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        海泡石纖維表面包覆二氧化硅增強(qiáng)油井水泥的力學(xué)性能

        2024-09-28 00:00:00胡陳張春梅蘇曉悅梅開元李錕程小偉
        中國(guó)粉體技術(shù) 2024年4期
        關(guān)鍵詞:二氧化硅力學(xué)性能

        摘要:【目的】降低天然海泡石纖維的吸水性,提高海泡石纖維水泥漿的流動(dòng)性能,改善水泥石的力學(xué)性能。【方法】通過酸-水熱法對(duì)天然海泡石纖維進(jìn)行除雜提純,并采用正硅酸乙酯(tetraethyl orthosilicate,TEOS)水解在海泡石纖維表面包覆二氧化硅降低海泡石纖維的吸水性,探究海泡石纖維對(duì)油井水泥的漿體性能、力學(xué)性能影響;運(yùn)用X射線衍射分析、熱分析和掃描電子顯微鏡分析等方法表征水泥石的物相組成、水化程度及微觀形貌。【結(jié)果】改性水泥的海泡石纖維最優(yōu)質(zhì)量分?jǐn)?shù)為5%,固化7d的水泥石抗壓、抗拉強(qiáng)度較未改性的分別提高了10.98%、10.58%;海泡石纖維質(zhì)量分?jǐn)?shù)為5%的改性水泥石的峰值應(yīng)力為35.76 MPa,峰值應(yīng)變?yōu)?.97×10-2。海泡石纖維表面包覆SiO?后,在較低質(zhì)量分?jǐn)?shù)下(5%)就能夠促進(jìn)水泥水化?!窘Y(jié)論】改性海泡石纖維水泥漿的流動(dòng)性優(yōu)于未改性的;在纖維摻量和養(yǎng)護(hù)時(shí)間相同的情況下,改性海泡石纖維水泥石的抗壓強(qiáng)度和抗拉強(qiáng)度均高于未改性的;改性海泡石纖維對(duì)水泥石的增韌強(qiáng)化能力高于未改性海泡石纖維。

        關(guān)鍵詞:海泡石纖維;油井水泥;力學(xué)性能;二氧化硅

        中圖分類號(hào):TU528;TB4文獻(xiàn)標(biāo)志碼:A

        引用格式:

        胡陳,張春梅,蘇曉悅,等.海泡石纖維表面包覆二氧化硅增強(qiáng)油井水泥的力學(xué)性能[J].中國(guó)粉體技術(shù),2024,30(4):51-61.

        HU Chen,ZHANGChunmei,SUXiaoyue,etal.Mechanical properties of oil well cement reinforced by silica-coated surface ofsepiolite fiber[J].China Powder Science and Technology,2024,30(4):51-61.

        固井是油氣井建井過程的重要環(huán)節(jié),是向套管和井壁間的環(huán)空泵注入水泥漿的過程[1-2]。環(huán)空中凝膠硬化后的水泥漿稱為水泥環(huán),主要目的是封堵井口,加固井壁,支撐套管,隔離地層3,水泥環(huán)封固系統(tǒng)質(zhì)量的好壞直接影響油氣井生產(chǎn)壽命和油氣藏的開發(fā)效益,然而,傳統(tǒng)水泥環(huán)在試壓、射孔等過程中遭受各種復(fù)雜的沖擊力作用下可能發(fā)生斷裂41,導(dǎo)致地層隔離失效,通常采用外摻纖維材料提高水泥石韌性來解決此問題[5-6]。

        碳纖維、玄武巖纖維、碳酸鈣晶須等廣泛應(yīng)用于水泥基材料增韌,但是這些纖維在水泥基材料應(yīng)用時(shí)存在成本高、難分散,與水泥基體界面結(jié)合差等特點(diǎn),因此急需一種低成本、在水泥漿中易分散、與水泥基體界面結(jié)合良好的纖維材料。海泡石是一種纖維狀富鎂硅酸鹽黏土礦物,化學(xué)式為Mg?Si?O??(OH)?·3H?O101,具有比表面積大,吸附力強(qiáng),收縮率小,可塑性、耐鹽性、熱穩(wěn)定性好等特點(diǎn),在我國(guó)主要分布在河南、河北、江西、湖南等地,儲(chǔ)量十分豐富。纖維結(jié)構(gòu)使它成為一種很好的增塑劑,能有效提高水泥石的力學(xué)性能和耐久性[14-15],優(yōu)化水泥石的孔結(jié)構(gòu),但天然海泡石含有蛇紋石、滑石、方解石等雜質(zhì),不能直接作為水泥外加材料使用。同時(shí)海泡石的特殊結(jié)構(gòu)使纖維內(nèi)部具有蜂窩狀孔道,在通道和孔洞中可以吸附大量的水或其他極性物質(zhì)18。海泡石纖維強(qiáng)大的吸水性使水泥漿流動(dòng)性變差,水泥顆粒可結(jié)合水減少,限制了海泡石纖維在水泥基材料中的應(yīng)用。研究人員提出酸改性、水熱改性、絮凝-浮選提純等方法對(duì)海泡石進(jìn)行提純、活化19-201,其中在纖維表面附著涂層是降低吸水率的有效方法。正硅酸乙酯(TEOS)在酸或堿條件下易水解,是制備SiO?的理想原料,海泡石表面的—OH、—Si—OH基團(tuán)促使SiO?在纖維表面形成涂層,從而有效提高纖維與介質(zhì)的界面附著力,進(jìn)一步提高纖維材料的增韌能力。

        本文中通過酸-水熱法對(duì)天然海泡石纖維進(jìn)行除雜提純,采用正硅酸乙酯水解在海泡石表面包覆SiO?,并探究改性海泡石纖維對(duì)油井水泥的漿體性能、力學(xué)性能以及對(duì)水泥石微觀結(jié)構(gòu)的影響,為海泡石在水泥基材料中的應(yīng)用提供依據(jù)。

        1材料與方法

        1.1試劑材料和儀器設(shè)備

        試劑、材料:G級(jí)高抗硫酸鹽油井水泥(四川嘉華特種水泥股份有限公司);天然海泡石纖維(河北省靈壽縣);降失水劑G33S(衛(wèi)輝市化工有限公司);減阻劑SXY-2(成都川鋒化學(xué)工程有限責(zé)任公司);濃鹽酸(質(zhì)量分?jǐn)?shù)為37%,成都市科隆化學(xué)品有限公司);氨水(質(zhì)量分?jǐn)?shù)為25%~28%)、正硅酸乙酯(TEOS)、無水乙醇(分析純,成都市科隆化學(xué)品有限公司)。表1所示為油井水泥與海泡石纖維化學(xué)組分的質(zhì)量分?jǐn)?shù)。圖1所示為油井水泥與海泡石纖維的粒徑分布,油井水泥中值粒徑為15.2 μm,海泡石纖維中值粒徑為2.8 μm。

        儀器、設(shè)備:TY-300B型電子液壓式壓力試驗(yàn)機(jī)(無錫建儀儀器機(jī)械有限公司);SHT4605型液壓伺服驅(qū)動(dòng)控制萬能試驗(yàn)機(jī)(美特斯工業(yè)系統(tǒng)(中國(guó))有限公司);DX-2700B型X射線衍射儀(XRD,丹東浩元儀器有限公司);TGA/SDTA85/e型熱分析儀(TGA,瑞士梅特勒托利多儀器有限公司);EVO MA15型掃描電子顯微鏡(SEM,德國(guó)卡爾蔡司顯微圖像有限公司);ZNN-D6B型電動(dòng)六速黏度計(jì)(青島奧斯特石油科技有限公司)。

        1.2試樣制備

        1.2.1海泡石纖維改性

        將天然海泡石纖維置于濃度為1 mol/L的鹽酸溶液中,在溫度為120℃的條件下水熱處理4h,隨后洗滌、抽濾、干燥,得到預(yù)處理海泡石纖維(即未改性海泡石纖維)。將質(zhì)量為10g的預(yù)處理海泡石纖維與90 mL的乙醇、10 mL的去離子水、5mL的氨水混合攪拌5 min,持續(xù)滴入5mL的正硅酸乙酯。在溫度為30℃的條件下攪拌2 h后進(jìn)行抽濾、洗滌、干燥,得到改性海泡石纖維。

        1.2.2水泥漿制備

        按照GB/T 19139—2012《油井水泥試驗(yàn)方法》的要求制備水泥漿。設(shè)定每組試樣中油井水泥的質(zhì)量為600 g,減阻劑SXY-2質(zhì)量為6g,降水失劑G33S質(zhì)量為6g,水為264 g,設(shè)置海泡石纖維的摻量(纖維占油井水泥的質(zhì)量分?jǐn)?shù))分別為0、2.5%、5%、7.5%、10%。海泡石纖維的摻量為0的水泥漿配方代號(hào)為對(duì)照組。未改性海泡石纖維的摻量為2.5%、5%、7.5%、10%時(shí),對(duì)應(yīng)水泥漿配方代號(hào)為H1、H2、H3、H4。改性海泡石纖維的摻量為2.5%、5%、7.5%、10%時(shí),對(duì)應(yīng)的水泥漿配方代號(hào)為MH1、MH2、MH3、MH4。

        1.3測(cè)試方法

        1.3.1水泥漿漿體性能測(cè)試

        水泥漿的密度通過密度計(jì)來測(cè)量,水泥漿流動(dòng)度采用阿茲圓錐測(cè)試。水泥漿的流變性能由電動(dòng)六速黏度計(jì)測(cè)試,測(cè)試數(shù)據(jù)通過冪律流體公式,如式(1)、(2)來計(jì)算。

        式中:n為流變指數(shù);k為稠度系數(shù);θ30為轉(zhuǎn)速為300 r/min的格數(shù);θ10為轉(zhuǎn)速為100 r/min的格數(shù)。

        1.3.2水泥石力學(xué)性能測(cè)試

        將配制的水泥漿倒入邊長(zhǎng)為50.8 mm的立方體模具中進(jìn)行養(yǎng)護(hù)。養(yǎng)護(hù)條件為60℃,養(yǎng)護(hù)時(shí)間分別為1、3、7 d。按照GB/T 19139—2012《油井水泥試驗(yàn)方法》的方法進(jìn)行測(cè)試。采用壓力試驗(yàn)機(jī),在加載速率為(71.7±7.2)kN/min時(shí)測(cè)定水泥石的抗壓強(qiáng)度值。每組測(cè)試4個(gè)試樣,并計(jì)算平均值,作為抗壓強(qiáng)度值;采用巴西劈裂法測(cè)試抗拉強(qiáng)度,試樣為直徑和高分別為50、25mm的圓柱。每組測(cè)試4個(gè)試樣,并計(jì)算平均值,作為抗拉強(qiáng)度值;水泥石的單軸壓縮應(yīng)力-應(yīng)變測(cè)試采用液壓伺服驅(qū)動(dòng)控制萬能試驗(yàn)機(jī)測(cè)試,試樣為直徑和高分別為25、50 mm的圓柱,加載速率為2.0 kN/min。

        1.3.3物相分析

        采用X射線衍射儀(XRD)對(duì)水泥石物相組成的變化進(jìn)行物相分析。測(cè)試條件為:掃描速率為0.04(°)/s,衍射角范圍是10°~70°。

        1.3.4熱重分析

        利用熱分析儀(TGA)對(duì)水泥石中水化產(chǎn)物進(jìn)行熱重分析。測(cè)試溫度為40~1000℃,升溫速率為10 ℃/min,保護(hù)氣體為氮?dú)?,體積流量為20 mL/min。

        1.3.5微觀形貌觀察

        將用無水乙醇中止水化的水泥石敲成小塊并噴金,通過掃描電子顯微鏡(SEM)對(duì)水泥石斷面微觀形貌進(jìn)行觀察。

        2結(jié)果與分析

        2.1海泡石纖維微觀形貌

        為了探究海泡石纖維改性的效果,對(duì)改性前、后的海泡石纖維進(jìn)行SEM測(cè)試,結(jié)果如圖2所示。如圖所示,未改性的海泡石纖維呈現(xiàn)出針狀、柱狀形態(tài),表面光滑;而經(jīng)改性處理的海泡石纖維表面覆蓋了一層SiO?。表2所示為是海泡石纖維的EDS分析結(jié)果。由表可見,改性海泡石纖維表面Si元素增多,纖維表面附著了TEOS水解形成的SiO?,反應(yīng)方程式如式(3)、(4)所示。TEOS中的Si—OH基團(tuán)通過氫鍵相互作用吸附在海泡石纖維表面,海泡石纖維表面的羥基與TEOS中的羥基發(fā)生脫水縮合反應(yīng),形成穩(wěn)定的化學(xué)鍵25。同樣,正硅酸分子與正硅酸分子之間以及正硅酸分子內(nèi)部也發(fā)生脫水縮合反應(yīng),形成的SiO?具有很強(qiáng)的吸附和結(jié)合作用,從而在纖維表面形成一層SiO?涂層。未改性海泡石纖維的比表面積為4.518 m2/g,表面包覆SiO?后比表面積降低至2.598 m2/g,海泡石纖維作為一種多孔材料,強(qiáng)烈的吸附作用會(huì)促使SiO?在纖維內(nèi)部的孔結(jié)構(gòu)形成,填充內(nèi)部孔隙,從而導(dǎo)致海泡石纖維的比表面積減小。

        2.2海泡石纖維對(duì)水泥漿漿體性能的影響

        表3所示為不同配方的水泥漿漿體性能測(cè)試結(jié)果。海泡石纖維水泥漿體的密度均為1.92 g/cm3。對(duì)照組水泥漿流動(dòng)度為24 cm,未改性海泡石纖維摻量為10%時(shí),流動(dòng)度僅為20 cm,改性海泡石纖維摻量為10%時(shí),流動(dòng)度為22 cm,表明改性海泡石纖維對(duì)水泥漿體的流動(dòng)性能具有較小的負(fù)面影響。同時(shí),改性前、后的海泡石纖維的摻入均使水泥漿的流變指數(shù)n增大,稠度系數(shù)k減小,表明改性前、后的海泡石纖維均能提升水泥漿的流變性能。海泡石纖維包覆SiO?后,水泥漿的流動(dòng)性優(yōu)于未改性海泡石纖維水泥漿。這是因?yàn)楹E菔w維表面包覆SiO?有利于降低海泡石纖維的吸水性,海泡石集束狀的纖維結(jié)構(gòu)對(duì)溶劑的束縛、吸附作用減弱,改善了水泥漿的流動(dòng)性能。

        2.3海泡石纖維對(duì)水泥石力學(xué)性能的影響

        圖3所示為海泡石纖維水泥石的抗壓強(qiáng)度。由圖可知,改性前后海泡石纖維的摻入顯著提高了水泥石的抗壓強(qiáng)度,且提升程度均隨海泡石纖維摻量的增加先增大后減小。對(duì)照組在齡期為1、3、7d的抗壓強(qiáng)度分別為(13.10±0.55)、(17.77±0.72)、(22.89±0.75)MPa,摻量為5%的未改性海泡石纖維的水泥石(試樣H2)的分別為(17.62±0.19)、(30.89±0.65)、(34.43±0.50)MPa,而海泡石纖維摻量為5%的改性水泥石(試樣MH2)的分別為(20.23±0.62)、(34.52±0.41)、(38.21±0.59)MPa,較H2試樣的提高了14.81%、11.75%、10.98%。試樣H4的1、3、7 d抗壓強(qiáng)度相對(duì)試樣H2的降低了11.41%、22.50%、26.46%,而試樣MH4的相對(duì)試樣MH2的僅降低了19.32%、12.43%、12.27%??傮w而言,海泡石纖維水泥石的抗壓強(qiáng)度均在海泡石纖維摻量為5%時(shí)達(dá)到最高值,改性海泡石纖維水泥石的抗壓強(qiáng)度高于未改性海泡石纖維水泥石的。

        圖4所示為海泡石纖維水泥石的抗拉強(qiáng)度柱狀圖。由圖可知,海泡石纖維的摻入顯著提高了水泥石的抗拉強(qiáng)度,摻量為5%的海泡石纖維水泥石抗拉強(qiáng)度達(dá)到最高值。對(duì)照組1、3、7d的抗拉強(qiáng)度值分別為(1.53±0.12)、(3.39±0.14)、(3.87±0.23)MPa,H2試樣的分別為(2.35±0.16)、(4.12±0.13)、(4.63±0.21)MPa,而MH2試樣的分別為(2.63±0.16)、(4.73±0.18)、(5.12±0.24)MPa,較H2試樣的分別提高了11.91%、14.81%、10.58%。改性海泡石纖維水泥石抗拉強(qiáng)度高于未改性海泡石纖維水泥石。造成改性海泡石纖維水泥石抗壓、抗拉強(qiáng)度均高于未改性海泡石纖維水泥石的原因主要來源于改性海泡石纖維表面包覆有SiO?。未改性海泡石纖維本身具有較強(qiáng)的吸水性,摻入海泡石纖維后水泥顆粒的可結(jié)合水減少,限制了水泥的水化,同時(shí)海泡石纖維作為多孔纖維材料,其自身力學(xué)性能較低,在水泥基體中為缺陷位點(diǎn),過量加入勢(shì)必導(dǎo)致水泥石力學(xué)性能衰退。在海泡石纖維表面包覆SiO?后,降低海泡石纖維的吸水能力,同時(shí)SiO?在水泥石中發(fā)生火山灰反應(yīng),在一定程度上實(shí)現(xiàn)纖維內(nèi)部孔隙的填充,進(jìn)而消除缺陷,使改性海泡石纖維水泥石具有更優(yōu)異的力學(xué)性能。

        采用單軸壓縮應(yīng)力-應(yīng)變測(cè)試評(píng)價(jià)海泡石纖維對(duì)水泥石韌性的影響,結(jié)果如圖5所示。根據(jù)單軸壓縮應(yīng)力-應(yīng)變曲線得出水泥石的峰值應(yīng)力、峰值應(yīng)變和彈性模量,結(jié)果如表4所示。改性海泡石纖維對(duì)水泥石的增韌能力強(qiáng)于未改性海泡石纖維。對(duì)照組水泥石峰值應(yīng)力僅為22.86 MPa,峰值應(yīng)變?yōu)?.32×10-2;摻量為5%的未改性海泡石纖維水泥石(試樣H2)的峰值應(yīng)力為33.31 MPa,峰值應(yīng)變?yōu)?.84×10-2;摻量為5%的改性海泡石纖維水泥石(試樣MH2)的峰值應(yīng)力為35.76 MPa,峰值應(yīng)變?yōu)?.97×10-2。海泡石纖維的摻入顯著提高了水泥石的峰值應(yīng)力、峰值應(yīng)變,減小了水泥石的彈性模量,表明海泡石纖維具有顯著的增韌性能。同時(shí)試樣H2、H4在應(yīng)變?yōu)?~2×10-2時(shí)應(yīng)力-應(yīng)變曲線出現(xiàn)了一個(gè)臺(tái)階,這是因?yàn)樗嗍谶M(jìn)行應(yīng)力-應(yīng)變實(shí)驗(yàn)時(shí),在初始階段,水泥石骨架能承受一定的外力,孔結(jié)構(gòu)產(chǎn)生輕微變形,此時(shí)應(yīng)變?cè)鲩L(zhǎng)緩慢,應(yīng)力增長(zhǎng)較快。當(dāng)應(yīng)力到達(dá)一定程度時(shí),水泥石中孔結(jié)構(gòu)大量被壓縮破壞,這一階段稱為原始孔隙的壓密,而試樣MH2、MH4并未出現(xiàn)此臺(tái)階,原因是改性海泡石纖維內(nèi)部孔徑被SiO?填充,原始孔隙減少,有利于水泥石力學(xué)性能的發(fā)展。

        2.4海泡石纖維對(duì)水泥石微觀結(jié)構(gòu)的影響

        2.4.1 XRD分析

        圖6所示為水泥石在溫度為60℃下固化7d后的XRD圖譜。從圖中可以看出,海泡石纖維的摻入并未導(dǎo)致新物相的生成。以氫氧化鈣(CH)的最強(qiáng)峰20=18.048°峰強(qiáng)從高到低排序?yàn)镸H2、對(duì)照組、MH4、H2、H4,表明摻入適量的改性海泡石纖維能有效促進(jìn)CH的形成與結(jié)晶,H2、H4的CH衍射峰強(qiáng)度較低,表明未改性海泡石纖維抑制了CH的形成與結(jié)晶。因?yàn)槲锤男院E菔w維的摻入吸附了部分水,使水泥顆粒的可結(jié)合水減少,減慢水泥顆粒的水化速率。MH2中的硅酸二鈣(C?S)衍射峰峰強(qiáng)降低,甚至消失,也表明改性海泡石纖維能促進(jìn)水泥的水化反應(yīng)。

        2.4.2 TG分析

        圖7所示為不同海泡石纖維水泥石的TG-DTG分析。圖7(a)為海泡石纖維水泥石的熱重曲線。水化產(chǎn)物受熱分解分為多個(gè)階段:第1段是水泥水化產(chǎn)物水化硅酸鈣凝膠(C-S-H)、三硫型水化硫鋁酸鈣(AFt)和單硫型水化硫鋁酸鈣(AFm)的脫水,溫度范圍是40~380℃,水泥石XRD分析結(jié)果中并未出現(xiàn)AFt和AFm衍射峰,表明水泥石中AFt和AFm的含量較低,故此處的質(zhì)量損失主要為C-S-H脫水;第2段對(duì)應(yīng)水化產(chǎn)物CH的失水,溫度范圍是380~500℃;第3段為CaCO?的受熱分解,溫度范圍為500~700℃;第4段為海泡石的結(jié)構(gòu)水失去[27],溫度范圍為600~800℃。因第3、4段的質(zhì)量損失的溫度范圍部分重合,因此將水泥石的質(zhì)量損失分為3個(gè)部分:C-S-H脫水、CH的失水、CaCO?分解與海泡石結(jié)構(gòu)水失去。以第1部分和第2部分的質(zhì)量損失來計(jì)算水泥石的水化程度,計(jì)算公式如式(5)所示,結(jié)果如圖7(b)所示。試樣H2、H4的C-S-H、CH的質(zhì)量損失均小于對(duì)照組,表明未改性海泡石纖維會(huì)降低水泥石水化程度。MH2的C-S-H、CH的質(zhì)量損失均大于對(duì)照組與試樣H2的,而試樣MH4的C-S-H的質(zhì)量損失略小于對(duì)照組的,CH的質(zhì)量損失略大于對(duì)照組的,表明適量的改性海泡石纖維能提高水泥水化程度。海泡石纖維表面的SiO?在進(jìn)行火山灰反應(yīng)時(shí)會(huì)消耗CH,但海泡石纖維與SiO?也會(huì)作為水泥水化產(chǎn)物的形核位點(diǎn),加速水泥水化,當(dāng)水泥石中新生成的CH多于火山灰反應(yīng)所消耗的CH時(shí),表現(xiàn)為水泥石中CH含量增加。同時(shí)按水化程度從高到低為MH2、對(duì)照組、MH4、H2、H4,與XRD分析結(jié)果相符,表明SiO?包覆在海泡石纖維表面能促進(jìn)水泥水化反應(yīng)的進(jìn)行。試樣H2、H4在第3部分(CaCO?與海泡石結(jié)構(gòu)水失去)的質(zhì)量損失大于對(duì)照組,表明H2、H4在第3部分的質(zhì)量損失主要來源于海泡石結(jié)構(gòu)水的失去,同時(shí)試樣MH2、MH4的TG-DTG曲線中并未出現(xiàn)明顯的海泡石結(jié)構(gòu)水失質(zhì)量峰,這可能是因?yàn)楦男院E菔w維表面的SiO?在水泥中的火山灰反應(yīng)促使海泡石纖維結(jié)構(gòu)改變。

        式中:α為水泥石水化程度;w為溫度為40 ℃時(shí)水泥石試樣的質(zhì)量分?jǐn)?shù);w'為溫度為500 ℃時(shí)水泥石試樣的質(zhì)量分?jǐn)?shù)。

        2.4.3微觀形貌

        圖8所示為試樣H2、MH2養(yǎng)護(hù)3、7 d齡期后的水泥石SEM圖像。試樣H2水泥石養(yǎng)護(hù)3 d齡期后,未改性的海泡石纖維表面只附著了少量水泥顆粒,表面較為光滑,如圖8(b)所示,未改性纖維在水泥石受到外力作用時(shí)出現(xiàn)纖維斷裂與纖維拔出,起到增韌的作用,但纖維與水泥基體存在明顯的界面過渡區(qū),纖維拔出留下的孔洞較為光滑,表明在水化早期,未改性的海泡石纖維與水泥基體還未建立較為良好的界面膠結(jié),增韌效果較差。由圖8(c)、(d)可以看出,改性海泡石纖維表面附著了大量水化產(chǎn)物,且隨養(yǎng)護(hù)時(shí)間增加,表面附著水化產(chǎn)物進(jìn)一步增加。這是因?yàn)楹E菔w維表面附著的SiO?能與水泥顆粒發(fā)生火山灰反應(yīng)形成水化產(chǎn)物,使得改性海泡石纖維與水泥基體具有良好的界面膠結(jié),宏觀表現(xiàn)為改性海泡石纖維水泥石具有良好的韌性與強(qiáng)度,與力學(xué)性能的分析結(jié)果相符合。

        3結(jié)論

        1)改性海泡石纖維水泥漿的流動(dòng)性優(yōu)于未改性海泡石纖維水泥漿,同時(shí)能提升水泥漿的流變性能。

        2)纖維摻量和養(yǎng)護(hù)時(shí)間相同時(shí),改性海泡石纖維水泥石的抗壓強(qiáng)度和抗拉強(qiáng)度均高于未改性海泡石纖維水泥石的。改性海泡石纖維的最優(yōu)摻量為5%,固化7d的改性海泡石纖維水泥石的抗壓、抗拉強(qiáng)度較未改性海泡石纖維水泥石的分別提高了10.98%、10.58%。改性海泡石纖維摻量為5%的水泥石峰值應(yīng)力為35.76 MPa,峰值應(yīng)變?yōu)?.97×10-2,改性海泡石纖維對(duì)水泥石的增韌強(qiáng)化能力高于未改性海泡石纖維。

        3)海泡石纖維表面包覆SiO?提升海泡石纖維的火山灰活性,摻入質(zhì)量分?jǐn)?shù)為5%的改性海泡石纖維能促進(jìn)水泥水化。改性海泡石纖維表面更易附著水化產(chǎn)物,表現(xiàn)出更為優(yōu)異的纖維與水泥基體界面黏結(jié)能力。

        利益沖突聲明(Conflict of Interests)

        所有作者聲明不存在利益沖突。

        All authors disclose no relevant conflict of interests.

        作者貢獻(xiàn)(Author's Contributions)

        胡陳、張春梅和程小偉進(jìn)行了方案設(shè)計(jì);胡陳、張春梅、蘇曉悅、梅開元、李錕、程小偉參與了論文的寫作和修改。所有作者均閱讀并同意了最終稿件的提交。

        The study was designed by HU Chen,ZHANGChunmei and CHENG Xiaowei.The manuscript was writtenand revised by HU Chen,ZHANGChunmei,SUXiaoyue,MEIKaiyuan,LI Kun and CHENG Xiaowei.Allauthors have read the last version of paper and consented for submission.

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        Mechanical properties of oil well cement reinforcedby silica-coated surface of sepiolite fiber

        HU Chen,ZHANGChunmei,SUXiaoyue,MEIKaiyuan,LIKun,CHENG Xiaowei

        School of New Energy and Materials,National Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu 610500,China

        Abstract

        Objective Fiber reinforcement proves to be an effective approach in enhancing the mechanical properties of oil well cement.Sepiolitefibers,known for their remarkable dispersibility in cement slurry and strong bonding to the cement matrix,arepromis-ingcandidates.However,the presence of high impurity levels and significant water absorption in natural sepiolite fibers not onlyhinder the fluidity of cement slury but also compromise the compressive and tensile strengths of cement paste,thereby constrain-ing the broader utiliation of sepiolite fibers in cement-based materials.To overcome these challenges,this study employed ahydrochloric acid-hydrothermal purification method to refine natural sepiolite fibers,followed by surface coating with SiO?usingtetraethyl orthosilicate(TEOS).The impact of modified sepiolite fibers on the properties of cement slurry,mechanicalstrength,and microstructure of oil well cement was systematicllyinvestigated.The findings and methodologies presented in this studyoffer valuable insights into harnessing sepiolite fibers in various applications involving cement-based materials.

        Methods This study focused on the purification of natural sepiolite fibers using the HCI-hydrothermal method,followed by thecoating of SiO?on the purified sepiolite surface using TEOS to produce modified sepiolite fibers.Scanning electron microscopy(SEM)was employed to characterize both unmodified and modified sepiolite fibers.Subsequently,these fibers were separatelyincorporated into cement slurry to evaluate their impact on flowability and rheological properties.Additionally,themechanicalproperties of the resulting cement paste,including compressive strength,tensilestrength,and stress-strain curves,were exam-ined to evaluate the influence of sepiolite fibers.The reinforcement mechanism of both unmodified and modified sepiolite fibersin oil well cement was analyzed using X-ray diffraction(XRD),thermal analysis(TGA),and SEM.

        Results and Discussion Unmodified sepiolite fibers exhibited a needle-like,columnar morphology with a smooth surface,whilemodified sepiolite fibers displayed a thin film coating.Energy-dispersive X-ray spectroscopy(EDS)analysis revealed anincreased Si content on the surface of the modified sepiolite fibers,indicatingSiO?attachment from the TEOS hydrolysis.Thespecific surface area of unmodified sepiolite fibers decreased from 4.518 m2g to 2.598 m2g after SiO?coating,attributed to SiO?forming in and flling the internal pores of the fibers.Cement slurry containing modified sepiolite fibers showed superior flowabil-ity with improved rheological properties compared to unmodified fibers.This improvement was attributed to the SiO?coatingreducing water absorption of the fiber,and weakening binding and adsorption of solvents by the bundled fiber structure of sepio-lite,thus enhancing slurry flowability.At the same mass fraction of sepiolite fibers,cement-based material with modified fibersexhibited higher compressive and tensile strengths compared to those with unmodified fibers under identical curing times.Opti-mal mechanical properties were observed at 5%mass fraction of modified sepiolite fibers.After 7 days of curing,thecompres-sive and tensile strengths of the modified sepiolite fiber cement-based material were 10.98%and 10.58%higher,respectively,than those of the unmodified sepiolite fiber cement slurry.The stress-strain curve from uniaxial compression demonstrated a sig-nificant increase in peak stress and strain of cement paste with sepiolite fiber addition,alongside a reduction in its elastic modu-lus.Specifically,at a 5%mass fraction of modified sepiolite fibers,the cement paste exhibited a peak stress of 35.76 MPa anda strain of 3.97×102,indicating significant reinforcing and toughening properties.The toughening and strengthening effects ofmodified sepiolite fibers on the cement paste exceeded those of unmodified fibers.Sepiolite fiber addition did not induce the for-mation of new phases in the cement paste.Unmodified fibers inhibited cement hydration,while a 5%mass fraction of modifiedfibers facilitated it.Microscopic morphology results showed improved adherence of modified fibers to hydration products,lead-ing to enhanced bonding with the cement matrix.Modified sepiolite fibers improved cement paste toughness through mechanismsinvolving fiber fracture and pull-out.

        Conclusion This study investigated the impact of SiO?-coated sepiolite fibers on the properties and mechanical characteristics ofoil well cement slurry.The introduction of SiO?coating onto the fiber surface effectively reduced water absorption and enhancedthe flowability of cement slury containing sepiolite fibers.Optimal performance was achieved with a 5%mass fraction of SiO?-coated sepiolite fibers,significantly enhancing the mechanical properties and toughness of oil well cement slury.Furthermore.the interface bonding between SiO?-coated sepiolite fibers and the cement matrix was notably improved.The preparation processforSiO?-coated sepiolite fibers was found to be simple and compatible with cement slurry,offering valuable insights for theirapplication in cement-based materials.

        Keywords:sepiolitefiber;oil well cement;mechanicalproperty;silica

        (責(zé)任編輯:王雅靜)

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