Composite Sand Bodies Architecture of Deep-Water Turbidite Channels in the Niger Delta Basin

Deep-water turbidite channels have attracted much attention as a focused issue in petroleum exploration and development. Extensive studies have been performed on the architecture of turbidite channels, and most researches have focused on their geometric shapes, sedimentary processes and controlling factors. However, little attention has been paid to the distribution patterns, distribution laws and quantitative studies of composite sand bodies of turbidite channels. Taken one slope area of the Niger Delta Basin as an example, this study conducted a semi-quantitative to quantitative analysis on architecture of composite sand bodies of turbidite channels based on cores, well logging and seismic surveys. It is shown that turbidite channel systems can be classified as confined and unconfined channel systems. For confined channel systems, the vertical evolution process involves four stages. The sinuosity of a channel system is controlled by slope, with a negative power function relationship between them. When slope gradient reaches four degrees, the channel system is nearly straight. Based on the migration direction and migration amount of single channels within channel complexes, channel composite patterns can be divided into four classes（the lateral composite, en-echelon composite, swing composite and vertical composite） and several subclasses. Various channel composite patterns show specific distribution laws spatially. For meandering channel complexes at the middle-late evolution stage of confined channel systems, the lateral migration amongst single channels shows the features of integrity and succession. The sinuosity of single channels in the late period is greater than that in the early period, and cut-offs may occur locally when the sinuosity is larger than five degrees. This study provides a better understanding for the geological theory of deep-water sedimentary, and also improves exploitation benefits of this type of reservoirs.

Geochemistry and origins of hydrogen-containing natural gases in deep Songliao Basin,China:Insights from continental scientific drilling

The different reservoirs in deep Songliao Basin have non-homogeneous lithologies and include multiple layers with a high content of hydrogen gas.The gas composition and stable isotope characteristics vary significantly,but the origin analysis of different gas types has previously been weak.Based on the geochemical parameters of gas samples from different depths and the analysis of geological settings,this research covers the diverse origins of natural gas in different strata.The gas components are mainly methane with a small amount of C_(2+),and non-hydrocarbon gases,including nitrogen(N_(2)),hydrogen(H_(2)),carbon dioxide(CO_(2)),and helium(He).At greater depth,the carbon isotope of methane becomes heavier,and the hydrogen isotope points to a lacustrine sedimentary environment.With increasing depth,the origins of N_(2)and CO_(2)change gradually from a mixture of organic and inorganic to inorganic.The origins of hydrogen gas are complex and include organic sources,water radiolysis,water-rock(Fe^(2+)-containing minerals)reactions,and mantle-derived.The shales of Denglouku and Shahezi Formations,as source rocks,provide the premise for generation and occurrence of organic gas.Furthermore,the deep faults and fluid activities in Basement Formation control the generation and migration of mantle-derived gas.The discovery of a high content of H_(2)in study area not only reveals the organic and inorganic association of natural-gas generation,but also provides a scientific basis for the exploration of deep hydrogen-rich gas.

Geochemical characteristics and origins of natural gases in the eastern Cote d’Ivoire Basin,West Africa

The gas sources in the eastern Cote d’Ivoire Basin(Tano Basin)are seldom reported and remain controversial due to multiple sets of potential source rocks and poorly documented geochemical characteristics of natural gases.The marine source rock potential from the Upper Albian to Turonian as well as the molecular composition and the stable carbon isotope composition of natural gases in the eastern Cote d’Ivoire Basin were studied in detail to investigate the origins of natural gases.The total organic carbon(TOC),hydrogen index(HI),and generation potential(S_(1)+S_(2))of source rocks indicate that both sapropelic source rocks and humic source rocks developed during the late Albian,whereas sapropelic source rocks developed during the Cenomanian and the Turonian.The normal order ofδ^(13)CH_(4)<δ^(13)C_(2)H6<δ^(13)C_(3)H_(8)(δ^(13)C_(1)<δ^(13)C_(2)<δ^(13)C_(3)),the relationship between C_(2)/C_(3)molar ratio andδ^(13)C_(2)-δ^(13)C_(3),and the plot ofδ^(13)C_(1)versus C_(1)/(C_(2)+C_(3))collectively show that the natural gases are thermogenic due to the primary cracking of kerogen,including the typical oil-associated gases from Well D-1,the mixed oil-associated gases and coal-derived gases from Well G-1 and Well L-1.Based on the plot ofδ^(13)C_(1)versusδ^(13)C_(2)and the established relationship betweenδ^(13)C_(1)and equivalent vitrinite reflectance(Ro),we proposed that the natural gases are in a mature stage(Ro generally varies from 1.0%to 1.3%).Combined with results of basin modelling and oil-to-source correlation,the transitional to marine source rocks during the late Albian were thought to have made a great contribution to the natural gases.Our study will make a better understanding on petroleum system in the eastern Cote d’Ivoire Basin.

基于浅震和钻探的中卫盆地北缘隐伏断层定位及活动性研究

为查明宁夏中卫盆地北缘隐伏断层(河滩-郭滩隐伏断层)的构造特征、展布情况及活动时代,采用浅层地震勘探方法获得该隐伏断层的产状、性质、位置和上断点埋深。在此基础上,利用钻孔联合剖面探测出断层的准确位置和更可靠的上断点埋深,并测试样品年代确定该隐伏断层的最新活动时代。结果表明,河滩-郭滩隐伏断层是一条走向近EW、倾向S的正断层,长度约12.5 km;断层上断点埋深在38 m以下,视倾角75°;最新活动时代为中更新世中晚期,晚更新世以来不活动,不属于活动断层。

鄂尔多斯盆地东北缘神府区块南部8+9号煤层地应力评价方法与应用

现今地应力方向和大小影响着煤层水力压裂缝的延伸,是煤层气井网部署、压裂设计的重要地质参数。合理评价煤层现今地应力方向和大小,对煤层气勘探开发具有重要意义。以鄂尔多斯盆地东北缘神府区块南部8+9号煤层现今地应力方向和大小为研究内容,基于阵列声波测井、微地震监测和成像测井,评价煤层及顶底板现今最大水平主应力方向;在注入—压降实测地应力参数约束下,确定煤层组合弹簧模型参数,并计算煤层现今地应力大小。结果显示,研究区东部8+9号煤层及顶底板现今最大水平主应力方向整体近NNE向,西部最大水平主应力方向可能受大量的压裂改造和不活动断层周围应力场扰动,发生不同方向偏转;20口井地应力测井计算结果显示,垂深1902~2181 m的8+9号煤层垂向主应力范围47~54 MPa,最小水平主应力范围35~44 MPa;最大水平主应力范围42~50 MPa,侧压系数小于1,表现为正断层地应力状态。研究区东部NNE向最大水平主应力方向是经历中新生代印支期SN向挤压、燕山期NNW向挤压和喜马拉雅期NNE向挤压的继承。考虑东部裂缝预测区叠加不同构造阶段平均NNW走向的天然裂缝的分布和NNE最大水平主应力方向正断层地应力状态下NNE向竖直压裂缝的延伸模式,以提高水平井大规模极限体积压裂产量为目标,建议在垂直现今NNE向最大水平主应力方向和垂直NNW向平均天然裂缝走向的水平井方位区间内,综合利用天然裂缝产能和人工压裂缝产能进行水平丛式井布井,并进一步对地应力方向和天然裂缝参数进行精细化表征,以指导施工压裂设计,提高煤层气产量。

吐哈盆地台北凹陷水西沟群煤系烃源岩沉积有机相研究

吐哈盆地台北凹陷蕴含丰富的油气资源,侏罗系水西沟群煤系烃源岩作为区内主力烃源岩发育层位,生烃潜力巨大。然而对于水西沟群煤系烃源岩有机相类型及其与沉积环境的对应关系尚无明确定论,制约了整个凹陷乃至盆地范围油气资源勘探部署。为实现吐哈盆地水西沟群煤系烃源岩的精细划分与评价,基于显微组分、总有机碳(TOC)含量、生烃潜量(S_(1)+S_(2))等地球化学测试结果,建立了研究区煤系烃源岩沉积有机相划分标准,明确了有机相类型、生烃潜力及其与沉积相的对应关系。研究表明,台北凹陷水西沟群煤系烃源岩沉积有机相类型分为五类,即湖相强覆水高镜质组有机相、湖相覆水中高镜质组有机相、三角洲平原覆水中高镜质组有机相、三角洲平原弱覆水中镜质组有机相和三角洲前缘弱覆水低镜质组有机相。湖相强覆水高镜质组有机质丰度高且生烃潜力最强,TOC含量为5.05%~18.31%,S_(1)+S_(2)为6.35~20.93 mg/g,镜质组含量大于80%;其次为湖相覆水中高镜质组有机相和三角洲平原覆水中高镜质组有机相,二者TOC含量分别为3.83%~17.68%和2.30%~7.41%,S_(1)+S_(2)平均分别为6.35 mg/g和4.48 mg/g,镜质组含量均介于50%~80%;三角洲前缘弱覆水低镜质组有机相的生烃潜力最差,TOC含量平均仅为1.3%,S_(1)+S_(2)平均为4.1 mg/g。研究成果为预测台北凹陷水西沟群煤系优质烃源岩分布并准确评价其油气资源潜力提供了重要依据。

Hydrological and water cycle processes of inland river basins in the arid region of Northwest China

The increasing shortage in water resources is a key factor affecting sustainable socio-economic development in the arid region of Northwest China(ARNC). Water shortages also affect the stability of the region's oasis ecosystem. This paper summarizes the hydrological processes and water cycle of inland river basins in the ARNC, focusing on the following aspects: the spatial-temporal features of water resources(including air water vapor resources, runoff, and glacial meltwater) and their driving forces; the characteristics of streamflow composition in the inland river basins; the characteristics and main controlling factors of baseflow in the inland rivers; and anticipated future changes in hydrological processes and water resources. The results indicate that:(1) although the runoff in most inland rivers in the ARNC showed a significant increasing trend, both the glaciated area and glacial ice reserves have been reduced in the mountains;(2) snow melt and glacier melt are extremely important hydrological processes in the ARNC, especially in the Kunlun and Tianshan mountains;(3) baseflow in the inland rivers of the ARNC is the result of climate change and human activities, with the main driving factors being the reduction in forest area and the over-exploitation and utilization of groundwater in the river basins; and(4) the contradictions among water resources, ecology and economy will further increase in the future. The findings of this study might also help strengthen the ecological, economic and social sustainable development in the study region.

Origin and Accumulation of Natural Gases in the Upper Paleozoic Strata of the Ordos Basin in Central China

The natural gases in the Upper Paleozoic strata of the Ordos basin are characterized by relatively heavy C isotope of gaseous alkanes with δ^13C1 and δ^13C2 values ranging mainly from -35‰ to -30‰ and -27‰ to -22‰, respectively, high δ^13C excursions （round 10） between ethane and methane and predominant methane in hydrocarbon gases with most C1/（C1-C5） ratios in excess of 0.95, suggesting an origin of coal-derived gas. The gases exhibit different carbon isotopic profiles for C1-C4 alkanes with those of the natural gases found in the Lower Paleozoic of this basin, and believed to be originated from Carboniferous-Permian coal measures. The occurrence of regionally pervasive gas accumulation is distinct in the gently southward-dipping Shanbei slope of the central basin. It is noted that molecular and isotopic composition changes of the gases in various gas reservoirs are associated with the thermal maturities of gas source rocks. The abundances and j13C values of methane generally decline northwards and from the basin center to its margins, and the effects of hydrocarbon migration on compositional modification seem insignificant. However, C isotopes of autogenetic calcites in the vertical and lateral section of reservoirs show a regular variation, and are as a whole depleted upwards and towards basin margins. Combination with gas maturity gradient, the analysis could be considered to be a useful tool for gas migration.

Evolution and Structural Style of Tianshan and Adjacent Basins， Northwestern China

The Tianshan orogenic belt has a W-shape, composed of the V-shape Southern Tianshan and Northern Tianshan with different orogenic models .The Southern Tianshan broke off from the Sinian, forming a passive continental margin and ocean, and closed during Silurian and Devoaian. It belongs to the Wilson cycle orogenic model. The net duration is about 400 My.The Northern Tianshan began back-arc spreading during Devonian, forming the Devonian-Carboniferous marginal sea, and dosed during Late Carboaiferous. It belongs to the non-Wilson cycle orogeulc model or back-arc orogenic model. The duration is about 100 My .Deformation of the foreland fold-thrust belt occurred in two stages: in the early stage, folds and thrusts were formed by wedge-thrusting and lateral compression, while in the later stage, folds, gravitational normal faults and reveal faults were formed by the uplift of the Tianshan range and by gravity-gliding.

Mineral composition and organic geochemistry of the Lower Cretaceous Xiagou Formation source rock from the Qingxi Sag,Jiuquan Basin, Northwest China

The Lower Cretaceous Xiagou Formation contains the major source rocks for the crude oils discovered in the Qingxi Sag and the South Uplift in the Jiuquan Basin, northwestern China. The Xiagou Formation source rock was formed in a closed,anoxic, reducing, alkaline lacustrine environment with a high salinity. Its high content of brittle minerals is favorable for the fracturing of reservoirs in source rock formations in the Qingxi Sag. The Xiagou Formation contains a great number of fair to excellent source rocks, and their organic matter（OM） came chiefly from plankton/algae and high plants as well as possibly bacterial organisms. The Xiagou Formation source rocks mainly contain Type II OM and some Type III and Type I OM, with good oil-generating potential. The source rock maturity is mainly in the early-mature and mature stages, and its Rovalue corresponding to oil peak is about 0.8%, which is lower than classic oil peak Rovalue of 1.0%; therefore, a great deal of hydrocarbon was generated before the classic oil peak Ro= 1.0%. Mature source rock in the Xiagou Formation tends to be distributed in the older members and at a greater depth. There is a better exploration potential of tight oil in the deep Qingxi Sag.

Vegetation composition and distribution on the northern slope of Karlik Mountain to Naomaohu basin,East Tianshan Mountains

This paper reports the characteristics of plant flora in the region of the northern slope of Karlik Mountain to Naomaohu basin, based on field investigation of the vegetation and referring to relevant literature. The results show that the flora of the study area mainly consists of communities of single species or a limited number of species, genera and families. The flora composition is marked by the phenomenon of dominant families and genera; the temperate element occupies a dominant position, while in terms of the genera the Tethys element is an important component. Areal-types of the species are dominated by the floral element of Asian Central-part with xerophytic characteristic, and the life-forms of plants are mainly perennial and herbaceous. These characteristics reflect that the compositions of the species in this region possess both ancient and young elements. Analysis of the relationship between the species composition, plant community diversity and altitude gradient, we found that the structure of the vegetation has an obvi- ous vertical distribution. The lower and higher altitude areas, where the climate conditions are relative in- clement, are mainly occupied by the plant communities with simple structure and single dominant popula- tion, while the species richness in the mid-altitude area increases with favorable temperature and precipi- tation. Consequently, the species diversity and evenness indices show single-peak distribution with increasing elevation （about 〈 2500 m）, while the dominance indices decrease in elevation from 500 m to 2500 m and increase in elevation of 〉 2500 m.

Effect of Land Use on Soil Properties in Debris Flow Bottomland:A Case Study at Xiaojiang Basin, Yunnan

In order to understand the effect of different land use on soil physics and nutrients properties of the debris flow bottomland, a case study at Daqing gully （in Xiaojiang Basin, Yunnan） was conducted in 2004. Soil samples were taken at depth of 0-10,10-20,20-40,40-60,60-80 cm under three land use patterns crop bottomland （CL）, forest bottomland （FL）, and barren bottomland（BL）. The results showed that the developing bottomland to CL promoted soil toaccumulate total phosphorus （TP） and available phosphorus （AP）, pH value transferred from neutral to alkalescency, and organic matter decreased significantly. Furthermore, the contents of total nitrogen （TN） and available nitrogen （AN） in CL were lower than that of FL and BL because the growth of crops consumed more nutrients in soil. The results also showed that the contents of TP, AP and available potassium （AK） in soil were positively correlated with soil particle.

Characteristics and Origin of Yacheng Gas Field in Qiongdongnan Basin,South China Sea

The Yacheng gas field lies in the foot wall of the No. 1 fault, the boundary fault between the Yinggehai and Qiongdongnan basins. An overpressured system developed in the Meishan Formation near the No. 1 fault in the gas field and in the adjacent Yinggehai basin. Away from this fault into the Qiongdongnan basin, the overpressure diminishes. Below 3 600 m in the gas field, an obvious thermal anomaly occurs. The gases show obvious compositional heterogeneities which reflect reservoir filling process and origin of the gas field. The gas field was charged from both the Qiongdongnan and the Yinggehai basins but mainly from the former. Hydrocarbons sourced from the Qiongdongnan basin have relatively low maturities while hydrocarbons from the Yinggehai basin have relatively high maturities.

Lithofacies and Pore Structure of Fine-grained Sedimentary Rocks of Qing-1 Member of Cretaceous in the Southern Songliao Basin

Fine-grained sedimentary rocks often contain hydrocarbon and mineral resources.Compared with coarse-grained sedimentary rocks,fine-grained sedimentary rocks are less studied.To elucidate the lithofacies and pore structure of lacustrine fine-grained rocks,the 340.6 m continuous core of Cretaceous Qing-1 Member from five wells in the southern central depression of the Songliao Basin was analyzed using X-ray diffraction,Rock-Eval pyrolysis,low-temperature nitrogen adsorption,high-pressure mercury injection,argon ion polishing-field emission scanning electron microscopy,and laser scanning confocal microscopy.Based on mineral compositions,organic matter abundance and sedimentary structure,lacustrine fine-grained rocks in the study area were divided into ten lithofacies,with their spatial distributions mainly influenced by tectonic cycle,climate cycle and provenance.Furthermore,pore structure characteristics of different lithofacies are summarized.(1)The siliceous mudstone lithofacies with low TOC content and the laminated/layered claybearing siliceous mudstone lithofacies with medium TOC content have the highest proportion of first-class pores(diameter>100 nm),making it the most favourable lithofacies for the accumulation of shale oil and shale gas.(2)The massive claybearing siliceous mudstone lithofacies with low TOC content has the highest proportion of second-class pores(diameter ranges from 10 to 100 nm),making it a favourable lithofacies for the enrichment of shale gas.(3)The massive clay-bearing siliceous mudstone lithofacies with high TOC content has the highest proportion of third-class pores(diameter<10 nm),making it intermediate in gas storage and flow.Laser confocal oil analysis shows that the heavy component of oil is mainly distributed in the clay lamina,while the light part with higher mobility is mainly concentrated in the silty lamina.

Mineralogical and geochemical characteristics of Miocene pelitic sedimentary rocks from the south-western part of the Pannonian Basin System(Croatia):Implications for provenance studies

Fifty-two samples of Miocene pelitic sedimentary rock from outcrops on Medvednica,Moslavacka Gora and Psunj Mts.,and boreholes in the Sava Depression and the Pozega Sub-depression were investigated.These sediments formed in different marine（with normal and reduced salinity）,brackish,and freshwater environments,depending on the development stage of the Pannonian Basin System.Carbonate minerals,clay minerals and quartz are the main constituents of all pelitic sedimentary rocks,except in those from Moslavacka Gora Mt in which carbonate minerals are not present.Feldspars,pyrite,opal-CT,and hematite are present as minor constituents in some rocks.Besides calcite,dependent on the sedimentary environment and diagenetic changes,high-magnesium calcite,aragonite,dolomite and ankerite/Cadolomite are also present.Smectite or illite-smectite is the main clay minerals in the samples.Minor constituents,present in almost all samples,are detrital illite and kaolinite.In some samples chlorite is also present in a low amount.Major elements,trace elements and rare earth elements patterns used in provenance analysis show that all analysed samples have a composition similar to the values of the upper continental crust（UCC）.The contents of major and trace elements as well as SiO2/Al2O3,K2O/Al2O3,Na2O/K2O,Eu/Eu＊,La/Sc,Th/Sc,La/Co Th/Co,Th/Cr,Ce/Ce＊ and LREE/HREE ratios,show that the analysed pelitic sedimentary rocks were formed by weathering of different types of mostly acidic（silicic）,i.e.felsic rocks.

Origin and depositional environments of source rocks and crude oils from Niger Delta Basin: Carbon isotopic evidence

Thirty-nine crude oils and twenty-one rock samples from Niger Delta Basin,Nigeria have been characterized based on their isotope compositions by elemental analysis-isotope ratio mass spectrometry and gas chromatography-isotope ratio mass spectrometry.The bulk carbon isotopic values of the whole rock extracts,saturate and aromatic fractions range from–28.7‰to–26.8‰,–29.2‰to–27.2‰and–28.5‰to–26.7‰,respectively while the bulk carbon isotopic values of the whole oils,saturate and aromatic fractions range from–25.4‰to–27.8‰,–25.9‰to–28.4‰and–23.5‰to–26.9‰,respectively.The average carbon isotopic compositions of individual alkanes(nC12-nC33)in the rock samples range from–34.9‰to–28.2‰whereas the average isotopic values of individual n-alkanes in the oils range from–31.1‰to–23.8‰.Theδ13C isotope ratios of pristane and phytane in the rock samples range from–29.2‰to–28.2‰and–30.2‰to–27.4‰respectively while the pristane and phytane isotopic values range from–32.1‰to–21.9‰and–30.5‰to–26.9‰,respectively.The isotopic values recorded for the samples indicated that the crude oils were formed from the mixed input of terrigenous and marine organic matter and deposited under oxic to sub-oxic condition in lacustrine-fluvial/deltaic environments.The stable carbon isotopic compositions were found to be effective in assessing the origin and depositional environments of crude oils in the Niger Delta Basin.

Organic geochemical characteristics of Eocene crude oils from Zhanhua Depression,Bohai Bay Basin,China

Geochemical studies of crude oil and source rock play an important role in future exploration in Zhanhua Depression.In this study,thirty-one oil samples collected from Shahejie Formation in Zhanhua Depression,Bohai Bay Basin,NE China have been geochemically analyzed and their organic geochemical characteristics have been applied to differentiate groups of oils.These oil samples can be classified into two families based on multiple biomarker proxies and stable carbon isotopic values.FamilyⅠis characterized by a low ratio of pristane over phytane(Pr/Ph<0.7),a relatively high ratio of phytane over n-C18(Ph/n-C18),varying ratios of gammacerane over C30 hopane(Ga/C30H)and C22/C21 tricyclic terpane,and a low ratio of C19/C23 tricyclic terpane.FamilyⅡis marked by a relatively high Pr/Ph ratio(0.7-1.6),relative low ratios of Ph/n-C18 and C22/C21 tricyclic terpane,and avarying ratio of C19/C23 tricyclic terpane.Both familiesⅠandⅡwithin these crude oils can be subdivided into two families based on different values of stable carbon isotopic composition of individual n-alkanes.Moreover,the potential source rocks of oil samples in FamilyⅠand FamilyⅡwere likely derived from the upper Es4 member and Es3 member,respectively,based on the correlation of organic geochemical characteristics of the oils and source rocks.The results of oil-source rock correlation provide insight into the process from oil generation to migration and to final accumulation,providing a better understanding of factors controlling oil-gas distribution for prediction of sweet spots.

Carbon and oxygen isotopic composition of carbonate cements of different phases in terrigenous siliciclastic reservoirs and significance for their origin:A case study from sandstones of the Triassic Yanchang Formation,southwestern Ordos Basin,China

Early carbonate cements in the Yanchang Formation sandstones are composed mainly of calcite with relatively heavier carbon isotope(their δ18O values range from-0.3‰--0.1‰) and lighter oxygen isotope(their δ18O values range from-22.1‰--19.5‰).Generally,they are closely related to the direct precipitation of oversaturated calcium carbonate from alkaline lake water.This kind of cementation plays an important role in enhancing the anti-compaction ability of sandstones,preserving intragranular volume and providing the mass basis for later disso-lution caused by acidic fluid flow to produce secondary porosity.Ferriferous calcites are characterized by relatively light carbon isotope with δ13C values ranging from-8.02‰ to-3.23‰,and lighter oxygen isotope with δ18O values ranging from-22.9‰ to-19.7‰,which is obviously related to the decarboxylation of organic matter during the late period of early diagenesis to the early period of late diagenesis.As the mid-late diagenetic products,ferriferous calcites in the study area are considered as the characteristic authigenic minerals for indicating large-scaled hydrocarbon influx and migration within the clastic reservoir.The late ankerite is relatively heavy in carbon isotope with δ13C values ranging from-1.92‰ to-0.84‰,and shows a wide range of variations in oxygen isotopic composition,with δ18O values ranging from-20.5‰ to-12.6‰.They are believed to have nothing to do with decarboxylation,but the previously formed marine carbonate rock fragments may serve as the chief carbon source for their precipitation,and the alkaline diagenetic environment at the mid-late stage would promote this process.

Mineral characteristics and their geological significance of black shales in southeastern Ordos Basin by X-ray diffraction analysis

X-ray diffraction analysis of black shale of Upper Triassic Member Chang 7 of the Yanchang Formation in southeastern Ordos Basin showed that black shales were deposited in brackish, strongly reducing, semi-deep-deep lacustrine facies, and mainly composed of quartz, feldspar, carbonate(dolomite), clay minerals(illite and illite/smectite) and a certain amount of pyrite. The mineral composition characteristics of this set of black shales are similar to those of highly productive shale gas in North America, for example shallow burial, low clay mineral and abundant brittle mineral, so the strata are conducive to the development of cracks and fractures. Thus, this area is favorable for shale oil/gas exploration and development.

Reservoir Geochemistry of the Kuche Petroleum System in the Tarim Basin, China

The geochemical characteristics of crude oils and reservoir core extracts from the Kuche petroleum system are described and studied systematically by means of various geochemical techniques and methods to acquire molecular information. The results suggest crude oils from the petroleum system can be divided into two groups: marine oils and non-marine oils. The former represents the dominant oils found in the area. Tar mats were firstly discovered and determined accurately in terrestrial oil and gas reservoirs, with Lower Tertiary sandstone reservoirs in the Yaha oilfield of the Tarim Basin. However, based on the ratio of 20S/(20S+20R)C-29 sterane as a maturity parameter, lacustrine oils filled into the Tertiary reservoirs in the direction toward the western part of the petroleum system. In contrast, according to the fact that methylcyclohexane indices of eastern oils are greater than those of western oils, the location in which coal-generated oils filled into the Tertiary reservoirs lies in the eastern part of the petroleum system.