Geochemical Characteristics of the Upper Permian Longtan Formation from Northeastern Sichuan Basin:Implications for the Depositional Environment and Organic Matter Enrichment

A set of organic-rich shales of the upper Permian Longtan Formation,which is widely developed in the northeastern part of the Sichuan Basin,is a key formation for the next step of exploration and development.At present,most studies on this set of formations have focused on the reservoir characteristics and reservoir formation mechanism of the shales,and basic studies on the palaeoenvironment and organic matter(OM)enrichment mechanism have not been fully carried out.In this paper,we recovered the sedimentary palaeoenvironment by mineralogical,elemental geochemical and organic geochemical analyses,and explored the enrichment mechanism of OM under the constraints of palaeoenvironmental evolution.The shales can be divided into two stages of sedimentary evolution:compared with the shales of the Lower Longtan Formation,the shales of the Upper Longtan Formation are relatively rich in quartz,poor in clay and carbonate minerals,and the OM type changes from typeⅢto typeⅡ_(2).The depositional environment has undergone a change from sea level rise,from warm and wet climate to dry and cold climate,and from oxygen-poor condition restricted to open reduction environment;the land source input has decreased,the siliceous mineral content has increased,the biological productivity has improved,and the deposition rate has changed from high to low.A depositional model was established for the shales of the Longtan Formation,reflecting the differential reservoir formation pattern of organic matter.For the Lower Longtan Formation shales,the most important factors controlling OM content are terrestrial source input and deposition rate,followed by paleoclimate and paleooxygen conditions.For the Upper Longtan Formation shales,the most important controlling factor is paleo-productivity,followed by sedimentation rate.The depositional model constructed for the Upper and Lower Longtan Formation shales can reproduce the enrichment of organic matter and provide a basis for later exploration and development.

Geochemical characteristics of the Permian Changxing Formation reef dolomites,northeastern Sichuan Basin,China

The recent discovery of deep and ultra-deep gas reservoirs in the Permian Changxing Formation reefs, northeastern Sichuan Basin is a significant development in marine carbonate oil ＆ gas exploration in China. Reef dolomites and their origins have been major research topics for sedimentologists and oil ＆ gas geologists. The petrography, trace element and isotope geochemistry of the reef dolomites indicated that the dolomites are characterized by low Sr and Mn contents, relatively low Fe contents, very similar δ13C and 6180 values and very different 87Sr/86Sr ratios. Although the calculated results of the fluid mixing suggested that a mixture with 85%-95% meteoric water and 50/o- 15% seawater seemed to be the dolomitizing fluids of the reef dolomites, the low Mn contents, relatively low Fe contents, high δ13c values and high homogenization temperatures of the dolomites did not support that there were large proportions of meteoric water in the dolomitization process, and the 87Sr/86Sr ratios which were close to coeval seawater also did not support the possibility of the mixture of deep-burial circulated fluids from clastic rocks. High temperature deep-burial circulated seawater with low Mn and Fe contents, high Sr content and high δ13C values from the dissolution of widely distributed Triassic evaporites during the burial diagenetic processes （including dehydration of water-bearing evaporites） could have been the dolomitizing fluids of the reef dolomites.

Formation mechanism of reservoir oolitic dolomite in Lower Triassic Feixianguan formation, northeastern Sichuan Basin, southwest China

A series of marine natural gas fields were recently discovered in oolitic dolomites of the Lower Triassic Feixianguan formation, northeastern Sichuan Basin, southwest China. The mechanism forming these reservoir dolomites is debatable, limiting the ability to characterize these reservoir successfully. Based on the investigation of the representative Dukouhe, Luojiazhai, and Puguang areas, this issue was addressed by examining the distribution, petrology, and geochemistry of the dolomites, the most comprehensive study to date was provided. Dolomitization occurred at a very early stage of diagenesis, as shown by the petrological features of the rock fabric. Vadose silt, which is composed primarily of dolomitic clasts, is found in the primary and secondary pores of the oolitic dolomite. This indicates that the overlying strata were subjected to dolomitization when the Feixianguan formation was located in the vadose zone. Therefore, it may be inferred that the dolomitization which occurred before the formation was exposed to meteoric conditions. The spatial distribution and geochemical characteristics of the dolomite indicate that dolomitization occurred as a result of seepage reflux. The degree of dolomitization decreases with increasing distance from the evaporative lagoon. Furthermore, the type and porosity of the dolomite vary in different zones of the upward-shoaling sequence, with the porosity gradually decreasing from the highest layer to the lowest layer. This reflects a close relationship between dolomitization and seawater evaporation during the formation of the dolomite. Geochemical analysis provided further evidence for the relationship between the dolomitization fluid and the coeval seawater. The 87Sr/86Sr and 813C isotopes, as well as the abundances of trace elements, Fe and Mn, indicate that seawater concentrated by evaporation acted as the dolomitization fluid. These results also show that dolomitization most likely occurred in a semi-closed diagenetic environment. Therefore, the main mechanism of oolitic dolomite formation is seepage reflux, which occurred at an early stage of diagenesis.

Platform Edge Reef and Bank Structure and Depositional Model of Changxing Formation in Panlongdong Section,Xuanhan,Northeastern Sichuan

The Changxing （长兴） Formation has two sequences （sql and sq2） in the Panlongdong （盘龙洞） Section, Xuanhan （宣汉）, northeastern Sichuan （四川）. It belongs to the platform edge facies belt, rich in reefs and banks, which were developed in the highstand system tract （HST） of sql and sq2, respectively. During third-order relative sea level dropping, the platform edge reef bank were mainly developed in the overall progradation parasequence sets. The platform edge reefs were developed in three phases, while platform edge banks in two phases. Outcrop observation and microscopic identification for platform egde reefs and banks in the section show that the three-phase-reefs are all composed of reef base and reef core, with string of tube sponge as the major reef-building organisms and fiber sponge, hydrazoan and bryozoans as the minor, while the reef-attached organisms mainly being fo- raminifera, brachiopod, echinoderm and ostracod. The first-phase-reef rock type is baffling reefs, the second phase baffling reefs and framework reefs assembles, the third phase framework reefs. Typically, the second phase reefs were developed with the maximum sedimentary scale and thickness, with the most abundant reef-building organisms and reef-attached organisms, showing best physical properties for reservoirs. The platform edge banks mainly consists of gravel debris and ooide grains, mostly dolomized. The dolomitizition in the second phase was relatively intense, favoring good reservoirs.

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.

Reef Types and Sedimentation Characteristics of Changxing Formation in Manyue-Honghua Section of Kaixian,Northeastern Sichuan Basin

In Changxing （长兴） stage, Manyue （满月）-Honghua （红花） Section of Kaixian （开县）, northeastern Sichuan （四川） Province was located in the platform-margin slope, which was the advantage area of reef-shoal depositional system developing. The strata of Changxing Formation are continuously exposed on both Honghua Section and Manyue Section. Four and two depositional cycles ean be identified in Honghua Section and Manyue Section, respectively. They are all platform-margin reef-shoal deposits. Their lithologic associations have obvious sequence, which is as follows： micrite bioclast limestone, bafflestone, bindstone, framestone, and bioclast limestone, in order from below. The paleontological assemblages are controlled by water depth and genetic facies. Six paleontological as- semblages can be identified in Honghua Section and Manyue Section; they are coral-calcareous algaecalcareous sponge assemblage, calcareous sponge-calcareous algae assemblage, calcareous spongecalcareous algae-coral-bryozoan assemblage, calcareous sponge-calcareous algae-hydra assemblage, calcareous sponge-calcareous algae-hydra-bryozoan assemblage, and calcareous sponge-calcareous algae-hydra-bryozoan-coral assemblage. The study of lithologic associations and paleontological assemblages indicates that the water body shallowed upward in both the growth cycle of a single reef and the higher-grade depositional cycle. According to the water depth types of reef （bioherm） developing, three different reef-shoal depositional systems can be identified in study area： deep-water-type bioherm, transitional-type reef （bioherm）, and more shallow-water-type reef.

Isotopic evidence of TSR origin for natural gas bearing high H_2S contents within the Feixianguan Formation of the northeastern Sichuan Basin, southwestern China

The northeastern area of Sichuan Basin, southwestern China, is the area with the maximal reserve of natural gas containing higher hydrogen sulphide (H2S) that has been found among the petroliferous basins of China, with the proven and controlled gas reserve of more than 200 billion cubic meters. These gas pools, with higher H2S contents averaging 9%, some 17%, are mainly distributed on structural belts of Dukouhe, Tieshanpo, Luojiazhai, Puguang, etc., while the oolitic-shoal dolomite of the Triassic Feixianguan Fm. (T1f) is the reservoir. Although many scholars regard the plentiful accumulation of H2S within the deep carbonate reservoir as the re-sult of Thermochemical Sulfate Reduction (TSR), however, the process of TSR as well as its residual geological and geochemical evidence is still not quite clear. Based on the carbon iso-topic analysis of carbonate strata and secondary calcite, etc., together with the analysis of sulfur isotopes within H2S, sulphur, gypsum, iron pyrites, etc., as well as other aspects including the natural gas composition, carbon isotopes of hydrocarbons reservoir petrology, etc., it has been proved that the above natural gas is a product of TSR. The H2S, sulphur and calcite result from the participation of TSR reactions by hydrocarbon gas. During the process for hydrocarbons be-ing consumed due to TSR, the carbons within the hydrocarbon gas participate in the reactions and finally are transferred into the secondary calcite, and become the carbon source of secon-dary calcite, consequently causing the carbon isotopes of the secondary calcite to be lower (?18.2‰). As for both the intermediate product of TSR, i.e. sulfur, and its final products, i.e. H2S and iron pyrites, their sulfur elements are all sourced from the sulfate within the Feixianguan Fm. During the fractional processes of sulfur isotopes, the bond energy leads to the 32S being re-leased firstly, and the earlier it is released, the lower δ 34S values for the generated sulphide (H2S) or sulfur will be. However, for the anhydrite that participates in reactions, the higher the reaction degree, the more 32S is released, while the less 32S remains and the more δ 34S is increased. The testing results have proved the process of the dynamic fractionation of sulfur isotopes.

四川盆地东北部黄金口背斜三叠系富K、Li和B卤水成因和演化

四川盆地东北部地区三叠系嘉陵江组四、五段—雷口坡组一段赋存丰富的卤水资源,卤水中富集K、Li、B等元素,具有潜在的开发利用价值。长期以来,一般认为川东北三叠系中卤水因溶解地层中的钾盐矿物而富集K物质,但这一认识并没有得到确证,此外,对卤水中Li和B的成因和演化鲜有报道。本文以川东北三叠系深层卤水为研究对象,以地球化学和稳定同位素分析为主要方法,运用聚类分析对比采自13口钻井卤水的地球化学数据。与海水相比,区内深层卤水中的K^(+)、Ca^(2+)、Li和B明显富集,而Mg^(2+)和SO_(4)^(2-)则相对亏损。卤水的^(87)Sr/^(86)Sr和δ^(34)S值均与卤水储层的^(87)Sr/^(86)Sr和δ^(34)S值相一致,进一步说明深层卤水为海水原地蒸发浓缩形成。Q型聚类分析表明,北2井和川宣地1井的卤水化学组分相似,川25井、ZK601井、恒成1井、恒成3井的卤水化学组分相近,证明川25井和ZK601卤水中K的富集是由于卤水溶解了地层中的钾盐矿物(杂卤石)。白云岩化导致了卤水中Ca^(2+)明显富集,而Mg^(2+)明显亏损,地层中赋存的硫磺和H_(2)S证明了大量硫酸被还原,使得SO_(4)^(2-)出现明显亏损。还原作用不仅导致卤水和石膏δ^(34)S的升高,而且引起了区域内石膏和卤水的δ^(34)S高于同时期海水的δ^(34)S值。嘉陵江组沉积晚期,三江地区流纹质火山岩浆喷发产生了大量携带含Li和B元素的气体和热液载体,进而被搬运至蒸发盐盆中。火山热液和气体中的Li、B具有相对较低的δ^(7)Li值和δ^(11)B值,在提升卤水中Li和B含量的同时,也降低了卤水δ^(7)Li值和δ^(11)B值,使得其低于正常海水的δ^(7)Li值和δ^(11)B值。

川东北宣汉地区海相“新型杂卤石钾盐矿”的发现、突破与前景

全球探明钾盐资源主体为古代海相可溶性固体钾盐矿床(氯化钾、光卤石),仅少量来自现代盐湖卤水钾矿。与国外不同的是,目前我国探明钾盐资源主体为现代陆相盐湖钾矿,古代海相可溶性固体钾盐找矿40余年,未获突破。四川盆地是我国主要大型海相成钾盆地之一,前人在中—下三叠统发现大量与硬石膏和白云石共伴生或互层的杂卤石,但绝大部分埋深超过2000 m,目前尚难以开发利用。2017年以来,笔者通过对四川盆地东北部宣汉盐盆普光地区卤水探井(恒成2、3井)岩芯复查,发现杂卤石主要与石盐共伴生,大量破碎的杂卤石碎屑颗粒分布于石盐基质中,KCl含量达边界工业品位以上,不同于钾石盐和光卤石,亦不同于前人发现的与硬石膏和白云石共伴生或互层的杂卤石(石膏型杂卤石),将之命名为“新型杂卤石钾盐矿”。小试和中试结果表明,该“新型杂卤石钾盐矿”可以采用对接井注水溶采,是能够得到规模化开发利用的“活矿”,是一种全新的硫酸盐+氯化物复合型海相可溶性固体钾盐矿床新类型。通过成钾条件、成矿规律综合研究,笔者提出了新型杂卤石钾盐矿“双控复合成矿”理论新认识、建立了“三高、两低、一大”综合测井识别新模型,创新理论技术指导设计部署“钾锂兼探”基准井——川宣地1井,探获厚29.46 m、氯化钾(KCl)平均含量12.03%(最高20.5%)的“新型杂卤石钾盐矿”厚层高品位工业矿层。与此同时,采用岩芯样品实测数据和测井解释数据拟合的方法,建立矿石K含量和密度参数的测井定量预测模型,结合“气钾兼探”,利用33口钻井数据,依据古代固体盐类勘查规范(2020),运用“几何法”,初步估算“新型杂卤石钾盐矿”氯化钾(KCl)资源规模:推断资源量2.45亿t(超大型)、潜在资源4.65亿t,合计7.1亿t,奠定了川东北达州市宣汉地区形成中国首个亿吨级海相钾盐基地的资源基础,取得了我国海相可溶性固体钾盐找矿的重大突破。

川东北元坝地区上三叠统须家河组天然裂缝发育特征与主控因素

川东北元坝地区上三叠统须家河组致密砂岩储层物性较差,天然裂缝的发育改善了储层物性。天然裂缝是主要的储集空间和渗流通道,对天然气的运移、成藏和高产有着重要的影响。本文根据地表露头、岩心、薄片和成像测井等资料,对元坝地区须家河组天然裂缝成因类型及发育特征进行研究,并分析控制天然裂缝发育的主控因素。结果表明,研究区主要发育构造成因的低角度和高角度剪切裂缝,主要方位为NW-SE(300°±10°)和NEE-SWW(70°±5°)向,有效性好;裂缝充填程度较低,有效性好。构造部位、岩性和岩层厚度为影响裂缝发育的主要因素。鼻状构造部位及断层上升盘距离断层面400 m以内、垂直断距在60~120 m之间、北西向断层延伸线拐点附近为裂缝发育的有利部位,有利于天然气高产;中细粒石英砂岩和细粒长石岩屑砂岩中裂缝最为发育;高能量环境规模砂体(高石英含量,低泥质含量)更有利于裂缝发育;裂缝发育程度与岩层厚度呈明显的负相关关系,当岩层厚度小于1 m时,裂缝密度大,发育程度高。

川东北地区二叠系大隆组页岩储层特征及其主控因素

川东北地区二叠系大隆组发育一套海相优质页岩,页岩储层控制了页岩气的富集。以大隆组深水陆棚相页岩为研究对象,利用氩离子抛光扫描电镜、低温氮气吸附脱附法和高压压汞等测试资料,通过地球化学和矿物组成特征研究,与志留系龙马溪组、二叠系茅口组三段和吴家坪组二段等海相页岩储层进行差异性对比分析,提出了大隆组储层发育主控因素。研究结果表明:①深水陆棚相和盆地相区优质页岩发育,沿开江-梁平陆棚呈环带状分布,厚度介于20~35 m。川东北地区大隆组深水陆棚相页岩发育混合硅质页岩相和含灰硅质页岩相。南江地区深水陆棚相页岩厚度介于20~30 m,以混合硅质页岩相为主;在普光地区深水陆棚相页岩厚度相对较大,介于30~35 m,以含灰硅质页岩相为主;而靠近陆棚中间位置深水陆棚相页岩厚度略有减薄,在20 m左右,以硅质页岩相为主。②大隆组页岩储层具有“高碳、高脆、高孔、高含气”的“四高”特征。页岩为有机质发育的孔隙型储层,总体具有高孔-特低渗、微孔占比高和孔隙连通性较好的特征。③沉积环境控制了大隆组页岩储层孔隙发育程度及类型,流体超压使孔隙后期得以保存。④相比其他层系,海相页岩储层大隆组岩性组合以灰黑色硅质页岩夹薄层泥质灰岩为主,纵向灰岩夹层多,岩性非均质性强。不同层系页岩主要储集空间总体相似,均以有机质孔为主,但大隆组储层龙马溪组页岩储层孔隙度较其他层系页岩总体偏低。

川东北普光地区下三叠统蒸发岩沉积特征与演化及其对钾盐矿形成的控制作用

四川盆地中—下三叠统地层中发育大量膏-盐沉积,其中与石盐共伴生杂卤石(被命名为“新型杂卤石钾盐矿”)的大量发现和重新评估引起了近年来的广泛关注。但当前对此类杂卤石的研究主要集中在其矿物发育特征与成因类型等方面,对于其发育地层的沉积特征与演化规律的精细剖析及其对杂卤石形成的控制作用研究较少。本文利用川宣地1井连续取心的目的层段岩心资料进行了沉积微相和高精度层序地层学分析。共识别出14种沉积微相类型,并将其划分为6个微相组合,依次代表从局限台地到蒸发台地不同的沉积相带及能量、环境特征。在此基础上根据沉积微相的纵向发育演化、地层厚度以及典型诊断界面等信息,划分出4个四级沉积层序以及其内部的多个五级旋回。研究认为川东北地区与石盐共伴生的原生杂卤石是明显受不同级别海平面波动影响和控制的,主要发育在四级层序海退末期与五级旋回海侵的叠加时期,前者的强蒸发条件为杂卤石的形成提供了重要基础,但后者带来的海水补给则是其形成的必要条件。

川东北地区二叠系大隆组深层页岩气储层孔隙结构及其分形特征

页岩储层特性是影响页岩气富集和开采的关键因素之一。四川盆地北部发育的上二叠统大隆组是重要的海相优质烃源岩,而针对川东北地区大隆组页岩储层的研究还有待深入。以川东北地区大隆组深层页岩为研究对象,利用高分辨率场发射扫描电镜、二氧化碳吸附、氮吸附及高压压汞等技术,开展大隆组深层页岩储层不同孔径孔隙结构的定性—定量研究,并运用基于二氧化碳吸附的V-S模型、氮吸附的FHH模型和高压压汞的分形几何模型对不同孔径的孔隙进行分形拟合,表征页岩孔隙结构的复杂程度和非均质性特征。结果表明,川东北地区大隆组深层页岩储层发育丰富的纳米级有机孔和少量的无机孔,有机孔发育特征随有机质显微组分不同和分布形式差异而显示强的非均质性。大隆组深层页岩孔隙结构与龙马溪组深层页岩相似,以介孔和微孔为主,占总孔体积的90%以上;页岩孔隙结构主要受有机质丰度的影响。分形特征研究结果显示,深层页岩宏孔非均质性强于介孔和微孔。其原因可能为深层页岩微孔孔径较小,分布集中,成因单一,受成岩作用影响较小,孔隙结构较为简单,具有较小分形维数;而宏孔孔径较大,分布范围较广,成因多样,易受成岩作用影响,表现出强非均质性。深层页岩微孔—介孔因其丰富的储集空间和较强的自相似性,有利于页岩气的赋存、渗流和开采。

川东北地区二叠纪晚期古海洋环境与有机质富集

【目的】二叠纪晚期是一个关键的地质历史时期,地球系统在构造、火山活动、气候、古海洋环境和生物群落等方面都发生了巨大变化。重建这一时期的古地理、古气候、古海洋环境有助于理解不同地质因素的相互作用机制,及其对该时期富有机质岩系及生物演化的重要影响。【方法】通过对四川盆地建峰剖面上二叠统深水序列的沉积学和地球化学(主微量元素含量、有机碳同位素、总有机碳含量)研究,明确了该时期的古地理环境,重建了海洋初级生产力和氧化还原环境的时空演化,探讨了多种因素对有机质富集的控制作用。【结果】建峰剖面的氧化还原环境依次经历了氧化—铁化—硫化—氧化四个阶段(Ⅰ~Ⅳ),初级生产力和陆源输入均在阶段Ⅱ_(2)和阶段Ⅲ较高,上升流在阶段Ⅱ_(2)、Ⅱ_(3)、Ⅲ和Ⅳ较为发育,火山活动仅在阶段IV较为频繁。因此,建峰剖面高初级生产力可能主要受陆源物质输入的影响,而上升流的影响次之,火山活动的贡献较小。【结论】结合西北乡剖面,推测该时期川东北地区硫化水团的形成受高生产力的控制,其上侵、下退则与海平面的波动有关;大隆组沉积期间盆地中部的初级生产力受上升流影响更大,而盆地边缘的初级生产力受陆源输入影响更大;初级生产力对大隆组的有机质富集起主导作用。

川东北灯影组克劳德管富集层及其储集特征分析

【目的】近年来,继安岳气田的发现和绵阳—长宁裂陷的提出,四川盆地埃迪卡拉系—下寒武统得到了重点关注。这些油气藏的储集层主要发育在灯二段和灯四段的微生物岩和富岩溶孔隙白云岩中。通过讨论埃迪卡拉纪末期首次出现的动物骨骼化石克劳德管(Cloudina)对当时白云岩储层的潜在影响,可拓展区域油气勘探开发思路。【方法】基于四川盆地东部鹿页1井岩心资料,通过偏光显微镜、阴极发光、扫描电子显微镜观察和micro-CT分析,对灯四段顶部的岩矿特征、孔隙类型、成岩类型、成岩序列、孔隙演化进行了初步研究。【结果】川东巫溪地区灯影组顶部生物碎屑微晶白云岩中存在较丰富的管状动物化石,依据其形态特征可鉴定为Cloudina,其基质中存在大量微生物组构。识别出的孔隙类型有管状化石壳体构成的生物孔,以及基质中的粒间孔、沥青孔、晶间溶孔和晶内溶孔;识别出的主要成岩作用有多期的溶蚀作用、胶结作用以及充填作用。从重建的孔隙形态与分布来看,管状化石对生物碎屑微晶白云岩的孔隙度贡献显著,化石富集层的孔隙度至少为0.7%,而基质孔隙度仅为0.1%~0.4%。【结论】富集成层的Cloudina是灯四段局部层位中除微生物礁丘以外的另一个重要孔隙来源。这说明埃迪卡拉纪末期动物矿化骨骼的出现不仅是生物演化上的创新,也为油气储层的类型带来了深刻的改变。

岩石热解实验在页岩油储层含油性评价中的应用——以川东北地区侏罗系凉高山组为例

页岩油是保障国家长期稳产和上产的重要战略资源,含油性及可动性评价在页岩油勘探甜点预测中具有重要指导意义。采用液氮冷冻取制样和岩石热解实验方法,对川东北地区侏罗系凉高山组页岩油层系开展含油性及可动性评价实验研究和含油性影响因素分析,取得以下4点认识:(1)液氮冷冻取制样技术可有效避免样品中的轻烃损失,所获含油性参数可更为真实地反映储层含油性;(2)分段岩石热解方法可通过游离油、束缚油及固态烃含量表征储层含油性,并通过最大可动油量占比(游离油含量/总含油量)表征原油可动性;(3)凉高山组页岩油储层含油性和可动性受有机质丰度、成熟度、岩性和烃源体系的运移排烃及烃类运聚作用的共同影响,有机质丰度越大储层含油性越好,成熟度越高原油可动性越强,但储层含油性越好和可动性越强,原油越容易在储层中发生短距离运聚现象,从而改变储层含油性;(4)综合分析凉一段、凉三段的含油性、可动性、地球化学特征、物性和页岩油井的开发需求,发现凉一段为优质页岩油勘探层段。岩石热解实验手段为页岩油含油性及可动性评价提供了新思路和新方法,可有效支撑页岩油甜点区预测和开发方案设计。

川东北元坝西部须二段—须三段沉积相及其对储层控制作用

川东北元坝西部须二段—须三段是重要的油气产层。本文利用钻井岩心、测井资料和三维地震资料对川东北元坝西部上三叠统须二段—须三段沉积相类型、沉积特征、沉积模式及其对储层发育控制作用开展详细的研究,以指导该地区的油气勘探部署。结果表明,川东北元坝西部须二段—须三段主要为辫状河三角洲相和湖泊相沉积,能够识别出三角洲平原、三角洲前缘、前三角洲和浅湖4种亚相,可进一步划分出9种微相。须二段—须三段沉积时期发育两种沉积模式,须二段为缓坡型宽河道辫状河三角洲沉积模式,主要发育宽河道,砂体叠置连片;须三段为陡坡型窄河道辫状河三角洲沉积模式,主要发育窄河道,砂体沿河道呈条带状分布。须二段主要发育中粒长石岩屑砂岩和中粒石英砂岩两种有利储集岩类型,主要分布于三角洲前缘水下分流河道砂体中;须三段发育中粗粒钙屑砂岩和砂质细砾岩两种有利储集岩类型,主要分布于三角洲平原辫状河道—三角洲前缘水下分流河道过渡带砂体中。缓坡型宽河道辫状河三角洲中发育的中粒长石岩屑砂岩和中粒石英砂岩储层物性和孔隙结构明显好于陡坡型窄河道辫状河三角洲中发育的中粗粒钙屑砂岩和砂质细砾岩。

川东北地区陡山沱组页岩地球化学特征与古环境分析

下震旦统陡山沱组页岩是四川盆地震旦系成藏的主要烃源岩,是近年来海相古老地层天然气勘探的重点层位。根据川东北城口地区白包溪、柿坪两个剖面的46件样品的有机地球化学(总有机碳、岩石热解、干酪根碳同位素)和元素地球化学(主微量元素、稀土元素)特征,分析了陡二段和陡四段烃源岩的地球化学特征与沉积环境的变化情况。结果表明,该地区陡山沱组页岩有机质丰度高,总有机碳(TOC)含量在0.19%~20.38%(均值4.76%),有机质类型为Ⅰ型干酪根,成熟度已达到过成熟;黑色页岩较高的δEu异常值与异常富集V、Mn、Mo、Ba和U微量元素,揭示了该时期强烈的热液作用;稀土元素配分模式与氧化还原指标识别出川东北地区陡二段沉积时期水体在缺氧-贫氧-硫化的水体条件下反复波动,陡四段水体环境则由贫氧演变为缺氧-硫化环境,总体盆地环境水体连通性较强,沉积速率较高,上升流携带热液来源的营养元素造成了生产力的繁盛,促进了有机质页岩的形成。

川东北地区上三叠统须家河组物源分析

根据地质剖面野外考察、重点样品的重矿物含量及碎屑锆石U-Pb年龄测定,结合区域构造背景、周缘地质体年龄、地层展布特征及古水流等资料,对川东北地区上三叠统须家河组的物源进行了分析。研究结果表明:(1)川东北地区上三叠统须家河组沉积期的物源来自北东和南东2个方向,盆地腹部的七里乡地区须家河组沉积物是由东北部山前带的大巴山地质公园和东南部山前带的复平镇黑天池汇入,从山前带到腹部,沉积物粒度由粗变细,ZTR指数由小变大。(2)研究区须家河组沉积物主要来自北东方向的秦岭造山带和南东方向的江南造山带,碎屑锆石年龄总体呈现出210~282 Ma,400~500 Ma,650~850 Ma,1500~2000 Ma,2265~2600 Ma共5个年龄区间,峰值分别为~213 Ma,~427 Ma,~725 Ma,~1694 Ma,~2352 Ma,须家河组沉积年龄应不早于~213 Ma。(3)~213 Ma与勉略缝合带形成相对应,主要源自南秦岭造山带;~427 Ma与商丹洋俯冲关闭相对应,主要源自北秦岭造山带;~725 Ma与Rodinia超大陆裂解有关,江南造山带西段最可能成为该年龄段的物源;~1694 Ma年龄段锆石可能形成于Columbia超大陆拼合、裂解过程,该年龄段锆石主要来自华北板块南缘和江南造山带西段等外源区;含量较少的~2352 Ma的锆石来自再旋回物源。(4)研究区须家河组储层主要发育于北东和南东两大物源供给体系下的辫状河三角洲—滨浅湖沉积体系中,2个方向的物源控制着储层岩石类型和孔隙发育情况,使其具有较强的区域性。