PORE‐LINING CHLORITE CEMENTS IN LACUSTRINE‐DELTAIC SANDSTONES FROM THE UPPER TRIASSIC YANCHANG FORMATION,ORDOS BASIN,CHINA

Non‐marine sandstones in the upper Triassic Yanchang Formation constitute an important reservoir rock in the Zhenjing area of SW Ordos Basin, Central China. A study of the diagenetic history of these sandstones, including the formation of pore‐lining chlorite cements, was undertaken to investigate controls on reservoir quality. Data came from the petrographic analysis of cores from five wells. The sandstones were deposited in a lacustrine‐deltaic setting and consist of fine‐to medium‐grained feldspathic litharenites and lithic arkoses, and in general have low porosity and permeability. The principal diagenetic processes observed were compaction, cementation, dissolution and replacement. Mechanical compaction and calcite cementation caused a reduction in reservoir quality. The precipitation of pore‐lining chlorite inhibited quartz cementation and preserved porosities of up to 16%. The chlorite occurs in a double layer which lines pore spaces, particularly in distributary channel sandstones. Both chlorite layers grew by precipitation from pore waters containing the products of dissolution of volcanic rock fragments, biotites and feldspars. An increase of temperature during diagenesis was probably the cause of the two generations of chlorite cement, and also of the observed variations in elemental concentrations between the earlier‐ and later‐formed chlorite. The chlorite was precipitated after early compaction but before other diagenetic phases.     

RESERVOIR POTENTIAL OF DEEP‐WATER LACUSTRINE DELTA‐FRONT SANDSTONES IN THE UPPER TRIASSIC YANCHANG FORMATION,WESTERN ORDOS BASIN,CHINA

This paper investigates the reservoir characteristics of deep‐water lacustrine‐delta sandstones in the Upper Triassic Yanchang Formation in the western Ordos Basin, north‐central China. The Yanchang Formation has previously been interpreted as a shallow‐water lacustrine deltaic succession, and this interpretation has been used to guide petroleum exploration activities which have however met with only limited success. The present study integrates thin‐section, wireline log, X‐ray diffraction and SEM data from wells in the western Ordos Basin to determine the sedimentary and diagenetic characteristics of sandstones in the C6 and C4+5 sub‐members of the Yanchang Formation, and to interpret the units' depositional environment. The C6 and C4+5 sub‐members in the study area are composed of: mudstones and fine‐grained sandstones, which are interpreted as deep‐water pro‐delta deposits; laterally‐extensive sand sheets (outer delta‐front deposits); and small‐scale distributary channel and mouth bar sandbodies (inner delta‐front deposits). The sandstones have reservoir potential but diagenesis has had a range of effects on reservoir quality. Compaction together with cementation by calcite and clay minerals including chlorite and kaolinite may have affected pore throat geometry and permeability adversely. However dissolution of feldspars and calcite cement created secondary porosity. Hydrocarbon accumulations may occur in delta‐front channel and mouth bar sandbodies. Core studies show that some sandstone intervals have relatively good reservoir properties with porosity up to 15% and permeability up to 9mD.     

鄂尔多斯盆地长6油层组致密储层影响因素分析

鄂尔多斯盆地延长组广泛发育致密油藏.以致密油储集层的岩石学特征、物性及微观孔喉结构特征等测试分析结果为基础,对致密储层影响因素进行了分析.研究认为长6油层组岩石类型主要为中—细粒岩屑质长石砂岩,胶结类型主要为接触式胶结和接触—孔隙式胶结,物性总体较差,粒间残余孔、粒内溶蚀孔较发育,以微—细喉道为主,属低孔—特低渗储层;成岩早期的压实作用和中后期伊利石的胶结作用是造成储集层物性较差的主要原因,成岩中后期的溶蚀作用使储集层的物性得到一定改善.     

IMPACT OF DIAGENESIS ON RESERVOIR-QUALITY EVOLUTION IN FLUVIAL AND LACUSTRINE-DELTAIC SANDSTONES: EVIDENCE FROM JURASSIC AND TRIASSIC SANDSTONES FROM THE ORDOS BASIN, CHINA

The reservoir quality of Jurassic and Triassic fluvial and lacustrine‐deltaic sandstones in the intracratonic Ordos Basin is strongly influenced by depositional facies and various types of diagenetic modifications. The fluvial sandstones have higher average He‐porosity and permeability (14.8% and 12.7 mD, respectively) than the deltaic sandstones (9.8% and 5.8 mD, respectively). In addition to extensive mechanical compaction, eodiagenesis (220–97 Ma; depth < 2000 m; T < 70°C) has resulted in dissolution and kaolinitization of detrital silicates in the Jurassic fluvial sandstones, and in smectite infiltration and minor cementation by calcite and siderite in the Triassic fluvial and deltaic sandstones. Pervasive eogenetic carbonate cementation (> 20 vol.%) occurred in Triassic deltaic siltstones and very fine‐grained sandstones which are closely associated with organic‐rich mudstones. Mesodiagenesis (97–65 Ma), which occurred during rapid subsidence to depths of 3700–4400 m, resulted in the albitization of plagioclase, checmical compaction, the conversion of kaolinite into dickite, and cementation by quartz overgrowths, chlorite, illite, ankerite (δ¹³C_VPDB=?2.4‰ to +2.6‰; δ¹⁸O_VPDB=?21.5‰ to ?10‰) and calcite (δ¹³C_VPDB=?4.7‰ to +3.7‰; δ¹⁸O_VPDB=?21.8‰ to ?13.4‰). Oil emplacement (95 Ma) retarded cementation by mesogenetic quartz and carbonate but had little influence on dickite, illite and chlorite formation. Retardation of quartz cementation was also due to the presence of chlorite fringes around detrital quartz grains. Dickitization of eogenetic kaolinite together with the short residence time at maximum burial temperatures (105–124°C) has retarded the albitization of K‐feldspars and illite formation and hence prevented severe permeability destruction. Telodiagenesis, which occurred after uplift (Eocene to end‐Neogene), caused slight dissolution and kaolinitization of feldspars. This study demonstrates that despite complex patterns of diagenetic modifications in the Triassic and Jurassic successions, depositional porosity and permeability are better preserved in fluvial meandering channel sandstones than in deltaic sandstones. These results should be important for modelling of reservoir‐quality distribution and exploration risk evaluation in the basin.     

鄂尔多斯盆地西部三叠系长2油层组砂岩成岩演化特征

盐池―姬塬地区延长组长2油层组砂岩由三角洲前缘水下分流河道和河口坝砂体组成,以岩屑长石砂岩和长石砂岩为主(其中石英、长石和岩屑平均含量分别为32.6%、38.9%和8.0%,岩屑以变质岩屑和火成岩屑为主,占岩屑总量的87.5%)。指出砂岩目前处于早成岩阶段B期的晚期,RO为0.8%,温度在70～90℃之间,成岩组构特征受酸性成岩环境控制;长石类易溶颗粒普遍发生溶蚀作用,石英次生加大发育;孔隙类型组成中原生粒间孔隙所占比例多在30%～45%之间,粒间和粒内溶孔占40%～55%。在对砂岩各种组分含量统计和定量计算的基础上,认为机械压实作用是造成研究区原生孔隙消亡的最主要原因,其次为胶结作用,而由溶蚀作用增加的孔隙占初始孔隙度比例较小(<10%)。结合沉积相分析成果,在研究区划分出了5种沉积―成岩相带,其中有利的高孔高渗储层(孔隙度>14%,渗透率>5×10-3μm2)分布区主要由三角洲平原分流河道―次生溶孔相前锋带、三角洲平原分流河道―绿泥石粘土膜胶结次生溶孔相前锋带和台型三角洲前缘―绿泥石粘土膜胶结原生孔相主体以及坡型三角洲前缘―次生溶孔相主体组成。     

RESERVOIR QUALITY EVOLUTION OF UPPER CARBONIFEROUS (WESTPHALIAN) TIGHT GAS SANDSTONES,LOWER SAXONY BASIN,NW GERMANY

This paper investigates reservoir quality development in tight Upper Carboniferous fluvial sandstones (Westphalian C/D) in the Lower Saxony Basin, NW Germany. The study integrates data from three outcrops (Piesberg, Woitzel and Hüggel) in the south of the basin with that from two wells (Wells A and B) located at gas fields approximately 50 km to the north. Petrographic and petrophysical data are related to the diagenetic evolution of the sandstones and the burial and structural history of the Lower Saxony Basin. The outcrop and subsurface data sets are compared in order to investigate the factors controlling reservoir quality evolution. Upper Carboniferous fluvial sandstones from the Woitzel and Hüggel outcrops and from Wells A and B have similar matrix permeabilities (0.01 to 10 mD), but matrix porosities vary between Well A (average 6%), Well B (average 10%), Woitzel (average 15%), and Hüggel (average 19%). Permeability reduction during burial is related to the formation of clay mineral cement, which was mainly controlled by variations in both the palaeo‐climate and in the sandstones’ depositional composition. Matrix porosity was controlled by local differences in burial history related to basin inversion tectonics. The greater amount of inversion‐related uplift at Well B (about 2.8 km) resulted in lower thermal exposure of the Westphalian sandstones at this location, which thus show higher matrix porosities than the sandstones at Well A which were uplifted by only about 1.2 km. Further increases in porosity in the outcrop sandstones may be related to the dissolution of carbonate cement during late‐stage uplift in near‐surface conditions. Upper Carboniferous fluvial sandstones from the Piesberg quarry show the poorest reservoir characteristics compared to the samples from the subsurface and the other outcrops, with matrix porosities averaging 6% and permeabilities <0.01 mD. Reservoir quality reduction was controlled by thermal anomalies associated with a large fault at the Piesberg quarry. By contrast, a few outliers in the sample data sets from Well B and the Piesberg quarry, which have permeabilities of more than 100 mD, show that faulting or natural fracturing may enhance reservoir quality within a particular area. Faults/fractures may act as potential migration pathways for leaching fluids, or may provide fracture‐permeability systems with production potential. Depositional setting, burial‐related diagenetic processes and structural characteristics in the Lower Saxony Basin need to be carefully evaluated in order to provide an improved understanding of the reservoir quality of the Upper Carboniferous sandstones.     

DIAGENESIS OF TIGHT‐GAS SANDSTONES IN THE LOWER CRETACEOUS DENGLOUKU FORMATION,SONGLIAO BASIN,NE CHINA: IMPLICATIONS FOR RESERVOIR QUALITY

Non‐marine tight‐gas sandstones have not been studied intensively in terms of diagenesis and reservoir‐quality evaluation. This paper investigates the sandstones in the Lower Cretaceous Denglouku Formation in the Songliao Basin, NE China, which comprise a tight reservoir for natural gas. Core samples of the sandstones were obtained from eight wells located in two gasfields and were described in terms of lithology and sedimentology with the aid of wireline log interpretation; other data included thin section petrography, and X‐ray diffraction analyses and scanning electron microscopy. The sandstones mainly comprise moderate‐ to well‐sorted, fine‐ to medium‐grained feldspathic litharenites deposited in braided fluvial to braid‐delta settings under warm, arid to semi‐arid climatic conditions. Diagenetic processes which have affected the sandstones include compaction and cementation by calcite, dolomite, ferroan calcite, quartz, chlorite and illite. Porosity characteristics of the sandstones are closely linked to depositional facies, and the sandstones can be divided on the basis of sediment textures and depositional facies into three groups which have distinctive diagenetic features. The best reservoirs are represented by relatively coarse‐grained sandstones deposited in braid‐delta mouth bars and distributary channels and braided fluvial channels; these sandstones have relatively high porosity (up to 5%) and contain large amounts of chlorite and illite pore‐lining cements but relatively minor carbonate cement. A reservoir quality prediction model is proposed and incorporates textural, depositional and diagenetic attributes. The model will help to identify sweet spots in non‐marine tight‐gas sandstones elsewhere, and will contribute to more effective field development.     

鄂尔多斯大牛地气田上古生界储层成岩作用评价

对鄂尔多斯盆地北部大牛地气田上古生界地层的成岩作用阶段进行了综合研究,结果显示,太原组—山一段地层煤镜质体反射率在1.4%~1.5%之间,包裹体均一温度为140℃,伊/蒙混层矿物中蒙脱石层含量一般小于30%,属晚成岩作用阶段B期;下石盒子组(包括盒一、二、三段)—山二段地层中煤镜质体反射率在1.3%~1.4%之间,盒一、二、三段包裹体均一温度为126℃,伊/蒙混层矿物中蒙脱石层含量主要在32%~36%之间,属晚成岩作用阶段A期;山二段包裹体均一温度比较复杂,认为也为晚成岩作用阶段A期。大牛地上古生界储集层成岩作用类型主要有压实作用、胶结作用(包括硅质胶结、碳酸盐胶结、粘土胶结)、溶解溶蚀作用以及微裂隙作用,储集岩石的孔隙类型主要有(剩余的)原生粒间孔隙、粒间(晶间)微孔隙、粒间(粒内)溶蚀孔隙(包括铸模孔隙),微裂隙包括切穿颗粒的和粒缘微裂隙。储层物性主要属低孔、低渗储层,孔隙结构参数显示盒三、盒二、太一和太二平均喉道半径和中值压力评价好于盒一、山一、山二段,排驱压力和最大连通半径也具有相似的特征;盒三、盒二段产能高、压降慢,与微裂隙作用造成渗透率增加有关。     

川西前陆盆地上三叠统须家河组致密砂岩储层评价

川西前陆盆地须家河组发育的辫状河三角洲前缘砂体是研究区主要的储集砂体,其砂岩主要为富杂基、富岩屑的石英砂岩及岩屑砂岩,砂岩结构成熟度中等到较低。野外观察以及(铸体)薄片等分析研究表明,该区须家河组储层属特低孔特低渗致密性储层,以次生溶孔为主,以Ⅱ、Ⅲ类储层为主,Ⅰ类储层较少。     

鄂尔多斯盆地陇东地区三叠系延长组储层特征及影响因素分析

以三角洲-湖泊沉积体系为主的陇东地区三叠系延长组主产油层组长3、长6、长7和长8储层岩石类型主要有长石砂岩、岩屑长石砂岩及岩屑砂岩,成分成熟度普遍较低,结构成熟度中等-较好;经历了压实作用、胶结作用和溶解作用,孔隙类型以粒间孔、次生溶孔为主。纵向上,长3油层组储层物性最好;平面上,东北部储层物性明显优于西南部。优质储层多出现在三角洲前缘水下分流河道和河口坝中,碎屑组成、粒级、填隙物含量和成岩作用均对储层性能有重要影响。在陇东地区延长组中识别出简单韵律、复合韵律2大类6种类型储层物性垂向分布模式,而高频基准面旋回的升降控制着本区储层物性韵律的分布规律。     

鄂尔多斯盆地富县地区延长组长6储层特征

鄂尔多斯盆地富县地区长6油层组主要发育三角洲沉积,其中分流河道和水下分流河道是主要的油气储集层。长6油层组储集层岩石类型以岩屑长石细砂岩和长石细砂岩为主,颗粒间多为线、点—线接触,孔隙和薄膜式胶结,总体具有成分成熟度低、结构成熟度高的特征。粒间孔和长石溶孔是主要的储集空间,其中以小孔和微孔为主,渗透率小于3×10^-3μm²,为特低渗储层和接近致密储层。研究区较强的压实作用、胶结作用是形成低孔低渗的主要因素,而溶蚀作用是储层物性改善的主要因素。     

POROSITY PRESERVATION DUE TO AUTHIGENIC CHLORITE COATINGS IN DEEPLY BURIED UPPER TRIASSIC XUJIAHE FORMATION SANDSTONES,SICHUAN BASIN,WESTERN CHINA

Non‐marine sandstones in the Upper Triassic Xujiahe Formation form an important reservoir unit in the Sichuan Basin, western China. Widespread authigenic chlorite cement is present in the second and fourth members of the formation, referred to as the Xu II and IV members. This study, based on data from 12 wells from three gasfields, focusses on chlorite development and evolution and attempts to evaluate its influence on reservoir quality. Data included results of X‐ray diffraction (XRD) and electron microprobe analyses (EMPA), scanning electron microscopy (SEM), and stable carbon and oxygen isotope analyses. The results showed that chlorite coatings preserve primary pore spaces in the sandstones by inhibiting the nucleation of quartz cements on grain surfaces. Iron for chlorite growth came from the dissolution of Fe‐rich magmatic rocks derived from the palaeo‐Longmenshan fold‐belt, from dissolved and colloidal iron which had been precipitated in the Xujiahe Formation in a fluvio‐deltaic environment, and from compacting mudstones in other pars of the formation. The chlorite initially precipitated from pore waters during eodiagenesis (< 70 °C; < 2 km burial depth). During mesodiagenesis (>70 °C, > 2 km), the chlorite was modified due to exposure to Mg‐rich fluids derived from the underlying carbonate‐dominated Leikoupo Formation. Thus the Mg content of chlorite in the Xu II member increases with depth. However this phenomenon was not observed in the Xu IV member. The effects of authigenic chlorite on the sandstones' petrophysical properties were evaluated from correlations between chlorite content and porosity. Optimum thicknesses for chlorite coatings range from 5 to 10 microns. Thicker or thinner coatings appear to be less capable of preserving primary porosity and permeability.     

CONTROLS ON RESERVOIR QUALITY IN THE LOWER TRIASSIC KANGAN FORMATION,SOUTHERN PERSIAN GULF

The Lower Triassic Kangan Formation together with the underlying Upper Permian Dalan Formation forms one of the most important reservoirs for natural gas in the Middle East. The carbonate‐dominated Kangan Formation was studied at a gasfield in the southern Persian Gulf and some 100 m of core were examined at micro‐ and macro scales. Twelve microfaaes were identified. Previous studies have divided the Kangan Formation reservoir into Lower (K2) and Upper (K1) Units. The Lower Kangan can divided into two subunits (K2b and K2a), while three subunits (K1c, K1b and K1a) are recognised in the Upper Kangan. Diagenetic processes have affected reservoir quality in the Kangan Formation in different ways. Processes improving reservoir quality include dissolution, dolomitization and fracturing, while reservoir quality was decreased by cementation, and chemical and mechanical compaction. Micritization and neomorphism have had both positive and negative effects. Fracture development has improved reservoir quality, particularly in dolomitic intervals.     

DIAGENETIC ALTERATIONS AND RESERVOIR QUALITY EVOLUTION OF LOWER CRETACEOUS FLUVIAL SANDSTONES: NUBIAN FORMATION,SIRT BASIN,NORTH‐CENTRAL LIBYA

Lower Cretaceous meandering and braided fluvial sandstones of the Nubian Formation form some of the most important subsurface reservoir rocks in the Sirt Basin, north‐central Libya. Mineralogical, petrographical and geochemical analyses of sandstone samples from well BB6–59, Sarir oilfield, indicate that the meandering fluvial sandstones are fine‐ to very fine‐grained subarkosic arenites (av. Q₉₁F₅L₄), and that braided fluvial sandstones are medium‐ to very coarse‐grained quartz arenites (av. Q₉₆F₃L₁). The reservoir qualities of these sandstones were modified during both eodiagenesis (ca. <70°C; <2 km) and mesodiagenesis (ca. >70°C; >2 km). Reservoir quality evolution was controlled primarily by the dissolution and kaolinitization of feldspars, micas and mud intraclasts during eodiagenesis, and by the amount and thickness of grain‐coating clays, chemical compaction and quartz overgrowths during mesodiagenesis. However, dissolution and kaolinitization of feldspars, micas and mud intraclasts resulted in the creation of intercrystalline micro‐ and mouldic macro‐porosity and permeability during eodiagenesis, which were more widespread in braided fluvial than in meandering fluvial sandstones. This was because of the greater depositional porosity and permeability in the braided fluvial sandstones which enhanced percolation of meteoric waters. The development of only limited quartz overgrowths in the braided fluvial sandstones, in which quartz grains are coated by thick illite layers, retained high porosity and permeability (12–23% and 30–600 mD). By contrast, meandering fluvial sandstones underwent porosity loss as a result of quartz overgrowth development on quartz grains which lack or have thin and incomplete grain‐coating illite (2–15% and 0–0.1 mD). Further loss of porosity in the meandering fluvial sandstones occurred as a result of chemical compaction (pressure dissolution) induced by the occurrence of micas along grains contacts. Other diagenetic alterations, such as the growth of pyrite, siderite, dolomite/ankerite and albitization, had little impact on reservoir quality. The albitization of feldspars may have had minor positive influence on reservoir quality through the creation of intercrystalline micro‐porosity between albite crystals. The results of this study show that diagenetic modifications of the braided and meandering fluvial sandstones in the Nubian Formation, and resulting changes in reservoir quality, are closely linked to depositional porosity and permeability. They are also linked to the thickness of grain‐coating infiltrated clays, and to variations in detrital composition, particularly the amounts of mud intraclasts, feldspars and mica grains as well as climatic conditions.     

鄂尔多斯盆地镇北地区延长组长7致密油储层特征及其综合评价

为了明确长7致密油储层特征对其开展综合评价。首先,通过岩心观察、薄片鉴定和岩心分析等,认为长7致密油储层物性、含油性、脆性等属性参数具有分布频带宽、变化快的特征。其次,基于聚类分析方法,选取7个相对独立的参数用于储层分级评价,并界定了相应参数的分级标准。在此基础上,运用灰色系统理论,定量各评价参数的权系数,计算出储层综合评价因子,对镇北地区西233井区长721致密油储层开展综合定量评价。结果表明:西233井区以Ⅱ、Ⅲ类储层为主,两者分布面积约为65%,其中Ⅰ类、Ⅱ类储层主要分布于三角洲前缘水下分流河道,Ⅲ、Ⅳ类储层分布于河道砂体侧翼。     

鄂尔多斯盆地白豹地区延长组中段沉积特征与沉积模式

通过对鄂尔多斯盆地白豹地区延长组中段长4+5—长3油层组大量钻井岩心和测井资料综合研究,以及沉积体系、沉积相特征的描述,识别出其沉积特征,划分了沉积相类型。白豹地区长4+5—长3为湖泊—三角洲沉积体系,其中三角洲前缘沉积主要发育在研究区东北部,浅湖沉积主要发育在研究区西南部且规模较小。研究区三角洲主要为浅水台地型三角洲,缺乏完整的进积序列,在三角洲前缘沉积中,由于水下分流河道的迁移摆动,水下分流河道砂体与分流间湾泥质沉积在单井剖面上呈交替出现、反复叠置的特征序列,或者是水下分流河道砂体直接位于湖相泥岩之上的沉积序列。     

鄂尔多斯盆地上三叠统延长组米兰科维奇旋回的确定

由天体轨道周期变化引起的气候变化被广泛地记录在沉积地层中。自然伽马曲线很好地反映了气候变化引起的地层旋回。消除高频干扰和低频趋势以后,自然伽马曲线可以用来分析地层中的米兰科维奇旋回。对鄂尔多斯盆地陕 15井中延长组按油层段进行系统分析,得出陕15井由偏心率周期引起的地层旋回厚度在9.6～18.75m之间;地轴倾斜和气候岁差周期引起的旋回层厚度在1.18～6.82m之间。各油层组的沉积速率变化在7.8～14.2cm/ka之间。     

鄂尔多斯盆地白豹地区长6砂岩成岩作用及其对储层物性的影响

基于砂岩薄片、铸体薄片、扫描电镜和X-衍射分析,研究了鄂尔多斯盆地华庆油田白豹地区长6砂岩储层的成岩作用,认为长6储层处于中成岩B期阶段。压实作用和碳酸盐胶结作用对砂岩的原生孔隙结构破坏强烈,使物性变差;粘土矿物的胶结作用,使得渗透性变差,但由于绿泥石薄膜的发育,使得孔隙度有变好的趋势;溶蚀作用和破裂作用则有效地改善了砂岩的孔隙结构,对物性的改善起到建设性作用。     

鄂尔多斯盆地延长组米氏旋回分析及层序划分

通过典型探井自然伽马曲线的频谱分析,结合前人沉积速率研究,在延长组中识别出A、B、C、D、E等5组高频旋回周期,分别与米氏旋回中偏心率周期、地轴倾角长周期、地轴倾角短周期、岁差长周期、岁差短周期等存在近似的时间长度和对应关系。应用高分辨率层序地层理论,推测延长组的高频旋回发育受米氏旋回天文轨道力控制,其四级层序受123 ka的偏心率周期影响。在米氏旋回偏心率周期基础上,重新厘定了延长组层序地层划分方案,认为延长组存在4个二级层序、12个三级层序及数百个四级层序。     

鄂尔多斯盆地三叠系延长组层序地层与生储盖组合特征

鄂尔多斯盆地三叠系延长组地层层序划分方案较多。在V ail经典层序地层学理论指导下,综合利用露头、岩芯、钻井、地震和古生物等资料,通过古水深分析和层序界面的识别与划分,认为将鄂尔多斯盆地三叠系延长组划分为7个三级层序更为合理,指出层序4水进体系域(生)+层序5低位体系域(储)+层序5水进体系域(盖)和层序4水进体系域(生)+层序4低位体系域(储)+层序4水进体系域(盖)是相对较佳的2套生储盖组合,并指出了鄂尔多斯盆地延长组最主要的2套生储盖勘探目的层。