Genesis of the low-permeability reservoir bed of upper Triassic Xujiahe Formation in Xinchang gas field,western Sichuan Depression

The genesis of a reservoir is a result of the combined action of deposition, diagenesis, tectonic reworking, and interaction of rock and fluid and the evolutionary environment. We discuss the genetic and evolution mechanism of a low-permeability reservoir bed of the Xujiahe Formation in the western Sichuan Depression on the basis of the study of diagenesis, diagenetic reservoir facies and the diagenetic evolution sequence. The research indicated that this reservoir bed can be divided into five types of diagenetic reservoir facies, namely strong dissolution, chlorite-lined intergranular pores, compaction and pressure solution, carbonate cementation and secondary quartz increase. There are, however, just two diagenetic reservoir facies which provide low-permeability reservoir beds, namely strong dissolution and chlorite-lined intergranular pores. We also analyzed their diagenetic evolution sequences and the origin of the low-permeability reservoir bed. Besides, it was also indicated that the composition and structure of sandstones, types of sedimentary microfacies, diagenesis history as well as the tectonic reworking in later periods are the main factors controlling the formation of the low-permeability reservoir bed. The above- mentioned factors establish the foundation for the forecasting the distribution of high quality reservoir beds.

Factors controlling tight oil and gas reservoir development in the Jurassic siliciclastic-carbonate rocks in Sichuan Basin, China

The prediction of“sweet spot”of multi-lithology composite tight oil and gas reservoirs within mixed siliciclastic-carbonate sequences is a hot topic in oil and gas exploration.There are mixed lacustrine carbonate-siliciclastic rocks in the Da'anzhai Member of Ziliujing Formation in the Eastern Slope of western Sichuan Depression.The reservoir lithology is complex,and the main factors controlling the development of high-quality reservoirs are yet to be known.Based on a large number of drilling,core and thin section observation,well log and seismic data,this paper systematically studies the characteristics and factors controlling the development of the mixed siliciclastic-carbonate reservoir.The results show that the reservoir is composed primarily of coquina,sandstone,breccia and shale in lithology,and its development is mainly controlled by sedimentary microfacies,diagenesis,tectonism(fracturing)and paleogeomorphology during the sedimentary period.The effective fractures in reservoirs of the low-energy shell shoal facies are well developed with relatively good physical properties.With the change of sedimentary microfacies from low-energy shoal to high-energy shoal to arenaceous shoal,the hy-drocarbon production capacity worsens step by step.Diagenesis,such as dissolution and fracturing,has a certain effect on reservoir physical properties.The palaeogeomorphic highs and slopes had well-developed fractures during the sedimentary period which are conducive to constructive dissolution,and thus they are favorable zones for reservoir development.The development of structural fractures further amplifies the influence of dissolution;thus the fracture zones are also favorable for the devel-opment of high-quality reservoirs.The favorable sedimentary facies zone and fracture development degree serve as the core factors for the formation of high-quality mixed reservoirs.The muddy limestone with certain dissolved pores and structural fractures deposited under the low-energy shell shoal setting is of relatively high-quality reservoir in the Da'anzhai Member.

Reservoir Potential of Silurian Carbonate Mud Mounds in the Southern Sichuan Basin,Central China

Lower Silurian mud mounds of the Shinuilan Formation, located in the southern Sichuan Basin, China, have developed in open shelf settings in deeper water than shallow-water reef-bearing limestones that occur in the region. An integration of the outcrop, drill data and seismic profiles show that contemporaneous faults have controlled the boundary and distribution of the sedimentary facies of Lower Silurian rocks in the southern Sichuan Basin. Mounds appear to have developed in the topographic lows formed by synsedimentary faulting, on the sheff of the Yangtze Platform. Average mound thickness is 20 m, maximum 35 m. Mounds are composed mainly of micrite, possibly microbially bound, and are overlain by shales. Mound tops are preferentially dolomitized, with the Mg^2＋ source probably from the clay content of the mound-top carbonate. Microfacies analysis and reconstruction of the diagenetic history reveal that the mound tops have higher porosity, and are gas targets; in contrast, mound cores and limbs show pores filled by three generations of calcite cement, and therefore have a low gas potential.

Sedimentary microfacies of Member 5 of Xujiahe Formation in the Dongfengchang area, Sichuan Basin

Member 5 of the Upper Triassic Xujiahe Formation(T_(3)X_(5))in central Sichuan Basin has made a breakthrough in exploration recently.However,this new stratum has not been investigated sufficiently with respect to basic geology,making its types and distribution of sedimentary facies unclear,which severely restricts its subsequent exploration evaluation.In this study,types of sedimentary microfacies in the first sand group of T_(3)X_(5)(T_(3)X_(5)^(1))are clarified through core observation and logging interpretation using core,log and seismic data,and then distribution of sedimentary microfacies in T_(3)X_(5)^(1) is determined according to seismic waveform features and seismic prediction.The results show that T_(3)X_(5)^(1) in the Dongfengchang area is mainly composed of deltaic deposits of several microfacies,such as delta front underwater distributary channel,sheet sand,and interdistributary bay.On seismic sections,different microfacies are significantly different in waveform features,the underwater distributary channel is characterized by one trough between two peaks,while diversion bay exhibits chaotic reflections between T6 and T51.The sedimentary microfacies varied greatly during the depositional period of T_(3)X_(5)^(1) in the Dongfengchang area,this is because that the sediment supply was mainly controlled by the southwest and southeast provenance regions.Three superimposed underwater distributary channels are developed in the Dongfengchang area.The phase-1 superimposed underwater distributary channel in the northwest transition to sheet sand in the northeast,the phase-2 superimposed underwater distributary channel in the south extends shortly,the phase-3 superimposed underwater distributary channel in the northeast has a large development scale.These research findings are helpful to guide the subsequent exploration of T_(3)X_(5) gas reservoir and also theoretically significant for investigating the depositional evolution of the Xujiahe Formation in central Sichuan Basin.

Basin-Scale Sand Deposition in the Upper Triassic Xujiahe Formation of the Sichuan Basin, Southwest China: Sedimentary Framework and Conceptual Model

The Upper Triassic Xujiahe （须家河） Formation in the Sichuan （四川） Basin, Southwest China is distinctive for the basin-scale sand deposition. This relatively rare sedimentary phenomenon has not been well interpreted. Here we addressed this issue by discussing sedimentary framework and conceptual model. Analysis of sedimentary setting implied that the basin received transgression during the deposition. It had multiple provenance supplies and river networks, as being surrounded by old- lands in multiple directions including the north, east and south. Thus, the basin was generally charac-terized by coastal and widely open and shallow lacustrine deposition during the Late Triassic Xujiahe period. This is similar to the modern well-known Poyang （鄱阳） Lake. Therefore, we investigated the framework and conceptual model of the Sichuan Basin during the Xujiahe period with an analogue to the Poyang Lake. Results show that the conceptual model of the deposition can be divided into transgressive and regressive stages. The first, third and fifth mem- bers of the formation are in transgressive stage and the deposits are dominated by shore and shallow lacustrine mud. In contrast, the deposition is mainly of braided river channel sand deposits during the regressive stage, mainly including the second, fourth and sixth members of the formation. The sand deposited in almost the entire basin because of the lateral migration and forward moving of the cross networks of the braided rivers. The multiple alternations of short and rapid transgression and relatively long regression are beneficial to the basin-scale sand deposition. Thus, the main channel of the braided river and its extensional areas are favorable for the development of hydrocarbon reservoir. This provides practical significance to the reservoir evaluation and exploration. In addition, the results also justify the relatively distinctive sedimentary phenomenon in the study area and may also have im- plications for understanding the large-scale sand deposition elsewhere.

鄂尔多斯盆地石盒子组-山西组致密储层形成主控因素与发育模式:以彬长地区为例

明确致密储层“甜点”的分布是致密储层油气勘探的重点。通过岩心观察、薄片鉴定、X射线衍射、包裹体均一温度测定、常规物性分析等手段,对鄂尔多斯盆地南部彬长地区上古生界致密砂岩沉积特征、储层特征、成岩作用进行了详细研究,明确了储层形成的主要控制因素并建立了优质储层的发育模式。结果表明:沉积相是储层形成的基础,辫状河三角洲平原分流河道心滩微相岩石粒度粗,孔隙结构为小孔-中细喉型,储层物性相对较好;曲流河三角洲前缘水下分流河道及河口坝微相岩石粒度细,孔喉结构为微孔-微喉型,储层物性相对较差。成岩作用对优质储层的发育与分布具有重要控制作用。间歇性火山凝灰质在酸性地层蚀变为高岭石,而在碱性地层蚀变为绿泥石套膜,抑制了石英次生加大和方解石胶结,保护了储集空间。石英次生加大主要为泥岩转化形成的SiO_(2)渗滤到砂岩中形成的,中晚期方解石充填长石、岩屑溶孔为方解石顶底板胶结的主要原因。晚期构造改造形成的微裂缝无方解石胶结,改善了储层物性,对气藏起调整作用。彬长地区在3 750 m和3 900 m埋深段附近为2个溶蚀孔发育带。最优储层为溶蚀孔发育带内火山凝灰质转化形成的富含绿泥石套膜的中-粗砂岩;次优储层主要分布在溶蚀孔发育带内单砂体厚度较大、有旋回且无泥岩隔档的砂体的中下部,主要为缺少绿泥石套膜的中-粗砂岩,方解石胶结与石英次生加大作用最低。研究成果进一步深化了鄂尔多斯盆地南部地区上古生界致密砂岩优质储层发育的成因,对该地区天然气勘探开发具有重要指导意义。

孔隙型致密砂岩气藏产能控制因素

为了探究天然裂缝欠发育致密砂岩气藏的产能主控因素,以四川盆地北部元坝地区上三叠统须家河组二段和川中东峰场地区须家河组五段气藏为研究对象,分析了二者的地质特征、钻井工艺和储层改造技术,明确了孔隙型致密砂岩气藏天然气产能主控因素。研究结果表明:①古、今构造高部位是油气运聚成藏的指向区,天然气富集程度较高,气井高产概率较大,而构造低部位气井生产效果较差;②储层物性越好,成藏过程中天然气富集程度越高,且生产过程中天然气流动能力较强,故优质储层发育段越厚,气井产量越高;③裂缝欠发育致密砂岩气藏需通过储层改造才能获产,加大改造规模对优质储层发育的钻井增产效果明显;④由于致密砂岩储层局部发育,水平井能够钻遇更多的优质储层,故较直井而言,提产效果明显;⑤由于钻井液中的重晶石会对物性差—中等的储层造成污染,进而影响产量,故致密砂岩气藏钻井过程中需加强储层保护。结论认为:①孔隙型致密砂岩气藏产能主要受古、今构造位置,优质储层发育程度,储层改造规模和井型等因素控制;②优质烃源岩发育区、正向构造区和相对优质储层发育区的叠合部位可优先考虑部署井位。

四川盆地蓬莱—中江地区震旦系灯影组二段成藏特征

通过钻井、岩心、测录井及地震资料的综合分析,系统研究了四川盆地蓬莱—中江地区震旦系灯影组二段气藏的成藏特征。研究结果表明:(1)四川盆地灯影组沉积期,随着海水侵入,古陆多被淹没或侵蚀夷平,盆地逐渐演变为碳酸盐岩台地。灯二上亚段沉积期,川中北斜坡蓬莱—中江地区以发育台地边缘滩相和台地边缘丘相为特色,并可细分为滩核、滩缘、滩间海、丘核、丘缘、丘间海6种亚相,是储层发育的有利相带。(2)研究区灯二上亚段储层以藻云岩、藻砂屑云岩为主要储集岩,发育残余粒间孔+粒间溶孔型、粒内溶孔+藻格架孔型、裂缝型与孔洞型4种类型的储层,储层厚度分布特征与沉积相分布特征较吻合,位于台地边缘丘滩核的储层累积厚度大。(3)研究区灯二上亚段气藏的天然气主要来源于筇竹寺组烃源岩,烃源岩厚度大、有机碳含量及热演化程度高,气藏具备较好的烃源条件和封盖条件,具有“上生下储上盖”和“旁生侧储上盖”2种较好的生-储-盖配置关系。(4)研究区油气充注主要发生于三叠纪—白垩纪,为多期“准连续”型,灯二上亚段气藏主要经历了奥陶纪—志留纪古油气藏聚集阶段、志留纪—石炭纪古油藏破坏阶段、二叠纪—三叠纪再次生烃成油藏阶段和三叠纪—侏罗纪原油裂解生气阶段。

Hybrid Sedimentation in Late Permian-Early Triassic in Western Sichuan Basin,China

Mixed carbonate-siliciclastic sedimentation is common in the Upper Permian-Lower Tri-assic in the western Sichuan（四川） basin.The extensional movement was strong in the Late Permian,resulting in differential uplifting of fault blocks.During this period,there was an extensive retrogres-sion.The Kangdian（康滇） ancient land progressive uplifted and enlarged,forming the major prove-nance of terrigenous clastics.In Changxingian age,mixed terrigenous-carbonate sedimentation was dis-tributed in the area between Dafeishui（大飞水）-well Dashen（大深）-1-well Shoubao（寿保）-1 and Beichuan（北川）-well Guanji（关基）.The terrigenous clastics sourced from Kangdian ancient land input into the relatively shallow water,resulting in an extensive limited platform-mixing tidal flat where moderate-thick laminated grey limestone,thin muddy limestone and purplish red sandy shale were de-posited.The tectonic framework in Feixianguanian（飞仙关） stage was inherited from the Chang-xingian stage.The hybrid sedimentation was limited to the south of Dujiangyan（都江堰）-Xindu（新都）.In Jialingjiangian（嘉陵江） stage,the palaeogeographic features were also unchanged and two complete transgression-retrogression cycles also occurred.The mixing tidal flat was distributed to the west of Baoxing（保兴）-Ya＇an（雅安）-Hongya（洪雅）-Leshan（乐山）,where purplish red sandstone with thin limestone and shale interbeds and grey-dark grey silty mudstone with limestone were deposited.The carbonates in the mixed facies tract have few primary pores preserved and poorly-developed secondary pores due to the relatively high content of terrigenous clastics,strong compaction and weak dissolution.Therefore,they are unfavorable for the development of effective reservoirs.

资阳东峰场地区须家河组须五段气藏产能影响因素及稳产对策

针对四川盆地资阳东峰场地区上三叠统须家河组须五段气藏试采中表现出的单井天然气产能差异大、稳产效果差等问题,综合地质、动态监测、实验分析等资料,开展了产能主控因素及递减原因分析,提出了稳产对策。研究结果表明:①气井产能主要受井型和优质储层发育程度影响,水平井产能明显高于直井,优质储层越发育,气井产能越高;②气井稳产效果较差,稳产期平均为10个月,日产气量递减指数平均为0.0017,储层有效渗透率低、供气范围有限;③气井初期高配产带来大生产压差引发储层应力敏感伤害,地露压差小易析出凝析油造成储层反凝析伤害,使储层渗透率损失,导致气井产能迅速递减;④压裂砂回流使人工裂缝导流能力下降并在近井地带堆积造成砂堵,压裂液返排困难使气井积液甚至水淹,均会导致气井停产;⑤控压开采可有效降低储层渗透率的损伤,液氮助排、优化生产管柱有利于气井排液,延缓气井产能递减。该研究成果可以为类似地区致密砂岩气藏开发技术对策制订提供参考。

四川盆地须家河组坡折带发育特征及油气地质意义

前人针对断陷盆地坡折带开展了大量研究,但前陆盆地前渊向前缘隆起方向坡度较缓,大型构造欠发育,地形起伏小,坡折带研究较少。四川盆地晚三叠世须家河组四、五段沉积时期发育前陆盆地,学者们已关注到泸州—开江古隆起西侧川中—川西地区缓坡坡折带对沉积岩相的控制,但其他相关研究较少。通过对四川盆地地震反射剖面坡折带构造解释,结合区域地质已有成果,采用颗粒流数值模拟方法,厘清了川中—川西地区坡折带类型,以及坡折带与重力滑动构造之间的关系,分析了与重力滑动构造相关的新型油气圈闭特征。研究获得如下认识:(1)研究区发育断裂坡折带,以坡折带为界,东、西两侧各发育一套重力滑动形成的“前挤后拉”构造组合,构造变形强度弱于被动大陆边缘重力滑动构造;(2)研究区构造坡折带边缘断裂控制沉积相与砂体类型;(3)缓坡带重力滑动构造拉张区正断层下盘上升形成同沉积背斜发育的砂岩,与同期断陷内富有机质泥岩侧接,形成“旁生侧储”型油气藏;(4)陡坡带重力滑动形成的须五段同沉积背斜,被翼部泥岩以及滑动构造结束后沉积的泥岩所围限,形成源内砂体输导成藏;(5)与重力滑动构造相关的同沉积背斜油气藏是源内成藏新类型,研究区须五段可能存在平行坡折带NE向展布的此类油气藏。

致密砂岩微观特征及沉积古环境——以梓潼—秋林地区须三、二段为例

四川盆地西北部上三叠统须家河组纵向上发育多套致密砂砾岩气藏,具备多层系立体勘探的广阔前景。目前针对该区域须家河组沉积古环境及物源体系的认识还不够深入,导致勘探上有点无面,严重制约了下一步攻关方向,需要加强该区域沉积古环境的研究。通过显微薄片鉴定、全岩矿物X衍射、稀土微量元素分析,结合井、震资料,对主要层段须三段—须二段含气砂体岩石类型、矿物含量、物源条件、古气候、古盐度及古氧化还原条件进行系统分析和对比研究。研究结果表明:(1)须二上亚段以长石岩屑砂岩为主,石英及长石矿物发育,石英含量超过50%;(2)受龙门山碳酸盐物源供给影响,须三下亚段普遍含钙质,岩屑成分以碳酸盐岩为主,方解石与白云石矿物发育,石英含量低于50%;(3)须三下亚段砂体稀土元素特征较须二上亚段更为复杂,指示多物源特征,两者沉积时该区整体处于潮湿性干热古气候,沉积环境偏淡水氧化环境,但须三下沉积期比须二上沉积期气候更为潮湿、古盐度略高、氧化性也更强。研究成果对川西北部须家河组重点砂岩层段微观特征、沉积古环境及地层划分新方案具有一定参考意义。

川东北飞仙关组鲕滩储层分布规律、勘探方法与远景预测

20世纪末在四川盆地东北部发现了渡口河等以孔隙性鲕粒白云岩为储层的飞仙关组气藏。这些储层的分布与飞仙关组鲕粒滩的分布规律有关。研究表明当时的古地理格局控制了飞仙关组鲕粒滩的分布 ,因而影响着鲕滩气藏的分布。研究区的鲕粒滩集中分布在环早期开江—梁平海槽的碳酸盐岩台地边缘 ,它们随着碳酸盐岩台地沉积区的扩大和开江—梁平海槽的消亡而发育迁移 ,形成了宣汉黄金口—开县地区、达县—梁平地区等几个鲕粒岩集中发育区块。由于孔隙性鲕粒白云岩的形成与混合水白云石化作用和深埋藏溶解作用有关 ,故储层呈大小不等的透镜状分布在致密的鲕粒灰岩中 ,使鲕粒气藏具有岩性—构造复合圈闭的特点。孔隙性白云岩储层的声速平均 5 5 4 0m/s,致密灰岩的大于 6 2 0 0m/s ,故在地震剖面上储层表现为在一定层位的弱反射背景出现的一段连续的强振幅反射。因此 ,鲕滩气藏的勘探可遵循“占边缘、找亮点、套构造”的思路进行综合预测勘探。除目前重点勘探的五宝场地区外 ,宣汉黄金口—万源区块和达川—梁平区块是很有希望的勘探后备区块 ,万源—南江区块和广元—昌平区块是鲕滩气藏勘探的远景区块。

川西前陆盆地须家河组沉积相及岩相古地理演化

川西前陆盆地上三叠统须家河组是油气勘探的重点层位。依据新的地层划分方案、大量钻井、露头及岩芯资料,结合区域地质特征,详细研究了须家河组沉积相、岩相古地理特征及其演化。结果表明:研究区内主要发育了冲积扇、湖相三角洲、湖泊、海相三角洲、滨岸和海湾六种主要的沉积相类型;古地理演化经历了由海相环境—海陆过渡相环境—陆相环境的转变;在须四早期,受安县运动的影响,龙门山褶皱成山,使研究区与阿坝海域完全隔绝,整个四川盆地真正进入了陆相沉积环境。

中国三叠系陆相砂岩中自生绿泥石的形成机制及其与储层孔隙保存的关系

研究了中国三叠系陆相砂岩中自生绿泥石的产状、成因及其与储层发育的关系,证明了以孔隙环边衬里方式产出的绿泥石是深埋地层中孔隙保存的重要机制,环边绿泥石的沉淀及其在成岩过程中的再生长不仅提高了岩石的机械强度和抗压实能力,还降低了自生石英在碎屑颗粒上的成核数量并抑制石英的次生加大,从而使砂岩中的原生和次生孔隙得以保存。砂岩中自生绿泥石的成因还表明这种产状的绿泥石是三角洲前缘推进的良好标志,同时也说明中国中新生代的湖泊可能并不是真正的淡水湖泊,它们或多或少具有一定的盐度,其对海源流体具有继承性。

川西前陆盆地上三叠统沉积特征

应用层序地层学方法将川西前陆盆地上三叠统划分为4个三级层序和12个体系域。在层序格架内,研究了不同时期的古地理背景、物源、沉积类型和沉积相展布,明确了上三叠统存在龙门山古陆、米仓山—大巴山古陆、康滇古陆、江南古陆4个物源,识别出上三叠统海湾、冲积扇、曲流河、辫状河、扇三角洲、辫状河三角洲、曲流河三角洲和湖泊8种沉积相类型。层序Ⅰ沉积时期,盆地处于海陆交互相向陆相转变的时期,整体具有填平补齐的沉积特征,发育海湾等沉积;层序Ⅱ沉积时期,川西前陆盆地成为统一的内陆湖盆,其湖侵期为须家河期最大的湖侵期,主要发育三角洲沉积和湖相沉积;层序Ⅲ沉积时期,米仓山—大巴山古陆提供充足的物源,在米仓山—大巴山两逆冲推覆带前缘广泛发育大型冲积扇、辫状河、辫状河三角洲沉积体系;层序Ⅳ沉积时期,主要受江南古陆的影响,发育三角洲沉积和湖泊沉积。整体上,川西前陆盆地沉积相带的展布格局受构造控制,具有平行构造带展布的特点。盆地西北部陡坡带发育粗粒的冲积扇、扇三角洲—湖底扇,西南部陡坡带发育辫状河三角洲、北部—东北部陡坡带发育辫状河三角洲,而在东南部缓坡带则发育远源的曲流河、曲流河三角洲。

四川盆地东北部下三叠统飞仙关组碳酸盐蒸发台地沉积相

四川盆地早三叠世飞仙关早期的环境基本上继承了晚二叠世长兴期末的格局。在川东北地区演化为碳酸盐蒸发台地。飞仙关组蒸发台地为一套含硫酸盐的富白云岩的蒸发潮坪沉积层系。下部为薄层的含石膏、硬石膏晶体、团块及肠状石膏层的泥晶灰岩、微晶白云岩组成的小潮差蒸发潮坪层序。中部为层状鲕粒白云岩、鲕粒灰岩的潮下鲕粒滩相与萨布哈环境的富层状石膏岩的膏坪相、含石膏岩的膏云坪相组成的大潮差蒸发潮坪层序。上部为中薄层状富泥的含石膏质夹层的泥质泥晶灰岩、微晶白云岩组成的旋回性清楚的似蒸发潮坪层序。这三种层序的纵向组合在蒸发台地相区可以很好对比,尽管各层序厚度有明显变化。强烈白云石化的鲕粒白云岩是四川盆地飞仙关组大中型气藏的主要储层,依据鲕粒岩的相序特征可将其分为有障壁性质的台缘鲕粒坝和台内鲕粒滩两类。蒸发台地西缘的台缘鲕粒坝在飞仙关期基本稳定。东缘的台缘鲕粒坝在飞仙关中后期大幅度向盆地方向迁移。

四川盆地上三叠统香溪组二段和四段砂岩沉积模式

四川盆地上三叠统香溪组二、四段砂岩是盆地内主要天然气储层之一,近年来勘探形势喜人。香二和香四段砂岩分布面积约为10×104km2,厚度稳定,矿物和结构成熟度高,较厚砂岩层大多呈逆粒序构造,常发育冲洗层理和互成180°交角的楔形或板状斜层理,风暴岩频繁发育,伽马曲线成箱形,夹5%～10%的炭质泥岩或含薄煤层炭质泥岩。结合全川的资料,对川中4×104km2内数十条地面和岩心剖面研究结果表明,四川盆地香二和香四时周边各山系为构造活动期,经冲积扇、河流搬运入湖的碎屑物质经波浪和湖流反复簸洗、改造和再分配,形成了沿岸和近岸的滩坝相砂体,滩坝相砂体后发育为滨岸含煤沼泽。随湖盆脉动式的升降、岸线的迁移,滩坝砂体也将垂直或沿岸线迁移,最终形成遍布盆地内的砂岩体。提出了香二、香四段滩坝砂体及所夹炭质泥岩的发育、演化模式。

川中南河包场须家河组砂岩沉积-成岩作用

四川盆地上三叠统须家河组砂岩是盆地内主要天然气储层,其形成与演化的影响因素较为复杂。其中,沉积作用不仅控制着主要储层的宏观分布特征,而且影响着后期的成岩作用类型和强度;成岩作用使埋藏时期储层被改造,不仅影响了储集空间的演化过程和孔隙结构特征,还最终决定了现今储层的面貌和分布规律。对大量实测物性参数的统计分析表明,河包场区块须家河组储层物性从上到下逐渐变好,下部须二段砂岩中出现大量石英溶蚀产生的次生孔隙,其物性明显好于上部须四段、须六段,是导致深部储层物性变好的主要原因。综合考虑不同沉积微相砂岩所经历的成岩改造作用类型及其储层的响应特征,根据研究区的实际地质情况,归纳出6种沉积—成岩相组合类型。对这些组合类型造成的储层效应进行了建设性和破坏性的划分,初步建立了研究区的沉积—成岩相组合类型的分布模式。

川中—川南地区上三叠统沉积相研究

综合分析岩心、露头剖面和测井资料,认为川中—川南地区上三叠统发育三角洲相和湖泊相,其中,三角洲相可进一步划分为三角洲平原、三角洲前缘和前三角洲三个亚相,湖泊相则可细分为滨湖和浅湖两个亚相。不同时期三角洲相和湖泊相发育程度不同。须一段、须三段、须五段和须六段以湖泊沉积为主,由东向西,水体逐渐加深。须二段和须四段以三角洲沉积为主,湖泊沉积分布范围较小。须二段发育时期,研究区北部构造活动强烈,沉积物供给充分,三角洲相主要由北向南延伸;须四段沉积时期,由于北部构造活动逐渐减弱,东南部沉积物供给增加,三角洲相主要由东南向西北方向延伸。随着周缘构造活动的变化,研究区沉积范围逐渐扩大。早期沉积范围仅局限于宜宾—泸州以北地区,中晚期沉积范围扩大,宜宾—泸州以南地区开始接收沉积。