Research On The Coal-measure Source Rock Evaluation And Reservoir-forming Mechanism In The Shisanjianfang And Surrounding Area

The Shisanjianfang area in the Taibei depression of the Turpan-Hami basin is potential areas for oil and gas exploration.Due to the low degree of exploration,the source rock has not been systematically studied and analyzed.The characteristics and distribution of the source rocks are not clear.The condition of the reservoir cover is relatively shallow,and the correlation analysis between the characteristics of oil and gas and source rocks is not enough.The research on reservoir formation conditions and regularity of oil and gas reservoirs is lacking.Due to the above factors,greatly reducing oil and gas exploration process of the Shisanjianfang area.Using the geochemistry,sequence stratigraphy,petroleum geology and seismic stratigraphy theory,combining with the well logging technology,well-seismic joint inversion technology and basin simulation technology,the sequence stratigraphic features,hydrocarbon source rock characteristic,hydrocarbon accumulation and migration mechanism in Shisanjianfang and surrounding area are systematically studied.A set of research method of the hydrocarbon source rock evaluation,accumulation and migration mechanism are formed,so as to provide a scientific basis for oil and gas exploration in the Shisanjianfang area.The mainly achievements as follows:(1)Shisanjianfang and surrounding areas have good conditions for hydrocarbon source rocks.The TOC values in the study area are mainly concentrated in the SQ2 sequence.The conditions of the reservoir cover in the study area are more developed and have the certain potential for hydrocarbon generation.The hydrocarbon source rock organic matter characteristics of Shisanjianfang and surrounding area are analyzed using the hydrocarbon source rock geochemical data,and the hydrocarbon potential of coal,dark mudstone and mudstone are evaluated.The results show that the coal maceral of Jurassic system in the study area are mainly composed of Vitrinite,the content of Exinite and Sapropel group is larger,and with poor Inertinite.The organic matter of hydrocarbon source rocks are abundance,coal and dark mudstone are the best hydrocarbon source rock,and the mudstone is the low to moderate hydrocarbon source rock.The organic matter types of the source rock are mainly III.The organic mature of the source rock is in the low mature and mature stage.As the well drillings in the study area are exiguity,the quality and distribution of source rock in Shisanjianfang and surrounding area are couldn't detected by the measured geochemical data.In this study,basing on the measured geochemical data,the distribution and content of the TOC in the Shisanjianfang area are obtained using the borehole seismic inversion model.The results show that,the major hydrocarbon generation formation is the SQ2 sequence of Xishanyao formation in the study area.The hydrocarbon source in the SQ2 sequence is distribution among 0~350m,the average is 124 m,the most thickness hydrocarbon source rock is distributed in the northwest corner of piedmont zone and south slope.The maximum TOC of study area is 3.6% and distributed in the northwest south slope.The TOC value of source rock which is greater than 1% of the study is mainly distributed in the south slope and the middle of block uplift.The reservoirs of Xishanyao formation is development,while the reservoirs of Sanjianfang formation and Qiketai formation are not development.As the high geothermal gradient and the source rock buried deep in the early time(middle-late Jurassic),the reservoirs of the study area are compact.The study area is mainly development of secondary porosity,the reservoir space are mainly intergranular pore,intergranular dissolved pore,intercrystalline pore and intragranular dissolved pore,etc,and the primary intergranular pore and intragranular dissolved pore are the most common.In the vertical direction,the pores in the more than 600 m formation are main for the primary pore which control by compaction,the poresity in the formation between 600 m-1500 m are mainly the residue primary porosity that controlled by the compaction and pressolution.In the formation between the 1500-2200 m,the Dissolution enhancement,the formation are major development the mix-porosity that compared by the secondary porosity and residual primary pore.Under the 2200 m,the porosity type of the formation are the secondary porosity that produced by the dissolution.There are two sets of caprocks development in the Shisanjianfang area,the first set of cap rock is the mudstone of upper paragraphs in Qiketai formation,and along with the large set of mudstone overlying Qigu group.The thickness of this set of cap rock is higher,with the stable distribution,and with the good sealing performance.The second set of cap rock is the mudstone that distribution in the lower of Sanjianfang formation.The characteristic of this set of cap rock are thinner than the first set of cap rock,but with the small lateral variation and into the lithology well,have the certain ability of block.The study area is development two fault fold structure belts,the Dubu fault fold structure belt and Shisanjianfang fault fold structure belt,respectively.The traps in the piedmont zone are mainly faulted anticline.The traps that distribute in the south slope are relatively decentralized and with the poor ribbonization,and major are the faulted anticline and anticline.The oil and gas migration path system of the study are mainly for the fault,sand-body and fault sand body composite petroleum system,and have the conditions to forming the structure-lithology complex reservoirs.(2)The stratigraphic temperature and the maturity of the source rocks in the study area are as low as the north and south,and the west and east,which is related to the burial depth of the source rock.The early Jurassic and Cretaceous are the critical periods of oil and gas generation and accumulation in the study area.The crude oil in the study area is mainly derived from plant wax and sporopollen.Natural gas mainly that coal-based gas.The 1D,2D and 3D burial history,thermal history and maturity history are analyzed using the basin simulation technology.The burial history simulation results show that there are two stratigraphic sedimentation period of the study area,are the Upper-Middle Jurassic and middle-late Triassic,respectively.In these two sedimentary periods,the stratigraphic in the study area are sedimentary quickly and the sedimentation rate is generally larger.The thermal history simulation results show that the formation temperature of the study area is constantly decrease from the Jurassic.The deeper burial,the higher temperature,and the formation burial in the 3500 m,the formation temperature is surpass 150°C.In the gentle slope belt,with the shallow buried depth,the formaiton temperature is decreasing.The buried depth of Jurassic strata in the eastern gentle slope belt is less than 2500 m,and the temperature is below 105 ° C,according to the theory of thermal degradation of kerogen,the source rocks are just in mature stage.The formation temperature in the study area overall performance for lower from north to south,and higher from east to west,and the highest temperature area is located in the northwest of the study area.The maturity history simulation results show that the distribution range of Ro in study area is between 0.2%-1.6%.In the late Jurassic,the source rock of middle-lower Jurassic is entered the hydrocarbon generation threshold.The corresponding threshold depth is about 1500 m,the temperature is about 110 ° C.In the same horizon of the study area,the maturity of source rock in the north of the study area is higher than the south,and the maturity of source rock in the western is higher greater than the eastern.Under the deep sag area in northern,the main body of middle Jurassic hydrocarbon source rocks is in the medium maturity stage,the underneath part of hydrocarbon source rock has reached the peak hydrocarbon generation.The hydrocarbon source rocks of Upper Jurassic(Qigu formation and Qiketai formaiton)in the northern territory are born into the hydrocarbon generation threshold,the source rock is in the low-medium mature stage,corresponding burial depth is between 1500-2200 m.In south of the study area,most parts of the middle-lower Jurassic hydrocarbon source rock body has not entered the hydrocarbon generation threshold nowadays;the hydrocarbon source rock of upper Jurassic formation(Qigu formation and Qiketai foramtion)are in low mature stage only in the deep sag area,and the mian source rock has not yet entered the hydrocarbon generation threshold.On the whole,in addition to the source rock of the half of southern and the east of the study area are still in the immature stage,the source rock in the other tectonic units have been mature,and the source rock maturity in the study area overall performance for lower from north to south,and higher from east to west,and the most maturity area is located in the northwest of the study area.The results of simulation hydrocarbon generation and expulsion history show that the oil and gas generation are both started from the middle-late Jurassic.After the oil and gas generated quickly entered the stage of hydrocarbon expulsion,and enter the peak period of hydrocarbon generation in the early cretaceous.The quality of gas production of the hydrocarbon source rocks is greater than the amount of oil,the ratio is between 2~5.The deeper of hydrocarbon source rock burial,the higher of hydrocarbon generation.The expulsion time of hydrocarbon source rock is match with the time structure formation in the study area.The middle-late Jurassic and early Cretaceous is the critical period of oil and gas generation and accumulation.The genetic types of oil and gas,the type of oil and gas resources and the petroleum resources quantity in the studied area are analyzed,the organic matter of the samples are mainly comes from the lower aquatic organisms,the evolution degree of source rock is low,the crude materials mainly from plant wax,sporopollen that with the high carbon number.The accumulation period of the oil and gas in the study area into two phases,are early Cretaceous and Pliocene,respectively.The simulation results of basin simulation technology for the oil and gas resources in the studied area show that there are two kinds of petroleum resources in the study area,they are natural gas and petroleum oil,respectively.The oil amount is about 194.2 Mm3,and the gas amount is about 557.29 Mm3.(3)The source rocks of the study area began to produce natural gas at the end of the Jurassic sedimentary period,and the Cretaceous stage had a certain hydrocarbon generation scale.The oil and gas migration path in the study area is mainly controlled by the tectonic characteristics of the basin,and the accumulation of oil and gas reservoirs is high at the structural level.Oil and gas are mainly stored in the J2x4 and the J2s2.The oil and gas reservoirs are mostly self-contained.There are anticyclonic reservoirs,fault-type reservoirs and tectonic-lithologic reservoirs in the study area.The display of oil and gas migration in Shisanjianfang and surrounding area show that,oil and gas are mainly concentrated in Sanjianfang group,Xishanyao group,Sangonghe group and Badaowan group.Each group has containing multiple oil and gas layer,and the gas show absolute predominance,this suggests that there may be existed the gas reservoir in the study area.The advantages and disadvantages of the four simulation methods for oil and gas migration of the Petromod software are contrasted.And the hybrid migration simulation method is selected for simulation the oil-gas migration and accumulation of 2D profile and 3D stratigraphic framework in each geological history period of the study area.The study results show that in the study area in the late Jurassic(145 Ma)the source rocks began to creates gases,in the early cretaceous(136 ma),the source rock have a certain scale of hydrocarbon generation,and in this time the oil and gas secondary migration began.The stratigraphic deposition was interaction with the fault activity and the caprock development,the formation and open of fracture that promoted the gas migration into the reservoir and accumulation.The middle-late Jurassic sedimentary period is a key period of gas accumulation in the study area.The pathways of oil and gas migration in the study area are mainly controlled by the basin tectonic characteristics,and the reservoirs are major gathered in the structural high.On the lateral,the oil and gas migration along the sand body to the both sides,and accumulation in the structural high.In the vertical,class II fractures is the upward channel of oil and gas migration,and the oil and gas are mainly stored in J2x4 formation and J2s2 formaiton,the oil and gas reservoirs are mostly“self-storage”.From the results of oil and gas migration and accumulation,it can be seen that the oil and gas migration and accumulation in the study area are matched with the characteristics of structure,that is,oil and gas reservoirs are formed in tectonic development and qualitative period.The simulation results of three-dimensional of oil-gas migration show that there is little hydrocarbon formation of the Xishanyao Formation(J2x)source rocks in the middle Jurassic.In the late Jurassic(154Ma),the source rocks are gradually generated,and the oil and gas migration and accumulation characteristics are scattered,the migration distance is short,and the accumulation is close.In the 146 Ma,in Xishanyao groups,a large number of oil and gas are generated and started migration.The oil and gas migration path are mainly points to the high site.The main areas of oil and gas accumulation are the piedmont zone and the southern part of the study area.With the tectonic movement,the study area entered the large number of hydrocarbon generation and hydrocarbon expulsion stage.During the early Cretaceous(136Ma),a large number of oil and gas began to migration and accumulation.At this time,the oil and gas has been formed the secondary migration,and the direction of secondary migration of oil and gas was mainly the low potential area.From the present situation of oil and gas migration,it can be seen that the oil and gas are mainly concentrated in the low-lying area of the northwest in the study area.The oil and gas migration and accumulation are mainly controlled by the structural characteristics of the study area.Three types of oil and gas reservoirs are found in the study area,such as anticycling oil and gas reservoirs,fault-type oil and gas reservoirs and tectonic-lithologic reservoirs.The types of oil and gas reservoirs are mainly controlled by palaeo-structure background,faults and lithology.Through the above research,there is a new understanding of the source rock conditions and hydrocarbon accumulation laws in the Shisanjianfang area.By using the well-seismic joint inversion method,it is overcome the difficult that too sparse welldrilling to evaluate the source rock of the study area,and the quality and distribution characteristics of the source rock are described.At the same time,based on the measured data,the characteristics of source rock,hydrocarbon expulsion,hydrocarbon accumulation and migration are systematically analyzed by using basin simulation technology,and the main factors of hydrocarbon accumulation in the study area are summarized.Studies have shown that Shisanjianfang area have a certain potential for oil and gas resources.