1、第31卷第1期2024年1月Vol.31,No.1Jan.2024油 气 地 质 与 采 收 率Petroleum Geology and Recovery Efficiency致密砂岩油藏纳米乳液渗吸增产作用机理袁 帅1,2,周福建1,2,李 源3,梁星原1,2,梁天博1,2,姚二冬1,2(1.中国石油大学(北京)油气资源与工程全国重点实验室,北京102249;2.中国石油大学(北京)石油工程教育部重点实验室,北京102249;3.中国石油勘探开发技术研究院,北京100083)摘要:纳米乳液作为一种纳米级胶体分散体系,因其优异的界面性能以及提高采收率效果被广泛应用于非常规油藏开发。基于低能乳
2、化法制备了水包油型纳米乳液体系,通过室内实验明确纳米乳液静态吸附性能、润湿反转性能以及自发渗吸的内在联系,并分析纳米乳液在致密砂岩油藏中的渗吸增产作用机理。实验结果表明:纳米乳液的平均粒径小于10 nm,满足进入致密砂岩绝大部分孔喉的粒径要求,在致密孔喉内能充分扩散运移,从而扩大渗吸作用范围。纳米乳液的临界胶束质量分数为0.015%,能够有效降低油水界面张力至2 mN/m左右。纳米乳液的吸附等温线符合Langmuir吸附模型,其润湿反转机理以吸附机理为主。纳米乳液能够增溶原油,并通过乳化作用进一步分散原油,减小乳状液中油滴尺寸,减弱油滴通过孔喉时的贾敏效应,降低渗流阻力。岩心润湿性会影响渗吸采
3、收率,随着岩心亲水性增强而增加,不同润湿性岩心自发渗吸时孔隙动用程度存在差异,加入纳米乳液能显著提高油湿岩心内小孔渗吸采收率。同时,增加纳米乳液浓度与边界开放程度可以提高渗吸采收率,这主要是由于致密砂岩自发渗吸受毛细管力主导,边界开放程度增加能够扩大纳米乳液接触面积,纳米乳液浓度增加能够增强润湿反转作用与乳化作用,从而增强自发渗吸效果。关键词:致密砂岩;纳米乳液;润湿反转;静态吸附;自发渗吸文章编号:1009-9603(2024)01-0126-11DOI:10.13673/j.pgre.202308003中图分类号:TE258文献标识码:AMechanism of imbibition an
4、d production enhancement of nanoemulsion in tight sandstone oil reservoirsYUAN Shuai1,2,ZHOU Fujian1,2,LI Yuan3,LIANG Xingyuan1,2,LIANG Tianbo1,2,YAO Erdong1,2(1.National Key Laboratory of Petroleum Resources and Engineering,China University of Petroleum(Beijing),Beijing City,102249,China;2.Key Labo
5、ratory of Petroleum Engineering Education Ministry,China University of Petroleum(Beijing),Beijing City,102249,China;3.PetroChina Research Institute of Petroleum Exploration&Development,Beijing City,100083,China)Abstract:Nanoemulsion,as a kind of nanoscale colloidal dispersion system,has been widely
6、applied in unconventional oil reservoir development due to its outstanding interfacial properties and enhanced oil recovery effects.Water-in-oil type nanoemulsion systems are prepared based on the low-energy emulsification method.The intrinsic relationships among the static adsorption,wettability al
7、teration,and spontaneous imbibition of nanoemulsion are determined by laboratory experiments,elucidating the mechanism of imbibition and production enhancement of nanoemulsion in tight sandstone oil reservoirs.The laboratory results show that the average droplet size of nanoemulsion is less than 10
8、nm,which can meet the droplet size requirement of entering most of the pore 收稿日期:2023-08-03。作者简介:袁帅(1997),男,河南商丘人,在读博士研究生,从事非常规油气藏纳米流体提高采收率工作。E-mail:yuanshuai_。通信作者:周福建(1966),男,江苏沭阳人,教授,博士。E-mail:。基金项目:国家自然科学基金面上项目“分离压微尺度效应作用下的压裂液渗吸提高采收率机理”(52274051),国家自然科学基金青年基金项目“致密油储层压裂后渗吸动用程度微观控制机理研究”(52204059)。
9、引用格式:袁帅,周福建,李源,等.致密砂岩油藏纳米乳液渗吸增产作用机理 J.油气地质与采收率,2024,31(1):126-136.YUAN Shuai,ZHOU Fujian,LI Yuan,et al.Mechanism of imbibition and production enhancement of nanoemulsion in tight sandstone oil reservoirs J.Petroleum Geology and Recovery Efficiency,2024,31(1):126-136.第31卷 第1期袁帅等.致密砂岩油藏纳米乳液渗吸增产作用机理thr
10、oat of tight sandstone and can fully diffuse and migrate in the tight pore throat,thus expanding the imbibition range.The critical micelle mass fraction of the nanoemulsion is 0.015%,which can effectively reduce the oil-water interfacial tension to about 2 mN/m.The adsorption isotherm of the nanoemu
11、lsion conforms to the Langmuir adsorption model,and the wettability alteration mechanism is mainly adsorption.The nanoemulsion can dissolve the crude oil,further disperse the crude oil through emulsification,reduce the size of oil droplets in the emulsion,and weaken the Jamin effect when oil droplet
12、s pass through the pore throat,reducing seepage resistance.Core wettability will affect the spontaneous imbibition recovery,and the imbibition recovery will increase with the increase in core hydrophilicity.There are differences in the oil recovery at the pore scale in different wettability core spo
13、ntaneous imbibition,and the addition of nanoemulsion can significantly improve the recovery of small pores in the oil-wet core.Meanwhile,increasing nanoemulsion concentration and boundary openness can improve the spontaneous imbibition recovery efficiency.This is mainly because tight sandstone imbib
14、ition is dominated by capillary force,increasing boundary openness can expand the contact area of nanoemulsion,and increasing nanoemulsion concentration can improve the wettability alteration and emulsification,thus improving the effect of spontaneous imbibition.Key words:tight sandstone;nanoemulsio
15、n;wettability alteration;static adsorption;spontaneous imbibition纳米乳液是一种粒径为5500 nm的胶体分散体系,通常包含油相、水相以及乳化剂相,其中乳化剂相包括表面活性剂和助表面活性剂,主要起降低油水界面张力,促进形成纳米级液滴并使其保持稳定的作用1-3。纳米乳液作为动力学稳定体系,相较于微乳液体系动力学稳定性较高,环境适应性较强,当物理化学环境发生变化时仍能维持自身结构4-5。因其具有优异的界面性能以及不同环境下的高稳定性,在石油6-10、食品11、医药行业12得到广泛应用。丁彬等将二苯醚类表面活性剂、直链烷烃化合物与水制备
16、了一种纳米乳液体系,其较高的界面活性可以提高原油在微纳米孔隙内的渗流能力,从而显著提升致密油藏的开发效果13。肖立晓等通过自发乳化法制备了耐高温纳米乳液体系,基于岩心实验证实了纳米乳液能够通过乳化增溶作用以及超低油水界面张力提高致密砂岩的自发渗吸与动态渗吸吞吐过程中的渗吸采收率,同时在胜利油田现场试验也取得了较好的增产效果14。ZHAO等针对纳米乳液体系在碳酸盐岩储层中的动态吸附特性进行了研究,明确了不同润湿性、渗透率下纳米乳液动态吸附量以及粒径的变化规律15。周勤针对红河油田制备了一种平均粒径为20 nm左右的纳米乳液体系,岩心驱替实验表明其具有良好的降压增注效果以及提高采收率性能7。然而,
17、目前研究仅着重于纳米乳液整体性能的表征与渗吸效果评价,并未进一步明确纳米乳液吸附性能、润湿反转性能以及提高采收率性能之间的内在联系与作用机制16-19。为此,基于自发乳化法构建了一种适用于致密砂岩储层的纳米乳液体系并对其界面性能、吸附性能、润湿反转性能和乳化分散能力等进行了综合表征,明确了纳米乳液润湿反转性能、吸附性能与自发渗吸的关系。通过岩心实验探究了纳米乳液体系渗吸效率的影响因素,并利用核磁共振技术明确了其在岩心孔隙内的渗吸动用规律,阐明了纳米乳液在致密砂岩储层中的渗吸增产作用机理。1实验材料与方法1.1 实验材料实验岩心 实验用岩心取自鄂尔多斯盆地延长组长 7段露头,气测渗透率为 0.5
18、90.69 mD,孔隙度为 9.6%11.5%,X 射线衍射测试结果表明岩心矿物组分主要为石英和斜长石,其次为黏土矿物。实验岩心基本物性参数及实验方案如表1所示。实验流体 实验用原油为长庆原油与煤油按质量比为1 1混合的模拟油,常温下黏度为2.21 mPa s,密度为0.813 g/cm3。原油四组分分析可知,长庆原油的饱和分、芳香分、胶质与沥青质的质量分数分别为 70.46%,12.16%,7.41%和 0.5%。由于岩心的黏土矿物含量较高,选用含有质量分数为2%氯化钾的模拟盐水作为实验用水。纳米乳液的母液主要成分由非离子聚氧乙烯醇醚表面活性剂(15%20%)、低碳链醇类助表面活性剂(15%
19、30%)及萜类油核(5%10%)组成,剩余部分为去离子水。纳米乳液母液为通过自发乳化法制得的Winsor 型双连续型微乳液,与模拟地层水进行任意比例的稀释后即可得到澄清透明的水包油型纳米乳液体系20。1.2 实验方法1.2.1纳米乳液粒径分布测试配制质量分数分别为 0.01%,0.1%和 1%的纳米乳液,将制备好的纳米乳液用孔径为45 m的无机过滤器进行过滤。使用纳米粒度仪(Malvern 1272024年1月油 气 地 质 与 采 收 率Zetasizer Nano ZS,激光波长为633 nm,散射角度为175)基于动态光散射法(DLS)得到不同浓度纳米乳液的粒径组成及分布。1.2.2油水
20、界面张力测试配制质量分数分别为 0.001%,0.005%,0.01%,0.05%,0.1%,0.5%和 1%的纳米乳液,测试前将测量皿用蒸馏水润洗 23 次,然后使用待测液体润洗,测试用铂金环也按照相同流程进行润洗。使用BZY-2全自动表界面张力仪通过吊环法测量不同浓度纳米乳液的油水界面张力,每组测试重复3次取平均值。1.2.3增溶与分散原油实验对与模拟油混合后的纳米乳液粒径进行测试,具体实验步骤如下:配制质量分数为0.1%的纳米乳液,按照体积比为1 1加入等量的模拟油,通过机械搅拌的方式将模拟油与纳米乳液充分混合,搅拌速率为 100 r/min。用滴管取一定量的油水混合液置于光学显微镜下观
21、察乳状液中油滴的粒径大小。将上述油水混合液静置12 h,待油水分离后,使用离心机以4 000 r/min的转速离心20 min,用滴管取下层澄清溶液进行粒径测量。1.2.4静态吸附实验主 要 步 骤 如 下:配 制 质 量 分 数 分 别 为0.001%,0.005%,0.01%,0.025%,0.05%,0.075%和0.1%的标准溶液,在最佳波长下对不同浓度的标准溶液进行吸光度测试,绘制吸光度-浓度的标准曲线。将质量分数分别为 0.01%,0.025%,0.05%,0.075%,0.1%,0.25%,0.5%,0.75%和 1%的纳米乳液与岩石粉末按质量比 30 1装入离心管中,放入25
22、恒温烘箱内,并按一定时间间隔摇匀,使岩石粉末与液体充分接触24 h。将离心管以4 000 r/min的转速离心30 min,然后取上层澄清溶液进行吸光度测试,其中对高浓度(质量分数为 0.1%1%)范围内的上层澄清溶液需用去离子水稀释 10倍后再进行吸光度测试,并根据稀释倍数进行浓度换算,通过吸光度测试并与标准曲线进行比对,得到对应的吸附后溶液的平衡浓度,计算不同浓度纳米乳液的静态吸附量,其表达式为:=(C1-C0)Vlms(1)1.2.5润湿反转测试由于岩心原始润湿性为水湿,为了模拟储层实际条件,需对岩心薄片(厚度约为0.3 cm)进行原油老化处理,将其浸泡在模拟油中 90 恒温静置 14
23、d,老化完成后基于躺滴法测量原始接触角。配制质量分数分别为 0.01%,0.05%,0.1%和 1%的纳米乳液,将原油老化后的岩心薄片浸泡在不同浓度纳米乳液中静置 2 d,测定改性后岩心薄片的接触角,每组测量3次取平均值。岩心润湿性按接触角大小分为水湿(075)、中性润湿(75105)和油湿(1055时,重力作用对自发渗吸的影响可以忽略,此时渗吸主要受毛细管力主导。当N-1B1时,自发渗吸主要受重力作用控制。对于水湿岩心,当油水界面张力处于超低界面张力范围(两端封闭两端开放。根据(3)式计算全开放、两端封闭和两端开放条件下的 NB-1分别为173.6,173.8 和 171.1,由此可以判断不
24、同边界条件下纳米乳液自发渗吸主要受毛细管力控制,此时自发渗吸以逆向渗吸为主。随着边界开放程度增加,图12不同浓度纳米乳液下油湿岩心渗吸采收率随时间的变化Fig.12Change in imbibition recovery of oil-wet cores with time under different concentrations of nanoemulsion图13静态吸附量、接触角变化量与渗吸采收率随纳米乳液浓度的变化Fig.13Change in static adsorption capacity,contact angle,and imbibition recovery wit
25、h different concentration of nanoemulsion图14不同边界条件下油湿岩心渗吸采收率随时间的变化Fig.14Change in imbibition recovery of oil-wet cores with time under different boundary conditions表3不同实验方案不同孔隙渗吸采收率对比Table3Comparison of imbibition recovery of different experimental schemes and different pores实验方案水湿岩心+盐水油湿岩心+盐水油湿岩心+0
26、.1%纳米乳液小孔渗吸采收率/%43.4241.4大孔渗吸采收率/%28.921.625.5 1332024年1月油 气 地 质 与 采 收 率纳米乳液与岩心的接触面积增大,则纳米乳液在油湿岩心孔隙内的吸附作用越强,从而增强了纳米乳液的润湿反转效果,促进了自发渗吸的进行,提高了渗吸采收率并缩短了初始见油时间。2.7 纳米乳液渗吸增产作用机理基于纳米乳液的性能评价实验与自发渗吸实验结果,致密砂岩油藏中纳米乳液的渗吸增产作用机理(图15)分析如下:纳米乳液满足进入致密砂岩中绝大部分孔喉的要求,其纳米级液滴形式易于变形并通过孔喉,充分发挥其扩散、运移能力以扩大渗吸作用的波及范围,增强自发渗吸效果13
27、。纳米乳液的润湿反转作用是油湿致密砂岩自发渗吸的关键因素,低油水界面张力也为自发渗吸驱动力提供了保证28,36。通过润湿反转与静态吸附测试可知,纳米乳液的润湿反转作用主要受吸附作用控制,纳米乳液可以通过吸附在极性物质表面使其亲水部分朝外,从而使岩石润湿性由油湿改性为水湿。核磁共振结果表明小孔由于润湿性反转所需纳米乳液吸附量少,使其渗吸采收率高于大孔。纳米乳液的乳化增溶作用以及油水界面张力降低作用能有效地将大尺寸油滴分散成小尺寸,并通过增溶作用提高孔隙内的原油渗流能力。基于增溶与分散原油实验可知,纳米乳液能够将部分原油增溶进入自身油核中,通过表面活性剂与助表面活性剂的重新分配从而稳定混合油相,降
28、低原油产出时的渗流阻力。3结论通过纳米乳液性能评价与岩心实验明确了纳米乳液的静态吸附性能、润湿反转性能以及自发渗吸之间的内在联系,并明确了致密砂岩中纳米乳液的渗吸增产作用机理。纳米乳液的粒径足够小,能够进入致密岩心绝大部分孔喉,充分发挥其扩散、运移能力以扩大渗吸作用的波及范围。润湿反转作用是油湿岩心自发渗吸发生的关键因素,结合静态吸附实验明确了纳米乳液的润湿反转机理以吸附机理为主,其乳化增溶作用与油水界面张力降低作用有利于将大尺寸油滴分散成小尺寸,降低原油产出时的渗流阻力。边界开放程度增强有助于扩大纳米乳液与岩心的接触面积,缩短纳米乳液的作用时间,从而提高渗吸采收率,这也一定程度上说明储层中裂
29、缝发育程度越高,有助于进一步提升纳米乳液的渗吸增产效果。图15纳米乳液与储层相互作用机理Fig.15Interaction mechanism between nanoemulsion and reservoir 134第31卷 第1期袁帅等.致密砂岩油藏纳米乳液渗吸增产作用机理符号解释BTemkin吸附模型的无因次常数;C形状因子,一般取值为0.4;C0纳米乳液吸附前质量分数,%;C1纳米乳液吸附后质量分数,%;Ce吸附平衡浓度,%;g重力加速度,m/s2;H岩心高度,m;K岩石渗透率,mD;KFFreundlich平衡常数;KLLangmuir平衡常数;KTTemkin平衡常数;m0岩心干
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