Petrogenesis and tectonic implications of the Silurian adakitic granitoids in the eastern segment of the Qilian Orogenic Belt,Northwest China

Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and systematic whole-rock geochemical data for the Haoquangou and Liujiaxia granitoids within the North Qilian orogenic belt and the Qilian Block, respectively, to constrain their petrogenesis, and the Silurian tectonic evolution of the Qilian orogenic belt. Zircon U–Pb ages indicate that the Haoquangou and Liujiaxia intrusions were emplaced at423 ± 3 Ma and 432 ± 4 Ma, respectively. The Haoquangou granodiorites are calc-alkaline, while the Liujiaxia granites belong to the high-K calc-alkaline series.Both are peraluminous in composition and have relatively depleted Nd isotopic [ε_(Nd)(t) =(-3.9 – + 0.6)] characteristics compared with regional basement rocks, implying their derivation from a juvenile lower crust. They show adakitic geochemical characteristics and were generated by partial melting of thickened lower continental crust. Postcollisional extensional regime related to lithospheric delamination was the most likely geodynamic mechanism for the generation of the Haoquangou granodiorite, while the Liujiaxia granites were generated in a compressive setting during continental collision between the Qaidam and Qilian blocks.

Preliminary Estimation of Paleoproductivity via TOC and Habitat Types:Which Method Is More Reliable?—A Case Study on the Ordovician-Silurian Transitional Black Shales of the Upper Yangtze Platform, South China

New total organic carbon （TOC） data from the two Ordovician-Silurian transitional graptolite-bearing black shale intervals, the Wufeng （五峰） Formation and the Longmaxi （龙马溪） Formation in Central Guizhou （贵州） and West Hubei （湖北）, respectively, as well as previously reported TOC data from the same intervals in other places on the Yangtze platform of South China, have been used to produce an initial estimate of the primary paleoproductivity via a conventional inverse method （i.e., Rpp.inverse）. The values of the Rpp.inverse are estimated to be 32 （43-21） gC/（m^2·a）（Wufeng Formation） and 21 （27-16） gC/（m^2·a） （Longmaxi Formation）. Also, simultaneously, the habitat types （i.e., HT; cf., BA： benthic assemblage） and their temporal and spatial changes have been documented from the same succession, and an initial estimate of the primary paleoproductivity has been produced using a forward method （i.e., Rpp-forward） Beingbounded mainly by the peritidal to inner-shelf environment shelly-facies or mixed-facies successions with BA1 to BA3 faunas both at the top and the base, which indicates the habitat types from HT Ⅱ to HT Ⅲ2, the biohabitat type of the two graptolite-bearing black shale intervals can be limited to HT III to HT IV, corresponding to the inner shelf to the outer shelf, with depths from roughly 60 m to 200-300 m. Based on the current data from the South China Sea and the southern part of the East China Sea, values of Rpp-forward should be about 100 to 400 gC/（m^2·a）. The difference in the results via the two methods suggests that paleoproductivity estimates from the geological strata need to be made cautiously, with particular attention paid to the paleogeographic setting, oxic-anoxic conditions, as also the preservation factor of organic carbon.

Enrichment characteristics and exploration directions of deep shale gas of Ordovician-Silurian in the Sichuan Basin and its surrounding areas,China

The enrichment characteristics of deep shale gas in the Ordovician Wufeng-Silurian Longmaxi formations in the Sichuan Basin and its surrounding areas are investigated through experiments under high temperature and high pressure,including petrophysical properties analyses,triaxial stress test and isothermal adsorption of methane experiment.(1)The deep shale reservoirs drop significantly in porosity and permeability compared with shallower shale reservoirs,and contain mainly free gas.(2)With higher deviatoric stress and axial strain,the deep shale reservoirs have higher difficulty fracturing.(3)Affected by structural location and morphology,fracture characteristics,geofluid activity stages and intensity,deep shale gas reservoirs have more complicated preservation conditions.(4)To achieve the commercial development of deep shale gas reservoirs,deepening geological understanding is the basis,and exploring reservoir simulation technology befitting the geological features is the key.(5)The siliceous shale and limestone-bearing siliceous shale in the Metabolograptus persculptus-Parakidograptus acuminatus zones(LM1-LM3 graptolite zones)are the high-production intervals for deep shale gas and the most favorable landing targets for horizontal drilling.Deeps water areas such as Jiaoshiba,Wulong,Luzhou and Changning with deep shale reservoirs over 10 m thickness are the most favorable areas for deep shale gas enrichment.It is recommended to carry out exploration and development practice in deep-water shale gas areas deposited deep with burial depth no more than 5000 m where the geological structure is simple and the shale thickness in the LM1-LM3 graptolite zone is greater than 10 m.It is better to increase the lateral length of horizontal wells,and apply techniques including high intensity of perforations,large volume of proppant,far-field and near-wellbore diversions to maximize the stimulated deep reservoir volume.

A New Species of Jiangxialepis(Galeaspida)from the Lower Telychian(Silurian)of Jiangxi and its Biostratigraphic Significance

A new species of Shuyuidae(Eugaleaspiformes,Galeaspida),Jiangxialepis jiujiangensis sp.nov.,is described from the lower Telychian(Llandovery,Silurian)Qingshui Formation in Jiujiang,Jiangxi Province,China.The new species differs from the type species J.retrospina from Wuhan,Hubei Province in its sharp and posteriorly positioned median dorsal spine and narrow spine-shaped inner cornual processes.The Silurian strata in Xiushui–Wuning area has provided a standard framework for the correlation of Silurian shallow marine red beds in South China.Thus,the finding of J.jiujiangensis from the Silurian Lower Red Beds(LRBs)in Jiangxi Province bears very important biostratigraphic significance.It can directly compare to Jiangxialepis retrospina from the Fentou Formation in Wuhan,Hubei Province in the genus level.This indicates that the age of the fish-bearing strata in Wuhan is most likely to be the early Telychian rather than middle Telychian as previously assumed.

不同构造单元页岩孔隙结构差异及其油气地质意义——以四川盆地泸州地区深层页岩为例

不同构造单元页岩储层品质、含气性差异明显,构造改造作用对页岩气勘探开发具有控制作用,但关于深层页岩气的构造控制作用机理研究较少,相关认识尚不明确,制约了深层页岩气的勘探开发。为此,通过“岩心—薄片—扫描电镜”多尺度观察、全岩矿物X射线衍射分析、核磁共振等技术手段,对比分析了四川盆地南部泸州地区不同构造单元上奥陶统五峰组—下志留统龙马溪组深层页岩孔隙结构和储层特征的差异,探讨了不同构造单元页岩孔隙结构差异与储层品质的耦合关系,明确了页岩气产量差异的内在地质原因,落实了构造改造作用下的页岩气勘探开发有利区。研究结果表明:①向斜区页岩主要以有机质孔隙、非构造裂缝为主,孔径大;背斜区页岩孔隙结构被强烈改造,以矿物粒间孔、构造裂缝为主,矿物粒间孔狭长且定向排列,孔径小。②向斜区构造相对稳定,有机质孔隙、矿物粒间孔以及成岩裂缝保存较好,宏孔占比高,储集性能好,含气量和产量高;背斜区页岩储层发育大量构造裂缝与断层,孔隙和成岩裂缝被压实,孔径减小,储集性能变差,含气量和产量低。③距盆缘剥蚀区越远,构造越稳定的单元,保存条件越好,该类构造单元页岩储层越发育,含气量和产量越高,页岩气勘探开发潜力越大。结论认为,构造运动对于压力系统的影响是形成不同构造单元深层页岩孔隙结构特征差异的重要因素,并控制了页岩储层的含气性与产量;向斜区深层保存条件好,远离剥蚀区,为勘探开发的最有利区,该认识可为深层页岩气勘探开发提供技术支撑。

东昆仑大格勒农场南辉长岩锆石U-Pb年代学、地球化学特征及地质意义

东昆仑志留纪岩浆活动强烈,记录了东昆仑造山带原特提斯洋演化晚期大洋俯冲阶段与碰撞阶段转换地质过程。本次研究对东昆仑大格勒农场南志留纪基性侵入岩开展了详细的岩相学、岩石地球化学、锆石U-Pb年代学和Hf同位素研究,以确定其形成时代、岩石成因和构造环境。研究结果表明大格勒农场南辉长岩的结晶年龄为430.2±2.4 Ma,形成时代为中志留世。辉长岩SiO_(2)(51.40%~53.66%)含量较低,MgO(18.56%~22.16%)和FeO^(T)(7.54%~10.64%)含量高,Mg^(#)为79~82。微量元素富集Rb、Th、Ba、Cs等大离子亲石元素(LILE),亏损Nb、Ta、Ti等高场强元素(HFSE),具有高Ni(276~973μg/g)、Cr(2152~3574μg/g)和Sc(35.5~53.1μg/g)含量,低Nb/Ta值(3.23~8.68)和εHf(t)值(-7.3~-3.6)。大格勒农场南辉长岩的地球化学组成具有岛弧基性岩特征,其成因可能是流体和俯冲沉积物加入的富尖晶石橄榄岩部分熔融的结果。综合区域资料表明,大格勒农场南辉长岩形成于东昆仑原特提斯洋俯冲晚期阶段,进一步限定原特提斯洋晚期俯冲与碰撞转换时限为中志留世,随后转入碰撞造山阶段。

Enlightenment of calcite veins in deep Ordovician Wufeng-Silurian Longmaxi shales fractures to migration and enrichment of shale gas in southern Sichuan Basin, SW China

The relationship between fracture calcite veins and shale gas enrichment in the deep Ordovician Wufeng Formation-Silurian Longmaxi Formation (Wufeng-Longmaxi) shales in southern Sichuan Basin was investigated through core and thin section observations, cathodoluminescence analysis, isotopic geochemistry analysis, fluid inclusion testing, and basin simulation. Tectonic fracture calcite veins mainly in the undulating part of the structure and non-tectonic fracture calcite veins are mainly formed in the gentle part of the structure. The latter, mainly induced by hydrocarbon generation, occurred at the stage of peak oil and gas generation, while the former turned up with the formation of Luzhou paleouplift during the Indosinian. Under the influence of hydrocarbon generation pressurization process, fractures were opened and closed frequently, and oil and gas episodic activities are recorded by veins. The formation pressure coefficient at the maximum paleodepth exceeds 2.0. The formation uplift stage after the Late Yanshanian is the key period for shale gas migration. Shale gas migrates along the bedding to the high part of the structure. The greater the structural fluctuation is, the more intense the shale gas migration activity is, and the loss is more. The gentler the formation is, the weaker the shale gas migration activity is, and the loss is less. The shale gas enrichment in the core of gentle anticlines and gentle synclines is relatively higher.

“Rigid-elastic chimera” pore skeleton model and overpressure porosity measurement method for shale: A case study of the deep overpressure siliceous shale of Silurian Longmaxi Formation in southern Sichuan Basin, SW China

Based on analysis of pore features and pore skeleton composition of shale,a“rigid elastic chimeric”pore skeleton model of shale gas reservoir was built.Pore deformation mechanisms leading to increase of shale porosity due to the pore skeleton deformation under overpressure were sorted out through analysis of stress on the shale pore and skeleton.After reviewing the difficulties and defects of existent porosity measurement methods,a dynamic deformed porosity measurement method was worked out and used to measure the porosity of overpressure Silurian Longmaxi Formation shale under real formation conditions in southern Sichuan Basin.The results show:(1)The shale reservoir is a mixture of inorganic rock particles and organic matter,which contains inorganic pores supported by rigid skeleton particles and organic pores supported by elastic-plastic particles,and thus has a special“rigid elastic chimeric”pore structure.(2)Under the action of formation overpressure,the inorganic pores have tiny changes that can be assumed that they don’t change in porosity,while the organic pores may have large deformation due to skeleton compression,leading to the increase of radius,connectivity and ultimately porosity of these pores.(3)The“dynamic”deformation porosity measurement method combining high injection pressure helium porosity measurement and kerosene porosity measurement method under ultra-high variable pressure can accurately measure porosity of unconnected micro-pores under normal pressure conditions,and also the porosity increment caused by plastic skeleton compression deformation.(4)The pore deformation mechanism of shale may result in the"abnormal"phenomenon that the shale under formation conditions has higher porosity than that under normal pressure,so the overpressure shale reservoir is not necessarily“ultra-low in porosity”,and can have porosity over 10%.Application of this method in Well L210 in southern Sichuan has confirmed its practicality and reliability.

四川盆地东缘白马地区常压页岩气开发地质评价

涪陵气田是我国第一个实现商业开发的页岩气田,近几年年产气量稳定在70亿m^(3)以上,开发效果良好。随着开发需求不断增大,开发对象由焦石坝等高压页岩气藏逐步转向了白马常压页岩气藏。2021年白马地区提交探明储量1048.83亿m^(3),地质资源基础得到夯实,而开发地质评价与目标优选是实现储量有效动用第一环。以分析化验、测井解释、地震预测、压裂试气资料为基础,开展白马地区常压页岩气开发有利层段与有利目标评价研究。研究结果表明,白马地区奥陶系五峰组-志留系龙马溪组发育深水陆棚相富有机质页岩,其中深水陆棚硅质页岩是开发最有利层段。明确了地层压力系数、孔隙度、天然裂缝、应力性质是常压页岩气开发地质评价的关键参数。以此为基础,建立了白马常压页岩气藏开发选区地质参数体系,优选白马向斜南部为开发建产第一目标,实现了规模效益建产,对常压页岩气开发具有重要借鉴意义。

四川盆地深层页岩气钻井关键技术新进展及发展展望

四川盆地页岩气资源丰富,目前深层页岩气已成为该盆地天然气增储上产的重点领域,但随着埋深增加和构造背景变化,地质工程条件将更加复杂,钻井过程中将面临井漏风险高、井下工具高温易失效、水平井轨迹控制难度大等技术难题。为此,在系统分析已完钻井实钻数据的基础上,依据深层页岩气区块地质工程特征,系统梳理了影响安全优快钻井的关键技术难点,形成了以地质工程一体化导向技术、钻井提速技术、防漏治漏与复杂防治技术为主体的深层页岩气安全优快钻井关键技术系列。研究结果表明:(1)以精细地质建模优选地质工程“双甜点”、实时靶体追踪为主的地质工程一体化导向技术,实现了地质目标的精准优选和精确追踪;(2)以“高效PDC钻头选型+个性化优化+大扭矩螺杆”高效破岩技术、“MSE+CCS”参数实时优化技术、油基钻井液地面降温+高温旋转导向技术为主的钻井提速技术,实现了页岩气钻井提速提效;(3)以井壁稳定性评价、裂缝性漏层识别、井漏与复杂防治为主的复杂防治技术,从源头降低了井下漏失和卡钻风险。结论认为:(1)形成的深层页岩气安全优快钻井技术,显著提高了机械钻速和铂金靶体钻遇率,在现场规模化推广应用200余口井,单井平均钻井周期降低42.7%,钻井提速效果显著,有力支撑了深层页岩气效益规模开发;(2)深层页岩气钻井将聚焦“地质工程一体化、水平段一趟钻、防漏治漏及智能钻井决策”等方面的技术攻关。

深层富有机质页岩孔隙结构分形特征及其地质意义——以四川盆地威远地区下志留统龙马溪组为例

与中、浅层页岩不同,四川盆地南部地区上奥陶统五峰组—下志留统龙马溪组深层富有机质页岩经历了复杂的成岩作用,发育不同的孔隙结构,影响页岩气的赋存状态。为了探讨深层富有机质页岩的孔隙结构、分形特征及其对页岩气富集的影响,以该盆地南部威远地区龙马溪组页岩为研究对象,综合运用有机碳分析、X射线衍射、高分辨率扫描电镜和低温氮气吸附等测试手段,定量表征研究区深层富有机质页岩储层的基础参数及其孔隙结构特征;并运用FHH分形理论,结合低温氮气吸附实验,计算页岩孔隙分形维数,讨论孔隙结构的影响因素及其地质意义。研究结果表明:(1)研究区龙马溪组深层页岩有机质含量(TOC)高,平均值为2.04%,石英等脆性矿物含量占38.00%~73.00%;(2)龙马溪组深层页岩储层普遍发育墨水瓶状有机孔、狭缝型或平板状无机孔等,BET比表面积介于1.252~28.676 m^(2)/g,BJH孔体积介于0.013 192~0.063 874 cm^(3)/g;(3)深层页岩孔隙分形具有明显的分段性,分形维数D_(2)>D_(1),孔隙结构受页岩组成控制,分形维数受控于比表面积和孔径,且与TOC密切相关;(4) LM1—LM3笔石带沉积的富有机质硅质页岩TOC高、分形维数D_(1)和D_(2)值大,介孔BET比表面积和BJH孔体积最大,既有较多的气体吸附位点赋存吸附气,又有良好的孔隙空间贮存游离气,是深层页岩气富集的“甜点段”。结论认为,综合页岩品质参数和分形维数特征可有效评价页岩气富集的“甜点段”,并对实现深层页岩气的增储上产具有现实的指导意义。

沉积矿床中重要(变价)金属元素与古海洋环境关系综述--以新元古代-早古生代扬子板块周缘为例

对氧化—还原敏感元素和生命必需元素地球化学性质和相关沉积矿产形成机制及其时空分布特征的分析、总结和归纳,有助于对古海洋环境演化与相关沉积矿产形成关系的深入认识,这对沉积矿床学理论的发展具有重要意义。新元古代南华纪—早古生代早志留世,扬子板块周缘黑色岩系中依次沉积了举世瞩目的南华纪锰矿、震旦纪—早寒武世沉积磷块岩、早寒武世重晶石矿、镍—钼—钴多金属矿、钒矿和早志留世铀矿的完整沉积矿床系列,不同时代地层、同一时代不同沉积环境地层赋存不同类型的沉积矿产,有必要对其成矿机理进行系统研究、总结和归纳。笔者等在对氧化—还原敏感金属元素、生命必需元素和海底热液元素等元素地球化学性质综述的基础上,兼论了它们在结合黄铁矿矿物学对氧化—还原环境、生物生产力和盆地限制性分析方面具体作用;进一步结合新元古代—早古生代扬子板块古环境演化特征,对扬子板块周缘特定时代中特定沉积矿产的分布、成因机理进行分析、总结和归纳;最终得出扬子板块周缘相关沉积矿产,是在全球氧化事件、冰期—间冰期、Rodina大陆裂解大背景下,海洋中成矿金属元素得到长期积累,在特定时代区域性海水—海底热液—生物作用(根据不同矿种各有侧重)影响下,在相关重要元素地球化学性质的控制下、局部区域特殊氧化—还原环境的控制下形成的特定矿产的初步认识。最后,结合相关沉积矿床研究中存在的问题,提出下一步解决方案与展望。

四川盆地五峰-龙马溪组黑色页岩中钾质斑脱岩U-Pb年代学及其成因环境研究

中国华南地区晚奥陶世末期—早志留世初期沉积五峰—龙马溪组黑色页岩的同时,也发育有多套钾质斑脱岩层,斑脱岩层的多次出现证实华南地区该时期曾间歇性发生了火山活动,但对于斑脱岩的来源尚存在分歧。本文选取了四川盆地多个五峰—龙马溪组剖面内发育较多层且厚度较大的斑脱岩为研究对象,通过野外考察和岩石矿物学、元素地球化学、锆石年代学等分析方法,对四川盆地五峰组—龙马溪组黑色页岩内所发育斑脱岩的年龄、火山活动持续时间及火山灰来源进行了分析研究。野外观察显示,钾质斑脱岩颜色醒目,易于区分,且具有一定的可塑性,多与黄铁矿条带或集合体共生。X衍射结果显示,其主要由黏土矿物和非黏土矿物组成,其中黏土矿物由伊利石和伊蒙混层组成,非黏土矿物以石英、长石、方解石、白云石和黄铁矿等为主。钾质斑脱岩主量元素以高K_(2)O含量、低TiO_(2)含量为特征,稀土元素成分分析显示,其轻稀土轻微富集、重稀土亏损,具负铕异常,球粒陨石标准化稀土配分曲线具有右倾的特点;对各斑脱岩内的锆石进行LA-ICP-MS定年研究,结果表明,斑脱岩的形成年龄在(448±2)Ma~(440.4±5.6)Ma之间,证实该时期火山活动延续了至少8 Myr;岩浆判别图(Nb/Y–Zr/TiO_(2))指示这些钾质斑脱岩的原始岩浆为中酸性成分;依据微量元素特征和构造环境判别图(Nb–Y,Y+Nb–Rb,Zr–TiO_(2),Hf/3–Th–Ta,Nb/Yb–Th/Yb),初步认为原始岩浆形成于岛弧环境。据斑脱岩层数及厚度自北向南逐渐减少的事实,及现阶段华南大地构造性质的新认识,认为其来源可能与扬子北缘早古生代秦岭洋闭合过程中的板块俯冲有关。

川南长宁地区奥陶系五峰组—志留系龙马溪组页岩气储层低电阻率响应特征及主控因素

以川南长宁地区NX22井五峰组—龙马溪组低电阻率页岩气储层为例,利用岩心矿物组分、扫描电镜、总有机碳(TOC)含量、含水饱和度测试及测井曲线等资料,确立了低电阻率页岩气储层岩石体积物理模型,采用随机法构建了三维数字岩心模型,进而利用有限元数值模拟方法模拟计算各矿物组分含量、含水饱和度及有机质石墨化的电阻率响应特征,并分析其主控因素。研究结果表明:(1)长宁地区五峰组—龙马溪组低电阻率页岩气储层岩石体积物理模型由骨架(石英、长石、方解石和白云石等)、黏土矿物、黄铁矿、未石墨化有机质以及石墨化有机质、孔隙6个部分组成。(2)三维数字岩心模型的长、宽、高分别为100×100×100像素,融入了上述物理模型中的6个部分,并采用不同的颜色对导电组分进行标识,可以显示不同方向上的切片,表征低电阻率页岩气储层的组分特性。(3)黏土矿物含量、黄铁矿含量、含水饱和度以及有机质石墨化程度等4个参数增大都会造成页岩气储层的电阻率下降,而有机质的高石墨化程度(25%)和高含水饱和度(88.0%)使页岩气储层的电阻率从正常电阻率(大于15Ω·m)降到低阻甚至超低阻(小于5Ω·m),是导致研究区页岩气储层超低阻响应的2个核心因素。

北秦岭饭铺闪长岩的岩石成因及其构造意义

饭铺闪长岩的岩石成因模型可为深入认识北秦岭古生代中性岩浆作用的活动规律及深部过程提供进一步的限定。饭铺岩体两件样品的锆石U-Pb同位素年龄值分别为422.1±5.5 Ma和424.2±5.2 Ma,表明其形成于晚志留世。其锆石的^(176)Hf/^(177)Hf比值介于0.282560~0.282676,ε_(Hf)(t)值介于-8.48~14.45,T_(DM2)为1938~488 Ma。地球化学分析结果显示,饭铺岩体属钙碱性系列,均具有富硅、碱、钙和镁,Mg^(#)值介于41.7~57.4。在微量元素蛛网图中,饭铺岩体具有Nb、Ta、Ti异常。饭铺岩体的稀土总量为117×10^(-6)~171×10^(-6),(La/Yb)_(N)比值范围是6.71~18.1,δEu值介于0.82~0.95,表现为轻稀土元素富集、重稀土元素亏损的配分特征,未显示明显的负Eu异常。饭铺岩体形成于岛弧构造环境,岩浆起源于下地壳,可能受到少量幔源物质的混合,推测是商丹洋向北深俯冲作用的产物。

川南地区志留系龙马溪组页岩力学性质及微观破裂机理

为揭示页岩力学性质和微观破裂机理,对川南地区志留系龙马溪组页岩开展了X射线衍射、三轴压缩、微米CT扫描和扫描电镜测试。研究发现:页岩矿物成分和围压对其力学性质和储层物性具有显著影响。随着脆性矿物含量的增加,页岩弹性模量和峰值应力增大,指示两者具有正相关关系。随着黏土矿物含量的增加,页岩塑性增强,岩石强度降低。随着围压的增加,页岩中的裂缝逐渐闭合、孔隙变形收缩、孔隙度减小,围压越大,压缩越严重。页岩在破坏过程中主要发育矿物颗粒边界裂缝和矿物颗粒内部裂缝两种裂缝。对于力学性质相近的页岩,随着围压的增大,页岩从矿物颗粒边界裂缝占主导演变为矿物颗粒内部裂缝占主导。围压增大导致矿物颗粒内部和颗粒边界裂缝向破碎带演变,页岩发育更多的裂缝。

川南地区下志留统龙马溪组有机质热演化及其主控因素

为研究川南地区下志留统龙马溪组有机质热演化特征,根据钻井、岩性和温度实验数据,研究了现今地温场特征,利用激光拉曼光谱测定计算了龙马溪组页岩有机质镜质体反射率,以镜质体反射率(R_(o))为约束,用BasinMod盆地数值模拟技术重建了该区热流史及龙马溪组有机质热演化史。研究结果表明,川南地区龙马溪组储层沥青激光拉曼镜质体反射率(RmcR_(o))为2.7%~3.9%,有机质现均已到过成熟阶段,平面上从威远—泸州—长宁区块成熟度逐渐增加。加里东期大部分有机质尚未进入生烃门限。东吴期—印支期威远北部及渝西北部有机质处于低成熟-成熟阶段,同期长宁—宁西及泸州南部有机质分别进入高成熟和过成熟阶段。燕山期川南龙马溪组有机质普遍达到过成熟阶段。川南地区龙马溪组有机质热演化受古地貌、古埋深、峨眉山玄武岩喷发及构造隆升等地质因素的共同影响,其中古埋深及峨眉山玄武岩喷发是有机质热演化最主要的控制因素。

页岩储层渗吸过程微观孔缝演变特征及影响因素——以四川盆地渝西地区龙马溪组龙一1亚段为例

水力压裂已成为页岩气开采的重要手段,明确渗吸过程页岩储层孔隙、微裂缝的演变特征与影响因素,对指导页岩气井压后增产措施优化具有重要意义。为此,选取四川盆地渝西地区大足区块主力产层龙马溪组龙一1亚段底部黑色页岩为研究对象,开展渗吸水过程的氩离子抛光场发射扫描电镜(FE-SEM)定点观察实验,明确了渗吸水不同时间页岩储层微观孔缝演变规律。研究表明:①页岩储层渗吸水7 d后,有机质边缘有机孔出现不同程度的减小,而内部孔隙形态、大小基本不变;②粒内溶蚀孔和粒间孔会出现明显的扩溶现象,引起矿物颗粒溶蚀、脱落,增大页岩气泄气面积;③页岩储层渗吸水后不会大量萌生新的微裂缝,仅在原有微裂缝的基础上进行扩展,在吸水14 d后缝宽扩展为原来的5~10倍;④页岩储层面孔率在渗吸水后7 d达到最大值,大于7 d后微裂缝缝宽受黏土矿物持续膨胀影响出现不同程度的减小;⑤页岩储层增孔扩缝强度主要受矿物组成与孔渗性质影响,不稳定矿物与脆性矿物含量越高、粒径越大,增孔现象越明显,越有利于压后页岩气的渗流。

北秦岭二郎坪群抱树坪组沉积时代与构造环境

二郎坪群抱树坪组作为北秦岭早古生代重要的沉积记录,其研究程度较低。本文通过对抱树坪组内火山岩夹层和花岗斑岩脉进行岩石学、地球化学和锆石U-Pb测年研究,旨在进一步确定其沉积时代与构造环境。研究结果表明:豫西夏馆地区抱树坪组火山岩夹层已变质为(黑云)阳起钠长片岩,常与黑云石英片岩呈“互层状”产出;岩石原岩为安山质凝灰岩,具有相对低的SiO_(2)(52.56%~62.04%)、较高的Al_(2)O_(3)(10.70%~18.55%)、低的MgO(4.06%~6.21%)和FeO^(T)/MgO(1.23~1.81),富集轻稀土元素和大离子亲石元素Rb、Th、U、K,相对亏损高场强元素Nb、Ta、P、Ti,具镁安山质岩石的特点;结合地球化学特征及前人研究认为,抱树坪组可能形成于活动陆缘弧后盆地。获得黑云阳起钠长片岩原岩的结晶锆石U-Pb年龄为446.0±1.7 Ma,以及侵入其中花岗斑岩脉的成岩年龄为430.0±3.0 Ma,首次将抱树坪组的形成时代准确地限定为晚奥陶世至早志留世。综合区域研究成果认为,小寨组和抱树坪组在地层层序和地层时代上符合广义二郎坪群的划分方案,但大庙组、火神庙组及由小寨组和抱树坪组构成的整体三者在形成时代上表现为近于同时性,在空间上主体呈现近平行关系,可能主体属时代大体相当的不同沉积环境的产物;在大地构造属性方面,认为二郎坪群是在约470 Ma之前由于商丹洋向北俯冲而形成的火山岛弧,在470~436 Ma转化为弧后盆地,至约430 Ma之前最终完成消减闭合。

页岩气运移证据及其动态富集模式——以四川盆地南部深层页岩气为例

页岩气存在运移现象,但页岩气运移现象对页岩气富集的影响尚不明确。为了查明深层页岩气运移证据及其富集模式,以四川盆地南部下志留统龙马溪组深层页岩气藏为例,基于页岩气藏天然气地球化学特征、赋存于顺层低角度裂缝中方解石脉包裹体特征、储层孔隙结构,查明了页岩气运移通道及运移能力,并结合典型气藏解剖,划分了龙马溪组页岩气动态富集模式。研究结果表明:①页岩气藏流体势场指示运移方向与气体组分指示方向一致,表明页岩气存在运移现象,且赋存于顺层裂缝中的流体包裹体揭示了研究区龙马溪组页岩气存在2期运移,分别发生在生烃高峰和后期抬升阶段;②现今研究区龙马溪组页岩储层存在满足页岩气运移的孔隙,且龙马溪组页岩孔隙以满足菲克扩散的孔隙为主,其次为满足滑脱渗流的孔隙和满足达西渗流的孔隙;③页岩气运移对页岩气富集具有重要的影响,研究区可划分出高抬升过渡带富集型、断裂散失背斜过渡带富集型、断裂散失向斜核部富集型、高部位富集型、弱运移能力断裂散失型5种页岩气动态富集模式。结论认为,在地质历史时期,页岩气存在运移现象,多期次的运移现象决定了现今的页岩气富集程度与富集区的优选。