Characteristics and exploration targets of Chang 7 shale oil in Triassic Yanchang Formation, Ordos Basin, NW China

The geological characteristics and enrichment laws of the shale oil in the third submember of the seventh member of Triassic Yanchang Formation(Chang 7_(3)) in the Ordos Basin were analyzed by using the information of core observations, experiments and logging, and then the exploration potential and orientation of the Chang 7_(3) shale oil were discussed. The research findings are obtained in three aspects. First, two types of shale oil, i.e. migratory-retained and retained, are recognized in Chang 7_(3). The former is slightly better than the latter in quality. The migratory-retained shale oil reservoir is featured with the frequent interbedding and overlapping of silty-sandy laminae caused by sandy debris flow and low-density turbidity current and semi-deep-deep lacustrine organic-rich shale laminae. The retained shale oil reservoir is composed of black shale with frequent occurrence of bedding and micro-laminae. Second, high-quality source rocks provide a large quantity of hydrocarbon-rich high-quality fluids with high potential energy. The source-reservoir pressure difference provides power for oil accumulation in thin interbeds of organic-poor sandstones with good seepage conditions and in felsic lamina, tuffaceous lamina and bedding fractures in shales. Hydrocarbon generation-induced fractures, bedding fractures and microfractures provide high-speed pathways for oil micro-migration. Frequent sandstone interlayers and felsic laminae provide a good space for large-scale hydrocarbon accumulation, and also effectively improve the hydrocarbon movability. Third, sand-rich areas around the depression are the main targets for exploring migratory-retained shale oil. Mature deep depression areas are the main targets for exploring retained oil with medium to high maturity. Theoretical research and field application of in-situ conversion in low-mature deep depression areas are the main technical orientations for exploring retained shale oil with low to medium maturity.

Predicting the present-day in situ stress distribution within the Yanchang Formation Chang 7 shale oil reservoir of Ordos Basin, central China

The Yanchang Formation Chang 7 oil-bearing layer of the Ordos Basin is important in China for producing shale oil.The present-day in situ stress state is of practical implications for the exploration and development of shale oil;however,few studies are focused on stress distributions within the Chang 7 reservoir.In this study,the present-day in situ stress distribution within the Chang 7 reservoir was predicted using the combined spring model based on well logs and measured stress data.The results indicate that stress magnitudes increase with burial depth within the Chang 7 reservoir.Overall,the horizontal maximum principal stress(SHmax),horizontal minimum principal stress(Shmin) and vertical stress(Sv) follow the relationship of Sv≥SHmax>Shmin,indicating a dominant normal faulting stress regime within the Chang 7 reservoir of Ordos Basin.Laterally,high stress values are mainly distributed in the northwestern parts of the studied region,while low stress values are found in the southeastern parts.Factors influencing stress distributions are also analyzed.Stress magnitudes within the Chang 7 reservoir show a positive linear relationship with burial depth.A larger value of Young's modulus results in higher stress magnitudes,and the differential horizontal stress becomes higher when the rock Young's modulus grows larger.

Formation patterns of Chang 9 oil reservoir in Triassic Yanchang Formation, Ordos Basin, NW China

Based on analysis of main controlling factors of Chang 9, the source rock, driving force of migration, migration and accumulation modes, reservoir forming stages and model and enrichment law of Chang 9 reservoir were examined. The study showed that the oil of Chang 9 reservoir in the Jiyuan and Longdong(Eastern Gansu) areas came primarily from the source rock of Chang 7 Member, but the oil of Chang 9 reservoir in the Zhidan area came primarily from the source rock of Chang 9 Member. There developed lithologic-structural oil reservoirs in Gufengzhuang-Mahuangshan area in northwest Jiyuan, structural-lithologic oil reservoirs in east Jiyuan, and lithologic reservoirs in Huachi–Qingcheng area and Zhidan area. The overpressure of Chang 7 Member was the driving force of oil migration. The burial history showed that Chang 9 Member experienced two stages of reservoir forming, the reservoir formed in the Late Jurassic was smaller in charging scope and scale, and the Early Cretaceous was the period when the source rock generated oil and gas massively and the Chang 9 reservoir came into being. Along with the tectonic movements, Chang 7 bottom structure turned from high in the west and lower in the East in the sedimentary stage to high in the east and lower in the west in the hydrocarbon accumulation stage and at last to gentle western-leaning monoclinal structure at present. In Early Cretaceous, the Chang 7 bottom structure was the lowest in the west of Huanxian-Huachi-Wuqi-Dingbian areas, so the oil migrated laterally towards the higher positions around after entering the reservoir. In the main reservoir forming period, Chang 7 bottom had an ancient anticline in Mahuangshan-Hongjingzi area of west Jiyuan, controlling the oil reservoir distribution in west Jiyuan.

Geological characteristics and exploration of shale oil in Chang 7 Member of Triassic Yanchang Formation, Ordos Basin, NW China

A set of shale-dominated source rocks series were deposited during the heyday of lake basin development in the Member 7 of Triassic Yanchang Formation,Ordos Basin,and the thickness is about 110 m.Aimed at whether this layer can form large-scale oil enrichment of industrial value,comprehensive geological research and exploration practice have been carried out for years and obtained the following important geologic findings.Firstly,widely distributed black shale and dark mudstone with an average organic matter abundance of 13.81%and 3.74%,respectively,lay solid material foundation for the formation of shale oil.Secondly,sandy rocks sandwiched in thick organic-rich shale formations constitute an oil-rich"sweet spot",the average thickness of thin sandstone is 3.5 m.Thirdly,fine-grained sandstone and siltstone reservoirs have mainly small pores of 2–8μm and throats of 20–150 nm in radius,but with a large number of micro-pores and nano-throats,through fracturing,the reservoirs can provide good conductivity for the fluid in it.Fourthly,continued high-intensity hydrocarbon generation led to a pressure difference between the source rock and thin-layer reservoir of up to 8–16 MPa during geological history,driven by the high pressure,the oil charged into the reservoirs in large area,with oil saturation reaching more than 70%.Under the guidance of the above theory,in 2019,the Qingcheng Oilfield with geologic oil reserves of billion ton order was proved in the classⅠmulti-stage superimposed sandstone shale reservoir of Chang 7 Member by the Changqing Oilfield Branch through implementation of overall exploration and horizontal well volume fracturing.Two risk exploration horizontal wells were deployed for the classⅡthick layer mud shale interbedded with thin layers of silt-and fine-sandstones reservoir in the Chang 73 submember,and they were tested high yield oil flows of more than 100 tons per day,marking major breakthroughs in petroleum exploration in classⅠshale reservoirs.The new discoveries have expanded the domain of unconventional petroleum exploration.

A quantitative evaluation for well pattern adaptability in ultra-low permeability oil reservoirs:A case study of Triassic Chang 6 and Chang 8 reservoirs in Ordos Basin

Based on the previous studies and development practice in recent 10 years, a quantitative evaluation method for the adaptability of well patterns to ultra-low permeability reservoirs was established using cluster analysis and gray correlation method, and it includes 10 evaluation parameters in the four aspects of optimal evaluation parameters, determination of weights for evaluation parameters, development stage division, and determination of classification coefficients. This evaluation method was used to evaluate the well pattern adaptability of 13 main ultra-low permeability reservoirs in Triassic Chang 6 and Chang 8 of Ordos Basin. Three basic understandings were obtained: Firstly, the well pattern for ultra-low permeability type-I reservoirs has generally good adaptability, with proper well pattern forms and well pattern parameters. Secondly, square inverted nine-spot well pattern is suitable for reservoirs with no fractures; rhombic inverted nine-spot injection pattern is suitable for reservoirs with some fractures; and rectangular well pattern is suitable for reservoirs with rich fractures. Thirdly, for the ultra-low permeability type-Ⅱ and type-Ⅲ reservoirs, with the principles of well pattern form determination, the row spacing needs to be optimized further to improve the level of development of such reservoirs.

Distribution of shallow water delta sand bodies and the genesis of thick layer sand bodies of the Triassic Yanchang Formation, Longdong Area, Ordos Basin

Based on the cores from 47 wells and logging data of 130 wells,the main types of sand bodies in the shallow water delta of the Chang 8_(2) sub-member in the Triassic Yanchang Formation,Longdong Area,Ordos Basin were comprehensively analyzed,the distribution characteristics of sand bodies more than 20 m thick were identified,and the genetic types of the thick sand bodies were sorted out.In this region,thick-bed sand bodies can be divided into two types according to the shape and position:type 1 is the sand body in wide strip and is distributed between the average high water mark and the average low water mark;type 2 is distributed on both sides of the average low water mark and is in irregular lump shape.Based on the principle of the volume distribution of sediments and the change rule of accommodation space,the genetic models of two types of thick-bed sand bodies in the Chang 8_(2) sub-member are superimposed distributary channel sand bodies in high accommodation space and superimposed composite sand bodies in low accommodation space.

姬塬地区长8油层组储层特征分析

为确定长8油层储层现今表征,储层物性受黏土矿物胶结物控制模式,储层沉积作用和沉积后期所经历的成岩变化,通过铸体薄片、扫描电镜等方法研究了储层基本特征和成岩作用及沉积作用,在整体低渗的背景下,部分位于相对渗透率较高区域的油井有较高的产量,理清研究区长8储层富集规律,对地区内岩石孔隙度下降因素进行剖析。结果表明,姬塬地区有利储层多发育水下分流河道和河口坝沉积,特别是砂体中心部位储层物性是最好,可见长8油层组的储集性能和渗流性能好,即粒间孔型、粒间孔+溶孔型和溶孔+粒间孔型。溶孔型、粒间孔+微孔型两种孔隙组合类型的渗流性能较差。微孔型和溶孔+微孔型两种孔隙组合类型的储集空间主要由半径极小的微孔构成,连通性较差,其孔隙内表面积和渗流阻力,储集性能和渗流性能较差。

鄂尔多斯盆地陇东地区长8油层组物源分析

鄂尔多斯盆地陇东地区延长组沉积物来源,尤其是西部物源争议较大。为探究陇东地区延长组中长8油层组的物源,对陇东地区周缘母岩的特征、碎屑岩中轻重矿物和岩屑组合特征,以及古水流和稀土元素对比分析,对研究区长8油层组的物源进行了总结。结果表明:研究区长8油层组轻矿物、岩屑、重矿物物源分区表现出较好的一致性;油层组受多个物源控制,主要为西南和东北物源,次要为西北、西部和南部物源,各个物源在樊家川-华池-安置农场一带汇聚;延长期沉积走廊与鄂尔多斯盆地具有一定的连通性,西部物源供给以河西走廊源区为主,海源古隆起为辅,二者叠加影响。

吴起油田白河北部长8储层特征及其控制因素研究

为对吴起油田长8地区的储层特征存进行进一步深入的了解,利用研究区内高压压汞、岩石薄片、铸体薄片以及物性特征等资料,对吴起油田白河北部长8储层的岩石学特征、孔隙类型及结构、孔渗特征等进行研究,并对可能影响储层物性的因素进行讨论,得出:沉积微相和成岩作用是影响该储层的主要因素。储层特征:分流间湾、下分流河道和远砂坝是白河北部长8沉积微相主要的存在形式,其河口坝的发育程度较低,以浅灰、灰色细粒长石砂岩和岩屑长石砂岩为主要的岩石类型,研究区孔隙类型以岩屑溶孔、长石溶孔、粒间孔隙居多,晶间孔的数量较少,可见少量的微裂隙。总体上看长8储层的类型属特低孔、超低渗致密储层。分析研究范围各小层的物性可得,其中长8_(2)^(2)物性最好。

富县M区延长组长8资源潜力分析

富县M区自勘探以来,对长8油藏特征了解较少。为阐明其油藏分布规律,在大量资料与研究成果的基础上,对该区沉积微相、储层特征及油藏特征进行分析,预测油气勘探有利区,为该区的下步详细勘探与开发提供依据。

Factors controlling the reservoir accumulation of Triassic Chang 6 Member in Jiyuan-Wuqi area,Ordos Basin,NW China

In the Triassic Yanchang Formation, Jiyuan-Wuqi area, Ordos Basin, the Chang 6 reservoir is contacted to the Chang 7 high-quality source rock, but the oil pools are unevenly distributed, and complex in oil and water distribution. Through cores observation and fracture statistics, combined with comprehensive analyses of physical property, mercury injection, logging and geochemical data, and comparisons of the sandbodies scales, reservoir physical properties, argillaceous laminae and fractures between source and reservoir in the eastern and western oil-bearing areas and in the central water producing area, it is found that the hydrocarbon accumulation patterns are different in the eastern, central and western areas, and the characteristics of hydrocarbon migration under the background of double-provenance were sorted out. The study results show that the crude oil in the eastern area has different Pr/Ph and sterane distribution from that in the western area. The oil and gas primarily migrated vertically. The high-quality source rocks and favorable source-reservoir-cap combinations lay the foundation for large-scale oil and gas accumulations. Vertically, the oil and gas enrichment is controlled by the scale of sandbody and the difference of physical properties, while on the plane, it is controlled by the connectivity of sandbodies, the argillaceous laminae between source rock and reservoir, the reservoir physical property and the fractures. The sandbodies of oil-rich zones in the eastern and western areas have large thickness, low shale content, good physical properties, weak heterogeneity, few argillaceous laminae and abundant fractures, all of which are favorable for the vertical migration and accumulation of oil and gas. In contrast, in the middle area with converging provenances, the reservoirs, composed of thin sandbodies, features rapid variation in lithology and physical properties, strong heterogeneity, poor continuity of sandbodies, abundant argillaceous laminae between source rock and reservoir, and few fractures, makes it difficult for the oil and gas to migrate vertically, and results in low oil enrichment degree ultimately. For the exploration of continental multiple-provenance tight reservoirs, not only the good-property source rocks and reservoirs, but more importantly the source-reservoir contact relationship and the effect of fractures on the hydrocarbon migration and accumulation should be considered.

吴起油田白豹地区东部长8、长9储层特征研究

对鄂尔多斯盆地吴起油田白豹东部地区长8、长9储层进行储层特征研究。结果表明:白豹东部长8和长9储层的砂岩多为长石砂岩和岩屑长石砂岩;储层孔喉类型属于细孔粗喉,渗透率为强非均质型;长8砂体发育好,长9砂体发育程度差。同时储层敏感性研究表明:白豹项目区的长8、长9储层均为弱-中速敏、弱水敏和弱碱敏及中偏弱应力敏特征,但长8储层显示为弱酸敏,长9储层为强酸敏。

鄂尔多斯盆地富县地区长8段油气成藏主控因素研究

近年来,富县地区延长组长8段油层组发现了工业油流井,但平面分布不均,具有点状含油的特点,勘探开发总体显示出该区具有多层位含油、局部层位富集的特征,但油水分布主控因素与富集规律尚不清楚,制约了该区下组合油气的勘探开发,为此,基于钻井和生产资料,分析了研究区长8段油层组的油藏类型、主控因素和成藏模式,研究表明,区内长8段油藏类型主要为上倾尖灭岩性油藏、透镜状岩性油藏和致密层遮挡岩性油藏;油气成藏受烃源岩、储层物性、砂体厚度、局部构造共同控制;长8段油气成藏模式为典型的三明治型,有利于致密油的形成。

鄂尔多斯盆地平凉北地区上三叠统长8段储层低含油饱和度油藏特征及成因

通过岩心物性分析、恒压压汞和核磁共振测试,结合油源、构造等资料,对鄂尔多斯盆地平凉北地区上三叠统长8段储层低含油饱和度油藏的特征及成因进行了分析。研究结果表明:①平凉北地区上三叠统长8段储层含油饱和度普遍低于20%,而含水饱和度则普遍高于50%,属于典型的低含油饱和度油藏,且单井产量低,油水分异差,油藏呈零星状分布在长8段储层顶部。②供烃量不足是研究区油藏含油饱和度低的根本原因。M53井区为异地成藏,供烃距离较远导致供烃量不足;Y80井区为原地成藏,原地烃源岩排烃量小导致油气充注不足。③M53井区受低幅度构造影响,油气垂向和侧向运移动力不足。全区储层物性非均质性强,微细孔喉较为发育,束缚水占比大,可动水占比小,导致油气驱替可动水后其饱和度较低,从而使研究区油藏分布较分散、含油饱和度较低。④M53井区上新庄地区西南部构造高部位物性较好的储层为下一步增储上产的重要目标。

甘泉油田长8油藏水下分流河道砂体钙质夹层特征及成因

钙质夹层研究对油田开发初期井网布置、后期增储上产等具有重要意义。通过岩心观察、铸体薄片观察、扫描电镜观察、测井资料分析等手段,对甘泉油田延长组长8段钙质夹层岩性、电性、分布成因及其对储集层非均质性的影响开展了系统研究。结果表明,钙质夹层发育受水下分流河道微相控制,主要发育在砂体顶部和底部,具有稳定性较高、厚度较大等特征,此外,具有低自然伽马、低声波时差、高电阻率的测井响应特征。钙质夹层发育主要受控于2期方解石胶结,第一期与同生成岩期方解石的过饱和沉淀有关,此时期,壳类生物残体的溶解、河流携带的Ca^(2+)及CO_(2)^(3-)、大气中CO_(2)的溶解等是方解石胶结的物质来源;第二期方解石胶结为中成岩阶段B期的孔隙式胶结,地层中残留流体的Ca^(2+)及CO_(2)^(3-)、不稳定组分溶蚀、黏土矿物转化等为钙质胶结提供了Ca^(2+)及CO_(2)^(3-)。钙质夹层的发育增强了储集层砂体的层内非均质性,导致砂体垂向连通性变差和油水关系复杂。在油藏注水开发过程中,钙质夹层与相邻非渗透性隔夹层斜交形成有效隔挡,形成局部剩余油富集区。

鄂尔多斯盆地陕北地区长8致密砂岩流体包裹体特征与石油成藏

【研究目的】鄂尔多斯盆地陕北地区延长组长8含油分布范围广,是下步勘探重要的目标领域,但其石油烃类演化和油藏分布的关系尚不清楚。【研究方法】基于流体包裹体产状特征、成分及均一性分析结果,综合地质与地球化学方法,探讨了鄂尔多斯盆地陕北地区长8致密砂岩储层内石油的来源及成藏特征,揭示了长8油藏形成时间以及与油气成藏的关系。【研究结果】长8砂岩储层中的流体包裹体以气液烃包裹体、气液两相盐水包裹体为主,主要分布于细砂岩的石英加大边或裂隙中,可分为早、晚两期,与气液烃包裹体伴生的盐水包裹体均一温度主要存在85~105℃和115~135℃两个峰值区间,分布连续,油气为连续充注;成藏演化史表明,长8石油主要充注时期为110~135 Ma,在晚侏罗世发生早期充注,在早白垩世发生大规模充注。在区域上主要发育长7烃源岩,在最大生排烃阶段烃源岩Ro值接近1.0%,达到生烃门限,大量生烃,长9烃源岩在志丹地区局部分布。【结论】结合包裹体特征与烃类形成的关系,陕北地区长8油藏受烃源岩、储层及充注动力等因素控制,石油充注程度不一,发育平面上分布不均匀的岩性油藏,区域上具有“双源供烃、差异聚集”的成藏特点。

陇东地区HQ区块东部长8致密砂岩储集层成岩相划分

为确定鄂尔多斯盆地陇东地区HQ区块东部长8致密砂岩储集层成岩相及其演化规律,综合铸体薄片、岩石物性、岩心、测井等资料,在划分单砂层岩心成岩相和测井相后,采用优势相法,对研究区长8含油层系成岩相进行分类,筛选出对油气勘探有利的成岩相,预测其有利成岩相带展布。依据成岩作用的影响,可将目的层成岩相划分为5类:剩余粒间孔与长石溶蚀相、绿泥石胶结剩余粒间孔相、绿泥石与伊利石强胶结相、自生碳酸盐胶结相和黏土杂基压实相。剩余粒间孔与长石溶蚀相为研究区最利于油气储集的成岩相类型,有利成岩相总体上呈条带状展布,连续性较好,分布面积较大,研究区中部是有利成岩相带的主要发育区。

Kinetic simulation of hydrocarbon generation and its application to in-situ conversion of shale oil

The kinetic parameters of hydrocarbon generation are determined through experimental simulation and mathematical calculation using four typical samples selected from the Cretaceous Nenjiang Formation in the northwest of Songliao Basin,Chang 7 Member of Triassic Yanchang Formation in the southwest of Ordos Basin,Paleogene in the southwest of Qaidam Basin,and Lucaogou Formation of Jimusar Sag in the east of Junggar Basin.The results show that activation energy of hydrocarbon generation of organic matter is closely related to maturity and mainly ranges between 197 kJ/mol and 227 kJ/mol.On this basis,the temperature required for organic matter in shale to convert into oil was calculated.The ideal heating temperature is between 270℃and 300℃,and the conversation rate can reach 90%after 50-300 days of heating at constant temperature.When the temperature rises at a constant rate,the temperature corresponding to the major hydrocarbon generation period ranges from 225 to 350℃at the temperature rise rate of 1-150℃/month.In order to obtain higher economic benefits,it is suggested to adopt higher temperature rise rate(60-150℃/month).The more reliable kinetic parameters obtained can provide a basis for designing more reasonable scheme of in-situ heating conversion.

镇原油田H45区长8断块油藏地质综述

随着勘探开发的不断深入,镇原油田H45井区以长8为目的层滚动建产取得了较好效果。通过小层对比、沉积微相、构造特征、砂体展布、油气成藏特征等方面,深入认识H45区三叠系长8油藏。结果表明,研究区长8油藏储层物性较差,属特低-超低渗储层,砂体南西—北东走向,H45井区附近砂体最厚。受断层影响,本区长8主要发育构造—岩性油藏,油藏主要受岩性因素控制,储层物性不同造成含油性存在差异。结合开发井参数,明确了长8油藏的出油下限及油水界面。甩开井实施结果表明,本区东南部仍有扩边潜力,下一步将针对长8油层继续滚动实施。研究成果为后期建产提供了可靠的地质依据。

下寺湾油田桥镇区长8致密油藏主控因素分析

下寺湾油田桥镇区长8油藏属于典型的致密油藏。通过分析认为,长8沉积期三角洲前缘砂体控制致密油藏规模,优质烃源岩的分布控制致密油分布范围,有效的储集空间控制石油储集量,良好源储配置控制着致密油藏的富集程度,多重因素的有利组合是桥镇区长8致密油藏的主控因素。