Shale gas exploitation with supercritical CO2 technology

Shale gas exploitation with supercritical CO, technologyWang Haizhu, Shen Zhonghou, Li genshengTian Shouceng, Cheng YuxiongState Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, ChinaAbstract: This paper analyzes the physicochemical properties of supercritical CO2, the characteristic of shale gas andshale gas reservoirs. The technologies of drilling, production, fracturing using the supereritical CO in shale gas explo-ration are proposed, to increase the penetration rate, decrease the damage to formation while fracturing, and enhancethe recovery of shale gas. It is believed that the huge economic benefits of shale gas exploration with the supercriticalCO2 fluid will be obtained, and it also can initiate a new technology field of CO2 in the petroleum engineeringKey words: shale gas exploration; supercritical CO,: drilling1 Introductiondevelopment costs, further reduceing the economic andtechnical recoverable reserves of shale gas.ThereforeShale gas is a type of unconventional nature gas it is a priority how to enhance the drilling speed, imresource which is born in the mud shale, and it exists prove well productivity, extend the production pericas adsorbed and free state in the formation mainly com- and achthe purpose of low cost exploitationposed by mudstone and shale. It is rich in shale gas of Through the study of supercritical Co, application inhich resource extent is about 456. 24 x 10min to- petroleum engineering at home and abroad, it can betal in the world. There were nearly 42 000 shale gas believed that the shale gas exploitation with supercriti-production wells in 2007 in America, and the annual cal CO, will achieve a great successproduction of shale gas was about 450 x 10 m, ac- 2 The physical properties of supercriticalcounting for about 8 of the total gas production ofU.S., while the annual production in 2011 reachedCO,180 x 10"m',34 of total natural gas production ofCO2 is a type of greenhouse gas, and in mostU.S., which had been far more than China's annualses, it is treated as exhaust gas. It is widely foundconventional gas production'nature and has a close relationship with our lives.With regard to the recoverable resources and ex- When the temperature and pressure are higher than theploitation potential of shale gas, it is expected to be the critical point(T. >31.1 C, P.>7.38 MPa),it isthird important nature gas resource after the tight sand- called as supercritical C0, fluid. Fig. I illustrates thestone gas and coal bed gas. China is very rich in shalephase diagram of carbon dioxide.gas resources, the expected amount of resources up to100 x 10m, which has a great exploitation poten-tial,33.However, with the characteristics of low per-meability and high clay content for shale gas reservoirshale gas reservoir development is extremely difficult 4According to thce of United States. the10. oo Solidconventional drilling and fracturing technology often31.1℃7.38MPacontainliquid water which can make the clay in thereservoir swelled seriously, and decrease the permea0.52 MPa/ Gasbility of shale rock. In general, the shale gas wellsmust be fractured to produce gas. Secondly, shale rockTemperature℃is difficult to drill, and the well construction cycletakes time The above factors have led to increasedH中国煤化工oon dioxidesCNMHGReceied 23 April 2012势方数 eering Sciencessupercritical fluid is different from the gas and sure and temperature can transfer to any room whereliquid, which has many unique physicochemical prop- the molecule of supercritical CO2 can reach. In theertIesTable 1 shows the comparison of physical prop- condition of compressing the gaseous CO2 will beerties among supercritical fluid, gas and liquid. The transformed to liquid when the temperature is below thedensity of supercritical CO2 is similar to liquid, and the critical temperature. The supercritical CO2 fluid inviscosity and diffusivity are similar to the gas S; and it creases its density, but the phase interface and inter-is a good material for heat transfer and mass transfer. face effect dont exist. The density, viscosity, diffu-Additionally, the surface tension of supercritical CO2 is sion coefficient, solvating power etc. of CO2 greatlyzero, so it can enter into any room easily which is big- fluctuate with a small change of temperature and pres-ger than the molecule of supercritical CO2 and the pres- sure near the critical point 6, 7JTable 1 The character cecomparison between supercritical fluid, gas and liquid[s)Physical propertyGas( normal temperatureand pressure)Supercritical fluidLiquid( normal temperatureand pressure)0.0006~0.0020.6-1.6viscosity/(mPa·s)0.03~0.10.2~3.0Diffusion/(cm2·s4)3 Shale gas reservoir and characteristic ofwater,they will swell and block the pores, reducingshale gas exploitationthe rock permeability radically and setting higherrequests for drilling and production technology.Shale gas refers to the unconventional gas which What's more, according to the developing experiencedeposits on shale. The shale can be regarded as dense overseas, only in the presence of fractures, can shalerock while the shale gas is also a kind of dense rock gas reservoirs have an economical value for productiongas. Shale gas mainly accumulates in dark-colored otherwise a fracturing stimulation must be taken. 90 %0shale rock and mud rock with high carbon content and of the shale gas wells have been fractured before pro-andwich of power psammite, at free state or absorptioction,developing costs. In con-state,and the percentage of shale gas at absorption clusion, the development of shale rock demands highlystate is in range of 20 %-85%3.8Jof drillingfracturing stimulations andBecause of its own characteristics, the develop- flooding productionment of shale gas reservoirs faces more challenges than 4 Advantages of shale gas exploitation withconventional natural gas reservoir. First of all, the ma-trix pores of shale, most of which are micro-capillarysupercritical CO2pores, are extremely undeveloped, while the porosityThe special nature of supercritical CO,( such asof shale might be more than 10 in shallow layers density, viscosity, diffusibility etc. makes the superand usually be less than 10 below 2 300 m depth. critical CO2 fluid with great superiority in drillingMeanwhile, shale should be regarded as sedimentary fracturing, replacement, and so on, mainly in therocks with an extremely low permeability, which isfollowing areasrange of 10-10"mD, and is far less than that of 4.1 Easy to drill hard rock, enhancing rate ofdense sand. As a result the flow resistance of shalepenetrationgas is far more than that of conventional natural gasThe supercritical CO, jet can erode the hardand recovery ratio of shale gas, which is in range of shale, granite and marble easily, and its threshold5 %-20 %, is far less than that of conventional pressure is far smaller than that of water, especiallynatural gas, which is about 60 % So the drilling and with a high penetration rate. The experiment resultsdeveloping costs must be controlled strictly to ensure an from Kolle and Marvin 9, 0J illustrated that the coeconomical value for shale gas production 2)threshold pressure was 2/3 of that of water in theIn addition, since shale is composed of micro- granite and less中国煤化工 in theparticles which are formed after the clay hardened,nB-:吗工cNMH可C02wa kind of clay rock containing a large amount of clayminerals, such as kaolinite, montmorillonite, hydromica, 3. 3 times of that with water, and meanwhile the drillillite and so on. When thing specific energy is only about 20 of that valueVol.10No.4,Aug.201213with waterTherefore, the supercritical CO, drilling can effecFig 2 shows the projected jet erosion rate fortively protect the reservoir from pollution, which will100 kW, 50 mm diameter drilling system based on become an efficient drilling technology for low and ultrawater and supercritical CO2 jet erosion data in Mancos low permeability shale gas reservoir developmentshale. Water jet can not cut this formation when pres- 4. 3 Enhancing the output of single well and oilsure is below 124 MPa, but supercritical CO, jet is stilleffective at 55 MPa l0Supercritical CO, don' t pollute reservoir, and is10easy to drill horizontal wells, multilateral wells andcomplex structural wells; it can also be used to jetfracturing and displacement, which can raise the output of single well greatlyal co fluidtrol in drilling and transform between overbalanceance and underbalance during drilling, and it does notpollute the reservoir at any condition Besides, it canWaterdecrease the probability of down hole complex occur-rence. The low-cost coiled tubing drilling with superJet pressure/MPacritical CO2 can drill multilateral wells, fish bone welland other complex structural wells easily, which willFig 2 Jet-erosion drilling rates comparison inbuild a radiated wells net and connect the differenthard shale with different fluidsformations near the main wellbore to achieve the aimof increasing oil and gas flow channel, improve the4. 2 Protecting the ultra-low permeability reservoirflow direction and enhance the production extent andGenerally speaking, the water-based drilling fluid shale gas recoveryis usually used for conventional drilling technology toecondly, the supercritical CO2 can be used indrill the reservoir, and the solid particle would enter fracturing for reservoir stimulation, and enhance theinto formation to plug the pores and tiny fractures; the permeability of reservoir and improve the flow capacitymud filtrate would invade the reservoir, and then com- of fractures, and then increase the output and recoverybine with clay minerals in the shale layer, which willThirdly, due to stronger adsorption ability of CO2result in clay swelling and pores blocking, and the per- molecule with shale than that of CH, molecule, it canmeability would decrease at last. Besides, the mud filreplace the Cha absorbed on the shale rock andtrate invasion would result in water lock effect, which increase the free gas content when it is injected intocan increase the gas flow resistanceshale gas reservoir, and theen enhancegasSupercritical CO2 fluid dont contain liquid water recovery and output further.and solid particles when the reservoir is drilled by the 5 Development of shale gas exploitationsupercritical CO2. On the contrary, the formation po-rosity and permeability would be further increased andwith supercritical CO2the gas flow resistance would be decreased when theThe drilling, completion and stimulation technolosupercritical CO2 invades into reservoir. The mecha- gies develop rapidly, such as horizontal wells, multi-nismlateral wells, directional wells, multi-stage hydraulicFirstly, the density of supercritical CO2 is high, fracturing, re-fracturing, synchronization fracturingand it can dissolve the heavy oil and other contamina- and crack integrated monitoring technologies etc. Howtion near the wellbore area, then decrease the gas flow ever, the implementations of these technologies are inresistance near wellbore area; secondly, the surface separable from the liquid water, which is fatal for clay.tension of supercritical CO, is zero, and the viscosity is Although the advanced drillirsmall and the diffusion coefficient is big, so it can en- niques above can produce better development resultster into any other room which is bigger than the Co, the injury of shale gas reservoir is inevitable, whichmolecule and is beneficial for the nature gas to drive hasresource. Thereforeinto the wellbore. In addition, supercritical CO, can how中国煤化工 king and make techni-make the tight clay sand stratum dehydrated, build upCN MHGtransform the recover-new pores, reduce the wellbore skin factor, clear flow able resource into the economic and technical reservespath between the reservoir and wellbore(nlShale gas exploitation with supercritical CO, tech万夯数蛳 ineering Sciencesnology exactly adapts to the development characteristics it is very easy for supercritical CO, to flow in the poreof shale gas, which include drilling and fracturing and enter into any room which is bigger than the COstimulation technology for shale gas development. For molecule. Therefore, supercritical CO, fluid can dis-drilling technology, it can improve the efficiency of place the free gas effectively in the micro-pores and mirock breaking and enhance the drilling speed; for shale cro-fractures at the external force, and can drive thegas exploitation, it has stronger adsorption ability with nature gas into wellbore for production. And it canshale than that of CH4 molecule, so it can replace the change the adsorbed CH, molecule into free state alsoCH, absorbed on the shale rock, and enhance the gaseding up the production rate and enhancing the gasrecovery; for fracturing, it does not contain solid phase well production and gas recoveryand liquid water and does not pollute the reservoir,4)CO, has no pollution, and is easy to controland the characteristics of low viscosity enable more and helpful to solve the problem of greenhouse gascomplex micro-cracks occurrence in the formation, emissions when it is injected into the shale reservoirwhich is beneficial for the development of shale gas; its5)It is suggested that the experimental study ofiggest advantage is no pollution to the nature environ- supercritical CO, and its related technologies should bement, and is helpful to solve the problem of greenhouse carried out, and the tools development related to thegas emissions when it is injected into the shale technology is needed, to facilitate the realization of in-reservoir.dustrial applications quickly, and lay a solid technicalIt is expected that the technology of shale gas de- foundation for the efficient development of shale gasvelopment with supercritical CO2 will develop into anew and efficient exploitation technology in the next Referencesfew years, and be applied to the field. The different [1] Zhao Qun, Wang Hongyan, Liu Renhe, et al. Global developmenttype of down hole tools and its supporting technologyand Chinas exploration for shale gas [J]. Natural Gas Technolo-will bered in several years, and put into compre- [21 Li Xinjing, Hu Suyun, Cheng Keming. Suggestions from the de-hensive use. By then, the shale gas development techvelopment of fractured shale gas in North America [J].Petroleumnology of our country will be upgraded to a high levelExploration and Development, 2007, 34(4): 392-400and our rich shale gas resources are effectively devel-[3] Xu Shilin, Bao Shujing. Preliminary analysis of shale gas resourceoped. The shale gas will become a new growth point forpotential and favorable areas in Ordos Basin [J]. Natural Gas Ge-futurtence,2009,20(2):405460energy with less environmental [4] Jiang Huaiyou, Song Xinmin, An Xiaoxuan, et al. Current statepollution.and outlook of exploration and development of the shale gas re-6 Conclusionssources in the world [J]. Petroleum Geology and Oilfield Develop-qing,2008,27(6):10-11)Rock breaking efficiency and drilling speed [5] Peng Yingli, Ma Chengyu. Application Manual of Super CriticalFluid Technology[ M]. Beijing: Chemical Industry Press,2005canenhanced by supercritical CO2 drilling, which [6]wang Zaiming. Feature research of supercritical carbon dioxidecan decrease the drilling cost and improve the value ofdrilling fluid [D]. Shandong: China University of PetroleumecononicoitationEast China), 2008:1-22.2)The viscosity of supercritical CO, is ultra[7] Faisal Al-Adwani, Julius P, Langlinais, et al. Modeling of an un-derbalanced drilling operation utilizing supercritical carbon dioxidesmall, which can produce many tiny fractures nearbyR].SPE14050,2008the main fracture when we use the supercritical CO, [8] Zhang Kang, Tan Yundong. The status of world shale gas re-fracturing, and it will not pollute the reservoir; on thesources potential and production status as well as developmentcontrary, it can improve the flow conductivity of frac-prospect of China's shale gas [J]. Petroleum and PetrochemicalToday,2009,17(3):9-12tures, and enhance the output of single well and oil re- [9] Kolle JJ. Coiled-tubing drilling with supercritical carbon dioxidefinall[R].SPE65534.20003)CO2 molecule has stronger adsorption abilit[10] Kolle JJ, Marvin M H. Jet assisted drilling with supercritical car-with shale than that of CH, molecule, so the replacebon dioxide [R]. Tempress Technologies, 2000[11] Gupta A P, Gupta A, Langlinais J. Feasibility of supercriticalnent reaction will occur between CO and CH ad-arbon dioxide as a drilling fluid for deep underbalanced drillingsorbed on organic matter and tiny particles of clay min-peration [R].SPE96992200eral surface. Besides, supercritical CO2 fluid has thetraits of low viscosity and big diffusion coefficient and中国煤化工"P.42)most important character is zero surface tension, soCNMHGVol.10No.4,Aug.201215[3] Huang Baojia, Li Junliang, Li Li, et al. A discussion on the hydrocarbon accumulation characteristics and distribution in Wen- [5] Wang Chunxiu, Zhang Qunying. Typical oil and gas reservoirs andhang A sag [J]. China Offshore Oil and Gas, 2007, 19(6): 361heir forming conditions in AHU Il sag [J]. China Offshore Oand Gas,1999,13(4):248254.[4] Xu Xinde, Huang Baojia, Li Li, et al. A study on the migration [6] Hindle A D. Petroleum migration pathways and charge concentra-and accumulation of oil and gas in Qionghai uplift, Zhusan depres-tion: a three-dimensional model [ J]. AAPJ Bulletin, 1997. 8on [J]. Petroleum Exploration and Development, 2000, 27 (4)(9):1451-1481AuthorXie Yuhong, male, borm in 1962, graduated from Hebei Geology Collegical. He is a Ph. D and professorMr. Xie has published over 30 papers and 10 books. His current research is exploration and development study andmanagementetc.HecanbereachedbyE-mail:xieyh@cnooc.com.cn(cont. from p. 15)AuthorWang Haizhu, male, born in 1981, graduated from Xi'an Petroleum University and now he is a post-doctor inthe College of Petroleum Engineering at China University of Petroleum, Beijing, China. Mr. Wang has publishedover 20 papers. His current research is basic theory and technology research of the application of supercriticalcarbon dioxide in petroleum engineering, multiphase flow in the wellbore etc. He can be reached by E-mail:whz0001@126.comFoundation item: Key Project of Chinese National Programs for Fundamental Research and Development (973Program)( No. 2010CB226704); Chinese National Natural Science Foundation ( No. 51034007)the ChinaNational Petroleum Corporation Key Project Foundation( No 2011A-4205); China Postdoctoral Science Foundation(No.201lM500492)中国煤化工CNMHG方毁孺 eening Scien