SEQUENCE STRATIGRAPHY AND RESERVOIR CHARACTERISTICS OF THE TURONIAN-CONIACIAN KHASIB FORMATION IN CENTRAL IRAQ

Bioturbated chalky limestones of the Khasib Formation (Upper Turonian – Lower Coniacian) form potential reservoir rocks at oilfields and structures in central Iraq. Core and cuttings samples and wire-line logs from wells in the East Baghdad, Balad, Samarra and Tikrit fields (wells EB-77, EB-57, Ba-1, Ba-2, Sr-1, Sr-2, and Ti-1) were used to investigate microfacies types and porosity evolution. Facies modelling was applied to predict the relationship between facies distribution and reservoir characteristics to construct a predictive geologic model which will assist future exploration in central Iraq. Microfacies analysis and electrofacies identification and correlations indicate that the limestones of the Khasib Formation were deposited in a ramp setting. The ramp developed over the distal margin of the Upper Cretaceous proforeland basin, adjacent to the evolved forebulge. Inner ramp facies are characterized by carbonate bank bioclastic packstones intercalated with lagoonal green shales. Middle ramp facies dominate the Khasib Formation and consist of bioturbated, chalky, dolomitic and bioclastic limestones. Bioclasts include benthic and planktonic foraminifera. Intense Thalassinoides and less common Palaeophycus bioturbation has enhanced the porosity of this facies. Outer ramp deposits consist of alternating mid-ramp bioturbated bioclastic chalky limestones and argillaceous and marly limestones. The latter contain basinal bioclasts including planktonic foraminifera, oligosteginids, dwarf rotaliids, and sponge spicules. Sequence stratigraphic analyses of the Khasib Formation indicate that it represents a third-order depositional cycle. At the base is a type 1 sequence boundary which separates it from the underlying LST deposits of the Kifl Formation. Shaly and argillaceous limestones in the lower part of the Khasib Formation represent the early TST. These are overlain by a thick, deepening-upwards succession of outer ramp facies. The maximum flooding surface is represented by a thin and extensive horizon of Oligosteginal limestones with Palaeophycus bioturbation. HST deposits are represented by aggradational build-ups of bioturbated chalky dolomitic limestones, followed by progradational late HST shales and limestones. The boundary with the overlying Tanuma Formation is a type 2 sequence boundary. Bioclastic packstones and intensively bioturbated (Thalassinoides) bioclastic limestones of the mid-outer ramp are the primary source of fabric-selective porosity which is greatly enhanced by diagenetic overprints. These two units constitute the prime target for future exploration in central Iraq.     

川中地区茅口组一段沉积相新认识

四川盆地中二叠统茅口组一段具有较大的天然气勘探潜力,但一直存在沉积相认识不清的问题。基于四川盆地中部2口最新钻井岩心厘米级精细描述以及多个野外露头观测,结合分析化验资料及测井曲线,开展了详细的沉积相标志分析,提出了新的茅一段沉积相划分方案。“眼球灰岩”与“眼皮灰岩”的主要区别在于泥质含量的多少,用自然伽马曲线能够有效区分这2种岩相;海相缺氧环境、大量风暴沉积构造以及硅质生物碎屑表明,茅一段沉积于缓坡型碳酸盐岩台地环境之下,受到风暴作用及与之伴生的风暴上升流的影响。基于沉积相标志,将茅一段划分为中缓坡外带和外缓坡上部2个亚相,中缓坡外带包括风暴碎屑流、风暴滩、风暴滩间洼地3个微相,外缓坡上部“眼皮灰岩”含量较高,微相组合为颗粒流、静水泥夹碎屑流,一般发育在茅一段上部或顶部。     

川西中三叠统天井山组风暴沉积的发现及古地理意义

笔者首次发现川西地区中三叠统天井山组（T2t）中有大量的风暴岩。其中包含许多典型的与风暴相关的沉积构造．包括冲刷一充填构造、粒序层理和块状层理、丘状和凹状交错层理、扁平砾屑岩层等。该区风暴岩有6种沉积层序,Ⅰ型、Ⅱ型层序为远源风暴岩,Ⅲ型、Ⅳ型、Ⅴ型和Ⅵ型层序为近源风暴岩。风暴岩的区域展布差异和广泛分布表明,拉丁期上扬子西缘处于风暴活动频繁的低纬度陆棚缓坡沉积环境。天井山组风暴岩是四川盆地的一种新型储层。     

四川盆地西部上三叠统须家河组二段风暴岩沉积特征

通过研究,发现了四川盆地西部上三叠统须家河组二段沉积具有典型的风暴沉积特征,主要包括渠模构造(或口袋构造)、冲刷面和截切构造、风暴滞积层段、丘状交错层理、包卷层理、浪成层理、倒“小”字状构造、生物扰动等。须二段的风暴沉积类似于鲍马序列,垂向沉积序列可以划分出Sa,Sb,Sc,Sd,Se等5段。风暴沉积是由风暴作用引起的强烈振荡风暴浪作用于三角洲、扇三角洲,使沉积物经搬运再沉积的产物。风暴岩沉积构造类型丰富多样,而又以风暴成因的泥砾为特征,泥砾的形态,排列样式,组合方式,反映了风暴沉积的强度和频度。须二段风暴沉积是四川盆地的一种新型储集层     

扬子地台北缘城口地区上寒武统洗象池组风暴沉积特征及其地质意义

上寒武统洗象池组是四川盆地的一个潜在勘探层位，但对其沉积相带展布及储层主控因素的认识还十分薄弱。在扬子地台北缘洗象池组发现的风暴沉积可以为此提供一些重要的约束。通过野外剖面实测和室内薄片鉴定，对扬子地台北缘城口地区洗象池组风暴沉积特征进行了深入分析，并探讨了其古地理含义及其对川东北地区洗象池组储层发育的指示意义。研究区洗象池组风暴沉积的典型识别标志包括底冲刷-充填构造、风暴撕裂构造、粒序层理和丘状交错层理等。根据风暴沉积标志组合的不同，划分出5种风暴沉积序列:序列1、序列2、序列3、序列4及序列5，且风暴段自下而上整体表现为由序列1向序列5逐渐过渡。根据沉积构造、岩性组合及风暴序列变化，结合经典浅水碳酸盐岩风暴沉积的发育模式，认为风暴段沉积环境整体以中缓坡为主，且自下而上由内缓坡、中缓坡向外缓坡变化，构成向上变深序列。结合区域地质背景，推测扬子地台北缘洗象池组在城口以北东地区处于中-外缓坡地带，而城口以南西地区则为内缓坡地带，从而认为洗象池组在城口南西方向的川东北地区具备发育大规模优质颗粒滩储层的地质条件，值得进一步勘探。      

FACIES HETEROGENEITIES AND 3D POROSITY MODELLING IN AN OLIGOCENE (UPPER CHATTIAN) CARBONATE RAMP,SALENTO PENINSULA,SOUTHERN ITALY

Appraisal of the volumes of fluid in a carbonate reservoir will typically require a reliable predictive model. This can be achieved by combining studies of well-exposed carbonate successions with 3D models in order to obtain reliable quantitative data. In this paper, we present a detailed outcrop study and a 3D porosity model of a well-exposed Oligocene carbonate ramp (Salento Peninsula, southern Italy) to investigate the nature of small-scale facies and porosity heterogeneities. Porosity and permeability in the ramp carbonates appear to be controlled by the original mineralogy of skeletal components and by depositional textures. The aims of the study were therefore to identify the factors controlling porosity development in an undeformed carbonate ramp; to model the scale-dependent heterogeneities characteristic of the facies associations; and finally to produce a 3D model of the porosity distribution. The upper Chattian Porto Badisco Calcarenite which crops out along the coast of the Salento Peninsula consists of six lithofacies ranging from inner ramp deposits to fine-grained outer ramp calcarenites. The lithofacies are: inner ramp small benthic foraminiferal wackestone-packstones associated with (i) sea grass meadows (SG) and (ii) coral mounds (CM) consisting of coral bioconstructions with a floatstone/packstone matrix; middle ramp (iii) large rotaliid packstones to wackestone-packstones (LR), (iv) rhodolith floatstone-rudstones (RF), and (v) large lepidocyclinid packstones (LL); and (vi) outer ramp fine-grained bioclastic calcarenites (FC). A total of 38 samples collected from six stratigraphic sections (A, B, D, J, E, LO), measured in the Porto Badisco ravine, were investigated to discriminate the types of porosity. Effective and total porosity was measured using a helium pycnometer. The 3D porosity modelling was performed using PETREL™ 2016 software (Schlumberger). Four main types of porosity were recognized in the carbonates: interparticle, intraparticle, vuggy and mouldic. Primary porosity (inter- and intraparticle) is limited to middle ramp lithofacies (LL and LR) and outer ramp lithofacies (FC), whereas secondary porosity (vuggy and mouldic) was present in both inner ramp lithofacies (CM and SG) and middle ramp red algal lithofacies (RF). In the Porto Badisco carbonates, stratigraphic complexity and the distribution of primary porosity are controlled by lateral and vertical variations in depositional facies. Significant secondary porosity was produced by the dissolution of aragonitic and high-magnesium calcite components, which are dominant in the sea-grass and coral mound facies of the inner ramp and in the rhodolith floatstone-rudstones of the middle ramp. 3D models were developed for both effective and total porosity distribution. The porosity models show a clear correlation with facies heterogeneities. However of the two models, the effective porosity model shows the best correlation with the 3D facies model, and shows a general increase in effective porosity basinwards in the middle ramp facies.     

鄂尔多斯盆地志丹-富县地区三叠系延长组长8油层组风暴沉积特征及意义

根据露头勘查和岩心观察描述，系统分析了鄂尔多斯盆地志丹-富县地区延长组长8油层组风暴沉积的特征及沉积模式。分析表明，风暴岩的岩性以细砂岩和泥质粉砂岩为主，缺乏粗粒沉积，沉积构造主要包括截切构造、"V"字形泥砾、泥岩撕裂屑、冲刷面、丘状和洼状交错层理、浪成沙纹层理、波状交错层理、准同生变形构造等。风暴沉积序列在垂向上具备"似鲍马序列"的特征，自下而上可划分为底面侵蚀构造段（A段）、平行层理段（B段）、丘状和洼状交错层理段（C段）、浪成沙纹层理段（D段）、波状层理段（E段）和泥岩段（F段）。沉积序列主要包括5种类型，其中Ⅰ型的层理构造（A段-F段）发育齐全，Ⅱ型缺失丘状和洼状层理段、Ⅲ型缺失平行层理段、Ⅳ型缺失底面侵蚀构造和平行层理段、Ⅴ型仅发育浪成沙纹层理、波状层理段和泥岩层段。志丹-富县地区半深湖相的主要物源来自其NE方位的三角洲前缘沉积，根据风暴岩的沉积特征和搬运距离，可将志丹-富县地区发育的风暴岩划分为近源型和远源型2种类型。风暴岩的发现完善了志丹-富县地区沉积体系和沉积演化的认识，并可为古纬度与古环境的恢复、地层的划分与对比提供依据，拓展志丹-富县地区延长组油气勘探的新思路。     

DOLOMITIZATION AND RELATED FLUID EVOLUTION IN THE OLIGOCENE – MIOCENE ASMARI FORMATION, GACHSARAN AREA, SW IRAN: PETROGRAPHIC AND ISOTOPIC EVIDENCE

Petrographic and stable isotope investigations of Oligocene‐Miocene carbonates in the Asmari Formation from the Gachsaran oilfield and surrounding area in SW Iran indicate that the carbonates have been subjected to extensive diagenesis including calcite cementation and dolomitization. Diagenetic modification occurred in different diagenetic realms ranging from marine, meteoric and finally burial. Asmari carbonates were in general deposited in a ramp setting and are represented by intertidal to subtidal deposits together with lagoonal, shoal and low‐energy deposits formed below normal wave base. Lithofacies include bioclastic grainstones, ooidal and bioclastic, foraminiferal and intraclastic packstones, and mudstones. Multiple episodes of calcite cementation, dolomitization and fracturing have affected these rocks to varying degrees and control porosity. Four types of dolomites have been identified: microcrystalline matrix replacement dolomite (D1); fine to medium crystalline matrix replacement dolomite (D2); coarse crystalline saddle‐like dolomite cement (D3); and coarse crystalline zoned dolomite cement (D4). Microcrystalline dolomites (D1) (6–12 μm) replacing micrite, allochems and calcite cements in the mud‐supported facies prior to early compaction show δ¹⁸O and δ¹³C values of ?4.01 to +1.02‰ VPDB and ?0.30 to +4.08‰ VPDB, respectively. These values are slightly depleted with respect to postulated Oligocene‐Miocene marine carbonate values, suggesting their precipitation from seawater, partly altered by later fluids. The association of this type of dolomite with primary anhydrite in intertidal facies supports dolomitization by evaporative brines. Fine to medium crystalline matrix dolomites (D2) (20–60μm) occur mostly in grainstone facies and have relatively high porosities. These dolomites formed during early burial and could be considered as recrystallized forms of D1 dolomite. Their isotopic values overlap those of D1 dolomites, implying precipitation from similar early fluids, possibly altered by meteoric fluids. Coarse crystalline saddle‐like dolomites (D3) (200–300 μm) partially or completely occlude fractures and vugs. The vugs developed through the dissolution of carbonate components and rarely matrix carbonates, while fractures developed during Zagros folding in late Oligocene to early Miocene times. A final diagenetic episode is represented by the precipitation of coarse crystalline planar e‐s zoned dolomite (D4) (80–250 μm) that occurs in fractures and vugs and also replaces earlier dolomite and post‐dates stylolitization. Fluids responsible for the formation of D3 and D4 dolomites are affected by brine enrichment and increasing temperatures due to increasing burial. Reservoir porosity is dominated by microcrystalline pore spaces in muddy, dolomitized matrix and mouldic and vuggy porosity in grainstone. Porosity was significantly enhanced by the formation of multiple fracture systems.     

LATE CRETACEOUS TECTONIC AND SEDIMENTARY EVOLUTION OF THE BANDAR ABBAS AREA,FARS REGION,SOUTHERN IRAN

The Upper Cretaceous succession in the SE Zagros (Bandar Abbas area) is characterized by marked changes in fades and thickness. These changes relate to sediment deposition in a foreland basin along the NE margin of the Arabian plate. The succession was measured at eight outcrop sections in the Khush, Faraghun, Gahkum, Genow and Khamir anticlines. The measured sections illustrate a transition from shallow‐water carbonate platform deposits (Cenomanian to Coniacian) to deep‐water fades (Santonian to Maastrichtian). Outcrop observations were compared to data from ten off‐ and onshore wells and to a series of seismic profiles. Four cross‐sections were constructed using well and outcrop data and illustrate fades and thickness variations within the Upper Cretaceous. Based on these regional profiles, the Late Cretaceous depositional history of the Bandar Abbas area was reconstructed and can be divided into two tectono‐sedimentary phases suggesting a transition from a passive to an active margin. Sedimentation during Phase I (late Albion to Coniacian) took place in shallow‐water carbonate platform and intrashelf basin settings (Sarvak Formation), and four third‐order sequences can be recognised. The uppermost sequence is locally capped by fresh‐water, pisolith‐bearing carbonate sand and conglomerates with local laterite and palaeosols of the Coniacian Laffan Formation. Shallow‐water facies consist mainly of wackestone to packstones with abundant benthic foraminifera. Sediments deposited in intrashelf basins are dominated by oligosteginid‐bearing fades. Eustatic variations in sea level, the creation of a foreland basin and salt tectonics most probably controlled patterns of sedimentation during this phase. During the second tectono‐sedimentary phase (Phase II: Santonian to Late Maastrichtian), sediments were dominated by pelagic marls and gravity flow deposits. Lateral thickness variations become more marked to the NE as a result of obduction processes and the creation of the foreland basin. Allochthonous ophiolitic and radiolarite‐bearing units are common in the northern part of the Fars region but are restricted to a few localities in the Bandar Abbas area. Traces of allochthonous materials occur in the SE‐most part of the Khush anticline; thrust slices in offshore seismic profiles may link to the Hawasina nappes of Oman. At the top of the Phase II succession, pelagic facies locally interfinger with Omphalocyclus and Loftusia‐bearing fades (Tarbur Formation) and evaporites (Sachun Formation). These deposits are overlain by slumped and dolomitized shallow‐water carbonates of the Paleocene – Eocene Jahrum Formation. The sedimentary sequence in the Bandar Abbas area illustrates a far‐field response to Late Cretaceous obduction processes and foreland basin development, as well as to halokinetic activity. Rapid variations in thickness and fades document the evolution of depositional processes in the foreland basin.     

二连盆地阿南地区早白垩世风暴沉积

阿南地区早白垩世腾格尔组一段下亚段湖相碎屑岩中存在风暴沉积,层序自下至上依次为:(1)突变的底界与冲刷充填构造;(2)滞留沉积段;(3)大波状层理段;(4)丘状交错层理段,(5)波纹段;(6)生物活动段。本区风暴岩属搅混成因,其主要特征是;(1)不具单向底模;(2)底部粗碎屑段表现出振荡和多向水流形成的组构特征,无明显的粒序;(3)缺乏平行层理,发育丘状交错层理和波状层理。根据其层序差异和分布位置,划分出近岸型(粗型)和远岸型(细型)两类。     

DEPOSITIONAL ENVIRONMENT AND DIAGENESIS OF THE EOCENE JDEIR FORMATION, GABES-TRIPOLI BASIN, WESTERN OFFSHORE, LIBYA

The late Ypresian (early Eocene) Jdeir Formation was deposited in the Mesozoic‐Cenozoic Gabes‐Tripoli Basin, offshore Libya. The basin developed on the northern passive margin of the African Plate and was relatively unstable being affected by syn‐sedimentary tectonic movements. Deposition was coeval with a relative rise of sea‐level and the subsequent highstand. A lower, thinly‐developed nummulitic bank facies with restricted distribution records the transgressive event and is succeeded by more micritic sediments that record the time of maximum flooding. The succeeding sea‐level highstand is represented by a thick, and widely developed, progradational‐aggradational nummulitic sequence that displays lateral changes across WE‐ESE trending facies belts. Three major lithofacies are recognized in the Jdeir Formation: Nummulites packstone‐grainstone, Alveolina‐Orbitoliteswackestone‐packtone, andFragmental‐Discocyclina‐Assilina wackestone‐packstone, depositedin bank, back‐bank, and fore‐bank environments, respectively. The formation passes to the NNE into the pelagic lithofacies of the Hallab Formation; landward, to the south, it passes into shoreline evaporitic facies of the Taljah Formation. The lithofacies were structurally controlled by contemporaneous and/or syndepositional tectonic movements, with nummulitic facies tending to develop on uplifted areas. Petrographic and petrophysical studies indicate that porosity in the Jdeir Formation is controlled by depositional environment, tectonic setting and diagenesis. The combined effects of salt tectonics, a major unconformity at the top of the formation and meteoric diagenesis have produced excellent‐quality reservoir facies at the Bouri oilfield and in other areas. Porosity is highest in the nummulitic bank facies and lowest in the Alveolina‐Orbitolites micrite facies. Good to excellent reservoir quality occurs in the upper part of the nummulitic packstone‐grainstone facies, especially where these sediments overlie structurally high areas. High rates of dissolution found at the crests of domes and anticlines suggest that early diagenetic processes and features are, in part, structurally controlled. Future exploration success will depend on investigation of similar structures within the Gabes‐Tripoli Basin. Both porosity initiation and preservation are related to early depositional and diagenetic processes. The wide time‐gap between hydrocarbon generation and reservoir formation points to the role of the seal in porosity preservation and rules out the assumption that early emplacement of oil had preserved the porosity.     

IMPACT OF DIAGENESIS ON RESERVOIR QUALITY IN RAMP CARBONATES: GIALO FORMATION (MIDDLE EOCENE), SIRT BASIN,LIBYA

The reservoir quality of Middle Eocene carbonates in the intracratonic Sirt Basin is strongly influenced by depositional facies and various diagenetic processes. Based on data from core samples and well logs from five boreholes in the Assumood and Sahl gasfields in the subsurface of the north‐central Sirt Basin, six major carbonate facies (and fourteen microfacies) are distinguished in the Middle Eocene Gialo Formation (thickness ～1100 ft/335 m). Wackestones‐packstones dominate the Gialo Formation with abundant grains of larger benthic foraminifera, especially nummulites, in a matrix composed mostly of finely comminuted bioclastic material. Sediments were deposited as a mosaic of facies on a broad carbonate ramp in moderate‐energy nummulite‐packstone banks, with locally restricted back‐bank lagoons and fore‐bank areas of foraminiferal debris passing to offshore lime mudstones. Marine diagenesis was minor with micritization of bioclasts and rare vadose marine fibrous cements. Sparry calcite cements are ubiquitous and were precipitated during shallow to moderate burial from seawater and/or meteoric water, the latter largely unaffected by surface‐pedogenic processes. This is indicated by the fabrics and pre‐ and post‐compaction precipitation of drusy spar and echinoderm overgrowths, and supported by their bright‐to‐dull luminescence and low negative δ¹⁸O signatures (‐2.68 to ‐4.16%° PDB). Some early neomorphic alteration of calcitic bioclasts is suggested by bright CL and marine to low negative δ¹⁸O values (‐1.06 to –3.93%° PDB). Bioclastic grains have δ¹³C values ranging between 0.76 and 1.19%° PDB, interpreted as marine signatures. Similar low positive δ¹³C values of the cements (0.9 to 1.05 %°) indicate a source of carbonate from dissolution of grains and/or seawater/meteoric water, but without any near‐surface/soil effects. Dissolution of grains and matrix, notably originally aragonitic grains but also the originally high‐Mg calcite nummulites, was a major porosity‐enhancing process, and took place from shallow to moderate burial depths. Fractures may locally have increased porosity too. Shallow‐water packstones/rudstones containing both primary intergranular and secondary biomouldic porosity have the best reservoir quality and these are concentrated in the upper parts (top ～100 ft/30 m) of the wells, with porosity‐permeability decreasing downwards. This trend relates to the broad, large‐scale facies pattern of more mud‐dominated facies giving way upwards to more grainy, nummulite‐dominated facies as a result of an overall shallowing of the depositional environment. In addition, the influx of meteoric waters in the upper part of the Gialo platform, before drowning and deposition of the overlying Augila Shale, increased porosity through dissolution. This integrated study has helped in understanding the reservoir heterogeneity and hydrocarbon potential of the Gialo carbonates.     

MID-CRETACEOUS RUDIST-BEARING CARBONATES OF THE MISHRIF FORMATION: AN IMPORTANT RESERVOIR SEQUENCE IN THE MESOPOTAMIAN BASIN, IRAQ

This paper reports on the sedimentology and stratigraphy of the mid-Cretaceous Mishrif Formation, one of the principal carbonate reservoirs in Central and Southern Iraq. The Cenomanian Mahilban, Maotsi and Fahad Carbonate Formations of Central Iraq are the lateral chronostratigraphical equivalents of the Mishrif and underlying Rumaila Formations of Southern Iraq. Together, these units represent a single mid-Cretaceous carbonate succession in the Mesopotamian Basin. The Mishrif Formation in Central Iraq reflects the continuous deposition of shallow-shelf carbonates; periodic rises in sea level led to episodes of deeper-water sedimentation, during which the outer-shelf and basinal deposits of the Rumaila Formation were laid down. A ramped platform was the principal depositional setting for the entire Cenomanianearly Turonian carbonate succession. The best reservoir conditions in the Mishrif Formation occur in rudist-bearing facies, such as rudstones and rudistid packstone/grainstones. Reservoir units are characterised by porosities of >20% and by permeabilities of 100 mD to 1 Darcy. Other carbonate facies, such as pelagic mudstone/ wackestones, bioclastic wackestones and peloidal packstones, are less significant as reservoir rocks. All the carbonates were affected by a range of diagenetic processes, among which dissolution and dolomitization led to the formation of secondary porosity; porosity was reduced by compaction, stylolitization, micritisation, neomorphism and cementation. The Mishrif Formation is divisible by a prominent unconformity into two large-scale regressive sequences, which are particularly distinguishable in the east of the Mesopotamian Basin. Multiple reservoir units are present in both sequences. The west of the basin is dominated by the lower sequence, which has relatively few reservoir intervals. The shallow-water reservoir units in the east of the basin are thick, reflecting relatively high subsidence rates throughout the Cenomanian (e.g in the Amara oilfield and nearby areas). Subsidence rates in the western side of the basin were lower, and reservoir units are thinner and more limited. The Mishrif Formation carbonates wedge-out in the western and SW deserts of Iraq.     

鄂西建南地区长兴组沉积相及生物礁沉积演化模式

在前人研究基础上,结合鄂西建南地区最新钻井资料和地震解释成果,详细解剖该区长兴组沉积相特征及礁滩体沉积演化模式,提出了长兴组沉积早期发育碳酸盐缓坡、中-晚期发育碳酸盐台地的沉积模式,其中台地模式包括镶边台地和孤立台地,礁滩沉积主要发育于台地边缘相带。建南地区长兴组礁滩分布特征研究表明,南部以滩相沉积为主、北部以礁相沉积为主,其中礁、滩沉积体均发育于各层序的高位体系域,尤以第1个三级层序高位体系域最为发育。该区礁滩沉积是在相对海平面不断下降的背景下发育的,形成了一套规模较大的加积-进积型台地边缘生物礁、滩沉积序列。主要礁滩发育期可分为3个演化阶段,第1阶段以小规模低能滩相沉积为主,也是生物礁奠基阶段;第2阶段为大型障积型生物礁和生屑滩发育期;第3阶段为生物礁逐渐消亡阶段,该期生物礁以黏结-障积型生物礁为主。礁滩发育晚期的暴露浅滩白云石化作用强烈,形成良好的储集岩。     

ORGANIC GEOCHEMISTRY AND SOURCE ROCK CHARACTERISTICS OF THE ZAGROS PETROLEUM PROVINCE, SOUTHWEST IRAN

The Zagros of SW Iran and its continuation into N Iraq forms the tectonised NE margin of the Middle East basin. Sedimentation in the Zagros began in the late Precambrian and continued with comparatively few interruptions until the Pliocene, when strong earth movements affected the area and gave rise to the present day large. elongated NW-SE trending structures. Some of the world's largest structurally-controlled oil fields are located in the Zagros. The most productive pay zone is the Oligo-Miocene Asmari Formation, although significant oil pools are present also in the Cenomanian-Turonian Sarvak limestone and in the Neocomian-Jurassic Khami Group carbonates. Recently, large gas deposits have been discovered in the Permo-Triassic carbonates assigned to the Deh Ram Group. Geochemical studies were carried out five potential source beds of Eocene-Palaeocene (Pabdeh Formation). Coniacian-Neocomian (Garau Formation) and Silurian (Ghakum Formation) age. The results showed that the organic matter in these formations is almost exclusively of marine algal origin, and that the Kazhdumi is the major source of the hydrocarbons in the Asmari and Sarvak reservoirs. The origin of the hydrocarbons in the Khami and Deh Ram reservoirs is at present speculative.     

华蓥溪口剖面中二叠统栖霞组沉积相分析

在大量前人研究的基础上,通过野外实测,华蓥溪口剖面中二叠统栖霞组分为两段,总厚度115.11 m。该剖面岩石以石灰岩为主,含少量白云岩和硅岩。石灰岩进一步分为生屑微晶灰岩、泥晶灰岩、微晶生屑灰岩以及泥晶生屑灰岩。结合野外剖面、显微分析和区域沉积背景等资料的综合分析,认为栖霞组一段下部沉积环境为深缓坡的上带,栖霞组一段上部沉积环境为浅缓坡的上带,栖霞组一段顶部为局限台地亚相的泻湖微相,栖霞组二段沉积环境为开阔台地亚相的生屑滩微相和台内洼地微相。     

塔里木盆地早、中寒武世古地理与沉积演化

基于二维地震剖面精细解释,结合最新钻井地质资料分析,在构造控沉积的指导思想下,对塔里木盆地早、中寒武世岩相古地理及沉积演化进行研究。塔里木盆地早寒武世构造古地理整体呈现“中间高、南北低”的隆-坳格局,巴楚隆起-塔中隆起东部一带发育近东西向展布的同沉积古隆起,往北和往西南方向由隆起向坳陷逐渐过渡。早寒武世玉尔吐斯组沉积期塔里木盆地为以深水陆棚为主的缓坡沉积,由中央古隆起向南北两侧依次发育潮坪相、斜坡相和深水盆地相;早寒武世肖尔布拉克组沉积期塔里木盆地为具有一定台地性质的碳酸盐岩缓坡沉积,由中央古隆起向南北两侧依次发育内缓坡、中缓坡、外缓坡和盆地相,外缓坡在地震资料上可见典型前积反射特征,反映为远端变陡的缓坡。研究证实了塔里木盆地早寒武世中央古陆的存在,并初步厘定了早寒武世玉尔吐斯组和肖尔布拉克组沉积期古陆及相应的沉积相带展布。通过构造-沉积演化分析,首次明确了塔里木盆地早寒武世并没有形成真正意义上的碳酸盐台地,而是受整体上南北分异的隆-坳构造格局控制的缓坡沉积模式,至中寒武世中西部大台地才逐渐形成。     

Sedimentological and petrophysical characteristics of Raha Formation at Wadi Tubia,Northern Gulf of Aqaba,Sinai, Egypt

The main aim of this study is to shed some light on the microfacies association, geochemistry and petrophysical properties of the rock types: dolomite, sandstone, shale and limestone forming the Raha Formation.The microfacies association includes: ferroan dolomite, sublithic arenite, ferruginous sublithic arenite, dolomitic lithic arenite, sandy bioclastic wackstone, bioclastic packstone, calcareous ferruginous lithic arenite and fossiliferous bioclastic grainstone.The depositional environments of these sediments are interpreted as restricted, shelf lagoon and open circulation.The dominant diagenetic processes presented in the studied samples are cementation, compaction, replacement, dissolution and dolomitization in sandstone rocks, while neomorphism, micritization, cementation, dolomitization, compaction and dissolution are present in carbonate facies. Geochemically, the ferruginous sublithic arenite microfacies are characterized by phosphate bands and high chemical weathering. Calcareous ferruginous lithic arenite microfacies are characterized by high concentration of iron oxides and fossiliferous bioclastic grainstone is characterized by high concentration of barium, as indicated from the chemical index of alteration (CIA).Statistical analysis of the measured petrophysical data shows that, the dolomitic lithic arenite and fossiliferous bioclastic grainstone microfacies have a good storage capacity in the Raha Formation of Wadi Tubia, Northern Gulf of Aqaba, Sinai, Egypt.     

鄂尔多斯盆地西部奥陶纪岩相古地理特征

综合野外露头、钻井岩心、薄片观察以及测井等相关资料分析,在鄂尔多斯盆地西部奥陶系共识别出 6 种沉积相类型及 3 类 10 种微相序。 受贺兰坳拉槽持续性扩张的影响,鄂尔多斯盆地西部奥陶纪不同时期的岩相古地理展布具有明显的差异性,早奥陶世发育缓坡型台地沉积,至中奥陶世演化为台地- 斜坡-盆地沉积模式。 桌子山组内缓坡和克里摩里组台地边缘相沉积岩性以泥亮晶粉砂屑灰岩、生屑灰岩、鲕粒灰岩为主,为优质储层的发育提供了重要的物质基础。乌拉力克组-拉什仲组发育深水盆地相泥岩、含灰泥岩,是烃源岩发育的有利相带。     

RESERVOIR CHARACTERISTICS OF THE ALBIAN UPPER QAMCHUQA FORMATION CARBONATES,TAQ TAQ OILFIELD,KURDISTAN, IRAQ

The Albian Upper Qamchuqa Formation in NE Iraq is part of an extensive dolomitized carbonate platform developed during the Barremian – Albian over the passive continental margin of NE Arabia. Recent drilling at the Taq Taq oilfield in Kurdistan has renewed interest in this formation as a reservoir unit. In this paper, the reservoir and petrophysical characteristics of the Upper Qamchuqa Formation at Taq Taq are described using data from wireline logs, cores and thin‐sections from four wells. At Taq Taq oilfield, the Qamchuqa Formation can be divided on the basis of lithology into two units: an upper Dolomite Unit and a lower Limestone Unit. The Dolomite Unit is 140–190 m thick and is dominated by massive dolomites and dolomitic limestones. High porosity values (up to 26%, estimated from well logs) were recorded in intervals comprising fine to medium crystalline planar‐e to planar‐s type dolomite which were frequently oil stained. Pore types include microvugs, moulds, fractures, stylolites and intercrystalline porosity. The Limestone Unit is 72–55 m thick and is composed mainly of bioturbated bioclastic limestones with minor dolomites. A wide range of carbonate facies are present and are dominated by foraminiferal wacke‐packstones and rudist packstones. Wireline log data was used to characterize the reservoir quality of the Qamchuqa Formation at Taq Taq. Four porosity units were recognized. The upper porosity units has the best reservoir quality with average porosities of 15 %, compared to the second unit (7.5%), the third unit (7%) and the fourth unit (4%). Different cut‐off values were estimated, and related petrophysical parameters were evaluated and were used to subdivide the reservoir succession into three reservoir units. The uppermost of these units was found to have the best reservoir characteristics and represents the upper part of the Dolomite Unit. It has a thickness of 31–43.5 m with 25–41 m of net pay and 82% oil saturation. Flow in this unit is dual, dominated by fracture flow superimposed on matrix flow.