PETROGRAPHY AND DIAGENETIC CHARACTERISTICS OF THE UPPER OLIGOCENE – LOWER MIOCENE GHAR FORMATION IN SE IRAQ

This paper investigates the petrography, sedimentology and diagenetic evolution of the upper Oligocene – lower Miocene Ghar Formation in the subsurface of SE Iraq based on data from well logs, cuttings and core samples from boreholes in the Zubair, Majnoon and nearby oilfields. Lateral facies variations permit the Ghar Formation to be divided into two principal facies, a pebbly sandstone (facies A) and carbonate (dolomite) and calcareous sandstone (facies B), each of which can be divided into subfacies. Facies A rocks, interpreted as alluvial fan deposits, pass into facies B, paralic and shallow-marine sediments in a number of fining-upward successions. This facies change from mainly clastics (facies A) to mainly carbonates (facies B) suggests that the Ghar Formation may have some potential as a stratigraphic trap in SE Iraq.
Diagenetic processes include compaction, authigenesis, dolomitization and dedolomitization. In facies A, authigenic minerals were quartz, palygorskite, haematite, Fe-rich dolomite and smectite. In facies B, the main authigenic minerals were kaolinite, illite and illite-smectite. This difference in diagenetic mineralization may indicate variable interstitial waters ranging from fresh to marine. Dolomite was the main carbonate mineral encountered and could be divided into early matrix and pervasive types. The first type was represented by smooth crystals less than 20 microns in size which were associated with illite and illite-smectite mixed layer clays. Pervasive, fabric-destructive dolomite was represented by crystals 30-300 microns in size which were found as void fillings. Dedolomitization was observed where high-Mg calcite filled cavities near the contact with the overlying Fat'ha (Lower Fars) Formation. These diagenetic processes may enhance the reservoir characteristics of the Ghar Formation.     

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.     

蜀南河包场地区须家河组气藏成藏机理及成藏模式

蜀南河包场地区上三叠统须家河组气藏为自生自储的含油气系统。须二、须四、须六段砂岩厚度较大、分布广,以低孔、低渗储层为主。根据储层毛细管压力曲线估算,天然气长距离的二次运移需要克服的毛细管阻力为2.5~3.5 MPa,相应的临界气柱高度为150~300 m。须家河组的区域构造平缓,储层天然气聚集成藏的驱动方式主要受储层砂体分布范围和储层物性控制。优质储层的毛细管阻力虽然相对较低,但是分布范围较小,多为透镜状或条带状。天然气二次运移以气体膨胀驱动为主,近距离运聚成藏。     

Thermal modeling and hydrocarbon generation of the Late Jurassic-Early Cretaceous Chia Gara Formation in Iraqi Kurdistan region,northern Zagros Fold Belt

The Late Jurassic-Early Cretaceous Chia Gara Formation is an important oil-source rock in Iraqi Kurdistan region. Chia Gara source rock is characterised by high organic matter and sulphur content with Type II_S kerogen. 1D basin models were integrated with geological information and geochemical data from Chia Gara Fm at four well locations in Kurdistan region, northern Iraq. The models of the burial/thermal history indicate that Chia Gara Fm is presently in the peak-oil generation window and some oil cracked to gas during Late Eocene to Late Miocene time. Onset of oil-generation began during the Middle Paleocene- Early Oligocene (60–30?Ma). Oil was generated during the Late Eocene to Late Miocene (48–9 Ma). The models also suggest that the oil was expelled from Chia Gara source rock during the Late Eocene to Late Miocene (37–9 Ma), with a transformation ratio more than 50%. The high transformation ratio of more than 80% in two wells suggests that the generated oil was cracked to gas during the end of Middle Miocene time and continued to present day. The basin modeling results further suggest that Chia Gara Formation acts as a prolific petroleum-source rock and significant of oil and limited of gas have been generated and expelled to any nearby prospect reservoir rocks in the Kurdistan region.     

SOURCE‐ROCK MATURITY,HYDROCARBON POTENTIAL AND OIL – SOURCE‐ROCK CORRELATION IN WELL SHORISH‐1, ERBIL PROVINCE,KURDISTAN REGION,IRAQ

The Shorish‐1 exploration well is located in Erbil Province in the Kurdistan region of Iraq, on the outskirts of Erbil City near the dividing line between the Low Folded and High Folded Zones of the Zagros foldbelt. The well penetrated rocks which are between Miocene and Late Triassic in age. The depositional environment, source potential and maturity of organic‐rich intervals within the well succession were investigated using 38 cuttings samples. All samples were analysed for bulk geochemical parameters (i.e. total organic carbon, total carbon, sulphur, Rock‐Eval). A subset of 13 samples was selected for biomarker analysis, pyrolysis – gas chromatography and isotope investigations. In addition non‐commercial oil and oil impregnations were investigated for oil‐source correlations. Source rocks occur in the Jurassic Sargelu and Naokelekan Formations and the lowermost Cretaceous Chia Gara Formation. Analytical results suggest that these source rocks were deposited in a carbonate‐rich, anoxic environment in an intrashelf basin setting with free H₂S in the water column. Oxygen‐depleted conditions were favoured by salinity stratification. The average preserved TOC contents of the 100 m thick Sargelu Formation and the 25 m thick Naokelekan Formation are 2.2% and 4.6%, respectively. The TOC content of the Chia Gara Formation decreases upwards and averages 3.2% within its lower 40 m. Very high sulphur contents suggest the presence of kerogen Type II‐S, and that all the formations have generated sulphur‐rich hydrocarbons at relatively low maturities. In contrast to the oil impregnations within Jurassic strata, the oil and the oil impregnations within Cretaceous rocks are heavily biodegraded. Oil biomarker and isotope data indicate generation from the above‐mentioned Jurassic and Cretaceous source rock formations. As a result, generation from Triassic and Paleogene rocks can be excluded or is of negligible significance. Numerical models show that hydrocarbon generation rates from the Sargelu, Naokelekan and Chia Gara Formations peaked firstly at about 55 Ma (Paleocene/Eocene) and then again at 5 Ma before present (late Miocene/Pliocene). The first peak resulted from increased Paleocene subsidence, and the second peak was related to deep late Miocene/Pliocene burial. Hydrocarbon generation ceased during Recent uplift, during which ～2000 m of the Late Neogene succession was eroded.     

SOURCE ROCK POTENTIAL OF THE UPPER JURASSIC – LOWER CRETACEOUS SUCCESSION IN THE SOUTHERN MESOPOTAMIAN BASIN,SOUTHERN IRAQ

This paper reports on the hydrocarbon potential of subsurface samples from the Upper Jurassic Lower Cretaceous succession at the Rumaila (North and South), Zubair, Subba and West Qurna oilfields in southern Iraq. A total of 37 fine‐grained core samples of the Sulaiy, Yamama, Ratawi and Zubair Formations from ten wells were analyzed. Contents of organic carbon and sulphur were measured; other analyses included Rock‐Eval pyrolysis, optical microscopy in incident light, solvent extraction and gas chromatography of non‐aromatic hydrocarbons. The results indicated that the samples from the Cretaceous succession (Yamama, Zubair and Ratawi Formations) are at moderate levels of thermal maturity, whereas samples from the Upper Jurassic – Lower Cretaceous Sulaiy Formation are at a stage of thermal maturity beyond peak oil generation. According to the results of this study, the Sulaiy Formation is an excellent highly‐mature source rock and it is probably responsible for the generation of large quantities of oil in the study area. The samples differ with respect to their organic fades and biomarker distribution, indicating that palaeo depositional conditions varied significantly.     

STRATIGRAPHIC CORRELATION AND SOURCE ROCK CHARACTERISTICS OF THE BALUTI FORMATION FROM SELECTED WELLS IN THE ZAGROS FOLD BELT,KURDISTAN REGION,NORTHERN IRAQ

The Upper Triassic Baluti Formation has been identified and mapped based on its log response in selected wells from the Zagros foldbelt in the Kurdistan Region of northern Iraq. A preliminary evaluation of the formation's source rock potential was made by Rock-Eval screening analysis in four wells along a NW-SE profile (Atrush-1, Shaikan-5B, Taq Taq-22 and Miran-2) with maturity determined from reflectance measurements in samples from well Taq Taq-22. The Baluti Formation consists of thinly interbedded shales, carbonates and anhydrite ranging in thickness from 48 m in well Atrush-1 to 118 m in well Miran-2. The Rock-Eval screening was conducted primarily on bulk cuttings samples plus selected picked cuttings. The TOC content is low to moderate (0.23 to 1.14 wt%). However, the shale content in many of the analysed bulk samples was relatively low, making assessment of the source potential problematic. The highest TOCs are recorded from the thickest analysed sections from wells Miran-2 and Taq Taq-22, where high-gamma bituminous shales are present. Rock-Eval T_max values ranging from 295 to 438°C are not consistent with estimates of pre-Zagros burial to depths of between 4600 m (Atrush-1) and 6900 m (Miran-2). The relatively low T_max values suggest that the S2 response does not reflect kerogen pyrolysis in these samples and may be due to the presence of solid bitumen, which is observed in the Baluti Formation in at least three of the study wells (Taq Taq-22, Miran-2 and Shaikan-5B). Little pyrolysable organic matter remains in the formation due to the interpreted deep pre-Zagros burial and the consequent high maturity in Taq Taq-22 (VR = 1.51%R_o) and Miran-2 (estimated VR >2%R_o), and the poor source character in Atrush-1 and Shaikan-5B. Organic petrography suggests the presence of vestiges of Types I and II kerogen in Taq Taq-22, with bitumen observed as stains in the matrix of the shales and also in the pores and fractures of interbedded dolostones. However, bitumen reflectance determinations for Taq Taq-22 indicate an equivalent vitrinite reflectance maturity of no more than 0.93%R_o, which is significantly less than that of the indigenous vitrinite, implying the solid bitumen in this well is derived primarily from migrated hydrocarbons. Further detailed analysis is required, but the results suggest that the Baluti Formation may have sourced hydrocarbons in its depocentre which is identified in this study as covering a NW-SE trending area between Bekhme and Sangaw.     

膏盐岩层对油气成藏的影响

大量的勘探实践和研究结果表明,世界上许多油气藏的形成都与膏盐岩层有关。膏盐岩层对油气成藏的影响主要表现在:1膏盐岩的形成环境有利于有机质的保存和烃类的生成;2膏盐层有利于其下部岩层保持较高的孔隙度,并形成次生孔隙;3膏盐层有利于形成异常压力;4膏盐层具有很好的封盖能力,为非常优质的盖层;5膏盐岩层可以形成油气运移通道和含油气圈闭,为油气运移和聚集创造了条件。     

江汉盆地潜江凹陷潜江组岩性油藏勘探方向及对策

潜江凹陷位于江汉盆地中部,是江汉盆地油气最为富集的富烃凹陷。潜江组勘探程度高,岩性油藏已成为主要的勘探对象与目标。该文通过对潜江组岩性油藏发育条件、分布规律及主控因素的分析,指出潜江凹陷构造斜坡带、构造反转区、断裂发育带及挠曲带是岩性油藏的有利勘探方向。发展高分辨率三维地震、建立以相控砂体预测为核心的岩性圈闭识别与评价技术,推广薄油层改造技术是深化潜江盐湖岩性油藏勘探的主要对策与方法。     

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.     

川中地区须家河组天然气成藏机制研究

以天然气形成时期研究、天然气地球化学特征分析及运移地质条件分析为基础，对川中地区上三叠统须家河组天然气成藏机制进行了系统研究。研究认为川中地区须家河组气藏为2期气相充注，在燕山末期-喜山期构造抬升过程中，储层水溶气脱溶可能性小、残余气相的卸压膨胀具有一定贡献；虽然须家河组砂岩厚度大、分布广，但储层强烈的非均质性以及较平缓的区域地层，限制了油气进行长距离运移；天然气及凝析油等地球化学特征表现为近距离运聚成藏特点。从而为川中地区须家河组构造-岩性气藏的勘探提供了新的依据。     

准噶尔盆地腹部油气生,运,聚及成藏特征分析

准噶尔盆地腹部可划分出５凸、６凹１０个二级构造带；存在３套可信的烃源岩层：下二叠统风城组、上二叠统下乌尔禾组和侏罗系煤系，确定了其空间分布和热演化史；分析了油气二次侧向运移的聚散规律，指出油气聚集的有利地区并定量计算了油气聚集量，最后，探讨了该区油气藏的形成条件和特征。     

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位于准噶尔盆地腹部的陆梁油气田是准噶尔盆地的又一个亿吨级油气田。笔者运用地球化学方法分析了陆梁油气田石炭纪—早白垩世地层水的类型、平面和纵向分布特征，将其划分为3个水文地质旋回，第一旋回为石炭系—三叠系，为深层静止开放的滞流型水力系统；第二旋回为侏罗系八道湾组—西山窑组，为中层弱开放的压实驱动型水力系统；第三旋回为侏罗系头屯河组—白垩系，为浅层强开放的重力驱动型水力系统。第一、二水文地质旋回是油气生成和初次运移的有利时期，淋滤期前的一段时间是油气二次运移和成藏的较好时期，第三水文地质旋回是油气藏破坏及次生油气藏形成的时期。     

THE USE OF WELL LOGS TO DETERMINE THE RESERVOIR CHARACTERISTICS OF MIOCENE ROCKS AT THE BAHAR NORTHEAST FIELD, GULF OF SUEZ, EGYPT

This paper is concerned with the petrophysical evaluation by means of electric logs of Miocene reservoir rocks at the Bahar Northeast field, Gulf of Suez, Egypt. The reservoir rocks are assigned to the Hammam Faraun and Sidri Members of the Middle Miocene Belayim Formation and the Lower Miocene Kareem Carbonate.
Computer-assisted log analyses were used to evaluate petrophysical parameters such as the shale proportion (V_sh), effective porosity (φ_E), water saturation (S_W), hydrocarbon saturation (S_h), flushed zone saturation (S_xo) and true resistivity (R_t).
Lithological compositions, effective porosity, and water and hydrocarbon saturations are illustrated on cross-plots of depth versus lithology and saturation. Isoparametric maps are used to illustrate the spatial variation of petrophysical parameters and to show their relationships with the geologic setting of the study area.
Based on the results obtained, the Hammam Faraun and Sidri Members of the Belayin Formation and the Kareem Carbonate appear to possess promising reservoir characteristics which should be taken into consideration during future development of the field area.     

渤海湾盆地义和庄凸起北坡成藏特征与油藏分布规律

义和庄凸起北坡是一个典型的多含油层系、多油藏类型的复式油气聚集带。受多期构造运动、沉积间断等因素影响,义和庄凸起北坡形成了复杂多样的圈闭及油藏类型。本文在储层、油源、圈闭等成藏条件分析的基础上,系统总结了义和庄凸起北坡的油藏类型、控制因素及分布规律,并根据目前的勘探现状,指出潜山、地层超覆、地层不整合等隐蔽性油藏是主要勘探方向,可为油气勘探提供科学依据。     

琼东南盆地中新统油气运聚成藏条件及成藏组合分析

对琼东南盆地中新统油气的研究程度甚低、勘探成效欠佳。虽然在中新统普遍见良好油气显示和通过电测解释发现油气层 ,但由于多种原因 ,迄今为止仅在崖 1 3 -1构造和崖 1 3 -4构造、崖1 3 -6构造的中新统三亚组和 BD1 9-2构造的中新统梅山组获得高产商业性天然气流 ,在其它区域均未有所发现。因此 ,本区中新统油气勘探潜力仍然较大。若能全面而系统地分析和总结中新统勘探经验、研究油气运聚成藏规律、加大勘探力度 ,相信不久后一定会取得进展     

苏北盆地阜三段油气成藏规律

阜三段成油气组合是苏北盆地近年增储上产的主要目的层系.该盆地阜二段中下部半咸水相优质烃源岩是阜三段成藏的主力烃源岩,有利储层则位于阜三段上砂组及阜三段下砂组的上部,与阜二段中下部烃源岩之间夹着厚层生烃能力极差的湖相泥岩,使其生储盖配套性较差,必须依靠断层沟通.受此控制,阜三段油气成藏具明显部位性,主要发育于继承性鼻状隆起带及同生断裂或大型晚期断裂附近.有利的构造格式类型、沉积体系与构造格局、圈闭体的有机配置则是形成阜三段油气藏的必备要素.阜三段油气成藏模式表明,在生储配置不利的区块,应重点围绕继承性隆起带及同生断层或大型晚期断层开展油气勘探.      

低熟油气成因理论与勘探实践

本文对低熟油气的源岩评价、成因机理、油气运移、成藏特征及油气勘探等几个方面进行简要剖析。源岩在低熟阶段仅能生成一部分烃类,因而对各个地区的低熟源岩评价标准应适当调整。低熟油的源岩主要形成于淡水湖相、沼泽相和半咸水-咸水湖相,可通过多种成因机理早期生烃。低熟油的排烃仍受源岩层与储层流体的压差驱动,因而排烃较为有利,且运移距离较短。低熟油藏常位于储层物性好、靠近油源区、继承性好的同沉积构造圈闭上。     

松辽盆地富拉尔基油田油气输导体系

通过对松辽盆地西斜坡北部300余口探井的沉积学和石油地质学分析,研究下切谷充填体对富拉尔基油田油气成藏的输导作用。富拉尔基油田的主力产层是姚家组二、三段砂岩,油气主要来源于80 km以东的齐家—古龙凹陷,油气远距离运移的输导层主要为充填下切谷的逐层超覆砂岩复合体。向盆地方向,下切谷充填体与齐家—古龙凹陷的三角洲砂体叠覆衔接;向盆地边缘方向,下切谷充填体与最大湖泛期形成的滨浅湖砂质滩坝叠覆衔接,形成三角洲—下切谷充填沉积体—滨岸砂质滩坝叠覆的富砂沉积体系。向盆地方向,三角洲砂体分叉尖灭在泥岩(成熟烃源岩)中,将有效烃源灶生成的油气输导至下切谷充填体中,沿下切谷底界面溯源逐层叠置超覆的下切谷充填沉积体远距离输导油气,上倾尖灭的滨浅湖砂质滩坝岩性圈闭捕集油气,形成富拉尔基油藏。与下切谷充填体相关的富砂沉积体系中,有效油气输导体系局限于杜412井—杜71井—杜65井—江39井—江41井及富拉尔基油田一线。单纯油气输导通道为油气浸染程度高、残余油饱和度低的产水层,北西向串珠状分布的白音诺勒、二站、阿拉新、江桥等油气田的形成与这一油气有效输导体系密切相关。图7参47     

焉耆盆地含氮化合物分布与油气运移特征

利用含氮化合物作为油气运移示踪剂,探讨了含氮化合物在焉耆盆地油气充注方向研究中的应用。盆地侏罗系油藏原油中含氮化合物存在一定的运移分馏作用,表现为自生烃中心向外,含氮化合物绝对含量由高到低,屏蔽型化合物相对富集而暴露型化合物相对减少,异构体参数[a]/[c]的相对含量则由大变小。在同一构造带中,随埋深的减小,含氮化合物同样存在着运移分馏效应。研究表明,宝浪油田油气注入方向在平面上自南向北,在纵向上自深层向浅层运移聚集。