Dolomite formation is a crucial aspect of natural gas reservoirs in the marine strata of the Sichuan Basin,particularly in the exploration of deep carbonate reserved oil and gas resources.Understanding the genetic mechanism of dolomite is essential for predicting the distribution of favorable dolomite reservoirs in deep forma-tions.Taking the third member of the Maokou Formation in the southeastern Sichuan Basin as an example,present work systematically investigates the genetic mechanism of dolomite by analyzing geochemical characteristics such as carbon and oxygen isotopes,strontium isotopes and rare earth elements.The analysis is based on data from outcrops,core samples and thin sections.The results reveal that the dolomites of the third member of the Maokou Formation in the southeastern Sichuan Basin can be categorized into laminated fine-crystalline dolomite,laminated fine to medium-crystalline dolomite,and saddle dolomite cement.Among these,the laminated fine to medium-crystalline dolomite is the most common type.The δ18 O values of this dolomite type(-7.04‰ to-6.08‰)appeared unaffected by hydrothermal fluids,and are similar to those of mud-crystal limestone.Additionally,the 87Sr/86Sr ratio(0.707 550 to 0.707 740)locate within the range of contemporaneous seawater,indicating a diagenesis process of quasi-syngenetic to burial-induced restricted marine water infiltration dolomitization. The δ18 O values of hydrothermally influenced dolomite range from -7.33‰ to -7.11‰, showing slightly negative compared to those of mud-crystal limestone. These dolomites also showed relatively higher 87 Sr/ 86 Sr ratios (0.707 950 to 0.708 171) than those of contemporaneous seawater. The laminated fine-crystalline dolomite, which was not affected by hydrothermal fluids, shares a common genetic mechanism with the previously mentioned laminated fine to medium-crystalline dolomite. Saddle dolomite cement found in caves and fractures is either directly precipitated or recrystallized from hydrothermal fluids. This type of dolomite is characterized by higher 87Sr/ 86 Sr ratios (with a mean value of 0.707970), significantly negative δ18O values (with a mean value of-7.32‰), and positive Eu anoma-lies. A gradient change from laminated fine-crystalline dolomite to laminated fine to medium-crystalline dolomite and finally to saddle dolomite cement is observed, controlled by a transition from marine water to hydrothermal fluids. The dolomite in the study area is proposed to be the product of multi-stage fluid-induced diagenesis.

四川盆地二叠系热液白云岩备受关注,但缺乏对于热液矿物和热液流体贡献的深刻认识,对泰来地区富硅质碳酸盐岩储层的研究也相对较少.该研究以四川盆地泰来地区茅三段富硅质碳酸盐岩储层为例,根据碳氧锶同位素、主微量及其他稀土元素组成,结合岩石学特征,对热液矿物(如鞍形白云石、硅质等)进行系统研究.研究结果表明:鞍形白云石成因为热液流体直接沉淀,碳酸盐充填矿物流体来源为海水和热液的混合流体,以海水为主.岩浆作用在研究区内不仅通过其加热盆地,促进鞍形白云石和其他热液矿物的沉淀,而且提供了 1％～5％、甚至更多的现代黑烟囱流体(热液流体)的等量物质对充填物的地球化学特征进行重印.热液流体(包括白云化和硅质流体)活动期间促进裂缝的发育,是改善储层最重要的因素;热液矿物充填裂缝导致储层破坏.研究区有效储层的勘探方向应为高能滩相热液改造弱或少泥质含量、易于产生破碎裂缝的区域.

中二叠世末期,海水退出四川盆地,元坝地区茅口组上部灰岩普遍可见暴露、岩溶现象,但岩溶带的发育特征及其分布规律尚不明确.基于井-震联合解释的思路,通过岩心观察、测井岩性解释、三维地震数据体的层位标定与地震相解译等,特别是通过相对声波阻抗转换、地震地层切片分析等技术手段提高了地震数据的解释分辨率,建立了茅口组的层序地层格架,进而描述茅口组的沉积与岩溶特征,预测岩溶带的分布规律及模式.结果表明:(1)元坝地区茅口组共发育3个三级海侵—海退层序,生屑滩发育于第2个和第3个三级层序的海退旋回内,其中前者是在沉积古地貌高部位发育台内生屑滩,后者是在YB7井一带的台地边缘坡折带发育台缘生屑滩;(2)岩溶带的发育和分布受生屑滩控制,在岩心尺度主要表现为地表岩溶带、垂直渗流带、深部缓流带的高角度溶缝和溶洞、水平潜流带的顺层溶洞;(3)平面上,岩溶带集中发育在生屑滩内部靠近海岸的一侧,发育模式具有海岸型岩溶的特点;(4)水平潜流带顶部发育的顺层溶洞为茅口组岩溶带主要的储集空间,但大多已在表生期被火山凝灰质和灰岩碎屑等流水搬运物质和方解石等化学沉淀物质充填,现今储集能力总体较差.在此基础上,提出了元坝地区茅口组岩溶带的分布模式,并对其油气勘探意义与风险进行了讨论.

Dolomite bodies in the Middle Permian of the central Sichuan Basin have been reported as favorable natural gas reservoirs. The Middle Permian dolomite consists of three types of recrystallized dolomite (Rd1, Rd2, and Rd3) and one type of dolomite cement (Sd). Rd1 might be formed as the primary mineral along the calcite in the original sea-water. Its δ13C value and 87Sr/86Sr ratio, consistent with those of marine limestone and Permian seawater, support that the dolomitizing fluid for Rd1 was Permian seawater preserved in the strata. Rd2 consists of fine to medium (50 μm to 250 μm) and planar to curved crystals. Geochemical indicators (slightly high 87Sr/86Sr ratio, similar rare earth element patterns, negative δ18O, slightly high salinity) confirm that the dolomitizing fluid of Rd2 was mainly Permian seawater during shallow burial, with a small number of hydrothermal fluids. Rd3 and Sd are featured by very large (>250 μm), curved crystals, and high-temperature, high-salinity, and obviously positive Eu anomalies, suggesting that their diagenetic fluids were mainly hydrothermal fluids from deep. Additionally, inherited carbon sources and the 87Sr/86Sr ratios of some samples fall within the range of Permian seawater distribution, confirming the contribution of Permian seawater. ELIP activity caused the formation of this dolomite through the mixing of seawater and hydrothermal fluids. The main fluid circulation channels were activated basement faults, epigenetic karst pores, and shallowly buried high-permeability strata. During the peak period of ELIP activity, the continuous upwelling of deep hydrothermal fluids led to the continuous formation of Rd2, Rd3, and Sd. The dolomitization fluid of Rd2 was mainly composed of seawater and featured a certain lateral extension, which was away from faults. Rd3 and Sd are mainly distributed along the fault system, and excessive dolomitization caused by the hydrothermal activity, to some extent, inhibited the lateral movement of hydrothermal fluids. This study provides a good example for exploring the genetic mechanism and distribution pattern of structurally controlled dolomites under a volcanic activity background.

四川盆地中二叠统茅口组白云岩中蕴藏丰富的天然气资源,但是这套白云岩的成因多年来一直存在争议.盆地东部茅口组白云岩储集层多发育在茅三段中下部,纵向上厚度介于3.0～46.8m之间,平面上沿北西—南东向基底断裂呈带状展布.野外和钻井岩心观察发现,白云岩内发育交织状张性裂缝,将岩石切割呈角砾状,裂缝多被粗晶方解石、白云石充填或半充填.根据围岩和裂缝中白云石晶体形貌和产出状态,在显微镜下识别出4类不同组构的白云石:第1类为灰泥基质中"星散状"自形粉晶—细晶白云石;第2类为半自形面状组构细晶白云石,呈他形—半自形镶嵌状;第3类为具"雾心亮边"的自形晶面状组构细晶—粗晶白云石,具糖粒状结构,晶间孔隙发育;第4类为脉体充填的粗晶鞍状双晶白云石.背散射照片显示前3类白云石的"雾心"部分晶面混浊、表面分布方解石残斑及微孔,而第3类白云石的"亮边"部分与第4类鞍状粗晶白云石脉则晶体明亮、洁净、致密,属新生矿物.上述4类白云石的成分均具有富Ca和贫Fe、Mn、Sr的特点,MgO含量变化较大,其中前两类白云石MgO含量总体低于白云石标准计量,而后两类白云石的MgO含量则接近或略高于标准计量.岩石学、矿物学和地球化学特征表明:茅口组白云岩主要经历了 2期白云化作用,初次白云化作用形成第1类、第2类白云石及"雾心"白云石,二次白云化作用形成"亮边"白云石和粗晶白云石脉体;2期白云化作用均发生得很早,可能始于同沉积期至浅埋藏期.白云石原位微量元素和原位锶同位素分析表明,白云化作用流体具有混源的特点,流体可能由富Ca地下水以及与火山活动有关的热液混合而成.推测中二叠世末期峨眉山地幔柱的喷发引起四川盆地内基底断裂再次活动,造成茅口组内张性构造裂缝发育,这为白云化流体混合及运移提供了通道.

对于四川盆地上二叠统长兴组到下三叠统飞仙关组界面的性质一直都存在着争议.为了进一步明确长兴组顶部是否发育不整合岩溶作用,以野外、钻井、岩心等资料为研究对象,分析了川南广大台内地区长兴组储层情况,指出了大量的溶沟、溶缝、溶洞等岩溶证据,进一步证实长兴组顶部发育不整合面.研究结果表明:①长兴组与飞仙关组之间存在沉积间断,表现为短期暴露不整合,古岩溶储层发育;②不整合岩溶作用形成的溶洞、溶缝叠加裂缝改造,形成的裂缝溶洞系统是长兴组的主要储集空间,为裂缝—孔洞型储层;③綦江地区长兴组天然气成藏模式属于"下生上储"型,龙潭组烃源岩是长兴组天然气的主要来源,烃源岩优质,成藏条件优越.结论认为:①长兴组天然气高产、稳产井与层间断裂匹配明显,断裂和裂缝为长兴组主要的油气运移通道,沟通烃源岩,从而控制了油气富集高产;②长兴组不整合岩溶储层的发现拓展了綦江地区乃至整个四川盆地的油气勘探领域,为下一步油气勘探提供了方向.

针对热液白云岩展布非均质性强的问题,开展基底断裂与茅三段沉积演化关系研究,分析断裂样式与白云岩分布关系,建立沉积演化模式,预测白云岩的分布.研究结果表明:茅三段可划分为5个小层,1～3小层为白云岩发育主要时期,4～5小层为台地均一化时期,不发育白云岩;15-1、15-2和16号基底断裂控制了早期"台-洼"相间的沉积地貌,断裂附近的地貌高部位为生屑滩发育有利部位,为白云岩的发育提供物质基础;15-1、15-2号基底断裂样式为花状,周边生屑滩白云石化程度高,为白云岩发育最有利区;16号基底断裂为直立状,附近白云石化发育程度较低,为白云岩发育较有利区.研究成果可为热液白云岩领域的进一步勘探提供指导依据.

利用露头和岩心资料,通过大量的薄片、扫描电镜和主量元素、微量元素、稀土元素、锶同位素等分析化验资料,深入分析川东地区中二叠统茅口组白云岩储层成因机理,取得3个方面的新认识:①根据晶粒结构及其产状将白云岩进一步细分为三大类,基质镶嵌状白云岩,距构造热液脉相对较远;基质"雾心亮边"白云岩,多与构造热液脉体伴生;构造裂缝白云岩,主要分布在热液破裂形成的张性构造裂缝和孔洞中,半充填;②白云岩主要经历2期白云化改造,均为热液成因,其中基质镶嵌状白云岩形成于同沉积及浅埋条件下,而基质"雾心亮边"白云岩是在早期白云化作用的基础上,后期受到了强烈的热液改造作用形成,构造裂缝白云岩则是由热液流体沉淀形成;③浅滩是白云岩发育的基础,基底断裂为同沉积断裂,且为富镁热液的运移通道,是白云岩"似层状"展布的关键,明确了15#基地断裂南侧为白云岩勘探首选目标区.

为了明确川东南涪陵地区茅口组热液白云岩气藏富集规律,基于钻井、岩心和涪陵地区连片三维地震资料,分析了研究区基底断裂特征与形成演化及其对茅口组油气成藏的意义,建立了油气成藏模式.研究结果表明:研究区基底断裂剖面上发育"Y"字形与反"Y"字形、"花状"、直立状3种构造样式;平面上识别出15、15-1、16号3条基底断裂,均以北西—南东向展布为主;基底断裂纵向上具有分层特征,同时沿断裂走向又体现出分段差异性;15、15-1号基底断裂中、上构造层活动性强于16号基底断裂,15号基底断裂西段活动性强于中段和东段.基底断裂控制了茅口组油气藏的形成与分布;白云岩储层沿基底断裂两侧呈条带状展布,距基底断裂越近,下伏志留系烃源岩对茅口组成藏贡献越大,含气性越好,测试产量越高.综合研究区基底断裂、烃源岩和储层发育特征等,建立了"下生上储、双源供烃"油气成藏模式.研究成果对深化涪陵地区茅口组热液白云岩研究具有重要指导意义,同时可为其他基底断裂发育区油气成藏研究提供借鉴.

近期于四川盆地部署完成的南充1井、焦石1井和双探1井等在下二叠统茅口组都获得了良好的工业气流,体现了四川盆地及周缘地区茅口组具有良好的天然气勘探潜力.川东南地区茅一段主要发育于外缓坡环境,岩石类型复杂,储层非均质性强,为加强对茅一段储层的评价工作,结合野外露头观察和测井、镜下薄片等把茅一段岩性分为3大类,即灰泥灰岩、泥晶灰岩和瘤状灰岩.通过大量先进的储层物性描述手段,识别出川东南地区茅一段为低孔、低渗致密碳酸盐岩储层,平均孔隙度1.36％,平均渗透率0.82× 10-3 μm2,孔、渗条件与TOC和滑石含量呈正相关关系,灰泥瘤状灰岩的整体物性条件要优于泥晶瘤状灰岩.茅一段储层的孔隙主要由无机孔和有机孔组成,其中无机孔占主要地位且无机孔主要由矿物收缩孔(缝)构成,而有机质孔主要由5～ 50 nm的中孔组成.

近年来，川东地区长兴组—飞仙关组礁滩相勘探取得了一系列重大发现，礁滩气藏形成机理成为了研究的热点。兴隆场气田的解剖以及气藏形成演化的系统研究表明：长兴组岩性圈闭古油藏为孤立的油藏，现今气藏气—水界面不受海拔控制，具有各自相互孤立的特点，从古油藏形成到现今气藏经历了一定的调整改造。天然气成藏过程主要包括3个阶段：晚印支期为早期古油藏的聚集阶段，形成多个独立的礁—滩相储层岩性油藏；早—中燕山期为古油藏裂解形成古气藏阶段；晚燕山期以来为现今气藏定位阶段。

利用地震、地质资料,系统分析了川东南涪陵地区印支期至今构造演化特征及其对油气聚集的控制作用.研究认为涪陵地区印支期—燕山早期构造抬升呈现南北高,中部低的鞍状特点、晚燕山期开始挤压,至喜山期挤压作用最活跃.结合涪陵地区沉积埋藏史,认为海相上组合各层系油气成藏受构造作用控制,整体经历了印支期—燕山早期古油藏形成、燕山中晚期古气藏发育和喜山期气藏调整改造的过程,但不同层位不同圈闭类型受构造控制作用不同.

以长兴组台地边缘礁滩储层发育认知为指导,将三维与二维地震资料相结合,开展台洼边缘礁滩与台地边缘礁滩的沉积背景、发育模式、古地貌的综合对比研究,对四川盆地中部蓬溪—武胜台洼边缘礁滩发育演化特征进行分析,提出了四川盆地东南部泰来、永兴场及义和地区3种台洼边缘礁滩发育模式.受开江—梁平陆棚、峨眉地裂运动以及微古地貌影响,泰来地区以台洼边缘礁滩沉积为主,永兴场地区沉积低能生屑滩,义和地区发育成排生物礁带及点礁.从长兴期整个四川盆地沉积格局分析,蓬溪—武胜台洼边缘礁滩与开江—梁平陆棚边缘礁滩整体沉积格局相似,但台洼边缘生物礁滩纵向发育规模偏小,横向分布面积广泛.

On the basis of the seismic data and geological information,we analyzed the tectonic characteristics, evolution and formation mechanism of high and steep structures in eastern Sichuan.The high and steep fault folding belt experienced the dynamic environment change from extension to compression,and is divided into four tectonic evolution stages:the formation of incompetent folding (The Indosinian before), the formation of embryonic folding (The Indosinian period ), the formation of active folding (The Yanshanian period ),the formation of fold forming (The Himalayan period ).The present tectonic framework of high and steep fault folding belt in eastern Sichuan is controlled by pre-existing structures, and multiple stages of compression tectonic superimposition,finally resulted in the formation of high and steep fault folding belt with is ejective structure.Influenced by two sets of gypsum-salt detachment layer and one set of shale detachment layer,the high and steep fault folding belt in eastern Sichuan can be divided into three tectonic deformation layers.During the multiple stages of extrusion stress,each structural layer shows various structures evolution due to the differences in the longitudinal formation and evoluation.There is some guiding significance to the further study on the control of the multi-phase tectonic superimposition on the salt deposits and the oil and gas preservation.

从綦江及邻区须家河组地层特征、沉积特征、储层特征及烃源岩特征等方面,分析了须家河组含油气地质条件及勘探潜力.研究表明:①綦江地区上三叠统须家河组发育辫状河三角洲平原沉积,岩性组合具有“砂包泥”的特点,整体上辫状河道砂体发育,具备形成规模储层的基础;②储层岩石致密-超致密,为特低孔、特低渗储层,裂缝和次生溶孔是储层发育的关键;③通过寻找相对低砂地比层系,叠合深大断裂沟通的须家河组构造,寻找混合气源的构造-岩性油气藏;④有深大断裂沟通深部海相气源的须家河组构造是有利的勘探目标.

The combination patterns and depositional characteristics of the carbonate banks are investigated based on outcrop sections, thin sections, and carbon isotopes of Ordovician in the western Tarim Basin, China. Four carbonate bank combination patterns are deposited in the Ordovician, western Tarim Basin, including: Reef-Bank Complex (RBC), Algae-Reef-Bank Interbed (ARBI), Thick-Layer Cake Aggradation Bank (TLCAB), and Thin-Layer Cake Retrogradation Bank (TLCRB). All combination patterns show clear periods vertically. The RBC is mainly composed of reefs and bioclastic banks, and the dimension of the RBC depends on the scale of the reefs. Bioclastic banks deposits surround the reefs. The range of the ARBI is determined by the scale of algae-reefs, algae peloid dolomite microfacies and algal dolomite microfacies deposit alternating vertically. TLCAB and TLCRB are deposited as layer-cakes stacking in cycles and extending widely with cross bedding developed. The grains of TLCAB and TLCRB are diverse and multi-source. With the impacting of relative sea level change, biological development and geomorphology, the ARBI, TLCAB or TLCRB, RBC are successively developed from the Lower Ordovician Penglaiba Formation to the Middle Ordovician Yijianfang Formation. The depositional environment analysis of Ordovician indicates that the RBC and ARBI can form effective oil and gas reservoirs, and the TLCAB and TLCRB have the potential to form the huge scale oil and gas reservoirs and to be the crucial targets of exploration for the Ordovician carbonate banks in the future.

According to the theory and approach of high resolution sequence stratigraphy and sedimentology,combining with core,drilling well,well-logging and seisimic data,detailed studies has been carried out on the Upper Triassic Yanchang Formation of the southern Ordos Basin.Totally five sequence boundaries,four 3rd and eleven 4th sequences were identified and the sequence stratigraphy framework was built up.Four types of sedimentary facies were developed in this area,including meandering fluvial delta,braided fluvial delta,lacustrine and deep-water gravity flow facies.The characteristic distribution of sedimentary facies in sequence stratigraphic framework was illustrated,and the law of evolution and distribution of sedimentary facies in sequence stratigraphic framework was established and the distribution of sandbodies in sequence stratigraphy was generalized.Taking the constantly deepening understanding of the sedimentary facies as the guidance,great breakthrough has been made in the petroleum exploration of the Yanchang Formation in the Ordos Basin.

The lower bitumen-bearing sandstone Member of Kepingtage Formation in Tazhong Area is one of the major oil and gas-rich layers in Palaeozoic clastic rock series in Tarim basin.Based on description of drilling cores,combined with logging,seismic and test data,it is showed that transgressive shore-tidal-braided-river delta depositional system was developed in target stratum.Littoral facies is made up of up-nearshore and down-nearshore microfacies,whose lithology includes fine sandstone,siltstone,pebbled anisomerous sandstone.Tidal flat facies is made up of tidal sand bar,tidal channel,sand flat microfacies.The sediments of tidal channel mainly include sandstone,gritstone and pebbled sandstone.Its sedimentary structures include wedge shaped cross bedding,tabular cross-stratification,and herringbone cross-bedding.There are some erosion surfaces and lots of pyrite in the bottom of tidal channel.Braided-river delta is made up of underwater distributary channel,interdistributary bay,and sand sheet microfacies.During marine transgressive period,there are four depositional periods sandbodies from the basin central to the south overlapping onto Tazhong low uplift one by one.According to sedimentary overlap evolution law,the microfacies of these four periods of sandbodies are littoral,tidal flat and braided-river delta facies in the plane.In terms of controlling factors,distribution range and transgression direction,the four periods microfacies have similarity and regularity.

Carbonate reef-bank reservoirs have been the current hot spot of oil and gas exploration in Tarim Basin.Taking the Shihuiyao and Dawangou outcrop profiles in Keping Area of Tarim Basin as the examples,the intraplatform shoal petrographic constitute and sequence stratigraphic features in Ordovician Yingshan Formation are deeply compared,based on which,the controlling factors of intraplatform shoal strata development are analyzed.The results show that:(1)There are some differences on Yingshan Formation development in Shihuiyao and Dawangou Areas.Shihuiyao section mainly develops thin grain limestone and mudstone,while Dawangou section deposits thick layered grain limestone.(2)The sequence characteristics of retrogradation in Shihuiyao Area and aggradation in Dawangou Area reflect that the sea-level change has different control actions in different microtopography fields.The sea-level rising inhibited the limestone development of Shihuiyao Area in the lower topography field,but promoted the limestone development of Dawangou Area in the high topography field.(3) The two intraplatform shoal sedimentary styles of Yingshan Formation in Keping Area may become the favorable targets for oil and gas exploration.