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.

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.

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.

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.

Shale Oil Reservoir Characteristics and Enrichment in the Jiyang Depression, Bohai Bay Basin, East China

Based on the observation of the well cores, thin section and FESEM, combined with X-ray diffraction, physical property testing and geochemical indicators, the reservoir characteristics and the controlling factors of the shale oil enrichment of the Ess 4–Esx 3 shale in the Jiyang depression were detailed analyzed. Studies show that carbonate and clay minerals are dominated in the shale. According to the triangle chart, the TOC content(2% and 4%), carbonate and clay minerals, nine lithofacies have been identified. The reservoir space types are rich in the shale, in which, the laminated fractures, recrystallization intracrystalline pores and organic pores are high-quality reservoir spaces. The shale oil enrichment is mainly determined by the hydrocarbon-producing potential and reservoir capacity. The hydrocarbon-producing capacity is controlled by the organic geochemistry indicators, especially the TOC content for the study area, and the thickness of the organic-rich shale. The reservoir capacity is mainly affected by the lithofacies, the TOC content and the structural activities. In addition, the shale oil production is influenced by the fracability of the shale, which is mainly controlled by the lithofacies, structural activities, formation pressure, etc. The shale oil reservoir evaluation should focus on the TOC content, the thickness of the organic-rich shale, lithofacies and structural factor.

Geochemical characteristics, genetic types, and controlling factors of natural gas in Jiyang Depression, Bohai Bay Basin (eastern China)

The Jiyang Depression is an important oil and gas production zone in the Bohai Bay Basin.Through a systematic investigation of the gas components and stable carbon isotopes,the genetic types of natural gas found in the Jiyang Depression were determined,that is,biogas,oilassociated gas,coal-derived gas,high-mature oil-related gas,and mantle-derived carbon dioxide(CO_(2)).From the results,natural gas in the Jiyang Depression can be divided into four groups.Group I,which is distributed in the northwest area,is the only typical oil-associated gas.Group II,distributed in the northeast area,is dominated by oil-associated gas,and involves biogas,coal-derived gas,and high-mature oil-related gas.Group Ⅲ,distributed in the southeast area,has all genetic types of gas that are dominated by oil-associated gas and have mantle-derived CO_(2).Group IV,distributed in the southwest area,is dominated by biogas and involves coal-derived gas and oil-associated gas.The differences in each group illustrate the lateral distribution of the natural gas types is characterized by the eastern and southern areas being more complex than the western and northern areas,the vertical distribution of gas reservoirs has no obvious evolutionary law.The main controlling factor analysis of the spatiotemporal changes of the gas reservoirs revealed that the synergy of geochemical characteristics,thermal evolution of the Shahejie Formation and Carboniferous-Permian source rocks,and sealing properties of various faults are jointly responsible for determining the gas reservoir spatiotemporal changes.

山东济阳拗陷第三纪玄武岩的铅同位素研究

山东济阳拗陷第三纪玄武岩的Pb同位素组成变化明显:^(206)Pb/^(204)Pb值为16.864～18.361,^(207)Pb/^(204)Pb值为15.268～15.599,^(208)Pb/^(204)Pb值为36.770～39.118。在Pb-Pb和Pb-Sr图上,所有数据点形成良好的线性关系,而且都分布于DMM、EMⅠ和EMⅡ3个地幔端员组分之间。这些特征表明,同位素组成的明显变化应主要归因于玄武岩浆形成过程中地幔源区中不同端员组分之间的混合作用,地壳混染作用影响不明显。

济阳拗陷第三纪玄武岩的Nd-Sr同位素研究

本文报道了济阳拗陷29个第三纪玄武岩的Nd,Sr同位素组成。结果表明,该区早、晚第三纪玄武岩的Nd-Sr同位素组成变化较明显且具有一定的区别:早第三纪玄武岩的εNd值为-2.4～3.3,87Sr/86Sr比值为0.70481～0.70930;晚第三纪玄武岩的εNd值为0.1～2.3,87Sr/86Sr比值为0.70421～0.70530。鉴于εNd与1/Nd及87Sr/86Sr与1/Sr之间不存在相关特征,Nb正异常以及SiO2与MgO,Fe2O3+FeO,P2O5呈负相关,与Al2O3呈正相关,但与K2O不存在相关特征,因此,地壳混染作用并不是第三纪玄武岩同位素组成变化的主要原因。玄武岩87Sr/86Sr比值的升高是由热液蚀变造成的,而εNd值的变化则归因于源区混合。如果热液蚀变作用没有发生,这些玄武岩的所有数据点在Nd-Sr相关图上将可能位于地幔系列内部。这表明第三纪玄武岩主要是由DMM和EMI两个端员组分不同程度混合形成,EMII的贡献是次要的。

济阳拗陷第三纪玄武岩的氧同位素

研究了山东济阳拗陷 2 9个第三纪玄武岩样品的氧同位素组成。结果表明 ,这些玄武岩的全岩氧同位素组成变化明显 ,δ18O值为 6 .3‰～ 12 .2‰。其中 ,蚀变轻微的晚第三纪玄武岩的δ18O值为 6 .3‰～ 7.9‰ ,与正常大陆玄武岩的值 (5 .0‰～ 7.4‰ )相似 ;而蚀变明显的早第三纪玄武岩的δ18O值为 6 .7‰～ 12 .2‰ ,并且 90 %以上样品的δ18O值都大于 7.5‰。结合岩石学与岩石化学研究 ,早第三纪玄武岩δ18O值不同程度升高是由低温雨水热液蚀变 (碳酸盐化 )

Seismic description and fluid identification of thin reservoirs in Shengli Chengdao extra-shallow sea oilfield

The meandering channel deposit of the upper member of Neogene Guantao Formation in Shengli Chengdao extra-shallow sea oilfield is characterized by rapid change in sedimentary facies.In addition,affected by surface tides and sea water reverberation,the double sensor seismic data processed by conventional methods has low signal-to-noise ratio and low resolution,and thus cannot meet the needs of seismic description and oil-bearing fluid identification of thin reservoirs less than 10 meters thick in this area.The two-step high resolution frequency bandwidth expanding processing technology was used to improve the signal-to-noise ratio and resolution of the seismic data,as a result,the dominant frequency of the seismic data was enhanced from 30 Hz to 50 Hz,and the sand body thickness resolution was enhanced from 10 m to 6 m.On the basis of fine layer control by seismic data,three types of seismic facies models,floodplain,natural levee and point bar,were defined,and the intelligent horizon-facies controlled recognition technology was worked out,which had a prediction error of reservoir thickness of less than 1.5 m.Clearly,the description accuracy of meandering channel sand bodies has been improved.The probability semi-quantitative oiliness identification method of fluid by prestack multi-parameters has been worked out by integrating Poisson’s ratio,fluid factor,product of Lame parameter and density,and other prestack elastic parameters,and the method has a coincidence rate of fluid identification of more than 90%,providing solid technical support for the exploration and development of thin reservoirs in Shengli Chengdao extra-shallow sea oilfield,which is expected to provide reference for the exploration and development of similar oilfields in China.

第三纪济阳盆地大地构造性质及其演化

依据中-小型构造、深部构造、地温场、岩浆活动、沉积建造、地貌和水文特征判断,早第三纪济阳盆地大地构造性质属大陆裂谷,其演化经历了前裂谷期裂谷孕育、裂谷期初始扩张裂陷—强烈扩张裂陷—晚期扩张裂陷—衰亡和后裂谷期拗陷漫覆6个阶段,晚第三纪为拗陷盆地.