Sequence Stratigraphy of the Palaeogene in the HGZ Area of Qaidam Basin

Sequence stratigraphy can be used to predict the oil and gas reservoir bodies and to choose the oil targets. Fan delta and sublacustrine fan systems are developed in the HGZ Area, which is located in front of the Altun Mountain in the west of the Qaidam Basin. On the basis of seismic and well drilling data, the deposits in the area were studied by using sequence stratigraphy and reservoir prediction techniques. Various reservoir prediction techniques used under the constraint of high resolution sequence framework could help to improve the precision of reservoir prediction and to recognize the pinch out line of sand layers, the distribution of isolated sandstone bodies and the types of oil pools. The study of sequence stratigraphy makes reservoir prediction more effective by dividing different scales of sequences and distinguishing the system tracts and parasequence sets, and indicates the internal relationship between oil/gas and sedimentary bodies in different system tracts with evolution in time and space.     

Geochemical studies of the Silurian oil reservoir in the Well Shun-9 prospect area, Tarim Basin, NW China

Commercial oil flow has been obtained from the sandstone reservoir of the Lower Silurian Kelpintag Formation in the Well Shun-9 prospect area.In the present studies,10 Silurian oil and oil sand samples from six wells in the area were analyzed for their molecular and carbon isotopic compositions,oil alteration（biodegradation）,oil source rock correlation and oil reservoir filling direction.All the Silurian oils and oil sands are characterized by low Pr/Ph and C21/C23 tricyclic terpane（〈1.0） ratios,＂V＂-pattern C27-C29 steranes distribution,low C28-sterane and triaromatic dinosterane abundances and light δ13C values,which can be correlated well with the carbonate source rock of the O3 l Lianglitage Formation.Different oil biodegradation levels have also been confirmed for the different oils/oil sands intervals.With the S1k2 seal,oils and oil sands from the S1k1 interval of the Kelpintag Formation have only suffered light biodegradation as confirmed by the presence of ＂UCM＂ and absence of 25-norhopanes,whereas the S1k3-1 oil sands were heavily biodegraded（proved by the presence of 25-norhopanes） due to the lack of the S1k2 seal,which suggests a significant role of the S1k2 seal in the protection of the Silurian oil reservoir.Based on the Ts/（Ts＋Tm） and 4-/1-MDBT ratios as reservoir filling tracers,a general oil filling direction from NW to SE has been also estimated for the Silurian oil reservoir in the Well Shun-9 prospect area.     

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.     

Alluvial Fan Facies and Their Distribution in the Lower Talang Acar Formation, Northeast Betara Oilfield, Indonesia

This paper studies the alluvial fan facies characteristics and distribution in the Lower Talang Acar Formation in the Northeast Betara Oilfield. The conglomerate sedimentary characteristics and its distribution were studied based on core data, logging interpretation and seismic property analysis. The research indicated that alluvial fan deposits of Bed F in the Lower Talang Akar Formation were characterized by coarse granularity, poor sorting and low quality. Sand-bodies accumulate longitudinally, and inter-layers are poorly developed, extending locally in the transverse orientation. Typical logging response of alluvial fan system is summarized, and conglomerate is characterized by low gamma-ray (GR) intensity, low resistance, high density and low value between DLD and LLD, which reflects poor physical reservoir properties, coarse rocks and relatively high density. Conglomerate is developed mainly in the northeast and middle-south of the studied area. The upper part of bed F is found in a small area in the middle-south, while the lower part of bed F is developed in a relatively large area in the middle-south.     

Prediction of Interbeds Intercalated into Complex Heterogeneous Reservoirs at a High Water Cut Stage

The occurrence of interbeds in thick oil formations is one of the main reasons that cause the difference of remaining oil distribution. A quantitative method for predicting interbeds was proposed and the sedimentary origin and division criterion were demonstrated. The distribution of interbeds in different types of sedimentary sand bodies were predicted and analyzed by combining the theory of sedimentology and reservoir bed architectural-element analysis. The interbeds in a single well were recognized from high resolution well logs, and inter-well interbeds were predicted by using the methods of cyclothem correlation, physical properties truncation, and conditional simulation. Finally a 3-D model of interbed was built. Application to the Gudao Oilfield was successful.     

Micro-geological causes and macro-geological controlling factors of low-resistivity oil layers in the Puao Oilfield

Low-resistivity oil layers are often missed in logging interpretation because of their resistivity close to or below the resistivity of nearby water layers. Typical low-resistivity oil layers have been found in the past few years in the Putaohua reservoir of the Puao Oilfield in the south of the Daqing placanticline by detailed exploration. Based on a study of micro-geological causes of low-resistivity oil layers, the macro-geological controlling factors were analyzed through comprehensive research of regional depositional background, geological structure, and oil-water relations combined with core, water testing, well logging, and scanning electron microscopy data. The results showed that the formation and distribution of Putaohua low-resistivity oil layers in the Puao Oilfield were controlled by depositional environment, sedimentary facies, diagenesis, motive power of hydrocarbon accumulation, and acidity and alkalinity of reservoir liquid. The low-resistivity oil layers caused by high bound-water saturation were controlled by deposition and diagenesis, those caused by high free-water saturation were controlled by structural amplitude and motive power of hydrocarbon accumulation. Those caused by formation water with high salinity were controlled by the ancient saline water depositional environment and faulted structure and those caused by additional conductivity of shale were controlled by paleoclimate and acidity and alkalinity of reservoir liquid. Consideration of both micro-geological causes and macro-geological controlling factors is important in identifying low-resistivity oil layers.     

Mechanism of diagenetic trap formation in nearshore subaqueous fans on steep rift lacustrine basin slopes—A case study from the Shahejie Formation on the north slope of the Minfeng Subsag,Bohai Basin,China

Diagenetic traps in conglomerate in nearshore subaqueous fans in the steep slope zones of rift basins have been important exploration targets for subtle reservoirs in eastern China. However, the mechanism of how those traps were formed is not clear, which inhibits further exploration for this type of reservoir. In order to solve the problem, we take as an example nearshore subaqueous fans in the upper part of the fourth member of the Shahejie Formation(Es4s) on the north slope of the Minfeng Subsag in the Dongying Sag. Combining different research methods, such as core observation, thin section examination, scanning electron microscope(SEM) observation, fluid-inclusion analysis, carbon and oxygen isotope analysis of carbonate cements, and analysis of core properties, we studied the genetic mechanisms of diagenetic traps on the basis of diagenetic environment evolution and diagenetic evolution sequence in different sub/micro-facies. Conglomerate in Es4 s in the north Minfeng Subsag experienced several periods of transition between alkaline and acidic environments as "alkaline–acidic–alkaline–acidic–weak alkaline". As a result, dissolution and cementation are also very complex, and the sequence is "early pyrite cementation / siderite cementation / gypsum cementation / calcite and dolomite cementation——feldspar dissolution / quartz overgrowth——quartz dissolution / ferroan calcite cementation / ankerite cementation / lime-mud matrix recrystallization / feldspar overgrowth——carbonate dissolution / feldspar dissolution / quartz overgrowth / pyrite cementation". The difference in sedimentary characteristics between different sub/micro-facies of nearshore subaqueous fans controls diagenetic characteristics. Inner fan conglomerates mainly experienced compaction and lime-mud matrix recrystallization, with weak dissolution, which led to a reduction in the porosity and permeability crucial to reservoir formation. Lime-mud matrix recrystallization results in a rapid decrease in porosity and permeability in inner fan conglomerates in middle-to-deep layers. Because acid dissolution reworks reservoirs and hydrocarbon filling inhibits cementation, reservoirs far from mudstone layers in middle fan braided channels develop a great number of primary pores and secondary pores, and are good enough to be effective reservoirs of hydrocarbon. With the increase of burial depth, both the decrease of porosity and permeability of inner fan conglomerates and the increase of the physical property difference between inner fans and middle fans enhance the quality of seals in middle-to-deep layers. As a result, inner fan conglomerates can be sealing layers in middle-to-deep buried layers. Reservoirs adjacent to mudstones in middle fan braided channels and reservoirs in middle fan interdistributaries experienced extensive cementation, and tight cemented crusts formed at both the top and bottom of conglomerates, which can then act as cap rocks. In conclusion, diagenetic traps in conglomerates of nearshore subaqueous fans could be developed with inner fan conglomerates as lateral or vertical sealing layers, tight carbonate crusts near mudstone layers in middle fan braided channels as well as lacustrine mudstones as cap rocks, and conglomerates far from mudstone layers in middle fan braided channels as reservoirs. Lime-mud matrix recrystallization of inner fan conglomerates and carbonate cementation of conglomerates adjacent to mudstone layers in middle fan braided channels took place from 32 Ma B.P. to 24.6 Ma B.P., thus the formation of diagenetic traps was from 32 Ma B.P. to 24.6 Ma B.P. and diagenetic traps have a better hydrocarbon sealing ability from 24 Ma B.P.. The sealing ability of inner fans gradually increases with the increase of burial depth and diagenetic traps buried more than 3,200 m have better seals.     

Hydrocarbon accumulation characteristics of beach-bar sandstones in the southern slope of the Dongying Sag, Jiyang Depression, Bohai Bay Basin, China

A number of beach-bar sandstone reservoir beds are developed in the upper fourth member of the Eocene Shahejie Formation （Es4s） on the southern slope of the Dongying Sag.Based on the analysis of seismic and logging data,with characterization and petrographic studies of core and cutting samples,this paper analyzes the hydrocarbon accumulation characteristics in two typical blocks of the Boxing and Wangjiagang oilfields,especially reservoir bed heterogeneity and migration conditions that influence oil and gas distribution,calculates the index of reservoir bed quality （IRQ） with a mathematical method,and discusses the relationship between driving force and resistance of hydrocarbon accumulation.Taking into account the characteristics of thin interbeds in beach-bar sandstones,an experimental model simulated the characteristics of hydrocarbon migration and accumulation in thin interbedded sandstones with reservoir bed heterogeneity.The results showed that hydrocarbon distribution and properties were extremely non-uniform.Reservoir bed and migration conditions controlled hydrocarbon accumulation in beach-bar sandstones.IRQ is above 0.4 in the main hydrocarbon region.Sand body distribution,structural configuration and fault systems controlled the direction of regional migration and location of hydrocarbon accumulation.Simulation experiments indicated that the change of driving force for hydrocarbon migration affected selective accumulation mechanisms.Hydrocarbon moved vertically along fault zones to the reservoir and resulted in the distribution of hydrocarbon in the reservoir.Two kinds of hydrocarbon accumulation models exist in the study area.One is a hydrocarbon accumulation model controlled by reservoir bed heterogeneity and the second is a hydrocarbon accumulation model controlled by a complex migration system with faults connecting sandbodies.Finally,different exploration strategies should be adopted for the detailed exploration for beach-bar sandstone reservoirs according to different geological backgrounds.     

The Chang 7 member of the upper Triassic in the southwest Ordos Basin： Carbon isotope studay of dispersed organic matter and its paleoclimate significance

The Taoudeni Basin is a typical steady intracratonic basin. Based on the distribution of effective source rocks in the Taoudeni Basin, combined with the structure characteristics of the basin and the distribution characteristics of reservoir beds, two petroleum systems are recognized in the basin： the infra-Cambrian petroleum system and the Silurian petroleum system. Structural uplift and timing of petroleum generation controlled the timing of petroleum charging and preservation of hydrocarbon accumulations. Maturity, evolution history, and distribution of effective source rocks controlled hydrocarbon richness. The geological key factors and geological processes controlled the type of hydrocarbon accumulations.     

河流成因储层剩余油分布规律及控制因素探讨

通过对河流成因储层剩余油分布规律的研究认识 ,从影响水驱采收率的控制因素分析入手 ,阐明了储层非均质性及注采状况是剩余油分布的两大控制因素 ,进而认识到河流成因储层沉积微相是剩余油分布的主要宏观地质控制因素。对河流成因储层剩余油的认识和挖潜具有较好的指导作用。     

康台区长6油藏分布规律与主控因素分析

鄂尔多斯盆地中生界三叠系延长组长6油藏为典型的岩性油藏,油藏具有连通性差,非均质性强等特点。通过对康台区长6油藏的分布规律进行研究表明:油藏的分布主要受油源、沉积微相、储层物性等因素的控制。长7优质油页岩为本区提供了充足的油源,长6有利的沉积相带为水下分流河道和分流河道,长4+5的平原沼泽化为本区提供了区域盖层。长7、长6、长4+5的叠置关系为本区提供了非常有利的生储盖配置条件,为油藏的形成提供了有利条件。     

渤中25-1南油田明下段储层宏观非均质性研究

为了提高油田的开发效果,通过对研究区明下段浅水三角洲沉积体系内微相类型、层内韵律特征、隔层分布特征、砂体的几何形态、钻遇率、孔渗特征等研究,定量或半定量表征了该区储层的宏观非均质性,揭示了研究区主力含油层段受沉积微相所控制,具有较强的层内、层间及平面非均质性。根据研究成果,提出了针对油田切实可行的综合治理建议。     

鄂尔多斯盆地太阳湾油区长2 储层非均质性研究

储层非均质性是影响剩余油分布的重要因素之一。 近年来,太阳湾油区剩余油滞留现象严重。 针对这一现象,结合该区实际地质情况,利用区内岩性、物性、电性及含油性等资料,定性评价该区长 2 储层非均质性及其成因,并分析非均质性对储层剩余油分布的影响。 采用实验、测井及标准对比等方法,将区域非均质性分为层内、层间、平面和微观非均质性 4 类进行探讨。 结果表明：研究区层内非均质性较强,主要受沉积构造、粒度韵律、渗透率非均质性及夹层分布等因素的控制;层间非均质性总体较强,各小层发育不均一,长 2³ 小层层间非均质性相对最强,长 2² 和长 2¹ 小层次之;平面非均质性受砂体及沉积微相展布影响较大;微观上孔隙结构复杂,各种成岩作用加剧了储层非均质性程度。通过对储层非均质性的研究,可以为掌握研究区剩余油分布状况及后期勘探开发提供重要依据。     

子洲气田山2段储层非均质性研究

以子洲气田山2段(S2段)储层的测井资料为基础,结合沉积相资料,从层内、层间、及平面的非均质性三个方面研究储层的非均质性特征。研究认为,S2段储层内普遍存在夹层,以泥质夹层和致密夹层为主,通过对渗透率非均质性参数的定量计算,认为该储层S23段层内非均质较强,S21段和S22段为相对均质型储层;S2段储层具有较大的分层系数,存在层间隔层,主要为泥质隔层,分布不稳定,具有层间差异性;S2段储层各小层砂体连通性受沉积微相控制,S23段砂体连通性较好,物性分布稳定,平面非均质性差,但是其它小层平面非均质性相对较强。     

五号桩—长堤地区沙河街组砂体储集性及控制因素研究

沙河街组是沾化凹陷东部五号桩-长堤地区重要的储油层系，主要目的层段为沙三段和沙二段。沙三段和沙二段主要发育有浊积扇、水下冲积扇和滩坝沉积体系，在浊积扇、水下冲积扇中发育辫状水道、扇中前缘、辫状水道间以及扇根、扇缘等沉积微相类型，其中辫状水道、扇中前缘砂体物性好，原生孔隙及次生孔隙均较发育，辫状水道间以及扇根砂体物性较差。其储集特征主要受岩性、沉积微相、成岩作用等因素控制，结合该地区实际情况，将沙二段、沙三段储集层划分为好、中、差3种类型。图4表1参7     

河西务构造带Axx断块Es4上段沉积微相分布及其对开发的影响

以精细的小层对比为基础,通过对岩心相、地质录井相、测井相的研究,明确了河西务油田Axx断块主要为辫状河三角洲沉积,沉积微相主要为辫状河道、分流水道、席状砂;通过储层非均质性、沉积微相的分布、油层分布的研究,表明沉积相带的展布决定了平面的非均质性以及高渗条带的分布,油层分布特征表明油层的分布受构造、砂体的双重控制。沉积微相的研究指导了本断块的开发。     

三角洲平原相低弯度分流河道砂体微相及水淹变化特征——以大庆油田北部萨葡油层为例

低弯度分流河道砂体在大庆油田北部萨葡油层中占有重要比例,深入研究这类砂体的非均质特征,对油田调整挖潜具有实际意义。以沉积学知识为指导,应用密井网的测井资料和取心资料,结合微相平面展布组合特征识别出主河道、废弃河道、决口水道、河间薄层砂、泥岩等五种主要微相,并应用水淹层解释及各种动态监测资料开展了水淹变化特征研究。认为砂体层内非均质性,窄条带的河道砂体几何形态及微相间的物性差异是影响平面及纵向水淹变化特征的主要因素;随着注水开发时间的延续和强度的增加,不同微相水淹面积和水淹程度变化各不相同;剩余油主要分布在远离注水井的决口水道和河道间砂体中。     

利用测井曲线研究沉积微相及其含油有利区展布

利用测井曲线,分析地层信息与各种成因标志及其相应沉积环境中水动力因素作用关系,研究了测井相与沉积微相及其储集砂体分布发育,确认了三角洲前缘亚相水下分流河道微相及其河道叠置型河口沙坝微相是形成研究区低渗透储集砂体的有利相带。它们控制砂体的走向和分布,具有砂体连片、连通性好、厚度较大的特点。只要具备适当的圈闭条件,往往可以控制该区长3、长4+5油藏有利区的范围和规模。通过该区长332储层沉积微相和含油有利区油藏分布预测研究,油藏处在区域由西北到东南发育的5条水系水下分流河道中部及西南部主体带上,这些有利沉积相带控制和圈定的含油有利区油藏,总体具有中部向西南方向的中下游不断加强的特点,勾画出河道中部油藏与西南部华池油藏连片延伸趋势及特征,为该区油藏进一步滚动扩边开发提供了可靠的地质依据。     

砂砾岩储层分布非均质性和质量非均质性研究——以克拉玛依油田五2东区克上组为例

克拉玛依油田五2东区克上组为扇三角洲砂砾岩储层,砂体叠置关系复杂、储层非均质性严重,部分井组注水效果差。综合该区岩心、测井和实验室分析化验资料,对储层的分布和质量非均质性进行了定性分析和精细定量表征;并在相控约束下,利用熵权法计算综合非均质指数进行评价;最后将分析结果与实际生产数据相结合,总结出储层分布和质量非均质性对实际注采效果的影响。结果表明：各砂层组层间质量非均质性中等;层内渗透率以正韵律、复合正韵律和均质韵律为主,质量非均质性较强;平面上在相控约束下的同一砂体内部,储层质量非均质性表现为中等到强。垂向上S5和S1砂层组内部中厚层砂体组合分层多,其余各砂层组表现为孤立单砂体形式;平面上砂体的分布整体受沉积微相控制。储层分布非均质性是造成注采不见效的原因,储层质量非均质性则导致注采见效难,效果差,该结论对油藏下一步调整注采井网和注采措施具有重要意义。