Control of Facies and Potential on Jurassic Hydrocarbon Accumulation and Prediction of Favorable Targets in the Hinterland Region of the Junggar Basin

<正>Exploration practices show that the Jurassic System in the hinterland region of the Junggar Basin has a low degree of exploration but huge potential,however the oil/gas accumulation rule is very complicated,and it is difficult to predict hydrocarbon-bearing properties.The research indicates that the oil and gas is controlled by structure facies belt and sedimentary system distribution macroscopically,and hydrocarbon-bearing properties of sand bodies are controlled by lithofacies and petrophysical facies microscopically.Controlled by ancient and current tectonic frameworks,most of the discovered oil and gas are distributed in the delta front sedimentary system of a palaeo-tectonic belt and an ancient slope belt.Subaqueous branch channels and estuary dams mainly with medium and fine sandstone are the main reservoirs and oil production layers,and sand bodies of high porosity and high permeability have good hydrocarbon-bearing properties;the facies controlling effect shows a reservoir controlling geologic model of relatively high porosity and permeability.The hydrocarbon distribution is also controlled by relatively low potential energy at the high points of local structure macroscopically, while most of the successful wells are distributed at the high points of local structure,and the hydrocarbon-bearing property is good at the place of relatively low potential energy;the hydrocarbon distribution is in close connection with faults,and the reservoirs near the fault in the region of relatively low pressure have good oil and gas shows;the distribution of lithologic reservoirs at the depression slope is controlled by the distribution of sand bodies at positions of relatively high porosity and permeability.The formation of the reservoir of the Jurassic in the Junggar Basin shows characteristics of favorable facies and low-potential coupling control,and among the currently discovered reservoirs and industrial hydrocarbon production wells,more than 90%are developed within the scope of faciespotential index FPI0.5,while the FPI and oil saturation of the discovered reservoir and unascertained traps have relatively good linear correlation.By establishing the relation model between hydrocarbonbearing properties of traps and FPI,totally 43 favorable targets are predicted in four main target series of strata and mainly distributed in the Badaowan Formation and the Sangonghe Formation,and the most favorable targets include the north and east of the Shinan Sag,the middle and south of the Mobei Uplift,Cai-35 well area of the Cainan Oilfield,and North-74 well area of the Zhangbei fault-fold zone.     

沉积盆地超压系统演化与深层油气成藏条件

晚期成藏是大中型油气田形成的重要特征。从晚期成藏的观点出发，深层油气藏的形成需要盆地深层发育仍处于有利生，排烃阶段的源岩，具有较高孔隙度，渗透率的深部储层，以及有利的储层－盖层能量配置，在超压盆地中，超压对生烃的抑制作用使常压盆地中已过成熟的源岩保持在有利的生，排烃阶段，从而为深层油气成藏提供较好的烃源条件，超压条件下低有效应力引起的机械压实程度减弱，流体流动性减弱引起的化学胶结作用减缓及有机酸对矿物的溶解作用使深埋超压储层保持较高的孔隙度和渗透率。然而，由于超压引起的地层天然水力破裂和流体穿层运移。超压环境深部油气藏的形成和保存需要有效的储层－盖层能量配置。     

隐蔽油气藏研究的难点和前沿

隐蔽油气藏已成为中国油气勘探的主要领域之一。随着勘探程度的提高,隐蔽油气藏勘探向复杂条件拓展,深层隐蔽油气藏发育与保存、不整合面结构与隐蔽油气藏分布、调整改造型隐蔽油气藏形成和保存机理成为隐蔽油气藏勘探和成藏机理研究的难点和前沿。深部存在活跃源岩和具有较高孔隙度和渗透率的储层是深层隐蔽油气藏成藏的基础。超压环境生烃作用动力学的研究进展提高了预测深层源岩生烃潜力的能力,已知的深层高孔隙度储层保存机理可成为预测深部储层孔渗条件的基础。不整合面结构特别是古土壤层的厚度及封闭能力、古土壤层之下半风化岩层的厚度及渗透率是研究与不整合面有关的隐蔽油气藏的关键。由于多期构造叠加、多期生烃和多期成藏,叠合盆地很多隐蔽油气藏经历了不同程度的调整改造,形成有成因联系的一系列调整改造型隐蔽油气藏,研究晚期构造与早期构造的叠加方式是预测调整改造型隐蔽油气藏的基础。准噶尔盆地中部,隐蔽油气藏同时具有埋藏深、不整合面结构复杂、多期成藏多期调整改造的特点,是建立复杂隐蔽油气藏成藏与勘探理论的天然实验室。     

Analysis of Reservoir Forming Conditions and Prediction of Continuous Tight Gas Reservoirs for the Deep Jurassic in the Eastern Kuqa Depression, Tarim Basin

The exploration targets in the Kuqa Depression at present are mainly structure traps in Cretaceous-Tertiary. Due to the complexity of mountain distribution and reservoir forming conditions, the exploration of Jurassic in the eastern Kuqa Depression has been in a state of semi-stagnation since the discovery of the Yinan-2 gas reservoir. According to the concept and theory of “continuous petroleum reservoirs” and the re-analysis of the forming conditions of the Yinan-2 gas reservoir and regional natural gas in the eastern Kuqa Depression, it is believed that the deep Jurassic has good natural gas accumulation conditions as well as geological conditions for forming continuous tight gas reservoirs. The boundary of the Yinan-2 gas reservoir is not controlled by a structural spillpoint. The downdip part of the structure is dominated by gas, while the hanging wall of the fault is filled by water and forming obvious inverted gas and water. The gas reservoir has the normal temperature and ultra-high pressure which formed in the near source or inner-source. All of these characteristics indicate that the Yinan-2 gas reservoir is different from conventional gas reservoirs. The deep Jurassic in the eastern Kuqa Depression has multisets of source-reservoir-cap assemblages, which comprise interbedded sandstones and mudstones. These assemblages are characterized by a self-generation, self-preserving and self-coverage model. Reservoir sandstones and coal measure mudstones are interbedded with each other at a large scale. As the source rocks, Triassic-Jurassic coal measure mudstones distribute continuously at a large scale and can generate and expel hydrocarbon. Source rocks contact intimately with the overlying sandstone reservoirs. During the late stage of hydrocarbon expulsion, natural gas charged continuously and directly into the neighboring reservoirs. Petroleum migrated mainly in a vertical direction over short distances. With ultra-high pressure and strong charging intensity, natural gas accumulated continuously. Reservoirs are dominated by sandstones of braided delta facies. The sand bodies distribute continuously horizontal. With low porosity and low permeability, the reservoirs are featured by strong heterogeneity. It is hypothesized that the sandstones of the interior depression tend to be relatively tight with increasing depth and structure stress weakness. Thus, it is predicted that continuous tight gas reservoirs of ultra-high pressure may exist in the deep formations of the eastern and even the whole Kuqa Depression. So, it is worth evaluating the exploration potential.     

低渗透砂岩油气成藏特征及其勘探启示

低渗透油气藏在国内外分布都非常广,占有很大的资源量和储量。低渗透砂岩具有特殊的成藏特征,主要表现在：（1）储层颗粒细、分选差、胶结物含量高,长石和岩屑含量普遍较高,成分成熟度和结构成熟度低,孔隙度、渗透率低,主要为细小孔微细喉型、微孔微喉型,裂缝相对发育,排驱压力大;（2）除了具有一般油气藏的异常高压外,低渗透砂岩油气藏还表现为异常低压,并且出现异常高压和异常低压共存;（3）油气藏内缺乏油（气）水分异,油水关系复杂,常出现油（气）水关系倒置;（4）浮力对低渗透砂岩油气运移的作用非常有限,油气运移的主要动力为异常高压等,油气的运移表现为非达西运移特征,输导体系以裂缝、相对高渗的砂体和局部不整合为主,运移距离比较短,侧向运移不强;（5）低渗透砂岩的含油（气）饱和度一般都小于60%,并且含油饱和度与孔隙度和渗透率的关系比较复杂,储量丰度比较低,主要聚集在岩性或岩性-构造复合圈闭中,受构造影响不大,油气呈大面积分布。因此,低渗透砂岩区的油气勘探应当突破传统的构造高点勘探油气的思想,在构造斜坡下倾部位或向斜区勘探油气,在勘探中注意寻找低渗透砂岩油气富集的“甜点”。      

鄂尔多斯盆地陇东地区延长组低渗透砂岩油藏成藏机理与成藏模式

低渗透油藏在国内外分布十分广泛,逐渐成为未来石油勘探开发的重要接替领域。与常规油藏不同,低渗透砂岩油藏具有以下特征：(1)含油饱和度低,与储层物性关系复杂;(2)油水关系复杂,无明显的油水界面;(3)大面积广泛分布,受构造高低控制不明显;(4)距离源岩越远,石油富集程度越差。陇东地区延长组低渗透砂岩油藏的成藏机理研究表明：低渗透砂岩储层排替压力较大,浮力很难驱动石油发生明显的运移,石油在优质烃源岩生烃作用产生的剩余压力驱动下,向上、向下连续充注进入邻近砂体,近源聚集,形成原生油藏;裂缝发育条件下,已聚集石油可在浮力驱动下沿裂缝进行垂向、侧向运移调整,远源成藏,形成次生油藏。综合石油成藏期次、裂缝特征及形成时间、储层孔隙演化史以及成藏动力演化等特征,建立了陇东地区延长组油藏的成藏模式：早期低熟油小规模充注模式、中期成熟油大规模充注成藏模式、晚期构造抬升调整成藏模式。其主要控制因素为源储大面积广泛接触奠定了低渗透砂岩储层石油富集的基础,优质烃源岩生排烃范围控制了原生油藏分布范围,裂缝发育特征控制了次生油藏分布部位。     

Geochemical Characteristics of the Upper Triassic Xujiahe Formation in Sichuan Basin, China and its Significance for Hydrocarbon Accumulation

The alternative development of coal-bearing hydrocarbon source rocks and low-porosity and low-permeability tight sandstone reservoirs of the Triassic Xujiahe Formation in the Sichuan Basin is favorable for near-source hydrocarbon accumulation. The natural gas composition of the Xujiahe Formation in the Sichuan Basin is dominated by hydrocarbon gases, of which the methane content is80.16%-98.67%. Typically, the C_2~+ content is larger than 5% in main wet gas. The dry gas is mainly distributed in the western and northern regions of the basin. The non-hydrocarbon gases mainly contain nitrogen, carbon dioxide, hydrogen, and helium, with a total content of 2%. The carbon isotope ranges of methane and its homologues in natural gas are: δ~(13)C_1 of-43.8‰ to-29.6‰, δ~(13)C_2 of-35.4‰ to-21.5‰, δ~(13)C_3 of-27.6‰ to-19.8‰,and δ~(13)C_4 of-27.7‰ to-18.8‰. δ~(13)C_3δ~(13)C_4 occurs in some natural gas with a low evolution degree; such gas is mainly coal-related gas from humic-type source rocks of the Xujiahe Formation. As for the natural gas, δ~2 H_(CH4) values ranged from-195‰ to-161‰,δ~2 H_(C2H6) values ranged from-154‰ to-120‰, and δ~2 H_(C3H8) values ranged from-151‰ to-108‰. The dry coefficient,δ~(13)C and δ~2 H_(CH4) are all positively correlated with the maturity of source rocks. The higher the maturity of source rocks is, the larger the natural gas dry coefficient is and the larger the δ~(13)C and δ~2 H_(CH_4) values are, indicative of the characteristic of near-source accumulation. The δ~2 H_(C2H6) value of natural gas is influenced by paleosalinity to a relatively large extent; the higher the paleosalinity is, the larger the δ~2 H_(C2H6) value is. The Pr/Ph value of the condensate oil ranged from 1.60 to 3.43, illustrating light oxidization-light reduction and partial-oxidization characteristics of the depositional environment of coal-bearing source rocks of the Xujiahe Formation. The natural gas light hydrocarbon(C_5-C_7) from the Xujiahe Formation presented two characteristics: the first was the relatively high aromatic hydrocarbon content(19%-32.1%), which reveals the characteristic of natural gas with humic substances of high-maturity; the second was the low content of aromatic hydrocarbon(0.4%-9.3%),reflecting water-washing during the accumulation of the natural gas. The reported research outcomes indicate a potential mechanism for natural gas accumulation in the Xujiahe Formation, which will further guide natural gas exploration in this region.     

鄂尔多斯盆地延长组致密油成藏控制因素

鄂尔多斯盆地延长组发育我国典型的低渗透和特低渗透油气资源,其油藏呈现出储层致密、储集砂体预测难度大、成藏机理复杂等特征.目前,根据勘探开发实践,长庆油田成功实现对渗透率大于0.3×10^-3μm²油藏的开发,目前正在开展渗透率为(0.1~0.3)×10^-3 μm²致密砂岩储层的技术攻关.笔者结合国外最新致密油气资源研究成果和鄂尔多斯盆地延长组低渗透油藏的特征,从延长组致密油分布、致密油流体特征、赋存状态、储集体和致密油形成的控制因素入手,对鄂尔多斯盆地延长组致密油形成与分布规律进行了探讨.确定了延长组致密油形成的控制因素:①长7优质烃源岩分布范围广,生烃强度大,为致密油形成提供了充足的油源供给和资源基础;②大面积广泛展布的复合叠加的碎屑岩储集体,为致密油藏形成提供了储集空间;③油页岩与致密砂岩互层共生,形成了近源成藏的有利配置关系;④成藏期生烃增压,致密储层石油充注程度高,为致密油形成提供了运移动力.     

Coupled accumulation characteristics of Carboniferous-Permian coal measure gases in the Northern Ordos Basin,China

The northern Ordos Basin provides a favorable geological environment for the accumulation and development of coal measure gases (CMG). The hydrocarbon generation potential and reservoir systems of the coal measures have been studied based on data from experimental tests and production and exploration wells, respectively. Further, the coupled accumulation characteristics were determined. The results show that the source rocks are characterized by favorable hydrocarbon generation potential, high thermal evolution (Ro%?=?1.3–2.3%), and mainly type III kerogen. Coals, typically aggregated organic matter, with a huge hydrocarbon generation potential (avg. 89.11 mg/g) and total organic content (TOC) (avg. 65.52%), are predominantly involved in gaseous hydrocarbon generation. Shales with good TOC contents (avg. 2.36%) and large cumulative thicknesses have an important role in gaseous hydrocarbon generation. Coal seams, shale layers, and sandstone layers occur as variably interbedded deposits, which form a favorable environment for CMG coupled accumulation. The porosity and permeability are ranked as follows: sandstone?>?coal?>?shale, with significant stress sensitivity and anisotropy. Two continuous gas generation peaks occurred in the Late Jurassic and Late Cretaceous, with an abundant amount of coal-derived and thermogenic gas generation, respectively. Potential gas-bearing sandstone layers can be formed by gas migration via short distances from nearby coal seams and shale layers. Coupled accumulation of CMG occurred in three stages: (1) stacked and interbedded reservoirs formation stage; (2) gas generating and charging stage; and (3) coupled accumulation adjustment stage. Coalbed methane (CBM)–tight sandstone gas (TSG) assemblage is a favorable target for CMG accumulation and development.     

Geochemistry and geological significance of the Upper Paleozoic and Mesozoic source rocks in the Lower Yangtze region

The Lower Yangtze region is one of the important marine sedimentation areas of oil and gas distribution in southern China,for its favorable source rocks,reservoirs and covers.However,the intense tectonic movements and complex hydrocarbon generation process made it highly impossible to form large-sized oil and gas reservoirs.So it was divided to different hydrocarbon-bearing preservation units in oil-gas exploration.Recent study shows that the Permian and Lower Triassic source rocks in the Lower Yangtze region are complicated in lithology.The hydrocarbon generation potential of limestone there is low while argillaceous source rocks are overall of high abundance with excellent organic types,now in the process of hydrocarbon generation,so differences in high maturity influence the evaluation of organic matter abundance and type.Biomarker characteristics indicate a reductive environment.n-alkanes are marked by a single peak,with no odd-even predominance.The composition and distribution of the carbon numbers of n-alkanes,and the high abundance of long-chain tricyclic terpanes are indicative of marine sedi-mentation.The high contents of pregnane,homopregnane,rearranged hopane suggest that the source rocks are of high maturity.There is a good linear correlation between methylphenanthrene index and vitrinite reflectance.The correlation of oil-source rocks indicated that the oil of Well HT-3 may come from the Permian Longtan Formation in the Huangqiao area,the oil of Wells Rong-2 and Juping-1 came from the Lower Triassic Qinglong Formation in the Jurong area.The exploration here is promising in those different source rocks which all have great potential in hy-drocarbon generating,and oil and gas were produced in the late stage of hydrocarbon generation.     

柴达木盆地中东部地区储层特征与天然气成藏条件

柴达木盆地中东部地区第四第七个泉组是重要的储集层，也是主要的产气层段。通过研究储层的沉积特征以及气藏形成条件认为：（）储集层的岩石粒度普遍较细，以粉砂岩、泥质粉砂岩为主，属滨浅湖沉积体系；（2）储集层成岩程度低，岩石结构松散，原生孔隙发育并具有良好的渗透性；（3）在第四纪更新统湖盆总体上经历了扩张－稳定－收缩的变化过程，因而沉积相在垂向上表现为滨湖、浅湖、较深湖的相互交替；（4）研究区的气藏具有自生、自储、自盖的特点，产气层主要分布于K2－K10层段。     

准噶尔盆地陆东-五彩湾地区火山岩中天然气富集的主控因素

近年来准噶尔盆地陆东-五彩湾地区石炭系火山岩中发现了丰富的天然气资源,包括克拉美丽和五彩湾两个气田,
因此石炭系成为北疆油气勘探的主要目的层之一,陆东-五彩湾地区天然气主要位于石炭系顶部的火山岩风化壳内,主要
为煤成气,来自石炭系腐殖型烃源岩。本文在对陆东-五彩湾地区典型气藏剖面进行分析的基础上,探讨了石炭系火山岩
中天然气富集的主控因素。结果表明,邻近烃源岩和生烃凹陷有利于形成气藏;风化淋滤和构造作用的改造是火山岩物性
得到改善而发育有效储集空间的关键因素;断裂和不整合构成了油气垂向和侧向运移的有利通道;海西期以来的各个构造期,
陆东-五彩湾地区石炭系圈闭和油气藏受到了不同程度的影响,其中火山岩气藏良好的生储盖配置定型于海西期,而燕山
中期则是该区天然气成藏的关键时期。     

Origin and Source of Deep Natural Gas in Nanpu sag,Bohai Bay Basin,China

Natural gas exploration in Nanpu sag, Bohai Bay Basin, has achieved breakthroughs in recent years, and a number of natural gas and condensate wells with high yield have been found in several structures in the beach area. Daily gas production of single wells is up to 170,000 m3, and high-yield wells are mainly distributed in?the Nanpu No. 1 structural belt.?Studies have shown that these natural gases are mainly hydrocarbon gases, with methane content about 80% to 90% and ethane 6%-9%, so they are mainly wet gas; and non-hydrocarbons are at a low level.?Carbon isotopes of methane range from -42‰ to -36‰, and ethane from -28‰ to -26‰. Calculated maturity based on the relationship between δ13C and Ro of natural gas, the gases are equivalent to those generated from organic matter when Ro is 1.0%-1.7% (mainly 1.25%-1.32%). The natural gas is oil-type gas generated from the source rocks at mature to high mature stage, associated with condensate, so carbon isotopes of the gases are heavier. Natural gas in the Nanpu No.1 structural belt is mainly associated gas with condensate. The analysis of the origin and source of natural gas and condensate, combined with the monomer hydrocarbon carbon isotopes and biomarker, indicated that the main source rocks in the Nanpu No.1 structural belt were Es3 (the lower member of the Shahejie Formation), followed by Es1 (the upper member of the Shahejie Formation).?The high-mature hydrocarbons from source rocks in the deep sag mainly migrated through deep inherited faults into shallow traps and accumulated to form oil and gas pools. Therefore, there is a great potential for exploring gas in deep layers.     

徐家围子断陷安达凹陷火石岭组天然气成藏条件分析

DS28井的勘探研究表明徐家围子断陷火石岭组具有良好的勘探前景.笔者通过对岩芯地化测试、铸体薄片、孔隙度测试等资料的分析,探究安达凹陷火石岭组天然气的气源条件、储层特征、盖层条件和成藏模式,以期深入认识松辽盆地北部火石岭组天然气富集规律,指出有利勘探区带和勘探方向.研究表明,安达凹陷火石岭组具备天然气藏形成的基本地质条...     

油气藏中沥青垫的研究进展

沥青垫是油气藏中沥青质相当富集的含油储层带，其沥青质的相对含量为２０％￣６０％，而对应的油层中其值不足２０％，沥青垫在凝析油气藏和轻质油藏中出现的频率高，常位于非渗透性隔层之上的高孔隙和较高水平渗透率的砂岩储层中，研究表明沥青垫的主要形成机理为：脱沥青作用，重力分离作用，生物降解作用和油－水相互作用，石油运移作用。     

Hydrocarbon Accumulation Conditions of Ordovician Carbonate in Tarim Basin

<正>Based on comprehensive analysis of reservoir-forming conditions,the diversity of reservoir and the difference of multistage hydrocarbon charge are the key factors for the carbonate hydrocarbon accumulation of the Ordovician in the Tarim Basin.Undergone four major deposition-tectonic cycles, the Ordovician carbonate formed a stable structural framework with huge uplifts,in which are developed reservoirs of the reef-bank type and unconformity type,and resulted in multistage hydrocarbon charge and accumulation during the Caledonian,Late Hercynian and Late Himalayan. With low matrix porosity and permeability of the Ordovician carbonate,the secondary solution pores and caverns serve as the main reservoir space.The polyphase tectonic movements formed unconformity reservoirs widely distributed around the paleo-uplifts;and the reef-bank reservoir is controlled by two kinds of sedimentary facies belts,namely the steep slope and gentle slope.The unconventional carbonate pool is characterized by extensive distribution,no obvious edge water or bottom water,complicated oil/gas/water relations and severe heterogeneity controlled by reservoirs. The low porosity and low permeability reservoir together with multi-period hydrocarbon accumulation resulted in the difference and complex of the distribution and production of oil/gas/water.The distribution of hydrocarbon is controlled by the temporal-spatial relation between revolution of source rocks and paleo-uplifts.The heterogenetic carbonate reservoir and late-stage gas charge are the main factors making the oil/ gas phase complicated.The slope areas of the paleo-uplifts formed in the Paleozoic are the main carbonate exploration directions based on comprehensive evaluation.The Ordovician of the northern slope of the Tazhong uplift,Lunnan and its periphery areas are practical exploration fields.The Yengimahalla-Hanikatam and Markit slopes are the important replacement targets for carbonate exploration.Gucheng,Tadong,the deep layers of Cambrian dolomite in the Lunnan and Tazhong-Bachu areas are favorable directions for research and risk exploration.     

Research Advances and Exploration Significance of Large-area Accumulation of Low and Medium Abundance Lithologic Reservoirs

In recent years, a series of large low and medium abundance oil and gas fields are discovered through exploration activities onshore China, which are commonly characterized by low porosity-permeability reservoirs, low oil/gas column height, multiple thin hydrocarbon layers, and distribution in overlapping and connection, and so on. The advantageous conditions for large-area accumulation of low-medium abundance hydrocarbon reservoirs include： （1） large （fan） delta sandbodies are developed in the hinterland of large flow-uncontrolled lake basins and they are alternated with source rocks extensively in a structure like ＂sandwiches＂; （2） effective hydrocarbon source kitchens are extensively distributed, offering maximum contact chances with various sandbodies and hydrocarbon source rocks; （3） oil and gas columns are low in height, hydrocarbon layers are mainly of normal-low pressure, and requirements for seal rock are low; （4） reservoirs have strong inheterogeneity and gas reservoirs are badly connected; （5） the hydrocarbon desorption and expulsion under uplifting and unloading environments cause widely distributed hydrocarbon source rocks of coal measures to form large-area reservoirs; （6） deep basin areas and synclinal areas possess reservoir-forming dynamics. The areas with great exploration potential include the Paleozoic and Mesozoic in the Ordos Basin, the Xujiahe Formation in Dachuanzhong in the Sichuan basin, deep basin areas in the Songliao basin etc. The core techniques of improving exploration efficiency consist of the sweetspot prediction technique that focuses on fine characterization of reservoirs, the hydrocarbon layer protecting and high-speed drilling technique, and the rework technique for enhancing productivity.     

川中广安地区上三叠统须六段储层特征及控制因素分析

广安地区上三叠统须六段为辫状河三角洲平原分流河道的大套砂岩复合体沉积,以中—细粒长石岩屑砂岩、岩屑砂岩为主;孔隙度主要分布在3%~15%之间,渗透率主要分布在0.01×10-3~1×10-3μm2之间。主、次分流河道为该区有效储层,复合砂体内渗透层与致密层交互分布形成了复杂的储层分布特征。在此基础上,结合成岩作用分析储层物性的影响因素认为,物源成分的不同影响储层发育富集区的分布,沉积演化特征控制储层发育层段,沉积微相控制层内非均质性。在煤系地层酸性环境下,强烈压实作用是形成普遍低渗的主要原因。主分流河道沉积的中、粗粒长石岩屑砂岩次生孔隙较发育,是主要的储层岩石类型。     

中国大型气田形成的主要条件及潜在勘探领域

20世纪90年代以来,中国天然气工业进入了快速发展的阶段。天然气探明地质储量和天然气产量的高速增长主要依赖于大、中型气田的发现,全国天然气探明地质储量和探明可采储量的89%主要分布于地质储量大于100×108m3的大、中型气田中。近年来很多新领域天然气勘探取得了重大进展,文中通过总结中国大、中型气田的地质特点和形成条件,提出中国大、中型气田的形成主要受控于四大因素:(1)煤成气和油型气是中国主要的天然气成因类型,煤系和高过成熟海相烃源岩是大、中型气田形成的气源基础;(2)大面积分布的孔隙型储层是天然气的主要储集类型,包括大型河流三角洲砂体、大面积礁滩型灰岩、风化壳型碳酸盐岩、溶蚀白云岩、火山岩等;(3)煤系及膏泥岩是大、中型气田保存的优质区域盖层;(4)前陆盆地大型构造圈闭和克拉通盆地、断陷盆地大面积岩性圈闭是大、中型气田聚集的关键。未来天然气勘探领域主要是前陆盆地、克拉通盆地大型海相碳酸盐岩和河流-三角洲砂岩岩性体、东部断陷盆地的深层、东海和南海海域。     

海拉尔盆地呼和湖凹陷致密砂岩气成藏特征

海拉尔盆地呼和湖凹陷具备形成大面积致密砂岩气藏的地质条件,其断陷期地形比较宽缓,后期改造弱,主要发育低幅度的断背斜或宽缓的向斜,在局部具备稳定的构造条件。南二段煤系源岩广泛发育,丰度均达到中等--好烃源岩级别,为致密砂岩气藏的形成提供了充足的物质基础。洼槽区南二段储层属低孔--特低渗型储集层。南二段致密储层与煤、泥岩呈频繁互层状分布,形成致密砂岩气有利的的生储盖组合。构造高部位在一定程度上控制油气丰度,稳定的负向构造区有利于寻找储层富集区。呼和湖凹陷致密砂岩气主要表现为两种成藏组合,自生自储型和内生外储型,油气呈南北向条带状分布。