MICROPOROSITY IN THE UPPER JURASSIC ARAB‐D CARBONATE RESERVOIR,CENTRAL SAUDI ARABIA: AN OUTCROP ANALOGUE STUDY

This study investigates microporosity in an outcrop analogue of the Upper Jurassic (Kimmeridgian) Arab‐D carbonate reservoir in central Saudi Arabia, integrating outcrop facies analysis, petrographic and SEM data and statistical analyses. At the study location in Wadi Nisah, the outcropping succession includes the uppermost Jubaila Formation and the entire Arab‐D Member of the Arab Formation which together comprise the Arab‐D reservoir interval. The succession is composed of eight lithofacies which can be grouped into three lithofacies associations based on their depositional environments. The stromatoporoid lithofacies association includes dolomitic mudstones, dolomitic wackestones and stromatoporoid wackestones and packstones; the skeletal bank lithofacies association includes burrowed fossiliferous wackestones and peloidal fossiliferous grainstones; and the tidal flat lithofacies association comprises laminated mudstones, wave‐rippled sandy grainstones, and supra‐ and intertidal muds with rip‐up clasts. The lithofacies were classified into mud‐dominated, grain‐dominated and dolostone textural groups. Microporosity and associated permeability in the analysed samples (n = 125 for porosity and n = 61 for permeability) range from 0.11% to 4.8 % and 0.36 to 4.35 mD, respectively. Three types of microporosity were observed: (i) between macro‐ and micro‐sparry calcite crystals; (ii) between micrites of varying morphologies; and (iii) within macro‐sized dolomite crystals. Microporosity distribution was controlled by sparry calcite cement, micrite crystal size, sorting and shape, and the presence of dolomite crystals. Statistical analyses of microporosity and associated permeability show non‐normal distributions for both variables. Coefficients of variation indicated high variability for porosity and permeability, which may be attributed to the high degree of heterogeneity in the pore system. In general there was a poor correlation between microporosity and permeability, but the correlation improved when visualized for individual textural groups.     

DEPOSITIONAL FACIES,PORE TYPES AND ELASTIC PROPERTIES OF DEEP‐WATER GRAVITY FLOW CARBONATES

Quantitative petrographic analyses of deep‐water resedimented carbonates from the Gargano Peninsula (SE Italy) were integrated with petrophysical laboratory measurements (porosity, P‐and S‐wave velocities) to assess the impact of sedimentary fabrics and pore space architecture on velocity‐porosity transforms. Samples of Upper Cretaceous carbonate came from the Monte Sant'Angelo, Nevarra and Caramanica Formations and can be classified into four depositional facies associations: F1, lithoclastic breccias; F2, bioclastic packtones to grainstones; F3, interbedded grainstones‐packstones and wackestones; and F4, (hemi‐) pelagic mudstones. Five pore type classes were distinguished: I and II, dominant intercrystalline microporosity; IIIa, dominant intergranular macroporosity; IIIb, dominant mouldic macroporosity; and IIIc, mixed intergranular and mouldic macroporosity. Pore type was found to strongly control velocity‐porosity transforms, unlike depositional facies associations. The equivalent pore aspect ratio (EPAR), derived from differential effective medium models, is proposed to identify pore types from elastic properties. The EPAR originates from the bulk modulus or shear modulus of the samples (K‐ and μ‐EPAR, respectively). Regardless of porosity values and depositional facies, microporous samples (type I) and samples with dominant intergranular porosity (type IIIa) are characterized by low values of K‐ and μ‐EPAR (<0.22) and by K‐EPAR > μ‐EPAR By contrast, samples with dominant mouldic porosity (type IIIb) display high values of K‐ and μ‐EPAR (>0.25 and 0.4 respectively) and K‐EPAR < μ‐EPAR. High permeability limestones with dominant intergranular porosity cannot be discriminated from low permeability microporous carbonates. The petrophysical classes derived from elastic properties are shown to be distinct from reservoir property‐driven rock types. In the present case, a seismic‐based poro‐elastic model does not match the reservoir property model. Hence, a sedimentary facies model for the studied carbonates cannot accurately represent the petrophysical properties, which are determined by pores types and pore network architecture.     

PETROPHYSICAL AND SEDIMENTOLOGICAL CHARACTERIZATION OF THE APTIAN SHU'AIBA (LOWER QAMCHUQA) FORMATION RESERVOIR AT THE KHABBAZ OILFIELD,NORTHERN IRAQ

The Aptian Shu'aiba Formation is a shallow‐marine carbonate which occurs in the subsurface of central and southern Iraq and in other parts of the Arabian Plate including Oman, the UAE and Saudi Arabia. An equivalent unit is exposed at outcrop in northern Iraq where it is known as the lower part of the Qamchuqa Formation. For this study, core, cuttings and well log data from six wells in the Khabbaz oilfield (20 km SW of Kirkuk) were used to investigate the reservoir properties of the Shu'aiba Formation. The formation is 180–195 m thick at Khabbaz field and the reservoir section can be divided into three lithological units: an upper unit (A, 8–15 m thick) consisting of partly dolomitized marly limestones; a middle unit (B, 52–56 m thick) which is composed of vuggy dolomitic limestone and dolostone; and a lower unit (C, >110 m thick) which consists of shale‐rich and dolomitic limestones. Limestone microfacies include shelfal bioclastic wackestones, Orbitolina bioclastic packstones, Orbitolina grainstones, and pelagic bioclastic wackestones. Dolomite fabrics show little variation and are dominated by coarse crystalline planar‐e types. Most matrix porosity is associated with intercrystalline pores in medium‐crystalline (100–50 µm) planar‐e dolostone. Fracturing of variable intensity has resulted in a flow type which is dominated by fracture flow superimposed on matrix flow.     

SEQUENCE STRATIGRAPHY OF THE UPPER PERMIAN ZECHSTEIN MAIN DOLOMITE CARBONATES IN WESTERN POLAND: A NEW APPROACH

The Upper Permian Main Dolomite in the Zechstein 2 cyclothem in the Gorzów Block (part of the Zechstein Basin in western Poland) contains both hydrocarbon source and reservoir rocks, and is sealed both above and below by evaporites. In this paper we propose a new sequence stratigraphic model for the development of potential reservoir rocks in toe‐of‐slope locations. Data came from detailed analyses of 35 cores from wells in and at the margins of the Wielkopolska platform, a palaeogeographic element composed of Main Dolomite carbonates. In basinal areas, the Main Dolomite carbonates begin with a transgressive interval overlain by laminated dolomudstones interpreted as transgressive facies. The TST begins in the upper part of the underlying Alg anhydrites. The dolostones are underlain by a ravinement surface on the platform, and by a maximum regressive surface in toe‐of‐slope and basinal locations. In well Gorzów Wielkopolski‐2, a hardground marks the maximum flooding surface. Overlying the TST deposits are thick intervals of intraclast‐oolitic grainstones and floatstones which are interpreted as highstand deposits and indicate “highstand shedding”. Toe‐of‐slope facies are composed of alternating laminated dolomudstones, intraclast‐oolitic grainstones, packstones and floatstones which make up submarine fans (prisms) interpreted as falling stage facies which are capped by dolomudstones. A subaerial unconformity was recognized on the platform, and a slope onlap surface on the slope and toe‐of‐slope, respectively. In platform areas, the Main Dolomite begins with thin intervals containing microbial complexes deposited during the early HST, which pass into thick oolitic grainstones (HST to late HST) and terminate as microbial‐to‐oolitic wackestone and mudstone complexes interpreted as falling stage facies. Thrombolitic bioherms constitute a reference horizon which can be correlated between wells in the study area. The beginning of the LST occurs in the upper part of the Main Dolomite. The boundary between lowstand and transgressive deposits was identified in the lower part of the Basal Anhydrite and is marked by sabkha and salina facies, respectively, where an erosional ravinement surface and maximum regressive surface were identified. Thus, the upper part of the underlying Upper Anhydrite and the upper part of the Main Dolomite deposits form a second depositional sequence in the study area. The depositional environment of the Main Dolomite platform carbonates was variable, and was influenced by the topography of the pre‐existing evaporitic platform. The newly proposed sequence stratigraphic model emphasises the role of forced regressive submarine fans as potential hydrocarbon accumulations and traps in the toe‐of‐slope area.     

EFFECT OF MICRITE CONTENT ON CALCITE CEMENTATION IN AN UPPER JURASSIC CARBONATE RESERVOIR,EASTERN SAUDI ARABIA

Cementation is a primary factor reducing the porosity of carbonate rocks. It is a challenge to accurately model cementation for reservoir quality prediction because cementation is often a syndepositional process. In addition, cementation requires fluid flow to transport chemical species for precipitation within the pore spaces in a sediment. The development of fully‐coupled depositional‐hydrogeochemical models for cementation prediction is desirable, but the parameters which control the extent of cementation need to be identified and evaluated. This study uses petrographic data from 583 carbonate samples from 15 wells in an Upper Jurassic (Kimmeridgian) reservoir at a giant oilfield in eastern Saudi Arabia to investigate the controlling effects of micrite content on cementation in carbonate rocks. The results indicate that the amount of cement decreases with increasing micrite content in the carbonate rocks analysed. In addition, a modified Houseknecht method has been developed to assess the relative fractions of porosity reduction in carbonate sediments due to compaction and cementation. The method highlights variations in depositional porosity for different rock textures and distinguishes microporosity from interparticle porosity. In the studied samples, the total porosity loss due to compaction and cementation is generally less than 45%, and samples lose more porosity due to compaction than cementation. The relative importance of compaction and cementation in reducing porosity is different for different rock textures: wackestones and mudstones lose porosity mostly as a result of compaction, while grainstones, mud‐lean packstones and packstones lose porosity due to both compaction and cementation.     

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.     

川东北地区飞仙关组储层中的埋藏溶蚀作用

根据沉积特征、孔隙类型及孔隙充填物的地球化学特征认识到川东北地区飞仙关组储层中有2期埋藏溶蚀作用：第一期埋藏溶蚀作用与上二叠统海槽相烃源岩成熟产生的有机酸有关；第二期埋藏溶蚀作用与热化学硫酸盐还原反应产生的H₂S有关。两期埋藏溶蚀作用主要发生在台地边缘鲕粒滩相中，台地内泻湖及点滩相中溶蚀作用则相对较弱。分析认为：台地边缘成为天然气勘探的有利地区，台地内为欠有利地区。     

伊拉克米桑油田群Mishrif组MB21段碳酸盐岩储层特征及成因

以岩心、录井、测井、地震及相关生产资料为基础,对伊拉克米桑(Missan)油田群Mishrif组MB₂1段储层特征及其成因进行分析。结果表明,Mishrif组MB₂1段储层沉积环境属于碳酸盐岩开阔台地,发育有台内滩、台内礁和开阔潮下亚相。岩石类型主要有生物礁灰岩、生屑颗粒灰岩、生屑似球粒颗粒灰岩及生屑似球粒泥粒灰岩。储集空间类型主要为原生粒间孔、次生粒间溶孔、铸模孔、基质微孔及少量小型溶蚀孔洞和微裂缝。受沉积作用和成岩作用控制,储层横向分布相对稳定,但纵向物性变化较大、层内非均质性严重,是制约原油采出程度的关键因素。      

AN INTRODUCTION TO THE PRECAMBRIAN PETROLEUM SYSTEM IN THE SANKURU‐MBUJI‐MAYI‐LOMAMI‐LOVOY BASIN,SOUTH‐CENTRAL DEMOCRATIC REPUBLIC OF CONGO

This study presents a preliminary assessment of the petroleum potential of the Meso‐Neoproterozoic Mbuji‐Mayi Supergroup in the Sankuru‐Mbuji‐Mayi‐Lomami‐Lovoy Basin in the southern‐central Democratic Republic of Congo. This basin is one of the least explored in Central Africa and is a valuable resource for the evaluation of the petroleum system in the greater Congo Basin area. Highly altered carbonates (potential reservoir rocks) and black shales (potential source rocks) are present in the Mbuji‐Mayi Supergroup, which can be divided into the BI and overlying BII groups (Stenian and Tonian, respectively). For this study, samples of the BIe to BIIe subgroups from five boreholes and two outcrops were evaluated with petrographic, petrophysical and geochemical analyses. Carbonates in the BIe to BIIe subgroups with reservoir potential include oolitic packstones and grainstones, stromatolitic packstones and boundstones, various dolostones, and brecciated and zoned limestones. Thin section studies showed that porosity in samples of these carbonates is mainly vuggy and mouldic with well‐developed fractures, and secondary porosity is up to 12%. Black shales in the BIIc subgroup have TOC contents of 0.5–1%, and the organic matter is interpreted to have been derived from precursor Type I / II kerogen. The thermal maturity of asphaltite in carbonate samples is indicated by Raman spectroscopy‐derived palaeo‐temperatures which range from ～150 to ～260°C, which is typical of low‐grade metamorphism. Raman reflectance (R_mcR_o%) values on asphaltite samples were between 1.0 and 2.7%, indicating mature organic matter corresponding to the oil and wet gas windows. Source rock maturation and primary oil migration are interpreted to have occurred during Lufilian deformation (650–530 Ma). The solid asphaltite present in fractures in the dolostones of the BIIc subgroup may represent biodegraded light oil from an as‐yet unknown source which probably migrated during the Cambrian‐Ordovician (～540–480 Ma). This migration event may have been related to the effects of the peak phase of Lufilian deformation in the Katanga Basin to the SE. This study is intended to provide a starting‐point for more detailed evaluations of potential hydrocarbon systems in the Sankuru‐Mbuji‐Mayi‐Lomami‐Lovoy Basin and the adjacent greater Congo Basin area.     

STRONTIUM ISOTOPE STRATIGRAPHY OF THE ASMARI FORMATION (OLIGOCENE - LOWER MIOCENE), SW IRAN

The Asmari Formation has been studied in the subsurface at the Bibi Hakimeh, Marun and Ahwaz oilfields and in an outcrop section from the Khaviz anticline. It consists of approximately 400 m of cyclic platform limestones and dolostones with subordinate intervals of sandstone and shale. The method of Sr‐isotope stratigraphy is well suited for dating these strata because of the rapid rate of change of marine ⁸⁷Sr/⁸⁶Sr during Asmari deposition (roughly 32‐18 Ma) and the common presence of well‐preserved macrofossils. Profiles of age against depth in the four areas show a decrease from higher stratigraphic accumulation rates in the lower Asmari to lower rates in the middle to upper part of the formation. There is also a trend towards less open‐marine depositional conditions and increasing early dolomitization and anhydrite abundance above the lower part of the formation. These changes reflect the dynamics of platform progradation across the areas studied, from early deposition along relatively high accommodation margin to slope settings to later conditions of lower accommodation on the shelf top. Ages of sequence boundaries are estimated from the age‐depth profiles at each locality, providing a framework for stratigraphic correlation. Asmari deposition began in early Rupelian time (34‐33 Ma) in the Bibi Hakimeh area, when the studied areas to the NW were accumulating basinal marl facies. Progradation of the platform across the Marun and Ahwaz areas took place in mid‐Chattian time (27‐26 Ma) and somewhat later (26‐25 Ma) in the more basinward Khaviz area. Depositional sequences have durations of 1‐3 Ma, whereas component cycles represent average time intervals of 100‐300 Ky. Sr analyses of most dolomite, anhydrite and celestite samples plot close to or below the macrofossil age‐depth trend for each locality, indicating formation from waters preserving seawater ⁸⁷Sr/⁸⁶Sr approximately contemporaneous with or slightly younger than the time of sediment deposition. Local deviations from this trend are interpreted as indicating episodes of seepage‐reflux and also a contribution of Sr from non‐marine sources during formation of the Gachsaran cap rock anhydrite.     

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.     

�Ĵ������ϵ��Ӱ������ŵ��������ģʽ

??For predicting the distribution of favorable reservoir facies belts of the super-large ancient Anyue carbonate gas field in the Sichuan Basin, through an analysis of structure and lithofacies palaogeography, the lithofacies palaeogeography and sedimentary model of the Sinian Dengying Fm was reconstructed based on the field outcrop, drilling and seismic data. As a result, achievements are made in four aspects. First, the basin and its periphery resided in an extensional tectonic setting in the Sinian. Intense extension led to the formation of the Deyang–Anyue intra-platform rift. Finally, the Sichuan Basin was divided into the palaeo-geographic pattern of "two uplifts and four sags". The "two uplifts" evolved into the platform, and the "four sags" evolved into the slope-basin environment. Second, in the depositional stage of the Deng 2 Member, some favorable reservoir belts developed, such as bioherm-shoal at the continental margin, bioherm- shoal at the rift margin, and bioherm-shoal in the platform. The bioherm-shoal at rift margin developed along both sides of the Deyang– Anyue rift, in a U-shape, with a width of about 5–40 km and a length of about 500 km. It connected with the platform margin belt at the continental margin to the west in the Shifang area, and to the north near Guangyuan area. Third, in the depositional stage of the Deng 4 Member, when the lithofacies palaeogeographic features in the Deng 2 Member remained, the platform margin belt at the rift margin evolved into two parts in the east and the west as a result of the continuous southward extensional faulting of the Deyang–Anyue rift until it finally crossed the basin from north to south. The eastern platform margin belt was located in the Guangyuan–Yanting–Anyue–Luzhou area, showing NS distribution with a length of about 450 km and a width of about 4–50 km. The western platform margin belt mainly developed in the Dujiangyan–Chengdu–Weiyuan–Yibin–Mabian area, showing an eastward arc distribution with a length of about 300 km and a width of 4–30 km. And fourth, the sedimentary model of rimmed platform with double platform margins in the Dengying Fm was established, providing a guidance for predicting the distribution of favorable reservoir facies belts.     

宝岛23-1构造生物礁地质评价

宝岛 2 3- 1构造生物礁 (115 8礁 )位于珠江口盆地神狐隆起南缘一个四面封闭的块状碳酸盐台地上 ,礁体顶面 T5 2 层 (珠江口二段下部顶面 )的圈闭面积为 80 km2 。综合分析地震、测井、岩石化学、古生物、岩心等资料 ,证明神狐隆起南缘存在碳酸盐岩台地边缘礁。据生物礁的发育特征和产状 ,宝岛 2 3- 1- 1井钻在礁滩相部位 ,储集性较好的礁核位于宝岛 2 3- 1构造的南高点。南高点的含油面积为 2 2 km2 ,圈闭资源量为 5 32 0万 m3,因此是值得钻探的目标。     

塔中地区中上奥陶统有利油气富集的地震相特征及分布

中上奥陶统是塔中地区最主要的油气勘探目的层之一。通过大量二维、三维地震资料解释分析，笔者发现塔中地区中上奥陶统广泛分布着一种特殊的地震相。该相沉积厚度相对较大，在地震剖面上反映为丘状隆起，内部反射杂乱，呈乱岗状反射，多沿主要构造线延伸。结合岩矿分析，笔者认为这种地震相就是碳酸盐岩台地上在不同期次发育的礁、滩相，它们主要分布于中上奥陶统碳酸盐岩台地向海一例的边缘或在台地内部古地貌上相对凸起的构造部位。勘探、开发实践证明，它们是油气富集的有利相体。为此，我们勾绘出了其地震相平面展布图，由图可见，它们主要分布于塔中I号断裂构造带、TZl0井构造带及塔中南缘构造带上。该项研究成果对塔中地区油气勘探具有重要指导意义。     

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.     

琼东南盆地崖北凹陷崖城组煤系烃源岩分布及其意义

崖北凹陷位于南海北部大陆边缘西区琼东南盆地北部坳陷西段,是新生代凹陷,连续沉积了始新世到第四纪地层。该凹陷古近纪为裂谷期,发育始新世陆相、早渐新世崖城组海陆过渡相和晚渐新世陵水组海相3套地层。中新世到第四纪为热沉降和新构造期,均为海相地层。崖北凹陷主力烃源岩是崖城组海陆过渡相煤系和泻湖相泥岩,其中,煤层、炭质泥岩及其伴生的暗色泥岩是烃源岩的重要组成部分。已钻井揭示崖城组发育35层煤,累积厚度16.8m。煤层与炭质泥岩主要分布于崖一段和崖三段,形成于潮坪与辫状河三角洲。崖城组地震相与沉积相对应关系良好,据此建立了煤系烃源岩沉积模式,煤系主要发育在凹陷缓坡带的辫状河三角洲和潮坪环境中,其次是陡坡带的扇三角洲和潮坪,暗色泥岩主要发育在深洼漕的泻湖环境。崖北凹陷崖城组煤系和泻湖湘泥岩都是有利烃源岩,生烃潜力大,凹槽内部渐新统-中新统为有利成藏组合。      

SEQUENCE STRATIGRAPHIC ANALYSIS OF THE MID‐CRETACEOUS MISHRIF FORMATION,SOUTHERN MESOPOTAMIAN BASIN,IRAQ

The middle Cenomanian – early Turonian Mishrif Formation, a major carbonate reservoir unit in southern Iraq, was studied using cuttings and core samples and wireline logs (gamma‐ray, density and sonic) from 66 wells at 15 oilfields. Depositional facies ranging from deep marine to tidal flat were recorded. Microfacies interpretations together with wireline log interpretations show that the formation is composed of transgressive and regressive hemicycles. The regressive hemicycles are interpreted to indicate the progradation of rudist lithosomes (highstand systems tract deposits) towards distal basinal locations such as the Kumait, Luhais and Abu Amood oilfield areas. Transgressive hemicycles (transgressive systems tract deposits) represent flooding of the shallow carbonate platform and are recorded in oilfields such as Amara, Halfaya and Zubair. A sequence stratigraphic framework has been constructed for the Mishrif Formation based on correlation of the transgressive and regressive hemicycles which are separated by maximum flooding surfaces. Three third‐order sequences are identified which show lateral and vertical facies variations depending on relative sea‐level changes. Sequence boundaries are characterized by karstic, exposure and drowning features. Middle Cenomanian – Turonian eustatic sea‐level changes together with regional‐scale tectonic deformation of the Arabian Plate controlled the availability of accommodation space and therefore the depositional profile during development of each sequence. Both of these factors controlled the maximum flooding surfaces and sequence boundaries which have been identified. The sequence stratigraphic key surfaces presented in this study represent typical candidate horizons or datum surfaces for future seismic or resevoir modelling studies. Also, lateral facies variations in each transgressive‐regressive sequence and associated carbonate bodies (i.e. prograding shelf margin, forced regressive wedge) may form important stratigraphic traps in the Mesopotamian Basin.     

塔北地区上奥陶统良里塔格组台缘带分段性及石油地质意义

碳酸盐岩台缘带类型对储层形成与油气产能具有重要的控制作用。利用塔北地区大量最新的地震资料与钻井资料,通过上奥陶统良里塔格组地层厚度变化刻画台缘带平面展布,基于台缘带地层坡度的计算揭示其不同段台缘类型的差异。在此基础上,探讨台缘带分段性对储层发育的控制作用。结果表明：①良里塔格组台缘带具有明显地层加厚的特点,平面上环塔北古隆起呈条带状展布,长约240km、宽约10~20km,面积达2600km²。②基于台缘带地层坡度的变化,明确了良里塔格组台缘带沿东西方向表现为不同的类型,具有一定的分段性。西段为弱镶边型台地边缘,分布在英买力—哈拉哈塘—托普台地区,地震响应为向盆地方向减薄的楔形反射,地层坡度较大,介于1°~3°;东段为宽缓的缓坡型台地边缘,分布在塔河东部—轮古东—于奇地区,在地震剖面上由台地向盆地方向表现为一个波谷同相轴逐渐变细直至消失,地层坡度较小,介于0.2°~1°。③台缘带的分段性造成东、西段储层发育的差异性。西段储层品质好,厚度大,横向变化大;东段储层品质稍差,厚度小,平面分布广。塔北地区良里塔格组台缘带分段性对于优选有利勘探区带具有一定的指导意义。