【作者】 吴勘；

【导师】 冯庆来；

【作者基本信息】 中国地质大学 ， 古生物学与地层学， 2013， 博士

【摘要】 近来,我国对页岩气资源的关注度不断提升,页岩气独特的赋存状态,“连续成藏”的聚集模式,区别于常规天然气储层的特征,决定了页岩气储层研究的特殊性。目前,国内针对页岩气储层特征及评价的工作开展得相对较少,需要建立相应的评价标准。扬子北缘中二叠统孤峰组主要由黑色硅-泥质岩石组成,化石丰富,有机碳含量高,成藏条件较好,是我国页岩气勘探开发有利区带之一。新兴的地球生物学理论采取正演方法,对烃源岩进行评价,为高热成熟度、低有机质丰度地区的烃源岩评价提供了可行的途径。用地球生物学理论评价页岩气藏值得探索。由于扬子北缘大多是山地,露头虽多,但地表地质条件较差,交通不便,我们选择了相对地表条件较好,交通较方便的三条剖面进行页岩气地质意义研究,分别是建始罗家坝剖面、建始茅草街剖面和恩施田凤坪剖面。应用地球生物学理论对其地层的地球生物学过程进行定性和定量的分析研究,对于我国页岩气勘探开发具有典型指导意义。放射虫是一种海生微体浮游生物,在全球古海洋中分布广泛,可作为全球地层对比的有效工具。尤其在深海缺乏其它生物化石的条件下,它是划分地层最重要的依据之一。鄂西建始地区中二叠统孤峰组硅质岩中含有极其丰富的放射虫化石。通过对该区罗家坝剖面孤峰组硅质岩段中的放射虫化石进行了详细的鉴定,获得放射虫5属16种,主要由阿尔拜虫类(Albaillellids),球形多囊虫类(Spherical polycystine)和十字多囊虫类(Stauraxon polycystine)组成。根据特征放射虫分布,该剖面自下而上依次为Pseudoalbaillella globosa带、Follicucullus monacanthus带和Follicucullus scholasticus带,并可与日本西南部、美国Oregon地区、苏皖地区及广西钦州地区同时代的放射虫带进行精确对比。根据放射虫带的对比可确定该剖面地质年代为中二叠世的茅口期,年代地层为瓜德鲁普统的沃德阶-卡匹敦阶。茅草街剖面孤峰组地层主要由黑色硅质岩和泥岩组成,可以细分为四段：(1)硅质岩与泥岩互层段；(2)硅质岩段；(3)夹灰岩透镜体炭质泥岩段；(4)泥岩与粉砂岩夹薄层灰岩段。沉积学和矿物学特征指示缺氧的上升流环境。经过对剖面中放射虫样品的分离与鉴定,获得放射虫10属27种。依据放射虫组合,也可以划分为3个放射虫带：Pseudoalbaillella globosa带、Follicucullus monacanthus带和Follicucullus scholasticus带。其年代地层分别对应于上罗德阶-沃德阶、沃德阶-下卡匹敦阶和下卡匹敦阶。生物(尤其是微生物)的繁盛和有利的沉积埋藏条件是形成优质烃源岩的两个最基本的条件。解决评价这两个条件问题的思路,就是应用地球生物学理论正演烃源岩形成的动力学过程。根据地球生物学理论对烃源岩形成的动力学过程的演示,解决烃源岩的两个基本问题,就转化为定量评估从生物生产力,到沉积有机质,再到埋藏有机质这三个关键环节和过程中有机质的变化及其数量和类型的问题。对孤峰组的地球生物学过程做出探索对整个扬子北缘黑色岩系烃源岩的研究有着重要的意义。根据岩性和放射虫丰度,以及生物硅、生物铜、总有机碳等指标的变化趋势,茅草街剖面和罗家坝剖面孤峰组的地球生物学构成均可划分为4个阶段。茅草街剖面阶段Ⅰ的放射虫动物群以球形放射虫为主,伴有少量阿尔拜类放射虫。根据生境型参数的划分,此阶段可能处于Ⅳ2下部浅海下部生境型,水深大致100-200m,具备相对较高的原始生产力。阶段Ⅱ岩性由硅质岩与泥岩互层转变为硅质岩,阿尔拜类放射虫大规模繁盛,同时伴有球形放射虫,但球形放射虫的丰度相对较低。说明这一时期海平面上升,海水深度加大,此阶段处于Ⅴ1上部大陆坡生境型,水深200-1000m。此时TOC和生物铜的含量都很低。由于水深的增加和低生物铜含量,生产力总体处于较低的水平。阶段Ⅲ中球形放射虫大量繁盛,而阿尔拜类放射虫丰度极低。反映了水深变浅,放射虫动物群的主导类型又由阿尔拜类放射虫转变回球形放射虫,此阶段适宜浅海放射虫的生长,处于Ⅳ1下部浅海上部生境型,水深大约60-100m。同时TOC、生物铜也呈现了与球形放射虫丰度一致的变化趋势。此阶段合适的生境型、球形放射虫的繁盛以及极高的TOC和生物铜显示了该阶段具备很好的生物组成和极高的生产力。阶段Ⅳ中几乎没有放射虫产出,说明水深进一步变浅,当时的环境已经不适合放射虫和其它硅质生物生活。生产力的演化过程由下至上可以划分为(降低-升高-衰退)3个演化阶段。剖面第一段至第二段时期,由于水深的增加,生产力呈现一个小低谷期。从第三段开始进入生产力的繁盛期,该时期初级生产力的的繁盛为后生动物提供丰富的营养物质。第四段海水环境恶化,海洋后生动物出现大量火绝,很多初级生产者已经不适应当时的海洋环境。建始罗家坝剖面中,球形放射虫的高丰度与总有机碳和生物成因二氧化硅具有很好的相关性,阶段Ⅰ中TOC含量较低,位于3.65%到14.6%,,平均值为4.51%。生物硅含量较高,最高值超过90%,平均值为75.9%。此阶段类似于茅草街剖面的阶段Ⅱ,深水分子阿尔拜类放射虫的繁盛使得它们死后壳体保留在沉积物中形成大量的生物硅,总体生产力仍然偏低。阶段Ⅱ,球形放射虫丰度有所增加,同时阿尔拜类放射虫丰度明显下降,反映了水深变浅。相对第Ⅰ阶段生产力水平呈升高趋势。阶段Ⅲ中球形放射虫和阿尔拜类放射虫丰度均进一步增加。TOC含量变化与球形放射虫呈一致趋势,达到最高值34.79%,平均值为13.3%。球形放射虫的大量繁盛以及高TOC含量说明此阶段初级生产力达到最高。阶段Ⅳ没有放射虫产出,TOC、生物硅的值均达到最低,反映了水深变浅以及环境恶化,生产力水平最低。生产力的演化过程和茅草街剖面相似,由下至上也可以分为(降低-升高-衰退)3个演化阶段。上述例子也可以说明放射虫动物群的组成和繁盛均受环境控制,其中水深是对放射虫的地球生物学行为影响较大的因素之一。放射虫的地球生物学过程是受多方而因素控制影响的,而放射虫动物群的组成、丰度、分异度等特征的变化也可以对当时的环境进行反演。球形放射虫的丰度可以作为古生产力替代指标,阿尔拜类放射虫则不能作为古生产力指标。球面放射虫中的Entactinia、Copicyntra和Paracopicyntrα能反映二叠纪高生产力。为了探讨孤峰组的沉积埋藏条件,本论文选取V/(Ni+V)、U/Th、Ce/Ce*三项指标对罗家坝剖面的氧化还原条件和沉积速率进行了分析。结果显示孤峰组黑色岩系形成于干燥气候的浅海还原环境。依据古环境氧化还原条件判定标准,该剖面的古氧化-还原条件可划分出3个明显的演化阶段,即中部为明显的厌氧环境,各指标均显示其还原程度异常强烈,下部及上部虽也以还原条件为主但缺氧程度相对稍弱。一定程度上说明氧化-还原条件是影响有机碳富集程度的重要因素之一,在热液活动较弱或海平面相对较低的阶段形成泥页岩沉积,但由于其总体上处于较为深水的沉积背景,沉积速率较低,因此泥页岩中的沉积有机碳含量较高：在热液活动较强、上升流较强以及海平面相对较高的时期发育热液成因的硅质岩沉积,此阶段由于沉积速率较高,沉积物对有机质产生稀释作用,造成硅质岩中的沉积有机碳含量偏低。应用以上地球生物学参数对研究剖面烃源条件进行评价,研究显示,孤峰组碳质泥页岩段具有最佳的生境型和生产力组成,是最有利的页岩气勘探岩层；其次是泥质硅质岩层段,亦具有良好的储气能力。孔隙是页岩层系是否具有生烃能力、储气能力和开采价值的主要标志。本论文采用场发射扫描电镜对鄂西建始中二叠统孤峰组硅质页岩、泥质灰岩和碳质页岩3类岩石采取二次电子模式扫描,发现和分析了5大类9小类孔隙,即(1)絮凝作用孔隙；(2)有机质化石孔;(3)有机质碎片沥青孔；(4)黄铁矿粒间孔;(5)矿物颗粒晶间孔;(6)微型通道；(7)微裂缝；(8)钙质化石孔；(9)碎屑与围岩间孔。研究显示：硅质页岩中发育较多的黄铁矿微球粒以及絮凝结构,有机质孔隙从纳米级至数微米；泥质灰岩中以矿物质孔隙为主,微裂缝比较发育,脆性矿物多;碳质页岩中存在大量蜂窝状孔洞和广泛分布的微裂缝,孔隙类型主要为有机质纳米孔。碳质页岩与传统储层孔隙特征具有很大差异,标志着油气储层纳米级孔隙研究的来临,是页岩气勘探最为有利的岩层。加快页岩气勘查、开发攻关,重点在于对页岩气资源进行科学评价。页岩气储层是否具有足够的天然气储量和是否具备足够的渗流能力是页岩气资源评价涉及的两个核心问题。笔者通过对页岩气储层孔隙度、渗透率、含水饱和度、裂缝等物性参数的测试意义、技术与方法的调研和分析,指出页岩气储集层的物性参数的测试和评价是页岩气勘探开发的重要课题。并结合我国页岩气储层与北美页岩气地质条件的差异和与常规天然气藏的不同,将页岩气储层烃源条件评价指标划分为沉积环境、地球化学、地球生物相和含气量四大类,同时将地球生物学烃源岩评价方法纳入页岩气储层资源评价方法之中,并作为传统烃源岩评价法的重要补充评价方法之一,为低残余有机质丰度、高热演化程度烃源岩的评价提供了一种新的探索途径。为了做好该区的页岩气勘探开发工作,有必要在进一步明确页岩的概念的基础上,对该区页岩地层进行综合研究和分类对比研究,划分出有利的页岩气勘探目标岩层和地区。笔者通过对鄂西野外露头剖面实测和钻孔岩心原始资料以及前人研究成果的收集,依照60余条剖面和钻井资料探讨扬子北缘中二叠统孤峰组分布特征和烃源岩发育规律,对冯增昭等(1993)的茅口期孤峰组古地理图做出了修正,并按三大类岩性段对孤峰组空间分布做了进一步细分。根据页岩气成藏的主控因素及目前资料现状,利用岩性地层分段厚度、地球生物学特征、有机碳含量和有机质热演化程度等参考指标,以研究区孤峰组富有机质页岩厚度大于20m,有机碳含量大于3.0%为主要评价依据,优选出有利目标区块。评价结果显示宜昌-潜江-黄石一带属于Ⅱ类选区;繁昌-径县-宿松一带属于Ⅲ类选区；建始—利川—石柱一带为Ⅰ类选区,其碳质页岩层段为今后勘探开发的最有利区带。最后采用类比法和体积法计算得到扬子北缘中二叠统孤峰组页岩气预计资源量为1.96×1012m3。更多还原

【Abstract】 Recently, the attention of the shale gas resources are constantly rising in China, the unique mode of occurrence and the continuous accumulation aggregation model in shale gas are different from the characteristics of conventional natural gas reservoirs, so the research of shale gas reservoirs is significant. Currently, the work on evaluation of the shale gas reservoir are relatively less in the domestic, we need to establish the appropriate evaluation criteria. Middle Permian stratum from the Gufeng formation in the North Margin of Yangtze outcropping abundant black shales and fossils, the organic carbon content is also high, which can be the favorable zones for shale gas exploration and development. The emerging geobiological theory, which take the forward modeling to evaluate the hydrocarbon source rocks, provides a feasible way for the area with high thermal maturity and low abundance of organic matter. It is worth exploring to apply geobiological methods on the evaluation of shale gas reservoir.The North Margin of Yangtze are mostly mountainous region, even if the outcrops are numerous, the geological conditions are poor, the traffic is inconvenient, therefore we have chosen three sections which have relatively better surface conditions and slightly better traffic to study the geological significance of shale gas, they are Luojiaba section, Maocaojie section and Tianfengping section. Using geobiological theory to do some analysis on their stratigraphic geobiology process of qualitative and quantitative, which has the typical guiding significance for shale gas exploration and development in China.Radiolarian is a marine micro-plankton. It can be used as an effective tool for the global stratigraphic correlation since they distributed widely in the ancient ocean of the world. As we known, it is one of the most important standards in stratigraphic division especially on the condition of lacking other fossils in deep-sea. Abundant radiolarians have been found in the Middle Permian Gufeng Formation in Jianshi, Hubei Province. By detailed appraisal to the radiolarians fossils,16species belonging to5genera had been identified, including the albaillellids, the spherical polycystine and the stauraxon polycystine. According to the radiolarian distribution in the sequence, three assemblage zones, Pseudoalbaillella globosa assemblage zone、Follicucullus monacanthus assemblage zone and Follicucullus scholasticus assemblage zone, are proposed. The three radiolarians zones can be compared with contemporary radiolarians zones in the southwest of Japan, Oregon region in America, and South China. According to the ages of the radiolarian assemblage zones, the Kufeng Formation in Lujiaba section of Jianshi, Hubei Province can be correlated to Maokouan stage (Middle Permian), corresponding to the Wordian stage-Capitanian stage (Guadalupian).The Gufeng Formation in Maocaojie section consists mainly of black siliceous rocks and mudstones, and can be subdivided into four beds:(1) chert and mudstone interbedded,(2) siliceous rock,(3) carbonaceous mudstone with limestone lenses, and (4) mudstone and siltstone with thin-bed limestone. Sedimentology and mineralogical characters indicate a suboxic-anoxic upwelling environment. After processing and identifying the samples from this section,27species belonging to10genera were recovered. Based on the radiolarian assemblages,3radiolarian assemblage zones are recognized, including Pseudoalbaillella globsa, Follicucullus monacanthus, and Follicucullus scholasticus assemblage zones, the three zones are assigned to be upper Roadian to Wordian, Wordian-lower Capitanian and lower Capitanian.Prosperous organisms (especially microorganisms)and favorable conditions of burial are the two basic conditions for the development of high-quality hydrocarbon source rocks. The idea to evaluate these two conditions is to apply the geobiological theory, which take the forward modeling to evaluate the dynamic process of the hydrocarbon source rocks. According to the demonstration of the dynamic process of the formation of hydrocarbon source rocks, to solve the two basic problems of hydrocarbon source rocks, is converted to quantitative assess biological productivity, the sedimentary organic matter and burial organic matter. The research of geobiological processes from the Gufeng formation has a important significance on the exploration of black rock series source rocks in the entire North Margin of Yangtze.According to the tendency of the indicators such as lithology, radiolarian abundance, biological silicon, Excess Cu and total organic carbon, the geobiological process form the Gufeng formation in Maocaojie section and Luojiaba section can be divided into four stages. In Maocaojie section, the interval1, radiolarian fauna are mainly the spherical radiolarian, accompanied by a small amount of albaillellarians. According to habitat type parameters, this interval may be in IV2lower shallow water habitat type, the depth of the water is roughly100-200m, which have a relatively high primary productivity. The interval2, lithology characters by siliceous rock and mudstone alternating layers change into siliceous rocks, albaillellarians are mass prosperity, accompanied by spherical radiolarian, but spherical radiolarian abundance is relatively low. The sea level rising during this period, the depth of the sea water increases. This interval should be in V1upper continental slope habitat type, the depth is200-1000m. At this stage, the TOC and biological Cu content is very low. Due to the increase of water depth and low biological Cu content, the productivity is low overall. The interval3, the spherical radiolarians flourish in great quantities, and albaillellarians abundance is extremely low. Reflects the depth of the water becomes shallow, this interval is suitable for shallow sea radiolarian growth, belongs to Ⅳ1lower shallow sea habitat type, the depth of the water is about60-100m. The TOC and biological Cu also presented consistent trends with spherical radiolarian abundance.The suitable habitat type and extremely high TOC at this stage shows good biological composition and high productivity. The interval4, no radiolarian is discovered from this interval, explaining the environment is not suitable for radiolarian and other siliceous biological life. The evolution of productivity can be divided into (lower-rise-recession) three evolutionary stages from bottom-up. In the period of the first and second bed from the section, due to the increase of water depth, productivity appears a small trough. The productivity boom starting from the third bed, the flowering of primary productivity in this period provide rich nutrients for metazoan. Marine metazoan extinction occurred in the period of the fourth bed, many primary producers have not adapted to the marine environment at that time.In Luojiaba section, high abundance of spherical radiolarians tends to have a good correlation with the total organic carbon(TOC) and biogenic SiO2. The interval1, TOC content is low, at3.65%to14.6%, average4.51%. Biological silicon content is higher, the highest value of more than90%, average75.9%. This interval is similar to the second interval in Maocaojie section, the shells of the deep water molecules albaillellarians remain in the sediments after their death, formed a large number of biological silicon, the overall productivity remains low. The interval2, spherical radiolarian abundance increased, at the same time, albaillellarians abundance obvious drop, reflects the depth of the water becomes shallow. The productivity levels show a trend of rise relative to the interval1. The spherical radiolarian and albaillellarians abundance are further increased in the interval3. TOC content change present a consistent trend with the spherical radiolarian, maximum34.79%, average13.3%. This interval reach the highest stage of primary productivity. The interval4, no radiolarian is discovered, the biogenic SiO2and TOC meet the minimum. The depth of the water becomes shallow and productivity reach the lowest levels. The evolution of productivity can be divided into (lower-rise-recession) three evolutionary stages similar to the Maocaojie section. The above example also illustrate the composition and flourishing of the radiolarian fauna are subject to environmental control, the depth of water is one of the influential factors on radiolarian geobiological behavior. The radiolarian geobiological processes are affected and controlled by many factors, the environment at that time can also be inversion in accordance with the changes in radiolarian fauna composition, abundance, and differentiation degree. The abundance of spherical radiolarians can be used as a good indicator for paleoproductivity, but albaillellarians can not do. The spherical radiolarians mainly include Entactinia, Copicyntra, and Paracopicyntra, and they may be index genera for the Permian high productivity.In order to research the sedimentary burial conditions of the Gufeng formation, we choose V/(Ni+V), U/Th, Ce/Ce*three indicators to analyze the redox conditions and deposition rate in Luojiaba section. Results show black rock series from the Gufeng formation form in the dry climate of shallow water reduction environment. According to paleoenvironment redox condition criteria, the oxidation-reduction conditions can be divided into three obvious evolution stages. Middle part is apparent anaerobic environment, lower and upper parts are also reduction conditions but relatively less hypoxia. Condition of oxidation-reduction is one of the important factors influencing the enrichment of organic carbon, The deposition of the shales are formed in weak hydrothermal activity during the sea level is relatively low, sedimentary organic carbon content is higher in mud shale due to the deposition rate is low. In the period of strong hydrothermal activity and upwelling, siliceous rock deposits are developed. Sediments dilute organic matter due to the high deposition rate, so the sedimentary organic carbon content is low in siliceous rock. Applying above geobiological parameters to evaluate hydrocarbon source conditions of the research sections, studies show that carbonaceous shale from the Gufeng formation has the best habitat type and high productivity, which is the most favorable strata for shale gas exploration; argillaceous siliceous rock strata also has good capacity of gas storage.The pore is the main aspect to evaluate the hydrocarbon generation capacity、gas storage capacity and exploitation value of shale series. In this paper, we use field emission scanning electron microscopy to take the secondary electron mode to scan three types of shale from the Gufeng Formation in Jianshi, which are siliceous shale, argillaceous limestone and carbonaceous shale. Five categories and nine types of pore have detected, that is (1) porous floccules;(2) pores of organic matter fossils;(3) asphalt pores from organic matter debris;(4) pores of pyrite grain;(5) intercrystal pores within mineral grains;(6) microchannels;(7) microfracture;(8) pores from calcium fossils;(9) pores between the debris surrounding rock. The main pore types in argillaceous limestone are intercrystal pores within mineral grains, microfracture and brittle mineral are well developed; In siliceous mudstone, we find many pyrite microspherulites and floccules,organopores size from the nanoscale to several microns; A large number of honeycomb holes and microfracture widely distributed in carbonaceous shale, the main pore types are organic matter nanopores. This shows:the nanoscale pore characteristics in carbonaceous shale are of great difference with traditional reservoir, which is the most favorable rock stratum for shale gas exploration.To speed up the shale gas exploration and development project, the key lies in the scientific evaluation of shale gas resources. The gas reserves and permeable capability of shale gas reservoir are the two core issues of shale gas resource evaluation. In this paper, we test the physical parameters of the shale gas reservoir, which contain porosity, permeability, water saturation and cracks, it should be pointed out that the test and evaluation of the physical parameters is the most important topics in shale gas exploration and development. We compare the shale gas reservoirs in China with the shale gas on different geological conditions in Northern American, and divide the shale gas reservoir evaluation index of hydrocarbon source conditions into four major categories, which are depositional environment, geochemistry, Geo-biological facies and gas content. We bring geobiology hydrocarbon source rock evaluation into shale gas reservoir resource evaluation method for the first time, as one of the important complement to traditional hydrocarbon source rock evaluation method.In order to accelerate shale gas exploration and development in this region, it is necessary to do some comprehensive and classified comparative study of the shale stratum on the basis of a clear definition of the concept of shale, mark out the favorable target strata and regions for shale gas exploration. Through the measurement of outcrop sections in western Hubei and the collection of boring core original data along with predecessors’studying results, according to more than60sections as well as drilling data, we have discussed the distribution characteristics and regularity of hydrocarbon source rock development from the Gufeng formation in north margin of Yangtze, we made the correction of paleogeographic map from the Gufeng formation by Feng Zengzhao et al., and made further subdivided of the spatial distribution from the Gufeng formation according to three types of lithology. On the basis of the main controlling factors of shale gas accumulation and the present status of the data, using reference index of lithostratigraphic section thickness, characteristics of geobiology, organic carbon content, organic matter thermal evolution degree and so on, choosing the organic-rich shale from the Gufeng formation in the study area that more than20m thick, organic carbon content is more than3.0%as the main evaluation basis, optimizing the favorable target block. Evaluation results show Yichang-Qianjiang-Huangshi area belongs to II selection region, Fanchang-Jingxian-Susong area belongs to III selection region, the bed of carbonaceous shale in Jianshi-Lichuan-Shizhu area are the most favorable zones for exploration and development in the future. Finally we using analogy method and volume method to calculate middle Permian shale gas resources from the Gufeng formation in the North Margin of Yangtze, the inferred shale gas resource is1.96×1012m3.更多还原