成都理工大学学报（自然科学版）
成都理工大學學報（自然科學版）
성도리공대학학보（자연과학판）
JOURNAL OF CHENGDU UNIVERSITY OF TECHNOLOGY(SCIENCE & TECHNOLOGY EDITION)
2014年
5期
612-624
,共13页
黄可可%胡作维%李小宁%兰叶芳%吕杰%黄思静
黃可可%鬍作維%李小寧%蘭葉芳%呂傑%黃思靜
황가가%호작유%리소저%란협방%려걸%황사정
川东北%飞仙关组%白云岩储层%海水白云岩化%台内热对流模式
川東北%飛仙關組%白雲巖儲層%海水白雲巖化%檯內熱對流模式
천동북%비선관조%백운암저층%해수백운암화%태내열대류모식
Sichuan Basin%Feixianguan Formation%dolomite reservoir%sea water dolomitization%thermal convection
根据作为川东北三叠系飞仙关组作为重要储层的结晶白云岩（包括用以对比的原始结构保存的粒屑白云岩）的结构、元素构成、包裹体均一化温度和碳、氧、锶同位素特征，以及结晶白云岩在时间上和空间上的分布，讨论了这类白云岩形成的流体、温度和白云化机制，解释了结晶白云岩具有较好物性的原因。川东北飞仙关组结晶白云岩主要由细-中晶的平直晶面半自形-自形晶白云石构成，缺乏可进行均一化温度分析的气-液两相包裹体，具有低的锰、铁含量和较高的锶含量，显示较低温条件下海水或海源流体在白云化过程中的控制作用。结晶白云岩的碳、氧、锶同位素组成说明先驱鲕粒灰岩的碳是其主要碳源，白云化流体主要是早三叠世印度阶晚期海水，其次是奥伦尼克阶海水，白云化作用发生时鲕粒灰岩处于埋藏深度＜1 km的埋藏阶段，40～60℃的温度主要由地热增温提供，台地内部埋藏环境的热对流模式可以解释川东北飞仙关组结晶白云岩的形成机制。开江-梁平台棚以东的孤立（或半孤立）碳酸盐台地具有陡峻的边缘，两侧同时对海水开放，鲕粒岩分布层位较低（飞1-飞2段）都有利于热对流作用，台地内较为发育的蒸发盐造成纵向热传导率的差异并加强台内热对流。在白云岩分布样式的控制机理上，由于高渗透率鲕粒岩仅分布在台地边缘，使得海水进入台地后的垂向对流大于水平对流，白云化作用发生在台地边缘，飞3段鲕粒岩没有足够时间完成白云化，台地边缘结晶白云岩的体积向上减少。另外，川东北还存在回流白云化作用和塞卜哈白云化作用，由此形成的白云岩主要分布在台地上部或顶部，保留有很好的原始粒屑灰岩与泥微晶灰岩的结构，具有与同期海水类似的锶同位素组成，稍低的δ13 C值和偏正的δ18 O值以及稍高的锰、铁含量，显示白云化流体是同期海水，白云化系统对大气环境相对开放，白云化流体盐度高于同期海水。由于结晶白云岩是在不对大气水环境开放、但对非同期海水开放的条件下进行的，白云化反应的外来CO2-3较少，白云化过程岩石孔隙相对增加，储层质量较好。原始结构保存的粒屑白云岩是在对大气水环境相对开放的条件下进行的，白云化反应的外来CO2-3较多，白云化过程岩石孔隙增加有限甚至减少，白云岩为差储层或致密层。开江-梁平台棚以西的镶边陆棚飞仙关组虽然也发育高能环境的鲕粒灰岩或其他高能环境的粒屑灰岩，但形成优质储层结晶白云岩的条件差于台棚以东的孤立（或半孤立）碳酸盐台地。
根據作為川東北三疊繫飛仙關組作為重要儲層的結晶白雲巖（包括用以對比的原始結構保存的粒屑白雲巖）的結構、元素構成、包裹體均一化溫度和碳、氧、鍶同位素特徵，以及結晶白雲巖在時間上和空間上的分佈，討論瞭這類白雲巖形成的流體、溫度和白雲化機製，解釋瞭結晶白雲巖具有較好物性的原因。川東北飛仙關組結晶白雲巖主要由細-中晶的平直晶麵半自形-自形晶白雲石構成，缺乏可進行均一化溫度分析的氣-液兩相包裹體，具有低的錳、鐵含量和較高的鍶含量，顯示較低溫條件下海水或海源流體在白雲化過程中的控製作用。結晶白雲巖的碳、氧、鍶同位素組成說明先驅鮞粒灰巖的碳是其主要碳源，白雲化流體主要是早三疊世印度階晚期海水，其次是奧倫尼剋階海水，白雲化作用髮生時鮞粒灰巖處于埋藏深度＜1 km的埋藏階段，40～60℃的溫度主要由地熱增溫提供，檯地內部埋藏環境的熱對流模式可以解釋川東北飛仙關組結晶白雲巖的形成機製。開江-樑平檯棚以東的孤立（或半孤立）碳痠鹽檯地具有陡峻的邊緣，兩側同時對海水開放，鮞粒巖分佈層位較低（飛1-飛2段）都有利于熱對流作用，檯地內較為髮育的蒸髮鹽造成縱嚮熱傳導率的差異併加彊檯內熱對流。在白雲巖分佈樣式的控製機理上，由于高滲透率鮞粒巖僅分佈在檯地邊緣，使得海水進入檯地後的垂嚮對流大于水平對流，白雲化作用髮生在檯地邊緣，飛3段鮞粒巖沒有足夠時間完成白雲化，檯地邊緣結晶白雲巖的體積嚮上減少。另外，川東北還存在迴流白雲化作用和塞蔔哈白雲化作用，由此形成的白雲巖主要分佈在檯地上部或頂部，保留有很好的原始粒屑灰巖與泥微晶灰巖的結構，具有與同期海水類似的鍶同位素組成，稍低的δ13 C值和偏正的δ18 O值以及稍高的錳、鐵含量，顯示白雲化流體是同期海水，白雲化繫統對大氣環境相對開放，白雲化流體鹽度高于同期海水。由于結晶白雲巖是在不對大氣水環境開放、但對非同期海水開放的條件下進行的，白雲化反應的外來CO2-3較少，白雲化過程巖石孔隙相對增加，儲層質量較好。原始結構保存的粒屑白雲巖是在對大氣水環境相對開放的條件下進行的，白雲化反應的外來CO2-3較多，白雲化過程巖石孔隙增加有限甚至減少，白雲巖為差儲層或緻密層。開江-樑平檯棚以西的鑲邊陸棚飛仙關組雖然也髮育高能環境的鮞粒灰巖或其他高能環境的粒屑灰巖，但形成優質儲層結晶白雲巖的條件差于檯棚以東的孤立（或半孤立）碳痠鹽檯地。
근거작위천동북삼첩계비선관조작위중요저층적결정백운암（포괄용이대비적원시결구보존적립설백운암）적결구、원소구성、포과체균일화온도화탄、양、송동위소특정，이급결정백운암재시간상화공간상적분포，토론료저류백운암형성적류체、온도화백운화궤제，해석료결정백운암구유교호물성적원인。천동북비선관조결정백운암주요유세-중정적평직정면반자형-자형정백운석구성，결핍가진행균일화온도분석적기-액량상포과체，구유저적맹、철함량화교고적송함량，현시교저온조건하해수혹해원류체재백운화과정중적공제작용。결정백운암적탄、양、송동위소조성설명선구이립회암적탄시기주요탄원，백운화류체주요시조삼첩세인도계만기해수，기차시오륜니극계해수，백운화작용발생시이립회암처우매장심도＜1 km적매장계단，40～60℃적온도주요유지열증온제공，태지내부매장배경적열대류모식가이해석천동북비선관조결정백운암적형성궤제。개강-량평태붕이동적고립（혹반고립）탄산염태지구유두준적변연，량측동시대해수개방，이립암분포층위교저（비1-비2단）도유리우열대류작용，태지내교위발육적증발염조성종향열전도솔적차이병가강태내열대류。재백운암분포양식적공제궤리상，유우고삼투솔이립암부분포재태지변연，사득해수진입태지후적수향대류대우수평대류，백운화작용발생재태지변연，비3단이립암몰유족구시간완성백운화，태지변연결정백운암적체적향상감소。령외，천동북환존재회류백운화작용화새복합백운화작용，유차형성적백운암주요분포재태지상부혹정부，보류유흔호적원시립설회암여니미정회암적결구，구유여동기해수유사적송동위소조성，초저적δ13 C치화편정적δ18 O치이급초고적맹、철함량，현시백운화류체시동기해수，백운화계통대대기배경상대개방，백운화류체염도고우동기해수。유우결정백운암시재불대대기수배경개방、단대비동기해수개방적조건하진행적，백운화반응적외래CO2-3교소，백운화과정암석공극상대증가，저층질량교호。원시결구보존적립설백운암시재대대기수배경상대개방적조건하진행적，백운화반응적외래CO2-3교다，백운화과정암석공극증가유한심지감소，백운암위차저층혹치밀층。개강-량평태붕이서적양변륙붕비선관조수연야발육고능배경적이립회암혹기타고능배경적립설회암，단형성우질저층결정백운암적조건차우태붕이동적고립（혹반고립）탄산염태지。
This paper discusses the characteristics of fluids, temperature and mechanism of dolomitization based on the fabrics,elemental composition,cathodoluminescence,homogenization temperature,carbon/oxygen/strontium isotopes of the crystalline dolomite (and also the fabric-preserved grain dolomite phases for comparison)and combined with the space-time distribution of the crystalline dolomites in Northeast Sichuan Basin.The crystalline dolomite has low manganese and iron contents and higher strontium content,indicating the controlling of the sea water or marine-derived fluid on the dolomitization.The crystalline dolomite consists of dolomite crystals with small size and planar crystal boundaries and the gas-liquid fluid inclusions are absent,showing the low temperature of dolomitization.The carbon/oxygen/strontium isotope compositions of the crystalline dolomite indicate that the primary carbon source of the crystalline dolomite is the precursor oolitic limestone, that the sea waters of late Indo-Chinese stage (major)and Olenekian stage (minor)are the fluid for dolomitization of the crystalline dolomite,and that the dolomitization occurs in relatively shallow burial stage with depth less than 1000 m.The thermal convection of the burial environment within the platform is the essential mechanism of forming the Feixianguan crystalline dolomites.The carbonate platform to the east of Kaijiang-Liangping Trough has the steep margin opening to sea water and the oolitic rocks develop in the lower horizon (1st to 2nd Member of Feixianguan Formation).These benefit the thermal convection.The thick evaporite developed in the platform enhances the thermal convection of internal fluids in the platform.The oolitic rocks with high permeability are distributed over the edge of the platform,the impacts of the vertical convection exceed that of the horizontal convection and the dolomitization is restricted within the rim of the platform.There is not enough time for oolitic rocks of Member 3 of Feixianguan Formation to finish the dolomitization,so,the volume of the crystalline dolomite in the upper horizon is less than that in the lower horizon.In addition,the reflux and Sabkha dolomitization model responsible for the fabric-preserved dolomites also exist in the upper part and the top of the platform.These dolomites have the 87 Sr/86 Sr ratios similar to the contemporary sea water.Relatively high manganese and iron contents and relatively negativeδ13 C and positiveδ18 O indicate that the dolomitization fluids responsible for these dolomites are the contemporary sea water and they may develop in the environment open to meteoric water,the salinity of the dolomitization fluids is higher than the contemporary sea water. The crystalline dolomites develop in the environment not open to meteoric water but open to non-contemporary sea water,and consequently,have little external CO2-3 and increase the porosity of rocks and thereby have the higher reservoir quality,whereas the fabric-preserved dolomites have more external CO2-3 and limitedly increase the porosity (or even decrease the porosity )and thereby have the lower quality reservoirs.In the Feixianguan Formation with the rimmed shelf to the west of Kaijiang-Liangping platform-shelf,there also develops the oolitic limestone of high energy environment,however,the crystalline dolomite conditions of forming good quality reservoirs are more than that of the carbonate platform to the east of the platform-shelf.
