鄂尔多斯盆地下古生界碳酸盐岩构造-沉积分异及成藏效应

鄂尔多斯盆地碳酸盐岩是当前的油气勘探热点。当前对鄂尔多斯盆地不同构造区的潜在碳酸盐岩储层及圈闭仍认识不清,阻碍了勘探目标优选。本文通过构造-沉积分异特征分析,揭示了鄂尔多斯盆地早古生代碳酸盐岩台地的构造-沉积分异演化过程及其后期构造改造分异特征。结果表明,受中央古隆起和陆表海环境的控制,盆地南缘以发育镶边礁滩相储层为特征,西缘以发育层状弱镶边礁滩储层为特征,内克拉通则以局限的台地潮坪白云岩储层为特征;三个不同构造-沉积分异区的碳酸盐岩建造都具备成藏条件,但遭受的构造形变具有显著差异,可分为西缘压性构造区、南缘张性构造区和内克拉通稳定构造区;西缘陆内前陆盆地的破碎褶皱带的有利圈闭包括逆掩断层遮挡圈闭和向斜中的次级背斜圈闭;南缘受渭北地堑影响形成的张性构造带发育基底潜山相关圈闭;内克拉通的伊陕斜坡带为一长期保持构造稳定的弱改造的大型单斜构造,以发育岩性圈闭型为特征,岩性圈闭的沉积相分布主要受陆表海旋转潮汐流的约束。

封闭系统中的白云石化作用过程及其油气地质意义——以南羌塘拗陷中侏罗统布曲组白云岩为例

南羌塘拗陷中侏罗统布曲组结晶白云岩作为盆地最优质的储层是通过埋藏成岩过程中封闭条件下的白云石化作用形成的,岩石所具有的高孔隙度与封闭系统中白云石化反应有关。根据对羌资11井和羌资12井布曲组的岩石结构分类、碳氧同位素组成及温度计算、流体包裹体均一温度等分析结果,可以认为:结晶白云岩碳同位素值分布区间较窄(2.86‰~4.27‰),氧同位素值随着白云石晶体变粗(自形程度变差)逐渐偏负(-3.27‰^-8.17‰),显著低于保留原始组构的白云岩,表明结晶白云岩碳源来自于先驱灰岩中的碳,其白云石化作用应是在远离大气水的封闭成岩环境中进行;结晶白云岩流体包裹体均一温度主峰值区间为90~140℃,且随着白云石晶粒变粗(自形程度变差),均一温度呈升高的趋势,与氧同位素计算温度变化趋势一致,表明白云石化作用过程是在封闭的条件下进行,白云石随地热增温而生长,并非受外来流体的影响。开放系统中的白云石化作用对油气储集空间的形成没有实际意义,而埋藏成岩过程中封闭系统的白云石化是形成南羌塘拗陷优质储层最为重要的成岩机制。

黔西北毕节地区中二叠统碳酸盐岩成岩作用

黔西北毕节地区中二叠统栖霞组和茅口组碳酸盐岩发育,地层出露良好。通过野外剖面的观察和实测,室内铸体薄片的鉴定、阴极发光分析以及碳氧同位素分析,结合区域地质背景和前人研究成果,认为黔西北毕节地区中二叠统碳酸盐岩的成岩作用具有如下特征:(1)中二叠统主要发育颗粒结构的灰岩和白云质灰岩(豹斑灰岩),岩石样品整体显示不发光—弱发光的阴极发光特征,碳同位素比值为1.2‰~4.6‰,表明岩石未受大气淡水的显著影响;(2)中二叠统碳酸盐岩受成岩改造作用强烈,发育海水潜流环境的泥晶化作用、海水渗流环境的等厚环边和马牙状方解石胶结作用、淡水渗流和潜流环境的等轴粒状—块状胶结和方解石的共轴生长、以及硅化作用、白云化作用和白云石的溶解作用、破裂作用、压实压溶作用等成岩作用,据此建立了相应的成岩演化序列;(3)硅化作用和白云化作用可能受到局部特殊热事件的影响,但具体的影响程度需要进一步的研究。

珠江口盆地珠江组碳酸盐岩储层质量评价

岩芯观察、薄片鉴定及物性分析等研究表明,珠江口盆地东沙隆起惠州、流花和陆丰3个地区珠江组碳酸盐岩储层质量明显不同。惠州地区珠江组碳酸盐岩在成岩过程中发育多期次的胶结作用,强烈的胶结作用严重阻塞孔隙,面孔率大多小于1%,渗透率以小于1 m D为主,储层质量最差;广泛的不同期次的溶解作用使得流花地区以粒间溶孔、铸模孔、超大孔及晶洞孔等次生孔为主,孔隙度和渗透率值在3个地区中最高,孔渗分布显著正偏,显示良好的孔隙度渗透率关系,对于获得某一特定渗透率所需的较低的截止孔隙度值,储层质量最好;陆丰地区成岩早期发育的胶结作用有利于原生孔隙的保存,后期受到一定的溶解作用改造,但溶解作用远不及流花地区发育,孔隙构成以粒间孔、生物骨架孔、粒内孔等原生孔为主,原生孔相对较差的连通性使其孔隙度虽然与流花地区大致相当,但渗透率却要比流花地区低得多,获得相同渗透率所需要的截止孔隙度比流花地区高,储层质量中等。

The relationship between dolomite textures and their formation temperature: a case study from the Permian-Triassic of the Sichuan Basin and the Lower Paleozoic of the Tarim Basin

Study of dolomite texture can contribute to understanding the process of dolomitization.This research reports textures and homogenization temperatures of dolomites from the Permian-Triassic strata in the Sichuan Basin and the Lower Paleozoic strata in the Tarim Basin,which provided insights into relationships between dolomite textures and their formation temperatures.Our results are summarized as follows：1） dolomites with well-preserved texture indicate low dolomitization temperature.However,in certain diagenetic environments,the hydrothermal dolomitization may completely or partially preserve the original texture of dolomites.2） The formation temperatures of non-planar dolomites are always higher than those of planar dolomites.3） The formation temperatures of dolomite cements are generally higher than those of replacive dolomites.4） Although the formation temperatures of saddle dolomite cements have a wide range,they show higher values than those of the planar subhedral to euhedral dolomite cements.Thus,saddle dolomites could generally be an indicator of high precipitation temperature.5） The fluid Mg/Ca ratio is another element controlling dolomite morphology.Micritic dolomites,which precipitate from hypersaline fluids with a high Mg/Ca ratio in a subaerial environment could also have features of non-planar anhedral crystal shape because of rapid nucleation and crystallization during dolomitization.

黔西北燕子口地区五峰组—龙马溪组泥页岩储层特征

在野外地质露头剖面测量和样品采集的基础上,通过铸体薄片鉴定、阴极发光、X射线衍射、扫描电镜、总有机碳含量和镜质组反射率等地球化学分析,结合区域地质背景和前人研究成果,探讨黔西北燕子口地区奥陶系五峰组—志留系龙马溪组泥页岩储层特征。结果表明:①研究区五峰组—龙马溪组主要沉积浅水—深水陆棚相的粉砂质页岩、云灰质页岩、泥质粉砂岩,烃源岩主要为五峰组以及龙马溪组下部黑色炭质/硅质页岩。②矿物组成主要由黏土矿物(22%~51%)、石英(21%~41%)和碳酸盐矿物(10%~35%)构成,含少量的黄铁矿和石膏,其中黏土矿物以伊/蒙混层和伊利石为主,总体具有脆性矿物含量高(平均值为59.4%),非均质性强,纵向变化大的特征。③储集空间主要为层间裂缝及溶蚀孔、顺层缝隙,尤以碳酸盐和长石溶蚀现象较明显,有机质孔不发育。④五峰组—龙马溪组总有机碳含量大于1%的中等以上的有效烃源岩的厚度约为20 m。⑤等效镜质组反射率约为2.5%,热演化程度高,处于过成熟的干气阶段,尚具备一定的生烃能力。

扬子西南缘大红山铁铜多金属矿床交代蚀变岩岩石学及其成矿意义

扬子西南缘是我国重要的铁铜金矿产资源产区,分布许多小—大型铁铜多金属矿床,而本次研究的大红山矿床属扬子西南缘内最大的铁铜多金属矿床之一.基于铁、铜矿体的主要赋矿岩石岩石学研究,并结合成矿背景和同位素资料研究,认为其岩性并非火山岩,实际上是由伴随基性岩浆上升的不混溶富硅碱和碳酸盐流体交代混染辉长岩岩体或原地层岩石在大红山岩群某些部位形成的交代蚀变岩(包括蚀变辉长岩).同时,根据矿区观察到的磁铁矿石与钠长石碳酸岩相互穿插、包裹所表现出的不混溶特点,暗示交代蚀变岩形成和铁成矿是同时的,可为下一步在周边寻找铁矿提供新的思路.

Carbon isotopic composition of Early Triassic marine carbonates, Eastern Sichuan Basin, China

As the interval following the biggest Phanerozoic mass extinction at the end of Permian, the Early Triassic is characterized by an immature, poorly functioned ecosystem.The effects of these extreme environmental conditions can be mirrored by the changes in the δ13C record of marine carbonates.However, the details about the carbon isotopic composition and evolution of the Early Triassic seawater remain poorly understood.A dataset of new δ13C and δ18O values as well as selected major and trace element data (including concentrations of CaO, MgO, Mn, and Sr) was obtained from 113 marine carbonate samples collected in Eastern Sichuan Basin.The isotopic and elemental data are used to evaluate effects of thermochemical sulfate reduction on δ13C.The δ13C values of a few samples affected by thermochemical sulfate reduction were corrected.By combining carbonate δ13C results in our investigated sections, we constructed a composite curve of the Lower Triassic.The results reveal a δ13C anomaly of carbonate rocks throughout the Early Triassic, accompanied by some rapid jumps and falls, such as those from approximately -2‰ to the extremely high value of 8‰ within a period of about 5 Ma.The Early Triassic δ13C profile derived from Eastern Sichuan Basin shows a close correspondence with Guandao section in Guizhou Province, whereas it yields an excursion pattern differing from Chaohu section in Anhui Province of the Lower Yangtze region (with the δ13C value from the minimum around -6‰ to the maximum near 4‰).The higher δ13C values and the positive carbon isotope excursions in the Lower Triassic from Eastern Sichuan Basin were most likely a consequence of the principal environmental change that may include: (1) the barren land surface due to the absence of vegetation, (2) the loss of diverse marine invertebrate groups and marine carbonates, (3) the thriving of bacteria, algae and methanogenus in ocean ecosystems, and (4) the local effect of the repositories of isotopically light carbon occurred in the form of methane hydrates.This process ended at the Early-Middle Triassic boundary, which indicates that the biotic recovery started at the end of the Lower Triassic.The terrestrial vegetation and marine invertebrates, as the regulators for carbon cycle, are irreplaceable and demand strong protections.

Temperatures of dolomitizing fluids in the Feixianguan Formation from the Northeastern Sichuan Basin

The discovery of natural gas reservoirs from the Triassic Feixianguan Formation in the Northeastern Sichuan Basin is an important breakthrough in the field of marine carbonate rocks for Chinese oil and gas exploration in recent years.Because of the dolomite-hosted reservoirs in the Feixianguan Formation,these dolomites and their formation mechanisms have been a research focus for sedimentary geologists and petroleum geologists.Based on the homogenization temperatures of fluid inclusions,oxygen isotopic composition and their calculated temperatures,and the burial and thermal history of the typical well,it is considered that the majority of dolomites are formed by low-temperature dolomitizing fluids in the Triassic Feixianguan Formation,Northeastern Sichuan Basin.Only a minority of dolomites are formed by high-temperature dolomitizing fluids.The ending depth interval of low-temperature dolomitizing fluids was about 1000-2500 m,of which the correspondingly ending timing interval was approximately from early-middle Middle Triassic to early-middle Late Triassic.The main depth interval of high-temperature dolomitizing fluids was about 3200-4500 m,of which the correspondingly main timing interval was approximately early-middle Middle Jurassic.The low-temperature and high-temperature dolomitizing fluids have different meanings to the formation and evolution of the pore volumes of dolomite reservoirs in the Feixianguan Formation,Northeastern Sichuan Basin.