海陸過(guò)渡相煤系頁(yè)巖氣成藏條件及儲(chǔ)層特征——以四川盆地南部龍?zhí)督M為例

張吉振,李賢慶,王 元,付慶華,蔡月琪,牛海巖

(1.中國(guó)礦業(yè)大學(xué)(北京)煤炭資源與安全開(kāi)采國(guó)家重點(diǎn)實(shí)驗(yàn)室,北京 100083; 2.中國(guó)礦業(yè)大學(xué)(北京)地球科學(xué)與測(cè)繪工程學(xué)院,北京100083)

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海陸過(guò)渡相煤系頁(yè)巖氣成藏條件及儲(chǔ)層特征
——以四川盆地南部龍?zhí)督M為例

張吉振1,2,李賢慶1,2,王 元1,2,付慶華1,2,蔡月琪1,2,牛海巖1,2

(1.中國(guó)礦業(yè)大學(xué)(北京)煤炭資源與安全開(kāi)采國(guó)家重點(diǎn)實(shí)驗(yàn)室,北京 100083; 2.中國(guó)礦業(yè)大學(xué)(北京)地球科學(xué)與測(cè)繪工程學(xué)院,北京100083)

摘 要:結(jié)合揚(yáng)子地區(qū)海陸過(guò)渡相煤系頁(yè)巖分布與地質(zhì)特征,以四川盆地南部二疊系龍?zhí)督M為例,采用有機(jī)碳、Rock-eval熱解、顯微組分定量、X射線衍射(XRD)、掃描電鏡(SEM)、高壓壓汞、低溫氣體吸附等多種實(shí)驗(yàn)分析方法,對(duì)海陸過(guò)渡相煤系頁(yè)巖氣成藏條件及儲(chǔ)層特征進(jìn)行了研究。結(jié)果表明:海陸過(guò)渡相煤系頁(yè)巖,累計(jì)厚度較大,多在100 m以上,而單層厚度較小,一般小于40 m,通常與煤層和致密砂巖甚至與灰?guī)r互層。四川盆地南部海陸過(guò)渡相龍?zhí)督M煤系頁(yè)巖有機(jī)碳含量較高(TOC含量為0.85%~35.70%,平均6.73%),有機(jī)質(zhì)類型以腐殖型為主(干酪根碳同位素δ13C為-28.0‰~-23.5‰),有機(jī)質(zhì)成熟度達(dá)高—過(guò)成熟階段(Ro為1.95%~2.40%,平均2.22%);頁(yè)巖中黏土礦物較為發(fā)育(20.3%~92.3%,平均61.9%),脆性礦物含量較低(6.3%~65.7%,平均27.7%),頁(yè)巖儲(chǔ)層可壓裂性較海相頁(yè)巖差。龍?zhí)督M煤系頁(yè)巖孔隙度多大于3%,孔隙類型多樣,常見(jiàn)粒間孔(含量占29.08%)和溶蝕孔(占30.18%),其次是有機(jī)質(zhì)孔(占16.74%)和粒內(nèi)孔(占10.56%),還有晶間孔(占4.94%)和微裂縫(占8.5%),為頁(yè)巖氣賦存提供了儲(chǔ)集空間;頁(yè)巖含氣性較好,含氣量主要介于1.0~3.0 m3/ t。

關(guān)鍵詞:海陸過(guò)渡相;頁(yè)巖氣;成藏條件;儲(chǔ)層特征;龍?zhí)督M頁(yè)巖;四川盆地南部

責(zé)任編輯:韓晉平

張吉振,李賢慶,王 元,等.海陸過(guò)渡相煤系頁(yè)巖氣成藏條件及儲(chǔ)層特征——以四川盆地南部龍?zhí)督M為例[J].煤炭學(xué)報(bào),2015, 40(8):1871-1878.doi:10.13225/ j.cnki.jccs.2015.0320

海陸過(guò)渡相頁(yè)巖氣是頁(yè)巖氣研究的重要領(lǐng)域之一[1]。全球海陸過(guò)渡相頁(yè)巖氣成藏潛力較海相差,勘探開(kāi)發(fā)程度低[2-6]。目前,中國(guó)海、陸相頁(yè)巖氣研究取得了較大進(jìn)展[1-3,7-11],而對(duì)于海陸過(guò)渡相煤系頁(yè)巖氣研究較少。我國(guó)海陸過(guò)渡相煤系頁(yè)巖分布廣泛,累計(jì)厚度大,頻繁與煤層、致密砂巖層互層,具有可觀的天然氣資源潛力。國(guó)內(nèi)一些學(xué)者已對(duì)揚(yáng)子地區(qū)海陸過(guò)渡相龍?zhí)督M頁(yè)巖氣成藏條件、勘探前景及儲(chǔ)層特征進(jìn)行過(guò)研究[12-16],多數(shù)認(rèn)為海陸過(guò)渡相頁(yè)巖氣儲(chǔ)層的非均質(zhì)性較強(qiáng),縱橫向厚度變化大,受地質(zhì)構(gòu)造、沉積相、地化特征影響較大。但是,對(duì)上揚(yáng)子四川盆地龍?zhí)督M煤系頁(yè)巖氣成藏條件和儲(chǔ)層特征進(jìn)行系統(tǒng)研究尚較少。筆者擬結(jié)合揚(yáng)子地區(qū)海陸過(guò)渡相煤系頁(yè)巖分布與地質(zhì)特征,以四川盆地南部二疊系龍?zhí)督M(P2l)為例,采用有機(jī)碳、Rock-eval熱解、顯微組分定量、X射線衍射(XRD)、掃描電鏡(SEM)、高壓壓汞、低溫氣體吸附等多種實(shí)驗(yàn)分析方法,對(duì)四川盆地南部龍?zhí)督M海陸過(guò)渡相煤系頁(yè)巖氣成藏條件及儲(chǔ)層特征進(jìn)行了研究,以期揭示海陸過(guò)渡相煤系頁(yè)巖氣成藏特征。

1 煤系頁(yè)巖分布特征

煤系頁(yè)巖據(jù)沉積相不同可進(jìn)一步分為海陸過(guò)渡相、湖沼相煤系富有機(jī)質(zhì)頁(yè)巖,分別形成于克拉通邊緣沼澤相和前陸盆地湖沼相[1,2,8]。中國(guó)大陸在石炭—二疊紀(jì)沉積環(huán)境由海相向陸相逐步轉(zhuǎn)化,境內(nèi)廣泛沉積了一套海陸過(guò)渡相頁(yè)巖,多為砂質(zhì)和炭質(zhì)頁(yè)巖[2,8]。我國(guó)南方地區(qū)二疊系頁(yè)巖分布面積廣[2-3,8],介于(20~50)×104km2,累計(jì)厚度10~125 m,最大單層厚度達(dá)25 m。

揚(yáng)子地區(qū)龍?zhí)督M(P2l)炭質(zhì)頁(yè)巖是一套典型的海陸過(guò)渡相煤系頁(yè)巖,厚度20~200 m,川中、滇黔桂地區(qū)及下?lián)P子地區(qū)沉積厚度大,多在50~200 m,最大累計(jì)厚可達(dá)670 m,分布面積約(30~50)× 104km2[3,8],頁(yè)巖類型可分單獨(dú)發(fā)育以及與煤層交互發(fā)育兩種(圖1,部分井位資料據(jù)文獻(xiàn)[17])。其中,滇黔桂地區(qū)上二疊統(tǒng)龍?zhí)督M頁(yè)巖單層厚度較大,一般為20~60 m,四川盆地上二疊統(tǒng)頁(yè)巖厚度縱橫向變化大[3,8,13],介于10~125 m,川中一帶均厚在50~120 m,而川南地區(qū)頁(yè)巖厚度在20~120 m,多在50~100 m,川北邊緣一帶頁(yè)巖厚度較薄,多小于20 m(圖2,根據(jù)文獻(xiàn)[13,16,18-19]修改)。由此可見(jiàn),海陸過(guò)渡相煤系富有機(jī)質(zhì)泥頁(yè)巖單層厚度都不大,相對(duì)海相頁(yè)巖較薄,平均厚度一般小于40 m,累計(jì)厚度則相對(duì)較大,多在100 m以上,最大可超過(guò)600 m;通常與煤層和致密砂巖甚至灰?guī)r互層,在適宜地質(zhì)條件下可以形成頁(yè)巖氣藏或與煤層氣、致密砂巖氣疊置型氣藏。

2 煤系頁(yè)巖有機(jī)質(zhì)特征

研究表明[4-6,17],經(jīng)濟(jì)效益較好可實(shí)現(xiàn)高產(chǎn)的頁(yè)巖氣儲(chǔ)層一般具有有機(jī)質(zhì)豐度高( TOC含量> 2.0%)、成熟度適中(Ro為1.1%~2.5%)[4-6,8]。揚(yáng)子地區(qū)海陸過(guò)渡相二疊系煤系頁(yè)巖有機(jī)質(zhì)含量與類型受沉積環(huán)境影響,TOC含量介于0.1%~38.5%,平均4.7%,多數(shù)超過(guò)3.0%;有機(jī)質(zhì)類型屬腐殖型, Ro為1.2%~3.2%[17]。

圖1　揚(yáng)子地區(qū)海陸過(guò)渡相龍?zhí)督M煤系頁(yè)巖巖性剖面及氣藏模式對(duì)比Fig.1 Lithologic profile of marine-terrigenous facies Longtan formation measures shale and the comparison of gas reservoir model in the Yangtze area

圖2　揚(yáng)子地區(qū)海陸過(guò)渡相龍?zhí)督M煤系頁(yè)巖厚度分布Fig.2 Thickness distribution of marine-terrigenous facies Longtan formation coal measures shale in the Yangtze area

四川盆地南部海陸過(guò)渡相龍?zhí)督M煤系頁(yè)巖進(jìn)行地化特征分析實(shí)驗(yàn),有機(jī)碳(TOC)含量測(cè)定在LECO-230碳硫分析儀上完成,測(cè)試依據(jù)GB/ T 19145—2003;顯微組分定量分析和鏡質(zhì)體反射率(Ro)測(cè)定均在MPV-3型顯微鏡光度計(jì)完成,測(cè)試依據(jù)SY/ T 6414—1999、SY/ T 5124—1995;Rock-eval熱解分析在OGE -Ⅱ型油氣評(píng)價(jià)儀完成,測(cè)試依據(jù)GB/ T 18602—2001。分析表明,四川盆地南部龍?zhí)督M煤系頁(yè)巖樣品的TOC含量分布范圍為0.8%~35.7%,平均7.51%,其中80%以上的樣品TOC含量大于3.0%;鏡質(zhì)體反射率Ro為1.96%~2.40%,平均2.22%,處于主生氣窗范圍,利于干氣大量生成;大多數(shù)樣品熱解最高峰溫Tmax大于530℃,處于高—過(guò)成熟階段,從而龍?zhí)督M頁(yè)巖熱解生烴潛量(S1+S2)低,介于0.13~2.75 mg/ g,平均0.63 mg/ g,氫指數(shù)(HI) 為4.8~17.1 mg/ g,平均7.61 mg/ g(圖3)。干酪根碳同位素δ13C為-28.0‰~-23.5‰,都小于-29‰,據(jù)以往經(jīng)驗(yàn),以δ13C= -29‰,-26‰作為區(qū)分I,II和III型干酪根的兩個(gè)指標(biāo)界限值[17]。表明其屬于Ⅲ型干酪根(圖4(a))。有機(jī)巖石學(xué)分析結(jié)果顯示:四川盆地南部龍?zhí)督M煤系頁(yè)巖樣品富含有機(jī)顯微組分,以鏡質(zhì)組為主(62.5%~100%,平均80.3%),惰質(zhì)組較少(2.7%~37.5%,平均15.3%),少量腐泥組和殼質(zhì)組(不足5%),顯示其母質(zhì)來(lái)源以高等植物輸入為主(圖4(b))。

圖3　四川盆地南部龍?zhí)督M頁(yè)巖樣品地化特征剖面Fig.3 Geochemical characteristics profile of the Longtan Formation shale samples in south Sichuan Basin

圖4　海陸過(guò)渡相煤系頁(yè)巖有機(jī)質(zhì)類型判別Fig.4 Organic matter type identification of marine-terrigenous facies coal measures shales

3 煤系頁(yè)巖儲(chǔ)層礦物組成與脆性特征

頁(yè)巖儲(chǔ)層礦物中的脆性礦物可直接影響頁(yè)巖可壓裂性,控制孔隙及裂隙的發(fā)育及頁(yè)巖含氣性;而黏土礦物的富集則是氣體吸附的主要原因,影響頁(yè)巖氣的賦存和開(kāi)采[20-21]。四川盆地南部海陸過(guò)渡相龍?zhí)督M煤系頁(yè)巖的礦物成分較為復(fù)雜。對(duì)該區(qū)龍?zhí)督M煤系頁(yè)巖樣品進(jìn)行了X-衍射(XRD)分析,是在Rigaku公司產(chǎn)的D/ Max 2500 PC型粉末X射線衍射儀上完成,采用粉末衍射聯(lián)合會(huì)國(guó)際數(shù)據(jù)中心(JCPDS-ICDD)提供的標(biāo)準(zhǔn)粉末衍射分析數(shù)據(jù)庫(kù)進(jìn)行礦物成分含量的定量分析。XRD分析結(jié)果顯示:四川盆地南部龍?zhí)督M煤系頁(yè)巖富含黏土礦物(20.3%~92.3%,平均61.9%),其中伊/蒙混層(12%~25%)、高嶺石(0~50%)和伊利石(6%~21%)較為發(fā)育,蒙脫石含量極低;脆性礦物含量次之(6.3%~65.7%,平均27.7%),其中以石英(4.2%~46.2%,平均20.1%)和方解石(0~40.3%,平均4.7%)為主,長(zhǎng)石含量較低(0~6.8%,平均1.9%),碳酸鹽礦物白云石含量變化較大(0~13.6%,平均1.2%)?？傮w而言,龍?zhí)督M頁(yè)巖與北美地區(qū)頁(yè)巖礦物種類較為類似,但含量差異較大(圖5,北美頁(yè)巖數(shù)據(jù)來(lái)自文獻(xiàn)[4-6]),北美地區(qū)頁(yè)巖石英含量較高(大于20%),而龍?zhí)督M頁(yè)巖中黏土礦物較為發(fā)育,脆性礦物和石英含量相對(duì)較低,碳酸鹽礦物含量與北美地區(qū)頁(yè)巖相當(dāng)(10%~20%)。頁(yè)巖脆性指數(shù)是頁(yè)巖氣儲(chǔ)層評(píng)價(jià)的一個(gè)重要參數(shù),鑒于四川盆地南部龍?zhí)督M頁(yè)巖因其礦物組成的復(fù)雜而采用如下公式計(jì)算,即:脆性指數(shù)=(石英+長(zhǎng)石+方解石+白云石) / (石英+長(zhǎng)石+方解石+白云石+黏土礦物)×100%。

圖5　四川盆地南部龍?zhí)督M頁(yè)巖礦物組成及與北美地區(qū)頁(yè)巖對(duì)比Fig.5 Mineral composition of Longtan Formation shale in South Sichuan Basin and its comparison to that of North America

計(jì)算結(jié)果表明,四川盆地南部龍?zhí)督M煤系頁(yè)巖脆性指數(shù)分布范圍為6.4%~76.4%,平均31.0%,主值位于30%~50%[22]?？傮w而言,與北美地區(qū)海相頁(yè)巖(脆性指數(shù)平均>50%)相比,四川盆地南部龍?zhí)督M煤系頁(yè)巖脆性指數(shù)較低,頁(yè)巖儲(chǔ)層可壓裂性較差。

4 煤系頁(yè)巖儲(chǔ)層孔隙類型與特征

頁(yè)巖孔隙是頁(yè)巖氣藏中氣體的儲(chǔ)集空間[1,4,7],孔隙的微觀特征影響頁(yè)巖氣儲(chǔ)集性能[5-6,21]。頁(yè)巖中微裂縫的發(fā)育不僅為頁(yè)巖氣提供有利的儲(chǔ)集空間,而且利于吸附氣的解析[23]。

為研究四川盆地南部海陸過(guò)渡相龍?zhí)督M煤系頁(yè)巖儲(chǔ)層孔隙特征,進(jìn)行了孔隙度測(cè)定、高壓壓汞、低溫氣體(N2,CO2)吸附實(shí)驗(yàn)分析?？紫抖葴y(cè)定在QKYZN型孔隙度分析儀上完成,測(cè)定依據(jù)SY/ T5336—2006。高壓壓汞實(shí)驗(yàn)是在美國(guó)康塔公司產(chǎn)的Pore Master GT60全自動(dòng)孔隙分析儀(壓汞儀)上完成,孔徑測(cè)定范圍為0.003 6~950 μm。N2和CO2氣體吸附實(shí)驗(yàn)在美國(guó)康塔公司產(chǎn)的NOVA4200e比表面及孔隙分析儀完成,比表面積測(cè)定范圍大于0.01 m2/ g,孔徑測(cè)定范圍為0.35~200 nm。分析結(jié)果(圖6)表明,四川盆地南部龍?zhí)督M煤系頁(yè)巖樣品孔隙度多數(shù)分布在2%~8%,平均為6.3%,多數(shù)頁(yè)巖樣品孔隙度大于3%,一定程度上利于頁(yè)巖氣賦存;龍?zhí)督M頁(yè)巖N2吸附的比表面積、孔容分別為4.72~13.90 m2/ g和0.77~1.87 cm3/ (100 g),頁(yè)巖CO2吸附的比表面積、孔容分別為12.5~43.9 m2/ g和0.38~1.31 cm3/ (100 g),稍低于北美Barnett頁(yè)巖[24]。龍?zhí)督M頁(yè)巖中納米級(jí)孔隙以微孔(<2 nm)和介孔(2~50 nm)為主,宏孔(>50 nm)較少,微孔和介孔之和占總孔隙體積的56.2%,占總比表面積的80%以上,是頁(yè)巖氣賦存的主要載體。

圖6　四川盆地南部龍?zhí)督M頁(yè)巖樣品孔隙度分布Fig.6 Porosity distribution of the Longtan Formation shalesamples in south Sichuan Basin

應(yīng)用掃描電子顯微鏡(SEM)分析法,觀測(cè)了四川盆地南部龍?zhí)督M煤系頁(yè)巖儲(chǔ)層微觀孔隙類型、形貌特征和賦存狀態(tài),在VEGALSHⅡ掃描電子顯微鏡儀上完成,最大放大倍率高達(dá)100萬(wàn)倍,在高分辨率模式下具有高達(dá)3.0 nm/ (30 kV)分辨率,電鏡觀察方式包括背散射電子成像和二次電子成像。結(jié)合SEM圖像分析法,使用ImageJx2軟件二值化處理分析,獲得頁(yè)巖樣品孔隙相對(duì)含量及孔徑分布范圍的半定量數(shù)據(jù)。分析結(jié)果表明:四川盆地南部海陸過(guò)渡相龍?zhí)督M煤系頁(yè)巖發(fā)育多種類型微孔隙(圖7):常見(jiàn)粒間孔(含量占29.08%,孔徑0.1~13.6 μm)和溶蝕孔(含量占30.18%,孔徑0.1~16 μm),其次有機(jī)質(zhì)孔(含量占16.74%,孔徑0.1~16 μm)和粒內(nèi)孔(含量占10.56%,孔徑0.1~6.3 μm),還有晶間孔(含量占4.94%,孔徑0.1~2.6 μm)和微裂縫(含量占8.5%,孔徑0.1~8 μm);龍?zhí)督M頁(yè)巖樣品中孔隙形狀以圓形、橢圓形、三角形、不規(guī)則狀為主,孔隙之間有一定的連通性,這些孔裂隙作為頁(yè)巖氣賦存載體,為頁(yè)巖氣賦存提供了儲(chǔ)集空間。

圖7　四川盆地南部龍?zhí)督M煤系頁(yè)巖樣品孔隙特征SEM圖像Fig.7 SEM images of Pores characteristics of Longtan Formations shale samples in south Sichuan Basin (a)為粒間孔,ZK13104井,黑色頁(yè)巖,埋深612.91~615.21 m;(b)為有機(jī)質(zhì)孔,ZK11104井,炭質(zhì)頁(yè)巖,埋深977.12~979.42 m; (c)為溶蝕孔,ZK3504井,黑色頁(yè)巖,埋深745.55~749.07 m;(d)為微裂縫,ZK1501井,黑色頁(yè)巖,埋深678.01~679.41 m

5 煤系頁(yè)巖含氣性

頁(yè)巖氣含氣量是衡量頁(yè)巖氣富集區(qū)是否具備開(kāi)采價(jià)值和進(jìn)行資源潛力評(píng)價(jià)的一項(xiàng)重要指標(biāo)[1-4,23-25]。揚(yáng)子地區(qū)二疊系龍?zhí)督M煤系頁(yè)巖含氣量變化大,分布范圍為1.00~9.42 m3/ t,主要位于1.0~3.0 m3/ t,與成功開(kāi)發(fā)頁(yè)巖氣的北美頁(yè)巖含氣量[1,4-5]相比,具備了頁(yè)巖氣成藏的含氣性條件。周東升等[14]對(duì)揚(yáng)子地區(qū)龍?zhí)督M泥頁(yè)巖樣品進(jìn)行等溫吸附實(shí)驗(yàn)測(cè)得最大吸附氣量為2.0 m3/ t,含氣量介于1.0~2.6 m3/ t;黔西北地區(qū)西頁(yè)1井龍?zhí)督M頁(yè)巖現(xiàn)場(chǎng)解析氣含氣量變化范圍較大,介于1.24~9.42 m3/ t,平均6.65 m3/ t[26];黔中地區(qū)方頁(yè)1井龍?zhí)督M炭質(zhì)樣品吸附氣含量介于1.34~5.56 m3/ t,總含氣量達(dá)1.65~6.78 m3/ t[27];湘中地區(qū)湘頁(yè)1井含氣量介于1.37~1.83 m3/ t,平均1.60 m3/ t[15];下?lián)P子巢湖地區(qū)姚家山剖面龍?zhí)督M頁(yè)巖由于黏土礦物含量較低,不利于吸附,吸附氣含量要低于有機(jī)碳含量更低的西頁(yè)1井,含氣量為1.2~4.8 m3/ t[28]。揚(yáng)子地區(qū)龍?zhí)督M頁(yè)巖氣吸附氣含量一般隨有機(jī)碳含量增加而遞增,主要介于1.0~4.5 m3/ t(圖8(a))。目前北美已商業(yè)開(kāi)發(fā)的頁(yè)巖氣,其含氣量最低為1.1 m3/ t[1-2]。揚(yáng)子地區(qū)龍?zhí)督M煤系頁(yè)巖含氣性較好(圖8(b)),含氣量主要為1.0~3.0 m3/ t,頁(yè)巖氣含氣量已達(dá)到商業(yè)性頁(yè)巖氣開(kāi)發(fā)下限,具備一定的頁(yè)巖氣資源開(kāi)發(fā)潛力。

圖8　揚(yáng)子地區(qū)龍?zhí)督M頁(yè)巖等溫吸附曲線和含氣量(據(jù)文獻(xiàn)[1,12-16,25-27]修改)Fig.8 Isothermal adsorption curves and gas content of the Longtan Formation shales in Yangtze area

6 結(jié) 論

(1)揚(yáng)子地區(qū)海陸過(guò)渡相龍?zhí)督M煤系富有機(jī)質(zhì)泥頁(yè)巖單層厚度不大,相對(duì)海相頁(yè)巖較薄,單層平均厚度一般小于40 m,累計(jì)厚度則相對(duì)較大,多在100 m以上,最大可超過(guò)600 m;它常與煤層和致密砂巖甚至灰?guī)r互層,在適宜地質(zhì)條件下可以形成頁(yè)巖氣藏或與煤層氣、致密砂巖氣疊置型氣藏。

(2)四川盆地南部海陸過(guò)渡相龍?zhí)督M煤系頁(yè)巖有機(jī)碳含量較高(其中80%以上的樣品TOC含量大于3.0%),頁(yè)巖母質(zhì)來(lái)源為陸源輸入,鏡質(zhì)體含量較高,有機(jī)質(zhì)類型屬腐殖型;熱解最高峰溫Tmax多大于530℃,有機(jī)質(zhì)成熟度達(dá)高—過(guò)成熟階段( Ro為1.95%~2.40%,平均2.22%),處于主生氣窗范圍,利于干氣大量生成。

(3)四川盆地南部海陸過(guò)渡相龍?zhí)督M煤系頁(yè)巖中黏土礦物較為發(fā)育( 20.3%~92.3%,平均61.9%),其中伊/蒙混層、高嶺石和伊利石較為發(fā)育,蒙脫石含量極低;脆性礦物含量較低(6.3%~65.7%,平均27.7%),以長(zhǎng)石、方解石為主,碳酸鹽礦物含量變化大;龍?zhí)督M煤系頁(yè)巖脆性指數(shù)介于6.4%~76.4%,平均31.0%,主值為30%~50%,頁(yè)巖儲(chǔ)層的可壓裂性較北美地區(qū)海相頁(yè)巖差。

(4)四川盆地南部海陸過(guò)渡相龍?zhí)督M煤系頁(yè)巖孔隙度分布在0.6%~8.0% (平均6.32%),多數(shù)頁(yè)巖樣品孔隙度大于3%,孔隙類型多樣,常見(jiàn)粒間孔和溶蝕孔,其次是有機(jī)質(zhì)孔和粒內(nèi)孔,還有晶間孔和微裂縫,孔隙形態(tài)不規(guī)則,具一定連通性,為頁(yè)巖氣賦存提供了儲(chǔ)集空間;揚(yáng)子地區(qū)二疊系龍?zhí)督M煤系頁(yè)巖含氣量變化大,主要位于1.0~3.0 m3/ t,具備了頁(yè)巖氣成藏的含氣性條件。

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Accumulation conditions and reservoir characteristics of marineterrigenous facies coal measures shale gas from Longtan Formation in South Sichuan Basin

ZHANG Ji-zhen1,2,LI Xian-qing1,2,WANG Yuan1,2,FU Qing-hua1,2,CAI Yue-qi1,2,NIU Hai-yan1,2

(1.State Key Laboratory of Coal Resources and Safe Mining,China University of Mining and Technology(Beijing),Beijing 100083,China;2.College of Geoscience grad Surveying Engineering,China University of Mining and Technology (Beijing),Beijing 100083,China)

Abstract:Combined with the shale distribution and geological characteristics of marine-terrigenous facies coal measures in the Yangtze area,taking the Permian Longtan Formation in South Sichuan Basin as example,the authors investigated the accumulation conditions and the reservoir characteristics of marine-terrigenous facies coal measures shale gas using many experimental methods,such as organic carbon,Rock-eval pyrolysis,maceral identification,X-ray dif-book=1872,ebook=167fraction (XRD),scanning electron microscope (SEM),high pressure mercury injection,low temperature gas sorption, etc.The results show that the marine-terrigenous facies coal measures shale has the features of rapid vertical-lateral variation,huge cumulative thickness (mainly over 100 m),small individual thickness (generally <40 m),and commonly accompanied with coal bed,limestone and tight sand.The marine-terrigenous facies coal measures shale from Longtan Formation in South Sichuan Basin,which featured with high organic matter abundance (TOC = 0.85% -35.70%,average 6.73%),mainly with humic type organic matter (kerogen δ13C = -28.0‰--23.5‰),high-over thermal evolution level (Ro=1.95% -2.4%,average 2.22%),rich in clay minerals content(20.3% -92.3%,average 61.9%),and relatively low brittle minerals content (6.3% -65.7%,average 27.7%).The shale reservoir fracturing from Longtan Formation is worse than that of marine shale.The porosity of the Longtan Formation shale in South Sichuan Basin is mainly over 3%.Many types of pores were developed,including intergranular pore (29.08%),dissolution pore (30.18%),organic pores (16.74%),intragranular (10.56%),inter-crystalline (4.94%) and microfracture (8.5%),which provide reservoir space for the accumulation of shale gas.Gas generation capability from the Longtan Formation shale is relatively better,and its main gas content can be 1.0-3.0 m3/ t.

Key words:marine-terrigenous facies;shale gas;accumulation condition;reservoir characteristics;Longtan Formation shale;South Sichuan Basin

通訊作者:李賢慶(1967—),男,浙江富陽(yáng)人,教授,博士生導(dǎo)師。Tel:010-62331854,E-mail:Lixq@ cumtb.edu.cn

作者簡(jiǎn)介:張吉振(1991—),男,山東濟(jì)寧人,碩士研究生。E-mail:ZJZcumtb@126.com。

基金項(xiàng)目:國(guó)家重點(diǎn)基礎(chǔ)研究發(fā)展計(jì)劃(973)資助項(xiàng)目(2012CB214702);國(guó)土資源部公益性行業(yè)科研專項(xiàng)基金資助項(xiàng)目(201311022);教育部高等學(xué)校博士學(xué)科點(diǎn)基金資助項(xiàng)目(20110023110017)

收稿日期:2015-03-11

中圖分類號(hào):P618.13

文獻(xiàn)標(biāo)志碼:A

文章編號(hào):0253-9993(2015)08-1871-08