Oil & Gas Geology-1980, Volume 1 Issue 1

INVESTIGATIONS ON THE MARINE SEDIMENTARY ENVIRONMENTAL MODEL OF CHINA IN LATE PROTEROZOIC TO TRIASSIC PERIODS

Guan Shicong, Yan Huaiyu, Qiu Dongzhou, Wang Shoude, Chen Xianqun, Zhou Jingcai

1980, 1(1): 2-17. doi:10.11743/ogg19800102

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The comprehensive marine sedimentary environmental model of Chinain late Proterozoic to Triassic periods is established on the basis of twosets of facies,including six facies zones and fifteen facies belts,namely:1,The trough basin facies which includes the deep sea trough-basinand the shallow sea trough-basin facies zones;and 2,The platform shelffacies which includes the shallow sea basin,the plat form margin,the platform and the continental margin facies zones.The shallow sea basin facies zone consists of the shelf margin basin,the shallow shelf and the inner-margin shelf slope facies belts.The plat-form margin facies zone comprises the foreslope,the reef and the bankfacies belts.The platform facies zones comprise the trough-like platform,the open platform,the semi-restricted platform and the restricted plat- form facies belts.The continental margin facies zone includes the lit-toral bar-beach,the tidal flat lagoon,the coastal marsh,the coastalterrigenous clastic beach and the delta facies belts.The marine sedimentary environmental model of China in late Prote-rozoic to Trissic periods can be classified into three types and fifteenforms These are the trough basin type,the platform shelf type and thetrough-platform type.The first one comprises the shallow sea trough-basin,the deep sea trough-basin and the shallow-deep sea trough-basin.The second one includes nine different forms.They are the trough-likeplatform shelf,the open platform shelf,the semi-restricted platformshelf,the restricted platform shelf,the bar-beach platform shelf,thedeltaic platform shelf,the terrigenous clastic beach platform shelf,themargin basin platform shelf and the marsh platform shelf.The third onecomprises the joint form of trough-platform,the forms of platform snr-rounded by troughs and of trough surrounded by platforms.The marine sedimentary environments of China in late Proterozoicto Triassic periods are characterized by the development of continentalmargin facies zone and by the complexity and variousness of platformfacies belts,frequent occurrence of high-energy facies belts,and the pre-sence of source-reservoir-cap combinations in the platform facies zones.

SOME IDEAS ON THE OIL AND GAS POTENTIAL OF SICHUAN BASIN AND ORDOS PLATFORM DOWNWARP

Huang Jiqing(T. K. Huang)

1980, 1(1): 18-25. doi:10.11743/ogg19800103

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From the viewpoint of polycyclic formation and accumulation of pe-troleum,the target for petroleum prospecting in Sichuan Basin and Or-dos Platform Downwarp has been discussed.It was pointed out that quitea number of unconformity and disconformity planes in the stratigraphical sequences within Sichuan Basin are important for petroleum accumulation.In oil prospecting work,the stress should be put on the piedmont down-warp zone of the Longmenshan Mountain,and the Triassic and Jurassic rocks should be considered as the target for searching oil.The Yangxinlimestone and its underlying rocks may bear only gas but no oil.According to the tectonic and stratigraphical characteristics,the cen-tral part of Majiatan-Shajingzi Uplift(i.e.the Yuanyang Lake area)with in the Ordos Platform Downwarp is an oil-promising area,and the Tianhuan Downwarp is a second best area in oil potentiality.The Liu-panshan Mountain,especially its northern part,must be one of the sig-nificant areas for future oil searching work.The Yikezhaomeng Upliftmay not contain much oil.

THE OIL AND GAS POTENTIAL IN THE PALAEOZOIC OF TARIM BASIN

Yi Ronglong, Jiang Shengbang

1980, 1(1): 26-36. doi:10.11743/ogg19800104

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The Tarim Basin is an important target area for petroleum prospec-ting in Palaeozoic rocks in China.The platform marine carbonates and clastic rocks of Palaeozoic age are 4000—10000 meters thick and widely spread in Tarim Basin,and lie beneath the Meso-Cenozoic of 1000—10000 meters thick,occupying an area of appoximately 500000 squarekilometers.Frequent oil and gas in dications and commercial amount ofoil flows already found there are possibly derived from the Palaeozoicrocks.In Tarim,the basement is composedof Archaean-Proterozoic crystal-line complexes and metamorphic rocks.The emergence of this platformstarted from Jinning movement.It is suggested that the latitudinal upliftand subsidence formed by this event had controlled the marine regression and transgression and the sediment distribution.The NWW trending,the prototype,both of uplift and subsidence formed in Caledonian mo-vement,were further developed during the period of Hercynian movementand had simultaneously Controlled the distribution of Palaeozoic sedimen-tary zones.Now,eight tectonic units,either NEE and NWW strike,can be subdivided on the basis of the Hercynian tectonic framework.The Yanshanian and,especially,the Himalayan movements exerted an activeeffect on the remigration and accumulation of the Palaeozoic oil and gas.The Palaeozoic oil source rocks are in good abundance.The majoroil source rocks are Carboniferous,Lower Permian and Lower Cambrian,while the less impotant are Middle and Lower Ordovician,Lower Silurian and Upper Sinian.Preliminary study shows that both light oiland gas may occur in the Upper Palaeozoic,but only gas occurs in Lower Palaeozoic rocks.The Carboniferous-Lower Permian carbonates are the most importantoil reservoirs Nevertheless the Upper Sinian dolomites are also of great significance.It is suggested that fractures,planes of unconformity andorganic reefs are probably well developed in these rocks.The data available demonstrate that the marginal zone of the Bachu Uplift and the updip parts of the Maigaiti and northern Tarim PlatformSlopes are promising Palaeozoic belts for oil and gas prospecting.

OIL AND GAS RESERVOIR CHARACTERISTICS OF TIDAL-FLAT EVAPORATION CARBONATES

Tang Zeyao, Wu Enguo

1980, 1(1): 37-46. doi:10.11743/ogg19800105

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The tidal-flat evaporation carbonates,widely spread in the Upper Sinian,the Middle Carboniferous and the Middle and Lower Triassic of the Sichuan Basin,are important reservoir rocks,The carbonates are often interbeded or intercalated with evaporites.The constituents ofthe carbonates are mainly lime-mud and algae-cohered,the fossils beingseldom and few in species.The tidal sedimentary features are welldeveloped,and the cyclothem and rhythms are clear.These rocks wereobviously formed under conditions of regional arid climate,restricted andextremely shallow waters and strong tidal activities on a wide and gentleplatform.These reservoir rocks are characterized by:1.Well developed porosity mainly appearing in crypto-algae dolo-mites of algae-flat microfacies in intertidal zone.The combining effectof intercrystal pores and cavities produced by diagenetic and epigeneticdolomitzation and solution,along with algae-supported fenestal and in-tergranular pores,will certainly cause an increase in the porosity;2.Wide spread fractures and fissures greatly improve the permea-bility of reservoir rocks.Because of their thin bedding and pure qualityand of their intercalation with soft evaporites and/or agrillaceous rocks,the carbonates usually yield easily to fracturing when a tectonic eventhappens;3.Weathering in the interval of sedimentation gap,which makes theevaporites expand and dissolve,thus the carbonates may be compressedto form collapse breccia.Obviously,these cavity and fracture-rich rocksmay constitute a collapse breccia type of reservoir generated by dissolu-tion;4.Evaporated tidal flat deposits,intercalated within thick carbona-tes are apt to produce deep-seated karst and thus may form a reservoirwith high productive potentiality.Generally,these reservoirs are usually formed from dolomites withfractures and pores of secondary nuture.Such a sort of reservoir usually contains many productive horizons and is wide-spread,but shows little homogeneity.It is a notable sedimentation type of carbonate platform.

EVOLUTION OF KEROGEN IN THE OIL-GAS FORMATION IN THE PALAEOZOIC SEDIMENTS OF SHAANXI-GANSU-NINGXIA BASIN

Fan Pu, Shen Ping, Rong Guanghua, Wang Hongyong, Ye Jisun

1980, 1(1): 47-55. doi:10.11743/ogg19800106

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The characteristics of pyrolysis(P-FID),thermogravimetric analysis (TGA),infrared spectrums(IR),elements composition and carbon isotope ratios of kerogen in the Palaeozoic rocks of the Shaanxi-Gansu-Ningxia Basin have been investigated,and the types of kerogen in vari-ous sequences have been described in this paper.The main types of ke-rogen favourable to oil-gas formation in this basin are sapropel(O₂)and mixed humus and sapropel(C₂b,C₃t),because of their high con-tents of C degradation hydrocarbons,It is suggested that,with the grade of metamorphism getting higher,the H/C(atomic ratio) and O/C(atomic ratio)of kerogen tend to de-crease,the H/C(atomic ratio)of asphaltene and the fractionation ofδC¹³ to increase.

ON CORRELATION AND DIVISION OF THE UPPER TRIASSIC IN SICHUAN BASIN WITH REFERENCE TO SOME CRUSTAL MOVEMENT PLANES

Liang Enyu

1980, 1(1): 56-68. doi:10.11743/ogg19800107

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Stratigraphical correlation and classification of the Upper Triassic of Sichuan Basin have been worked out here in the light of crustal mo-vement planes,sedimentation cycles,paleontological data and litho-facies analysis with consideration of the local lithological reference hori-zons.

GOODNESS OF PORE GEOMETRY——THE MOST IMPORTANT PARAMETER FOR ESTIMATING PORE GEOMETRY IN RESERVOIRS

Chen Liguan, Wang Bojun, Li Hongzhi

1980, 1(1): 69-74. doi:10.11743/ogg19800108

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Mercury injection is one of the efficient methods for investigating pore geometry of reservoirs.A lot of capillary curves from mercury apparatus have been accumulated in an oil field in northwest China.The most important parameter for estimating pore geometry in resevoirs,which is called Gg,has been found out by multivariated analysis combined with geological studies.It can be used to estimate the mode of pore geo-metry of reservoir rocks.It is found that,the smaller the value of Gg,the better is the pore geometry and vice versa.Gg can also be used tohelp estimate the water advance of water driving pools or injection exp-loitation.Thus,it is a useful parameter in exploitation analysis.Onthe basis of our observation of the relationship between Gg,porosityand permeability,a polynomial has been suggested for estimating the Ggvalue and a simple formula is obtained by means of regression.

TECTONIC FEATURES OF QIYANG ∈-TYPE TECTONIC SYSTEM AND ITS MECHANISM OF FORMATION

Qiu Zhijun, Zhong Junxian, Zhan Shiyun

1980, 1(1): 75-81. doi:10.11743/ogg19800109

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The Qiyang ε-type tectonic system in central Hunan has been stu-died and its bearing on oil and gas potential discussed.Partly on the basis of model experiments,some new ideas about the characteristics ofthis tectonic system and the mechanism of its formation have been putforward.This paper contains three parts:the first part deals with the tec-tonic features of the Qiyang ε-type tectonic system.The second partdiscusses the mechanism of formation of the Qiyang ε-type tectonicsystem.The third part discusses briefly the relationaship between the Qiyang ε-type tectonic system and the hydrocarbon ocurrence.

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