Study on water saturation computation model in complex pore volcanic reservoir

Global Geology, 15(1):53-57(2012)doi: 10.3969/j. in. 1673-9736. 2012. 01. 08Article ID: 1673-9736(2012 )0I -0053-05Study on water saturation computation modelsin complex pore volcanic reservoirBIAN Huiyuan' ，SHI Danhong2，HAN Shuang' , PAN Baozhi' and ZHANG Lihua'1. College of Geo -Exploration Science and Technology, Jilin University, Changchun 130026, China;2. No.2 Well Logging Company, Daqing Driing & Exploration Engineering Corp. , Songyuan 138000, Jilin, China;3. Ressearch Institute of Exploration and Development, Northeast Oil & Gas Branch , SINOPEC, Changchun 130026 , ChinaAbstract: Deternination of water saturation is important for reservoir evaluation. When complex pore strueturessuch as fracture and cavity are present in reservoir，Archie equation is no longer suitable. According to differentmodels of pore structure division, the authors studied water saturation computation models. The results showthat dual porosity system is divided into four models. The first model is based on dual laterolog, the second isDual Porosity I，the third is Dual Porosity I，and the last one is based on the conductive pore. Besides, thetriple porosity system is triple porosity model. Compute water saluration was using all the above five models involcanic reservoir in Songnan gas field. The triple porosity system is the most suitable model for water saturationcomputation in complex pore structure volcanie reservoir.Key words: water saturation; triple porosity model; dual porosity model; complex pore structuretwo improved dual porosity models for reservoirs, and1 IntroductionAguilera and Aguilera (2004) published a triple po-Quantitative description of water saturation inrosity model. They discussed the change law of thereservoirs is an important basis for forecasting whethercementation exponent m with the change of the differ-the aimed interval has the production with industryent porosities. However, the parameters of these mod-value. Matrix porosity, fractures and non-connectedels are from lab, so it is difficult to apply actually. Asvugs are the main reservoir space in complex pora result, the developments of these models are still instructure reservoirs such as carbonate reservoirs andtheory stage. Based on the model published by Aguil-volcanic reservoirs. With pore structures and types areera and Aguilera ( 2004), Pan ( 2006) researched onmore complicated, the variation range of cementationthe method of different porosity parameter computa-exponent m is larger, so water saturation computationtion, which greatly enhanced the practicability of thehas great challenges. In order to get better effect ，model. Liu et al. ( 2009) published the dual lateralscholars have been researching into complex porelogging conductive laws in triple porosity system, giv-structure characteristics to get the method to determineing out the computation method of connected fracturedthe cementation exponent m ( Pan et al. ，2006).( and/or) vuggy porosity and non-connected vuggyBased on the series and parallel circuit conductiveporosity.中国煤化工law，Aguilera M S and Aguilera ( 2003 ) presentedSeconda; volcanice res-YHCNM HGReceived 14 November 2011. accepted 25 December 2011Supported by the National Natural Science Foundation of China ( No.41174096 )54Bian H. Y., Shi D.H., HanS., et al.ervoir in Songnan gas field, and the main types areφp= "Cus- Cm)/(Cng-C.) (3)gas pore, residual pore, amygdaloidal pore，fracture ，Where Cus and CuD are the dual lateral loggingmicro fracture and so on. This paper analyzed differ-conductivities, Cmg and C。are the conductivities of theent water saturation computation models, and sortedmud filtrate and the formation water.out the most suitable model in this complex pore struc-2. 2 Water saturation computation method usingture volcanic reservoir.dual porosity modelWater saturation computationIt is so complex in reservoirs containing fracturesmethods in dual porosity sys-and vugs that different physical interpretation modelsare established in different geological conditions. Fotemsexample，Aguilera and Aguilera ( 2003 ) presented2.1 Water saturation computation method usingtwo improved dual porosity models for reservoirs.dual lateral loggingIn the dual porosity model I，the porosity isThe porosity in fractured reservoirs is mainlycomposed of matrix and non-connected vugs, with thecomposed of matrix porosity (φn) and fractured poros-conductive law of series circuit ，the cementation expo-ity (φr). Fractured porosity is small compared withnent m is computed as follows.total porosity. However, fractures have great influenceon resistivity and permeability. For the difference bem =-log[um$ + (1一Us)φ](4)logptween fractured permeability and matrix permeabilityWhere φ is the total porosity, Vae is the volumeis considerably， when the reservoir is invaded bymud, the fractures in invaded zone are full of mud fil-中一甲bof the non-touching vugs,φ(1 -φ。)trate before it is replaced by interstitial fluid. So thedual lateral logging resistivities are as follows (Li etal.，2008).composed of matrix and connected factures or vugs,o"Sm, φ" ●S%with the conductive law of parallel circuit, the cemen-RuDRR,tation exponent m is computed as follows.(1)φ"Smm, φ"y●S%log[uφ + (1 - up)/φ"°](5)'RusRmtlogp .Where S.. and Swf are the water saturations in2.3 Water saturation computation method basedmatrix and fractures, m and mq are the cementationon the conductive poreexponents in matrix and fractures, n and n; are theIn theory ，resistivity logging reflcts the conduc-saturation exponents in matrix and fractures, Sxo is thetivity of the connected pore space flled with conduc-water saturation in fractured flushed zone.tive water. But actually, the resistivities of tight layersFor oil containing formations, when all the frac-are not infinite. According to cores, tight layers con-ures in uninvaded area are flld with oil, and all thetaining conductive minerals exist in volcanic rocks.fractures in invaded area are flled with mud filtrate ，The apparent resistivity is composed of pore fluid re-the fractured porosity is computed by following equa-sistivity, water-bearing micropore resistivity, conduc-tion.tive mineral resistivity and the resistivity caused by pitφr = VRme(Cus - Cun)(2)shaft fluid, and they are parallel( Han, 2010; Yan elFor water containing formations, when the differ-al.，2011) . Then the water saturation is calculatedence between the formation water resistivity and theas follows.中国煤化工mud filtrate resistivity is obviously, the fractured poMHCNMH GSw =cT。wt UBC τ liL. + Cpc)'rosity is computed with equation (3).Study on water saturation computation models in complex pore volcanic reservoir55-4C.C.s._ k(C,- Cua)]12pporosity model, in which total pore volume was made4up of the matrix pore volume Vp, connected fractured(6)and/or vuggy pore volume V. and non-connected VugIn Eq. (6)， C, is the reservoir logging conduc-gy pore volume V.(Fig. 1). The matrix and the ma-ivity, h is the factor of pore space connectivity and ittrix pore volume form the matrix system. (Shou et al..is used to distinguish the connected pore space and2005; Wang et al., 2003; Wang, 2005; Zhang et .the total pore space, Sm is the water saturation whichal.，2008). In this paper, we discussed the changeis not in the conductive system, Sar =φ,/φ,, φ, is thelaw of the cementation exponent m with the change ofcutoff porosity.the different porosities. But in this method, in order3 Water saturation computation meth-to use triple porosity model, connected porosity shouldbe calculated using dual porosity model (Liu et al.，od using triple porosity model2009) . When certain types of pore volume are veryThe reservoir effectiveness can be estimated u-lttle, the triple porosity model reduces to dual porosi-sing the dual porosity models if acoustoelectric ima-ty or single porosity model.ging logging data is available. However, many wellsWe gain analysis equations containing porositydon't have the acoustoelectric imaging data in Songnanparameters using dual lateral logging resistivity, angas field, so the dual porosity models are not fit forevaluate the fractured and/ or vuggy reservoir withthis area.these equations. This method is based on connectedAguilera and Aguilera (2004) published a triplefractures and/ or vugs porosity.。O|Ve Non-conected vuggy pore volumeV。 Connected fractured and vuggy pore volume| Total> volumeMatrix pore volumeMatrix system|Matrix(having no pore) ,volume VFig. 1 Composition of the triple porosity modelLiu et al. ( 2009 ) presented the conduction lawWhen the dual lateral logging resistities showof dual lateral logs in the triple porosity model. Whennegative separation and the formation contains low an-the dual lateral logging resistivities show positive sepa-gle fractures , Ru can be described as following com-ration and the formation contains high angle fractures,posite system: (1) the series circuit for the resistanceRup can be described as following composite system:measured by shallow lateral logs and the resistance of(1) the parallel circuit for the resistance measured bynon-connected vugs; (2) the parallel circuit for theshallow lateral logs and the resistance of connectedresistance obtaining in (1) and the resistance of con-fractures ( and/or vugs); (2) the series circuit fornected fractures. It can be expressed as follows:the resistance obtained in (1) and the resistance of1_ Pe, 1- 4。non-connected vugs. It can be expressed as follows :RuDRR(8)pRuo = φmeRmg+(1 -φn)Rp+1n RmyFusP。。1-φRuus(7)Matrix中国煤化工using conven-lR。“ Rmj+ RuFus',Fus= Rtional log dYHCNMHG and(8), the5Bian H. Y., Shi D.H., HanS., et al.connected fractured porosity， non-connected vuggysis of water saturation data, and its correct rate isporosity of the reservoir can be calculated.83. 9%. Fig. 2 is a comparison diagram on water satu-The cementation exponent m in the triple porosityration computed in different models. We choose Tourmodel is computed as follows.logs (logs A, B, C and D) with different fluids. Thefirst three tracks are the results of the conventionalvp+(1-vp)p"Jlogging suite; the forth track is the calculated matrix(9)log4porosity and total porosity, the fifth track is the rela-4 Examples and discussiontive connected fractured ( and/ or vuggy ) porosity andthe non-connected vuggy porosity; from the sixth trackThe volcanic reservoir in Songnan gas field is lo-to the tenth track are the calculated water saturations.cated in a deep fault depression, and its pore struc-ture is complex. The methods described above haveWe can see that all the five methods are efective, andbeen used for the effectiveness estimation of the car-they correspond with the testing for gas. All kinds ofbonate reservoir in this area. In 14 wells that we stud-these methods have their advantages and disadvanta-ied, there are 31 intervals having the laboratory analy-ges respectively.GRiAPFLLD/Qm} CNL/%100一200 I 2一20004020|ParM/| PorNC/LLS/0nDEN/.c30-30Swll0---2002.2000| 2 一一3arie for descn-1s ptionPorT/%PorF/% .CAL/inMSFL/QmI AC/us. 的0]002000 450---150ogGas《Gias |{王LogWateras |日Fig.2 Comparison diagram on water saturation computed in different modelsThe water saturation calculated using dual laterallogging and assumes that " when the reservoir is inva-logging Sum ( track 6) is low when gas is contained inded by mud中国煤化工one are full ofthe reservoir. This method depends on dual lateralmud filtrate"| YHC N M H Gn actual forma-.Stud:ly on water saturation computation models in complex pore volcanic reservoir5:tion are not flled as we assumed. The water saturationphysical analysis of dual porosity reservoirs. Petrophysics ，based on the conductive pore ( SwC in track 9) is .44(1):21-35.AguileraR F, Aguilera R. 2004. A lriple porosity model for50% in the water bearing formation, so the result ispetrophysical analysis of naturally reservoirs. Petroplys-not satisfactory. What's more, this method is based onics, 45(2) :157-166.too many parameters and when there is no laboratoryHan s.2010. Volcanic reservoir parameter evaluation of welldata the parameters are difficult to get, so this methodlogging for Yingcheng Formation in Changling Depression,is hard to achieve. The water saturations calculated u-South Songliao Basin: master degree's thesis. Changchun:sing dual porosity model I (SwI in track 7) and IIJilin University. ( in Chinese with English abstract)(SwII in track 8) are not good enough to apply in realLiuRL, QingN, LiF F, et al.2009. Application of the tri-data. The tenth track is based on the triple porosityple porosity model in well-log efectiveness estimation ofmodel. The water saturation SwT is high in waterthe carbonate reservoir in Tarim. Journal of Petroleum Sci-bearing formation, and it is low in gas bearing forma-ence and Engineering, 68(1) :40-46.LiZ B, PanBZ, FanX M, et al. 2008. Processing and com-tion.prehensive interprelation of geophysical well-logging data.5 ConclusionBeijing: Geological Publishing House, 151-152. (in Chi-Compared the five methods and get a conclusion:PanBZ, ZhangL H, ShanG Y, et al. 2006. Progress in po-The water saturation calculated using dual lateral log-rosity model for fractured and vuggy reservoirs.Progress inging Swm depends on dual lateral logging and assumesGeophysics, 21(4):1232-1237. ( in Chinese with Englishthat " when the reservoir is invaded by mud, the frac-abstract)tures in invaded zone are full of mud filtrate". How-ShouH, Wang W H, Liu H, et al. 2005. Well-logging evalu-ever, the fractures in actual formation are not flled asation for threefold fracture and pore construction of com-plex reservoir and its application. Journal of the Universitywe assumed. The water saturation based on the con-of Petroleum, China: Edition of Natural Science , 29(6):ductive pore SwC depends on too many paramelers23-24. (in Chinese with English abstract)and when there is no laboratory data the parametersWangQ, Li G P, Zhao X M. 2003. On log interpretationare difficult to get, so this method is hard to achieve.method for complex pore structure reservoirs. Well Log-The water saturation calculated using dual porosityging Technology, 27(5) :389-393. ( in Chinese with Eng-model I ignores fractures, and the water saturationlish abstract)calculated using dual porosity model I ignores non-WangJ. 2005. Logging evaluation method for complex reser-connected vugs. The triple porosity model considersvoir in Futai buried hill reservoir. Acta Petrolei Sinica, 3the affection to cementation exponent caused by fac-(26) :86-89. ( in Chinese with English abstract)tures and connected vugs. this model is a combinationYanW L, Qin H, Li H J.2011. Study on the gas saturationcomputation model of neutral and basic volcanic rocks res-of the dual porosity model I and I，and this is closerervoir based on the conductive pore. Journal of Jilin Uni-to real formations. Compute water saturation using allversity : Earth Science Edition, 41(3):915-920.( in Chi-the above five models in volcanic reservoir in Songnannese with English abstract)gas field. We find that triple porosity system is theZhangL H, Pan B z, Shan G Y. 2008. Tri-Porosity Modelmost suitable model for water saturation computationnd Its Application in Igneous Reservoir. Well Loggingin complex pore structure volcanic reservoir.Technology, 32(1):374. ( in Chinese with English ab-stract)ReferencesAguilera M S, Aguilera R. 2003. Improved models for petro-中国煤化工MHCNM HG