川西坳陷鴨子河地區(qū)基于多種古溫標(biāo)的鉆井熱史恢復(fù)

朱傳慶， 邱楠生， 江強(qiáng)， 胡圣標(biāo)， 張碩

1 中國石油大學(xué)(北京) 油氣資源與探測國家重點(diǎn)實(shí)驗(yàn)室, 北京 102249 2 中國石油大學(xué)(北京) 地球科學(xué)學(xué)院, 北京 102249 3 中國科學(xué)院地質(zhì)與地球物理研究所巖石圈演化國家重點(diǎn)實(shí)驗(yàn)室, 北京 100029

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川西坳陷鴨子河地區(qū)基于多種古溫標(biāo)的鉆井熱史恢復(fù)

朱傳慶1,2， 邱楠生1,2， 江強(qiáng)1,2， 胡圣標(biāo)3， 張碩1,2

1 中國石油大學(xué)(北京) 油氣資源與探測國家重點(diǎn)實(shí)驗(yàn)室, 北京 102249 2 中國石油大學(xué)(北京) 地球科學(xué)學(xué)院, 北京 102249 3 中國科學(xué)院地質(zhì)與地球物理研究所巖石圈演化國家重點(diǎn)實(shí)驗(yàn)室, 北京 100029

利用鏡質(zhì)體反射率(Ro)、磷灰石裂變徑跡(AFT)和伊利石結(jié)晶度(IC指數(shù))等古溫標(biāo)恢復(fù)了四川盆地川西坳陷的鉆井熱史,對比了不同溫標(biāo)最高古地溫的恢復(fù)結(jié)果.研究表明,研究區(qū)晚白堊世至今總體表現(xiàn)為冷卻及抬升剝蝕的過程,地溫梯度由約26 ℃·km-1降低至約22 ℃·km-1,剝蝕量約1.3～1.9 km.約80 Ma以來開始抬升剝蝕, 40—2.5 Ma經(jīng)歷了一個熱平靜期,第四紀(jì)存在一定的增溫,地溫梯度增高約5 ℃·km-1.三種古地溫恢復(fù)結(jié)果具有較高的一致性,相對于鏡質(zhì)體反射率(Ro)和磷灰石裂變徑跡(AFT)等成熟古溫標(biāo),伊利石結(jié)晶度作為有機(jī)質(zhì)成熟度指標(biāo)和沉積巖古溫標(biāo)的應(yīng)用處于定性分析階段,該指標(biāo)的熱演化模型仍需進(jìn)一步探索.

鏡質(zhì)體反射率； 磷灰石裂變徑跡； 伊利石結(jié)晶度； 熱史恢復(fù)； 川西坳陷

1 引言

沉積盆地?zé)釟v史是指在地質(zhì)歷史中盆地?zé)釥顟B(tài)的變化,包括了熱流、地溫梯度以及地層溫度的演化等,是地球動力學(xué)和石油地質(zhì)學(xué)研究中的重要內(nèi)容(邱楠生等,2005).溫度是諸多地球動力學(xué)過程的驅(qū)動力(Morgan,1984;Wang,1996),是油氣成藏的重要因素之一,尤其對烴源巖有機(jī)質(zhì)成熟度演化和生烴史影響重大(Tissot and Welte,1984;Tissot et al.,1987; 邱楠生等,2004).在盆地尺度上,熱史主要通過各種古溫標(biāo),如鏡質(zhì)體反射率(Ro)、磷灰石裂變徑跡(AFT)、磷灰石和鋯石(U-Th)/He、瀝青和鏡狀體反射率、氫指數(shù)、流體包裹體等來重建(胡圣標(biāo)等,1998;邱楠生等,2004;秦建中等,2009a;2009b).各種古溫標(biāo)中,應(yīng)用最為普遍、模擬方法相對成熟的是鏡質(zhì)體反射率(Ro)和磷灰石裂變徑跡(AFT).近年來,伊利石結(jié)晶度、激光拉曼光譜、巖石聲發(fā)射等在古地溫的定量恢復(fù)中也有了較成功的探索和應(yīng)用(徐春華等,2005;王河錦等,2007;秦建中等,2009a;2009b;李佳薇等,2011;Liu et al.,2013).

中國大陸地區(qū)海相盆地形成時代早(古生代或更早),經(jīng)多期次構(gòu)造疊加與改造,其長期和復(fù)雜的構(gòu)造-熱演化過程決定了其熱史的多期性和復(fù)雜性,而且其上覆陸相盆地或陸相地質(zhì)時期熱史與海相時期熱史的演化特征、恢復(fù)方法和有效古溫標(biāo)亦有所差別.在以四川、塔里木等為代表的海陸相疊合盆地中,古生代海相地層往往是油氣的重要烴源層,發(fā)育時代老,熱演化程度高,且缺乏鏡質(zhì)體等傳統(tǒng)古溫標(biāo)和磷灰石樣品,其有機(jī)質(zhì)成熟度的準(zhǔn)確標(biāo)定和熱史恢復(fù)一直是一個難題(秦建中等,2009b).因此,這類海陸疊合盆地的熱史恢復(fù),除要求多樣化、且彼此補(bǔ)充的熱史恢復(fù)方法體系(胡圣標(biāo)等,2008)外,更需要探索有效的古溫標(biāo),并對不同溫標(biāo)之間的等效性進(jìn)行研究,進(jìn)而建立起可系統(tǒng)應(yīng)用于多期熱史恢復(fù)的古溫標(biāo)組合.本文利用鏡質(zhì)體反射率(Ro)、磷灰石裂變徑跡(AFT)和伊利石結(jié)晶度(IC指數(shù))恢復(fù)了四川盆地川西坳陷的鉆井熱史,并對比了不同溫標(biāo)最高古地溫的恢復(fù)結(jié)果,對于分析不同古溫標(biāo)之間的等效性、建立適合于研究區(qū)熱史恢復(fù)的古溫標(biāo)組合具有一定意義.

2 地質(zhì)背景

川西坳陷(圖1)位于四川盆地西部,西以龍門山前大斷裂為界,東以龍泉山斷裂為界,面積約為5×104km2(陳冬霞等,2010),是在古生代克拉通盆地之上發(fā)展起來的前陸盆地.晚三疊世印支運(yùn)動前,川西位于上揚(yáng)子克拉通盆地西緣,整體為一西傾的碳酸鹽臺地(馬永生等, 2009),印支期,隨著龍門山、大巴山造山帶的形成(劉樹根等, 2009;李智武等, 2011),海水退出,進(jìn)入陸相沉積階段,大量碎屑物質(zhì)進(jìn)入川西,沉積形成了巨厚的以巖屑砂巖為主的上三疊統(tǒng)(陳楊等,2011),此后進(jìn)入前陸盆地演化階段.川西地區(qū)前陸盆地演化階段的構(gòu)造-沉積特征已有較多的研究(郭正吾等, 1996;陶曉風(fēng),1999;劉和甫等,2006; 劉樹根等,2009;2011;劉金華等,2010;李智武等, 2011;Tian et al.,2013),由于龍門山自印支期以來向川西坳陷多次逆沖推覆,在產(chǎn)生區(qū)域斷裂的同時也使盆山結(jié)合部位地層抬升剝蝕,喜山期隨著印度與歐亞大陸發(fā)生碰撞,在龍門山區(qū)激起了更為強(qiáng)烈的逆沖運(yùn)動,導(dǎo)致龍門山逆沖帶及川西前陸盆地的定型(王天澤,1997;趙建成等,2011).由研究區(qū)川鴨92井的埋藏史恢復(fù)(圖2)可以看出,陸相沉積初期,晚三疊世沉積速率較大;早侏羅世經(jīng)歷了抬升剝蝕和沉積間斷,造成下侏羅統(tǒng)的沉積厚度較薄;中侏羅世-晚白堊世,研究區(qū)接受沉積;白堊紀(jì)晚期開始持續(xù)的抬升剝蝕;新生代晚期(主要為第四紀(jì))接受了少量的沉積.

鴨子河構(gòu)造位于川西坳陷中南段,為龍門山推覆構(gòu)造帶中段前緣關(guān)口斷裂下盤的半背斜構(gòu)造,形成于喜馬拉雅晚期,受控于關(guān)口和彭縣斷層,為一北東向斷背斜(朱彤和梁恩宇,2001; 劉大成等,2002).根據(jù)生儲蓋發(fā)育情況,該區(qū)的含油氣系統(tǒng)可以分為上三疊統(tǒng)-上侏羅統(tǒng)的上部陸相含油氣系統(tǒng)和中三疊統(tǒng)及下伏地層構(gòu)成的下部海相含油氣系統(tǒng)(張永剛等,2007;趙建成等,2011).鴨子河構(gòu)造的鉆井,如川鴨92井、川鴨95井等,主要鉆遇地層為上侏羅統(tǒng)至上三疊統(tǒng)的陸相層系(圖1),上三疊統(tǒng)煤系地層烴源巖包括煤、炭質(zhì)頁巖、灰-黑色泥巖和粉砂質(zhì)泥巖,烴源巖較發(fā)育,以烴源巖為主的馬鞍塘組、小塘子組、須三段和須五段的暗色泥巖厚度達(dá)幾百米,須二段和須四段儲層段內(nèi)部也發(fā)育有機(jī)質(zhì)豐度較高烴源巖的夾層(楊克明等,2003;陳冬霞等,2010).須家河組砂巖和侏羅系以陸內(nèi)沖積扇、河、湖三角洲相沉積層構(gòu)成該區(qū)陸相含油氣系統(tǒng)的主要儲集層.須三段、須五段、上侏羅統(tǒng)遂寧組泥、頁巖作為上三疊統(tǒng)的區(qū)域蓋層具有厚度大、突破壓力高和分布穩(wěn)定的特征,白堊系內(nèi)的膏、鹽層可作為侏羅系的直接蓋層(汪澤成等,2002).

3 古溫標(biāo)數(shù)據(jù)及熱史恢復(fù)

3.1 鏡質(zhì)體反射率熱史恢復(fù)

鏡質(zhì)體是一種煤素質(zhì),主要由芳香稠環(huán)化合物組成.隨熱成熟的增加,鏡質(zhì)體分子結(jié)構(gòu)中的芳香環(huán)縮合度增大,形成更加密集的結(jié)構(gòu)單元,從而使反射率增大(陳義才等,2007).Ro值的演化主要與有機(jī)質(zhì)受熱溫度和時間有關(guān),且以溫度為主.隨著鏡質(zhì)體反射率演化的熱動力學(xué)機(jī)制研究的深入,利用Ro恢復(fù)古地溫的方法也由早期的圖版法(Hood and

圖3 川鴨92井Ro數(shù)據(jù)(a)及古地溫梯度法熱史恢復(fù)結(jié)果(b)(反演中的巖石熱物性參數(shù)采用了徐明等(2011)的研究成果)Fig.3 Ro data (a) and thermal history reconstruction of CY92 using the paleo-temperature gradient method (b); the rock thermal properties data refer to Xu et al. (2011)

et al.,1975; Cooper,1977)、TTI擬合法(Lopatin,1971; Waples,1980; Lercheet al.,1984) 發(fā)展為干酪根熱降解的化學(xué)動力學(xué)模型方法(Antia and David,1986; Braun and Burnham,1987; Armagnac et al.,1989;Burnham et al., 1987,1989; Burnham and Sweeney,1989; Sweeney and Burnham,1990),其中,Sweeney 和 Burnham (1990)建立的EASYRo%模型在目前的熱史恢復(fù)中應(yīng)用較廣.

川鴨92井Ro數(shù)據(jù)主要集中在2000～5000 m的三疊系,Ro值主要在0.8%～2.0%之間,顯示出隨深度而增大的變化趨勢.基于EASYRo%模型,采用古地溫梯度法(Duddy et al., 1991;胡圣標(biāo)等,1998;邱楠生等,2004)恢復(fù)了川鴨92井的最高古地溫(圖3).

該井的古地溫梯度反演得到一條連續(xù)的最高古地溫剖面,古地溫梯度約26 ℃·km-1,熱流約60 mW·m-2,上侏羅統(tǒng)與新生界之間不整合面的剝蝕量約1900 m.該井最高古地溫梯度大于現(xiàn)今約22 ℃·km-1的地溫梯度,即地層達(dá)到最高古地溫之后至現(xiàn)今,研究區(qū)的熱演化總體上體現(xiàn)為冷卻及抬升剝蝕的過程.

3.2 磷灰石裂變徑跡熱史模擬

用于沉積盆地?zé)崾费芯康牡蜏責(zé)崮甏鷮W(xué)方法主要包括磷灰石和鋯石等礦物的裂變徑跡和(U-Th)/He分析.磷灰石裂變徑跡(AFT)的退火溫度(約60～120 ℃)與烴源巖生油的溫度范圍基本一致(Green et al.,1986;1989),又與地殼3～5 km深度范圍內(nèi)的多種地質(zhì)過程相關(guān)(李天義等,2013),加之其獨(dú)特的退火敏感性,逐步成為造山帶抬升、沉積盆地沉降剝蝕歷史和烴源巖熱史模擬的重要手段,對于低溫?zé)崮甏鷮W(xué)方法的原理和模擬方法已有較多的文獻(xiàn)介紹(Gleadow,1981;Gleadow et al.,1983;Gleadow and Fitzgerald,1987;Fitzgerald and Gleadow,1990;Fitzgerald et al.,1993; Armstrong et al.,1997;Armstrong,2005;Ketcham et al.,2007).在應(yīng)用磷灰石裂變徑跡分析技術(shù)研究古地溫時,常用兩個方面的信息是裂變徑跡的年齡和裂變徑跡的長度(封閉徑跡長度).

川鴨92井裂變徑跡采樣分布于2000～4500 m深度范圍,CY92-1樣品深度為2142 m,磷灰石裂變徑跡中心年齡為42.3±3.0 Ma,徑跡平均長度為11.76±0.26 μm,深度4474 m的CY92-3樣品磷灰石裂變徑跡年齡為4.3±0.6 Ma,沒有測到長度數(shù)據(jù)(圖4).利用HeFty v1.7.4軟件采用隨機(jī)反演法(Corrigan,1991)模擬樣品溫度史,采用Ketcham等(2007)退火模型對CY92-1樣品熱歷史模擬的結(jié)果(圖5)顯示:220—140 Ma為盆地沉降過程,145—80 Ma經(jīng)歷了一個熱平靜期;80 Ma以來開始抬升剝蝕,40—2.5 Ma之內(nèi)盆地經(jīng)歷了一個熱平靜期,而后開始增溫.晚期增溫幅度在10 ℃左右,而該井新生界沉積僅有23.5 m,由沉積埋藏所造成的增溫幅度基本可以忽略,因此,該次增溫可能反應(yīng)了地溫梯度(以及熱流)的增高,增高幅度約5 ℃·km-1.結(jié)合古地溫梯度恢復(fù)結(jié)果,可推斷約80 Ma以來研究區(qū)總體上體現(xiàn)為冷卻及抬升剝蝕,但地溫梯度的演化存在一定的波動,經(jīng)歷了降低再升高的過程,地溫梯度在新近紀(jì)時期較小,可能低于20 ℃·km-1.根據(jù)模擬結(jié)果,CY92-1最高古地溫在115～120 ℃左右,地層達(dá)到古地溫的時期也是沉積埋藏達(dá)到最深時,參照約26 ℃·km-1的地溫梯度,此時樣品埋深為4040 m,現(xiàn)今樣品深度2142 m,剝蝕量約1900 m,與鏡質(zhì)體反射率恢復(fù)的結(jié)果基本一致.

3.3 伊利石結(jié)晶度熱史恢復(fù)

伊利石是沉積巖中主要黏土礦物之一,自生伊利石是沉積巖成巖演化階段的重要產(chǎn)物,其晶體的結(jié)晶程度與地層巖石的成巖變質(zhì)演化程度密切相關(guān),隨溫度的增加而提高.因此,伊利石結(jié)晶度除了被用于成巖演化和極低級變質(zhì)作用研究外,也可作為最高地溫計用于樣品熱史的恢復(fù)(王河錦等,2007;朱莉和朱敏,2006; Bignall et al.,2001;Miller and Macdonald, 2004;Aldega et al.,2003; Di, 2003;Ji and Browne,2000).利用X射線衍射方法對伊利石結(jié)晶度進(jìn)行研究,國際上普遍接受的測定伊利石結(jié)晶度的方法是采用Kübler指數(shù)來反映伊利石的結(jié)晶度,它用伊利石10?(001)衍射峰的半高寬來表示(Kübler,1964;1967;1968;楊獻(xiàn)忠,1993;朱光,1995;王河錦等,2000;游建昌等,2008),伊利石結(jié)晶度與Kübler指數(shù)負(fù)相關(guān).

圖4 川鴨92井樣品AFT年齡、長度數(shù)據(jù)(a)及CY-2樣品AFT年齡輻射圖(b)Fig.4 AFT data of the samples of CY92 (a) and the radar map of AFT ages of CY92-1 (b)

圖5 川鴨92井CY92-1磷灰石裂變徑跡熱史模擬結(jié)果(a)及徑跡長度分布擬合(b);蒙特卡洛擬合法模擬10000條路徑,擬合優(yōu)度: GOF(age)=0.98;GOF(length)=0.95)Fig.5 AFT thermal history modelingresult of CY92-1 (a) and the fitting of AFT length distribution (b)(10000 paths have been modeled using Monte Carlo method, GOF(age)=0.98;GOF (length)=0.95)

圖6 川鴨92井伊利石結(jié)晶度KI指數(shù)及古地溫估算Fig.6 KI data and the estimationpaleo-temperature of CY92

為了減小因樣品制備、儀器條件、測試方法等差異所造成的測試結(jié)果差異(王河錦,1998),提高數(shù)據(jù)的可比性,測Kübler指數(shù)時可使用國際標(biāo)樣對數(shù)據(jù)進(jìn)行校正.本文川鴨95井伊利石結(jié)晶度(圖6)測試為中國石油勘探開發(fā)研究院石油地質(zhì)實(shí)驗(yàn)測試中心采用國際標(biāo)樣校正方法(游建昌等,2008)的測定結(jié)果.伊利石結(jié)晶度Kübler指數(shù)體現(xiàn)為隨深度減小的線性關(guān)系(線性擬合:Y=-9168.76X+9988.64).

由成巖階段經(jīng)近變質(zhì)階段到淺變質(zhì)階段溫度逐漸升高,伊利石結(jié)晶度增大,Kübler指數(shù)變小.一些研究者提出或歸納總結(jié)了伊利石結(jié)晶度與形成溫度之間的關(guān)系以及基于伊利石結(jié)晶度的成巖-極低級變質(zhì)作用的劃分方案:晚期成巖帶(高級成巖帶),伊利石結(jié)晶度KI處于1.0～0.42(°Δ2θ)之間,溫度上限200 ℃(KI=0.42(°Δ2θ)時,T=～200 ℃);埋藏變質(zhì)階段KI處于0.42～0.25(°Δ2θ)之間,溫度為200～300 ℃(KI=0.25(°Δ2θ)時,T=～300 ℃);淺變質(zhì)階段(相當(dāng)于低綠片巖相)KI<0.25(°Δ2θ),溫度大于300 ℃(Kübler, 1967;Arkai,2002;畢先梅和莫宣學(xué),2004).伊利石結(jié)晶度在研究較低級的變質(zhì)作用方面的應(yīng)用較為成熟,而對于成巖階段(KI>0.42(°Δ2θ))的KI尚不能精確地建立與溫度的對應(yīng)關(guān)系.根據(jù)成巖-變質(zhì)作用的劃分(Arkai et al.,2002),參考前人發(fā)表的數(shù)據(jù),KI=0.57(°Δ2θ),T=～141 ℃(125～163 ℃)(秦建中等,2009a);KI=0.56(°Δ2θ),T=156 ℃(136～177 ℃)(胡大千等,2012);KI=0.60～0.62(°Δ2θ),T=150 ℃(朱莉和朱敏,2006),可估算KI=0.60(°Δ2θ)時,最高古地溫約為150 ℃.由此推斷川鴨95井深度在約4080 m時,KI=0.60(°Δ2θ),最高古地溫約150 ℃;深度約6000 m時,KI=0.42(°Δ2θ)最高古地溫約200 ℃,因J3-T3地層在抬升剝蝕前同時達(dá)到了最高古地溫,故根據(jù)該兩處深度上確定的古地溫即可建立川鴨95井的最高地溫剖面.

4 結(jié)果及討論

4.1 熱史恢復(fù)結(jié)果

圖7為利用鏡質(zhì)體反射率(Ro)、磷灰石裂變徑跡(AFT)恢復(fù)的川鴨92井和利用伊利石結(jié)晶度恢復(fù)的川鴨95井的最高古地溫剖面.川鴨92井利用磷灰石裂變徑跡恢復(fù)的最高古地溫與鏡質(zhì)體反射率(Ro)的恢復(fù)結(jié)果較為一致,表明這兩種應(yīng)用較為成熟的古溫標(biāo)具有良好的可對比性.川鴨92井和川鴨95井的最高古地溫剖面近于平行,表明兩口鉆井經(jīng)歷了相近的最高古地溫梯度(約26 ℃·km-1)和古熱流(約60 mW·m-2),這與其空間距離接近,處于相同地質(zhì)背景,具有相似的構(gòu)造、沉積演化歷史的地質(zhì)實(shí)際(劉大成等,2002)是吻合的.

圖7 川鴨92井、川鴨95井古地溫恢復(fù)結(jié)果對比Fig.7 Comparison of the paleo-temperature reconstruction between CY91 and CY95

由于川鴨95井未有鏡質(zhì)體反射率(Ro)數(shù)據(jù),根據(jù)其巖芯的巖石熱解數(shù)據(jù)1)統(tǒng)計分析,2200～3000 m,Tmax=450～470 ℃,因川西地區(qū)上三疊統(tǒng)與侏羅系烴源巖有機(jī)質(zhì)以Ⅲ型干酪根為主,參照Ⅲ型生油巖Tmax與Ro關(guān)系圖版,推測對應(yīng)鏡質(zhì)體反射率Ro=1.2%～1.4%;3300～4000 m,Tmax=480～500 ℃,推測Ro=1.6%～1.8%,均略小于川鴨92井對應(yīng)深度的Ro值(圖3),而與伊利石結(jié)晶度所恢復(fù)的最高古地溫有較好的對應(yīng)關(guān)系.

1)地質(zhì)礦產(chǎn)部西南石油地質(zhì)局第十一普查勘探大隊,四川省彭縣鴨子河構(gòu)造川鴨95井完井地質(zhì)總結(jié)報告.1985.s

兩口井最高古地溫剖面與現(xiàn)今地表交點(diǎn)處,T1約為72 ℃,T2約為54 ℃,差值約18 ℃,以約26 ℃·km-1的古地溫梯度計算,剝蝕量差值約為690 m.結(jié)合磷灰石裂變徑跡的模擬結(jié)果,可認(rèn)為由晚白堊紀(jì)至今,研究區(qū)經(jīng)歷了冷卻及抬升剝蝕的過程,地溫梯度由約26 ℃·km-1降低至約22 ℃·km-1,剝蝕量大約1.3～1.9 km.

4.2 存在問題

本次研究中,各種古溫標(biāo)的熱史恢復(fù)結(jié)果具有較好的一致性,但由于不同古溫標(biāo)之間的適用溫度范圍以及對溫度的敏感區(qū)不同,在進(jìn)行等效性對比時,仍存在一定的限制. AFT的封閉溫度在120～130 ℃左右，對60～120 ℃的溫度范圍敏感,可以模擬樣品的溫度演化路徑,Ro、伊利石結(jié)晶度則是最高古地溫計,只能恢復(fù)樣品經(jīng)歷的最高古地溫.

利用伊利石結(jié)晶度Kübler指數(shù)估算埋藏變質(zhì)或者淺變質(zhì)時期的溫度較為準(zhǔn)確,而對于成巖階段的古溫度估算,雖有一些研究者建立起了利用KI進(jìn)行溫度估算的計算公式,如:T(℃)=249-89.3×IC, (Browne and Harvey,1992)

(1)

T(℃)=384.98 e-06219×IC, (Ji and Browne,2000)

(2)

或探索了KI與Ro之間的對應(yīng)關(guān)系(Guthrie et al.,1986;秦建中等,2009a,2009b),但其實(shí)際利用結(jié)果則不夠理想.如:利用公式(1)計算的古地溫與其他古溫標(biāo)確定的地溫梯度相差較大(王強(qiáng),2007);作為新生界斷陷盆地,濟(jì)陽坳陷的地層溫度現(xiàn)今為最高,因此利用公式(2)計算的濟(jì)陽—昌維凹陷的古地溫梯度(約40 ℃·km-1)(周建國,2006;姜惠超等,2008)代表了現(xiàn)今地溫梯度,該值較現(xiàn)今地溫梯度(約35 ℃·km-1)(龔育齡等,2003)也偏高.秦建中等(2009a,2009b)建立的川東地區(qū)KI-Ro對應(yīng)關(guān)系中,KI大于0.42(°Δ2θ)的數(shù)據(jù)較少,因而KI=0.57(°Δ2θ)的值偏離Ro-KI關(guān)系曲線.伊利石結(jié)晶度反映的古溫度與鏡質(zhì)體反射率相似,不僅與經(jīng)歷的最高古溫度相關(guān),而且還與最高古溫度所持續(xù)的時間有關(guān)(秦建中等,2009b),但它們隨溫度、時間演化的性質(zhì)并不一致,因而某一確定的溫度估算公式或等效關(guān)系,可能并不適用于更廣泛的結(jié)晶度范圍.如本文中伊利石結(jié)晶度KI數(shù)據(jù)隨深度的線性擬合關(guān)系,推廣至KI=0.25時,估算的最高古地溫則與圖4中川鴨95井的最高古地溫剖面不一致.相對低級-淺變質(zhì)階段伊利石結(jié)晶度的研究,成巖階段伊利石結(jié)晶度演化過程的研究相對缺乏,而該階段對自生伊利石的挑選以及測試精度、不同實(shí)驗(yàn)室之間數(shù)據(jù)對比等方面的要求更高,因此,伊利石結(jié)晶度作為成巖階段有機(jī)質(zhì)成熟度指標(biāo)的應(yīng)用,無論是測試標(biāo)準(zhǔn)還是熱演化性質(zhì)等,仍需要進(jìn)一步探索.

5 結(jié)論

1) 川西坳陷鏡質(zhì)體反射率(Ro)、磷灰石裂變徑跡(AFT)、伊利石結(jié)晶度(KI指數(shù))的古地溫恢復(fù)結(jié)果具有較高的一致性,可以作為研究區(qū)有效的古溫標(biāo)組合進(jìn)行熱史恢復(fù).

2) 熱史恢復(fù)結(jié)果表明,晚白堊世至今,盡管第四紀(jì)可能存在地溫梯度的增高,研究區(qū)總體仍表現(xiàn)為冷卻與抬升剝蝕的過程:地溫梯度由約26 ℃·km-1降低至約22 ℃·km-1,剝蝕量約為1.3～1.9 km；145—80 Ma為熱平靜期,沉積緩慢或沉積間斷,約80 M以來開始抬升剝蝕,約40—2.5 Ma再次經(jīng)歷了一個熱平靜期,第四紀(jì)以來地溫梯度增高約5 ℃·km-1.

3) 相對于鏡質(zhì)體反射率(Ro)和磷灰石裂變徑跡(AFT)等模擬方法成熟古溫標(biāo),伊利石結(jié)晶度用于沉積埋藏階段的古地溫恢復(fù)尚缺乏有效和統(tǒng)一的熱演化模型,其作為有機(jī)質(zhì)成熟度指標(biāo)和沉積巖古溫標(biāo)的應(yīng)用仍需進(jìn)行定量化方面的探索.

致謝 樣品采集得到中國石化西南油氣分公司熊亮主任、何志國高工的幫助.

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(本文編輯 汪海英)

Thermal history reconstruction based on multiple paleo-thermal records of the Yazihe area, western Sichuan depression

ZHU Chuan-Qing1,2, QIU Nan-Sheng1,2, JIANG Qiang1,2， HU Sheng-Biao3, ZHANG Shuo1, 2

1StateKeyLaboratoryofPetroleumResourcesandProspecting,ChinaUniversityofPetroleum,Beijing102249,China2CollegeofGeosciences,ChinaUniversityofPetroleum,Beijing102249,China3StateKayLaboratoryofLithosphericEvolution,InstituteofGeologyandGeophysics,ChineseAcademyofSciences,Beijing100029,China

Thermal history is significative to the geodynamics and petroleum geology of a sedimentary basin, for temperature is important for many geodynamic and the hydrocarbon accumulation process, especially the maturation evolution of hydrocarbon source rocks and the history of hydrocarbon generation.In the western Sichuan Basin, a continental depression is superimposed on the Paleozoic craton. The Paleozoic source rocks in this area have experienced a multi-stage and complex structural-thermal evolution and thus require different methods and effective geothermal indicators to reconstruct the thermal history,which will help discover the equivalence between different geothermal indicators and establish a set of geothermal indicators for the thermal history reconstruction of the area.The thermal history of a basin is usually reconstructed using various paleo-temperature indicators, including vitrinite reflectance (Ro), apatite fission track (AFT), (U-Th)/He in apatite and zircon, reflectance of bitumen and vitrinite-like macerals, the hydrogen index, and fluid inclusions.Roand AFT are the most widely used indicators and the related modeling methods are relatively well established, other indicators such asillitecry stallinity (IC), Raman spectroscopy, and acoustic rock emissions have also been studied and used in the quantitative reconstruction of paleo-temperatures.In this paper, the thermal history of the western Sichuan depression was reconstructed based on three geothermal indicators:Ro, AFT and the IC index, using the paleo-temperature gradient method, Monte Carlo modeling and the estimation of metamorphic temperature stage respectively, and the maximum paleo-temperatures reconstructed based on different indicators were compared.The thermal history reconstruction of CY92 using the paleo-temperature gradient method shows that the maximum paleo-temperature gradient of this borehole was ～26 ℃·km-1, the maximum paleo-heat flow was ～60 mW·m-2, both was larger than the present. The thickness of removed sediments on the surface of the unconformity between the Upper Jurassic and the Cenozoic was approximately 1900 m. This indicates that the area has undergone an overall, continuing structural-thermal evolution of cooling, uplifting, and denudation since the rock strata reached the maximum temperatures.AFT thermal history modeling result of CY92-1 reveals that the basin had experienced subsidence between 220 and 140 Ma and a thermal quiet period between 145 and 80 Ma, crustal uplift and erosion occurred in this area between 80 and 40 Ma, but after another thermal quiet period from 40 to ～2.5 Ma, the temperatures of the strata began to rise. The thickness of the removed sediments was estimated to be ～1900 m, which is generally consistent with theRoanalysis results.In borehole CY95, at a depth of ～4080 m, theKIwas 0.60 (°Δ2θ), and the maximum paleo-temperature was ～150 ℃; at a depth of ～6000 m, theKIwas 0.42(°Δ2θ), and the maximum paleo-temperature was ～200 ℃. The paleo-temperature profile of CY95 indicates a less of ～690 m in the thickness of removed sediments.In conclusion, the structural-thermal evolution in the western Sichuan depression since the late cretaceous to present is denudating and cooling, the geothermal gradient reduced from about 26 ℃·km-1to about 22 ℃·km-1, the erosion thickness is about 1.3～1.9 km. The uplifted and eroded is continuous since ～80 Ma to 40 Ma, a thermal quiet period kept from 40～2.5 Ma, then the geothermal gradient raised about 5 ℃·km-1since about 2.5 Ma. There was high consistency between the paleo-temperatures of the western Sichuan depression that were reconstructed based onRo, AFT, andKI. Thus, these three indicators can be used as paleo-temperature indicators for the thermal history reconstruction of the area. However, relative toRoand AFT, the illitecry stallinity index is still controversial and needs more research for using it as a maturity and geothermal indicator in the sedimentary rocks.

Vitrinite reflectance; Apatite fission track; Illite crystallinity index; Thermal history reconstruction; Western Sichuan depression

10.6038/cjg20151019.

Zhu C Q, Qiu N S, Jiang Q, et al. 2015. Thermal history reconstruction based on multiple paleo-thermal records of the Yazihe area, western Sichuan depression.ChineseJ.Geophys. (in Chinese),58(10):3660-3670,doi:10.6038/cjg20151019.

國家自然科學(xué)基金(41102152), 國家重點(diǎn)基礎(chǔ)發(fā)展研究計劃(2012CB214703),中國石油科技創(chuàng)新基金(2013D-5006-0102)和中國石油大學(xué)(北京)科研基金(YJRC-2013-02)資助.

朱傳慶,男,1981年生,博士,講師, 地?zé)釋W(xué)和石油地質(zhì)學(xué)專業(yè), 主要從事沉積盆地構(gòu)造-熱演化方面的研究.E-mail: zhucq@cup.edu.cn

10.6038/cjg20151019

P314

2015-03-30，2015-09-24收修定稿

朱傳慶， 邱楠生， 江強(qiáng)等. 2015. 川西坳陷鴨子河地區(qū)基于多種古溫標(biāo)的鉆井熱史恢復(fù).地球物理學(xué)報，58(10):3660-3670,