Chlorite cement and its effect on the reservoir quality of sandstones from the Panyu low-uplift, Pearl River Mouth Basin

Based on porosity and permeability measurements,mercury porosimetry measurements,thin section analyses,SEM observations,X-ray diffraction(XRD) analysis and granulometric analyses,diagenetic features of reservoir sandstones taken from the Zhuhai formation in the Panyu low-uplift of the Pear River Mouth Basin were examined.This study shows that chlorite cements are one of the most important diagenetic features of reservoir sandstones.The precipitation of chlorite was controlled by multiple factors and its development occurred early in eo-diagenesis and continued till Stage A of middle diagenesis.The precipitation of chlorite at the early stage was mainly affected by the sedimentary environment and provenance.Abundant Fe-and Mg-rich materials were supplied during the deposition of distributary channel sediments in the deltaic front setting and mainly in alkaline conditions.With the burial depth increasing,smectite and kaolinite tended to be transformed into chlorite.Smectite cements were completely transformed into chlorite in sandstones of the studied area.Volcanic lithics rich in Fe and Mg materials were dissolved and released Fe2+ and Mg 2+ into the pore water.These cations precipitated as chlorite cements in middle diagenesis in an alkaline diagenetic environment.Chlorite coatings acted as porosity and permeability,thus helping preserve cements in the chlorite cemented sandstones.The reservoir quality of chlorite cemented sandstones is much better than sandstones without chlorite cements.Chlorite cements play an important role in the reservoir evolution that was mainly characterized by preserving intergranular porosity and forming better pore-throat structures of sandstones.     

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.     

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.     

THE INFLUENCE OF CEMENTATION ON THE RESERVOIR QUALITY OF THE RISHA SANDSTONE MEMBER (UPPER ORDOVICIAN), RISHA GASFIELD, NE JORDAN

Shallow-marine sandstones of the Upper Ordovician Risha Member of the Dubaydib Formation constitute important reservoir rocks for natural gas in the Risha area of NE Jordan. However, reservoir quality is frequently reduced by diagenetic effects including extensive cementation. This paper reports on the petrology of the Risha Sandstones and the nature of diagenetic alteration, based on standard petrographic analyses of 147 core samples collected from nine wells at Risha gasfield. In addition ten representative samples were investigated using scanning electron microscopy (SEM).
The sandstones comprise subarkoses and quartzarenites which are texturally submature to supermature. Petrographic analyses suggest a continental provenance, most probably from precursor plutonic rocks from the Arabian Shield. A generalized model of paragenesis includes early compaction and development of syntaxial feldspar overgrowths with quartz cementation of variable intensity. Carbonate cements occur as replacement and pore-filling phases. Dolomite and siderite cementation occurred during later-stage burial, together with pressure solution and the growth of authigenic clays. Most of the cements originated from meteoric or compaction-derived waters. Separate pathways of sandstone diagenesis were recognized for the texturally supermature and submature sandstones, both of which were facies-controlled.
Occlusion of most of the porosity preceded hydrocarbon accumulation, which is therefore restricted to areas where cementation was minimized or where cements were dissolved.     

松辽盆地南部扶余-新立地区扶余油层成岩作用初步研究

扶余油层是松辽盆地南部主要开采和勘探的目的层,作者通过大量岩石薄片的研究,认为该油层是由砂岩、粉砂岩、泥岩及其过渡岩类组成的一套韵律沉积;砂岩的矿物成分和结构,明显地影响着物理和化学成岩作用;自生高岭石、自生石英和方解石分布广、含量大,是对储集性能影响较大的胶结物;而富含长石、岩屑和矿物成熟度低,则是本区砂岩的特点。      

DIAGENETIC CONTROLS ON THE RESERVOIR QUALITY OF TIGHT OIL-BEARING SANDSTONES IN THE UPPER TRIASSIC YANCHANG FORMATION,ORDOS BASIN,NORTH-CENTRAL CHINA

Tight oil-bearing sandstones in the Chang 4+5, 6 and 7 Members of the Upper Triassic Yanchang Formation in the Ordos Basin, north-central China, in general consist of fine-grained, moderately- to poorly-sorted lithic arkoses (average Q₅₃F₃₀R₁₇) deposited in a fluvial-dominated lacustrine-deltaic environment. Diagenetic modifications to the sandstones include compaction and cementation by calcite, dolomite, ankerite, quartz, chlorite, kaolinite and illite, as well as partial dissolution of feldspars and minor rock fragments. Porosity ranges up to ~7% of the rock volume and was reduced more by cementation than by compaction. Fractures (tectonic macrofractures and diagenetic microfractures) provide important oil migration pathways and enhance the sandstones' storage potential. The pore network is heterogeneous due to processes related to deposition and diagenesis, and there are considerable spatial variations in porosity and pore connectivity. The pore system includes both macropores and micropores, and pore network variations depend on the type and distribution of authigenic cements. An analysis of the diagenetic and porosity characteristics of core samples of the Yanchang Formation sandstones from wells in the Youfangzhuang oilfield resulted in the recognition of six petrofacies (A-F) whose characteristics allow reservoir quality to be predicted. Fluid performance analysis for selected sandstone samples using nuclear magnetic resonance combined with helium porosity and air permeability shows that high permeability and large pore throats together result in high movable fluid saturation potential, and that effective pore spaces and throats are beneficial for hydrocarbon storage and flow. Relatively higher porosity and permeability tend to occur in petrofacies B sandstones containing abundant pore-lining chlorite with lesser kaolinite and minor carbonate cements, and in petrofacies C sandstones with abundant pore-filling kaolinite cement but little chlorite and carbonate cements. These petrofacies represent the best reservoir-quality intervals. A reservoir quality prediction model is proposed combined with the petrofacies classification framework. This model will assist future development of tight sandstone reservoirs both in the Upper Triassic Yanchang Formation in the Ordos Basin and elsewhere.     

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.     

渤中地区第三系碎屑岩储层成岩作用研究

根据大量岩石薄片、X衍射、扫描电镜、压汞试验等资料 ,对渤中地区第三系馆陶组—沙河街组碎屑岩储层成岩作用及孔隙演化进行了研究 ,并在此基础上划分了成岩阶段 ,初步探讨了其成岩模式。研究结果表明 ,渤中地区第三系碎屑岩储层处于早成岩期 B阶段—晚成岩期 A阶段 ,局部达到晚成岩期 B阶段初期 ;储层的岩石性质及成岩程度有利于次生孔隙的发育。由于长石溶蚀形成次生孔隙时伴随大量自生高岭石的生成 ,故自生高岭石高含量带可作为寻找次生孔隙发育带的标志     

四川盆地川西坳陷须家河组砂岩致密化研究

从岩石学特征、成岩作用特征、储集空间类型研究入手,并结合盆地模拟分析结果,对四川盆地川西坳陷须家河组砂岩致密化进程进行系统分析。导致须家河组砂岩致密化的主要成岩事件包括机械和化学压实作用、碳酸盐胶结物及自生石英的沉淀。压实作用是造成砂岩孔隙度降低的最主要因素,较高石英、长石、钙屑含量可以提高岩石抗机械压实能力。碳酸盐胶结作用在须四段钙屑砂岩和须二段细粒砂岩中较为普遍,对储层具有明显的破坏作用。相对开放环境以及古构造高位置不利于碳酸盐胶结物的沉淀,对储层发育有利。自生石英主要来自碎屑石英的压溶,具一定厚度、连续性较好的绿泥石衬边可以抑制压溶作用进行以及石英胶结物的形成,对须家河组砂岩储层孔隙保存具有双倍积极作用。      

三塘湖盆地马朗凹陷西山窑组储层成岩作用类型及特征

三塘湖盆地马朗凹陷中侏罗统西山窑组存在多个一定规模的砂岩油气藏，具备较大的油气开发潜力。通过薄片观察、电镜扫描、X射线衍射、镜质体反射率等分析手段，划分了马朗凹陷西山窑组储集砂岩的成岩作用类型及成岩阶段，分析了成岩作用对储层物性的影响。该区西山窑组储集砂岩中发育8类成岩作用，其中蚀变、溶蚀和破裂作用为建设性成岩作用，压实-压溶、硅质胶结和碳酸盐胶结作用为破坏性成岩作用，而绿泥石胶结和交代作用会随着成岩阶段的向后推移由建设性作用转为破坏性作用；西山窑组砂岩以中成岩A期的晚期阶段为主。压实作用是该区主要的减孔因素，高岭石化和溶蚀作用是主要的増孔因素。发育绿泥石环边胶结，储集空间为剩余原生粒间孔与溶蚀孔组合的砂岩是最优质的储集砂体。      

苏北盆地高邮凹陷北斜坡阜宁组成岩作用及储层特征

高邮凹陷北斜坡阜宁组碎屑岩储层以细砂岩和粉砂岩为主,砂岩类型主要为长石砂岩、岩屑长石砂岩和少量长石岩屑砂岩。主要成岩矿物类型为粘土矿物、石英和碳酸盐等。储层以次生孔隙发育为主,粒间孔隙和骨架颗粒溶孔最为发育。阜宁组成岩演化阶段处于早成岩B期至晚成岩A期。机械压实作用比较明显,但次生溶蚀作用亦表现得十分强烈。阜宁组储层性质明显地受到沉积微相和成岩作用的影响。在阜一段三角洲主要砂体微相中,沉积物粒度较粗、厚度较大的河道和砂坝砂的储集物性明显优于各种粒度较细、厚度较薄的席状砂体。阜三段三角洲前缘砂体发育,水下分流河道和河口砂坝物性最好,前缘席状砂及其他侧翼砂体的物性较差。平面上储层性质主要表现为相控特点,并具有较好的规律性     

元坝地区须家河组砂岩成岩作用与孔隙演化

元坝地区上三叠统须家河组砂岩属于典型的低孔低渗型储层。通过显微镜下常规及铸体薄片鉴定、扫描电镜观察、X-衍射等手段,对研究区砂岩储层的成岩作用、孔隙演化及其对储集物性的影响进行了深入研究。研究区发育的成岩作用类型主要有压实作用、压溶作用、交代作用、胶结作用、溶蚀作用及破裂作用。其中破坏性成岩作用为压实压溶、硅质胶结和碳酸盐岩胶结作用;而绿泥石环边胶结、溶蚀和破裂作用则对储层起到了保护和改善作用。元坝地区须家河组砂岩目前已达中成岩阶段A期,一些地区已经达中成岩B期。储层经历强烈的成岩作用后原生孔隙基本被破坏,孔隙类型主要为次生孔隙并伴生裂缝。     

RESERVOIR SANDSTONES OF THE CRETACEOUS NAPO FORMATION U AND T MEMBERS IN THE ORIENTE BASIN,ECUADOR: LINKS BETWEEN DIAGENESIS AND SEQUENCE STRATIGRAPHY

This paper investigates whether diagenetic alterations in sandstones and resulting changes in reservoir quality are influenced by depositional environments and sequence stratigraphy. The study focusses on the Cretaceous U and T sandstone members of the Napo Formation in the Oriente Basin of Ecuador. The sandstones were deposited in fluvial, transitional and marine environments, and comprise Lowstand (LST), Transgressive (TST) and Highstand Systems Tract (HST) deposits. The data were obtained by detailed petrographic observations supported by microprobe, stable isotope, and fluid inclusion analyses. The sandstones consist of fine- to medium-grained quartzarenites and subarkoses. Diagenetic events include cementation by chlorite, early and late kaolinite/dickite, early and late carbonates (siderite, Fe-dolomite/ankerite), and quartz. Early (eogenetic) processes included formation of chlorite grain coatings, kaolinite pore filling, and siderite (SI) cementation. Chlorite is absent in TST sandstones but was found frequently in LST-HST sandstones. Early kaolinite is not present in LST sandstones but occurred frequently in LST-HST sandstones. The distribution of mesogenetic cements relative to sequence stratigraphy is different in the U and T units. In the U sandstones, calcite is frequent in LST deposits and absent in the LST-HST. Fe-dolomite/ankerite is abundant only in the TST. S2 siderite is present in the TST and LST, but absent in the LST-HST. Quartz cement and kaolinite/dickite are equally distributed in all systems tracts. In the T sandstones Fe-dolomite/ankerite is only abundant in the TST, whilst calcite, quartz and dickite have similar distributions in all the systems tracts. The distribution of kaolinite cement is interpreted to be the result of relatively more intense meteoric-water flux occurring during sea-level fall, whereas chlorite cement may have formed through burial diagenetic transformation of precursor clays e.g. berthierine which was precipitated in mixed marine-meteoric waters in tidal channel and estuarine environments. Chlorite cement in the T and U sandstones appears to have retarded development of quartz overgrowths, and 12–13% primary porosity is retained. The T sandstones (LST-HST) contain up to 4% chlorite cement. Little evidence for chemical compaction was found with the exception of occasional concave-convex grain contacts. Eogenetic siderite appears to have helped to preserve reservoir quality through supporting the sandstone framework against further compaction, but mesogenetic calcite has considerably reduced primary porosity. Eogenetic siderite (SI) was partly replaced by later carbonate cements such as late siderite (S2) and Fe-dolomite. Although there appears to be a relationship in the Napo Formation between the occurrence of siderite SI and sequence stratigraphy, the relationship may change when original volumes of siderite are considered. There is likewise partial replacement of early kaolinite and recrystalization to dickite which masks the amount of original early kaolinite. Since the amount of early kaolinite could not be confirmed, the relationship to sequence stratigraphy is tentative. Only chlorite seems to have a clear relationship to sequence stratigraphic framework in the Napo Formation. The high intergranular volume (IGV) of the sandstones indicates that cementation played a more important role than mechanical and chemical compaction in both Napo Formation sandstone members. Later dissolution of feldspar grains and siderite cements was the main process of secondary porosity development (up to 11% in the U sandstones).     

内蒙乌兰格尔地区上古生界砂岩的成岩作用

内蒙乌兰格尔地区的上古生界厚逾400m,大部分砂岩属于致密型低孔渗性的岩体。本文主要论述这些砂岩的成岩作用及其对储层孔渗性的影响。记砂岩具有四个成岩阶段:1.机械压实作用和早期胶结作用;2.碳酸盆的胶结作用和交代作用;3.溶蚀作用;4.晚期自生粘土矿物的形成和早期粘土矿物的重结晶作用。其中强烈的机械压实作用减少砂岩的孔隙,碳酸盆矿物的胶结作用尤其显著地减少了孔隙度和渗透率。但是,胶结物和部分颗粒的后期溶蚀作用是改善某些层段储集性能的有利因素。      

FLOW UNIT DISTRIBUTION AND RESERVOIR MODELLING IN CRETACEOUS CARBONATES OF THE SARVAK FORMATION,ABTEYMOUR OILFIELD,DEZFUL EMBAYMENT,SW IRAN

Carbonate sediments within the Mid‐Cretaceous Sarvak Formation form an important reservoir at the Abteymour oilfield in the western Dezful Embayment, SW Iran. The poroperm characteristics of this reservoir were controlled by factors including deposition under tropical climatic conditions and early diagenesis, repeated phases of subaerial exposure due to local, regional and global‐scale tectonism, and diagenetic modification during burial. From microfacies analysis, the Sarvak Formation carbonates in the Abteymour field were interpreted in a previous study as having been deposited on a homoclinal ramp‐type platform. Three third‐order sequences were recognized in the middle Cenomanian to middle Turonian part of the formation. The reservoir quality of the carbonates was enhanced both by dissolution (comprising separate phases of eogenetic and telogenetic meteoric dissolution) and dolomitization (especially stylolite‐related dolomitization). In this paper, a rock/pore type approach was used in order to integrate petrophysical data with facies and diagenetic models within a sequence stratigraphic framework. Two different rock‐typing methods for the determination of flow units were considered. Hydraulic flow units (HFUs) were identified firstly using flow zone indicators and secondly using a stratigraphic modified Lorenz plot. The flow units resulting from these two methods are compared, and their close correspondence within the sequence stratigraphic framework is discussed. In addition, the previously‐used large‐scale reservoir zonation scheme for the Abteymour field is correlated with the defined flow units, and four new Integrated Reservoir Zones are introduced. By integrating geological information with petrophysical parameters (including porosity, permeability and saturation) within a sequence stratigraphic framework, field‐scale variations and controls on reservoir quality are described.     

鄂尔多斯盆地山城-演武地区三叠系延长组长6-长8低渗储层特征及成岩作用研究

鄂尔多斯盆地山城-演武地区三叠系延长组长6-长8段砂岩属于典型的低孔低渗储集岩,具有粒度细、成分成熟度低、磨圆度差、分选中等等特征。通过薄片、X射线衍射、扫描电镜、压汞、阴极发光等分析手段,研究了延长组长6-长8段砂岩储层的特征、成岩阶段及演化模式,分析了低渗储层物性的影响因素,指出沉积相带是影响储层储集性能的地质基础,机械压实作用和晚期的铁方解石胶结作用是影响低渗透砂岩储层形成的主要因素,绿泥石包膜、溶蚀作用及微裂缝对储层储集性能的改善起到了积极作用。     

岩相约束下的深层致密砂岩气藏储层演化特征

东海盆地深层致密气藏沉积和成岩演化复杂，不同岩相储层的成岩演化是揭示沉积-成岩耦合及认识致密储层甜点成因的关键，也是甜点预测的基础。本研究将岩心观察、铸体薄片、扫描电镜、粒度分析和X-衍射等资料相结合，选取东海西湖凹陷中央反转构造带深层花港组典型致密气藏，研究不同岩相储层的成岩演化。通过开展岩石学特征研究，划分主要岩相类型，结合埋藏史分析成岩演化序列，分析不同岩相砂岩成岩差异及成岩演化过程，建立不同岩相的成岩演化模式，揭示沉积对成岩的控制作用。结果表明，研究区花港组储层以水下分流河道沉积为主体，主要发育块状层理中-粗砂岩、砾质砂岩、平行层理中-细砂岩和泥砾质砂岩四种岩相类型。块状层理中-粗砂岩和砾质砂岩刚性石英含量较高，粘土含量较低，胶结物类型以薄层绿泥石和硅质胶结为主；前者经历的成岩作用较为完整，埋藏后期仍然发育有一定的原生孔隙和次生溶孔，容易形成较好储层；但后者常常因为分选性较差，最终易形成压实紧密，硅质胶结强烈的致密储层。平行层理中-细砂岩刚性石英含量较低，粘土含量较高，胶结物类型以厚层绿泥石、伊/蒙混层和伊利石相伴生为主；由于沉积分异作用，碎屑颗粒常呈层状定向排列，埋藏后期细粒层部分压实致密，粗粒层部分保留有块状层理砂岩性质，发育局部孔隙带，形成次一级储层；泥砾质砂岩塑性泥岩撕裂屑含量较高，同时混杂有大量泥质杂基，在埋藏早期就已经压实致密，各类孔隙均不发育，基本为非储层。     

Reservoir quality of fluvial sandstone reservoirs in salt-walled minibasins: an example from the Seagull field, Central Graben, North Sea, UK

The Triassic fluvial sandstones of the Skagerrak Formation were deposited in a series of salt-walled mini-basins and act as important hydrocarbon reservoirs for several high-pressure, high-temperature (HPHT) fields in the Central Graben, North Sea. The HPHT reservoirs exhibit excellent reservoir quality considering their depth of burial and hence have been of high interest for hydrocarbon exploration. This research uses a multidisciplinary approach to assess the Skagerrak Formation fluvial reservoir quality from the Seagull field incorporating core analysis, petrography, electron microscopy, XRD analysis, fluid inclusion appraisal and burial history modelling. Halokinesis and salt withdrawal at the margin of the saltwalled mini-basin induced early disaggregation bands and fractures at shallow burial and led to increased influx of meteoric water and clay mineral infiltration from overlying sedimentation. The density of disaggregation bands correlates with the occurrence and magnitude of pore-filling authigenic clay minerals, concentrated along the margin of the saltwalled mini-basin. The fluvial channel sandstones of the Skagerrak Formation are subject to strong intra-basinal spatial reservoir quality variations despite diagenesis and low vertical effective stress having played a favourable role in arresting porosity loss.     

渤海海域中部古近系湖相碳酸盐岩储层成岩演化特征

渤海海域中部石臼坨凸起沙河街组优质储层分布是决定油气藏分布的关键要素,而成岩作用是控制沙河街组湖相碳酸盐岩储层发育的关键因素,准确分析成岩作用是提高该地区沙河街组储层预测的重要保障。利用偏光显微镜、荧光显微镜、扫描电镜、阴极发光、电子探针等实验分析技术,确定储层特征和成岩演化序列;利用黏土矿物X-射线衍射确定成岩阶段;利用气液两相包裹体均一温度和氧同位素地质温度计分析碳酸盐自生矿物的形成时期。沙河街组碳酸盐岩储层的岩石类型主要是生屑云岩,其次为砂屑云岩;储集空间以残余粒间原生孔和生物体腔孔为主;成岩作用主要特征为发育不同产出形态、多期次的自生白云石;建立了成岩演化序列,最终成岩阶段为中成岩B期;对储集物性有利的成岩作用是早成岩阶段形成的衬垫状白云石和同生期形成的包壳状白云石,其早期形成减弱了随后的压实作用对储层孔隙的破坏强度。