致密油藏表面活性剂渗吸影响因素研究.pdf

第 53 卷 第 8 期2023 年 8 月Vol.53 No.8Aug.2023857 日 用 化 学 工 业（中英文）China Surfactant Detergent&CosmeticsReceived:April 10,2023;Revised:July 18,2023.*Corresponding author.Tel.:[phone],E-mail:.国家自然科学基金青年项目资助（52204062）；克拉玛依市创新人才专项资助（20212022hjcxrc0037）；中国石油大学（北京）克拉玛依校区科研启动基金资助（XQZX20230013）DOI：10.3969/j.issn.2097-2806.2023.08.001Research on the influence factors of surfactant imbibition in tight reservoirsDerongXu1,WeiLian1,JinzhaoXiong1,WanliKang2,*（1.School of Petroleum,China University of Petroleum（Beijing）at Karamay,Karamay,Xinjiang 834000,China;2.School of Petroleum Engineering,China University of Petroleum（East China）,Qingdao,Shandong 266580,China）Abstract:Tight reservoirs always show poor physical properties,resulting in difficulties to be effectively exploited by conventional water flooding.Imbibition with surfactant solutions is the main means for exploitation of tight reservoirs.In this work,the effects of rock wettability,surfactant types,interfacial tension（IFT）of imbibition solutions,oil viscosities,temperature and surfactant slug combinations on imbibition efficiencies were studied with Changqing tight outcrop cores by Amott cells.The results showed that,the higher the wettability of the rock was,the higher the imbibition recovery would be obtained.The imbibition recovery of different types of surfactants was decreased in the sequence:anionic surfactantsnonionic surfactantscationic surfactants.When the oil-water IFT of imbibition liquid was at the level of 10-1 mN/m,the imbibition efficiency was the highest.Reducing the viscosity of crude oil and increasing temperature were both beneficial to the imbibition recovery.The earlier the surfactant imbibition was carried out,the higher the imbibition efficiency was.In addition,the imbibition efficiency could be further improved by using ultra-low IFT imbibition solution after primary imbibition with non-ultra-low IFT imbibition solutions.Key words:tight reservoir;surfactant;imbibition;interface tension;wettability?CTABSDSAPG10t/min10 0008 0006 0004 0002 000Imbibition recovery/%01020506030407080Brine0.05%SDS0.05%CTAB0.05%APG10858第 53 卷基 础 研 究日 用 化 学 工 业（中英文）The production of oil and gas plays important roles in the worldwide energy supplies.However,with the development of conventional reservoirs,the recoverable oil decreases year by years.Thus,the exploration and development of tight reservoirs become the focuses of petroleum engineering 1.Tight sandstone reservoirs in China usually possess the characteristics of poor porosity,low permeability,small pore-throat radius and significant heterogeneity（with natural fracture development）3.Thus,conventional methods,such as water flooding,show poor application in these reservoirs,facing with the difficulties of poor injectivity and low oil recovery efficiencies.In recent years,oil recovery with fluid spontaneous imbibition in low-permeability reservoirs,which shows high efficiencies and strong implementation,attracts much attention 4,5.Spontaneous imbibition refers to the invasive process of a wetting phase displacing a non-wetting phase by means of capillary and/or gravity forces 6.The capillary pressure can be described using the Young-Laplace equation（Eq.（1）7:（1）Where PC represents the capillary pressure;is the interfacial tension（IFT）;is the contact angle;and r is the pore radius.The is related to the wettability of the reservoir.Thus,the main influence factors for imbibition are wettability and IFT.As shown in Eq.（1）,the capillary r2 cos PC=pressure is inversely proportional to the capillary radius.Hence,low-permeability reservoirs,which possess a large amount of small-radius throats,show great imbibition potential.In addition,it has been found that the capillary pressure acts as the driving force in water imbibition process when the reservoir is water-wet.However,they will act as resistance forces if the reservoir is oil-wet.Thus,the wettability alteration of the cores is of crucial importance on the imbibition enhanced oil recovery（IEOR）.Rock wettability can be measured with several methods,such as contact angle measurement,wettability index,NMR 8,and X-ray micro-computed tomography 9.Contact angle measurement,which possesses simplest operation and is able to quantitatively evaluate the wettability alteration of rock surfaces,is the most commonly used.In water-oil-rock systems,the rock is defined as water-wet when the contact angle ranges from 0-75 degrees,neutral-wet from 75-105 degrees,and oil-wet from 105-180 degrees 10,respectively.IFT reduction is not conducive for imbibition according to Eq.（1）because the capillary pressure would decrease with IFT reduction.However,adhesion work would also decrease with IFT reduction,which facilitates the oil to be detached from the core surfaces.Thus,the effect of IFT on imbibition efficiency is complex.Adhesion work is shown in Eq.（2）11：W=（1-cos）（2）Where W represents the adhesion work.致密油藏表面活性剂渗吸影响因素研究徐德荣 1，连 威 1，熊金钊 1，康万利 2,*（1.中国石油大学（北京）克拉玛依校区 石油学院，新疆 克拉玛依 834000；2.中国石油大学（华东）石油工程学院，山东 青岛 266580）摘要：致密油藏储层物性差，常规水驱难以对其进行有效开采，表面活性剂渗吸采油是致密油藏开采的主要手段。针对长庆致密露头岩心分别研究了岩石润湿性、表面活性剂类型、界面张力、原油黏度、温度及表面活性剂段塞组合对渗吸效率的影响。结果表明，岩石亲水性越强渗吸效率越高；阴离子表面活性渗吸效率最佳，非离子表面活性剂次之，阳离子表面活性剂最差；当渗吸液油水界面张力为10-1 mN/m时渗吸效率最佳；降低原油黏度及升高温度均有利于渗吸采油；表面活性剂渗吸越早进行效果越好，并且，在非超低界面张力渗吸液体系一次渗吸结束后采用超低界面张力渗吸液体系渗吸能进一步提高渗吸效率。关键词：致密油藏；表面活性剂；渗吸；界面张力；润湿性中图分类号：TQ423 文献标识码：A 文章编号：2097-2806（2023）08-0857-08859第 8 期基 础 研 究DerongXu,etal:Researchontheinfluencefactorsofsurfactantimbibitionintightreservoirs Surfactants have the abilities of both IFT reduction and wettability alteration 12,which have become the main chemical additives for improving imbibition efficiencies.In this work,the effects of rock wettability,surfactant type,IFT,oil viscosity,experiment temperature,and surfactant slug combination on imbibition efficiency were investigated,which has guiding significance for the application of surfactant imbibition.1 Materials and methods1.1 MaterialsSandstone cores from the outcrop of Changqing oilfield（a typical low-permeability reservoir in China）were used.All core samples were from one outcrop to ensure the lithological similarity.The core characteristics were shown in Tab.1.The density of Changqing crude oil was 0.850 3 g/cm3 and its viscosity was 2.73 mPa s at 80.All surfactants were commercially available,including cationic surfactant（CTAB）,nonionic surfactant（APG10）and two types of anionic surfactants（SDS and KD）,which were provided by Qingdao Changxing Chemical Co.,Ltd.Distilled water was used.The distilled water was produced by purification through the Milli-Q Advantage A10 Ultrapure Water System.1%KCl brine was used in all experiments.Analytically pure KCl was provided by Sinopharm Chemical Reagent Co.,Ltd（Shanghai,China）.Tab.1 Characteristics of the core used in imbibition testsParametersValueDiameter/cm2.50.1Length/cm30.1Porosity/%9-11Permeability/mD0.1-0.3Median pore radius/m0.6151.2 Experimental methods1.2.1 Preparation of oil-wet coresThe influence of rock wettability on imbibition efficiency is of great significance.To study the effect of rock wettability on imbibition efficiency,the Changqing outcrop cores were treated with oleic acid solution.First,the outcrop cores were dried in the bake oven at 85 for 24 h.Then,the dried cores were saturated with 5%oleic acid solution by a vacuum pump for 12 h,and aged in oleic acid solution at 45 for 7 days.Finally,the saturated and aged cores were dried in the oven at 85 for 24 h.1.2.2 Imbibition testSpontaneous imbibition tests were conducted in Amott cells using the volume method,in which the oil volume could be directly read through the glass tube scale（the precision was 0.005 mL）to calculate the recovered oil volume.Before imbibition,the cores and the imbibition solutions were all preheated in an oven at 45 for 1 h;then the cores were placed in Amott cells,and the imbibition solutions were quickly filled into the cells to a desired height;thereafter,the cells were placed in a thermostatic water bath of 45,and the oil volume was recorded versus time.The cores were left in the cells until the recovered oil volume stopped increasing,and then the ultimate recovery was calculated.The imbibition rate in the specific time period was calculated by the imbibition recovery increment in each period of time（the time interval between two recorded points）,which is defined as Eq.（3）.（3）Where i is the point number;ti is the imbibition time at the i point;vti is the imbibition rate at ti moment;Rti is the imbibition recovery during different ti period.2 Results and discussion2.1 Effect of rock wettability on imbibition efficiencyFig.1 shows the contact angles of cores that were untreated and treated with oleic acid.The results showed that the initial contact angle was 20,behaving water-wet.After treated with 5%oleic acid solution,the contact angle was increased to 96,indicating that the core wettability was changed from water-wet to neutral-wet.The imbibition experiments were then carried out on the cores with different wettability using 1%KCl solution at 45.Fig.2 shows the imbibition recovery versus time.It could be seen that the imbibition recovery of the two cores presented the same change trend,i.e.,the imbibition recovery increased sharply at the first stage,then increased slightly at the middle stage and finally reached a stable value.The imbibition recovery of water-wet core was 44.6%,and that of neutral-wet core was 33.9%.Fig.3 ti-ti-1Rti-Rti-1vti=860第 53 卷基 础 研 究日 用 化 学 工 业（中英文）shows the plots of imbibition rate versus time for the cores with different wettability.It could be seen that both imbibition rates rapidly increased to a maximum value and then decreased until finally reaching zero.Moreover,the maximum imbibition rate of water-wet core was higher,and the imbibition process ended in a very short time.In addition,the water-wet core began to drain out oil within ten minutes,while the neutral-wet core after one hour.Similar findings were also reported by Xu et al 13.Their work suggested that the imbibition began to take place on the core surface,and the oil-water channels were established quickly by the capillary force and other forces;thus,the imbibition rate rapidly increased in a short time.However,the oil became more difficult to be driven out as the imbibition depth increased because of more resistances,such as the Jamin effect,occurred during the migration process,resulting in the failure of establishing effective channels.Subsequently,the imbibition rate slowed and finally dropped to zero.Compared with neutral-wet core,water-wet core possessed larger capillary forces and smaller adhesion work,therefore,faster imbibition rate,higher imbibition recovery and shorter imbibition equilibrium time.The results of contact angle measurement and imbibition recovery both proved the wettability alteration of the core.Therefore,the oleic acid treated cores were used in the subsequent experimental studies.2.2 Effects of surfactant type on imbibition efficiencyThe imbibition efficiencies of three surfactants（anionic SDS,nonionic APG10,and cationic CTAB）were investigated using oleic acid treated Changqing outcrop sandstones at 45.Fig.4 shows the imbibition recovery versus time of three surfactant solutions.As shown in Fig.4,SDS achieved the highest imbibition efficiency（50.4%OOIP）,closely followed by APG10（44.1%OOIP）,which were both higher than that of brine（33.9%OOIP）,indicative of the IEOR potential of anionic and nonionic surfactants.However,CTAB only recovered 16.2%OOIP,Fig.1 Contact angles of cores before and after treated with oleic acidBefore treatedAfter treated9620Contact angle/()020401001206080140160t/min10 0008 0006 0004 0002 000Imbibition recovery/%01020506030407080Water wet Neutral wetFig.2 Sp ontaneous imbibition recovery of the cores with different wettabilityt/min500400300200100Imbibition rate/(%/min)00.40.60.20.81.0Water wet Neutral wetFig.3 Sp ontaneous imbibition rate of the cores with different wettabilityt/min10 0008 0006 0004 0002 000Imbibition recovery/%01020506030407080Brine0.05%SDS0.05%CTAB0.05%APG10Fig.4 Sp ontaneous imbibition recovery for different types of surfactants861第 8 期基 础 研 究DerongXu,etal:Researchontheinfluencefactorsofsurfactantimbibitionintightreservoirs which was much less than that of brine,showing the poor applicability of cationic surfactants in sandstone reservoirs.Fig.5 shows the relationship between imbibition rate and time.It could also be seen that the imbibition rate was the highest in 0.05%SDS solution,and the lowest in 0.05%CTAB solution.Fig.6 shows the contact angle of core surface after imbibition with different solutions.As shown in Fig.6,compared with brine,SDS and APG10 increased the water wettability of cores,however,CTAB decreased the water wettability of the core.The anionic surfactant SDS could increase the negative charge of the core surface,enhancing the electrostatic repulsion between oil and rock,thus the oil would be more easily stripped from the rock surface,favoring to increase the water wettability,and finally achieving the highest imbibition recovery 14.However,the addition of positively charged CTAB would cause electrostatic attraction which made the oil film more strongly adhere to the rock surface,leading to longer time for oil beginning to desorb from rock surface（as shown in Fig.5）;moreover,the adsorption of CTAB molecules on rock surface with hydrophobic tails facing the solution,would increase the wettability of cores to oil.Hence,CTAB solution resulted in the most oil wetting,and thus the lowest imbibition recovery ultimately.All these imbibition results indicated that the imbibition potential of surfactants for Changqing sandstones was in the sequence of anionic surfactantnonionic surfactantbrinecationic surfactant.2.3 Effect of IFT on imbibition efficiencyIn this part,anionic surfactant KD,which was able to form ultra-low IFT with Changqing crude oil at the concentration of 0.05%,was mixed with SDS to achieve different IFT.Tab.2 showed the IFT of solutions and the contact angles on core after imbibition.Fig.7 shows the imbibition recovery versus time for the solutions with different IFT.As shown in Fig.7,the imbibition recovery first slightly increased with the decrease of IFT,and then decreased when the IFT was further decreased.Among the four IFT values investigated,the imbibition efficiency was the highest at the IFT of 0.11 mN/m.As shown in Tab.2,the four solutions could all transform neutral-wet cores into water-wet ones,and the contact angles were similar.According to Eqs.（1）and（2）,the differences of capillary pressure and adhesion work caused by contact angle change were much less than by IFT change.Therefore,the difference in imbibition recovery of the four imbibition fluids was mainly caused by the difference in IFT.Fig.8 shows the imbibition rate versus time for different IFT solutions.It showed that,the imbibition rate for the system at the IFT of 2.31 mN/m was the lowest in the initial stage,and