鄂尔多斯地区奥陶系马家沟群中部块状白云岩的深埋藏白云石化机制

鄂尔多斯地区奥陶系马家沟群中部发育一套厚层块状白云岩。在西部地区定边至鄂托克旗一带,这套块状白云岩连续厚度达数百米。定探 1井揭示的最大厚度为 431m。自西向东,白云岩体由厚变薄,并与石灰岩呈指状交织。这套块状白云岩由粗粉晶-细晶白云石组成,斑状结构发育。常见云斑的边界为缝合线,这表明斑状白云石化明显受缝合线控制。白云岩有序度平均值为 0.85,CaCO₃ 摩尔含量平均为 5 0.6 5 g/mol。δ13 C的平均值为 0.6‰ (PDB),δ18O的平均值为 - 7.4‰ (PDB)。主体细晶白云石中液态包体常见,最低均一温度为 104℃,包体成分中含有大量的有机成分CH₄ 和无机成分H₂ S。上述特征表明,这套白云岩是由深埋藏白云岩化作用形成的,它显示出良好的储集性能,是重要的后备储集岩。     

鄂尔多斯盆地奥陶系马家沟群块状白云岩的包体研究

鄂尔多斯盆地奥陶系马家沟群的块状白云岩，按晶粒结构可分为细硝糖状白云岩（晶粒大小为０．０１－０．１ｍｍ）和粗砂糖状白云岩（晶粒大小为０．０５－０．２５ｍｍ）。包体分析为块状白云岩的成因研究提供了最直接的信息，细砂糖状白云岩的主体白云石中液态包体不发育，但孔隙充填方解石中的包体发育，由２４个孔隙充填方解石中的包体测出均一温度为４９－７４℃，测算的包体形成深度的最大值为１７２ｍ。由此可以推断，其主体白     

鄂尔多斯盆地马家沟组白云岩地球化学特征及白云岩化机制分析

由岩石学和地球化学研究表明:马家沟组白云岩主要为泥微晶白云岩和晶粒白云岩两种。泥微晶白云岩常与石膏或岩盐伴生,阴极发光呈中等橘红色光,有序度低,具较高的Sr、Na含量,与泥晶灰岩具相似的δ¹³C分布区间及稀土元素配分模式,Sr同位素值接近同期海水,包裹体均一温度近于地表温度,表明白云岩化流体为与海水密切相关的高盐度流体,为准同生白云岩化,可用蒸发泵模式解释其成因。晶粒白云岩伴生矿物少,偶见黄铁矿,晶体结构多曲面他形,阴极发光为中-弱橘红色光,有序度高,Sr含量较低,Na、Mn含量与泥微晶白云岩相近,稀土元素配分模式与泥微晶白云岩相似且与泥微晶灰岩相近,δ¹³C分布区间与泥微晶灰岩趋于一致,包裹体均一温度较高,说明晶粒白云岩与泥微晶白云岩具相似的白云岩化流体,该种白云岩为埋藏白云岩化,上覆沉积物不断压实封存卤水使其侧向流动为白云岩化提供了源源不断的Mg离子。     

鄂尔多斯地区奥陶系马四组麦粒状白云石的发现及其成因探讨

鄂尔多斯地区的奥陶系主要由石灰岩和白云岩组成,在研究区东南缘的奥陶系马四绷带 发育一种特殊类型的白云岩,它主要由麦粒状白云石组成,其分布仅限于鄂尔多斯盆地的东南部,面积约２万平方公里。该区的相邻层位中均有膏岩及含膏岩类沉积,麦粒状白云石的晶体为一处延伸的菱面体,晶体的ｃ轴与延伸方向垂直,这与硬石膏晶体的光性特征类似。麦粒状白云石的有序度为０．５２～０．６０,平均为０．５６,ＣａＣＯ３的摩尔含量是５     

鄂尔多斯盆地奥陶系马家沟组白云岩储层特征及成因机制

鄂尔多斯盆地奥陶系白云岩是重要的天然气储集层,对其白云岩成因和储层发育规律的研究对于碳酸盐岩深层勘探理论的发展具有重要意义。文章基于大量岩心、薄片的观察,并结合稳定碳氧同位素、稀土元素、白云岩有序度、地层水、包裹体特征等地球化学分析,对盆地奥陶系存在的两种典型白云岩储层的发育特征和形成机理进行了详细研究。分析表明,含硬石膏结核或柱状晶的泥粉晶白云岩主要为潮坪蒸发环境的萨布哈成因,其规模储层的发育主要受到长时不整合的控制,不整合面以下发育大量硬石膏结核和柱状晶溶模孔;颗粒滩白云岩主要为回流渗透成因,其储层孔隙的发育主要受到海平面高频升降的影响,发育多旋回的粒（晶）间孔隙型储层。虽然两种白云岩的白云石化流体都为浓缩海水,但由于白云石化的机制和速率不同,二者的原始孔隙类型和特征迥异。两种白云岩孔隙在后期的成岩改造和演变过程中,既有相同之处,又有明显的区别。这一认识也将对深层的白云岩储层勘探提供指导作用。     

关于白云岩、白云石、白云岩化、白云石化和白云化等术语的辨析

白云岩是指以白云石为主要组分的碳酸盐岩,其中白云石矿物的含量应超过50%。在白云岩中常含有方解石、石膏等化学沉淀矿物,也可含有黏土、陆源砂、粉砂等。白云岩与石灰岩有相似的外貌,但白云岩与盐酸反应较石灰岩弱。白云石分子式是CaMg\[CO₃\]₂,其常含有Fe、Mn的类质同象混入物。白云石化,指方解石矿物中的钙离子部分地或全部地为镁离子代换,从而使方解石矿物转变为多镁方解石矿物或白云石矿物的作用,其英文术语为dolomitization。白云石化的结果可使石灰岩转变为白云石化的石灰岩或白云岩。由于白云石化的最终结果是石灰岩转变成白云岩,所以也可以把白云石化称作白云岩化。白云岩化的英文术语也是dolomitization。近几十年来,笔者基本上未使用白云石化和白云岩化这两个术语,而使用白云化这一笼统的或概括性术语代替白云石化和白云岩化。这样,许多有争议的问题就都避免了。白云石化作用、白云岩化作用、白云化作用,其含意与白云石化、白云岩化、白云化的含意相同。关于白云石和白云岩,在以前的英文文献中,均称作dolomite。近些年,一些作者用dolostone代表白云岩,而把dolomite仅限于白云石矿物。这是个很好的进展。近几十年来,笔者就是这么用的。现在,有些学者继续把dolomite兼指白云石和白云岩。可以这么兼指,只要把问题讲清楚就行。还有dedolomitization这一术语,其原意是去白云石化作用,指白云石中的镁离子被钙离子代换,从而使白云石矿物转变为多镁方解石矿物或方解石矿物的作用。其最终结果当然是白云岩转变为石灰岩。把它称作去白云石化或去白云岩化,均可。当然,笔者更倾向于把它称作去白云化。去白云石化作用、去白云岩化作用、去白云化作用,其含意与去白云石化、去白云岩化、去白云化的含意相同。看来,要把白云石化、白云岩化、白云化,去白云化、去白云岩化、去白云化,白云石、白云岩等术语的含意讲清楚,好似“绕口令”,令人不胜其烦。笔者建议：白云石（dolomite）专指矿物,白云岩（dolostone）专指岩石;白云化（dolomitization）兼指白云石化和白云岩化;去白云化（dedolomitization）兼指去白云石化和去白云岩化;“作用”二字要不要均可,不要更简单更好。     

鄂尔多斯盆地南部奥陶系马家沟组五段白云岩埋藏溶蚀作用研究

为了解鄂尔多斯盆地南部奥陶系马家沟组五段白云岩储集层不同类型埋藏溶蚀作用的作用过程及其对物性的影响,依据岩心和镜下观察,结合包裹体温度、微量元素和稀土元素数据分析,将马五段埋藏溶蚀作用分为有机酸流体埋藏溶蚀作用、热液埋藏溶蚀作用和TSR作用,其中有机酸流体溶蚀作用会导致层状溶孔、沥青薄膜和圆环的形成,而热液溶蚀作用会导致无组构无选择性溶孔、块状和脉状黄铁矿充填、热液矿物(组合)充填的出现。研究区马五段埋藏溶蚀作用发生模式为: (1)中侏罗世直罗期,低温热液埋藏溶蚀作用发生;(2)中侏罗世末期,伴随第1次烃类充注,有机酸流体埋藏溶蚀作用开始;(3)早白垩世东胜期,中—高温热液埋藏溶蚀作用发生;(4)早白垩世末期,伴随着第2次更大规模的烃类注入,TSR作用发生。对比发现,有机酸和热液溶蚀作用均对储集层有建设性作用,但热液比有机酸流体可以更有效地提高储集层物性。     

塔里木盆地中央隆起区寒武-奥陶系白云岩结构特征及成因探讨

白云岩研究的关键在于对白云石化作用的理解,而岩石结构作为白云石化作用分析的基础,不仅对白云岩的成因具有指示意义还深刻地影响着白云岩储层的质量。通过岩芯、薄片、扫描电镜、阴极发光以及碳、氧、锶同位素等测试手段,结合国际上常用的分类术语,对塔里木盆地中央隆起区寒武-奥陶系白云岩按结构进行了分类,并探讨了不同结构类型与其成因之间的关系。研究表明,白云岩结构与其形成环境和形成过程密切相关,其中保留原始结构的白云岩（包括泥-粉晶白云岩和颗粒白云岩）属于同生或准同生阶段、与蒸发海水有关的拟晶白云石化作用的产物,大量过饱和白云石化流体的通过有利于原始结构的保存;晶粒白云岩中,具有平直晶面结构的细晶、自形白云岩和细晶、半自形白云岩与浅埋藏成岩阶段的低温白云石化作用有关,云化流体以轻微蒸发的海源流体为主,浅埋藏晚期的过度白云石化作用导致晶体由平面-自形向平面-半自形转化;中-粗晶、他形白云岩是中或深埋藏成岩阶段的高温/热液白云石化或重结晶作用的结果,较高的形成温度导致晶体发生曲面化。     

鄂尔多斯盆地南部奥陶系马家沟组白云岩特征及成因机理分析

宏观与微观结合并以地球化学分析为主要手段,研究认为:鄂尔多斯盆地南部奥陶系马家沟组存在准同生白云岩化、渗透回流及混合水白云岩化、埋藏白云岩化和热液白云岩化4种白云岩化成因。准同生白云岩主要发育于马一、三、五段,由常规蒸发泵白云岩化形成;渗透回流及混合水白云岩由富镁盐水下渗白云岩化以及富镁盐水混同大气淡水对先成碳酸盐岩进行白云岩化共同作用形成;埋藏白云岩为大气降水溶蚀古陆老硅铝质岩石形成的盐水下渗和海(湖)水沿溶蚀孔洞下渗这两种白云岩化叠加形成的;热液白云岩为热液在粗晶粒白云岩孔隙或构造裂缝中溶蚀碳酸盐岩,过饱和后晶出。     

鄂尔多斯盆地下奥陶统马家沟组马五段白云岩的地球化学特征

鄂尔多斯盆地奥陶系马家沟组马五段属于浅海碳酸盐层系,间夹蒸发岩层。盆地中东部通常含有白云岩,它们是主要油气储集层。一些研究者把它们看成近地表回流白云岩。然而白云岩的岩石学和地球化学表明这些白云岩具有埋藏成因的证据。〓〓马家沟组白云岩（马五段）具有暗红色阴极发光,微量元素Fe为5 500×10-6～6 200×10-6,Mn为170×10-6~210×10-6,稳定同位素氧组分为-7.093‰～-9.932‰PDB,（平均值为-8.671‰PDB）,稳定同位素锶（87Sr/86Sr）为0.709 766～0.708 65（有硅质碎屑物的放射性87Sr的影响）。薄片下可以看到白云石沿着裂缝交代,上述特征表明白云岩可能在埋藏条件下形成。〓〓白云岩稀土元素的分布模式与海水的稀土元素分布有明显的差别,缺少Ce和Eu的负异常,表明交代流体不会是海水或蒸发海水。包裹体的均一化温度为160~220℃,盐度为5wt%～25wt%,暗示白云石化作用温度高,压力大,交代流体为卤水。〓〓密西西比谷型（MVT）矿化作用（方铅矿和闪锌矿）以及共生的低温热液矿物——钾长石、萤石、石英、黄铁矿等表明白云岩具有区域热液特征。     

塔里木盆地牙哈-英买力地区寒武系-下奥陶统白云岩形成机理

根据铸体薄片鉴定、阴极发光显微镜观察、碳、氧稳定同位素测定、微量元素分析及包裹体测温等手段,对塔里木盆地牙哈—英买力地区寒武—下奥陶统深埋热液白云岩类型及成因机理进行了详细的研究。认为研究区深埋藏白云岩主要由细晶或中晶白云石组成,白云石呈自形或半自形晶。δ13CPDB值为-1.63‰2.31‰,平均为0.25‰,δ18OPDB值为-11.49‰-6.02‰,平均为-8.72‰;锶含量较低,在77×10-6107×10-6之间,二价铁、锰含量较高,具有高的有序度和低的CaCO3摩尔含量的特点。各种资料表明,该类白云岩是在深埋藏环境中较高温度条件下形成的,白云岩的形成与海西期岩浆喷发活动有关,变质岩体的分布控制了白云岩的分布。白云化流体来自岩浆热液、变质热液、有机酸及区域地下热卤水的混合,白云化所需的Mg2+来自岩浆岩中铁镁矿物的分解、埋藏压实过程中粘土矿物的脱水作用等。因此其白云化机制可称之为“深埋热液白云化”。      

鄂尔多斯盆地奥陶系不同组构碳酸盐岩埋藏溶蚀实验

鄂尔多斯盆地奥陶系碳酸盐岩储层受埋藏溶蚀作用控制明显,而地层深部复杂的水-岩反应造成埋藏溶蚀研究难度较大,并进而影响了储层的评价与预测。分别利用CO₂溶液和乙酸溶液为流体介质进行溶蚀模拟实验,探讨埋藏条件下温度、压力、流体等因素对不同矿物及组构碳酸盐岩溶蚀作用的影响。结果表明:1）随着温度与压力升高,碳酸盐岩样品在乙酸溶液中的溶解速率均相应提高,在CO₂溶液中的溶解速率则先增加后减小,且在110℃~130℃区间内溶蚀速率最大;深埋藏环境下,各岩类溶蚀速率差异减小,并趋于一致;2）岩石矿物成分和组构,原岩初始孔隙度的大小及其连通关系,以及晶体的产状对成岩后期的埋藏溶蚀作用也具有重要的影响。不溶组分含量低、颗粒/灰泥比高、矿物成分复杂的碳酸盐岩由于组构选择性溶蚀作用而更易被溶蚀;碳酸盐岩的溶蚀速率随方解石含量的增加而增加,但深埋藏环境下,矿物成分含量差异对溶蚀速率的影响作用减弱;硬石膏与白云岩相伴生时,可优先溶蚀形成膏模孔,并促进白云石的溶解,改善储层效果。不同岩性,总体上灰岩较白云岩及过渡岩类更易发生埋藏溶蚀作用。结合研究区实际地质条件分析,砂屑灰岩、膏质白云岩等埋藏溶蚀强度较大,通过对原岩早期组构选择性溶蚀形成孔隙的继承和调整,叠加埋藏期岩溶作用后,可形成规模优质储层。     

Genesis of Dolomite from Ma55–Ma510 Sub-members of the Ordovician Majiagou Formation in the Jingxi Area in the Ordos Basin

We clarified three stages of dolomitization and secondary changes by studying the petrology and geochemistry characteristics of dolomite from the Ma55–Ma510 sub-members of the Ordovician Majiagou Formation in the Jingxi area in the Ordos Basin: (1) Syngenetic microbial dolomitization is characterized by formation of dolomite with a mainly micrite structure and horse tooth-shape dolomite cements. (2) Seepage reflux dolomitization during the penecontemporaneous period superposed adjustment functions such as recrystallization and stabilization in the middle-deep burial stage, forming dolomites mainly consisting of micro crystal and powder crystal structure. (3) Powder dolomite, fine dolomite, and medium-coarse crystalline dolomite formed in pores and fractures in the middle-deep burial stage. The secondary concussive transgression-regression under a regressive background is an important condition for the occurrence of many stages of dolomitization in the study area. The basin was an occlusive epicontinental sea environment in the Ma5 member of the Ordovician Majiagou Formation sedimentary period. In the sediments, sulfate content was high, which is conducive to the preservation of microbial activity and microbial dolomitization. Micritic dolomite formed by microbial dolomitization provides good migration pathways for seepage reflux dolomitization. Affected by evaporation seawater with increased Mg/Ca ratio, seepage reflux dolomitization was widely developed and formed large-scale dolomite, and underwater uplifts and slopes are favorable areas for dolomite. In the middle-deep burial stage, dolomitizing fluid in the stratum recrystallized or stabilized the previous dolomite and formed a small amount of euhedral dolomite in the pores and fractures.     

新疆三塘湖盆地二叠系湖相白云岩形成机理初探

利用薄片染色、微量元素和稳定同位素测试等方法对三塘湖盆地中二叠统芦草沟组与湖相暗色泥岩共存的白云岩的形成机理进行了探讨。白云岩分为纹层状藻云岩和斑块白云岩两种类型。白云岩的微量元素和同位素特征表明其形成于较高盐度、高Mg/Ca比、强还原的沉积环境。通过对白云岩镁离子来源的分析,认为纹层状藻云岩形成于准同生期,而斑块白云岩则是在埋藏成岩期火山物质淋滤、交代作用下形成的。     

Characteristics and Dolomitization of Upper Cambrian to Lower Ordovician Dolomite from Outcrop in Keping Uplift, Western Tarim Basin, Northwest China

Late Cambrian to Early Ordovician sedimentary rocks in the western Tarim Basin, Northwest China, are composed of shallow-marine platform carbonates. The Keping Uplift is located in the northwest region of this basin. On the basis of petrographic and geochemical features, four matrix replacement dolomites and one type of cement dolomite are identified. Matrix replacement dolomites include (1) micritic dolomites (MD1); (2) fine–coarse euhedral floating dolomites (MD2); (3) fine–coarse euhedral dolomites (MD3); and (4) medium–very coarse anhedral mosaic dolomites (MD4). Dolomite cement occurs in minor amounts as coarse saddle dolomite cement (CD1) that mostly fills vugs and fractures in the matrix dolomites. These matrix dolomites have δ18O values of ?9.7‰ to ?3.0‰ VPDB (Vienna Pee Dee Belemnite); δ13C values of ?0.8‰ to 3.5‰ VPDB; 87Sr/86Sr ratios of 0.708516 to 0.709643; Sr concentrations of 50 to 257 ppm; Fe contents of 425 to 16878 ppm; and Mn contents of 28 to 144 ppm. Petrographic and geochemical data suggest that the matrix replacement dolomites were likely formed by normal and evaporative seawater in early stages prior to chemical compaction at shallow burial depths. Compared with matrix dolomites, dolomite cement yields lower δ18O values (?12.9‰ to ?9.1‰ VPDB); slightly lower δ13C values (?1.6‰–0.6‰ VPDB); higher 87Sr/86Sr ratios (0.709165–0.709764); and high homogenization temperature (Th) values (98°C–225°C) and salinities (6 wt%–24 wt% NaCl equivalent). Limited data from dolomite cement shows a low Sr concentration (58.6 ppm) and high Fe and Mn contents (1233 and 1250 ppm, respectively). These data imply that the dolomite cement precipitated from higher temperature hydrothermal salinity fluids. These fluids could be related to widespread igneous activities in the Tarim Basin occurring during Permian time when the host dolostones were deeply buried. Faults likely acted as important conduits that channeled dolomitizing fluids from the underlying strata into the basal carbonates, leading to intense dolomitization. Therefore, dolomitization, in the Keping Uplift area is likely related to evaporated seawater via seepage reflux in addition to burial processes and hydrothermal fluids.     

Burial Dissolution of Ordovician Granule Limestone in the Tahe Oilfield of the Tarim Basin, NW China, and Its Geological Significance

With a comprehensive study on the petrology, geology and geochemistry of some Ordovician granule limestone samples in the Tahe Oiifieid of the Tarim Basin, two stages of burial dissolution were put forward as an in-source dissolution and out-source dissolution based on macro-microcosmic petrology and geochemistry features. The main differences in the two stages are in the origin and moving pass of acid fluids. Geochemical evidence indicates that burial dissolution fluids might be ingredients of organic acids, CO2 and H2S associated with organic matter maturation and hydrocarbon decomposition, and the in-source fluid came from organic matter in the granule limestone itself, but the out-source was mainly from other argillaceous carbonate rocks far away. So, the forming of a burial dissolution reservoir resulted from both in-source and the out-source dissolutions. The granule limestone firstly formed unattached pinholes under in-source dissolution in situ, and afterwards suffered wider dissolution with out-source fluids moving along unconformities, seams, faults and associate fissures. The second stage was much more important, and the mineral composition in the stratum and heat convection of the fluid were also important in forming favorable reservoirs.     

鄂尔多斯盆地西北部中奥陶统斑状白云岩成因研究

在鄂尔多斯盆地西北部,中奥陶统桌子山组和马五段到马三段斑状白云岩广泛分布。通过岩石、矿物学及地球化学特征研究,发现该白云岩具有岩溶、生物遗迹、深埋藏的证据,其原岩是早成岩阶段浅埋藏环境下形成的粉晶~细晶白云岩,在晚成岩阶段深埋藏环境下发生差异白云石化,形成细~粉晶白云石组成的斑块。因此,细晶~粗粉晶斑状白云岩受生物影响,是表生岩溶作用和深埋藏环境导致的差异白云石化作用的产物。     

Burial Metamorphism of the Ordos Basin in Northern Shaanxi

Burial metamorphism has been found in the Ordos basin of northern Shaanxi. On the basis of a rather intensive study of burial metamorphism of sandstone, it has been shown that the evolution from diagenesis to metamorphism involves four stages: cementation of clay minerals, regrowth of pressolved quartz and feldspar, cementation of carbonates and formation of laumontite. On that basis it has been put forward that the laumontite is formed by burial metamorphism of clay and carbonate minerals. According to the thermodynamic data of minerals, the conditions under which laumontite is formed are T<250℃ and X_(CO_2)<0.17. High-resolution SEM and TEM studies of clay minerals in mudstone show that there occur a mixed layer assemblage of bertherine and illite/chlorite and transformation from bertherine to chlorite. On that basis coupled by the X-ray diffraction analysis the author suggests the following transformation of clay minerals during burial metamorphism: the earliest smectite-kaolinite assemblage changes into the bertherine-illite mixture with increasing depth, then into the illite/chlorite mixed layer assemblage and finally into dispersed individual illite and chlorite. The reaction of the transformation is:smectite+kaolinite+K~+=illite+chlorite+quartz According to the study of the oxygen isotope thermometry of the coexisting illitequartz pair, the temperature of the above transformation is lower than 180℃.