Sedimentary facies and diagenetic features of the Early Cretaceous Fahliyan Formation in the Zagros Fold-Thrust Belt,Iran

The Early Cretaceous Fahliyan Formation (middle part of the Khami Group), is one of the important reservoir rocks in the Zagros Fold-Thrust Belt. The Zagros Fold-Thrust Belt is located on the boundary between the Arabian and Eurasian lithospheric plates and formed from collision between Eurasia and advancing Arabia during the Cenozoic. In this study area, the Fahliyan Formation with a thickness of 325 m, consists of carbonate rocks (limestone and dolomite). This formation overlies the Late Jurassic Surmeh Formation unconformably and underlies the Early Cretaceous Gadvan Formation conformably at Gadvan Anticline. The formation was investigated by a detailed petrographic analysis to clarify the depositional facies, sedimentary environments and diagenetic features in the Gadvan Anticline. Petrographic studies led to recognition of the 12 microfacies that were deposited in four facies belts: tidal flat, lagoon, and shoal in inner ramp and shallow open marine in mid-ramp environments. The absence of turbidite deposits, reefal facies, and gradual facies changes show that the Fahliyan Formation was deposited on a carbonate ramp. Calcareous algae and benthic foraminifera are abundant in the shallow marine carbonates of the Fahliyan Formation. The diagenetic settings favored productioning a variety of features which include cements from early to late marine cements, micritization, dolomitization, compaction features, dissolution fabric, and pores. The diagenetic sequence can be roughly divided into three stages: (1) eugenic stage: marine diagenetic environment, (2) mesogenic stage: burial environment, and (3) telogenic stage: meteoric diagenetic environment.     

Diagenetic and Depositional Impacts on the Reservoir Quality of the Upper Jurassic Arab Formation in the Balal Oilfield,Offshore Iran

The Kimmeridgian‐Tithonian aged Arab Formation, as the main reservoir of the Jurassic succession in the Balal oilfield, located in the offshore region of the Iranian sector of the Persian Gulf, is investigated in this study. The formation is composed of dolomites and limestones with anhydrite interbeds. Based on detailed petrographic studies, six microfacies are recognized, which are classified in four sub‐environments including supratidal, intertidal, lagoonal and the high energy shoal of a homoclinal carbonate ramp. The main diagenetic features of the studied succession include dolomitization, anhydritization, cementation, micritization, fracturing and compaction. Based on stable isotope data, dolomitization of the upper Arab carbonates is related to sabkha settings (i.e. evaporative type). In terms of sequence stratigraphy, three shallowing‐upward sequences are recognized, based on core and wireline log data from four wells of the studied field. Considering depositional and diagenetic effects on the reservoir quality, the studied facies are classified into eight reservoir rock types (RRT) with distinct reservoir qualities. Dolomitization has played a major role in reservoir quality enhancement, whereas anhydritization, carbonate cementation, and compaction have damaged the pore throat network. Distribution of the recognized RRTs in time and space are discussed within the context of a sequence stratigraphic framework.     

Impacts of Depositional Facies and Diagenesis on Reservoir Quality: A Case Study from the Rudist-bearing Sarvak Formation, Abadan Plain, SW Iran

An integrated geological-petrophysical analysis of the rudist-bearing sequence of the Cretaceous Sarvak Formation is given one giant oilfield, and provides an improved understanding of this main reservoir in the Abadan Plain, in the Zagros Basin, SW Iran. The main objective of this study is to evaluate reservoir potential of the Sarvak Formation, and then to utilize the calibrated well log signature to correlate reservoir potential in un-cored wells. Eight main facies are recognized and categori...     

伊拉克M油田白垩系Mishrif组沉积特征及控储机理

为明确伊拉克M油田白垩系Mishrif组碳酸盐岩储层成因,基于岩芯观察、铸体薄片、物性分析及测井资料,通过沉积微相分析确定研究区沉积环境,系统分析不同沉积相储层特征。结果表明:M油田Mishrif组为带障壁的缓坡环境,包括潟湖边缘坪、潟湖、台内滩、滩后、潮道、浅滩、滩前及开阔浅海。中、高渗储层主要发育于浅滩和滩前等高能沉积环境,储集层以粒间孔和粒间溶孔为主,发育大孔喉,生屑滩储集层和滩前储集层物性分布区间较大。潟湖边缘坪、潟湖、台内滩及滩后等低能沉积环境以低渗和特低渗储集层为主,孔隙度跨度大,孔隙类型主要为基质微孔、颗粒微孔、铸模孔和粒间孔,以微喉和中喉为主,喉道分选较好。综合分析认为:沉积相通过控制沉积物的结构组分控制了岩石的成岩演化。高能沉积型储集层以溶蚀作用和胶结作用为主,储集层物性是胶结物对孔隙和喉道充填封堵程度的函数;低能沉积型储层是生物多样性和差异成岩作用的结果,选择性溶蚀作用、与生物扰动相伴生的白云化作用、泥晶化作用、胶结作用、非选择性溶蚀作用和混合白云化作用形成的复杂孔隙控制了储集层物性。     

Facies mosaic and diagenetic patterns of the early Devonian (Late Pragian–Early Emsian) microbialite‐dominated carbonate sequences,Qasr Member,Jauf Formation,Saudi Arabia

The Al‐Jawf area of northern Saudi Arabia provides spectacular outcrops of Early Devonian carbonate bioherms in the Wadi Murayr and Dumat Al‐Jandal areas. These carbonate bioherms belong to the Qasr Member of the Late Pragian–Early Emsian Jauf Formation (~405 Ma) and are surrounded by a bioclastic carbonate succession. The Qasr Member is the first major carbonate unit of the Palaeozoic succession in Saudi Arabia that mainly consists of microbialite carbonates and metazoan reefs exhibiting distinct mound features. These bioherm complexes and their associated carbonate facies are pervasively dolomitized. Stratigraphic, petrographic and geochemical analyses were conducted to determine the facies distribution and interpret their depositional and diagenetic processes. A total of 11 facies are identified from a range of depositional environments within a carbonate platform system, ranging from tidal flats, lagoon, shoal, patch reefs to reef front. The main diagenetic processes are carbonate cementation and dolomitization. Dolomitization occurred as both fabric preserved (mostly in grain‐dominated facies) and fabric destructive (mud‐dominated facies). The microbialites and coralline sponges facies show poor reservoir with visual porosity less than 5%, but this succession may have a potential to serve as a good source for the underlying and overlying facies. Ooid and peloidal grainstone facies show fair to good visual porosity that locally exceeds 10% with intergranular porosity as the dominant type. However, in the most studied samples, vuggy and intraparticle porosities are observed as the dominant type. Copyright © 2015 John Wiley & Sons, Ltd.     

鄂尔多斯盆地南缘中寒武统张夏组鲕粒滩相储层特征及主控因素

鄂尔多斯盆地寒武系深层具有良好的勘探潜力,中寒武统张夏组为寒武系勘探的重要目的层系。通过野外剖面详测和岩心、薄片观察及实验分析,对张夏组储层的特征、成因及主控因素进行了分析和研究,并预测了有利储层发育区。研究表明:①张夏组主要发育台缘鲕粒白云岩和台内鲕粒白云岩2类储层。②台缘带鲕粒滩累计厚度集中在50~300 m之间,鲕粒粒径平均为1.25 mm,鲕粒白云岩储集空间以溶蚀孔洞、粒间溶孔和晶间(溶)孔为主,平均测井孔隙度和渗透率分别为2.0%和0.038×10^-3μm²。③台内鲕粒滩厚度在50~120 m之间,鲕粒粒径平均为0.85 mm,鲕粒白云岩储集空间以溶蚀孔洞、粒间溶孔为主,平均测井孔隙度和渗透率分别为3.3%和2.787×10^-3μm²。④张夏组储层受鲕粒滩相、白云石化以及三级/四级层序界面控制,台缘规模有利储层发育在四级海退层序中上部的鲕粒白云岩地层中,台内规模有利储层发育在寒武系顶部不整合面之下的鲕粒白云岩地层中。预测台缘岐山—旬邑一带和台内陇东地区为两大规模有利储层发育区。     

塔里木盆地西南坳陷昆仑山前古近系卡拉塔尔组储层沉积特征及其预测评价

塔里木盆地西南缘沿西昆仑山前古近系卡拉塔尔组沉积巨厚的碳酸盐岩与碎屑岩混层,分布范围西至喀什、东至叶城县克里阳地区,有3次大规模的海侵海退,即3个沉积微旋回;沉积储层展布的划分以同由路克、和什拉甫为界,同由路克地区为海湾泻湖区,七美干至和什拉甫为台地至台地边缘的碳酸盐岩沉积区,和什拉甫至普司格为碳酸盐岩与碎屑岩混合沉积区;成岩环境有浅海海底成岩环境、潮坪成岩环境、大气淡水成岩环境和埋藏成岩环境;因成岩白云石化作用形成的细晶白云岩伴生的晶间孔隙与因混合白云石化作用形成的粉晶砂屑白云岩、泥晶粉晶腹足云灰岩被溶蚀产生的粒内孔隙和粒间孔隙皆为较好的储层类型;评价结果显示:喀什凹陷卡拉塔尔组碎屑岩储层大部分具有超低孔超低渗的特点,碳酸盐岩储层属于超低孔特低渗储层,叶城凹陷卡拉塔尔组为特低孔特低渗储层。     

Facies, depositional environment and diagenetic processes of the early Mid-Miocene Jeribe Formation, Central and Southern Iraq

The Jeribe Formation (Early Middle Miocene) in the central and southern Iraq consists mainly of shallow marine carbonates. Many microfacies have been identified: mudstone, wackestone, packstone, and grainstone with seven submicrofacies. Four major depositional cycles were determined. Microfacies developments and their distribution are controlled by cyclicity and relative sea level fluctuations. The Allochems in the Jeribe Limestone Formation are dominated by bioclasts. Peloids, ooids, and intraclasts are less abundant. The fossils are represented by benthonic forams and very rare planktonic forams. Calcite and dolomite are the predominant mineral components of Jeribe Formation. The carbonates of Jeribe have been affected by a variety of diagenetic processes such as compaction, dissolution, cementation, neomorphism, dolomitization, anhydritization, and silicification. By using the lithofacies association concepts, the depositional model of the Jeribe Formation environment was built. The Jeribe was deposited in open to restricted platforms which indicated lagoonal environment with warm and restricted-open circulation and the lower part (in well Hemrin-2) was deposited in foreslope environment.     

川中地区中二叠统栖霞组滩控岩溶型白云岩储层特征及主控因素

四川盆地中部地区栖霞组的白云岩是该区主要储层,储层成因的主流观点是热液白云岩化。目前勘探实践发现,优质储渗体形成与早期相控岩溶作用有关。通过取芯及测录井资料进行了详细分析,研究结果表明,该类白云岩储层主要位于栖霞组中上部颗粒滩发育的地层中,按其宏微观产出状态可分为溶斑状云岩、溶洞充填云岩、针孔状基质云岩和致密基质云岩。储集岩物性以溶洞充填云岩最佳,储层类型属裂缝—孔洞型储层。进一步分析显示:研究区栖霞组滩相地层沉积后随即经历了一定时间的整体抬升暴露,期间接受早成岩期岩溶作用,形成了具相控特征的岩溶系统,早期淡水岩溶作用是优质孔洞型储层形成的关键。在中二叠沉积期后不久的东吴运动高峰期,热液流体上涌将岩溶系统及其部分围岩交代为白云岩。由于岩溶系统内部保留了较多的残余自由空间,经热液白云岩化调整后形成的白云石更为自形,且保存了较多的晶间孔隙。而相比之下,岩溶系统基岩已在早期埋藏中趋于致密,云化后形成的云岩物性较差。仅有部分颗粒岩仍然保留了一定的原始孔隙,云化后针孔较为发育。栖霞组白云岩储层具有相控性,规模性和继承性三大发育特点。提出优质储层分布受控于岩溶系统,为区内栖霞组白云岩储层成因提供了新的思路,对该区储层分布预测及进一步的勘探部署也具一定指导意义。     

伊拉克哈勒法耶油田Mishrif组滩相储层特征及其成因分析

伊拉克哈勒法耶油田Mishrif组滩相储层发育,是研究区内最主要的产油层位。利用岩心、薄片、测井资料对Mishrif组沉积相进行了研究,结果表明该组发育局限台地、开阔台地、台内洼地和台地边缘4种沉积相,滩相储层主要发育在开阔台地和台地边缘相带。并综合利用铸体薄片、物性实验数据及压汞曲线等资料对滩相储层特征和成因进行了分析。滩相储层岩石类型多样,发育生屑灰岩、生屑泥粒/粒泥灰岩、砂屑灰岩等多种岩石类型,岩石颗粒较粗。孔隙类型多样,主要以铸模孔、粒间孔、溶孔和体腔孔为主,其中以粒间孔和铸模孔发育最为广泛。各类滩相储层孔隙度较高,渗透率差异明显,平均渗透率为(2.35~139.17)×10~(-3)μm~2。整体孔隙结构较好,排驱压力较低,大喉道较为发育。滩相储层发育受沉积环境控制和成岩作用改造程度影响,有利的沉积条件是滩相储层原生孔隙发育的基础,同生期溶蚀作用的改造形成大量次生孔隙,从而提高了储层的储集性能。     

吉林新立油田下白垩统泉头组成岩储集相及储集空间演化

吉林新立油田位于吉林省松原市郭县以北新庙乡境内。综合应用25口取心井薄片、镜质体反射率、铸体、电镜、X衍射等岩心分析资料，研究了泉头组的成岩作用、成岩演化序列、成岩阶段划分及储集空间类型。根据成岩作用及特有的储集空间组合，划分了4种成岩储集相类型，即A相(不稳定组分强溶解次生孔隙成岩储集相)、B相(中等压实弱-中胶结混合孔隙成岩储集相)、C相(强压实中等胶结残余粒间孔成岩储集相)、D相(碳酸盐强胶结微孔隙成岩储集相)；并阐述了各类成岩储集相的特征，其中A相储集物性最好，B相次之，C相较差，D相最差。最后探讨了泉头组储集空间演化，在中成岩阶段A期形成了大量次生溶蚀孔隙，为首次在该区泉头组特低渗储层中预测相对有利的成岩储集相带提供了研究思路和科学依据，也为改善特低渗油田的开发效果奠定了坚实的地质基础。     

川东北二叠系长兴组碳酸盐岩深埋成岩过程及其意义

上二叠统长兴组储层是川东北地区主力产层之一,储层岩性主要为结晶白云岩、残余生屑/砂屑白云岩、生物礁白云岩和亮晶生屑灰岩,储集空间以晶间孔、晶间溶孔为主,生物体腔孔、残余粒间孔次之,溶洞和裂缝少量发育。长兴组优质储层主要分布于台地边缘生物礁、台地边缘滩等沉积相带,该相带发育大量原生孔隙,易遭受大气淡水溶蚀改造。原生孔隙的发育为白云岩化流体与岩石相互作用提供空间,早期孔隙演变为晶间孔。白云岩抗压实能力较强,有利于高孔隙白云岩的保存。早三叠世快速深埋使长兴组迅速进入中深埋藏,深埋阶段,裂缝少量发育,部分被方解石充填,对储层贡献有限。晚三叠世油气充注隔绝了岩石与地层水的接触,抑制了孔隙内白云石的溶蚀和沉淀,储层先存孔隙得到较好的保存。快速深埋使孔隙迅速被埋藏封闭,深埋阶段水-岩反应处于近封闭的平衡状态,溶蚀-沉淀现象有限,深埋藏环境主要是储层孔隙保存和调整的场所,孔隙空间的位置可能重新分配。     

Research on Diageneses of Cambrian Shoal Facies Carbonate Rocks in the Xiadong Area, Hubei Province

With continuous outcrops, developed shoal fades rocks, complete types of diagenesis and changeable diagenetic environments, Cambrian strata are well developed in the Xiadong area, Yichang, Hubei Province. Under the combined influence of numerous diageneses, secondary pores can be formed, which result in better reservoir properties of the rock strata.The Cambrian rocks in this area consist of mainly carbonate rocks and secondarily detrital rocks. The carbonate rocks are dominated by grainstones including wormkalk, calcirudite-calcarenite, oolitic limestone and oncolitic limestone. Graded bedding and cross bedding are well developed in the strata, which indicates that the formation environment is of a high-energy shoal facies.In this area, there has developed a sequence of stable Cambrian platform carbonate deposition. The evolution trend is as follows: open sea shelf facies→intertidal low-energy restricted sea facies→Hntertidal high-energy shoal facies→coastal shoal facies→evaporite tidal-flat facies     

RETRACTED ARTICLE: Depositional environments and porosity distribution in regressive limestone reservoirs of the Mishrif Formation,Southern Iraq

Eight subsurface sections and a large number of thin sections of the Mishrif Limestone were studied to unravel the depositional facies and environments. The allochems in the Mishrif Formation are dominated by bioclasts, whereas peloids, ooids, and intraclasts are less abundant. The sedimentary microfacies of the Mishrif Formation includes mudstone, wackestone, packstone, grainstone, floatstone, and rudstone, which have been deposited in basinal, outer shelf, slop followed by shoal reef and lagoonal environments. The formation displays various extents of dolomitization and is cemented by calcite and dolomite. The formation has gradational contact with the underlying Rumaila Formation but is unconformably overlain by the Khasib Formation. The unconformity is recognized because the skeletal grains are dominated by Chaophyta (algae), which denotes the change of environment from fully marine to lacustrine environment. Thus, the vertical bioclast analysis indicates that the Mishrif Formation is characterized by two regressive cycles, which control the distribution of reservoir quality as well as the patterns of calcite and dolomite cement distribution. Mishrif Formation gradationally overlies Rumaila Formation. This was indicated by the presence of the green parts of Chaophyta (algae) as main skeletal grains at the uppermost part of well Zb-47, which refer to lacustrine or fresh water environment. Petrographical study shows that the fossils, peloids, oolitis, and intraclasts represent the main allochem. Calcite and dolomite (as diagenetic products) are the predominant mineral components of Mishrif Formation. Fossils were studied as an environmental age and facial boundaries indicators, which are located in a chart using personal computer programs depending on their distributions on the first appearance of species. Fifteen principal sedimentary microfacies have been identified in the Mishrif Formation, which includes lime mudstone, mudstone–wackestone, wackestone, wackestone–packstone, packstone, packstone–grainstone, grainstone–floatstone, packstone–floatstone, packstone–rudstone, and wackestone–floatstone. Markov chain analysis has been used to study the transitional pattern of different microfacies types vertically in each well and laterally in all wells as a composite section. The vertical analysis indicates that the Mishrif Formation characterized by two regressive cycles, the main one started with basinal or outer shelf environment, slop environment followed by shoal or reefal environment, and ended with a lagoonal environment. The lateral analysis shows the same regressive cycle, and by using the lithofacies association concepts, we built the depositional model of the Mishrif Formation environment.     

开江-梁平地区上二叠统长兴组储层岩石学特征

以露头剖面测量、单井岩芯观察和室内薄片鉴定为依据,结合不同结构和成因类型白云岩(或白云石)的n(Mg)/n(Ca)比值,有序度和C、O、Sr同位素特征,对开江-梁平地区长兴组碳酸盐岩储层成岩作用与孔隙发育和演化规律进行了综合研究,确定研究区对储层破坏最大的成岩作用是胶结、压实-压溶、新生变形和次生矿物的充填等作用,而对储层贡献最大的建设性成岩作用主要为埋藏白云岩化、重结晶、溶蚀和破裂等作用,有效地改善了储层的孔渗性,形成以粒间溶孔、粒内溶孔、铸模孔、晶间溶孔、超大溶孔、溶洞和溶裂缝等多种次生孔隙类型组合的礁、滩相储层基本特征。在再造成岩序列和恢复孔隙演化历史的基础上,对储层发育与孔隙演化的关系可得出如下几点结论:①有利的礁、滩相带决定了储层发育的位置和空间展布规律;②礁、滩复合体的多期次埋藏白云岩化是形成储层的基础;③破裂作用和溶蚀作用是改造储层和提高储层质量的关键。     

四川资阳地区灯影组滩相沉积及储集性研究

一般认为,高能沉积体是储层形成的有利相带之一,但对于碳酸盐岩来说,高能沉积相带仅是储层发育的基本条件之一,后期的成岩改造可能更为明显,它可将原生孔隙发育的高能沉积体转变为致密岩体。因此,碳酸盐岩储层的预测研究应将沉积相与成岩作用研究相结合。本文根据区内灯影组钻井岩芯的宏观、微观特征,结合物性资料,研究了滩相类型、特征、所经历的主要成岩类型及对储集性的影响,认为浅色的内碎屑滩、绵层状藻砂屑滩和鲕粒滩是有利于储层形成与演化的沉积相带,它们多分布于以资3、7井、资4井和资5井为中心的区块内,向其周边井区,这些有利滩相沉积体变薄、储集性变差。     

Porosity distribution in cyclic dolomites of the Lower Qiulitag Group (Upper Cambrian) in northwestern Tarim Basin,China

Increasing interests in hydrocarbon resources at depths have drawn greater attentions to the deeply-buried carbonate reservoirs in the Tarim Basin in China. In this study, the cyclic dolomite rocks of Upper Cambrian Lower Qiulitag Group from four outcrop sections in northwestern Tarim Basin were selected to investigate and evaluate the petrophysical properties in relation to depositional facies and cyclicity. The Lower Qiulitag Group includes ten lithofacies, which were deposited in intermediate to shallow subtidal, restricted shallow subtidal, intertidal, and supratidal environments on a carbonate ramp system. These lithofacies are vertically stacked into repeated shallowing-upward, meter-scale cycles which are further grouped into six third-order depositional sequences (Sq1 to Sq6). There are variable types of pore spaces in the Lower Qiulitag Group dolomite rocks, including interparticle, intraparticle, and fenestral pores of primary origin, inter crystal, and vuggy pores of late diagenetic modification. The porosity in the dolomites is generally facies-selective as that the microbially-originated thrombolites and stromatolites generally yield a relatively high porosity. In contrast, the high-energy ooidal grainstones generally have very low porosity. In this case, the microbialite-based peritidal cycles and peritidal cycle-dominated highstand (or regressive) successions have relatively high volumes of pore spaces, although highly fluctuating (or vertical inhomogeneous). Accordingly, the grainstone-based subtidal cycles and subtidal cycle-dominated transgressive successions generally yield extremely low porosity. This scenario indicates that porosity development and preservation in the thick dolomite successions are primarily controlled by depositional facies which were influenced by sea-level fluctuations of different orders and later diagenetic overprinting.     

川西北地区下二叠统栖霞组白云岩分布与成因探讨

四川盆地川西北地区下二叠统栖霞组主要以灰—灰黑色灰岩及生物碎屑灰岩、白云岩为主,沉积相以深和浅缓坡相为主,局部发育浅水生屑滩体。该区内栖霞组白云岩集中发育于栖霞中上部。通过野外、钻井岩心及镜下观察,结合阴极发光、X衍射、碳氧同位素等分析,认为川西北地区下二叠统栖霞组白云岩主要经历了准同生期的混合水白云化过程,而后由于东吴运动的影响,叠加了成岩作用后期的混合水白云化过程和埋藏白云化作用。