二氧化氯作為煤儲(chǔ)層壓裂液破膠劑的可行性實(shí)驗(yàn)研究

郭紅玉,夏大平,蘇現(xiàn)波,馬俊強(qiáng),張雙斌,王 振

(1.河南省瓦斯地質(zhì)與瓦斯治理重點(diǎn)實(shí)驗(yàn)室——省部共建國(guó)家重點(diǎn)實(shí)驗(yàn)室培育基地,河南焦作 454000;2.河南理工大學(xué)能源科學(xué)與工程學(xué)院,河南焦作 454000)

二氧化氯作為煤儲(chǔ)層壓裂液破膠劑的可行性實(shí)驗(yàn)研究

郭紅玉1,2,夏大平2,蘇現(xiàn)波1,2,馬俊強(qiáng)2,張雙斌2,王 振2

(1.河南省瓦斯地質(zhì)與瓦斯治理重點(diǎn)實(shí)驗(yàn)室——省部共建國(guó)家重點(diǎn)實(shí)驗(yàn)室培育基地,河南焦作 454000;2.河南理工大學(xué)能源科學(xué)與工程學(xué)院,河南焦作 454000)

針對(duì)煤層溫度低、高黏壓裂液無法及時(shí)破膠返排的難題,探討二氧化氯作為壓裂液破膠劑的可行性及其對(duì)煤層氣開采的影響。實(shí)驗(yàn)選擇清潔壓裂液、交聯(lián)凍膠壓裂液和二氧化氯溶液對(duì)不同煤階煤樣進(jìn)行處理,對(duì)處理后煤樣再分別進(jìn)行光學(xué)顯微鏡、等溫吸附和壓汞等測(cè)試。結(jié)果表明:殘留的壓裂液會(huì)對(duì)煤層造成污染傷害,二氧化氯不但具有良好的低溫破膠作用,同時(shí)還可以提高大孔和中孔的孔容比,使得孔隙連通性得到改善,進(jìn)而提高儲(chǔ)層滲透率;經(jīng)二氧化氯處理后煤樣的朗格繆爾體積顯著降低,表明了煤的親甲烷能力顯著降低,從而使得煤層氣臨界解吸壓力、含氣飽和度與采收率均得到不同程度的提高。研究表明二氧化氯可以作為煤儲(chǔ)層壓裂液的破膠劑。

煤層氣;二氧化氯;壓裂液;破膠劑;親甲烷能力;采收率;含氣飽和度;臨界解吸壓力

郭紅玉,夏大平,蘇現(xiàn)波,等.二氧化氯作為煤儲(chǔ)層壓裂液破膠劑的可行性實(shí)驗(yàn)研究[J].煤炭學(xué)報(bào),2014,39(5):908-912.doi:10.13225/j.cnki.jccs.2013.0638

Guo Hongyu,Xia Daping,Su Xianbo,et al.Experimental study on the feasibility of chlorine dioxide as fracturing fluid gel-breaker for coal reservoirs[J].Journal of China Coal Society,2014,39(5):908-912.doi:10.13225/j.cnki.jccs.2013.0638

我國(guó)煤儲(chǔ)層滲透率普遍較低,煤層氣的開采面臨諸多不利條件[1-2]。水力壓裂是煤儲(chǔ)層增透的主要措施,壓裂液性能是影響壓裂成敗的關(guān)鍵因素之一[3-6]。目前,我國(guó)煤層氣井壓裂主要采用活性水,因其黏度接近清水,無法攜帶更多支撐劑進(jìn)入地層裂縫[7-9]。若添加增稠劑提高黏度,又面臨煤層低溫條件下破膠困難的問題,一旦壓裂液破膠不徹底而滯留地層裂縫,儲(chǔ)層污染嚴(yán)重,甚至抵消壓裂改造的效果[10-13]。為解決這一矛盾,亟需選擇一種低溫快速破膠劑,這對(duì)高黏壓裂液的推廣應(yīng)用尤為重要。二氧化氯主要在油氣田上用以解堵,即利用二氧化氯強(qiáng)氧化性和殺菌效率高的特點(diǎn),解除壓裂液、鉆井液濾液中有機(jī)高分子堵塞、溶除鐵垢、殺死細(xì)菌,達(dá)到解堵的目的,已在國(guó)內(nèi)外得到成功實(shí)踐,并取得較好的經(jīng)濟(jì)效益[14-17]。依據(jù)強(qiáng)氧化性的特性,選擇二氧化氯作為煤層氣井壓裂液的破膠劑,并通過壓裂液污染、破膠、等溫吸附和壓汞等實(shí)驗(yàn)手段,探討二氧化氯作為煤層壓裂液破膠劑的可行性對(duì)煤層氣開采的影響,為高黏壓裂液的破膠劑選擇提供實(shí)驗(yàn)支撐。

1 樣品與實(shí)驗(yàn)方法

1.1 樣品制備

(1)煤樣。分別在焦作古漢山煤礦、陽泉寺家莊煤礦、柳林沙曲煤礦、義馬千秋煤礦和大同泉嶺煤礦井下采集新鮮煤樣,進(jìn)行工業(yè)分析與反射率測(cè)試(表1)。

(2)壓裂液。清潔壓裂液配方:表面活性劑(0.8%VES)+膠束促進(jìn)劑(0.2%SYN)+防膨劑(鹽) (1.0%KCl)。交聯(lián)凍膠壓裂液配方:0.3%羥丙基瓜膠(HPG)+0.01%潤(rùn)濕劑+2.0%KCl+0.02%硼砂。

表1 煤樣基礎(chǔ)數(shù)據(jù)Table 1 Basic data of coal samples

(3)二氧化氯溶液。按照比例稱取A試劑和B試劑,加入小口錐形瓶中,加入蒸餾水充分?jǐn)嚢柚翢o顆?；驂K狀物;按比例加入C添加劑,充分?jǐn)嚢枞芤?直至溶液呈淺黃色,即二氧化氯溶液,并對(duì)其密封保存,本實(shí)驗(yàn)采用的二氧化氯的濃度為4 000×10-6。

1.2 實(shí)驗(yàn)方法

(1)光學(xué)顯微鏡實(shí)驗(yàn)。大同泉嶺煤礦和柳林沙曲煤礦煤樣拋光處理后放入交聯(lián)凍膠壓裂液中浸泡6 h,在光學(xué)顯微鏡下觀察浸泡前后的表面特征(圖1)。

(2)壓汞實(shí)驗(yàn)。選擇千秋煤礦煤樣,放入濃度為4 000×10-6的二氧化氯溶液中浸泡72 h,取出自然風(fēng)干后采用Auto poreⅣ9505全自動(dòng)壓汞儀對(duì)煤的孔隙結(jié)構(gòu)進(jìn)行測(cè)試,為避免水分對(duì)測(cè)試結(jié)果的影響,在實(shí)驗(yàn)前首先對(duì)煤樣進(jìn)行干燥處理(圖2)。

(3)等溫吸附實(shí)驗(yàn)。每個(gè)煤樣粉碎至60～80目,平均分為3份,每份質(zhì)量不小于150 g,其中一份保持原樣、一份被清潔壓裂液浸泡48 h、另一份放入清潔壓裂液和濃度為4 000×10-6的ClO2混合溶液浸泡48 h,分別烘干和稱重,然后在25.6℃下在IS-300型等溫吸附儀測(cè)試,實(shí)驗(yàn)嚴(yán)格執(zhí)行《煤的高壓等溫吸附試驗(yàn)方法》(GB/T 19560—2008)標(biāo)準(zhǔn)。等溫吸附實(shí)驗(yàn)結(jié)果見表2,等溫吸附曲線擬合如圖3所示。

圖1 凍膠浸泡前后煤表面污染對(duì)比Fig.1 Surface pollution comparison of coal samples before and after gel immersion

圖2 煤樣進(jìn)-退汞曲線Fig.2 Mercury injection and ejection curves of coal samples

表2 等溫吸附實(shí)驗(yàn)結(jié)果Table 2 Results of isothermal adsorption

圖3 不同方式處理煤樣的等溫吸附曲線Fig.3 Isothermal adsorption curves of coal samples with different actions

2 實(shí)驗(yàn)結(jié)果分析

2.1 二氧化氯破膠效果及其作用機(jī)理

煤層溫度一般僅20℃左右,遠(yuǎn)遠(yuǎn)低于油氣儲(chǔ)層,油氣田儲(chǔ)層改造常用的高黏壓裂液的破膠劑主要是過硫酸銨、雙氧水和過硫酸鉀等,但其普遍存在溫度低于40℃釋放游離氧速度減慢的問題,難以達(dá)到低溫煤層壓裂液徹底破膠的目的。從圖1可知,煤經(jīng)過凍膠壓裂液浸泡后,表面有許多附著物,表明若壓裂液不能及時(shí)破膠返排,滯留在煤儲(chǔ)層中,就會(huì)堵塞空隙和裂隙等煤層氣運(yùn)移產(chǎn)出的通道,造成儲(chǔ)層傷害,嚴(yán)重影響壓裂增透的效果。二氧化氯依靠強(qiáng)氧化性能使大分子有機(jī)物斷鏈降解為有小分子機(jī)物或無機(jī)物,可以在低溫條件下對(duì)高黏壓裂液進(jìn)行快速破膠。

2.2 二氧化氯對(duì)煤樣孔隙結(jié)構(gòu)的影響

由圖3可知在相同壓力下,處理煤樣的進(jìn)汞量增大,大孔與中孔的孔容比增加(表3)。原煤樣進(jìn)-退曲線存在明顯的拐點(diǎn),為“細(xì)頸瓶”孔;處理后煤樣拐點(diǎn)消失,為開放型孔。說明二氧化氯有助于提高煤層的孔隙連通性,這對(duì)改善煤層滲透率有重要意義。

表3 千秋煤礦煤樣孔隙結(jié)構(gòu)分析結(jié)果Table 3 Pore structure analysis results of coal samples in Qianqiu Coal Mine

2.3 二氧化氯對(duì)煤樣吸附性的影響

從圖3可看出,經(jīng)清潔壓裂液處理后,煤的吸附能力也相應(yīng)降低,這與文獻(xiàn)[18]得到的結(jié)論是一致的。但二氧化氯作為破膠劑加入到清潔壓裂液,煤樣經(jīng)過該破膠液浸泡處理,對(duì)甲烷的吸附能力將進(jìn)一步降低,其中義馬千秋煤礦和焦作古漢山煤礦的煤樣降低幅度更為明顯。該實(shí)驗(yàn)不但證實(shí)了清潔壓裂液對(duì)煤吸附能力影響的事實(shí),更說明二氧化氯作為清潔壓裂液的破膠劑將進(jìn)一步降低煤的親甲烷能力。二氧化氯作為壓裂液破膠劑降低了煤的親甲烷能力,在煤層含氣量相同的條件下,吸附能力降低意味著煤層含氣飽和度與臨界解吸壓力兩項(xiàng)參數(shù)均有提高,縮短了排采階段見氣時(shí)間,且含氣飽和度和臨界解吸壓力增加對(duì)提高煤層氣井的單井產(chǎn)量也有重要作用。

2.4 二氧化氯對(duì)煤層氣開采的影響

采收率、臨界解吸壓力和含氣飽和度是影響煤層氣開采的3個(gè)主要參數(shù)。依據(jù)表2中的等溫吸附實(shí)驗(yàn)結(jié)果、煤層含氣量、儲(chǔ)層壓力和廢棄壓力等對(duì)上述3個(gè)參數(shù)分別進(jìn)行計(jì)算(表4),其中廢棄壓力根據(jù)美國(guó)目前的經(jīng)驗(yàn),取0.70 MPa[19]。

表4 二氧化氯對(duì)煤層氣開采的影響Table 4 Impact of chlorine dioxide on CBM development

由表4可看出,清潔壓裂液對(duì)煤層氣開采3個(gè)參數(shù)有不同程度的增加;經(jīng)清潔壓裂液和二氧化氯的破膠液處理煤樣的3個(gè)參數(shù)在清潔壓裂液影響的基礎(chǔ)上進(jìn)一步提高,說明二氧化氯能有效降低煤的親甲烷能力,促進(jìn)煤層氣解吸脫附,這有利于煤層氣開采。

3 結(jié) 論

(1)二氧化氯具有良好的低溫破膠作用,同時(shí)還可以提高煤體大孔和中孔的孔容比例,在采用高黏壓裂液進(jìn)行水力壓裂后期注入適量的二氧化氯溶液,不但可以使高黏壓裂液迅速破膠返排,減少儲(chǔ)層污染,同時(shí)還能在水力壓裂形成裂縫增透的基礎(chǔ)上進(jìn)一步提高煤基質(zhì)滲透性,有利于煤層氣的運(yùn)移產(chǎn)出。

(2)等溫吸附實(shí)驗(yàn)表明二氧化氯可以有效降低煤吸附甲烷的能力,這有助于提高煤儲(chǔ)層的臨界解吸壓力與含氣飽和度,縮短排采初期的見氣時(shí)間。二氧化氯對(duì)煤層氣的吸附/解吸性能的改變,促進(jìn)煤層氣脫附,有利于煤層氣開采。因此,二氧化氯具有低溫破膠、提高含氣飽和度、臨界解吸壓力和采收率等多重效果,可以作為壓裂液的破膠劑。

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Experimental study on the feasibility of chlorine dioxide as fracturing fluid gel-breaker for coal reservoirs

GUO Hong-yu1,2,XIA Da-ping2,SU Xian-bo1,2,MA Jun-qiang2,ZHANG Shuang-bin2,WANG Zhen2

(1.State Key Laboratory Cultivation Base for Gas Geology and Gas Control(Henan Polytechnic University),Jiaozuo 454000,China;2.School of Energy Science and Engineering,Henan Polytechnic University,Jiaozuo 454000,China)

Based on the difficulty that fracturing fluid with high viscosity is unable to break and flow back timely in the low-temperature coal seams,the feasibility of chlorine dioxide(ClO2)as gel-breaker of fracturing fluid and its impact on coalbed methane(CBM)development were studied.Different rank coal samples were treated with clean fracturing fluid,cross-linked gel fracturing fluid and ClO2solution,and were tested by optical microscope,isothermal adsorption and mercury porosimetric method,etc.The experiment results show:First,residual fracturing fluid will damage the coal seam.ClO2not only has a good effect on gel breaking at low temperature,but also it can increase the pore volumes ratio of macropores and mesopores for coal samples treated by ClO2.It improves the pore connectivity and further enhances the permeability of coal reservoirs.Second,the Langmuir volume of coal samples soaked by ClO2decreases significantly,indicating the coals’affinity for methane has fallen.As a result,the critical desorption pressure,gas saturation and the recovery factor of CBM will increase to some degrees.The study show that ClO2can be used as gel-breaker of fracturing fluid for coal reservoir.

coal bed methane;chlorine dioxide;fracturing fluid;gel-breaker;affinity for methane;recovery factor;gas saturation;the critical desorption pressure

P618.11

A

0253-9993(2014)05-0908-05

2013-05-16 責(zé)任編輯:韓晉平

國(guó)家自然科學(xué)基金資助項(xiàng)目(41002047);山西省煤層氣聯(lián)合研究基金資助項(xiàng)目(2013012004);河南省教育廳科學(xué)技術(shù)研究重點(diǎn)項(xiàng)目(12A440005)

郭紅玉(1978—),男,河南遂平人,副教授,博士。Tel:0391-3987981,E-mail:ghy1026@126.com。通訊作者:蘇現(xiàn)波(1963—),男,河南孟津人,教授,博士生導(dǎo)師。Tel:0391-3987981,E-mail:1054608403@qq.com