; cushion gas; carboCLC number: TE822Document code: AArticle ID:10059113(2009)0140087404In recent years, much attenticto be paid ses[2. 31to the problem of warming up ofAs one of the carbon sequestration technical meas-cause the emission amount of greenhouse gases during ures, it has long term potential to inject carbon dioxidethe industrial production process is very large, global from industrial sources into the deep geological forma-warming becomes more and more serious. Research in- tions such as brine aquifers or depleted oil or gas reser-dicated that in order to avoid the significant disruption voirs 4. On one hand, the distribution of this kind ofof the climate system, CO, concentration must be stabi- geologic structures especially brine aquifers a is exten-lized within the next several decades. Otherwise, sive on the world scale; one the other hand, the geo-greenhouse effect will bring serious influence to global logic structures such as depleted oil or gas reservoirsclimate including the thawing out of the glacier of have the advantages of large storage capacity and highthe two poles, hoist of sea level and flooding coastal security. Research shows that carbon dioxide can dis-farther, causing rise of air temperature over the solve in water, incorporate with other minerals and formsurface,abnormal climate resulting in cata- stable carbonatite under high-pressure in reservoirs af-ter a long time since carbon dioxide was injected intoEfforts have been made to deal with the warming the underground geologic structures.up of global climate and the great emission amount of To inject CO 2 into oil reservoirs has been success-greenhouse gases. In December 1997, major countries fully carried out for more than 20 year, its main pur-cific steps and objects to decrease the Co, dischargepe. acs. being to enhance oil recovery by the displacementof the world convened a meeting at Kyoto Japan and pospassed"Kyoto protocol", the primary topic was theon to oil and natural gas .Economic feasibility ofa-carbon sequestration with enhanced gas collection wasmount, but the technology methods had not been sug- also appraised. This article will study some main prob-gested to deal with the current carbon dioxide1. lems concerming carbon dioxide being used as cushionThrough the efforts of the technicians for a number of gas in underground natural gas reservoirsyears,a technology of removing the produced CO2which was called carbon sequestration technology was 1 Carbon Dioxide as Cushion Gas for Carbon Se-paid much attention to main purpose of which is toquestrationgather up CO2 and to inject it into oceans, oil fieldsshafts or underground caverns. This technology may be-中国煤化工 nuch more attentioncome one of the best ways to decrease greenhousbyments, technologyCNMHGReceived 2007-02ponsored by the National Natural Science Foundation of China( Grant No, 50676025)Journal of Harbin Institute of Technology( New Series), Vol 16, No 1, 2009and industrial communities. Since 1996, Sleipner oil working gas in reservoirs and form a mixing zone. Iffields in Norway North Sea have injected 100 trillion ton gas load is very heavycarbon dioxide into brine saturation aquifers with 900 m mixing gas in working gas. Because the mixing gas in-depth per annum. Since October 2000, Canada delivers cludes much CO,, the quality of supplying natural gasabout 5000 t carbon dioxide from power plants in North will be to a certain extent influencedDakota state America to Weyburn oil field in willistooblem of working gas and cush-Basin by pipelines everyday and injects it into carbon-n gas, detailed researches and practices as wellatite reservoirs to enhance oil recovery, at the same numerical simulation have been conducted in Americatime, to store this part of carbon dioxide eternallyFrance and Denmark Pre-charge test has been car-Using carbon dioxide as cushionried out with tracers and gas composition change ofground natural gas reservoirs, can not only accomplish nearby gas well has been successfully monitored withthe mission of carbon sequestration, but also replace chromatograph in France. The acquired outcome andthe natural gas as cushion gas in reservoirs and exert its material can be used in the simulation of reservoirfunction of pressure maintenance. Recovering this part characteristics with three-dimensional networks. There-of sediment natural gas and realizing their economic by the mixing situation of working gas and cushion gasvalue is beneficial. There has already been much engi- in reservoir formations can be predicatedneering experience of making substitute gases as cush-Fig. 3 clearly illustrates the formation of mixingion gas in reservoirs according to foreign literatures. zone, prior to the injection of working gas, there isThese substitute gases should have the characteristics mainly cushion gas in reservoirs, when working gas wassuch as high condensability, low price and ready to be injected to construct the gas storage reservoir, workingavailable. At present, these substitute gases includes gas begin to replace cushion gas at the bottom of gasseparation n2 at low temperature from air, exhaust gas well, at the same time cushion gas replaces the sidefrom combustion engines( mainly N, and CO2), inert and bottom water in aquifer reservoirs, the storage cagases by dehydration from steam boiler( mainly inclu- pacity become larger and larger. During this processding N2 and CO2), carbon dioxide and so oncushion gas can not avoid mixing with working gas.Research on the physical properties of carbon diox- Accordingly, a mixing zone between pure working gaside under the conditions of reservoirs reveals that CO, is zone and pure cushion gas zone is formed. The degreea kind of supercritical fluid in engineering physical con- of this mixing is indicated by molar fraction namelyditions: it takes about 1. 34 m' storage spaces per toncushion gas 's molar proportion in mixing gas. In thisTherefore, CO 2 can be stored in underground space with way, when the molar fraction is about 0.5, it meansno extraordinary pressure conditions. Farther researches high mixing degree which reflects the situation of theproclaim: the density of CO, increases 5-8 times under middle of mixing zone; when the molar fraction is a-he temperature and pressure conditions of 31.5boutO or 1, it indicates low mixing degree which re-51.5 K and 5-13 MPa. Whereas, the density of CHflects the situation of the edge of mixing zoneincreases 2-3 times at the same conditions. Namely, 3 Mixing zone SimulationCO2 has high condensabilityallow more natural gas being injected; on the otherhand, CO, is high viscosity substance under those conA certain underground gas storage reservoirwhose physical dimension is 0. 4 km x0. 4 krusegditions, 10 t higher than that of natural gas, namely it carbon dioxide as cushion gas, the initial pressure andcan confine the mixing with natural gas because of its temperatureconditions of this reservoir are 6 MPahigh viscosity and higher rate of viscosity change. In 313. 15 K, porosity is p =0. 3, permeability rate is Kaddition, high density of CO, can lead to gravity segre= ID, there is a gas well in the middle of the reser-gation phenomena with natural gas in the geological for- voir, injection rate is 30 ke/s, Assume the diffusionnations of underground reservoirs which avoid the mix-coefficient of carbon dioxide diffusing within naturaling of working gas and cushion gas largelygas Is5×10°m2/ s under the 10 MPa pressure condi2 Mixing Region of Working Gas and Cushiontion. We set up the mixing model of working gas andcushion gas in the media of reservoirs and solve itsimulate the situation of injection of natural gas for10 d. FiThough using CO, as cushion gas for underground of garv中国煤化工 veals the movingreservoirs is an effective carbon sequestration technolo-gy and it is beneficial not only for environment protec eachCNMHG zone in the 10 dsituation of mixingon but also for reducing operation and management zone on that dayexpenses, there is one question that CO, can mix withJournal of Harbin Institute of Technology( New series), Vol. 16, No. 1, 2009Bottom of gas wellous. ththe mixing zone slowly moves far in the radial direc-CO, molar fractiontion. The length of mixing zone still increases, but itsshows oblique trend, above which gathers working gasCOthere is cushion gas with greater density.4 Discussion of Injection Mode and RatioThe above numerical modeling results show thatDistance from gas well/mig. 1 Situation of mixing of working gas and cushionif there is great amount of cushion gas around gas wellat the initial state, the mixing action of working gas(【=10d)and cushion gas will be aggravated, namely the devel-Bottom ofopment of mixing zone is on an upper formation start atfirst, it is not helpful to the control of mixing zoneWhen there is much working gas injected around thgasse. If the cushiegas can avoid this violently flowing region, the mixingwill be reduced. Fig. 3 shows the distributionand the characteristics of cushion gas. On account ofthe above issue, experiments have been conducted injecting cushion gas at the edge of the reservoirs, after18」injection, the production of natural gas proceed nor-020406080100120140160180mally, in this way, cushion gas can replaceDistance from gas well/mgas step by step. According to the examination of theFig 2 Migration situations of main bodyof mixing zonecomposition of the recovered natural gas, there(=10d)cushion gas ingredient being detected after acycles, this injectionThese two figures clearly reveal the formation and of cushion gas is comparatively rationaldevelopment status of mixing zone. Before the workinggas being injected, reservoir is filled with cushion gas.ection ofAt the beginning of injection, natural gas replacescushion gas netherward and in the radial direction ofas well, this phase is the generating phase of mixingone. In this phase, the degree of mixing is very highas the figures show that the development of mixing zonein the radial direction is relatively faster compared withPure working gas zonethe downward development of mixing zone. On onehand, the radial diffusion of working gas takes theleading position; on the other hand, because the densi-ty of cushion gas is usually greater than working gasthe downward diffusion of working gas in reservoir isconfined owing to the gravity.Fig 3 Distribution of working gas and cushion gasAfter this phase, cushion gas takes over the kinetic energy of working gas gradually and is driven byHowever, one problem has not been solved yet, itworking gas. Cushion gas diffuses far in the radial di- is the reasonable ratio of cushion gas in the reservoirs.rection. This diffusion reduces the mixing of workingthis rate is greater, the mixing zone still can migrategas and cushion gas and decreases the increasing exterto the neighborhood of gas well. The ratio of cushiof mixing zone. In the downward diffusion aspectgas can be calculated by numerical simuworking gas replaces the cushion gas to the bottom of Fig4.latinnshin hetween injection ratio ofthe reservoir and forms a pure working gas zone around cushi中国煤化工 nd the influencingCNMHGPparameters of gasally, the development of mixinmodel. Thenesstable. In this phase, the law of development is obvi. ulation shows that the range of influence of the injec-Journal of Harbin Institute of Technology( New Series), vol. 16, No. 1, 2009is almost the same with that of the produc- sequestration technologies, injection carbon dioxide in-Furthermore, the curves in the two periods to the deep geological formations such as depleted oilshow the same trendor gas reservoirs has been a proven technical and eco-The radial length of the model which is used in nomic success. It can not only enhance the oil recoverynumerical simulation is 400 m; the time of injection but also replace the natural gas in reservoir as cushionsimulation is also io d. The original Scale of Naturalesearch on the physical properties of carbon di-Gas represents the initial contact position of working oxide at the usual condition of reservoirs proves thatgas and cushion gas. Fig. 4 obviously shows that as carbon dioxide is a kind of supercritical fluid. Com-long as cushion gas is far away form the gas well, the pared with natural gas, it has the characteristics ofrange of influence of mixing zone will decrease largely. high condensability, high viscosity and high densityOf course, the actual numerical values of range of in- which are useful for being used as cushion gas. Highfluence in the picture only reflect the calculated values condensability is able to allow more natural gas beingin some settled parameter conditions. With the increase injected; High viscosity can avoid the mixing with natof the distance between cushion gas and gas well, the ural gas; high density can arouse gravity segregationinfluence range of cushion gas greatly declines. It is phenomena and avoid the mixing of working gas andshown that, the ratio of cushion gas is rational when it cushion gas largely. By numerical simulation, this pa-drops down to 20%-30%. If the amount of cushion per researches the formation and development status ofgas goes on decreasing, though the mixing zone is mixing zone, proves the great influence of dynamic in-small, the function of cushion gas is also at a discount. jection and production on mixing zone. In conclusion,Therefore, it is very important to reasonably ascertain the edging injection mode is imperative. At last,itthe ratio of cushion gas at the edge of reservoir.studies the balance of economical and technical actionof cushion gas and the impact of mixing gas, proposesthat the appropriate injection ratio of cushion gas is20%-30%References200[l] Thomas D C, Benson S M. Carbon Dioxide Capture forStorage in Deep Geologic Formations- Results from the CO,150apture Project: Geologic Storage of Carbon Dioxide withMonitoring and Verification. Elsevier, 2005[2] DNV Consulting. Risk Analysis of the Geological Seques-tration of CO2. Report to DTI CFT Programme, 2003[3] Gupta N. New project on geological storage of CO,.TEAGreenhouse Gas R&D Programme, Greenhouse Issues03,64:30.l0203040.506070.80910[4] The Intemational Energy Agency. Prospects for CO, Cap-ture and Storage. OECD/IEA, 2004.Fig4 Influence range of miing zone-original scale of nat. [5] Oldenburg C M, Benson S M. CO, injection for enhancedgas production and carbon sequestration. Society of Petro-5 Conclusionsleum Engineers SPE-74367, SPE Intermational PetroleumConference and Exhibition in Mexico. Villahermosa,Mexico 2002Carbon sequestration technology is very effective [6] Oldenburg C M. Carbon dioxide as cushion gas for naturalto control the warming up of global climate and emis-storage. Energy Fuels, 2003, 17(1): 240-246.sion amount of greenhouse gases. As one of the carbon中国煤化工CNMHG

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