Distribution of diagenetic alterations in glaciogenic sandstones within a depositional facies and sequence stratigraphic framework: Evidence from the Upper Ordovician of the Murzuq Basin, SW Libya

The spatial and temporal distribution of diagenetic alterations has been constrained in relationship to depositional facies and sequence stratigraphy of the Upper Ordovician glaciogenic quartzarenite sandstones in the Murzuq Basin, SW Libya, which were deposited during the Haritanian glaciation when the basin was laying along the continental margin of Gondwana. Eogenetic alterations encountered include: (i) replacement of detrital silicates, mud matrix and pseudomatrix by kaolinite in paraglacial, tide-dominated deltaic, in foreshore to shoreface (highstand systems tract; HST) and in post-glacial, Gilbert-type deltaic (lowstand systems tract; LST) sandstones, particularly below the sequence boundaries (SB). Kaolinite formation is attributed to the influx of meteoric water during relative sea level fall and basinward shift of the shoreline. (ii) Cementation by calcite (δ¹⁸O_VPDB = − 3.1‰ to + 1.1‰ and δ¹³C_VPDB = + 1.7‰ to + 3.5‰) and Mg-rich siderite in the paraglacial, tide-dominated deltaic and foreshore to shoreface HST sandstones, in the glacial, tide-dominated estuarine (transgressive systems tract; TST) sandstones and in the post-glacial, shoreface TST sandstones is interpreted to have occurred from marine pore-waters. (iii) Cementation by Mg-poor siderite, which occurs in the post-glacial, Gilbert-type deltaic LST sandstones and in the paraglacial, tide-dominated deltaic and foreshore to shoreface HST sandstones, is interpreted to have occurred from meteoric waters during relative sea level fall and basinward shift of the shoreline. (iv) Pervasive cementation by iron oxides has occurred in the glacial, shoreface–offshore TST sandstones and post-glacial, shoreface TST sandstones immediately below the maximum flooding surfaces (MFS), which was presumably enhanced by prolonged residence time of the sediments under oxic diagenetic conditions at the seafloor. (v) Formation of grain-coating infiltrated clays mainly in the glacial, fluvial incised-valley LST sandstones and in the post-glacial, Gilbert-type deltaic LST sandstones as well as, less commonly, in the paraglacial, foreshore to shoreface HST sandstones and in the tide-dominated deltaic HST sandstones below the SBs.

Mesogenetic alterations include mainly the formation of abundant quartz overgrowths in the glacial, fluvial incised-valley LST sandstones, post-glacial, Gilbert-type deltaic LST sandstones and glacial, shoreface TST sandstones, in which early carbonate cements are lacking. Illite, chlorite and albitized feldspars, which occur in small amounts, are most common in the glacial, tide-dominated estuarine TST sandstones and paraglacial, shoreface HST sandstones. This study demonstrates that the spatial and temporal distribution of diagenetic alterations and their impact on reservoir-quality evolution in glacial, paraglacial and post-glacial sandstones can be better elucidated when linked to the depositional facies and sequence stratigraphic framework.     

The influence of transgression and regression on the spatial and temporal distribution of diagenetic kaolin in the Upper Ordovician glaciogenic sandstones within a sequence stratigraphic framework, Murzuq Basin, SW Libya

Linking diagenesis to depositional facies and sequence stratigraphy can provide a better understanding of some of the parameters that control the spatial and temporal distribution of diagenetic alterations and of their impact on reservoir quality. A study of the paralic, glaciogenic sandstones of the Melaz Shuqran and Mamunyiat formations (Late Ordovician) of the Murzuq Basin, SW Libya, reveals that the distribution of diagenetic kaolin can be constrained within depositional facies and sequence stratigraphy. Eogenetic kaolinite was formed by the dissolution of unstable detrital grains as a result of influx of meteoric waters into: (i) glacial, fluvial incised-valley lowstand systems tract (LST), glacial, tide-dominated estuarine transgressive systems tract (TST) during formation of overlying sequence boundary, (ii) paraglacial, tide-dominated deltaìc highstand systems tract (HST), paraglacial, foreshore to shoreface HST during progradation and basinward shift of the shoreline and/or formation of overlying sequence boundary, (iii) postglacial, Gilbert-type deltaic LST sandstones during relative sea level fall. On the other hand, formation of kaolinite immediately below maximum flooding surfaces is attributed to dissolution of unstable detrital grains by organic acids that were presumably derived from thermal alterations of organic matter, possibly during mesodiagenesis. The transformation of eogenetic kaolinite into dickite during mesodiagenesis is probably a consequence of low α_K⁺ / α_H⁺ ratio in the pore waters due to the scarcity of detrital K-feldspars.     

Sequence stratigraphic distribution of diagenetic alterations in coal-bearing, paralic sandstones: evidence from the Rio Bonito Formation (early Permian), southern Brazil

Abstract Linking siliciclastic diagenesis to sequence stratigraphy allows a better understanding of the parameters controlling the spatial and temporal distribution of diagenetic alterations, and hence of reservoir quality. A study of the coal-bearing, alluvial, deltaic, estuarine and shallow-marine sandstones of the Rio Bonito Formation, early Permian, Paraná Basin (southern Brazil), reveals that the distribution of diagenetic alterations and of related reservoir quality evolution can be constrained within a sequence stratigraphic framework. Calcite, dolomite, siderite, kaolinite and pyrite cementation is consistently linked to sequence and parasequence boundaries, transgressive and maximum flooding surfaces and is systematically distributed within lowstand, transgressive and highstand systems tracts. Diagenesis of coal layers at parasequence boundaries has promoted the formation of stratabound calcite (detectable in resistivity wire line logs), concretionary pyrite and kaolinite and of silicate grain dissolution in sandstones located above and below these boundaries, particularly in the transgressive systems tract. Meteoric water diagenesis caused grain dissolution and the formation of kaolinite in sandstones below sequence boundaries and in lowstand systems tract sandstones. Carbonate bioclasts and low sedimentation rates in lag deposits at parasequence boundaries, transgressive and maximum flooding surfaces favoured the formation of grain-rimming siderite. The results of this study are relevant to the exploration of coal-bed methane and other coal-bearing reservoirs, where it is crucial to unravel and predict the distribution and quality of reservoirs and compartments.     

层序地层格架中碳酸盐岩准同生成岩作用分析——以轮南古隆起下中奥陶统碳酸盐岩为例

根据海平面升降而对海洋碳酸盐岩沉积划分的不同沉积体系域,和其准同生成岩作用之间存在着相关性,这种相关性可以通过不同体系域所发育的成岩作用类型体现出来。文章以塔里木盆地轮南古隆起下中奥陶统碳酸盐岩为例,把准同生成岩作用放在层序地层学格架范畴内来研究,总结了不同体系域内发育的成岩作用类型和特征,认为海侵体系域主要发育方解石胶结作用和白云石化作用,高位体系域主要发育有方解石胶结作用和大气淡水溶蚀作用等。在层序地层格架下进行成岩作用对比的结果表明,高位期以及海侵期下伏的前期高位期沉积,是有利的成岩作用改造层位,并在物性统计数据中得到了证明,为有利储集体的评价、预测提供了新的途径。     

Distribution of diagenetic alterations in fluvial and paralic deposits within sequence stratigraphic framework: Evidence from the Petrohan Terrigenous Group and the Svidol Formation, Lower Triassic, NW Bulgaria

Elucidation of diagenetic alterations in the Petrohan Terrigenous Group (fluvial; highstand systems tract HST) sandstones and Svidol Formation (tide-dominated deltaic and tidal flat, transgressive systems tract TST and highstand systems tract HST, respectively) sandstones and calcarenite, Lower Triassic, NW Bulgaria was constrained within a sequence stratigraphic framework. Eogenetic alterations in the fluvial HST sandstones include (i) formation of grain-coating infiltrated clays as a result of percolation of mud-rich surface waters into underlying coarse-grained and permeable channel-fills and crevasse splay sandstones; (ii) formation of pseudomatrix by mechanical compaction of mud intraclasts that were incorporated into the coarse-grained channel sandstones during their lateral avulsion; and (iii) cementation by calcite (δ¹⁸O_VPDB = − 6.5‰ to − 3‰; δ¹³C_VPDB = − 5.1‰ to + 0.6‰) and dolomite (δ¹⁸O_VPDB = − 6.1‰ to − 0.3‰; δ¹³C_VPDB = − 7.2‰ to − 5.8‰) in the crevasse splay and floodplain sediments. Mesogenetic alterations that are encountered in the fluvial HST sandstones include (i) illitization of grain-coating clays, mud intraclasts, and mica, possibly because of simultaneous albitization of feldspars; (ii) cementation by calcite (δ¹⁸O_VPDB = − 14.5‰ to − 8.4‰; δ¹³C_VPDB = − 7.7‰ to + 0.6‰) and dolomite (δ¹⁸O_VPDB = − 15.8‰ to − 5‰; δ¹³C_VPDB = − 7.9‰ to + 1.5‰); and (iii) limited amounts of quartz overgrowths in the channel sandstones owing to occurrence of thick grain-coating clays.

Conversely, the tide-dominated deltaic TST sandstones and the tidal flat HST calcarenite were pervasively cemented by calcite (δ¹⁸O_VPDB = − 6.6‰ to − 3.1‰; δ¹³C_VPDB = − 5.1‰ to + 0.6‰) and siderite (δ¹⁸O_VPDB = − 7.2‰ to − 5.7‰; δ¹³C_VPDB = + 0.3‰ to + 0.9‰) particularly below marine and maximum flooding surfaces, due to the presence of abundant bioclasts and prolonged residence time of the sediments under certain geochemical conditions along these surfaces. The remaining open pores were cemented during mesodiagenesis by calcite (δ¹⁸O_VPDB = − 6.6‰ to − 3.1‰ and δ¹³C_VPDB = − 5.1‰ to + 0.6‰) and dolomite (δ¹⁸O_VPDB = − 6.6‰ to − 3.1‰ and δ¹³C_VPDB = − 5.1‰ to + 0.6‰).

This study shows that constructing a conceptual model for the distribution of diagenetic alterations is possible by integration of diagenesis with sequence stratigraphy. The model shows that tide-dominated deltaic TST sandstones and tidal flat HST calcarenite were pervasively cemented by carbonates during near-surface eodiagenesis, owing to the presence of abundant bioclasts. Conversely, fluvial LST sandstones remained poorly cemented during near-surface eodiagenesis due to the lack of bioclasts, but were cemented by mesogenetic calcite, dolomite and quartz overgrowths instead.     

Miocene tidal-influenced sedimentation to continental Pliocene sedimentation in the forebulge–backbulge depozones of the Beni–Mamore foreland Basin (northern Bolivia)

Mio-Pliocene deposits of the forebulge–backbulge depozones of the Beni-Mamore foreland Basin indicate tidally to fluvially dominated sedimentation. Seven facies assemblages have been recognized: FAA–FAG. FAA represents a distal bottom lake assemblage, FAB and FAD are interpreted as tidal flat deposits, FAC and FAG are interpreted as fluvial systems, FAE sediments are deposited in a subtidal/shoreface setting, and FAG represents a meandering fluvial system. The identification of stratigraphic surfaces (SU, MFS, and MRS) and the relationship among the facies assemblages permit the characterization of several systems tracts: a falling-stage systems tract (FSST) followed by a lowstand systems tract (LST), a transgressive systems tract (TST), and a highstand systems tract (HST). The FSST and LST may have been controlled by the uplift of the Beni-Mamore forebulge, whereas TST may result from a quiescent stage in the forebulge. Subaerial unconformity two (SU2) records the passage from a tide-influenced depositional system to a fully continental depositional system. The Miocene tidal-influenced deposits in the Beni–Mamore Basin suggest that it experienced a connection, either with the South Atlantic Ocean or the Caribbean Sea or both.     

Integrated diagenesis and sequence stratigraphic study of tidal sandstones: the Adedia Formation (Cambro-Ordovician), Sinai, Egypt

This work examines the different effects meteoric versus marine diagenesis had on Cambro-Ordovician tidal sandstones during episodes of fluctuating sea level. The distribution of diagenetic fabrics was compared to a sequence stratigraphic framework. Initially, a rise in relative sea level (RSL) resulted in deposition of transgressive systems tract sands directly onto crystalline basement. These sandstones display evidence of limited cementation by marine, grain-fringing dogtooth-like and fibrous calcite. A fall in RSL resulted in the progradation of a tidal flat complex and deposition of highstand systems tract (HST) and lowstand systems tract (braided fluvial) sandstones. Contemporaneous meteoric-water flux into sands of all the systems tracts occurred. Sequence boundaries (SB) are marked by fluvial incision of tidal sands and by the development of palaeosols. Meteoric incursion during sea-level lowstands resulted in the dissolution and kaolinitization of feldspars, micas and mud intraclasts in all systems tracts, but is most extensive in HST sandstones below the SB. The effect of meteoric-water flux on the dissolution of marine calcite cements is poorly known. Mesogenetic alterations include intergranular pressure dissolution and formation of variable amounts of syntaxial quartz overgrowths in all systems tracts. Telogenetic alteration (i.e. weathering) in the sandstones includes the formation of goethite and calcite. Thus, the integration of diagenesis with sequence stratigraphy provides a useful tool with which to understand reservoir-quality distribution in sand-dominated, tidal sediments.     

Tectono-stratigraphic evolution and hydrocarbon exploration in the Eocene Southern Lufeng Depression,Pearl River Mouth Basin,South China Sea

The structural evolution and stratigraphic architecture of the Southern Lufeng Depression in the Pearl River Mouth Basin, South China Sea show two second-order sequences (SSQ1 and SSQ2) and nine third-order sequences (WSQ1-5 and ESQ1-4) within the Eocene rift-related successions. Based on integrated interpretations of seismic reflections, well logs and core data, five distinct tectono-stratigraphic patterns are identified: (1) the initial synrift-I sequence (WSQ1) of low tectonic subsidence, overfilled by alluvial fan or fan-delta deposits and volcanic deposits, with no clear systems tracts; (2) the climax synrift-I sequences (WSQ2–4) developed in response to rapid tectonic subsidence, generally consisting of a low-stand systems tract (LST), transgressive systems tract (TST) and high-stand systems tract (HST); (3) the late synrift-I sequence (WSQ5) characterised by a decreased tectonic subsidence rate, dominated by braided delta, deep and shallow lacustrine sediments, mainly constructed by TST and HST; (4) the early synrift-II sequences (ESQ1–2) rapidly filled by braided deltaic sandstone and mainly composed of TST and HST with less common LST units; and (5) the late synrift-II sequences (ESQ3–4), which are totally filled by braided deltaic system in a shallow-water lake setting, presenting typical imbricate clinoforms or sub-parallel seismic configurations, consisting of only TST and HST components. During the climax stage of synrift-I development, the depositional setting changed from a prominent shallow lake (WSQ2) to a deep-lucustrine with turbiditic deposits (WSQ3) and finally dominated by mostly braided deltaic-shallow lacustrine deposits (WSQ4); the HST occupies an increasing proportion from early to late. Furthermore, the stratigraphic patterns, especially LST units of the climax synrift-I stage, are significantly influenced by topographic variations and slope-break belt types in the hanging dip-slope. This study reveals that the spatial and temporal evolution of lacustrine depositional and stratigraphic patterns were significantly controlled by the interplay of tectonic subsidence and sediment supply, and provides a fundamental basis for predicting the favourable reservoirs and geometry of source rocks related to the general variability of Eocene rift-related tectonic subsidence in the Southern Lufeng Depression of the Pearl River Mouth Basin. Furthermore, the topographic responses of differential active fault-stepped patterns associated with magma intrusions, highlight the variability of relevant sequence architectures in the hanging dip-slope in lacustrine rift basins.     

Sequence stratigraphic controls on reservoir characterization and architecture: case study of the Messinian Abu Madi incised-valley fill, Egypt

Understanding sequence stratigraphy architecture in the incised-valley is a crucial step to understanding the effect of relative sea level changes on reservoir characterization and architecture. This paper presents a sequence stratigraphic framework of the incised-valley strata within the late Messinian Abu Madi Formation based on seismic and borehole data. Analysis of sand-body distribution reveals that fluvial channel sandstones in the Abu Madi Formation in the Baltim Fields, offshore Nile Delta, Egypt, are not randomly distributed but are predictable in their spatial and stratigraphic position. Elucidation of the distribution of sandstones in the Abu Madi incised-valley fill within a sequence stratigraphic framework allows a better understanding of their characterization and architecture during burial. Strata of the Abu Madi Formation are interpreted to comprise two sequences, which are the most complex stratigraphically; their deposits comprise a complex incised valley fill. The lower sequence (SQ1) consists of a thick incised valley-fill of a Lowstand Systems Tract (LST1)) overlain by a Transgressive Systems Tract (TST1) and Highstand Systems Tract (HST1). The upper sequence (SQ2) contains channel-fill and is interpreted as a LST2 which has a thin sandstone channel deposits. Above this, channel-fill sandstone and related strata with tidal influence delineates the base of TST2, which is overlain by a HST2. Gas reservoirs of the Abu Madi Formation (present-day depth ～3552 m), the Baltim Fields, Egypt, consist of fluvial lowstand systems tract (LST) sandstones deposited in an incised valley. LST sandstones have a wide range of porosity (15 to 28%) and permeability (1 to 5080mD), which reflect both depositional facies and diagenetic controls. This work demonstrates the value of constraining and evaluating the impact of sequence stratigraphic distribution on reservoir characterization and architecture in incised-valley deposits, and thus has an important impact on reservoir quality evolution in hydrocarbon exploration in such settings.     

山东惠民凹陷中央隆起带古近系沙三段层序地层及沉积演化?

根据山东惠民盆地中央隆起带古近系沙河街组第三段层序地层学研究，根据层序中湖平面变化特点和相应的沉积物特征，提出了陆相湖盆中层序内体系域的四分法，一个完整的层序由低位、湖侵、高位和下降四个体系域组成，并且层序界面位于湖平面最大下降的位置，介于下降域和低位域之间。层序地层中存在四个关键性界面：首泛面、最大湖泛面、始降面和最大下降面，其中首泛面对应于湖水由相对稳定到快速上升时的初始湖泛面，为低位域与湖侵域间的分界面；最大湖泛面对应于湖水快速上涨至最大限度时的湖泛面，为湖侵域与高位域间的分界面，在界面附近多形成特征的CS段；始降面对应于湖平面开始快速下降时的沉积界面，为高位域与下降域的分界面；最大下降面也是层序界面，为湖盆水体快速下降或湖盆岸线快速退到最低点时的沉积界面。结合研究区的岩芯、录井、测井、地震等资料综合分析，本文总结了四个关键面的识别标志。中央隆起带沙三段沉积共划分出六个体系域，分属三个层序。本文以层序II沉积为例，阐述了不同体系域的沉积体系特征，低位期湖盆水域面积小，河流-三角洲沉积体系发育，河流流经距离长，边缘地区形成似下切谷沉积；湖侵期发育小规模的退积式三角洲沉积，砂体较不发育；高位期湖盆水域面积大，砂体以深水浊积砂体为特征；下降期多发育进积式砂体，砂体发育。因此，位于层序界面之下的下降域和之上的低位域是湖盆砂体有利发育期，湖侵域和高位域是生油岩主要形成时期。     

塔中地区志留系沥青砂岩成岩作用及其对储层性质的影响

运用沉积学原理对塔中地区志留系经历复杂成岩演化的沥青砂岩进行研究分析,了解到该岩石主要经过压实作用、胶结作用和溶蚀作用等成岩作用。其胶结物的主要类型有绿泥石、伊利石、高岭石、伊-蒙混层等粘土矿物以及碳酸盐矿物、石英、长石、黄铁矿等。孔隙类型以粒间孔隙、粒内孔、铸模孔、特大孔、裂缝孔隙等为主,其中以粒间孔隙最为发育,低地温梯度有利于在深层形成次生孔隙。志留系沥青砂岩储层物性受沉积和成岩双重因素的影响,成岩演化阶段处于晚成岩A期。根据影响储层物性的储层成岩作用,可将成岩相类型划分为不稳定碎屑溶蚀成岩相、压实-弱溶蚀成岩相、压实充填成岩相、压实压溶成岩相、碳酸盐胶结成岩相等几种主要类型,成岩相类型决定了储层性质,不稳定碎屑溶蚀成岩相和压实-弱溶蚀成岩相是本区较好的油气储层。     

Sedimentology and palaeogeomorphology of four large valley systems incising delta plains, western Canada Foreland Basin: implications for mid-Cretaceous sea-level changes

The mid-Cenomanian Dunvegan Formation represents a delta complex deposited on a foreland basin ramp over about 2 my. The Dunvegan is divided into 10 transgressive–regressive allomembers, labelled J–A in ascending order, each defined by regional marine transgressive surfaces. Parasequences within allomembers show an aggradational to offlapping stacking pattern that reflects alternate generation and removal of accommodation. The upper surfaces of allomembers H–E are incised by extensive valley systems traceable for up to 320 km and over about 50 000 km². Valley depths range up to 41 m and can change significantly over short distances. However, the average depth of incision (mean 21 m) shows no systematic variation in longitudinal profiles and no evidence of headward shallowing. Valleys are typically 1–2 km wide, but locally widen to about 8 km. Widening is sometimes associated with confluence zones, but elsewhere it is not. Updip reaches of valleys are dominated by cross-bedded fluvial sandstone forming multistorey point-bar deposits. Sandstones contain widespread but uncommon paired carbonaceous drapes recognizable as tidal bundles. Inclined heterolithic stratification is locally well developed at the top of the valley fill. Downdip reaches of valleys, typically within 50 km of the lowstand shoreline, have a sandstone-dominated lower part and, locally, a mud-rich upper portion consisting of a variety of laminated heterolithic facies with a clear tidal signature. These heterolithic deposits may represent central basin, tidal flat, bayhead delta and point-bar environments. Valley filling took place mainly during the transgressive systems tract (TST) when tidally influenced environments migrated upvalley. Semi-diurnal tidal backwater effects extended at least 30 km landward of the regional maximum transgressive marine shoreline. The aggradational late TST and highstand systems tract (HST) includes deltaic and coastal plain deposits comprising lake and anastomosed river deposits that suggest a very low gradient (≈ 1:3000). Delta parasequences of the falling stage systems tract (FSST) offlap seaward and have no equivalent coastal plain deposits. The FSST has an average width of 60 km and an inferred gradient of 1:2500. The upper surfaces of the HST and FSST are extensively incised by valleys. The lowstand systems tract (LST) is subtly aggradational, lacks valleys and is characterized by large delta lobes fed by major distributaries. The width and inferred slope of the FSST, coupled with the thickness of aggradational TST and HST deposits on the coastal plain, suggest a vertical accommodation of about 35 m per transgressive event. About 11 m of this is attributed to isostatic subsidence resulting from water and sediment loads; the residual 24 m is attributed to eustatic rise. This sea-level change is of the same order of magnitude as the valley depths. The length of valleys, however, does not seem to be explicable solely in terms of downstream forcing by sea-level change, and an additional, upstream-forcing mechanism, possibly related to precipitation cycles in the Milankovitch band, might be inferred.     

Controlling factors of reservoir quality in low-permeability reservoir within a sequence stratigraphic framework: a case study of the lower Jurassic sandstones in the Northern margin of the Qaidam Basin,China

The Qaidam Basin, one of China’s most prolific petroliferous basins, is located in the northeastern corner of the Qinghai-Tibet Plateau. Using analytical data from cores, thin-sections and seismic data, and combined with the previous sequence stratigraphy research results, research on the reservoir characteristics was undertaken. The main controlling factors of reservoir quality in the sequence stratigraphy framework in the Lenghu area are discussed. The Lower Jurassic includes lowstand system tract (LST) and transitional systems tract (TST); the highstand systems tract are missing owing to tectonic uplift. The Lower Jurassic sandstones are composed of moderately to poorly sorted, subrounded sandstone representing several representative environments, including fan-delta and lacustrine facies. The main types of the Lower Jurassic sandstones are mostly feldspathic litharenite and lithic sandstone. The pore types of the Lower Jurassic sandstones are mainly secondary dissolution pores with few fracture types. The Lower Jurassic sandstones have experienced strong compaction that resulted in the loss of primary porosity. Carbonate cementation of the LST sandstones is greater than in the TST sandstones. Dissolution, which has an important role in reservoir development, is mainly caused by acidic fluids from the matured source rocks in the LST and meteoric water ingression from the top sequence boundary in the TST. Distributary channel sandstones adjacent to coal and mudstones are favourable reservoirs with turbidite sandstones adjacent to the sequence boundary less favourable reservoirs.     

塔里木盆地西北地区震旦系苏盖特布拉克组潮坪相碎屑岩成岩作用与成岩演化研究

塔里木盆地西北地区苏盖特布拉克组发育一套潮坪相沉积,是该层系油气勘探的主要目标。基于什艾日克剖面、奇格布拉克剖面、肖尔布拉克剖面的地质测量,采用薄片鉴定、阴极发光、扫描电镜、流体包裹体测温及黏土矿物X衍射等分析手段开展海相碎屑岩成岩作用和成岩演化研究,为塔里木盆地苏盖特布拉克组进一步开展油气勘探部署和甜点储层预测提供地质依据。结果表明：（1）研究区苏盖特布拉克组发育潮坪沉积环境的砂体,砂岩类型以岩屑石英砂岩、岩屑砂岩为主,偶见长石岩屑砂岩,成分成熟度和结构成熟度中等;（2）苏盖特布拉克组砂岩经历了压实（溶）作用、胶结作用、溶蚀作用及交代作用等成岩作用,压实作用是造成储层致密的直接原因,钙质胶结和硅质胶结是储层致密化的根本因素;（3）苏盖特布拉克组砂岩的成岩演化阶段已达到中成岩B期,成岩演化序列为：压实作用/自生黏土矿物（绿泥石）环边—第一期长石、岩屑溶蚀作用—第一期硅质胶结—第一期泥微晶方解石胶结/压溶作用/黏土矿物的伊利化—第二次硅质胶结/第二期铁方解石胶结—钙质胶结物溶蚀。据此建立的成岩演化模式为塔里木盆地超深层致密砂岩中甜点储层预测提供可靠的地质依据。     

鄂尔多斯盆地彬长地区长6储层成岩作用及有利成岩相带

鄂尔多斯盆地彬长地区长6油层组发育与深湖相泥岩相伴生的细粒砂岩沉积,是致密油勘探的有利区域。根据岩心观察、铸体薄片鉴定及各类分析测试资料,研究彬长地区长6油层组砂岩储层的孔隙类型及物性特征、成岩演化过程,建立成岩相分类方案,并通过成岩相带平面展布指出勘探有利区。结果表明,研究区长6储层成岩阶段主要处于晚成岩A-B期,压实作用造成原始孔隙大量损失,后期高岭石胶结作用使得渗透率进一步降低。早期绿泥石薄膜的发育可以使原生孔隙得到保存;后期长石、岩屑等不稳定组分发生的溶蚀作用,使孔隙再次分配,物性得到提高。根据成岩作用对物性的影响,划分出强压实成岩相、强溶蚀成岩相、弱溶蚀成岩相、强钙质胶结成岩相,以及微裂缝成岩相等5种成岩相带。优质储层与成岩相密切相关,强溶蚀成岩相的砂体物性、含油性最好,是研究区长6储集层油气最为富集的成岩相带。     

Diagenesis in the Middle Jurassic Khatatba Formation sandstones in the Shoushan Basin,northern Western Desert,Egypt

The Middle Jurassic Khatatba Formation acts as a hydrocarbon reservoir in the subsurface in the Western Desert, Egypt. This study, which is based on core samples from two exploration boreholes, describes the lithological and diagenetic characteristics of the Khatatba Formation sandstones. The sandstones are fine‐ to coarse‐grained, moderately to well‐sorted quartz arenites, deposited in fluvial channels and in a shallow‐marine setting. Diagenetic components include mechanical and chemical compaction, cementation (calcite, clay minerals, quartz overgrowths, and a minor amount of pyrite), and dissolution of calcite cements and feldspar grains. The widespread occurrence of an early calcite cement suggests that the Khatatba sandstones lost a significant amount of primary porosity at an early stage of its diagenetic history. In addition to calcite, several different cements including kaolinite and syntaxial quartz overgrowth occur as pore‐filling and pore‐lining cements. Kaolinite (largely vermicular) fills pore spaces and causes reduction in the permeability of the reservoir. Based on framework grain–cement relationships, precipitation of the early calcite cement was either accompanied by or followed the development of part of the pore‐lining and pore‐filling cements. Secondary porosity development occurred due to partial to complete dissolution of early calcite cements and feldspar. Late kaolinite clay cement occurs due to dissolved feldspar and has an impact on the reservoir quality of the Khatatba sandstones. Open hydraulic fractures also generated significant secondary porosity in sandstone reservoirs, where both fractures and dissolution took place in multiple phases during late diagenetic stages. The diagenesis and sedimentary facies help control the reservoir quality of the Khatatba sandstones. Fluvial channel sandstones have the highest porosities and permeabilities, in part because of calcite cementation, which inhibited authigenic clays or was later dissolved, creating intergranular secondary porosity. Fluvial crevasse‐splay and marine sandstones have the lowest reservoir quality because of an abundance of depositional kaolinite matrix and pervasive, shallow‐burial calcite and quartz overgrowth cements, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

再论陆相三级层序内四分方案及其在油气勘探中的应用

结合在陆相盆地中的实例研究,将一个发育完整的陆相三级层序细分为4个体系域：低水位体系域（LST）、水进体系域（TST）、高水位体系域（HST）和水退体系域（RST）,称为I型层序。或者一个层序可以不发育低水位体系域,而由水进体系域、高水位体系域和水退体系域组成,称为II型层序。低水位体系域发生在湖平面（基准面）快速下降时期;水进体系域出现在首次湖泛面到最大湖泛面之间;高水位体系域形成在高水位时期的湖平面相对静止期;水退体系域形成在湖平面缓慢下降期,在沉积物供给速率大于可容空间增加速率时形成。一般低水位体系域发育小型进积式准层序组,纵向沉积环境变浅,在盆地边缘形成河流下切作用;水进体系域发育退积式准层序组,沉积环境自下而上明显变深;高水位体系域发育加积型准层序组,纵向沉积环境变化不大,且多为静水沉积;水退体系域发育大型进积式准层序组,沉积环境自下而上明显变浅,沉积体系向盆地中心推进。结合对松辽盆地的实例研究,分别阐述了断陷盆地和坳陷盆地中各不同体系域的油气藏分布规律：低水位体系域主要在断陷盆地的陡坡侧和坳陷盆地的深水区发育透镜状岩性油气藏;水进体系域主要在断陷盆地的陡坡带发育上倾尖灭型岩性油气藏,在缓坡带和坳陷盆地的斜坡带发育地层超覆油气藏;高水位体系域主要以深水区的透镜状岩性油气藏为主;水退体系域在断陷盆地中主要发育地层不整合遮挡油气藏,在坳陷盆地中主要发育断块油气藏以及断层遮挡油气藏。从而,以理论与实践相结合的方式,阐明了陆相层序四分体系域的实用性。     

鄂尔多斯盆地东部下二叠统山西组山2段成岩相划分及展布

鄂尔多斯盆地东部下二叠统山西组山2段岩石类型主要为石英砂岩、岩屑质石英砂岩和岩屑砂岩,储集层经历了压实、压溶、硅质胶结、碳酸盐胶结交代、高岭石胶结、杂基蚀变以及溶蚀等多种成岩作用。在成岩作用研究的基础上,通过大量的岩心观察和薄片鉴定,结合阴极发光、探针分析等方法,将研究区划分出7种单因素成岩相,即：强压实、压溶-石英次生加大、蚀变高岭石、沉淀高岭石、杂基充填、碳酸盐胶结交代、不稳定组分溶蚀成岩相,在此基础上对其进行平面叠加,确定了利于储集层发育的优势成岩相。其中压溶-石英次生加大与杂基、假杂基溶蚀作用的综合作用（叠加和改造）决定了山西组山2段有利的成岩相带,在陕141井区、榆37井区、子洲-清涧地区山西组山2段形成了天然气优质储集层。     

鄂尔多斯盆地华庆地区长6油层组砂岩成岩相及储层质量评价

本文借助于薄片分析、扫描电镜分析、阴极发光分析和物性分析等研究手段,以鄂尔多斯盆地华庆地区长6油层组低渗透砂岩的形成机制为解剖对象,通过对砂岩埋藏前组成、化学成岩作用和物理成岩作用的相对重要性、自生矿物组成、孔隙构成、物性与孔隙结构等研究,明确了主要成岩作用对储层的影响。在此基础上,结合沉积相的研究,选择骨架颗粒构成、自生矿物组成、物性、孔隙构成以及粒间体积等有关的15个成岩相定量评价参数,对华庆地区长6油层组低渗透砂岩进行成岩相的定量评价。结果表明：① 华庆地区长6油层组砂岩经历了较强的物理成岩作用和较弱的化学成岩作用,原生孔隙是主要储集空间,压实作用是孔隙度降低的最主要因素,其次为方解石的胶结作用;② 成岩相定量评价表明,弱胶结、强压实成岩相以及强方解石胶结、中-强压实成岩相的储层质量均较差,受北部物源区控制的绿泥石胶结、弱-中等压实成岩相具有较好的储层质量,建议作为今后的优选勘探开发区。     

苏德尔特油田低渗透凝灰质砂岩成岩作用及储层质量差异性演化

海拉尔盆地贝尔凹陷苏德尔特油田兴安岭油层为典型的富火山物质的低渗致密砂岩储层。利用岩心观察、薄片鉴定、扫描电镜分析、压汞测试分析等方法,对兴安岭油层储层成岩作用及其控制下的储层质量演化过程进行了系统研究。结果表明,储层目前主要处于中成岩A期,整体经历了压实作用-早期方解石胶结作用/方沸石胶结作用-方沸石溶解/长石溶解作用/高岭石胶结作用/硅质胶结作用-晚期方解石胶结作用。兴安岭油层储层可以划分出强压实成岩相（I）、弱压实-方解石中强胶结成岩相（II）、中等压实-方沸石/长石强溶解成岩相（III）、中等压实-方沸石/长石中强溶解-高岭石强烈充填成岩相（IV）4种类型的成岩相。压实作用和早期方解石胶结作用导致储层孔隙度和渗透率降低,方沸石和长石的溶解作用有效提高储层孔隙度和渗透率,高岭石的沉淀作用导致储层渗透率大大降低。成岩相I和成岩相II储层质量最差,孔隙度和渗透率均较低,为典型的特低孔特低渗致密储层;成岩相III储层质量最好,具有较高的孔隙度和渗透率,为中孔-中低渗储层;成岩相IV储层质量中等,具有较高的孔隙度,但渗透率较低,为中孔（特）低渗储层。