Microfacies types and distribution of epicontinental shale: A case study of the Wufeng–Longmaxi shale in southern Sichuan Basin, China

For black shales,laminae and bedding are hard to identify,grain size is difficult to measure,and trace fossils do not exist.Taking the Ordovician Wufeng–Silurian Longmaxi shale in southern Sichuan Basin,China,as an example,the types,characteristics and models of microfacies in epicontinental shale are analyzed by means of full-scale observation of large thin sections,argon-ion polishing field emission-scanning electron microscopy(FE-SEM),and kerogen microscopy.The epicontinental sea develops delta,tidal flat and shelf facies,with black shale found in microfacies such as the underwater distributary channel and interdistributary bay under delta front facies,the calcareous and clayey flats under intertidal flat facies,the calcareous and clayey shelfs under shallow shelf facies,the deep slope,deep plain and deep depression under deep shelf facies,and the overflow under gravity flow facies.Basinward,silty lamina decreases and clayey lamina increases,the grain size changes from coarse silt to fine mud,the silica content increases from about 20%to above 55%,the carbonate and clay minerals content decreases from above 40%to around 10%,and the kerogen type changes from type II2 to type II1 and type I.Provenance and topography dominate the types and distribution of shale microfacies.The underwater distributary channel,interdistributary bay,clayey flat,clayey shelf,and overflow microfacies are developed in areas with sufficient sediment supply.The calcareous flat and calcareous shelf are developed in areas with insufficient sediment supply.The deep shelf shale area is divided into deep slope,deep plain,and deep depression microfacies as a result of three breaks.The formation of epicontinental shale with different microfacies is closely related to the tectonic setting,paleoclimate,and sea level rise.The relatively active tectonic setting increases the supply of terrigenous clasts,forming muddy water fine-grained sediment.The warm and humid paleoclimate is conducive to the enrichment of organic matter.The rapid sea level rise is helpful to the widespread black shale.

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.

The progress and prospects of shale gas exploration and development in southern Sichuan Basin, SW China

The Ordovician Wufeng Formation-Silurian Longmaxi Formation organic-rich shales distributed widely and stably in Southern Sichuan Basin were investigated based on drilling data.Geological evaluation of wells show that the shale reservoirs have good properties in the Yibin,Weiyuan,Zigong,Changning,Luzhou,Dazu areas,with key parameters such as TOC,porosity,gas content similar to the core shale gas production zones.Moreover,these areas are stable in structure,good in preservation conditions and highly certain in resources.The shale reservoirs have a burial depth of 4 500 m or shallow,a total area of over 2×10~4 km^2 and estimated resource of over10×10^(12) m^3,so they are the most resource-rich and practical areas for shale gas exploitation in China.Through construction of the Changning-Weiyuan national demonstration region,the production and EUR of shale gas wells increased significantly,the cost of shale gas wells decreased remarkable,resulting in economic benefit better than expected.Moreover,the localized exploration and development technologies and methods are effective and repeatable,so it is the right time for accelerating shale gas exploitation.Based on the production decline pattern of horizontal wells at present and wells to be drilled in the near future,at the end of the 13th Five Year Plan,the production of shale gas in southern Sichuan Basin is expected to reach or exceed 10 billion cubic meters per year.The resources are sufficient for a stable production period at 30 billion cubic meters per year,which will make the South Sichuan basin become the largest production base of shale gas in China.

Geological characteristics and high production control factors of shale gas reservoirs in Silurian Longmaxi Formation, southern Sichuan Basin, SW China

Marine shale gas resources have great potential in the south of the Sichuan Basin in China.At present,the high-quality shale gas resources at depth of 2000–3500 m are under effective development,and strategic breakthroughs have been made in deeper shale gas resources at depth of 3500–4500 m.To promote the effective production of shale gas in this area,this study examines key factors controlling high shale gas production and presents the next exploration direction in the southern Sichuan Basin based on summarizing the geological understandings from the Lower Silurian Longmaxi Formation shale gas exploration combined with the latest results of geological evaluation.The results show that:(1)The relative sea depth in marine shelf sedimentary environment controls the development and distribution of reservoirs.In the relatively deep water area in deep-water shelf,grade-I reservoirs with a larger continuous thickness develop.The relative depth of sea in marine shelf sedimentary environment can be determined by redox conditions.The research shows that the uranium to thorium mass ratio greater than 1.25 indicates relatively deep water in anoxic reduction environment,and the uranium to thorium mass ratio of 0.75–1.25 indicates semi-deep water in weak reduction and weak oxidation environment,and the uranium to thorium mass ratio less than 0.75 indicates relatively shallow water in strong oxidation environment.(2)The propped fractures in shale reservoirs subject to fracturing treatment are generally 10–12 m high,if grade-I reservoirs are more than 10 m in continuous thickness,then all the propped section would be high-quality reserves;in this case,the longer the continuous thickness of penetrated grade-I reservoirs,the higher the production will be.(3)The shale gas reservoirs at 3500–4500 m depth in southern Sichuan are characterized by high formation pressure,high pressure coefficient,well preserved pores,good pore structure and high proportion of free gas,making them the most favorable new field for shale gas exploration;and the pressure coefficient greater than 1.2 is a necessary condition for shale gas wells to obtain high production.(4)High production wells in the deep shale gas reservoirs are those in areas where Long11-Long13 sub-beds are more than 10 m thick,with 1500 m long horizontal section,grade-I reservoirs penetration rate of over 90%,and fractured by dense cutting+high intensity sand injection+large displacement+large liquid volume.(5)The relatively deep-water area in the deep-water shelf and the area at depth of 3500–4500 m well overlap in the southern Sichuan,and the overlapping area is the most favorable shale gas exploration and development zones in the southern Sichuan in the future.With advancement in theory and technology,annual shale gas production in the southern Sichuan is expected to reach 450×108 m3.

Sequence stratigraphy and lithofacies paleogeographic evolution of Katian Stage-Aeronian Stage in southern Sichuan Basin,SW China

Based on the lithologies,sedimentary structures,graptolite zones,inorganic geochemical characteristics,electrical data of 110 shale gas wells in southern Sichuan Basin and the mineral quantitative analysis technology of scanning electron microscope,the stratigraphic sequences of the Upper Ordovician Katian Stage-Himantian Stage-Silurian Rhuddanian Stage-Aeronian Stage are divided,the sedimentary characteristics and fourth-order sequence evolution are analyzed.The target layer can be divided into two sequences,namely SQ1 and SQ2.According to Ordovician-Silurian sedimentary background,the gamma value of the target layer and U/Th,5 maximum flooding surfaces and 12 system tracts are identified.According to system tracts and their combinations,eight fourth-order sequences are identified,namely,Pss1-Pss8 from old to new.The development period and scale of dominant shale facies from Katian stage to Aeronian stage in southern Sichuan are restored.The best-quality dolomite/calcite-bearing siliceous shale facies,siliceous shale facies,clay-bearing siliceous shale facies and feldspar-bearing siliceous shale facies mainly occur in Pss3-Pss5 of Weiyuan,Western Chongqing and Luzhou,Pss6 of Western Changning-Northern Luzhou-Central Western Chongqing and Pss3-Pss4 of Changning.The siliceous clay shale facies second in quality mainly occurs in Pss6 of Southern Luzhou-Changning area(excluding Western Changning area),Pss7 of Eastern Weiyuan-Northern Western Chongqing-Southern Luzhou and Pss8 of Northern Luzhou-Weiyuan-Western Chongqing.The fourth-order sequence evolution model of Katian stage-Aeronian stage in southern Sichuan is established.During the depositional period of Pss1-Pss8,the sea level had six regressions and five transgressions,and the first transgression SQ2-MFS1 after glaciation was the largest flooding surface.

Type and distribution of Mid-Permian Maokou Formation karst reservoirs in southern Sichuan Basin,SW China

Based on the analysis of the responses of conventional logs such as natural gamma(GR), density(DEN), acoustic interval transit time(AC), compensated neutron(CNL), dual lateral resistivity(Rlld, Rlls), and caliper log(CAL), combined with drilling data,cores, thin section and productivity of 65 wells, the reservoirs in the Mid-Permian Maokou Formation of southern Sichuan Basin were divided into four types, fractured-vuggy, pore-vuggy, fractured and fractured-cavity. The main reservoirs in high productivity wells are fractured-vuggy and pore-vuggy. The reservoirs of Maokou Formation are generally thin, and can be divided into the upper reservoir segment(layer a of the second member to the third member of Maokou Formation, P_2 m^2 a-P_2 m^3) and the lower segment(layer b of the second member of Maokou Formation, P_2 m^2 b). The two reservoir segments are mainly controlled by two grain beaches during the sedimentation of P_2 m^2 a-P_2 m^3 and P_2 m^2 b, the vertical zonation of karst, and the fractures. The upper reservoir segment is generally better than the lower one in development degree and single well productivity, and is much thicker than the lower one. It is thicker in the Yibin-Zigong-Weiyuan-Dazu area, the southwestern area of Chongqing and the southeastern area of Luzhou, while the lower segment is thicker in the Neijiang-Zigong-Luzhou area and the Dazu-Luzhou area. The areas with big reservoir thickness at tectonic slope or syncline parts are the favorable exploration areas.

Preliminary study on Late Triassic to Early Jurassic strata and floral variation in Hechuan region of Chongqing,southern Sichuan Basin

The end-Triassic mass extinction event is extensively known, however, the terrestrial response of this event is still poorly understood. Here we briefly report our preliminary results on the variation of floral diversity through the Triassic/Jurassic boundary deposits in the Tanha section of Hechuan region, Chongqing, southern China. It is recognized that the floral hiodiversity of the Hechuan region shows a distinct change through the Triassic and Jurassic transition; and the floral diversity loss reaches up to 92. 5% at species level. Meanwhile, in northeastern region of the Sichuan Basin, the floral diversity declines by about 50% across the T/J boundary at species level with a remarkable turnover of genera and species. The potential reasons and mechanisms that cause the floral diversity differentiation of the T/J boundary in the Sichuan Basin are briefly discussed in this note.

Petrophysical properties of deep Longmaxi Formation shales in the southern Sichuan Basin, SW China

Deep shale layer in the Lower Silurian Longmaxi Formation,southern Sichuan Basin is the major replacement target of shale gas exploration in China.However,the prediction of"sweet-spots"in deep shale gas reservoirs lacks physical basis due to the short of systematic experimental research on the physical properties of the deep shale.Based on petrological,acoustic and hardness measurements,variation law and control factors of dynamic and static elastic properties of the deep shale samples are investigated.The study results show that the deep shale samples are similar to the middle-shallow shale in terms of mineral composition and pore type.Geochemical characteristics of organic-rich shale samples(TOC>2%)indicate that these shale samples have a framework of microcrystalline quartz grains;the intergranular pores in these shale samples are between rigid quartz grains and have mechanical property of hard pore.The lean-organic shale samples(TOC<2%),with quartz primarily coming from terrigenous debris,feature plastic clay mineral particles as the support frame in rock texture.Intergranular pores in these samples are between clay particles,and show features of soft pores in mechanical property.The difference in microtexture of the deep shale samples results in an asymmetrical inverted V-type change in velocity with quartz content,and the organic-rich shale samples have a smaller variation rate in velocity-porosity and velocity-organic matter content.Also due to the difference in microtexture,the organic-rich shale and organic-lean shale can be clearly discriminated in the cross plots of P-wave impedance versus Poisson’s ratio as well as elasticity modulus versus Poisson’s ratio.The shale samples with quartz mainly coming from biogenic silica show higher hardness and brittleness,while the shale samples with quartz from terrigenous debris have hardness and brittleness less affected by quartz content.The study results can provide a basis for well-logging interpretation and"sweet spot"prediction of Longmaxi Formation shale gas reservoirs.

四川盆地南部向斜区二叠系岩溶孔隙型石灰岩储层成因与天然气勘探新领域

随着油气勘探程度不断提高,勘探方向逐渐从构造高部位往向斜区拓展。但是,传统认识认为向斜区岩性一般较致密,寻找向斜区优质储层成为其油气获得勘探突破的关键因素之一。为此,以四川盆地南部向斜区中二叠统茅口组石灰岩为例,基于钻井岩心、薄片、测井以及地球化学等资料综合分析,开展了向斜区孔隙型石灰岩储层特征及成因研究,并建立了储层发育模式,指出了天然气勘探新方向。研究结果表明:(1)四川盆地南部向斜区茅口组发育岩溶孔隙型碳酸盐岩储层,储层岩性主要为泥晶—亮晶生屑石灰岩和亮晶生屑石灰岩,储集空间主要为生物体腔孔、生物铸模孔及粒内溶孔等组构选择性溶蚀形成的孔隙;(2)研究区茅口组储层平均孔隙度为4.07%,平均渗透率为0.273 mD,孔隙度与渗透率有明显的正相关关系,为典型的孔隙型储层;(3)茅口组储层段的铝、钪、锆及总稀土元素含量较低,锰和铁含量也较低,碳同位素值位于中二叠世海水沉淀方解石碳同位素值分布范围内,氧同位素呈现出一定的负偏;(4)茅口组岩溶孔隙型储层的形成与沉积期微地貌及高频层序控制的准同生期岩溶有关,溶蚀流体主要为大气淡水。结论认为,岩溶孔隙型储层在盆地内普遍发育,且该类储层远离不整合面,受沉积古地貌、沉积相带控制的准同生期岩溶改造,因此,天然气勘探思路需要向“有利沉积相带规模控储”方向转变,向斜区将是盆地内未来天然气勘探的重要新领域。

四川盆地南部下寒武统筇竹寺组页岩孔隙结构特征与页岩气赋存模式

近年来,四川盆地南部地区(以下简称川南地区)下寒武统筇竹寺组页岩气勘探开发取得了实质性的突破,但是,关于筇竹寺组页岩气储层孔隙结构特征及其对页岩气赋存模式影响的研究还较为薄弱。为此,以川南地区W207井筇竹寺组页岩为例,以总有机碳含量(TOC)不小于1.0%为界,将筇竹寺组页岩划分出4个高有机碳页岩层段(H1—H4层),并基于大视域扫描电镜、流体注入法孔隙定量表征、三维分子结构建模与分子模拟等方法,研究了不同富有机质层段页岩孔隙特征,并着重分析了H3层页岩孔隙发育特征与页岩气赋存模式。研究结果表明:(1)筇竹寺组页岩纵向上孔隙发育差异较大,其中H3层页岩孔隙系统最为有利,发育粒缘缝—有机质纳米连通孔隙—有机质基质分子内孔隙3级孔隙网络,其矿物粒缘缝与有机质纳米孔隙提供了较大的游离气储集空间,页岩有机质分子结构中普遍发育微孔,提供了较大的吸附空间;(2)微孔对总吸附量的贡献随压力增高而降低,但在30.0 MPa时仍贡献了56%以上的总吸附气量;(3)高温高压下(30.0 MPa、70℃),页岩中游离气甲烷含量占总含气量的57%,当压力由30.0 MPa降低至16.5 MPa,游离气贡献总开采气量超过80%;(4)粒缘缝、有机质纳米连通孔隙和有机质基质分子内孔隙良好的配置关系为页岩气富集及开发提供了良好的连通体系,远离风化壳的超压层段有利于页岩孔隙发育。结论认为,川南地区筇竹寺组H3层页岩孔隙系统发育,具备页岩气高产地质条件,是筇竹寺组下一步重点关注层段,在此基础上寻找远离风化壳、孔隙发育的超压页岩储层是筇竹寺组选区选层的关键。

四川盆地南部地区五峰组—龙马溪组深层页岩气富集控制因素新认识

近年来,随着四川盆地五峰组—龙马溪组页岩气勘探开发迈向深层(埋深介于3500~4500 m),在四川盆地南部(下文简称川南)地区的泸州、长宁和渝西等区块深层页岩气不断取得了重要突破,展现了深层页岩气良好的开发前景。为了准确认识川南地区深层页岩在局部地区出现的低电阻率、高含水饱和度、测试微气现象,分别从页岩有机质成熟演化、页岩气源内运移特征和区域多期断裂活动影响等3个方面系统地分析了页岩气富集控制因素。研究结果表明:①高—过成熟度有机质石墨化造成了页岩电阻率和含气量明显降低,在有机质成熟度(Ro)大于3.6%以后,有机质生气能力衰竭,颗粒孔隙度明显降低,含水饱和度明显升高;②页岩气存在“源内侧向运移”特征,含气性与现今构造区带构造位置相对高低相关,表现为相对海拔高部位含气饱和度高,相对海拔低部位含气饱和度低;③Ⅰ级断裂对天然气的散失有显著的控制作用,建议距离Ⅰ级断裂1.5 km范围内勿部署实施井位,Ⅱ级断裂对含气性影响范围有限,距离Ⅱ级断层700 m以外时对页岩气体积压裂的影响较小。结论认为,充分考虑页岩有机质热演化程度、构造位置相对高低关系以及断裂发育特征等因素对深层页岩气富集的影响,有利于完善深层页岩气评价标准,对认识深层页岩气资源潜力以及优选有利区,具有重要现实意义,并可为推动实现深层页岩气规模增储和效益开发提供理论支撑。

四川盆地涪陵南地区奥陶系五峰组—志留系龙马溪组页岩古构造应力场及裂缝特征

通过岩石力学实验、声发射实验和地震资料综合解释,利用有限元数值模拟方法,对涪陵南地区奥陶系五峰组—志留系龙马溪组海相页岩古构造应力场进行了数值模拟,并结合岩心实测结果,预测了构造裂缝的发育特征。研究结果表明:①涪陵南地区裂缝主要形成期(燕山晚期)构造应力和裂缝的分布受断层、岩石力学性质和构造应力的影响,断层广泛发育的区域容易出现应力集中,并引起较大的应力梯度。②利用库伦-莫尔破裂准则预测了研究区构造裂缝的发育,同时引入剪切破裂指数R定量表征裂缝发育的强度,其值越大反映裂缝发育程度越高。窄陡断背斜和断层附近裂缝发育,以高角度剪切裂缝为主,而在宽缓向斜部位裂缝发育程度最弱,研究区五峰组—龙马溪组底部硅质页岩应力集中,裂缝最发育。③涪陵南地区海相页岩气保存有利区主要为3个区带:远离大断层的凤来向斜内部,主要构造变形期未遭受大的破坏作用,其位于应力低值区,具有良好的保存条件,为Ⅰ类有利区;白马向斜内部小断层发育,应力值位于中等水平,保存条件中等,为Ⅱ类较有利区;石门—金坪断背斜遭受到强烈改造作用,容易产生大规模剪切裂缝,破坏了保存条件,为Ⅲ类不利区。

深层天然裂缝性页岩储层水力压裂光纤监测远场应变分析

四川盆地南部地区(下文简称川南地区)深层(埋深大于4000 m)页岩储层天然裂缝发育,地应力分布复杂,水力压裂过程中套管变形等问题严重制约了页岩气资源的高效开发。为了解决深层页岩储层天然裂缝压裂过程中远场应变监测问题,采用邻井光纤(DAS)应变监测技术对泸州区块A平台2口井拉链式压裂过程进行监测,并结合压裂施工设计和储层特征对监测结果进行分析和讨论。研究结果表明:①300~350 m监测井距和泵送式套内光纤布设方式可以对远场裂缝窜通演化评估提供大量有利数据,但对压裂井主体改造区域提供的相关信息较少;②同一平台不同井压裂时远场应变响应差异可能很大,高风险井的压裂施工参数设计对远场裂缝窜通起到了关键影响作用,低风险井主要表现为跟随作用,裂缝窜通区域一旦形成,极易演变成2口压裂井共同的裂缝窜通区;③远场应变响应区域与当前压裂段相对位置可能相差200~300 m,同井不同段间的应变沟通会提前形成,与当前压裂段可能相差400~500 m;④深层页岩储层天然裂缝压裂形成的远场裂缝形态具有全新特征,包括普遍性的倾斜裂缝和挠曲段地层附近的水平层理缝2类情况。结论认为,低频DAS应变监测技术提供了深层页岩储层天然裂缝压裂过程中远场应变演化分析的新方法,可与地质工程一体化压裂设计方案、套变机理与防控研究等工作结合,助力该区深层页岩气的规模效益开发。

川南威远地区二叠系茅口组一段泥灰岩储层特征及其发育主控因素

四川盆地南部威远地区的二叠系茅口组一段(下文简称茅一段)勘探程度较低,根据早期的钻井资料所进行的铸体薄片和氩离子电镜分析认为,滑石孔缝为最主要储集空间,滑石化作用对储层贡献最大。而最新钻井实物资料显示,茅一段泥灰岩储层的储集空间类型及储层成因与前期的认识有较大偏差,因此,需要进一步明确该区茅一段泥灰岩储层发育主控因素。通过岩心观察、薄片鉴定、物性分析、氮气吸附—脱附、氩离子抛光扫描电镜和孔隙定量表征,从定性和定量的角度剖析了茅一段泥灰岩主要储集空间和储层类型,结合总有机碳(TOC)含量测定、稀土元素分析以及全岩X衍射等手段,明确了该套储层发育的主控因素。川南威远地区茅一段优质储层发育在泥灰岩中,为一套低孔、低渗裂缝—孔隙型泥灰岩储层,主要发育Ⅲ类储层,少量为Ⅱ类储层;储集空间以溶蚀孔、有机质孔和滑石孔缝为主,孔隙发育与TOC含量具有较好相关性,滑石化作用、白云岩化作用和硅化作用并未产生明显的次生储集空间,对孔隙贡献不明显;泥灰岩储层受早期溶蚀作用、沉积相和有机质丰度共同控制,早期溶蚀作用是泥灰岩溶蚀孔缝形成的关键,内缓坡浅水环境的高初级生产力和高有机质沉降率为有机质孔形成提供了物质基础。该认识可为盆地内相似油气储层的勘探部署提供理论支撑。

融合物理约束的压裂水平井产能智能预测框架构建与应用

水平井分段压裂是实现非常规油气藏有效开发的关键技术,准确预测压裂水平井产能对于井位优选和压裂参数优化至关重要。随着历史开发数据的不断积累和人工智能技术的迅速发展,数据驱动的人工智能方法为压裂水平井产能预测提供了新的渠道。为此,从压裂水平井生产物理过程出发,分析了产能智能预测的物理约束,提出了与物理过程相匹配的产能智能预测框架,并结合四川盆地南部(以下简称川南)地区页岩气开发生产数据开展了实例验证。研究结果表明:(1)压裂水平井产能智能预测需要以压裂段为单位进行特征融合处理,单井产能是由初始压裂段到末尾压裂段依次累计作用的结果,各压裂段之间存在顺序关系,各单井的因素输入维度存在差异;(2)采用循环神经网络能够完全匹配压裂段之间的顺序关系和汇聚作用,而Mask屏蔽机制则能够解决各单井压裂段数量不统一的矛盾。结论认为:(1)该智能预测模型能够学习各单井输入序列与产能之间的复杂映射关系,训练集相对误差为0.098、测试集相对误差为0.117,较循环神经网络(RNN)模型误差的下降幅度分别为37.6%和37.0%,较多层感知机(MLP)模型误差的下降幅度分别为77.3%和77.4%,展现出优异的预测性能;(2)该研究成果能够为非常规油气藏压裂水平井产能预测的技术进步和快速发展提供新的思路与借鉴。

基于构造样式的页岩气富集模式分类-以四川盆地五峰-龙马溪组为例

【研究目的】四川盆地及周缘五峰-龙马溪组页岩经历的构造活动复杂且改造作用强,构造改造程度与页岩气的聚集有着直接的影响,根据构造样式对页岩气富集模式进行划分具有重要意义。【研究方法】本文以构造分区及改造强度变化趋势为主线,整体研究四川盆地及周缘奥陶系上统五峰组-志留系下统龙马溪组页岩层系的构造分区、不同区块构造抬升时间差异,总结不同构造区的页岩气富集模式。【研究结果】通过研究不同地区五峰-龙马溪组页岩目的层系构造改造强度、构造形态、埋藏深度、埋藏抬升时间等的差异性,将四川盆地及周缘下古生界主力海相页岩层系划分为9个一级构造区和20个二级构造区。进一步研究了不同构造区典型井的构造埋藏史及生烃史,结合构造形态、保存条件及产气情况,将四川盆地及周缘划分为9种典型的页岩构造样式及页岩气富集模式:盆内大型斜坡型(威远型)、盆内低陡构造与宽缓向斜型(泸州型)、盆缘向斜型(长宁型)、盆缘复杂构造型(昭通型)、盆缘宽缓断背斜型(焦石坝型)、盆缘斜坡逆断层封堵型(丁山型)、盆外复杂背斜型(巫溪型)、盆外残留向斜型(彭水型)、盆外残留向斜逆断层封堵型(正安型),其页岩气富集及保存条件整体上依次变差。【结论】总结出的9种页岩气富集模式,概况了四川盆地内部到盆地外缘的整体构造演化及页岩气保存富集规律,可以为进一步的页岩气有利区优选提供范围和目标,更好地指导四川盆地及周缘的页岩气勘探。

页岩气井间压裂窜扰机理及影响规律

四川盆地南部地区(以下简称川南地区)页岩气水平井体积压裂改造过程中,受地质及工程等因素影响,水力裂缝易与单一方向大尺度天然裂缝沟通并过度扩展,从而诱导邻井压力快速上涨,最终导致压裂窜扰、套管变形等问题,直接影响页岩气单井产量。为此,针对川南地区页岩气储层压裂窜扰模式多样、机制认识不清以及防控效果有限等问题,建立了全耦合页岩气水平井压裂多簇同步扩展数值模拟模型,并阐明了不同类型压裂窜扰的影响规律,最后提出了有效治理压裂窜扰的方法。研究结果表明:①天然裂缝发育的储层中,水平井裂缝易沿单一方向大尺度天然裂缝优势条带扩展,直接或间接对邻井产生影响,造成其压力涨幅异常;②页岩气水平井通过避免在风险段压裂或降低改造强度在一定程度上可减轻压裂窜扰的影响;③压裂井附近存在衰竭邻井时,裂缝更易往邻井低应力区扩展产生压裂窜扰,窜扰程度与岩石孔隙弹性密切相关。结论认为,合理避开风险段射孔、控制压裂改造强度可有效降低页岩气水平井压裂窜扰的风险,该研究成果可为同类国内外页岩气区块页岩气水平井压裂开发提供技术指导。

四川盆地南部中二叠统茅口组岩溶古地貌恢复及特征

岩溶古地貌是含油气盆地沉积微相类型、分布范围及储层发育的主控因素,恢复岩溶古地貌对指导油气勘探至关重要。基于钻井、测井及地震等资料,采用沉积速率法和地层厚度对比法对四川盆地南部地区中二叠统茅口组顶部不整合界面的剥蚀厚度进行了精确计算,并根据剥蚀厚度的地区差异及古地貌指示,对岩溶古地貌单元进行了进一步划分。研究结果表明:①四川盆地南部中二叠统茅口组顶部主要发育平行不整合,仅在局部地区形成角度不整合。早中二叠世,上扬子地台内部沉积稳定,构造运动较弱,沉积速率法与地层厚度对比法相对更适用于研究区的岩溶古地貌恢复。②研究区中二叠统茅口组顶部剥蚀厚度为0~120m,其中北部剥蚀最强烈,如LG1井区、W4井区代表了岩溶古地貌地势的最高位置,向东南方向剥蚀强度逐渐减弱,地势逐渐降低;剥蚀最薄弱地区位于LS1井东北部,代表了岩溶古地貌地势的最低位置,整体呈现北部高,南部低,东北部最低的地貌格局。③研究区茅口组古地貌特征控制了岩溶作用的发育强度,可划分为岩溶高地、岩溶斜坡、岩溶盆地等3个二级岩溶古地貌单元以及溶峰盆地、溶丘洼地、丘丛谷地、丘丛洼地、丘丛沟谷、峰林平原、残丘平原等7个三级古地貌单元,其中岩溶斜坡易形成良好的储集空间,为油气圈闭的形成奠定了良好的基础,是下一步有利勘探方向。

四川盆地南部泸州—云锦地区走滑断裂构造变形特征

以多重滑脱褶皱冲断构造为主要变形的泸州—云锦地区同样发育走滑断裂。逆冲构造和走滑断裂的分类、分期厘定对于重新认识泸州—云锦地区的断裂系统具有重要意义。以泸州—云锦地区的高精度三维地震数据、钻测井数据为基础,通过平面—剖面结合精细构造解析和井—震标定分析,获得如下认识:1)北东向、北西向、近南北向等不同走向、不同级别的逆断层和褶皱带叠加、复合变形,构成了泸州—云锦地区网状的多重滑脱冲断褶皱构造变形系统。2)区内主要发育4条走滑断裂带,断层对关键界面的改造呈现出微小伸展地堑的变形特征,在剖面上则主要表现出“Y”字形负花状构造的变形样式。其中,蜀南1号走滑断裂带近南北走向,在左旋剪切作用下形成;蜀南2号、3号走滑断裂带由多条次级断层带或小型正断层左阶斜列构成,形成于右旋剪切背景。蜀南1号、蜀南2号、蜀南3号走滑断裂带均形成于二叠系沉积前(相当于泥盆纪—石炭纪)。蜀南4号走滑断裂带则呈北东走向,主体沿着背斜带的脊部发育,在右旋剪切作用下发育,形成于二叠系沉积后(相当于早-中三叠世)。蜀南4号断裂带、蜀南3号断裂带的局部区段以及主体发育在二叠系—三叠系内的逆冲断层,对志留系、二叠系、三叠系的多套源储组合具有良好的沟通作用;同时,它们对断控缝洞型储集层的形成具有积极影响,利于二叠系栖霞组、茅二段、嘉陵江组等多层系的油气聚集成藏。

方解石双晶古温标基本原理及其利用--以川南上奥陶统五峰组-下志留统龙马溪组为例

我国西部盆地深层—超深层古老碳酸盐岩层系由于缺少传统古温标/地质热温度计,其盆地热史演化与古地温场特征备受争议。笔者等介绍方解石机械双晶形成演化机制及其与变形温度相关性,以川南地区上奥陶统五峰组—下志留统龙马溪组脉体方解石为例,结合流体地球化学和埋深热史过程恢复,表明方解石机械双晶能有效揭示五峰组—龙马溪组热史特征。方解石机械双晶具有双晶位错形成、双晶增厚和合并生长增厚的3个演化过程,导致方解石不同双晶结构(薄片、板状、锥状弧形等)分别形成于低于170℃、170~200℃和大于200℃环境,且伴随温度增大具有双晶密度减小、宽度增大的趋势特征。川南威远地区五峰组—龙马溪组发育典型板状方解石双晶,双晶宽度为1~4μm、密度30~50条/mm;长宁五峰组—龙马溪组方解石双晶宽度较大(约为3μm)、密度较低(15~20条/mm)。包裹体均一温度和埋深热史综合表明,长宁地区包裹体均一温度峰值为120~140℃、160~180℃和200~220℃,其埋藏热史明显大于威远地区,它们共同揭示长宁地区五峰组—龙马溪组相对威远地区具有较高的机械双晶形成环境温度。因而,方解石机械双晶形态几何学能够作为典型的古温标应用于我国西部古老深层碳酸盐岩层系热史研究。