Structural characteristics of continental carbonate-rich shale and shale oil movability: A case study of the Paleogene Shahejie Formation shale in Jiyang Depression, Bohai Bay Basin, China

Based on rock mineral and geochemical analysis, microscopic observation, physical property measurement, and thin laminae separation test, etc., the characteristics of typical laminae of the Paleogene Shahejie Formation carbonate-rich shale in the Jiyang Depression were analyzed, and the organic matter abundance, reservoir properties, and oil-bearing properties of different laminae were compared. Typical shale storage-seepage structures were classified, and the mobility of oil in different types of shale storage-seepage structure was compared. The results show that the repeated superposition of mud laminae and calcite laminae are the main layer structure of carbonate-rich shales. The calcite laminae are divided into micritic calcite laminae, sparry calcite laminae and fibrous calcite vein. The mud-rich laminae are the main contributor to the organic matter abundance and porosity of shale, with the best hydrocarbon generation potential, reservoir capacity, and oil-bearing property. The micritic calcite laminae also have relatively good hydrocarbon generation potential, reservoir capacity and oil-bearing property. The sparry calcite laminae and fibrous calcite vein have good permeability and conductivity. Four types of shale storage-seepage structure are developed in the carbonate-rich shale, and the mobility of oil in each type of storage-seepage structure is in descending order: sparry calcite laminae enriched shale storage-seepage structure, mixed calcite laminae enriched shale storage-seepage structure, fibrous calcite vein enriched shale storage-seepage structure, and micritic calcite laminae enriched shale storage-seepage structure. The exploration targets of carbonate-rich shale in the Jiyang Depression Shahejie Formation are different in terms of storage-seepage structure at different thermal evolution stages.

Occurrence mechanism of lacustrine shale oil in the Paleogene Shahejie Formation of Jiyang Depression, Bohai Bay Basin, China

To determine the occurrence mechanism and mobility of shale oil in the Shahejie Formation in the Jiyang Depression, organic geochemistry analysis, thin-section petrological observation, low-temperature nitrogen adsorption, high-pressure mercury intrusion porosimetry, field emission scanning electron microscopy experiments were conducted on shale samples to reveal its storage mechanism, including pore size, ratio of adsorbed oil to free oil, mobility and its influencing factors, and mode of storage. Residual shale oil is mainly present in pores less than 100 nm in diameter under the atmospheric temperature and pressure. The lower limit of pore size for free oil is 5 nm, and the lower limit of pore size for movable oil occurrence is about 30 nm. The light components, low TOC and high porosity are the main factors contributing to the high proportion of movable oil. Each type of pore can contain residual shale oil, but not all pores have shale oil. Pore connectivity and surface wettability are the determinants of shale oil enrichment degree and enrichment state.

Origin and diagenetic evolution of dolomites in Paleogene Shahejie Formation lacustrine organic shale of Jiyang Depression,Bohai Bay Basin,East China

The origin of dolomite in Shahejie Formation shale of Jiyang Depression in eastern China were studied by means of petrologic identification, compositional analysis by X-ray diffraction, stable carbon and oxygen isotopic composition, and trace element and rare earth element analyses. The results show that the development of dolomite is limited in the lacustrine organic rich shale of Shahejie Formation in the study area. Three kinds of dolomite minerals can be identified: primary dolomite(D1), penecontemporaneous dolomite(D2), and ankerite(Ak). D1 has the structure of primary spherical dolomite, high magnesium and high calcium, with order degree of 0.3-0.5, and is characterized by the intracrystalline corrosion and coexistence of secondary enlargement along the outer edge. D2 has the characteristics of secondary enlargement, order degree of 0.5-0.7, high magnesium, high calcium and containing a little iron and manganese elements. Ak is characterized by high order degree of 0.7-0.9, rhombic crystal, high magnesium, high calcium and high iron. The micritic calcite belongs to primary origin on the basis of the carbon and oxygen isotopic compositions and the fractionation characteristics of rare earth elements. According to the oxygen isotopic fractionation equation between paragenetic dolomite and calcite, it is calculated that the formation temperature of dolomite in the shale is between 36.76-45.83 ℃, belonging to lacustrine low-temperature dolomite. Based on the maturation and growth mechanism of primary and penecontemporaneous dolomite crystals, a dolomite diagenetic sequence and the dolomitization process are proposed, which is corresponding to the diagenetic environment of Shahejie Formation shale in the study area.

Permeability damage micro-mechanisms and stimulation of low-permeability sandstone reservoirs: A case study from Jiyang Depression, Bohai Bay Basin, China

According to the characteristics of"structural elements"(framework grain,interstitial material and pore throat structure)of low-permeability sandstone reservoir,the"step by step dissolution and separation"acidification and acid fracturing technology has been developed and tested in field.There are three main mechanisms affecting permeability of low-permeability sandstone reservoir:(1)The mud fillings between the framework grains block the seepage channels.(2)In the process of burial,the products from crystallization caused by changes in salinity and solubility and uneven migration and variation of the syn-sedimentary formation water occupy the pores and throat between grains.(3)Under the action of gradual increase of overburden pressure,the framework grains of the rock is compacted tighter,making the seepage channels turn narrower.The"step by step dissolution and separation"acidification(acid fracturing)technology uses sustained release acid as main acidizing fluid,supramolecular solvent instead of hydrochloric acid to dissolve carbonate,and a composite system of ammonium hydrogen fluoride,fluoroboric acid,and fluorophosphoric acid to dissolve silicate,and dissolving and implementing step by step,finally reaching the goal of increasing porosity and permeability.By using the technology,the main blocking interstitial material can be dissolved effectively and the dissolution residual can be removed from the rock frame,thus expanding the effective drainage radius and increasing production and injection of single well.This technology has been proved effective by field test.

Evolution of Authigenic Minerals and Porosity in the Deep Formation of Paleogene of Jiyang Sub-basin

The clastic rocks in the depth of 2800-6000 m of the Paleogene in Jiyang sub-basin had undergone the middle diagenesis and late diagenesis.The reservoirs in main areas of the sub-basin developed 2-6 secondary pores zones.The reservoirs in the stage A of middle diagenesis of Bonan fault zone in Zhanhua depression and of the gentle slope belt of Chezhen depression are controlled by the acidic diagenetic medium and developed one secondary pores zone in each diagenetic sub-stage respectively.The contents ofautogenic quartz,pyrite and kaolinite are quite high in these reservoirs.The reservoirs’

Pore throat structure and classification of Paleogene tight reservoirs in Jiyang depression,Bohai Bay Basin,China

The pore throat structure characteristics of Paleogene tight sandstone and sandy conglomerate in the Jiyang depression are studied using cast thin section,conventional mercury injection,constant rate mercury injection and micro CT scanning data,and a reservoir classification scheme based on pore throat structure parameters is established.The material composition and structural characteristics of tight reservoirs are analyzed by casting thin section data.The pore throat structure characteristics of tight reservoirs are studied by conventional mercury injection,constant rate mercury injection and micro CT scanning.Ten pore throat structure parameters are analyzed by cluster analysis.Based on the classification results and oil test results,the classification scheme of Paleogene tight reservoirs is established.The Paleogene tight reservoirs in the Jiyang depression have the characteristics of macropores and microthroats,with pores in micron scale,throats in nano-submicron scale,and wide variation of ratio of pore radius to throat radius.The permeability of the tight reservoir is controlled by throat radius,the smaller the difference between pore radius and throat radius,and the more uniform the pore throat size,the higher the permeability will be.The lower limits of average pore throat radius for the tight sandstone and tight sandy conglomerate to produce industrial oil flow without fracturing are 0.6μm and 0.8μm,respectively.Reservoirs that can produce industrial oil flow only after fracturing have an average pore-throat radius between 0.2-0.6μm,and reservoirs with average pore throat radius less than 0.2μm are ineffective reservoirs under the current fracturing techniques.Different types of tight sandstone and sandy conglomerate reservoirs are classified and evaluated,which are well applied in exploratory evaluation.

A STRATIGRAPHIC UNCONFORMITY SURFACE BETWEEN THE NEOGENE AND THE PALEOGENE IN THE JIYANG DEPRESSION,BOHAI BAY BASIN, EASTERN CHINA:GEOLOGIC CHARACTERISTICS, FORMATIONPROCESS AND GEODYNAMIC ORIGIN

Regional stratigraphic unconformity surfaces are commonly observed in both orogenic beltsand sedimentary basins. They have superficially simple features, but in fact contain abundant geo-logic and geodynamic in formation on basin evolution, which was rarely systematically studied.Based on the elaborate research on geologic characteristics of the stratigraphic unconformity sur-face between the Neogene and the Paleogene in the Jiyang depression, Bohai Bay basin, EasternChina, this paper reconstructed its formation process and paleotopography in the late Oligocene. ltis the most interesting that this stratigraphic uncon formity surface represents the transiton of theJiyang depression evolution from rifting extension to thermal down-warping and also implies an u-plift process during the transition. This paper thought it worthy to study the origin of thisstratigraphic uncohformity surface and its relation to the stage transition of basin evolution. ThenpossibIe influences of regional stress field and deep dynamic process variations on the stratigraphicunconforrnity surface formation were anaIyzed. The stratigraphic unconformity surface betweenthe Neogene and the Paleogene in the Jiyang depression should be the direct result of extremestretching of llthosphere and diapirism of hot upper mantle, which can also possibly explain the co-incidence of the unconformity surface formation with the stage transition of basin evolution. Fur-thermore. the influences of the stratigraphic unconformity surface formation on oil and gas accu-mulation, the erosion amount calculation, and the elaborate time structure recorded by thestratigraphic unconformity surface were discussed.

Enrichment rules and exploration practices of Paleogene shale oil in Jiyang Depression, Bohai Bay Basin, China

Based on formation testing data of more than 40 wells with industrial oil flow, systematic observation of 1 010.26 m long cores taken from 4 wells and test data of over 10 000 core samples combining with drilling and pilot fracturing data of multiple wells, the geological characteristics of the upper submember of the Sha 4 Member to the lower submember of the Sha 3 Member of Paleogene(Es4s-Es3x) in the Jiyang Depression were investigated to find out factors controlling the enrichment of shale oil and the accumulation model of shale oil, and a comprehensive evaluation method for shale oil sweet spots was established. It is found through the study that the target shale layer is characterized by strong heterogeneity, weak diagenesis, low thermal evolution and high content of clay and carbonate minerals. Shale lithofacies, microcrack, thin interlayer and abnormal pressure are the main factors affecting enrichment and stable production of shale oil, the organic rich laminar shale has the best storage and oil-bearing capacity, microcrack network system improve the storage capacity and permeability of the shale, the thin interlayer is the main flow channel for stable shale oil production, and the abnormal high pressure layer is rich in free state shale oil and high in oil content. The shale oil layers in the target section were divided into three types: matrix, interlayer and fracture ones. According to the occurrence state and exploration practice of shale oil at home and abroad, it is concluded that the interlayer shale oil is the most profitable type at present. The selection parameters for the different types of shale oil were determined, and accordingly the favorable areas were pointed out by comprehensive evaluation of multiple factors. Vertical wells in the interlayer shale oil reservoir, such as Fan 159, Fan 143 and GX 26, were stimulated by volume fracturing and high conductivity channel fracturing jointly. After fracturing, they had a daily oil production of over 6 t, up to 44 t, and stable productivity. Shale oil is expected to become an important replacement energy resource in the Jiyang Depression.

Hydrocarbon Generation Potential Evaluation of Coal Shale Gas of Permo-Carboniferous in Jiyang Depression

In order to study the hydrocarbon-generating potential of Carboniferous-Permian coal shale in Jiyang Depression,geochemistry,petroleum geology and coal geology were applied to study the residual strata distribution of Carboniferous-Permian in Jiyang Depression,organic matter abundance,organic matter types and organic matter maturity of mudstone.The results show that the thickness of the Carboniferous-Permian residual strata in Jiyang Depression is generally 200-800 m,with a maximum thickness of 900 m;the organic matter abundance of coal-bearing shale is good,and it is type III kerogen,which is conducive to gas generation,and the maturity of organic matter reaches a mature-higher maturity stage;the hydrocarbon generation potential of Benxi Formation and Taiyuan Formation is better;Medium to good hydrocarbon source rocks is able to be found in every sag of Shanxi Formation hydrocarbon source rocks,but the scope is limited,and the overall evaluation is still medium.Generally speaking,the Permo-Carboniferous coal-bearing shale in Jiyang Depression has certain shale gas exploration potential.

Distribution and Geochemical Characteristics of Hydrogen in Natural Gas from the Jiyang Depression, Eastern China

Hydrogen gas accelerates hydrocarbon generation, but little is known about its distribution and origin in petroliferous basins, which has hindered the further exploration.Taken the Jiyang Depression in eastern China as an example, this study collected natural gas from different tectonic units, and analyzed various geochemical characters including gas contents, and carbon and hydrogen isotopic composition.The result shows that:(1) hydrogen gas is widespread distributed, but its content is very low, which typically ranges from 0.01% to 0.1% in this region;(2) the ratios of H2/3He, indicative of the origins of hydrogen gas, suggest that mantle-derived hydrogen is dominant.Even in tectonically stable areas absent with deep fluid activities, there is also mantle-derived;(3) the isotopic composition of hydrogen falls in the range of –798‰ to –628‰(relative to VSMOW standard).In areas with deep-derived fluids, the hydrogen gas has a similar isotopic composition with the previously documented deep-sourced gas, with lighter isotopic composition.In contrast, hydrogen gas has a heavier isotopic composition in relatively stable areas.The isotopic signatures suggest that there is a mixture of mantle- and crust-derived hydrogen gas in the relatively stable area, which is consistent with the H2/3He ratios.Therefore, it is clear that the hydrogen gas has a much wider distribution than found in the deep-derived fluid area, resulting in a much broader area with hydrogenating effect for resource rock.This understanding will provide new insights for hydrocarbon generation research and resource assessment in petroliferous basins.

Exploration of Subtle Trap in Jiyang Depression

This article analyses the procedure of exploration of the Tertiary subtle trap in Jiyang depression and divides the Tertiary subtle trap into 3 types (lithologic reservoir, stratigraphic reservoir and fractured reservoir) and 8 groups, then summarizes the common feature and founding discipline of the subtle trap and finds 4 accumulating modes including steep slope mode, depression mode, center anticline mode and gentle slope mode. Its main exploration methods are explicated from the viewpoint of reservoir geological modeling, description of recognizing traps and comprehensive evaluation of reservoir and so on.

Formation Conditions and Sedimentary Model of Over-Flooding Lake Deltas within Continental Lake Basins: An Example from the Paleogene in the Jiyang Subbasin, Bohai Bay Basin

A large quantity of drilling core, paleontology, geochemistry and geophysics data revealed several features of the Jiyang subbasin during the deposition of the Ek1-Es4 x members:(1) the paleotopography of the gentle slope belt had an extremely low gradient;(2) the paleoclimate frequently alternated between dry and wet periods in a generally arid setting;(3) there was strong weathering around the periphery of the basin;(4) the lake was very shallow;(5) the lake level frequently rose and fell; and(6) the sedimentary environment of the gentle slope belt was an overflooding lake. All of these factors provided favorable geological conditions for the development of an over-flooding lake delta. The lithologies of the continental over-flooding lake delta deposits are complex and diverse. The compositional maturity is moderate to low, and the grain size distribution curves and sedimentary structures indicate the presence of both gravity and traction currents. The sedimentary microfacies associations consist of a combination of ordered superposition of flood channels, distributary channels and sheet sands. The delta exhibits a weak foreset seismic reflection. The over-flooding lake delta deposits are laterally extensive. The sandstone content is high, and the individual sandstone beds are thin. The flood channel and distributary channel deposits exhibit evidence of bifurcation and lateral migration. The distribution of the sandbodies and the oxidation color of the mudstones provide evidence of cyclic deposition. The paleoclimate was the dominant factor controlling the development of the over-flooding lake delta. Due to the frequently alternating wet and dry paleoclimates, the over-flooding lake delta is characterized by the development of a broad upper plain and a lower delta plain. The upper delta plain is characterized by flood channel deposits, whereas the lower delta plain is represented by distributary channel deposits. The transition zone is characterized by the interaction of flood channels and distributary channels. Due to fault activity, the sandbodies of the over-flooding lake delta were juxtaposed against hydrocarbon source rocks, which was favorable for the development of lithologic reservoirs or structural-lithologic reservoirs. The lower delta plain deposits comprise the most favorable reservoirs.

Geochemistry and origin of gas pools in the Gaoqing-Pingnan fault zone, Jiyang Depression

In the surroundings of the Gaoqing-Pingnan fault zone are developed quite a number of gas reservoirs. Based on gas compositions, they can be divided into two groups, i.e., CO2 and CH4. Their composition and isotope geochemistry were dealt with in this study. The CO2 contents range from 60.72%–99.99%, the δ13CCO2 values from -3.41‰– -9.8‰, and the 3He/4He ratios from 4.35×10-6–6.35×10-6 (i.e. R/Ra=4.45–4.35). Based on the data on composition and isotope geochemistry, deep geological background, deep faults and volcanic rocks, it is shown that CO2 ,distributed in the Gaoqing area, mostly originated from mantle-source inorganic matter which is associated with magmatic rocks. The favorable tectonic environment for the formation of CO2 reservoirs is the rift, which is related to great fault-magmatic activity, the formation of CO2 gas pools and their space-time correlation to the most recent magmatic activities. Hydrocarbon gas pools occur in the Huagou area. The CH4 contents are within the range of 88.83%–99.12%, and the δ13CCH4 values, -44.7‰– -54.39‰. This indicates that the hydrocarbon gas resulted from the decomposition of oil-type gas at high temperatures. Volcanic rocks in the CO2 gas pool-and CH4 gas pool-distributed areas show significant differences in Fe2O3 and FeO contents. This has proven that the hydrocarbon gas may have resulted from various chemical reactions. Magmatic activities are the primary reason for the distribution of CO2 and CH4 gas pools in the Gaoqing-Pingnan fault zone.

Carboniferous–Permian marine transgressions in the Jiyang Depression

In recent years,great attention has been paid to oil and gas exploration in the Carboniferous–Permian strata of the Bohaiwan basin,especially the Carboniferous–Permian marine transgression,using data from drilling,outcrops and carbonate acid-insoluble residue experiments together with the tectonic evolutionary history of the peripheral orogenic zones of the North China plate and the Tan-Lu fault zones.The study concludes that marine transgressions took place on six occasions during Carboniferous–Permian time in the Jiyang Depression.The marine transgressions were concentrated in the Late Carboniferous:two marine transgressions occurred in the early Late Carboniferous,and the scale of the first was smaller and the time was shorter than those of the second.The other four marine transgressions happened in the late Late Carboniferous,the first and the fourth of which were larger in scale and longer in time than the second and the third.The seawater came from the Jiaobei area,the eastward part of the Qinling–Dabie residual sea basin,and invaded progressively as a planar flow from south to north and from east to west.These findings have great significance for thorough analysis of the sedimentary characteristics and evolution of the Carboniferous–Permian strata in the Jiyang Depression.

Genetic types and geochemicai characteristics of natural gases in the Jiyang Depression,China

Natural gases were widely distributed in the Jiyang Depression with complicated component composition, and it is difficult to identify their genesis. Based on investigation of gas composition, carbon isotope ratios,light hydrocarbon properties, as well as geological analysis, natural gases in the Jiyang Depression are classified into two types, one is organic gas and the other is abiogenic gas. Abiogenic gas is mainly magmatogenic or mantlederived CO2. Organic gases are further divided into coaltype gas, oil-type gas, and biogas according to their kerogen types and formation mechanisms. The oil-type gases are divided into mature oil-type gas(oil-associated gas)and highly mature oil-type gas. The highly mature oil-type gases can be subdivided into oil-cracking gas and kerogen thermal degradation gas. Identification factors for each kind of hydrocarbon gas were summarized. Based on genesis analysis results, the genetic types of gases buried in different depths were discussed. Results showed that shallow gases(\1,500 m) are mainly mature oil-type gases, biogas, or secondary gases. Secondary gases are rich in methane because of chromatographic separation during migration and secondary biodegradation. Secondary biodegradation leads to richness of heavy carbon isotope ratios in methane and propane. Genesis of middle depth gases(1,500–3,500 m) is dominated by mature oil-type gases.Deep gases(3,500–5,500 m) are mainly kerogen thermal degradation gas, oil-cracking gas, and coal-type gas.

Study on the base-level cycle and the sedimentology of Permian in Jiyang area

The identification of sequence boundaries is the key point for sequence stratigraphicclassification.Both the higher-order sequences and the units within the sequencesare bounded with the key sediments or isochronous surfaces.Eight sequences can be dividedin the whole Permo-Carboniferous strata (the Shiqianfeng Formation is not included)which is from the Benxi Formation,Taiyuan Formation,Shanxi Formation,Xiashihezi Formation,Wanshan Section,and Kuishan Section to the Xiaofuhe Section.Also,differentsystem tracts (lowstand system tract,transgression system tract and highstand systemtract) and some parasequences can be recognized in each sequence.Parasequenceanalysis was on the basis of the division of the base-level cycle.The base-level cycle wasmainly identified according to the change of the water area,which was reflected by thedepositional sequence.The physical characteristic of the strata was reflected by the welllog.It was supplied by the test of the minerals and rocks and the analysis of the microelementin the lab.The paleogeographic characteristic of the lowstand system tract in thesequence Ⅵ is that the east-north part takes the river system as its feature;the south partis the lake system,the river channel spreads from north to south,and the area of theflooding plain is great.The paleogeographic characteristic of the water-transgressive systemtract is that the range of the lake in the south extended distinctively,the range of theriver channel in the east reduced.The coastal shallow lake deposit is the main characteristicin the water-transgressive system tract.The paleogeographic characteristic of thehighstand system tract is similar to the one of the lowstand system tract.

济阳坳陷沾化东部古—中生界潜山构造样式与成藏模式

济阳坳陷古—中生界潜山经历多期挤压、伸展、走滑及剥蚀等构造作用的叠加,以沾化东部潜山为例,利用丰富的钻井与地震资料,在潜山构造层划分的基础上,剖析了潜山构造演化及构造特征,总结了潜山构造样式,建立了油气成藏模式。研究结果表明,晚古生代以来,在多期不同方向、不同性质构造运动的作用下,沾化东部古—中生界潜山经历了4期挤压作用、2期伸展作用、2期走滑作用、4期剥蚀作用,形成了高位、中位和低位3类潜山,发育了伸展、挤压、走滑与剥蚀4类9种构造样式。依据构造样式及潜山地层残留和上覆盖层的差异,建立了3类潜山成藏模式,其油气来源、油气富集层段及富集特征各不相同,其中高位潜山斜坡带上古生界与中生界、中位潜山下古生界和低位潜山中紧靠油源的潜山各层系油气成藏条件最为有利,油气富集程度高,是研究区下一步重点勘探对象。

页岩油藏水平井分段多簇压裂全井段裂缝扩展数值模拟——以济阳坳陷沙河街组为例

济阳坳陷古近系页岩油资源量达40.5×10^(8) t,展现出良好的勘探开发前景。但页岩油储层埋藏较深、构造复杂、非均质性强,页岩油储层水力压裂裂缝扩展规律尚不明确。为准确预测水力压裂裂缝的扩展形态,建立了基于无量纲近似解的裂缝扩展流固耦合模型。根据济阳坳陷页岩油储层地质工程特征,对该区块一口典型的页岩油水平井开展了裂缝扩展模拟,并将微地震和示踪剂监测结果与模拟结果进行了对比。结果表明:模拟缝长与微地震折算缝长的整体趋势基本一致;模拟结果和示踪数据监测结果的吻合度高于其与微地震监测结果的吻合度;在某些井段,示踪剂结果和微地震结果与模拟结果高度一致。该研究可为济阳坳陷页岩油藏压裂方法设计提供指导。

济阳坳陷孤西潜山带构造演化及其对油气差异富集的控制

为明确济阳坳陷孤西潜山带油气差异富集特征,指导下步油气勘探方向优选,综合利用钻井及地震资料,在潜山地质特征分析的基础上,对潜山构造演化及其对油气差异富集的控制作用进行了研究。结果表明,印支期以来,孤西潜山带经历了晚三叠世挤压抬升剥蚀、早—中侏罗世弱挤压到截凸填凹、晚侏罗世挤压抬升剥蚀、早白垩世左行走滑拉张、晚白垩世挤压抬升剥蚀、古近纪右行走滑拉张高位潜山剥蚀等4期挤压、2期拉张、2期走滑、5期剥蚀的演化过程,并于新近纪整体沉降定型,在孤西潜山带形成高位潜山和低位潜山2类潜山,整体具有“NW向断层控带、NE(EW)向断层控山、垒堑相间”的构造格局。多期构造活动作用的叠加,导致2类潜山在源储对接关系、油藏类型和油气富集特征上具有明显差异,高位潜山斜坡带上古生界和中生界地层油藏最为富集,低位潜山各层系均可成藏,且以古生界构造油藏最为富集,同种类型的潜山由于成藏要素配置关系的不同,其油气富集特征也有所差异。埕中、埕东、孤岛等高位潜山斜坡带地层油藏,孤北、垦利等低位潜山下古生界风化壳油藏及内幕构造油藏和上古生界及中生界构造油藏是下步重点勘探目标。

页岩核磁共振横向弛豫时间与孔径分布量化关系及应用

核磁共振横向弛豫时间(T2)常用于表征页岩的全孔径分布特征。为确定T2谱与页岩孔径的量化关系,选取济阳坳陷沙河街组7块页岩样品进行低温氮吸附、核磁共振实验。利用T2几何平均值和孔隙比表面积、孔隙体积之间的关系式,获得T2谱计算孔径分布的关键参数——表面弛豫率。7块页岩样品的表面弛豫率为1.52~3.06 nm/ms,平均值为2.53 nm/ms。由表面弛豫率计算的孔径分布结果与低温氮吸附的NLDFT模型计算结果相似度高,证实了页岩表面弛豫率确定方法和取值的合理性。利用上述方法确定了济阳坳陷典型页岩薄层的孔径分布,结合储层物性和地球化学分析结果,认为页岩中泥质薄层主要起到生-储作用,而纤维状方解石薄层、粉晶方解石薄层和长英质薄层则可以作为储-渗通道。在研究页岩油微观富集、流动机制及评价页岩油“甜点”时,需细化分析不同薄层的孔径分布特征及其生-储-渗作用。