The saline lacustrine hybrid sedimentary rocks are complex in lithology and unknown for their sedimentary mechanisms. The hybrid sedimentary rocks samples from the Neogene upper Ganchaigou Formation to lower Youshashan Formation (N1-N21) in the Fengxi area Qaidam Basin, were investigated through core-log and petrology-geochemistry cross-analysis by using the core, casting thin section, scanning electron microscope, X-ray diffraction, logging, and carbon/oxygen isotopic data. The hybrid sedimentary rocks in the Fengxi area, including terrigenous clastic rock and lacustrine carbonate rock, were deposited in a shallow lake environment far from the source, or occasionally in a semi-deep lake environment, with 5 lithofacies types and 6 microfacies types recognized. Stable carbon and oxygen isotopic compositions reveal that the formation of sedimentary cycles is controlled by a climate-driven compensation-undercompensation cyclic mechanism. A sedimentary cycle model of hybrid sedimentary rocks in an arid and saline setting is proposed. According to this model, in the compensation period, the lake level rises sharply, and microfacies such as mud flat, sand-mud flat and beach are developed, with physical subsidence as the dominant sedimentary mechanism; in the undercompensation period, the lake level falls slowly, and microfacies such as lime-mud flat, lime-dolomite flat and algal mound/mat are developed, with chemical-biological process as the dominant sedimentary mechanism. In the saline lacustrine sedimentary system, lacustrine carbonate rock is mainly formed along with regression, the facies change is not interpreted by the accommodation believed traditionally, but controlled by the temporary fluctuation of lake water chemistry caused by climate change. The research results update the interpreted high-resolution sequence model and genesis of hybrid sedimentary rocks in the saline lacustrine basin and provide a valuable guidance for exploring unconventional hydrocarbons of saline lacustrine facies.

Based on new data from cores, drilling and logging, combined with extensive rock and mineral testing analysis, a systematic analysis is conducted on the characteristics, diagenesis types, genesis and controlling factors of deep to ultra-deep abnormally high porosity clastic rock reservoirs in the Oligocene Linhe Formation in the Hetao Basin. The reservoir space of the deep to ultra-deep clastic rock reservoirs in the Linhe Formation is mainly primary pores, and the coupling of three favorable diagenetic elements, namely the rock fabric with strong compaction resistance, weak thermal compaction diagenetic dynamic field, and diagenetic environment with weak fluid compaction-weak cementation, is conducive to the preservation of primary pores. The Linhe Formation clastic rocks have a superior preexisting material composition, with an average total content of 90% for quartz, feldspar, and rigid rock fragments, and strong resistance to compaction. The geothermal gradient in Linhe Depression in the range of (2.0–2.6) °C/100 m is low, and together with the burial history of long-term shallow burial and late rapid deep burial, it forms a weak thermal compaction diagenetic dynamic field environment. The diagenetic environment of the saline lake basin is characterized by weak fluid compaction. At the same time, the paleosalinity has zoning characteristics, and weak cementation in low salinity areas is conducive to the preservation of primary pores. The hydrodynamic conditions of sedimentation, salinity differentiation of ancient water in saline lake basins, and sand body thickness jointly control the distribution of high-quality reservoirs in the Linhe Formation.

The Paleogene-Neogene strata in the Western Depression of the Qaidam Basin represent a primary focus for oil and gas exploration and development. Influenced by both terrigenous clastic influx and endogenic carbonate deposition, these strata exhibit significant variation in sedimentary systems and reservoir characteristics. This study comprehensively examines the depositional patterns and reservoir properties of the Paleogene-Neogene sequence across the inner, middle, and outer belts of the basin, employing core analysis, thin section petrography, and physical property assessment of reservoirs. Key findings include 1) The development of a concentric sedimentary system in the Western Depression during the Paleogene-Neogene period, characterized by increased carbonate mineral content and decreased clastic material from the periphery to the center of the basin. 2) Varied sedimentary facies associations across different zones, with the outer belt dominated by fan delta and braided river delta deposits, and the middle and inner belts characterized by near-shore shallow lacustrine carbonates and algal mat deposits, and offshore semi-to deep-lacustrine fine sediments, respectively. 3) The outer belt exhibits reservoirs with favorable physical properties and connectivity, while the inner and middle belts show high heterogeneity, indicating potential for lithological traps and shale oil exploration. These insights offer scientific guidance for further investigation into the depositional systems of lacustrine basins in the Western Depression of the Qaidam Basin and for identifying promising reservoirs.

In view of the key geological factors restricting reservoir development, the reservoir heterogeneity of an alluvial fan sandy conglomerate reservoir in the Qie12 block of Qaidam Basin, Northwest China, and its influence on remaining oil distribution, were studied according to geology, wireline logging data, and dynamic production data. This study illustrates that the difference in pore structures, which are controlled by different sedimentary fabrics, is the main cause of reservoir microscopic heterogeneity. Besides, the temporal and spatial distribution of architectural units in the alluvial fan controls reservoir macroheterogeneity. Our results show that the thick sandy conglomerate develops two types of pores, two types of permeability rhythms, two types of interlayers, two types of interlayer distribution, two types of effective sand body architecture, and four types of sand body connecting schemes. The strongest plane heterogeneity is found in the composite channel unit formed by overlapping and separated stable channels of the middle fan, and the unit’s permeability variation coefficient is >0.7. However, the variation coefficient in the range of 0.3–0.5 is found in the extensively connected body unit sandwiched with intermittent channels of the inner fan. The distributions of the remaining oil vary significantly in different architectural units because of the influence of reservoir heterogeneity, including distribution patterns of flow barriers, permeability rhythm, and reservoir pore structures. The composite channel unit formed by overlapping and separated stable channels, or the lateral alternated unit with braided channel and sheet flow sediment of the middle fan, is influenced by the inhomogeneous breakthrough of injection water flowing along the dominant channel in a high-permeability layer. The microscopic surrounding flow and island-shaped remaining oils form and concentrate mainly in the upper part of a compound rhythmic layer. Meanwhile, in the extensively connected body unit sandwiched with intermittent channels of the inner fan, poor injector–producer connectivity and low reservoir permeability lead to a flake-like enrichment of the remaining oil.

利用露头、钻井、地震及大量实验分析资料,从现今地层结构、沉降-沉积速率、古水体盐度、岩石组合及沉积相展布、烃源岩有机质类型等方面,论证了柴达木盆地腹部一里坪坳陷与柴西坳陷之间发育大型水下古隆起,并通过构造解析和古地貌恢复,分析其演化过程,最后从油气成藏角度阐述了古隆起对下一步油气勘探的意义.研究表明:①古新世早期,受早喜马拉雅挤压造山运动影响,形成了古隆起雏形,平面上呈北西—南东向展布,分隔了其东、西两侧的一里坪坳陷与柴西坳陷;始新世至渐新世,古隆起具有很好的继承性,下干柴沟组沉积时期隆起区最大面积约为3 500 km2;至中新世晚期,受柴西沉积中心向东迁移及南北向物源补给的影响,古隆起演变为宽缓斜坡.②古隆起对油气成储、成烃、成藏具有控制作用:古隆起南北两端近物源区发育规模三角洲砂体,而中心主体区远离物源,处于欠补偿咸化水体环境,发育规模湖相碳酸盐岩储层;受古隆起的分隔影响,西侧柴西坳陷下干柴沟组上段—上干柴沟组已证实发育优质咸化湖相烃源岩,东侧一里坪坳陷可能发育有效烃源岩;古隆起是油气运移有利指向区,有利于油气聚集成藏,可作为下一步有利勘探区带.

Lacustrine carbonate reservoirs, extensively distributed in China, have extensive oil and gas exploration potential. However, such reservoirs are characterized by high content of terrigenous debris and complex lithofacies, and the resultant high difficulty in lithofacies identification severely restrains exploration expansion and efficient development, especially for the Upper Member of the Paleogene Lower Ganchaigou Formation (E32) of the Yingxi area in the Qaidam Basin, with burial depths generally greater than 4000 m. This research targets this area and develops a methodology for detailed lithofacies identification, after systematically investigating the characteristics of lithofacies and well log responses of lacustrine carbonate rocks, on the basis of a massive volume of data of cores, thin sections, and experiments of the study area. The analysis identified lithofacies in the Upper Member of the Paleogene Lower Ganchaigou Formation of the Yingxi area, namely, pack-wackestone, mudstone, laminated carbonate, muddy gypsum, and limy claystone. The analysis of well log response characteristics suggested that natural gamma ray, matrix density, and bulk density were sensitive to lithofacies. Then, for the first time, the rock fabric factor (RFF) method was proposed, and the lithofacies identification plot was based on the calculated RFF and high-definition spectroscopy log. The presented methodology was applied to 55 wells in the study area. The average accuracy of lithofacies interpretation in 14 cored wells reached 82.4%, indicating good application performance. This method improves the lithofacies identification accuracy of lacustrine carbonate rocks, which is of great significance for investigating the reservoir distribution law and guiding exploration and development.

昆仑山前带古近系下干柴沟组下段是柴达木盆地油气勘探的重点目的层.受砂岩储层发育程度差异所控制,昆仑山前带不同地区油气富集程度存在差异.为了明确储层的差异性及形成机制,利用岩心、测井及分析化验等资料,对昆仑山前带的切6区、乌南斜坡带、东柴山地区及弯西构造带的储层特征及控制因素进行了分析,认为下干柴沟组下段储层在时空上的差异性明显.昆仑山前带下干柴沟组下段发育以原生粒间孔为主的碎屑岩孔隙型储层,储层砂体成因类型为辫状河三角洲相的平原分流河道、前缘水下分流河道、河口坝、席状砂及滨浅湖相的滩坝.沉积相及成岩作用的双重叠加影响导致昆仑山前带储层发育程度存在明显差异.在同等埋深条件下,受沉积微相控制的储层沉积组构差异与砂体规模差异是储层物性差异的主因,辫状河三角洲前缘水下分流河道储层物性最好,其次为河口坝、平原分流河道,滩坝与席状砂的储层物性较差.在不同埋深条件下,受最大古埋深和古地温梯度等因素影响而形成的差异压实作用是不同区带储层物性差异的主因,切6区和弯西构造带的储层物性最好,乌南斜坡带的储层次之,东柴山地区的储层物性差.

我国湖相碳酸盐岩储层分布广泛,具有极大的油气勘探前景.但该类储层陆源碎屑含量高、岩相种类多,导致岩相识别困难且严重制约了该领域勘探拓展和高效开发,这在埋藏深度普遍大于4000m的柴达木盆地英西地区古近系下干柴沟组上段(E32)尤为典型.以英西地区为例,充分利用区内大量岩心、薄片和实验分析资料,系统分析湖相碳酸盐岩岩相特征及测井响应特征,并建立了识别方法和图版.分析结果表明,英西地区E32发育颗粒灰云岩、泥晶灰云岩、纹层状灰云岩、泥质膏岩和灰云质泥岩等5种类型的岩相.基于测井响应特征分析,确定自然伽马、骨架密度、体积密度为岩相识别敏感参数,进而首次提出岩石结构因子(RFF)技术;利用计算得到的RFF参数,结合元素测井资料建立了岩相识别图版,将其应用于研究区48口井,在12口取心井中岩相解释平均符合率达到80.2％,应用效果较好.岩石结构因子技术提高了湖相碳酸盐岩岩相识别符合率,对研究储层分布规律、指导勘探开发具重要意义.

Based on the data of field outcrops, drilling cores, casting thin sections, well logging interpretation, oil/gas shows during drilling, and oil/gas testing results, and combined with modern salt-lake sediments in the Qinghai Lake, the Neogene saline lake beach-bars in southwestern Qaidam Basin are studied from the perspective of sedimentary characteristics, development patterns, sand control factors, and hydrocarbon accumulation characteristics. Beach-bar sand bodies are widely developed in the Neogene saline lake basin, and they are lithologically fine sandstone and siltstone, with wavy bedding, low-angle cross bedding, and lenticular-vein bedding. In view of spatial-temporal distribution, the beach-bar sand bodies are stacked in multiple stages vertically, migratory laterally, and extensive and continuous in NW-SE trending pattern in the plane. The stacking area of the Neogene beach-bar sandstone is predicted to be 3000 km(2). The water salinity affects the sedimentation rate and offshore distance of beach-bar sandstone, and the debris input from the source area affects the scale and enrichment of beach-bar sandstone. The ancient landform controls the morphology and stacking style of beach-bar sandstone, and the northwest monsoon driving effect controls the long-axis extension direction of beach-bar sandstone. The beach-bars have a reservoir-forming feature of "one reservoir in one sand body", with thick beach-bar sand bodies controlling the effective reservoir distribution and oil-source faults controlling the oil/gas migration and accumulation direction. Three favorable exploration target zones in Zhahaquan, Yingdong-eastern Wunan and Huatugou areas are proposed based on the analysis of reservoir-forming elements.

To identify the developmental characteristics and controlling factors of the beach‐bar sandstone in saline lake basins in the Qaidam Basin, China, the lithology and bedding structure of some representative outcrops of the Neogene saline lake basins were comprehensively investigated by means of experimental test data of local drilling cores, casting thin sections, and grain size, together with field outcrops in the basin and the modern salt lake deposition record of Qinghai Lake. Two types of sand bodies in the saline lake basins, that is, delta sand bodies and shore‐shallow lake beach‐bar facies were revealed. Neogene saline lake basins were found to host widespread beach‐bar sand bodies. Lithologically, the sand bodies were composed of fine‐grained sandstone and siltstone, with wavy bedding, low‐angle cross‐bedding, and bimodal cross‐bedding. The beach‐bar sandstone was characterized by multi‐layer superimposition, lateral migration, and NW–SE wide‐coverage continuation. Drilling data showed that beach‐bar sand bodies extended from 10 to 35 km in width and most of them occurred 3–15 km away from braided river delta front. It has been predicted that the total area of beach‐bar sand bodies of 14 sand groups in the Neogene spread across 5,000 km2. Four factors, that is, lake water salinity, terrigenous input, palaeogeomorphology, and monsoons, controlled the construction of the beach‐bar sand bodies developed in the Neogene saline lake of the Qaidam Basin. We can conclude that the settling velocity and transport distance of the sand bodies were affected by the water body salinity in such saline lake basins. Also, the distribution range of the beach‐bar sand bodies was affected by the clastic input from a terrigenous provenance. Furthermore, the wide‐coverage distribution and local enrichment of the beach‐bar sandstone were affected by palaeogeomorphology, and the distribution direction of the beach‐bar sandstone was affected by the driving effect of NW monsoons. We propose a deposition model of the beach‐bar sandstone in saline lake basins that can predict favourable beach‐bar sand body regions, to support the major discoveries of lithologic traps in southwestern Qaidam, China.

利用大量的岩心实验分析资料系统地研究了柴达木盆地西部同沉积体系和不同区带之间下干柴沟组下段碎屑岩储层物性差异的主控因素,指出沉积环境、岩石学特征、砂体厚度、地层埋藏史、地温梯度背景和湖水古盐度的不同是造成储层物性差异的重要因素.柴达木盆地西部下干柴沟组下段广泛发育的三角洲平原分流河道砂、三角洲前缘水下分流河道砂和滨浅湖滩坝砂是优质储层发育的基本条件.储层砂体厚度、杂基含量和碎屑粒径是储层物性的重要控制因素,成岩作用对储层的演化和储集性能具有决定性作用,其中压实作用对储层物性影响最大,胶结作用是局部区带储层物性重要控制因素.同沉积体系三角洲平原分流河道砂的碎屑颗粒分选和杂基含量控制储层压实程度的差异,三角洲前缘水下分流河道砂和滨浅湖滩坝砂厚度控制了储层胶结强度差异;不同区带地层埋藏史和地温梯度背景造成储层的较大压实差异,湖水古盐度沿盐湖中心环带状分布造成储层在平面上的胶结强度差异.

Taking the mixed pre-salt carbonate rocks in the upper member of Eocene Xiaganchaigou Formation (E32) of Yingxi area in the Qaidam Basin as an example, the lithofacies and controlling mechanisms of reservoir formation are analyzed based on a large dataset of cores, thin sections and geochemical analysis. The reservoirs in E32 pre-salt layers have five types of lithofacies, of them, mixed granular calcareous dolostone, massive calcareous dolostone, plaque calcareous dolostone, and laminated dolomtic limestone are of sedimentary origin, and breccia calcareous dolostone is of tectonic origin. The four types of sedimentary lithofacies are divided into two types of saline sedimentary sequence lithofacies combinations, low-energy type in the sag area and low to high-energy type in the slope and paleo-uplift zone in the depression. Affected by high-frequency supply of continental clastic material, the two types of salty sedimentary sequences are mostly incomplete subtypes of lithofacies. Lithofacies have strong impacts on pre-salt reservoirs in E32: (1) Lithofacies type and sedimentary sequence controlled the formation and distribution of dolomite intercrystalline pores and dissolved pores during the pene-sedimentary period. (2) The structure of laminated dolomitic limestone controlled the formation of large-scale laminated fractures and high permeability channels during the diagenetic period. (3) Granular, massive, plaque calcareous dolostones have low mud content and strong brittleness, in the late tectonic reactivation period, the distribution of the three types of lithofacies, together with their distance from the top large slip faults and secondary faults, controlled the formation and distribution of high-efficiency fracture-cave brecciaed calcareous dolostone reservoirs. The above research led to the composite lithofacies-tectonic formation model of pre-salt reservoir in E32 of Yingxi area. The tempo-spatial distribution of tectonic breccia calcareous dolostone reservoirs, laminated dolomitic limestone shale oil reservoirs and granular, massive calcareous dolostone dissolved-intercrystalline pore tight reservoirs in various structural belts of the studied area have been figured out. These findings gave new insights into tight-shale oil accumulation theory in mixed carbonate successions from saline lacustrine basins, aiding in high efficient exploration and development of petroleum in the studied area.

针对塔里木盆地库车坳陷依奇克里克地区中—下侏罗统深层砂岩储层成岩作用复杂、非均质性强、储层特征及其成因不明确的特点,综合利用铸体薄片、扫描电镜、物性分析、X射线衍射、CT扫描等多种分析手段,并结合区域地层埋藏史、古地温史、Ro演变史、沉积相等相关研究成果,详细分析了中—下侏罗统储层成岩作用演化阶段及其物性控制因素。研究结果表明:①中—下侏罗统储层具有低成分成熟度、高塑性岩屑含量及中等结构成熟度的特征。②储层现今主体埋深为4000～5000m,储层储集空间以次生溶蚀孔和裂缝为主,平均孔隙度为7.21%,平均渗透率为9.15mD,总体为低孔低渗储层,部分储层由于发育构造裂缝而渗透率较高。③储层成岩演化可分为两个阶段:第一阶段发生在新近纪之前,成岩作用为初期沉积埋藏压实减孔和长期浅埋藏期腐殖酸溶蚀增孔;第二阶段发生在新近纪之后,发生的成岩作用为储层快速深埋侧向挤压压实减孔和大量伊利石生成胶结减孔,并伴随发育大量裂缝改善储层渗透率。④优质储层物性主控因素为沉积水动力条件、后期成岩作用和构造裂缝发育。富含石英等刚性颗粒的粗砂级辫状河河道和水下分流河道砂岩有较强的抗压实能力,是优质储层形成的沉积基础。裂缝的发育大大改善了研究区储层的渗透率,是优质储层发育的主要控制因素。

Understanding the sedimentary sequence and architecture is important for planning the development strategy. We illustrate a case study of analyzing the sequence and architecture of a sandy conglomerate reservoir by integrating geology, petrophysics, seismic, and development data. The analysis indicates that the depostional environment of the target lower part of the Ganchaigou Formation is an alluvial fan. We defined eight lithofacies according to the core analysis and five sedimentary microfacies by integrating the core and petrophysical data. We next propose four sedimentary architectural models by integrating the lithofacies result, microfacies analysis, and high frequency sequence models. The four architecture models include the extensively connecting body sandwiched with intermittent channels, the composite channel formed by the overlapping and separation of stable channels, the lateral alternated braided channel and sheet flow sediment, and the runoff channel inlaid in flood plain mudstone. We finally build an architecture model for the alluvial fan. The model of the alluvial fan overall shows an upward-fining grain-size features and this feature indicates that the alluvial fan belongs to a retrograding sequence. The built model consists of six alluvial fan bodies that migrates from north.

为了明确柴达木盆地新生代湖相碳酸盐岩类型特征及发育规律,利用野外露头、钻井取芯、显微结构特征等资料,按照碳酸盐岩成因分类法,对碳酸盐岩类型进行划分.结果 表明,柴达木盆地新生代发育两种成因类型碳酸盐岩储层,即生物成因和机械-化学复合成因.生物成因碳酸盐岩为藻灰/云岩类;机械-化学复合成因碳酸盐岩为颗粒灰/云岩类和泥晶灰/云岩.柴达木盆地碳酸盐岩发育颗粒滩-灰/云坪、颗粒滩(鲕粒滩)-藻丘、藻席-灰/云坪、颗粒滩-藻丘(席)-灰/云坪4种类型组合样式;灰/云坪储层在柴达木盆地西部地区大面积分布,颗粒滩储层分布于水体较浅、水动力条件相对较强的滨浅湖亚相带中,藻丘(席)分布在滨浅湖亚相内的清水、富氧环境中.

In recent years, tight oil reservoirs have been found in the upper Ganchaigou Formation (Neogene) of Zhahaquan area, Qaidam Basin, but the source rock–reservoir relationship is unclear and the favorable source rock identification and prediction method need to be built urgently. Based on the experimental data of source rock samples in the study area, it is found that there are a lot of differences between favorable and useless source rocks such as color, degree of redox, salinity, paleo-water depth, carbonate content, TOC, and sedimentary environment. Moreover, after analyzing logging responses of source rock, ΔGR and Th/U are selected to calculate TOC because the two parameters are most sensitive to organic matter abundance. Furthermore, we found that the source rocks in the shallow lake area and beach bars are longitudinally superimposed on each other, and this combination is beneficial to form high-class source rock–reservoir collocation. And, the distribution of source rocks in shallow lake area is basically parallel to the lake shoreline and is consistent with the strike of beach bars. This method can be applied to favorable source rock identification and prediction of different types of areas.

英雄岭构造带位于柴达木盆地西部地区,先后发现了狮子沟、花土沟、油砂山、英东等多个新近系油气田,是柴达木盆地石油勘探的主战场.为了拓展英雄岭构造带新近系碎屑岩岩性油气藏勘探领域,通过野外露头、钻井岩心、粒度测试等资料的综合分析,明确新近系碎屑岩发育滨浅湖滩坝、辫状河三角洲水下分流河道两种类型砂体.在湖退沉积背景下,受西部物源控制的辫状河三角洲水下分流河道砂体逐步向湖盆进积,北西—南东向斜列式分布的滨浅湖滩坝砂体向湖盆迁移;上干柴沟组辫状河三角洲水下分流道砂体发育在构造带以西地区,滩坝砂体发育在构造带西翼及核部;下油砂山组辫状河三角洲水下分流河道砂体发育在构造带西翼及核部,滩坝砂体分布在构造带核部及东翼.构造演化特征表明,新近系上干柴沟组、下油砂山组沉积时期储层砂体分布在斜坡区,而现今的英雄岭构造带为新近系狮子沟组沉积末期形成的晚期反转构造,早期沉积的砂体在构造反转背景下可形成上倾尖灭岩性圈闭、砂岩透镜体岩性圈闭,是寻找规模岩性油藏的有利勘探目标区.

柴达木盆地昆北油田切12区发育厚层砂砾岩油藏.砂砾岩成因类型及分布规律认识不清是制约油藏开发的关键地质因素.综合利用地质、测井、地震及开发动态等资料,在等时层序地层格架内,系统研究砂砾岩的成因类型、分布规律及其对油气富集的控制作用.研究结果表明,切12区下干柴沟组下段发育冲积扇沉积,可划分出辫状水道、泥石流、漫流沉积、径流水道及洪泛平原5种沉积微相类型,可建立“泛连通体”夹间歇性水道、稳定水道形成的叠置分隔复合水道、辫状水道与漫流沉积侧向相间、径流水道镶嵌于洪泛平原泥岩4个沉积构型单元.垂向上,冲积扇整体表现为粒度下粗上细、湖进退积型的沉积序列;平面发育6个冲积扇体,呈由北向南迁移的规律.沉积相带对油气分布具明显控制作用,沉积构型单元控制油气纵向富集,扇体变迁控制油气平面聚集.

To examine the reservoir type and distribution regularity of high- and stable-yield lacustrine carbonates in the upper Member of Paleogene Xiaganchaigou Formation of Yingxi region and to determine the high-efficiency hydrocarbon exploration direction, the origin and significance of carbonate breccia in this area were investigated based on comprehensive analysis of a large number of well cores, thin sections, rock and mineral testing and log-seismic data. The study reveals that the carbonate breccia has three origins: (1) Sedimentary breccia, formed by the event-related collapse, fragmentation and re-deposition of the early weakly consolidated carbonate rock in the steep slope of underwater paleohighs due to short-term high-energy water body reformation and other geological processes. (2) Diagenetic breccia, with breccia-like structure, formed by deformation or breaking of host rock due to growth of idiomorphic and coarse crystalline gypsum-salt minerals in the weakly consolidated argillaceous carbonate rock of the penecontemporaneous period. (3) Tectonic breccia, can be further divided into fault breccia and interlayer slip breccia according to their occurrence characteristics, both of which are closely related to activity of the Shizigou thrust Fault. With a large number of partially filled pores, vugs and fractures between breccia, the two types of tectonic breccia are high- and stable-yield reservoirs in deep Yingxi region, and may occur extensively under gypsum-salt detachment layers of adjacent areas, so they are the exploration targets in the next step. Sedimentary breccia and diagenetic breccia are of great significance in searching for large-scale carbonate reservoirs.

Metamorphic rock gas reservoirs whose protolithic is sedimentary rock were found for the first time in Pingxi area, Altun foreland, Qaidam Basin. Comprehensive analysis containing core data, thin section analysis, X-ray diffraction analysis, scanning electron microscopy and confocal laser scanning shows that there are three types of shallow metamorphic rock reservoirs in Pingxi area, such as slate, “metamorphic limestone” and calc-schist which have good responses in logging and seismic data. Fractures and pores develop in epimetamorphic rock reservoir, and there are five types and eight subcategories of reservoir space. Industrial CT shows that there are differences in pores and throats of the three types of metamorphic rock reservoirs, and the fractures have a significant impact on the development of pore throats. The protolithic type is the genetic basis of epimetamorphic rock reservoirs in Pingxi area, and thin section, mineral characteristics and carbon and oxygen isotopes data show that the protolithic of epimetamorphic rock is Palaeozoic Ordovician marine sedimentary rock. Five kinds of actions, such as metamorphism, weathering, structural fragmentation, dissolution and filling, are external mechanisms of reservoir genesis. Metamorphic, weathering and structural fragmentation form fractures, and dissolution is the main cause of matrix porosity.