PALAEO‐EXPOSURE SURFACES IN THE APTIAN DARIYAN FORMATION,OFFSHORE SW IRAN: GEOCHEMISTRY AND RESERVOIR IMPLICATIONS

Palaeo‐exposure surfaces within and at the top of the carbonate‐dominated Aptian Dariyan Formation have been poorly studied in the Iranian sector of the Persian Gulf. This paper presents an integrated sedimentological and geochemical study of the Dariyan Formation at four oil and gas fields located in the western, central and eastern parts of the Gulf. Facies stacking patterns in general indicate shallowing‐upwards trends toward the exposure surfaces, which are interpreted to correspond to unconformities. The Dariyan Formation in the study area is divided into upper and lower carbonate units by a deep‐water, high‐gamma shale‐marl interval. At fields in the western and central Gulf, significant diagenetic changes were recorded in the top of the upper carbonate unit, including meteoric dissolution and cementation, brecciation and paleosol formation. An exposure surface is also present at the top of the lower carbonate unit in all the fields in the study area, and is associated with meteoric dissolution and cementation of grain‐dominated facies. Age calibration of studied intervals was carried out using microfossil assemblages including benthic and planktonic foraminifera. Negative excursions of both δ¹⁸O (?10‰ VPDB) and δ¹³C (?0.66‰ VPDB) were recorded in weathered intervals located below the unconformity surfaces. A sequence stratigraphic framework for the Dariyan Formation was established by integrating sedimentological, palaeontological and geochemical data. The δ¹³C curve for the formation in the Iranian sector of the Persian Gulf can be correlated with the reference curve for the northern Neotethys and used as a basis for regional stratigraphic correlation. Where the top‐Aptian unconformity is present, it has resulted in an enhancement of the reservoir characteristics of the underlying carbonate succession. Accordingly, the best reservoir zones in the Dariyan Formation occur in the upper parts of the lower and upper carbonate units which are bounded above by significant palaeo‐exposure surfaces.     

港东开发区东一段湖相三角洲沉积规律研究与储集层精细刻画

大港油田港东开发区东一段属于湖相三角洲沉积环境,砂体发育受沉积相控制,空间分布复杂、横向对比预测难,常规资料与地震识别方法难以满足储集层刻画需求。依托新采集的“两宽一高”高精度地震资料,以层序地层学、地震沉积学研究思路为指导,以区域沉积演化规律作为宏观约束,通过建立层序地层格架,应用测井相、地震相识别技术,开展区域沉积相平面特征描述,结合储集层发育特征、含油气性显示结果,多元耦合明确三角洲沉积优势储集相带。应用地震分频和地层切片技术,开展小尺度砂体追踪及属性切片分析,提高三角洲前缘分流河道等薄储集层识别精度,盘活了区块东营组的储量潜力,同时形成一套针对三角洲沉积的优势储集层识别与薄砂体追踪技术系列。     

砂岩成岩相地震预测——以松辽盆地齐家凹陷青山口组为例

以松辽盆地齐家凹陷青山口组为例,探讨应用地震沉积学和实验室岩心分析手段,采用常规三维地震资料预测砂岩成岩相的可行性。用地震资料划分地层和成岩相单元、建立岩心成岩相与地震属性的联系以及寻找有效的地震成岩相成图方法,是地震成岩相研究的3个关键步骤。井-震高分辨率层序分析和地层切片的制作可提供储集层尺度(20 m)成岩相单元的合理载体。砂岩成岩相分析和成岩序列的建立可揭示影响储集层质量的最重要因素——成岩作用。通过储集层参数和岩石物性分析可进一步了解成岩作用和波阻抗的关系并筛选适用地震检测的主要成岩作用。地震岩性体(如90°相位地震体)转换提供了成岩相的振幅(波阻抗)检测信号,用地震岩性体制作的地层切片可用于识别沉积相。在沉积相图上分析沉积相、波阻抗和成岩相的关系,可最终形成地震成岩相图。对青山口组泥质胶结砂岩和方解石胶结砂岩的实际分析表明,虽然砂岩成岩相地震检测尚处于起步阶段,但目前用常规三维地震资料预测砂岩成岩相是可行的。     

平面岩相解释法在河流相储层研究中的应用

与常规的剖面解释和传统的平面划相不同,平面岩相解释法是利用三维地震资料横向密集连续性好的特点,将地震属性信息与储层层序和地质过程相结合,运用地层切片技术、多属性融合成像技术、平面岩相自动追踪解释技术,结合地震资料、测井资料和钻井资料相,最终在平面上再现地下地层的岩相图像。在松辽盆地南部QD工区河流相储层研究中的应用结果表明,该方法具有解释精度高、速度快、微相解释和构造细节清楚等特点,在岩性油气藏勘探开发中具有广阔的应用前景。     

ARE SHOAL RESERVOIRS DISCRETE BODIES? A COQUINA SHOAL OUTCROP ANALOGUE FROM THE MID TRIASSIC UPPER MUSCHELKALK,SW GERMANY

Carbonate ramp reservoirs may show a much higher degree of complexity than the schematic and often layer‐cake type depositional models which are widely used in exploration and reservoir characterisation, especially in three dimensions. This complexity was investigated in an outcrop study of the Ladinian (Middle Triassic) Quaderkalk Formation (Upper Muschelkalk) from SW Germany. The formation was deposited on an epicontinental, gently inclined carbonate ramp in the regressive part of a third‐order depositional sequence and represents a sub‐seismic‐scale coquina‐dominated shoal reservoir analogue. In the study area, coquina carbonates make up a complex system of four stratigraphically separated shoal complexes. The present paper investigates the 1‐D to 3‐D facies distribution, reservoir architecture and sequence stratigraphic evolution of the largest shoal complex of the Quaderkalk Formation, the Oberer Hauptquader. The object of this outcrop analogue study was to improve the understanding of internal reservoir heterogeneities (such as connectivity and continuity) in similar carbonate shoal complexes in the subsurface. To that end, detailed analyses of 71 quarry outcrop and core samples were carried out, together with the study of more than 400 thin sections, the 2‐D analysis of three quarry wall panels and regional‐scale 2‐D correlations, and facies mapping. This investigation documents significant sedimentological heterogeneities at different scales within the studied shoal reservoir analogue. Instead of a continuous facies belt, a number of separate potential reservoirs form a shoal complex “mosaic”. Shoal development is controlled by sequence stratigraphic architecture, mainly by cycles which were responsible for shoal expansion during times of regression (forming potential reservoir‐volume) and shoal drowning during times of transgression (forming seals and potential stratigraphic traps). Within the individual shoal complexes, thickness and lithofacies types show gradational lateral changes. Correspondingly, lithofacies associations within the studied shoal analogue are not defined by sharp boundaries. Thus the present “shoals” do not in fact represent discrete “bodies”, as often depicted in reservoir models and as commonly used in reservoir simulation. In addition, shoal‐internal sedimentological heterogeneities (potential flow baffles in the subsurface) are strongly influenced by a combination of small‐scale cyclicity and event‐type deposition. This study therefore demonstrates the need for sedimentological studies of reservoir heterogeneities at various scales in order to decrease uncertainties and risks in exploration and production.     

SEISMIC STRATIGRAPHIC ANALYSIS AND STRUCTURAL DEVELOPMENT OF AN INTERPRETED UPPER CAMBRIAN TO MIDDLE ORDOVICIAN SEQUENCE IN THE NW BLANTYRE SUB‐BASIN,DARLING BASIN (WESTERN NEW SOUTH WALES,AUSTRALIA)

In this paper, a new interpretation is presented of the seismic stratigraphy of units equivalent to the upper Cambrian to middle Ordovician Scropes Range Formation in the NW Blantyre Sub‐basin in the central part of the Palaeozoic Darling Basin, western New South Wales. This succession was previously unrecognised, attributed to the lower part of the overlying Winduck Interval, or regarded as basement. The structural development of the study area is described, and may contribute to a better understanding of the regional stratigraphic evolution of the Lower Palaeozoic section in this part of the Darling Basin This study presents interpretations of a regional two‐dimensional seismic survey which investigated the upper Cambrian to middle Ordovician Scropes Range Formation in the NW Blantyre Sub‐basin. A shallow marine Cambro‐Ordovician succession is well established in the Bancannia Trough in the western Darling Basin but this interval appears to have been ignored in the central Darling Basin where a deeper‐marine environment and suitable kitchen conditions may have provided greater petroleum potential. Data from two shallow wells in the 831 km² study area were available to support the seismic investigations. Seismic sequences were defined by a combination of horizon mapping, the configuration of internal reflections, termination patterns and thicknesses. Six seismic reflection horizons were defined and used to identify five seismic sequences named Units A, B, C, D and E. These features were identified in three seismic lines and demonstrate the continuity of the Scropes Range Formation throughout the NW Blantyre Sub‐basin. All seismic sequence boundaries are based on fair to good continuous markers, with strong amplitudes throughout the study area. The acoustic basement beneath the Scropes Range Formation was metamorphosed in the Delamerian Orogeny (around 500 Ma). Acoustic facies recognized in the three seismic lines can be correlated with sedimentary facies observed in outcrops in the Scropes Range, 130 km west of the study area, and are comparable to acoustic facies in modern fluvial sandstones associated with local braided delta deposits. Complex geological features suggest potential structural and stratigraphic hydrocarbon traps. This study emphasizes the reservoir potential of the Scropes Range Formation in the central Darling Basin where extensive exploration efforts are currently occurring. The detailed interpretation of the seismic stratigraphy may lead to the definition of new exploration plays in this under‐explored region.     

薄砂体—窄河道地震识别技术研究及其在吐哈盆地SN地区应用

吐哈盆地SN地区三间房组油层段储层沉积相为辫状河三角洲前缘水下分流河道沉积,含油砂体单层厚度薄,横向变化快,且分布在厚砂岩附近5~10m的砂体在地震剖面上响应不明显,造成地震预测困难。因此,通过在层序地层格架控制下,应用正演模型分析结果,对目的层段地震资料进行针对性的目标处理,在处理后的地震剖面上,应用从岩层到层段、由点到面的研究思路,确定运用地层切片、属性分析、地震相分析、频谱分析以及岩性反演技术,对该区薄层砂体进行了预测。预测结果与钻井对比,该方法可预测的单砂体符合程度高。通过该项研究,形成适合该区薄砂体—窄河道地震预测的方法系列,提高该区储层和油气预测精度,指导老油区勘探开发。     

FACIES HETEROGENEITIES IN A RAMP CARBONATE RESERVOIR ANALOGUE: A NEW HIGH‐RESOLUTION APPROACH FOR 3D FACIES MODELLING

In contrast to the conventional view that facies distribution patterns on carbonate ramps are relatively simple, outcrop analogue studies point to a high degree of internal facies complexity. Depending on the diagenetic overprint, this complex pattern may result in reservoir compartmentalization due to the presence of interflow baffles. The often subseismic scale heterogeneities may not be included in conventional reservoir modelling. In order to evaluate how facies heterogeneities in shoal reservoirs can be modelled realistically, this paper presents a facies modelling workflow which includes a new approach to the design of training images for multiple‐point statistics (MPS). The workflow was developed in the course of a reservoir outcrop analogue study of a Ladinian (Middle Triassic) coquinadominated shoal complex in SW Germany which was deposited on an epicontinental, gently inclined carbonate ramp. The data set was based on an intensive field study and includes 3D facies and sequence stratigraphic analyses of the largest shoal complex in the Quaderkalk Formation (Upper Muschelkalk). This several metre thick shoal complex represents a subseismic scale, bioclast‐rich reservoir analogue and has a very heterogeneous facies pattern. Integrating 1D facies logs and sequence stratigraphic trends from tens of outcrop sections and cores, two nested 3D geocellular facies models were produced: (i) a large‐scale (30 × 30 km) model based on truncated Gaussian simulation (TGS); this formed the basis for (ii) a smaller‐scale (10 × 10 km), more detailed model based on multiple point statistics. In addition, a new approach for training image design was developed to honour small‐scale sequence stratigraphic trends and lateral facies patterns observed in modern analogues. Compared to facies patterns in modern analogues, the large‐scale model presents geologically‐feasible facies distribution patterns and geometries, and in addition shows a vertical facies distribution which is similar to the observed sequence stratigraphic architecture of the outcrop data‐set used. Due to the new training image design, the final small‐scale model has a distribution pattern of facies heterogeneities which looks similar to modern facies distributions in the offshore UAE and thus represents a valuable method of producing realistic reservoir facies models. The modelling workflow and the new approach for training image design presented will help to reduce uncertainties in the understanding and modelling of subsurface reservoirs by using a systematic combination of outcrop data and modern analogues, with the consistent application of sequence stratigraphic principles. In addition, this study emphasises the importance of careful training image design, derived from modern analogues, which can be used as realistic inputs in order to optimize multiple point simulations, and which may be applied to producing bioclastic reservoirs such as those located on the Arabian Plate or offshore Brazil.     

准噶尔盆地西北缘车排7井区八道湾组顶部有利储层分布预测

针对准噶尔盆地西北缘车排7井区八道湾组顶部有利储层分布及油水关系认识不清,导致油藏扩边评价难以取得进展的问题,综合运用录井、测井及地震等资料,通过沉积相划分、连井砂体对比、地震属性分析、地震波阻抗反演及地层切片等技术手段,对研究区内沉积相和有利储层分布进行精细研究。研究结果表明:八道湾组顶部主要发育扇三角洲前缘沉积亚相,水下分流河道是最有利储层;八道湾组顶部主要发育由西北向东南方向展布的3个相对独立的扇三角洲水下分流河道砂体,其中2个为含油气有利储层;车5027井和车369井所在砂体为2个不连通的独立砂体;车5027井和车排7井所在砂体可以分别向东南和东南、东北方向扩边评价。该研究成果对研究区八道湾组进一步勘探开发具有重要的指导意义。     

松辽盆地北部徐家围子断陷丰乐地区深层营城组有利火山岩储集体预测

火山岩储集体分布受火山机构、岩性、岩相等控制,复杂多变,准确预测和刻画十分困难。火山口-近火山口微相沉积体是最有利的火山岩储集体,该类相储集体通常具有高频杂乱无序、反射断续无规律、相变快、穹窿状或丘状外形等地震响应特征,地震解释手段易受地震资料品质的影响而无法精确描述储集体特征。针对此问题,基于三维成像分析技术,提出了一套有利火山岩储集体地震识别刻画的技术流程。首先采用构造方位约束滤波技术对叠后振幅数据去噪处理,然后利用包括混沌属性、方位约束不连续性属性等三维地震属性识别储集体,进而采用三维属性聚类成像、像素体检测技术及三维可视化技术对目标储集体进行三维成像分析,获取该类储集体空间分布认识。将该流程应用到松辽盆地北部徐家围子断陷丰乐地区,对营城组火山岩储层进行识别预测。结果表明,营城组火山岩有利储集体得到了良好成像,储集体平面分布趋势和三维影像都很清晰,为储层物性预测提供了宏观依据。     

埕岛油田东斜坡层序约束下的储层预测技术

由于埕岛油田东部斜坡带东营组储层埋藏深、相变快、且常常与围岩速度差异小,依据目前的三维地震资料分辨该区东营组单个砂层及进行层位标定难度较大,从而无法了解储层的空间展布规律。本文通过钻井、测井和地震资料的综合分析及东营组长期旋回内部界面的识别,将东营组长期旋回自上而下划分为层序S1、S2、S3、S4;根据东营组储层的各种沉积相具有独特的地震波组响应特征,通过扩大砂体研究对象,从层序约束的角度,以砂体所在沉积韵律或旋回为目标,充分利用地震资料进行储层预测,形成了一套有效的储层预测技术。主要流程包括层序划分与解释、宏观地震相解释、时窗界定、在无井控制下的聚类分析储层预测、在有井约束下的储层平面预测。通过宏观地震相解释、综合瞬时相位切片、BP神经网络储层预测图,进行该区块砂体追踪和解释,取得了良好的效果。     

塔里木盆地塔中卡1三维工区碳酸盐岩储层预测技术与应用

塔里木盆地塔中地区卡1三维工区前期勘探成果表明,奥陶系鹰山组碳酸盐岩储层以"裂缝、溶孔"型为主,但近期重新处理的地震数据中发现了一些"串珠、短轴状"强振幅地震反射异常体。针对这一现象,在新处理地震数据体的基础上,采用地震数字正演模拟、不连续性检测、古地貌恢复和地震多属性分析等技术,重新开展了卡1三维工区奥陶系鹰山组碳酸盐岩储层预测研究。结果表明,平面上呈"折线"状分布的强振幅异常体是火成岩的响应,而平面上呈散点状、剖面上呈"串珠"状的强振幅反射是较大尺度溶洞型碳酸盐岩储层的响应。这一成果已得到近期完钻井W20的证实,为本区下一步勘探部署开拓了新的方向。     

地震沉积学 ——地震解释的新思路及沉积研究的新工具

地震沉积学是继地震地层学和层序地层学之后出现的一门新兴学科。地震沉积学利用地震振幅信息和属性分析技术研究沉积岩石学、古地貌学、沉积结构以及沉积演化历史等。地震沉积学充分利用了三维地震数据的横向分辨力，其关键技术是层序地层框架的建立和地层切片体（等时地质切片）的生成。结合地震地层学、层序地层学和地震沉积学的发展历程对地震沉积学的现状和趋势进行了探讨，认为90°相位转换和分频解释仅仅是地震沉积学研究的技术手段，而不是其关键技术；对于地震同相轴的穿时性问题，也仅存在于3级或4级层中，并且这种穿时性与“沉积物体分配空间”和“相异作用”有关。     

储层精细描述的地震处理、解释一体化思路探讨——以准噶尔盆地腹部莫西庄地区为例

在高分辨率层序地层解释的基础上,利用AVO(振幅随炮检距变化)处理过的三维速度场进行高分辨率AVO属性反演、谱分解、属性提取、波形分析等手段获得的储层信息与储层地震相和沉积相解释相结合,剖面-平面-立体处理、解释同步,赋予地震属性信息以正确的地质意义,达到对储层分布精细预测的目的。运用这一方法,对准噶尔盆地腹部莫西庄八道湾组一段进行了研究,结果显示,利用AVO属性反演和波形分析等处理手段得到的储层平面图与用高分辩率层序地层原理研究出的储层平面图有很好的叠合关系。     

塔里木盆地东部古城—肖塘地区寒武纪—奥陶纪台地类型、演化过程及有利储集相带

基于岩心、岩石薄片和地震资料分析,对塔里木盆地东部（塔东）古城—肖塘台地—盆地过渡区寒武纪—奥陶纪碳酸盐岩台地类型、演化过程及其油气勘探潜力进行了系统研究。从盆地构造演化、岩性特征、地震相特征等方面详细分析了不同时期碳酸盐台地边缘的类型及特征,建立了4种碳酸盐岩台地边缘类型及沉积模式。寒武系纽芬兰统—黔东统肖尔布拉克组—吾松格尔组沉积期为匀斜碳酸盐岩缓坡,有利储集相带为古隆起围斜部位的浅缓坡微生物丘滩;寒武系苗岭统为镶边碳酸盐岩台地,发育加积型丘滩体,有利储集相带为古地貌高点的丘滩体核部及丘坪滩体;寒武系芙蓉统发育弱镶边碳酸盐岩台地,丘滩脊和前积滩体为有利储集相带;下奥陶统蓬莱坝组—鹰山组三段沉积期为远端变陡的碳酸盐岩缓坡,浅缓坡上部的白云石化滩为有利储集相带;中奥陶统鹰山组二段—一间房组沉积期为弱镶边开阔台地,有利储集相带为古地貌高点的泥粒灰岩滩及礁滩相;晚奥陶世演化为淹没台地。受构造运动和海平面变化影响,塔东古城—肖塘台地—盆地过渡区寒武纪—奥陶纪碳酸盐岩台地经历了"缓坡—镶边台地—缓坡—弱镶边开阔台地"的演化过程。苗岭统—芙蓉统镶边台缘带丘滩、蓬莱坝组—鹰山组三段远端变陡缓坡白云石化滩、鹰山组二段—一间房组弱镶边开阔台地颗粒灰岩滩是近期增储上产的3类现实勘探领域,纽芬兰统—黔东统肖尔布拉克组—吾松格尔组匀斜缓坡微生物丘滩、苗岭统—芙蓉统斜坡重力流是2类潜在的风险勘探领域。     

四川盆地寒武系沧浪铺组沉积演化特征

近年来,四川盆地在川中地区安岳气田、高磨气田的灯影组、龙王庙组取得了重大油气勘探发现,但受到构造条件复杂、前期基础研究欠缺以及钻井、地质、地震资料不足等因素的制约,盆地内震旦系—下古生界的其他领域和层系的勘探一直未取得较大进展。基于最新二维、三维地震资料精细解释,结合野外露头和钻井地质资料分析,在层序地层学、构造地质学、沉积岩石学等理论的指导下,对四川盆地寒武系沧浪铺组地层沉积特征和沉积演化开展研究。结果表明：①沧浪铺组顶底界在地震剖面上均表现为波谷反射,内部存在一至两条连续或断续的波峰,代表了沧一段碳酸盐岩顶界或沧二段内部岩性界面;②德阳—安岳裂陷槽和川中古隆起共同控制了沧浪铺组的沉积,地层沉积厚度在裂陷槽内向东、西两侧减薄,且在川中古隆起区由隆起核心向边缘部位增厚;③盆地范围内沧浪铺组沉积相可划分为滨岸相、三角洲相、陆棚相3类,同时可细分出各类相对应的多种亚相和微相,确定沧浪铺组的沉积模式为滨岸—浅海陆棚模式;④沧浪铺组具有明显的沉积分异,沧一段沉积时期裂陷槽西部以滨岸—碎屑陆棚相沉积为主,东部以清水陆棚碳酸盐岩沉积为主,沧二段沉积时期裂陷槽范围进一步缩小,盆地内大范围的清水浅水陆棚沉积和碎屑浅水陆棚沉积逐渐向混积浅水陆棚沉积演化。     

川东下三叠统飞仙关组沉积相研究

四川盆地东部下三叠统飞仙关组鲕滩主要发育在碳酸盐岩台缘带上，而台缘带与海槽密切相关，找到了海槽就意味着找到了鲕滩。以往的沉积相研究主要基于钻井资料，对于海槽和台缘相带边界的划分主要依据井间沉积相的变化趋势作人为的估计，这种划分缺少必要的依据，而地震技术在一定程度上可以弥补这种不足。为了在地震资料上找出准确的海槽位置，利用钻井分析结果，采用层拉平技术消除构造影响，恢复了本区的古地貌特征；运用地震地层学理论，横向上划分了沉积相，纵向上分析了沉积演化史；采用一种新的沉积相分析方法，以钻井层序、地震层段和地震反演为基础，在反演剖面上进行地层格架解释、沉积环境解释、以及岩性和储层解释，更清晰地描绘出本区的沉积相变化特征。最终结果显示：地震划分的海槽范围比钻井划分的范围更窄，边界更准确；在无沉积间断的前提下，下三叠统飞仙关组沉积早期是继承上二叠统沉积方式的欠补偿沉积，而非前人描述的快速充填沉积。     

利用地震沉积学定量刻画辫状河三角洲砂体——以委内瑞拉MPE-3区块为例

以委内瑞拉MPE-3区块Oficina组辫状河三角洲地层为例,将直井、水平井与三维地震资料相结合,通过层序界面地震识别、90°相位转换及地层切片处理,建立了研究区等时地层格架,在三级层序内识别出6个四级层序;利用横向高分辨率的水平井资料标定地层切片的地震沉积学解释方法,识别了心滩砂体内部由冲沟形成的细粒夹层,有效提高了地层切片的解释精度;利用井震联合刻画结果总结了心滩等沉积体的定量特征,建立了心滩长宽、心滩宽度、辫状河道宽度、冲沟宽度间的定量关系。该研究成果为油藏精细开发提供了地质依据。     

鄂尔多斯盆地南部上古生界致密碎屑岩储层预测——以镇泾地区为例

岩石物理特征难以有效区分储层与非储层,黄土塬叠后地震资料品质较差,储层预测成为鄂尔多斯盆地南部上古生界久攻不克的技术瓶颈,也成为制约该区勘探推进的原因之一。区带评价认为镇泾区块东北部是有利勘探区带,二叠系山西组二段、下石盒子组一段是主要勘探目的层。镇泾3D波形聚类地震相分析结果与镇泾地区物源、砂体展布特征一致,表明地震资料可以用来开展储层预测研究。结合沉积相展布特征的一系列地震正演模拟发现,山二段内与盒一段大套砂体有一定距离、具有一定厚度的砂体能够形成可识别的地震反射,这种地层岩性纵向上的空间组合与区域叠加型及厚层单一型砂体沉积模式吻合,正是周边已发现气藏的典型储盖组合类型。根据正演模拟结果优选的波峰数地震属性储层预测证实,山二段叠加型砂体及厚层单一型砂体呈SW-NE向宽幅条带状展布,进而开展的地震剖面特征同相轴的拾取解释与构造成图,直接圈定了山二段叠加型与厚层单一型砂体岩性圈闭的分布范围与埋深,为该区勘探部署提供了钻探目标。      

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.