Guided by the analysis of source-to-sink system,this study investigates the Paleogene Oligocene Lingshui Formation in the Qiongdongnan Basin by comparing the geological characterizes in land and sea areas and integrat...Guided by the analysis of source-to-sink system,this study investigates the Paleogene Oligocene Lingshui Formation in the Qiongdongnan Basin by comparing the geological characterizes in land and sea areas and integrating outcrop,core,drilling,logging and 3D seismic data,to systematically analyze the characteristics of the source,transport pathway,and sink during the deposition of Lingshui Formation,and reveal the patterns,controlling factors and petroleum geologic significance of the source-to-sink systems.The results are obtained in five aspects.First,during the fault-depression transition,the Qiongdongnan Basin received sediments from the provenances presenting as segments in east-west and zones in north-south,primarily with the Indosinian granites in the Shenhu Uplift in the east and the Yanshanian granites in the west.Overall,the sources are young in the southern and northern parts and old in the interior of the basin.Second,three types of sediment transport pathways are identified:paleo-valleys,fault troughs and trough-valley transitional zones.Third,based on differences in sediment supply modes,the unique source-to-sink systems during the fault-depression transition in marine rift basins are categorized into three types:exogenous,endogenous and composite.Fourth,the characteristics of these source-to-sink systems are primarily controlled by provenance,paleogeomorphology,and sea-level changes.Provenance lithology and scale dictated the composition and volume of sedimentary deposits.Paleogeomorphology influenced erosion intensity in the provenance and the development of paleodrainage systems,thereby affecting the distribution and types of sedimentary systems.Additionally,sea-level changes decided the extent of the provenance,but also regulated the sediment distribution patterns through oceanic processes such as waves and tides.Fifth,the exogenous source-to-sink systems may form large-scale reservoir bodies,the endogenous systems develop secondary pores due to presence of soluble minerals,and the composite systems demonstrate reservoir properties varying from area to area.展开更多
Based on a large amount of basic research and experimental analysis data from Shengli Oilfield,Bohai Bay Basin,guided by the theory of whole petroleum system,the distribution of sedimentary systems,the distribution an...Based on a large amount of basic research and experimental analysis data from Shengli Oilfield,Bohai Bay Basin,guided by the theory of whole petroleum system,the distribution of sedimentary systems,the distribution and hydrocarbon generation and expulsion process of source rocks,the variation of reservoir properties,and the control of fracture systems on hydrocarbon accumulation in the Paleogene of the Jiyang Depression,Boahai Bay Basin,were systematically analyzed,and the geological characteristics of the whole petroleum system in the rift basin were identified.Taking the Dongying Sag as an example,combined with the distribution of discovered conventional,tight,and shale oil/gas,a hydrocarbon accumulation model of the fault-controlled whole petroleum system in rift basin was proposed,and the distribution patterns of conventional and unconventional oil and gas reservoirs in large geological bodies horizontally and vertically were clarified.The research results show that paleoclimate and tectonic cycles control the orderly distribution of the Paleogene sedimentary system in the Jiyang Depression,the multi-stage source rocks provide sufficient material basis for in-situ shale oil/gas accumulation and other hydrocarbon migration and accumulation,the changes in reservoir properties control the dynamic threshold of hydrocarbon accumulation,and the combination of faults and fractures at different stages controls hydrocarbon migration and accumulation,and in-situ retention and accumulation of shale oil/gas,making the whole petroleum system in the rift basin associated,segmented and abrupt.The above elements are configured to form a composite whole petroleum system controlled by faults in the Paleogene of the Jiyang Depression.Moreover,under the control of hydrocarbon accumulation dynamics,a whole petroleum system can be divided into conventional subsystem and unconventional subsystem,with shale oil,tight oil and conventional oil in an orderly distribution in horizontal and vertical directions.This systematic understanding is referential for analyzing the whole petroleum system in continental rift basins in eastern China.展开更多
Typical reefs in the Paleogene and early Neogene strata of the Qaidam Basin, Tibetan Plateau, China, reveal their internal structures and sedimentation environments and consist mainly of algal reef, stromatolite reef ...Typical reefs in the Paleogene and early Neogene strata of the Qaidam Basin, Tibetan Plateau, China, reveal their internal structures and sedimentation environments and consist mainly of algal reef, stromatolite reef and thrombolite reef with distinct reef structures, fore-reef, back-reef and reef-plateau. The fore-reef is characterized by a combination of pinnacle reef, thrombolite and algal reef. The back reef is composed of stromatolite reef and algal reef. The pinnacle reefs (micro-atoll), most of which are several tens of centimeters in diameter (whereas some exceptionally big ones are over 200 cm in diameter), and several tens of centimeter to 2 m in height, are situated on the far front-edge of the reef; the pinnacle reef is also often of recumbent form with a gravel-filled circular hole in the center. The algal reef is in the form of dome and irregular beds, and filled with algal detritus, ostracodes, spirorbis fossils, ooid and terrigenous debris, and worm traces; cavities and scour marks are often developed. The algal reef is gray commonly when fresh and weathers to a brown color. The lacustrine thrombolite in the Qaidam Basin is light gray or deep gray when fresh, white-gray or brown when weathered, dense and homogeneous with abundant pores filled by oil and bitumen. Observed under the microscope, the thrombolite consists mainly of brown or brown-black clots with a little algal debris, ooid, pellet, ostracodes, spirorbis fossils and terrigenous debris, in some cases, terrigenous debris, even gravel, is abundant. Many features of the thrombolite suggest that it is formed in a high-energy envkonment. The stromatolite reefs developed on the lacustrine algal reef in the Qaidam Basin are very complex whether in shape or in internal structure. The simplest ones form laminated layers and the most complex ones have intensely branching structures. The size is also variable.展开更多
This paper was conducted on the shale reservoir in the Dongying depression in the Shahejie Formation of Paleogene. Based on detailed core description, rock thin sections, argon ion polishing, scanning electron microsc...This paper was conducted on the shale reservoir in the Dongying depression in the Shahejie Formation of Paleogene. Based on detailed core description, rock thin sections, argon ion polishing, scanning electron microscopy（SEM） analysis, CT scanning and carbon-oxygen isotopic test, the formation mechanism of the inter-laminar fractures（or seams） and their development conditions were discussed by comprehensive analysis of the diagenetic evolution features and the reservoir space evolution characteristics. The results show that the laminated composite pattern in Dongying depression was dominated by vertical distribution of laminated calcite and clay minerals. Contrasted to the traditional understanding, development degree of inter-laminar fractures was much lower. Pure fluid between layers cannot exist without framework minerals, and the pre-existing well connected pore or horizontal overpressure micro seam was favorable paths of fluid migration. From the points of inter-laminar fractures origin mechanism and its evolution, the so called seams, were much more complex than traditional understanding that hydrocarbon generation raised the pore pressure and led to the parallel microfractures. But the inter-laminar fractures had little relationship with that whether the lamination was developed or bedding boundary was clear or not. In fact, the shale reservoir inter-laminar fractures were not rigorous fracture. They were controlled by pre-existing inter-granular pore（or seam） or dissolved pore, which distributed along carbonate laminae boundary and were connected by later super pressure, dissolution and the seepage force. And the development conditions were burial depth（bigger than 3 000 m） and the Ro value（〉0.6%）. Discussion on its origin and evolution has important petroleum geological significance on optimizing reservoir segment and favorable target areas selection.展开更多
In recent years, deep water areas have become popular exploration fields because of their abundant hydrocarbon resource potential. There are only relatively poor planar seismic profiles and no wells for deepwater area...In recent years, deep water areas have become popular exploration fields because of their abundant hydrocarbon resource potential. There are only relatively poor planar seismic profiles and no wells for deepwater areas of the Lingshui Formation in the Qiongdongnan Basin. A lot of faults developed and strata are fragmented due to high temperatures and high pressure, and this has resulted in dim sequence boundaries. Based on seismic data of the deepwater area and well data of bordering shallow water areas, Lingshui Formation was divided into four third class sequences; namely SI, SII, SIII and SIV, and the three-dimensional isochronous stratigraphic framework of the Lingshui Formation in the studied area was shaped. Based mainly on seismic attributes such as amplitude, continuity, internal structure and external shape, six typical seismic facies were identified, including mat-shaped, filling, wedge-shaped, foreset, moundy-shaped and lenticular-shaped, and a seismic facies distribution map was subsequently drawn. With studies on wells of bordering shallow water areas, regional sedimentary characteristics, and isopach map as references, sedimentary planar distribution features were analyzed. The deepwater area of the Lingshui Formation has mainly developed littoral and shallow sea. Sandstone bodies of fan delta, braided river delta, slope fan, basin floor fan, and turbidite fan are at an interdigitate junction to marine hydrocarbon source rocks and thus are favorable prospecting targets.展开更多
There are known to be enormous Cenozoic coal-type oil and gas resources located in the basins of the South China Sea,among which the Paleogene coal-measure source rock are one of the main source rock.In order to more ...There are known to be enormous Cenozoic coal-type oil and gas resources located in the basins of the South China Sea,among which the Paleogene coal-measure source rock are one of the main source rock.In order to more effectively analyze the distribution laws of coal-measure source rock in marginal sea basins and guide coal-type oil and gas explorations,the Oligocene coal-measure source rock in the Qiongdongnan Basin were selected as examples in order to systematically analyze the types,development characteristics,control factors,and distribution prediction methods of coalmeasure source rock in marginal sea basins.The Qiongdongnan Basin is located in the northern region of the South China Sea.Previous explorations of the area have determined that the Oligocene coal-measure source rock in the Qiongdongnan Basin have typical"binary structures",which include coal seams and terrigenous marine mudstone.Among those,the terrigenous marine mudstone has been found to greatly expand the scope of the coal-measure source rock.In addition,the coal seams which have been exposed by drilling have been observed to have the characteristics of thin single layer thickness,many layers,and poor stability.Meanwhile,the terrigenous marine mudstone has the characteristics of large thickness and wide distribution.The development of coal-measure source rock is known to be controlled by many factors,such as paleoclimate and paleobotany condition,paleo-structure and topography,paleo-geography,rise and fall of base level,and so on.In accordance with the comprehensive analyses of various control factors of coal-measure source rock,and the changes in water body energy in sedimentary environments,a genetic model of the"energy belt"for the development and distribution of coal-measure source rock was proposed.Also,the development and distribution characteristics of coalmeasure source rock in different types of energy belts were clarified.Then,based on the development and distribution characteristics of coal-measure source rock and their controlling factors,prediction methods of the distribution ranges of coal-measure source rock were proposed from both qualitative and(semi-)quantitative aspects.That is to say,a method for(semi-)quantitative predictions of the distribution ranges of coal-bearing intervals based on model wave impedance inversion and neural network wave impedance inversion,along with a method for(semi-)quantitative predictions of the distribution ranges of terrigenous marine mudstone based on topographical slopes,were introduced in this study.展开更多
The sequence stratigraphy framework of Paleogene of Qikou Sag has been built in this paper. The evolution law of episodic subsidence in Qikou Sag has been expounded, with the analysis of the characteristic of sequence...The sequence stratigraphy framework of Paleogene of Qikou Sag has been built in this paper. The evolution law of episodic subsidence in Qikou Sag has been expounded, with the analysis of the characteristic of sequence thickness, as well as the study of consedimental tectonic activity, subsidence history, paleogeomorphology and the coupling relationship among them. The faults controlling action was the dominant mechanism during rifting stage I , as the depression was the dominant mechanism during rifting stage III, which embodies a process from intense disparity fault depression to integral subsidence. Meanwhile, under the control of regional faulting and later stage depression, subsidence rate centers and paleogeomorphic concave centers are always corresponding to the sequence thickness centers, and the changes of subsidence centers and paleogeomorphology concave centers are consistent with the migration of thickness centers, which presents the restriction, coupling and response among them and clarifies the law that tectonic activity controls the basin fill by means of controlling the subsidence rate and paleogeomorphology from contributing factor angle. On this basis, the dynamic evolution of the composite pattern of structure-subsidence-deposition in the fault controlling actic region during the three rifting stages and their petroleum geological significance has been discussed.展开更多
A systematic sedimentological and chronological study of typical Paleogene basins in eastcentral Tibet suggests that the depositional characteristics of extensively developed huge-bedded, purplish-red coarse clastic r...A systematic sedimentological and chronological study of typical Paleogene basins in eastcentral Tibet suggests that the depositional characteristics of extensively developed huge-bedded, purplish-red coarse clastic rocks formed in a tectonic setting of regional thrusting and strike-slipping represent a typical dry and hot subaerial alluvial fan environment formed in a proximal and rapidaccumulating sediment body in debris flows and a fan-surface braided river. Combining results from basin-fill sequences, sequences of coarse clastic rocks, fauna and sporo-pollen associations and thermochronological data, it is conduded that the coarse clastic rocks formed in the period of 54.2- 24.1 Ma, nearly coeval with the formation of Paleogene basins in the northern （Nangqen-Yushu thrust belt）, middle （Batang-Lijiang fault belt）, and disintegration of large basins in the southern （LanpingSimao fold belt） segments of Tibet. The widespread massive-bedded coarse clastic rocks, fold thrusting and strike-slip, thrust shortening, and igneous activities in the Paleogene basins of eastcentral Tibet indicate that an early diachronous tectonic uplift might have occurred in the Tibetan Plateau from Middle Eocene to Oligocene, related to the initial stage of collision of the Indian and Asian plates.展开更多
The Naij Tai Group-complex is a suite of tectonic-sedimentary méiange aggregation of the Eastern Kunlun orogenic belt, which is composed of two parts, i.e. the exotic blocks of various ages and the matrix strata....The Naij Tai Group-complex is a suite of tectonic-sedimentary méiange aggregation of the Eastern Kunlun orogenic belt, which is composed of two parts, i.e. the exotic blocks of various ages and the matrix strata. On the basis of coral, brachiopod and gastropod fossils found in the exotic blocks, the age of this group-complex was once defined to the Late Ordovician or the Paleozoic. This paper reports for the first time 44 genera and 31 species of Mid-Late Oiigocene sporopoilen in samples from the matrix strata in this group-complex and the Paleogene Quercoidites-Persicarioipollis assemblage is named. The paper aims to provide some detailed evidence for determining the age of the matrix strata in this group-complex based upon a study at the Caiyuanzigou section, which would be of great geological significance for further understanding this group-complex as a suite of tectonic-sedimentary méiange aggregation. The new finding will certainly benefit from now on the investigation of formation and evolution mechanism for the Eastern Kunlun orogenic belt.展开更多
The characteristics and formation mechanisms of the mixed siliciclastic-carbonate reservoirs of the Paleogene Shahejie Formation in the central Bohai Sea were examined based on polarized light microscopy and scanning ...The characteristics and formation mechanisms of the mixed siliciclastic-carbonate reservoirs of the Paleogene Shahejie Formation in the central Bohai Sea were examined based on polarized light microscopy and scanning electron microscopy observations, X-ray diffrac- tometry, carbon and oxygen stable isotope geochemistry, and integrated fluid inclusion analysis. High-quality reservoirs are mainly distributed in Type I and Type II mixed siliciclastic-carbonate sediments, and the dominant pore types include residual primary intergranular pores and intrafossil pores, feldspar dissolution pores mainly devel- oped in Type II sediments. Type I mixed sediments are characterized by precipitation of early pore-lining dolo- mite, relatively weak mechanical compaction during deep burial, and the occurrence of abundant oil inclusions in high-quality reservoirs. Microfacies played a critical role in the formation of the mixed reservoirs, and high-quality reservoirs are commonly found in high-energy environ- ments, such as fan delta underwater distributary channels, mouth bars, and submarine uplift beach bars. Abundant intrafossil pores were formed by bioclastic decay, and secondary pores due to feldspar dissolution further enhance reservoir porosity. Mechanical compaction was inhibited by the precipitation of pore-lining dolomite formed during early stage, and oil emplacement has further led to the preservation of good reservoir quality.展开更多
Gas-bearing deposits in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin consist of shoreface sandstones of the highstand systems tract（HST） and transgressive systems tract（TST）...Gas-bearing deposits in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin consist of shoreface sandstones of the highstand systems tract（HST） and transgressive systems tract（TST）, and deltaic sandstones of the lowstand systems tract（LST） and falling stage systems tract（FSST）.Detailed petrographic observations suggest that the diagenetic features and related evolution of these deposits cannot be simply characterized and demonstrated in the depth domain.However, the occurrence of diagenetic minerals systematically depends on the studied interval within the HST, TST, LST, and FSST; therefore, diagenesis in this region can be better constrained when studied in the context of the depositional environments and sequence stratigraphic framework.The eogenetic processes in such settings include：（1） microcrystalline siderite precipitated as concretions in almost all environments and systems tracts, which inhibited further mechanical compaction;（2） grain dissolution and kaolinitization occurred in shoreface HST sandstones and deltaic LST and FSST sandstones;（3） glaucony was locally observed, which did not clearly reflect the controls of facies or sequence stratigraphy; and（4） cementation by pyrite aggregates occurred in the shoreface HST sandstones and deltaic LST sandstones.The mesogenetic diagenesis includes：（1） partial conversion of kaolinite into dickite in deltaic LST sandstones, and minor chlorite cementation in deltaic FSST sandstones;（2） transformation of kaolinite into illite and quartz cementation in deltaic LST and FSST sandstones;（3） frequent precipitation of ankerite and ferroan calcite in shoreface TST sandstones and early HST sandstones, forming baffles and barriers for fluid flow, with common calcite in shoreface HST sandstones as a late diagenetic cement; and（4） formation of dawsonite in the deltaic LST and FSST sandstones, which is interpreted to be a product of the invasion of a CO2-rich fluid, and acts as a good indicator of CO2-bearing reservoirs.This study has thus constructed a reliable conceptual model to describe the spatial and temporal distribution of diagenetic alterations.The results may provide an entirely new conceptual framework and methodology for successful gas exploration in the continental margins of offshore China, thus allowing us to predict and unravel the distribution and quality evolution of clastic reservoirs at a more detailed and reliable scale.展开更多
Analyses of organic carbon, nitrogen, sulfur and iron have been performed in order to understand sources and preservation of organic matter in black shale of the Buxin Formation (Early Paleogene) from the Sanshui Basi...Analyses of organic carbon, nitrogen, sulfur and iron have been performed in order to understand sources and preservation of organic matter in black shale of the Buxin Formation (Early Paleogene) from the Sanshui Basin. The C/N ratios show that the organic matter is characterized by a mixture of terrestrial and phytoplanktonic contributions. The relative importance of different sources depend on climate conditions and most of organic matter is of terrestrial origin. The relationships between C, S and Fe indicate that the brackish environment with alternation of anoxia and low-O2 developed in the bottom waters during the deposition of these organic-rich sediments as a result of a mixed setting of thermal stratification and salinity stratification, the latter being the consequence of intermittent sea water incursion. Bacterial sulfate reduction is the most effective early diagenesis affecting the preservation of organic matter. The intensity of sulfate reduction is related to the relative proportion of metabolizable organic matter supplied to sediments.展开更多
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 Formatio...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.展开更多
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 adsorp...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.展开更多
The Upper Paleogene lacustrine fine-grained sandstones in the hinterlands of the northern Qaidam Basin mainly contain two sweet spot intervals.Fracture/fault,microfacies,petrology,pore features,diagenesis,etc.,were in...The Upper Paleogene lacustrine fine-grained sandstones in the hinterlands of the northern Qaidam Basin mainly contain two sweet spot intervals.Fracture/fault,microfacies,petrology,pore features,diagenesis,etc.,were innovatively combined to confirm the controlling factors on the reservoir quality of shallow delta-lacustrine fine-grained sandstones.The diagenesis of the original lake/surface/meteoric freshwater and acidic fluids related to the faults and unconformity occurred in an open geochemical system.Comprehensive analysis shows that the Upper Paleogene fine-grained sandstones were primarily formed in the early diagenetic B substage to the middle diagenetic A substage.Reservoir quality was controlled by fault systems,microfacies,burial-thermal history,diagenesis,hydrocarbon charging events(HCE),and abnormally high pressure.Shallow and deep double fault systems are the pathways for fluid flow and hydrocarbon migration.Sandstones developed in the high energy settings such as overwater(ODC)and underwater distributary channels(UDC)provide the material foundation for reservoirs.Moderate burial depth(3000-4000 m),moderate geothermal field(2.7-3.2℃/100 m),and late HCE(later than E3)represent the important factors to protect and improve pore volume.Meteoric freshwater with high concentrations of CO_(2)and organic acids from thermal decarboxylation are the main fluids leading to the dissolution and reformation of feldspar,rock fragments,calcite and anhydrite cements.Abnormally high pressure caused by the undercompaction in a large set of argillaceous rocks is the key to form high-quality reservoirs.Abnormal pressure zones reduced and inhibited the damage of compaction and quartz overgrowth to reservoir pores,allowing them to be better preserved.A reservoir quality evaluation model with bidirectional migration pathways,rich in clay minerals,poor in cements,superimposed dissolution and abnormally high pressure was proposed for the ODC/UDC finegrained sandstones.This model will facilitate the future development of fine-grained sandstone reservoirs both in the Upper Paleogene of the Qaidam Basin and elsewhere.展开更多
According to the theory of sequence stratigraphy based on continental transgressive-regressive(T-R)cycles,a 500 m continuous core taken from the second member of Kongdian Formation(Kong 2 Member)of Paleogene in Well G...According to the theory of sequence stratigraphy based on continental transgressive-regressive(T-R)cycles,a 500 m continuous core taken from the second member of Kongdian Formation(Kong 2 Member)of Paleogene in Well G108-8 in the Cangdong Sag,Bohai Bay Basin,was tested and analyzed to clarify the high-frequency cycles of deep-water fine-grained sedimentary rocks in lacustrine basins.A logging vectorgraph in red pattern was plotted,and then a sequence stratigraphic framework with five-order high-frequency cycles was formed for the fine-grained sedimentary rocks in the Kong 2 Member.The high-frequency cycles of fine-grained sedimentary rocks were characterized by using different methods and at different scales.It is found that the fifth-order T cycles record a high content of terrigenous clastic minerals,a low paleosalinity,a relatively humid paleoclimate and a high density of laminae,while the fifth-order R cycles display a high content of carbonate minerals,a high paleosalinity,a dry paleoclimate and a low density of laminae.The changes in high-frequency cycles controlled the abundance and type of organic matter.The T cycles exhibit relatively high TOC and abundant endogenous organic matters in water in addition to terrigenous organic matters,implying a high primary productivity of lake for the generation and enrichment of shale oil.展开更多
Major breakthroughs of shale oil exploration have been made recently in the upper member of Paleogene Lower Ganchaigou Formation of Yingxiongling area, Qaidam Basin. However, the low total organic carbon content of sa...Major breakthroughs of shale oil exploration have been made recently in the upper member of Paleogene Lower Ganchaigou Formation of Yingxiongling area, Qaidam Basin. However, the low total organic carbon content of saline-lacustrine source rock, and unclear genetic mechanism, evaluation criteria and resources potential of the shale oil have restricted the exploration and evaluation of Yingxiongling shale oil. Through analysis of large amounts of cores, well drilling, seismic, laboratory test data and integrated study, focusing on the shale and mixed types of shale oil reservoirs characterized by high-frequency interbedded organic-rich laminated shale and limy dolomite, it is concluded that the shale oil in the upper member of Lower Ganchaigou Formation in the Yingxiongling area have six geological characteristics:(1) two-stage hydrocarbon generation of hydrogen-rich source rock and large amount of retained oil;(2) multiple types of reservoir space and good reservoir properties;(3)source-reservoir integration, thick “sweet spot” and high oil-bearing grade;(4) high pressure coefficient between and under salt layers, and sufficient formation energy;(5) high content of light components, high gas-oil ratio, and good quality of the crude oil;(6) high content of brittle minerals and good fracability. The evaluation criterion of shale oil is preliminarily established based on the eight parameters: total organic carbon content, maturity, effective porosity, oil saturation, brittle mineral content,pressure coefficient, lamellation density, and burial depth. Combined with parameters of E32 source rock thickness, area, vertical distribution of oil layers, and free hydrocarbon content, the shale oil resources have been preliminarily estimated as 21×10^(8) t.The structurally stable area is the predominant objective of shale oil exploration and the favorable exploration area for Yingxiongling shale oil is nearly 800 km^(2).展开更多
The distribution and genesis of secondary pores in Paleogene clastic reservoirs of Beidagang structural belt in the Huanghua depression have been systematically studied. We investigated sedimentary facies and carried ...The distribution and genesis of secondary pores in Paleogene clastic reservoirs of Beidagang structural belt in the Huanghua depression have been systematically studied. We investigated sedimentary facies and carried out a comprehensive analy-sis of the vast amount of data from casting thin sections, scanning electron microscope and physical data. Then we analyzed the pore types, pore evolution, distribution and genesis of secondary pores in our study area and discussed the factors controlling the distribution of secondary pores. The results show that pores in the study area are largely composed of intergranular dissolution pores and constituent dissolved pores. Three secondary pore zones were developed in the study area at depths of 2800~3400 m, 3600~4200 m and 4500~4800 m. Secondary pores have been formed mainly because carbonate cement, feldspar, clastic debris and other plastic substances were dissolved by organic acid, released during the evolution of organic matter and acid water formed by CO2. The development and distribution of secondary pores are vertically controlled by the maturity time of source rocks and hori-zontally by the distribution of acid water. As well, this distribution was affected by the sedimentary facies belt and the development of fault zones.展开更多
基金Supported by National Natural Science Foundation of China Enterprise Joint Fund Project(U24B200849)National Natural Science Foundation of China(91528303).
文摘Guided by the analysis of source-to-sink system,this study investigates the Paleogene Oligocene Lingshui Formation in the Qiongdongnan Basin by comparing the geological characterizes in land and sea areas and integrating outcrop,core,drilling,logging and 3D seismic data,to systematically analyze the characteristics of the source,transport pathway,and sink during the deposition of Lingshui Formation,and reveal the patterns,controlling factors and petroleum geologic significance of the source-to-sink systems.The results are obtained in five aspects.First,during the fault-depression transition,the Qiongdongnan Basin received sediments from the provenances presenting as segments in east-west and zones in north-south,primarily with the Indosinian granites in the Shenhu Uplift in the east and the Yanshanian granites in the west.Overall,the sources are young in the southern and northern parts and old in the interior of the basin.Second,three types of sediment transport pathways are identified:paleo-valleys,fault troughs and trough-valley transitional zones.Third,based on differences in sediment supply modes,the unique source-to-sink systems during the fault-depression transition in marine rift basins are categorized into three types:exogenous,endogenous and composite.Fourth,the characteristics of these source-to-sink systems are primarily controlled by provenance,paleogeomorphology,and sea-level changes.Provenance lithology and scale dictated the composition and volume of sedimentary deposits.Paleogeomorphology influenced erosion intensity in the provenance and the development of paleodrainage systems,thereby affecting the distribution and types of sedimentary systems.Additionally,sea-level changes decided the extent of the provenance,but also regulated the sediment distribution patterns through oceanic processes such as waves and tides.Fifth,the exogenous source-to-sink systems may form large-scale reservoir bodies,the endogenous systems develop secondary pores due to presence of soluble minerals,and the composite systems demonstrate reservoir properties varying from area to area.
基金Supported by the National Science and Technology Major Project(2024ZD1400101)Project of Sinopec(P23234)。
文摘Based on a large amount of basic research and experimental analysis data from Shengli Oilfield,Bohai Bay Basin,guided by the theory of whole petroleum system,the distribution of sedimentary systems,the distribution and hydrocarbon generation and expulsion process of source rocks,the variation of reservoir properties,and the control of fracture systems on hydrocarbon accumulation in the Paleogene of the Jiyang Depression,Boahai Bay Basin,were systematically analyzed,and the geological characteristics of the whole petroleum system in the rift basin were identified.Taking the Dongying Sag as an example,combined with the distribution of discovered conventional,tight,and shale oil/gas,a hydrocarbon accumulation model of the fault-controlled whole petroleum system in rift basin was proposed,and the distribution patterns of conventional and unconventional oil and gas reservoirs in large geological bodies horizontally and vertically were clarified.The research results show that paleoclimate and tectonic cycles control the orderly distribution of the Paleogene sedimentary system in the Jiyang Depression,the multi-stage source rocks provide sufficient material basis for in-situ shale oil/gas accumulation and other hydrocarbon migration and accumulation,the changes in reservoir properties control the dynamic threshold of hydrocarbon accumulation,and the combination of faults and fractures at different stages controls hydrocarbon migration and accumulation,and in-situ retention and accumulation of shale oil/gas,making the whole petroleum system in the rift basin associated,segmented and abrupt.The above elements are configured to form a composite whole petroleum system controlled by faults in the Paleogene of the Jiyang Depression.Moreover,under the control of hydrocarbon accumulation dynamics,a whole petroleum system can be divided into conventional subsystem and unconventional subsystem,with shale oil,tight oil and conventional oil in an orderly distribution in horizontal and vertical directions.This systematic understanding is referential for analyzing the whole petroleum system in continental rift basins in eastern China.
文摘Typical reefs in the Paleogene and early Neogene strata of the Qaidam Basin, Tibetan Plateau, China, reveal their internal structures and sedimentation environments and consist mainly of algal reef, stromatolite reef and thrombolite reef with distinct reef structures, fore-reef, back-reef and reef-plateau. The fore-reef is characterized by a combination of pinnacle reef, thrombolite and algal reef. The back reef is composed of stromatolite reef and algal reef. The pinnacle reefs (micro-atoll), most of which are several tens of centimeters in diameter (whereas some exceptionally big ones are over 200 cm in diameter), and several tens of centimeter to 2 m in height, are situated on the far front-edge of the reef; the pinnacle reef is also often of recumbent form with a gravel-filled circular hole in the center. The algal reef is in the form of dome and irregular beds, and filled with algal detritus, ostracodes, spirorbis fossils, ooid and terrigenous debris, and worm traces; cavities and scour marks are often developed. The algal reef is gray commonly when fresh and weathers to a brown color. The lacustrine thrombolite in the Qaidam Basin is light gray or deep gray when fresh, white-gray or brown when weathered, dense and homogeneous with abundant pores filled by oil and bitumen. Observed under the microscope, the thrombolite consists mainly of brown or brown-black clots with a little algal debris, ooid, pellet, ostracodes, spirorbis fossils and terrigenous debris, in some cases, terrigenous debris, even gravel, is abundant. Many features of the thrombolite suggest that it is formed in a high-energy envkonment. The stromatolite reefs developed on the lacustrine algal reef in the Qaidam Basin are very complex whether in shape or in internal structure. The simplest ones form laminated layers and the most complex ones have intensely branching structures. The size is also variable.
基金supported by the National Basic Research Program of China (No. 2014CB239102)the National Science and Technology Major Project (No. 2016ZX05049-4)the National Natural Science Fundation of China (Nos. 41372107, 41572087)
文摘This paper was conducted on the shale reservoir in the Dongying depression in the Shahejie Formation of Paleogene. Based on detailed core description, rock thin sections, argon ion polishing, scanning electron microscopy（SEM） analysis, CT scanning and carbon-oxygen isotopic test, the formation mechanism of the inter-laminar fractures（or seams） and their development conditions were discussed by comprehensive analysis of the diagenetic evolution features and the reservoir space evolution characteristics. The results show that the laminated composite pattern in Dongying depression was dominated by vertical distribution of laminated calcite and clay minerals. Contrasted to the traditional understanding, development degree of inter-laminar fractures was much lower. Pure fluid between layers cannot exist without framework minerals, and the pre-existing well connected pore or horizontal overpressure micro seam was favorable paths of fluid migration. From the points of inter-laminar fractures origin mechanism and its evolution, the so called seams, were much more complex than traditional understanding that hydrocarbon generation raised the pore pressure and led to the parallel microfractures. But the inter-laminar fractures had little relationship with that whether the lamination was developed or bedding boundary was clear or not. In fact, the shale reservoir inter-laminar fractures were not rigorous fracture. They were controlled by pre-existing inter-granular pore（or seam） or dissolved pore, which distributed along carbonate laminae boundary and were connected by later super pressure, dissolution and the seepage force. And the development conditions were burial depth（bigger than 3 000 m） and the Ro value（〉0.6%）. Discussion on its origin and evolution has important petroleum geological significance on optimizing reservoir segment and favorable target areas selection.
基金sponsored by Ministry of Science and Technology of China (grant No. 2009CB219400)
文摘In recent years, deep water areas have become popular exploration fields because of their abundant hydrocarbon resource potential. There are only relatively poor planar seismic profiles and no wells for deepwater areas of the Lingshui Formation in the Qiongdongnan Basin. A lot of faults developed and strata are fragmented due to high temperatures and high pressure, and this has resulted in dim sequence boundaries. Based on seismic data of the deepwater area and well data of bordering shallow water areas, Lingshui Formation was divided into four third class sequences; namely SI, SII, SIII and SIV, and the three-dimensional isochronous stratigraphic framework of the Lingshui Formation in the studied area was shaped. Based mainly on seismic attributes such as amplitude, continuity, internal structure and external shape, six typical seismic facies were identified, including mat-shaped, filling, wedge-shaped, foreset, moundy-shaped and lenticular-shaped, and a seismic facies distribution map was subsequently drawn. With studies on wells of bordering shallow water areas, regional sedimentary characteristics, and isopach map as references, sedimentary planar distribution features were analyzed. The deepwater area of the Lingshui Formation has mainly developed littoral and shallow sea. Sandstone bodies of fan delta, braided river delta, slope fan, basin floor fan, and turbidite fan are at an interdigitate junction to marine hydrocarbon source rocks and thus are favorable prospecting targets.
基金granted by the National Natural Science Foudation of China(Grant No.4207218841872172)the SDUST Research Fund(2018TDJH101)。
文摘There are known to be enormous Cenozoic coal-type oil and gas resources located in the basins of the South China Sea,among which the Paleogene coal-measure source rock are one of the main source rock.In order to more effectively analyze the distribution laws of coal-measure source rock in marginal sea basins and guide coal-type oil and gas explorations,the Oligocene coal-measure source rock in the Qiongdongnan Basin were selected as examples in order to systematically analyze the types,development characteristics,control factors,and distribution prediction methods of coalmeasure source rock in marginal sea basins.The Qiongdongnan Basin is located in the northern region of the South China Sea.Previous explorations of the area have determined that the Oligocene coal-measure source rock in the Qiongdongnan Basin have typical"binary structures",which include coal seams and terrigenous marine mudstone.Among those,the terrigenous marine mudstone has been found to greatly expand the scope of the coal-measure source rock.In addition,the coal seams which have been exposed by drilling have been observed to have the characteristics of thin single layer thickness,many layers,and poor stability.Meanwhile,the terrigenous marine mudstone has the characteristics of large thickness and wide distribution.The development of coal-measure source rock is known to be controlled by many factors,such as paleoclimate and paleobotany condition,paleo-structure and topography,paleo-geography,rise and fall of base level,and so on.In accordance with the comprehensive analyses of various control factors of coal-measure source rock,and the changes in water body energy in sedimentary environments,a genetic model of the"energy belt"for the development and distribution of coal-measure source rock was proposed.Also,the development and distribution characteristics of coalmeasure source rock in different types of energy belts were clarified.Then,based on the development and distribution characteristics of coal-measure source rock and their controlling factors,prediction methods of the distribution ranges of coal-measure source rock were proposed from both qualitative and(semi-)quantitative aspects.That is to say,a method for(semi-)quantitative predictions of the distribution ranges of coal-bearing intervals based on model wave impedance inversion and neural network wave impedance inversion,along with a method for(semi-)quantitative predictions of the distribution ranges of terrigenous marine mudstone based on topographical slopes,were introduced in this study.
基金support from the National Natural Science Foundation of China (Grant No.40872077)National Major Science and Technology Project of China (Grant No. 2011ZX05009-002)Open Project Foundation of Ministry of Education Key Laboratory of Tectonics and Petroleum Resources (Grant No. TPR-2011-09)
文摘The sequence stratigraphy framework of Paleogene of Qikou Sag has been built in this paper. The evolution law of episodic subsidence in Qikou Sag has been expounded, with the analysis of the characteristic of sequence thickness, as well as the study of consedimental tectonic activity, subsidence history, paleogeomorphology and the coupling relationship among them. The faults controlling action was the dominant mechanism during rifting stage I , as the depression was the dominant mechanism during rifting stage III, which embodies a process from intense disparity fault depression to integral subsidence. Meanwhile, under the control of regional faulting and later stage depression, subsidence rate centers and paleogeomorphic concave centers are always corresponding to the sequence thickness centers, and the changes of subsidence centers and paleogeomorphology concave centers are consistent with the migration of thickness centers, which presents the restriction, coupling and response among them and clarifies the law that tectonic activity controls the basin fill by means of controlling the subsidence rate and paleogeomorphology from contributing factor angle. On this basis, the dynamic evolution of the composite pattern of structure-subsidence-deposition in the fault controlling actic region during the three rifting stages and their petroleum geological significance has been discussed.
基金This research was supported by the National Key Project for Basic Research on the Tibetan Plateau （Grant G1998040800-3）；National Natural Science Foundation of China （Grants 49972026 and 39972026）；Chinese Academy of Sciences （CAS） Projects （Grant KZ952-JI408） ； US-NSF project （Grant 980612）.
文摘A systematic sedimentological and chronological study of typical Paleogene basins in eastcentral Tibet suggests that the depositional characteristics of extensively developed huge-bedded, purplish-red coarse clastic rocks formed in a tectonic setting of regional thrusting and strike-slipping represent a typical dry and hot subaerial alluvial fan environment formed in a proximal and rapidaccumulating sediment body in debris flows and a fan-surface braided river. Combining results from basin-fill sequences, sequences of coarse clastic rocks, fauna and sporo-pollen associations and thermochronological data, it is conduded that the coarse clastic rocks formed in the period of 54.2- 24.1 Ma, nearly coeval with the formation of Paleogene basins in the northern （Nangqen-Yushu thrust belt）, middle （Batang-Lijiang fault belt）, and disintegration of large basins in the southern （LanpingSimao fold belt） segments of Tibet. The widespread massive-bedded coarse clastic rocks, fold thrusting and strike-slip, thrust shortening, and igneous activities in the Paleogene basins of eastcentral Tibet indicate that an early diachronous tectonic uplift might have occurred in the Tibetan Plateau from Middle Eocene to Oligocene, related to the initial stage of collision of the Indian and Asian plates.
基金supported by the National Natural Science Foundation of China(Grant No.40272019)the China Geological Survey(Grant No.200313000054).
文摘The Naij Tai Group-complex is a suite of tectonic-sedimentary méiange aggregation of the Eastern Kunlun orogenic belt, which is composed of two parts, i.e. the exotic blocks of various ages and the matrix strata. On the basis of coral, brachiopod and gastropod fossils found in the exotic blocks, the age of this group-complex was once defined to the Late Ordovician or the Paleozoic. This paper reports for the first time 44 genera and 31 species of Mid-Late Oiigocene sporopoilen in samples from the matrix strata in this group-complex and the Paleogene Quercoidites-Persicarioipollis assemblage is named. The paper aims to provide some detailed evidence for determining the age of the matrix strata in this group-complex based upon a study at the Caiyuanzigou section, which would be of great geological significance for further understanding this group-complex as a suite of tectonic-sedimentary méiange aggregation. The new finding will certainly benefit from now on the investigation of formation and evolution mechanism for the Eastern Kunlun orogenic belt.
基金financially supported by the National Science & Technology Specific Project (Grant No. 2011ZX05023-006)
文摘The characteristics and formation mechanisms of the mixed siliciclastic-carbonate reservoirs of the Paleogene Shahejie Formation in the central Bohai Sea were examined based on polarized light microscopy and scanning electron microscopy observations, X-ray diffrac- tometry, carbon and oxygen stable isotope geochemistry, and integrated fluid inclusion analysis. High-quality reservoirs are mainly distributed in Type I and Type II mixed siliciclastic-carbonate sediments, and the dominant pore types include residual primary intergranular pores and intrafossil pores, feldspar dissolution pores mainly devel- oped in Type II sediments. Type I mixed sediments are characterized by precipitation of early pore-lining dolo- mite, relatively weak mechanical compaction during deep burial, and the occurrence of abundant oil inclusions in high-quality reservoirs. Microfacies played a critical role in the formation of the mixed reservoirs, and high-quality reservoirs are commonly found in high-energy environ- ments, such as fan delta underwater distributary channels, mouth bars, and submarine uplift beach bars. Abundant intrafossil pores were formed by bioclastic decay, and secondary pores due to feldspar dissolution further enhance reservoir porosity. Mechanical compaction was inhibited by the precipitation of pore-lining dolomite formed during early stage, and oil emplacement has further led to the preservation of good reservoir quality.
基金Financial support was provided by the National Science and Technology Major Project of China (No.2011ZX05023-002-003)
文摘Gas-bearing deposits in the Lower Mingyuefeng Formation of Paleogene, Lishui Sag, East China Sea Shelf Basin consist of shoreface sandstones of the highstand systems tract（HST） and transgressive systems tract（TST）, and deltaic sandstones of the lowstand systems tract（LST） and falling stage systems tract（FSST）.Detailed petrographic observations suggest that the diagenetic features and related evolution of these deposits cannot be simply characterized and demonstrated in the depth domain.However, the occurrence of diagenetic minerals systematically depends on the studied interval within the HST, TST, LST, and FSST; therefore, diagenesis in this region can be better constrained when studied in the context of the depositional environments and sequence stratigraphic framework.The eogenetic processes in such settings include：（1） microcrystalline siderite precipitated as concretions in almost all environments and systems tracts, which inhibited further mechanical compaction;（2） grain dissolution and kaolinitization occurred in shoreface HST sandstones and deltaic LST and FSST sandstones;（3） glaucony was locally observed, which did not clearly reflect the controls of facies or sequence stratigraphy; and（4） cementation by pyrite aggregates occurred in the shoreface HST sandstones and deltaic LST sandstones.The mesogenetic diagenesis includes：（1） partial conversion of kaolinite into dickite in deltaic LST sandstones, and minor chlorite cementation in deltaic FSST sandstones;（2） transformation of kaolinite into illite and quartz cementation in deltaic LST and FSST sandstones;（3） frequent precipitation of ankerite and ferroan calcite in shoreface TST sandstones and early HST sandstones, forming baffles and barriers for fluid flow, with common calcite in shoreface HST sandstones as a late diagenetic cement; and（4） formation of dawsonite in the deltaic LST and FSST sandstones, which is interpreted to be a product of the invasion of a CO2-rich fluid, and acts as a good indicator of CO2-bearing reservoirs.This study has thus constructed a reliable conceptual model to describe the spatial and temporal distribution of diagenetic alterations.The results may provide an entirely new conceptual framework and methodology for successful gas exploration in the continental margins of offshore China, thus allowing us to predict and unravel the distribution and quality evolution of clastic reservoirs at a more detailed and reliable scale.
基金A financial support for this research was provided by the Natural Science Foundation of China under Grant No.4027201 1the Natural Science Foundation of Guangdong Province under Grant No.001203.
文摘Analyses of organic carbon, nitrogen, sulfur and iron have been performed in order to understand sources and preservation of organic matter in black shale of the Buxin Formation (Early Paleogene) from the Sanshui Basin. The C/N ratios show that the organic matter is characterized by a mixture of terrestrial and phytoplanktonic contributions. The relative importance of different sources depend on climate conditions and most of organic matter is of terrestrial origin. The relationships between C, S and Fe indicate that the brackish environment with alternation of anoxia and low-O2 developed in the bottom waters during the deposition of these organic-rich sediments as a result of a mixed setting of thermal stratification and salinity stratification, the latter being the consequence of intermittent sea water incursion. Bacterial sulfate reduction is the most effective early diagenesis affecting the preservation of organic matter. The intensity of sulfate reduction is related to the relative proportion of metabolizable organic matter supplied to sediments.
基金Supported by the China National Science and Technology Major Project(2017ZX05049-004)Sinopec Project(P22083,P23084).
文摘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.
基金Supported by Natural Science Foundation of China(41672116)the China National Science and Technology Major Project(2017ZX05049004)
文摘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.
基金supported by the National Major Science and Technology Projects of China(No.2016ZX05033-001002)the National Natural Science Foundation of China(No.41272155)the China Scholarship Council。
文摘The Upper Paleogene lacustrine fine-grained sandstones in the hinterlands of the northern Qaidam Basin mainly contain two sweet spot intervals.Fracture/fault,microfacies,petrology,pore features,diagenesis,etc.,were innovatively combined to confirm the controlling factors on the reservoir quality of shallow delta-lacustrine fine-grained sandstones.The diagenesis of the original lake/surface/meteoric freshwater and acidic fluids related to the faults and unconformity occurred in an open geochemical system.Comprehensive analysis shows that the Upper Paleogene fine-grained sandstones were primarily formed in the early diagenetic B substage to the middle diagenetic A substage.Reservoir quality was controlled by fault systems,microfacies,burial-thermal history,diagenesis,hydrocarbon charging events(HCE),and abnormally high pressure.Shallow and deep double fault systems are the pathways for fluid flow and hydrocarbon migration.Sandstones developed in the high energy settings such as overwater(ODC)and underwater distributary channels(UDC)provide the material foundation for reservoirs.Moderate burial depth(3000-4000 m),moderate geothermal field(2.7-3.2℃/100 m),and late HCE(later than E3)represent the important factors to protect and improve pore volume.Meteoric freshwater with high concentrations of CO_(2)and organic acids from thermal decarboxylation are the main fluids leading to the dissolution and reformation of feldspar,rock fragments,calcite and anhydrite cements.Abnormally high pressure caused by the undercompaction in a large set of argillaceous rocks is the key to form high-quality reservoirs.Abnormal pressure zones reduced and inhibited the damage of compaction and quartz overgrowth to reservoir pores,allowing them to be better preserved.A reservoir quality evaluation model with bidirectional migration pathways,rich in clay minerals,poor in cements,superimposed dissolution and abnormally high pressure was proposed for the ODC/UDC finegrained sandstones.This model will facilitate the future development of fine-grained sandstone reservoirs both in the Upper Paleogene of the Qaidam Basin and elsewhere.
基金Supported by the National Major Research and Development Project(2020YFA0710504,2022YFF0801204)PetroChina Science and Technology Major Project(2019E-26)。
文摘According to the theory of sequence stratigraphy based on continental transgressive-regressive(T-R)cycles,a 500 m continuous core taken from the second member of Kongdian Formation(Kong 2 Member)of Paleogene in Well G108-8 in the Cangdong Sag,Bohai Bay Basin,was tested and analyzed to clarify the high-frequency cycles of deep-water fine-grained sedimentary rocks in lacustrine basins.A logging vectorgraph in red pattern was plotted,and then a sequence stratigraphic framework with five-order high-frequency cycles was formed for the fine-grained sedimentary rocks in the Kong 2 Member.The high-frequency cycles of fine-grained sedimentary rocks were characterized by using different methods and at different scales.It is found that the fifth-order T cycles record a high content of terrigenous clastic minerals,a low paleosalinity,a relatively humid paleoclimate and a high density of laminae,while the fifth-order R cycles display a high content of carbonate minerals,a high paleosalinity,a dry paleoclimate and a low density of laminae.The changes in high-frequency cycles controlled the abundance and type of organic matter.The T cycles exhibit relatively high TOC and abundant endogenous organic matters in water in addition to terrigenous organic matters,implying a high primary productivity of lake for the generation and enrichment of shale oil.
基金Supported by the National Natural Science Foundation of China(42090025)the PetroChina Science and Technology Major Project(2019E-2601)。
文摘Major breakthroughs of shale oil exploration have been made recently in the upper member of Paleogene Lower Ganchaigou Formation of Yingxiongling area, Qaidam Basin. However, the low total organic carbon content of saline-lacustrine source rock, and unclear genetic mechanism, evaluation criteria and resources potential of the shale oil have restricted the exploration and evaluation of Yingxiongling shale oil. Through analysis of large amounts of cores, well drilling, seismic, laboratory test data and integrated study, focusing on the shale and mixed types of shale oil reservoirs characterized by high-frequency interbedded organic-rich laminated shale and limy dolomite, it is concluded that the shale oil in the upper member of Lower Ganchaigou Formation in the Yingxiongling area have six geological characteristics:(1) two-stage hydrocarbon generation of hydrogen-rich source rock and large amount of retained oil;(2) multiple types of reservoir space and good reservoir properties;(3)source-reservoir integration, thick “sweet spot” and high oil-bearing grade;(4) high pressure coefficient between and under salt layers, and sufficient formation energy;(5) high content of light components, high gas-oil ratio, and good quality of the crude oil;(6) high content of brittle minerals and good fracability. The evaluation criterion of shale oil is preliminarily established based on the eight parameters: total organic carbon content, maturity, effective porosity, oil saturation, brittle mineral content,pressure coefficient, lamellation density, and burial depth. Combined with parameters of E32 source rock thickness, area, vertical distribution of oil layers, and free hydrocarbon content, the shale oil resources have been preliminarily estimated as 21×10^(8) t.The structurally stable area is the predominant objective of shale oil exploration and the favorable exploration area for Yingxiongling shale oil is nearly 800 km^(2).
基金Financial support for this study by the National Basic Research Program of China (973) (No.2006CB 202300) is gratefully acknowledged
文摘The distribution and genesis of secondary pores in Paleogene clastic reservoirs of Beidagang structural belt in the Huanghua depression have been systematically studied. We investigated sedimentary facies and carried out a comprehensive analy-sis of the vast amount of data from casting thin sections, scanning electron microscope and physical data. Then we analyzed the pore types, pore evolution, distribution and genesis of secondary pores in our study area and discussed the factors controlling the distribution of secondary pores. The results show that pores in the study area are largely composed of intergranular dissolution pores and constituent dissolved pores. Three secondary pore zones were developed in the study area at depths of 2800~3400 m, 3600~4200 m and 4500~4800 m. Secondary pores have been formed mainly because carbonate cement, feldspar, clastic debris and other plastic substances were dissolved by organic acid, released during the evolution of organic matter and acid water formed by CO2. The development and distribution of secondary pores are vertically controlled by the maturity time of source rocks and hori-zontally by the distribution of acid water. As well, this distribution was affected by the sedimentary facies belt and the development of fault zones.
