西湖凹陷花港组储层致密化及其与油气成藏的关系

西湖凹陷花港组储层在埋深3 500m以下的深层普遍致密化且含气饱和度低。利用铸体薄片、扫描电镜、碳氧同位素、激光拉曼和流体包裹体等资料,探讨储层致密化过程及其与油气成藏的关系。结果表明,强烈压实作用是原生孔隙大量损失的主要原因,自生石英、碳酸盐及伊利石胶结是储层致密的关键因素。根据胶结矿物形成时间推算储层致密化发生在中成岩阶段A期末,对应距今约17~13 Ma的中新世中后期。由储层致密化过程与成藏期次匹配关系分析认为,花港组初次成藏期发生在中成岩阶段A期早期,储层尚未致密,但油气充注时间短且强度弱,不能大面积成藏,主成藏期发生在中成岩阶段A期末至中成岩阶段B期,成藏时间对应大致距今15~5Ma的中新世晚期,但由于储层普遍致密化,油气充注程度低。花港组深层储层"先致密后成藏"是造成含气饱和度普遍较低的重要原因。     

下二门油田储层成岩作用类型及微观孔隙结构特征

通过14口取心井普通薄片、铸体薄片的镜下观察及扫描电镜等资料的研究,认为影响下二门油田碎屑岩储层的成岩作用主要有3种:压实、胶结和溶蚀.其中,压实作用以机械压实为主,化学压实少见;胶结作用主要有碳酸盐胶结(如方解石、白云石等)、黏土矿物胶结(如高岭石、绿泥石等);溶蚀作用主要有长石颗粒和少部分岩屑溶蚀、碳酸盐胶结物溶蚀.这3种成岩作用的共同改造形成了下二门油田以粒间孔、粒内溶孔和铸模孔为主的孔隙结构特征.根据微观孔隙结构特征,结合沉积相展布特点,认为下二门油田有利储层主要分布在辫状三角洲前缘亚相带水下分流河道和前缘砂坝等砂体.这些新认识为该油田调整挖潜提供了地质指导.     

东海西湖凹陷保俶斜坡下第三系储层岩石学特征

东海西湖凹陷保俶斜坡下第三系储层砂岩为长石岩屑砂岩或岩屑长石砂岩，杂基含量小于5％，矿物成分主要为伊利石和绿泥石；胶结物主要成分为高岭石、石英次生加大边、碳酸盐矿物，总含量小于10％．     

北黄海盆地东部坳陷不同物源影响下储层的成岩演化

以北黄海盆地东部坳陷中生界碎屑岩储层为研究对象，运用岩石薄片光学显微鉴定、阴极发光和扫描电镜等技术方法和手段分析成岩特征，探讨不同物源-沉积体系控制下储层的成岩演化。研究认为，东部坳陷中生界储层主要处于中成岩阶段A期，发育的主要成岩作用类型为压实作用、胶结作用、凝灰质脱玻化作用、交代作用、蚀变作用和溶蚀-溶解作用，其中，东部地区压实作用强度要高于西南和北部地区，北部地区碳酸盐胶结物的含量明显高于其他地区，东部地区以凝灰质胶结为特征并发生凝灰质脱玻化作用，西南部以黏土矿质胶结为特征并发生明显的黏土矿物转化现象，西南和北部地区的溶蚀/溶解作用的发育程度要好于东部地区。综合分析认为，研究区不同物源沉积区储层具有差异的成岩特征，表现为不同的储层序列，从而影响储层的成岩演化。     

涠西南凹陷流三段储层成岩相分析与甜点储层预测

根据岩心、铸体薄片、扫描电镜、阴极发光、X衍射等资料并结合物性资料,对北部湾盆地涠西南凹陷流三段储层的储层特征、成岩作用特点进行了研究。结果表明研究区压实作用强烈是储层致密化的主要原因。胶结作用对储层有一定的破坏作用,但是早期碳酸盐胶结、自生高岭石有利于优质储层的发育。溶蚀作用是优质储层发育的基础,破裂作用改善了储层的渗流能力。在成岩作用研究的基础上,根据成岩作用的强度及特殊成岩矿物,划分了五类成岩相。其中,弱压实弱胶结相物性最好,中等压实中等溶蚀相、强压实中强溶蚀相物性次之,压实充填相和碳酸盐致密胶结相物性最差。通过成岩相的测井响应分析,识别了单井-剖面-平面的成岩相。预测研究区东部辫状河三角洲浅埋藏储层、西北部扇三角洲和西南部扇三角洲的水下分流河道中厚层砂砾岩体储层为甜点发育区。     

西湖凹陷Y构造花港组致密砂岩成藏特征

致密砂岩相对优质储层发育控制因素及其成藏特征是制约西湖凹陷深层勘探的关键问题。三潭深凹Y构造花港组是致密砂岩重要勘探领域。利用岩石薄片鉴定、扫描电镜、压汞实验等测试手段，从沉积环境相带、成岩矿物作用、构造幅度与储层有效充注和富集程度等方面，对Y构造致密砂岩储层发育特征、成藏过程及其控制因素开展研究。研究结果表明，研究区致密砂岩储层分为4类，其中，Ⅰ类储层是相对优质储层，是油气优先充注的优质通道。高能沉积环境中粗粒沉积是相对优质储层形成的前提，孔隙衬垫绿泥石利于原生粒间孔隙保存，并且促进晚期溶蚀，是物性改善的关键。Y构造致密砂岩发育叠覆跨越成藏组合，相对优质储层和构造幅度共同控制储层含气性，构造幅度增加，在相对较差储层（Ⅱ类和Ⅲ类）中同样发育气层。该研究对西湖凹陷致密砂岩气富集区的寻找及优选具有重要的指导意义。     

西湖凹陷玉泉构造油气成藏时空匹配关系研究

以地质录井资料为基础,结合流体包裹体、自生伊利石同位素等地球化学资料,运用平衡剖面、盆地模拟技术,研究玉泉构造断裂演化史、圈闭发育史、埋藏史、成岩史、生烃史、油气成藏史及其时空匹配关系。研究表明：玉泉构造经历了前挤压反转期、挤压反转早期和挤压反转晚期3个阶段,其中挤压反转早期和晚期为NWW向调节断层和圈闭发育、定型的关键阶段;花港组下段H6—H7自13.0 Ma以来油气持续充注成藏至今,储层物性较差,花港组上段为13.0～11.4 Ma和4.2 Ma至今两期油气充注成藏,且第二期为主要油气成藏期,储层物性较好,龙井组为3.4 Ma至今一期充注成藏,储层物性好。总结出玉泉构造寻找有利勘探目标的关键条件为：以花港组上段为勘探主要目的层,靠近早期发育的NNE油源断层,避开晚期NWW向调节断层,指出玉泉3井区北部、玉泉1井区北部花港组上段以及玉泉3井区NWW向断层上盘龙井组、玉泉1井区龙井组上段为有利勘探区。     

苏北盐城天然气储层成岩作用研究

盐城凹陷天然气储层为成分成熟度很低的砂砾岩、砾状砂岩、砂岩和少量粉砂岩,砂岩类型主要为长石岩屑砂岩和少量岩屑长石砂岩。成岩矿物主要类型有粘土矿物、石英、钠长石、碳酸盐、硬石膏和石膏等。储层以次生孔隙发育为特点,以粒间孔隙和骨架颗粒溶孔最为发育,溶解作用发育程度与泥质岩在成岩过程中粘土矿物和有机质的演化关系极其密切。盐城天然气进入储层发生在始新世———新近纪,主要成藏期发生在4.5~10Ma。天然气储层成岩演化阶段处于晚成岩A亚期。储层性质明显地受到沉积相和成岩作用的影响。沉积物粒度较粗、厚度较大的河道砂的储集物性明显优于各种粒度较细、厚度较薄的席状砂体。     

东海西湖凹陷南端砂岩储层特征及其控制因素

本研究区始新统—中新统地层内大套砂质岩储层发育，砂层厚度为２—３０ｍ。分析结果表明：具有一定储集和渗透能力的砂层主要分布在井深１９００—３２００ｍ（Ｃ—１井、ＣＨ—１井深度可达３６００ｍ），即花港组和龙井组，岩性以细砂岩、粉砂岩为主，还有少量中砂岩。其中的细砂岩、粉砂岩具有粒度分选好，胶结物含量低（＜１０％）、孔隙、渗透条件好（φ为１０—２８％、ｋ为＜１—１８００×１０￣（－３）ｕｍ￣２）；以次生粒间扩大孔、粒内孔、铸模孔和粘土矿物中的微孔及少量原生孔为其储集空间。胶结物以粘土矿物为主，其次为碳酸盐和氧化硅胶结物。本区砂岩体储层物性除受原始地质条件、储集岩的成份、结构、埋藏深度等控制外，同时受成岩后生作用的影响，压实作用和胶结作用使其物性降低，而骨架颗粒（长石为主）和胶结物的溶蚀改善了其储集条件。     

盐家地区沙四上亚段储层成岩作用及孔隙演化

盐家地区位于东营凹陷北部陡坡带,沙四上亚段形成了近岸水下扇沉积体系.本次研究利用扫描电镜、铸体薄片等方法.结合X-射线衍射分析化验资料,着重对成岩作用以及孔隙演化等方面做了研究.该区储层岩石类型主要为岩屑长石砂岩,成分成熟度和结构成熟度低;对储层有显著影响的成岩作用主要有机械压实作用,胶结作用,以及长石、岩屑等不稳定碎屑的溶蚀作用;通过有机质热演化、黏土矿物的含量变化及相互转化、石英加大程度以及溶蚀作用等的分析,可以推知盐家地区沙四上亚段储层处于中成岩阶段A期;2个次生孔隙发育带的形成分别与长石溶解与碳酸盐溶解有关.     

Lithologic characteristics and diagenesis of the Devonian Jauf sandstone at Ghawar Field, Eastern Saudi Arabia

The Lower Devonian Jauf Formation in Saudi Arabia is an important hydrocarbon reservoir. However, in spite of its importance as a reservoir, published studies on the Jauf Formation more specifically on the reservoir quality (including diagenesis), are very few. This study, which is based on core samples from two wells in the Ghawar Field, northeastern Saudi Arabia, reports the lithologic and diagenetic characteristics of this reservoir. The Jauf reservoir is a fine to medium-grained, moderate to well-sorted quartz arenite. The diagenetic processes recognized include compaction, cementation (calcite, clay minerals, quartz overgrowths, and a minor amount of pyrite), and dissolution of the calcite cements and of feldspar grains. The widespread occurrences of early calcite cement suggest that the Jauf reservoir lost a significant amount of primary porosity at a very early stage of its diagenetic history. Early calcite cement, however, prevented the later compaction of the sandstone, thus preserving an unfilled part of the primary porosity. Based on the framework grain–cement relationships, precipitation of the early calcite cement was either accompanied or followed by the development of part of the pore-lining and pore-bridging clay cement. Secondary porosity development occurred due to partial to complete dissolution of early calcite cements and feldspar. Late calcite cement occurs as isolated patches, and has little impact on reservoir quality of the sandstones.In addition to calcite, several different clay minerals including illite and chlorite occur as pore-filling and pore-lining cements. While the pore-filling illite and chlorite resulted in a considerable loss of porosity, the pore-lining chlorite may have helped in retaining the porosity by preventing the precipitation of syntaxial quartz overgrowths. Illite, which largely occurs as hair-like rims around the grains and bridges on the pore throats, caused a substantial deterioration to permeability of the reservoir. Diagenetic history of the Jauf Formation as established here is expected to help better understanding and exploitation of this reservoir.     

Depositional and diagenetic controls on deeply-buried Eocene sublacustrine fan reservoirs in the Dongying Depression,Bohai Bay Basin,China

This paper investigates the reservoir potential of deeply-buried Eocene sublacustrine fan sandstones in the Bohai Bay Basin, China by evaluating the link between depositional lithofacies that controlled primary sediment compositions, and diagenetic processes that involved dissolution, precipitation and transformation of minerals. This petrographic, mineralogical, and geochemical study recognizes a complex diagenetic history which reflects both the depositional and burial history of the sandstones. Eogenetic alterations of the sandstones include: 1) mechanical compaction; and 2) partial to extensive non-ferroan carbonate and gypsum cementation. Typical mesogenetic alterations include: (1) dissolution of feldspar, non-ferroan carbonate cements, gypsum and anhydrite; (2) precipitation of quartz, kaolinite and ferroan carbonate cements; (3) transformation of smectite and kaolinite to illite and conversion of gypsum to anhydrite. This study demonstrates that: 1) depositional lithofacies critically influenced diagenesis, which resulted in good reservoir quality of the better-sorted, middle-fan, but poor reservoir quality in the inner- and outer-fan lithofacies; 2) formation of secondary porosity was spatially associated with other mineral reactions that caused precipitation of cements within sandstone reservoirs and did not greatly enhance reservoir quality; and 3) oil emplacement during early mesodiagenesis (temperatures > 70 °C) protected reservoirs from cementation and compaction.     

东海陆架盆地N气田花港组储层特征及分类评价

东海陆架盆地西湖凹陷古近系花港组储层为典型的低孔、低渗储层。基于大量岩心物性、粒度、薄片、压汞等资料,对N气田目的层储层岩性、物性和孔隙结构特征进行精细评价。结果表明:N气田花港组储层岩性以细砂岩为主,矿物成分构成稳定,以石英为主,黏土含量低,岩性较纯;随着埋藏变深,孔隙变差,粒间孔减少,溶蚀孔增加,孔喉半径减小,连通性变差;局部发育砂砾岩,且渗透率大于细砂岩一个数量级以上,可作为甜点储层开发。基于实验和试油资料统计结果,建立了一套适用于花港组储层的综合分类评价标准,包含孔隙度、渗透率、饱和度和地质特征4类储层重要参数,分类结果特征鲜明,分类依据科学可靠,为该区域低孔、低渗储层勘探开发提供依据。     

西湖凹陷KX构造平湖组储层特征及主控因素研究

西湖凹陷KX构造始新统平湖组是重要产气层系.利用大量薄片、岩心和分析化验资料,对该平湖组储集层进行了详细的岩石学特征、储层物性分析以及影响储层发育的主控因素的研究.结果表明,该套储层的岩石类型以长石岩屑质石英砂岩主,填隙物丰富、分选中等—好、成分成熟度低、磨圆程度高;孔隙类型以次生孔隙为主;喉道类型以片状、弯曲片状喉道为主;孔喉组合类型为中孔小喉、小孔小喉组合;储层物性较差,为低孔低渗储层;平湖组储层主要受潮汐改造的分流河道微相控制,压实作用、胶结作用、溶蚀作用和破裂作用等成岩作用是研究区储集层物性的主要控制因素.     

Pore fluid evolution,distribution and water-rock interactions of carbonate cements in red-bed sandstone reservoirs in the Dongying Depression,China

The compositions, distribution and its interaction with rocks of the evolving pore fluids controls the distribution of carbonate cements and reservoir storage spaces. The reservoir quality of the red-bed sandstone reservoirs in the Dongying Depression was investigated by an integrated and systematic analysis including carbonate cement petrology, mineralogy, carbon and oxygen isotope ratios and fluid inclusions. The investigation was also facilitated by probing the mineral origins, precipitation mechanisms, pore fluid evolution and distribution, and water-rock interaction of carbonate cements and their influences on reservoir quality. Diagenetic-evolving fluids in the interbedded mudstones are the main source for the precipitation of calcite cements that completely fill the intergranular volume (CFIV calcite) with heavier oxygen and carbon isotopes. The ferro-carbonate cements in the reservoir sandstone are enriched in lighter carbon and oxygen isotopes. In addition to the cations released by the conversion of clay minerals in reservoirs, products of organic acid decarboxylation and the associated feldspar dissolution process provide important sources for such carbonate cementation. The carbon isotopes of CO₂ and the oxygen isotopic composition of fluids equilibrated with the CFIV calcite, ferro-calcite, dolomite and ankerite cements indicate that the pore in the red-bed reservoirs experienced high salinity fluids, which evolved from the early-formed interbedded mudstones, through organic acid input and to organic acid decarboxylation. Pore fluids from nearby mudstones migrated from the edge to the centre of sandbodies, causing strong calcite cementation along the sandbody boundaries and forming tight cementation zones. Pore fluids associated with organic CO₂ and acids and organic acid decarboxylation are mainly distributed in the internal portion of sandbodies, causing feldspar dissolution and precipitation of ferro-carbonate cements. The distribution of pore fluids caused the zonal distribution of carbonate cements in sandbodies during different periods. This may be advantageous to preserve the porosity of reservoirs as exemplified by the distribution of high-quality reservoirs in the red-bed sandbodies.     

Mechanism of carbonate cementation and its influence on reservoir in Pinghu Formation of Xihu Sag

Carbonate cements are the most abundant authigenic mineral and impact on physical properties greatly in sandstone reservoir. In this paper, Pinghu Formation of Xihu Sag was taken as a target. Characteristics,distribution and formation of carbonate cements were investigated via optical microscopy, cathodoluminescence(CL), electron probe and in-situ carbon-oxygen isotope. The results showed that carbonate cements varied in types and shapes. Calcite/dolomite mainly present as poikilotopic cements, ...     

Quantitative evaluation of the reservoir potential and controlling factors of semi-deep lacustrine tempestites in the Eocene Lijin Sag of the Bohai Bay Basin,East China

Ancient lacustrine storm-deposits that act as petroleum reservoirs are seldom reported. The Lijin Sag, which is located in the southeastern corner of the Bohai Bay Basin in East China, is a NE–SW trending Cenozoic half-graben basin. Some of its Eocene deposits (Bindong deposits) were interpreted as lacustrine tempestites. The Bindong tempestites, which developed in the lower part of the upper fourth member of the Shahejie Formation (Es4¹), constitute a new kind of petroleum reservoir and are novel petroleum exploration targets in the Bindong Area. However, the characteristics of the Es4¹ Bindong tempestite reservoirs and their controlling factors are poorly understood. Point-count analyses of thin sections, scanning electron microscope image analyses, X-ray diffractometry data, and the petrophysical parameters of the Bindong tempestite reservoirs were utilized to estimate the reservoir quality. The reservoirs have undergone significant diagenetic alteration, which can be divided into negative and positive aspects. The negative alteration includes compaction, authigenic minerals, and cementation such as carbonates, clay minerals and overgrowths of quartz and feldspar. The uneven distribution of carbonate cement increased the reservoir’s heterogeneity, with carbonate cement commonly precipitating along the sandstone-mudstone contacts. The primary porosity was severely reduced because of compaction and extensive carbonate cementation. Positive alteration includes dissolution, carbonate cementation, undercompaction and fractures. Carbonate cementation exhibited both positive and negative effects on the reservoir quality. Overall, the objective reservoir quality is quite poor. A quantitative evaluation of the reservoirs’ potential was conducted. The cutoff values of several of the reservoir’s parameters were calculated. The lower limits of the porosity and permeability are 8.35–5.85% and 1.2587–0.2753 × 10^–3 μm², respectively, depending on the depth. The upper limits of the carbonate and mud content are approximately 18.5% and 9–10%, respectively. A fundamental understanding of these characteristics will provide necessary information for extracting hydrocarbons from analogous subsurface reservoirs.     

Diagenesis and origin of calcite cement in the Flemish Pass Basin sandstone reservoir (Upper Jurassic): Implications for porosity development

The Flemish Pass Basin is a deep-water basin located offshore on the continental passive margin of the Grand Banks, eastern Newfoundland, which is currently a hydrocarbon exploration target. The current study investigates the petrographic characteristics and origin of carbonate cements in the Ti-3 Member, a primary clastic reservoir interval of the Bodhrán Formation (Upper Jurassic) in the Flemish Pass Basin.The Ti-3 sandstones with average Q_86.0F_3.1R_10.9 contain various diagenetic minerals, including calcite, pyrite, quartz overgrowth, dolomite and siderite. Based on the volume of calcite cement, the investigated sandstones can be classified into (1) calcite-cemented intervals (>20% calcite), and (2) poorly calcite-cemented intervals (porous). Petrographic analysis shows that the dominant cement is intergranular poikilotopic (300–500 μm) calcite, which stared to form extensively at early diagenesis. The precipitation of calcite occured after feldspar leaching and was followed by corrosion of quartz grains. Intergranular calcite cement hosts all-liquid inclusions mainly in the crystal core, but rare primary two-phase (liquid and vapor) fluid inclusions in the rims ((with mean homogenization temperature (T_h) of 70.2 ± 4.9 °C and salinity estimates of 8.8 ± 1.2 eq. wt.% NaCl). The mean δ¹⁸O and δ¹³C isotopic compositions of the intergranular calcite are −8.3 ± 1.2‰, VPDB and −3.0 ± 1.3‰, VPDB, respectively; whereas, fracture-filling calcite has more depleted δ¹⁸O but similar δ¹³C values. The shale normalized rare earth element (REE_SN) patterns of calcite are generally parallel and exhibit slightly negative Ce anomalies and positive Eu anomalies. Fluid-inclusion gas ratios (CO₂/CH₄ and N₂/Ar) of calcite cement further confirms that diagenetic fluids originated from modified seawater. Combined evidence from petrographic, microthermometric and geochemical analyses suggest that (1) the intergranular calcite cement precipitated from diagenetic fluids of mixed marine and meteoric (riverine) waters in suboxic conditions; (2)the cement was sourced from the oxidation of organic matters and the dissolution of biogenic marine carbonates within sandstone beds or adjacent silty mudstones; and (3) the late phases of the intergranular and fracture-filling calcite cements were deposited from hot circulated basinal fluids.Calcite cementation acts as a main controlling factor on the reservoir quality in the Flemish Pass reservoir sandstones. Over 75% of initial porosity was lost due to the early calcite cementation. The development of secondary porosity (mostly enlarged, moldic pores) and throats by later calcite dissolution due to maturation of organic matters (e.g., hydrocarbon and coals), was the key process in improving the reservoir quality.     

Facies controls on the distribution of diagenesis and compaction in fluvial-deltaic deposits

The Upper Triassic – Lower Jurassic Åre Formation comprising the deeper reservoir in the Heidrun Field offshore mid-Norway consists of fluvial channel sandstones (FCH), floodplain fines (FF), and sandy and muddy bay-fill sediments (SBF, MBF) deposited in an overall transgressive fluvial to lower delta plain regime. The formation has been investigated to examine possible sedimentary facies controls on the distribution of cementation and compaction based on petrography and SEM/micro probe analyses of core samples related to facies associations and key stratigraphic surfaces. The most significant authigenic minerals are kaolinite, calcite and siderite. Kaolinite and secondary porosity from dissolution of feldspar and biotite are in particular abundant in the fluvial sandstones. The carbonate minerals show complex compositional and micro-structural variation of pure siderite (Sid I), Mg-siderite (Sid II), Fe-dolomite, ankerite and calcite, displaying decreasing Fe from early to late diagenetic carbonate cements. An early diagenetic origin for siderite and kaolinite is inferred from micro-structural relations, whereas pore filling calcite and ankerite formed during later diagenesis. The Fe-dolomite probably related to mixing-zone dolomitization from increasing marine influences, and a regional correlatable calcite cemented layer has been related to a flooding event. Porosity values in non-cemented sandstone samples are generally high in both FCH and SBF facies associations averaging 27%. Differential compaction between sandstone and mudstone has a ratio of up to 1:2 and with lower values for MBF. We emphasize the role of eogenetic siderite cementation in reducing compactability in the fine-grained, coal-bearing sediments most prominent in MBF facies. This has implications for modeling of differential compaction between sandstone and mudstones deposited in fluvial-deltaic environments.