Distribution, evolution and structural properties of Wushenqi paleo-uplift in Ordos Basin, NW China

This paper depicts the distribution of the Wushenqi paleo-uplift in the Ordos Basin by using the latest drilling and seismic data, and analyzes the tectonic evolution of the paleo-uplift with the support of Bischke curve and balanced section. The compressional Wushenqi paleo-uplift which developed in the Early Caledonian orogeny(Huaiyuan orogeny) is approximately a ellipse extending in S-N direction. Its long axis is about 194 km and short axis is about 55-94 km in nearly W-E direction. The denudation thickness and area of the Cambrian in the core are 170-196 m and 11 298 km^(2), respectively. It was mainly formed during the Huaiyuan orogeny according to the chronostratigraphic framework. It was in the embryonic stage in the Middle-Late Cambrian, denuded after developed obviously at the end of Late Cambrian. The paleo-uplift of the 3rd member of the Ordovician Majiagou Formation was reactivated and reduced in area. In the sedimentary period of the Ma 4 Member-pre-Carboniferous, the paleo-uplift experienced non-uniform uplift and denudation. It entered the stable period of burial and preservation in the Carboniferous and later period. The Wushenqi paleo-uplift was formed on the weak area of the basement and tectonic belts, into an compressional structure with irregular morphology, under the control of the non-coaxial compression in the south and north and the stress transmitted by the uplift in the basin. The Wushenqi paleo-uplift has a controlling effect on the sedimentary reservoirs and hydrocarbon accumulation.

Migration of paleo-uplift in southwestern Tarim Basin and its implications for orogenesis and reservoir development, NW China

Based on well horizon calibration,the typical seismic profiles in southwestern Tarim Basin were interpreted systematically,regional geological sections were established,and the regional denudation thickness of each tectonic period was restored.On this basis,the plane morphology maps of ancient structures of the Cambrian pre-salt dolomites in different periods were compiled,and the spatial distribution,development,evolution and migration of paleo-uplift in the late Early Paleozoic were analyzed.In the late Early Paleozoic,there existed a unified regional paleo-uplift widely distributed in southwestern Tarim Basin,which is called the southwestern Tarim plaeo-uplift.The“Tarim SW paleo-uplift”and“Hetian paleo-uplift”proposed in previous literatures are not independent,but the result of the spatio-temporal migration and evolution of the southwestern Tarim paleo-uplift identified in this paper.The southwestern Tarim paleo-uplift emerged at the end of Middle Ordovician,and took its initial shape with increased amplitude in the Late Ordovician.During the Silurian,the southwestern Tarim paleo-uplift rose steadily and expanded rapidly to the east,incorporating Pishan-Hetian and other areas,with the structural high locating in the Pishan-Hetian area.During the Devonian,the southwestern Tarim paleo-uplift began to shrink gradually,to a limited range in the Pishan-Hetian area in the southern part of the basin.During the Carboniferous,the southwestern Tarim paleo-uplift became an underwater uplift,that is,the paleo-uplift gradually died out.The southwestern Tarim paleo-uplift belongs to the forebulge of the southwestern Tarim foreland basin in the late Early Paleozoic,and its formation and evolution are related to the early Paleozoic orogeny of the West Kunlun orogenic belt in the south of the Tarim Basin.The migration of the southwestern Tarim paleo-uplift from the northwestern part of the southwestern Tarim Basin to the Pishan-Hetian area indicates the early Paleozoic orogenic process of the West Kunlun orogenic belt,which started in the western section at the end of Middle Ordovician and extended from west to east in a“scissor”style.The migration and evolution of the southwestern Tarim paleo-uplift controlled the development of unconformities at the end of Middle Ordovician,the end of Late Ordovician,and the end of Middle Devonian,and the spatial distribution of dissolved fracture-cave reservoirs in weathered crust below the unconformities in the southwest of Tarim Basin.The migration of the structural high of the southwestern Tarim paleo-uplift also played an important role in controlling the development of dissolved fracture-cave reservoirs in weathered crust.

Structural Characteristics and their Significance for Hydrocarbon Accumulation in the Northern Slope of the Central Sichuan Paleo-uplift

Based on 2D and 3D seismic data,the latest drilling data and field outcrop data of the northern slope of the Central Sichuan paleo-uplift,the structural analysis method is used to analyze unconformity development characteristics and fault characteristics during the key structural transformation period,discussing the influence of the structural characteristics on the hydrocarbon accumulation of deep carbonate rocks.The results show that:(1)The two key unconformities of the Tongwan and Caledonian periods were primarily developed in deep carbonate rocks.Firstly,Tongwan’s unconformities are characterized by regional disconformities between the second and third members of the Dengying Formation,the top formation of the Sinian and the lower Cambrian,strips of which zigzag through the north and south sides of the study area.Secondly,the Caledonian unconformity is characterized by a regional unconformable contact between the lower Permian and the ower Paleozoic strata.From NE to SW,the age of the strata,which were subject to erosion,changes from new to old,the denudation distribution showing as a nose-shaped structure which inclines towards the ENE.(2)Boundary fault and transtensional strike-slip faults developed in the Sinian to Paleozoic strata.In profile,there are three types of structural styles:steep and erect,flower structures,’Y’and reversed’Y’type faults.In plane view,the Sinian developed extensional boundary faults extending in an almost NS direction,strike-slip faults developing and extending linearly in approximately EW,WNW and NE strikes in the Cambrian,with characteristically more in the south and less in the north.(3)The faults in the northern slope show obvious zonal deformations in transverse view as well as significant stages and stratified activity in a longitudinal direction.Among them,the activity of faults in the Sinian was the strongest,followed by the activity in the Cambrian period,the activity intensity of faults in the Permian period being the weakest.This fault activity can be divided into four periods:Sinian,Cambrian-Permian,the early Indosinian period and the late Indosinian-Himalayan period,the transtensional strikeslip faults being the products of oblique extensions of pre-existing weak zones in the Xingkai and Emei taphrogenesis,with a particular inheritance in the main faults.(4)Combined with hydrocarbon accumulation factors,it is considered that the epigenetic karstification of the Tongwan and Caledonian unconformities in the northern slope controlled the formation and distribution of carbonate karst reservoirs over a large area,also acting as a good pathway for oil and gas migration.The extensional faults developed at the margin of the NS trending rift,controlling the sag-platform sedimentary pattern in the Dengying Formation of the Sinian.Strike-slip faults in NE,WNW and ENE directions may control the microgeomorphological pattern inside the platform and intensify the differential distribution of grain beach facies.The multi-stage hereditary activity of strike-slip faults not only improved the porosity and permeability of the reservoirs,but also acted as the main channel of oil and gas migration,providing favorable conditions for the development of the current multi-layer gasbearing scenario in the northern slope of the Central Sichuan Basin.

Natural gas geology and exploration direction of the Cambrian Lower Canglangpu Member in central Sichuan paleo-uplift,Sichuan Basin,SW China

Based on drilling data of JT1 and CS1,outcrop profiles and seismic data,the sedimentary pattern,space configuration of source-reservoir-cap combinations and paleouplift evolution characteristics of the Cambrian Lower Canglangpu Member in the central Sichuan paleouplift have been investigated to determine the favorable exploration zones.Controlled by Deyang-Anyue rift,the Lower Canglangpu Member features differential characteristics from east to west in sedimentary framework.In the west side of the Deyang-Anyue rift,this member is composed of clastic sediments,while in the east side of the Deyang-Anyue rift,it is fresh water shelf sediments,with grain beaches occurring along edges of the depressions,shelf and lagoon.Among the beaches,the dolomitic ones are mainly distributed around the depression edge and in the north of the lagoon.The beach sediments could become high quality reservoirs under the effect of karstification.Underlying the Lower Canglangpu Member is the widespread source rock of the Qiongzhusi Formation,so oil and gas generated by the Qiongzhusi Formation source rock can directly charge into the beach reservoirs.The sandy mudstone of the Upper Canglangpu Member can serve as the caprock of the Lower Canglangpu Member reservoir.The dolomitic beaches are located at the higher part of the paleo-uplift during the main accumulation period,with good hydrocarbon accumulation elements.Blocks PT1-CS1,HT1-GT2 and east GT2 are favorable exploration zones.

Structural patterns of fault damage zones in carbonate rocks and their influences on petroleum accumulation in Tazhong Paleo-uplift, Tarim Basin, NW China

Based on the outcrop survey,3D seismic data interpretation,drilling data analysis,the structural patterns and distribution of fault damage zones in carbonate strata of Tazhong Paleo-uplift were established to reveal the oil and gas enrichment law in the fault damage zones.The following findings were reached:(1)Through the filed survey,the fault damage zone system consists of fault core,damage zone with branch fault and fracture network.Affected by the active nature of the major faults,the fault damage zones differ in planar pattern and scale along the major faults.(2)3D seismic profiles reveal that there are three types of fault damage zones in carbonate strata in Tazhong paleo-uplift,strike-slip fault damage zones,thrust fault damage zones and superimposed fault damage zones.Featuring3 flowers and 3 root belts in vertical,the strike-slip fault damage zone can be subdivided into linear type,oblique type,feather type and horsetail type in plane.Thrust fault damage zones can be further divided into fault anticline type,anticline type and slope type.As the superimposition result of the above two kinds of fault damage zones,superimposed fault damage zones appear in three patterns,intersect type,encompassment type and penetrating type.(3)Cores from wells and geochemical data show oil and gas may migrate along the major fault and laterally.The feather type in strike-slip fault system,fault anticline type in thrust fault damage zone and intersect type in superimposed fault damage zone are possible sites for high production and efficiency wells.

Paleo-uplift forced regional sedimentary evolution:A case study of the Late Triassic in the southeastern Sichuan Basin,South China

The sedimentary environment of the Upper Triassic in the southeastern Sichuan Basin is obviously controlled by Luzhou paleo-uplift(LPU).However,the influence of paleo-uplift on the sedimentary patterns of the initial stages of this period in the southeastern Sichuan Basin has not yet been clear,which has plagued oil and gas exploration and development.This study shows that there is a marine sedimentary sequence,which is considered to be the first member of Xujiahe Formation(T_(3)X^(1))in the southeastern Sichuan Basin.The development of LPU resulted in the sedimentary differences between the eastern and western Sichuan Basin recording T_(3)X^(1)and controlled the regional sedimentary pattern.The western part is dominated by marine sediments,but the eastern paleo-uplift area is dominated by continental sedimentation in the early stage of T_(3)X^(1),and it begins to transform into a marine sedimentary environment consistent with the whole basin in the late stage of the period recorded by the Xujiahe Formation.The evidences are as follows:(1)time series:based on the cyclostratigraphy analysis of Xindianzi section and Well D2,in the southeastern Sichuan Basin,the period of sedimentation of the Xujiahe Formation is about 5.9 Ma,which is basically consistent with the Qilixia section,eastern Sichuan basin,where the Xujiahe Formation is widely considered to be relatively complete;(2)distribution and evolution of palaeobiology:based on analysis of abundance evolution of major spore-pollen,many land plant fossils are preserved in the lower part of T_(3)X^(1),indicates the sedimentary environment of continental facies.In the upper part of T_(3)X^(1),the fossil of terrestrial plants decreased,while the fossil of marine and tidal environment appeared,this means that it was affected by the sea water in the late stages of T_(3)X^(1);(3)geochemistry:calculate the salinity of water from element indicates that the uplift area is continental sedimentary environment in the early stage of T_(3)X^(1),while the central and western areas of the basin are marine sedimentary environment.Until the late stage of T_(3)X^(1),the southeast of the basin gradually turns into marine sedimentary environment,consisting with the whole basin;(4)types of kerogen:type III kerogen representing continental facies was developed in the early stage of T_(3)X^(1)in the uplift area,and type II kerogen,representing marine facies,was developed in the late stage;while type II kerogenwas developed in the central and western regions of the basin as a whole in T_(3)X^(1).This study is of great significance for understanding of both stratigraphic division and sedimentary evolution providing theoretical support for the exploration and development of oil and gas.

四川盆地乐山—龙女寺古隆起地质结构及构造演化

乐山-龙女寺古隆起位于四川盆地中西部,紧邻龙门山构造带。古隆起的地质结构及构造演化对陆内变形和油气勘探具有重要的意义。利用最新的高分辨率地震和探井资料,结合盆地周边的露头资料,对乐山-龙女寺古隆起的地质结构进行了研究。其结果显示:乐山-龙女寺古隆起地质结构在整体上构造变形较弱,仅在龙门山前和龙泉山地区变形相对较强;剖面上存在多套滑脱层,具有上、下分层变形特征。通过地震剖面精细解释,并利用平衡剖面技术,分析了古隆起的构造演化。研究认为乐山-龙女寺古隆起受基底隆起控制、具有一定继承性,经历了多期同沉积隆起兼剥蚀过程,形成于前二叠纪,随后经过印支运动、燕山运动及喜马拉雅运动的调整改造最终定型;其构造演化经历了雏形阶段、发展阶段、强烈隆升剥蚀阶段、稳定埋藏阶段、川西前陆盆地发育阶段以及调整定型阶段,主要受基底和分层滑脱系统2方面因素的影响。

New understandings on gas accumulation and major exploration breakthroughs in subsalt Ma 4 Member of Ordovician Majiagou Formation,Ordos Basin,NW China

Geological conditions and main controlling factors of gas accumulation in subsalt Ma 4 Member of Ordovician Majiagou Formation are examined based on large amounts of drilling,logging and seismic data.The new understandings on the control of paleo-uplift over facies,reservoirs and accumulations are reached:(1)During the sedimentary period of Majiagou Formation,the central paleo-uplift divided the North China Sea in central-eastern of the basin from the Qinqi Sea at southwest margin of the basin,and controlled the deposition of the thick hummocky grain beach facies dolomite on platform margin of Ma 4 Member.Under the influence of the evolution of the central paleo-uplift,the frame of two uplifts alternate with two sags was formed in the central-eastern part of the basin,dolomite of inner-platform beach facies developed in the underwater low-uplift zones,and marl developed in the low-lying areas between uplifts.(2)From the central paleo-uplift to the east margin of the basin,the dolomite in the Ma 4 Member gradually becomes thinner and turns into limestone.The lateral sealing of the limestone sedimentary facies transition zone gives rise to a large dolomite lithological trap.(3)During the late Caledonian,the basin was uplifted as a whole,and the central paleo-uplift was exposed and denuded to various degrees;high-quality Upper Paleozoic Carboniferous-Permian coal measures source rocks deposited on the paleo-uplift in an area of 60000 km^(2),providing large-scale hydrocarbon for the dolomite lithological traps in the underlying Ma 4 Member.(4)During the Indosinian-Yanshanian stage,the basin tilted westwards,and central paleo-uplift depressed into an efficient hydrocarbon supply window.The gas from the Upper Paleozoic source rock migrated through the high porosity and permeability dolomite in the central paleo-uplift to and accumulated in the updip high part;meanwhile,the subsalt marine source rock supplied gas through the Caledonian faults and micro-fractures as a significant supplementary.Under the guidance of the above new understandings,two favorable exploration areas in the Ma 4 Member in the central-eastern basin were sorted out.Two risk exploration wells were deployed,both revealed thick gas-bearing layer in Ma 4 Member,and one of them tapped high production gas flow.The study has brought a historic breakthrough in the gas exploration of subsalt Ma 4 Member of Ordovician,and opened up a new frontier of gas exploration in the Ordos Basin.

Distribution and exploration direction of medium-and large-sized marine carbonate gas fields in Sichuan Basin, SW China

Based on the analysis of the basic characteristics of medium-and large-sized marine gas fields in Sichuan Basin, combined with the division of major reservoir forming geological units in the marine craton stage and their control on key hydrocarbon accumulation factors, the distribution law of medium-and large-sized marine carbonate gas fields in the basin was examined and the exploration direction was pointed out. Through the analysis of the periodic stretching-uplifting background, it is concluded that five large scale paleo-rifts, three large scale paleo-uplifts, five large scale paleo erosion surfaces were formed in the marine craton stage of Sichuan Basin, and these geological units control the key reservoir forming factors of medium and large sized gas fields:(1) Large-scale paleo-rifts control the distribution of high-quality hydrocarbon generation centers.(2) The margin of large-scale paleo-rifts, high position of paleo-uplifts and paleo erosion surfaces control the distribution of high-quality reservoirs.(3) Large-scale paleo-rifts, paleo-uplifts, paleo erosion surfaces and present tectonic setting jointly control the formation of many types of large and medium-sized traps.(4) Natural gas accumulation is controlled by the inheritance evolution of traps in large geological units. Based on the comparative analysis of the distribution characteristics of medium-and large-sized gas fields and large geological units, it is proposed that the superimposition relationship between single or multiple geological units and the present structure controls the distribution of medium-and large-sized gas fields, and the "three paleo" superimposed area is the most advantageous. According to the above rules, the main exploration fields and directions of medium-and large-sized marine carbonate gas fields in Sichuan Basin include periphery of Deyang-Anyue paleo-rift, eastern margin of Longmenshan paleo-rift, margins of Kaijiang-Liangping oceanic trough and Chengkou-western Hubei oceanic trough, the high part of the subaqueous paleo-uplifts around Central Sichuan, paleo erosion surfaces of the top boundary of Maokou Formation in eastern and southern Sichuan Basin, paleo erosion surfaces of the top boundary of the Leikoupo Formation in central and western Sichuan Basin.

Cenozoic structural deformation in the Yuqia-Jiulongshan region, northern Qaidam Basin, China

Based on field geological survey, interpretation of seismic reflection profile and thermochronology dating, this paper systematically studied the structural deformation of the Yuqia-Jiulongshan region in northern Qaidam Basin during the Cenozoic. The results show that the area is primarily dominated by a large box-shaped anticline, with steep limbs and a wide and gently-deformed core. The Mahaigaxiu and Jiulongshan anticlines are secondary folds controlled by secondary faults in the limbs of the box-shaped anticline. Whereas the Yuqia and the Northern Yuqia anticlines are secondary folds within the wide core of the box-shaped anticline. The geometry of the box-shaped anticline is mainly controlled by some high-angle reverse faults with certain right-lateral strike-slip components, displaying distinct positive flower structures in section view. Combining the sedimentary correlation and detrital apatite fission track analysis, we believe that the Yuqia-Jiulongshan region was a paleo-uplift that developed slightly in the early Cenozoic, resulting in the relatively thin Cenozoic strata. The intense deformation that shaped the present-day structural framework occurred in or after the sedimentary period of Shizigou Formation. The Yuqia – Jiulongshan paleo-uplift is adjacent to the Sainan depression that is rich in Lower-Middle Jurassic source rocks, and thus has high potential for future hydrocarbon exploration.

The dating and temperature measurement technologies for carbonate minerals and their application in hydrocarbon accumulation research in the paleouplift in central Sichuan Basin, SW China

A new method for reconstructing the geological history of hydrocarbon accumulation is developed, which are constrained by U-Pb isotope age and clumped isotope((35)47) temperature of host minerals of hydrocarbon-bearing inclusions. For constraining the time and depth of hydrocarbon accumulation by the laser in-situ U-Pb isotope age and clumped isotope temperature, there are two key steps:(1) Investigating feature, abundance and distribution patterns of liquid and gaseous hydrocarbon inclusions with optical microscopes.(2) Dating laser in-situ U-Pb isotope age and measuring clumped isotope temperature of the host minerals of hydrocarbon inclusions. These technologies have been applied for studying the stages of hydrocarbon accumulation in the Sinian Dengying gas reservoir in the paleo-uplift of the central Sichuan Basin. By dating the U-Pb isotope age and measuring the temperature of clumped isotope((35)47) of the host minerals of hydrocarbon inclusions in dolomite, three stages of hydrocarbon accumulation were identified:(1) Late Silurian: the first stage of oil accumulation at(416±23) Ma.(2) Late Permian to Early Triassic: the second stage of oil accumulation between(248±27) Ma and(246.3±1.5) Ma.(3) Yanshan to Himalayan period: gas accumulation between(115±69) Ma and(41±10) Ma. The reconstructed hydrocarbon accumulation history of the Dengying gas reservoir in the paleo-uplift of the central Sichuan Basin is highly consistent with the tectonic-burial history, basin thermal history and hydrocarbon generation history, indicating that the new method is a reliable way for reconstructing the hydrocarbon accumulation history.

The formation and evolution of Chepaizi-Mosuowan paleo-uplift and its control on the distributions of sedimentary facies in the Junggar Basin

The Chepaizi-Mosuowan paleo-uplift is a large-scale uplift stretching across the Junggar Basin formed during the Yanshanian. It has experienced four evolutionary stages: the initial forming stage (J1), the intense development stage (J2+3), the waning and burial stage (K-E), and the tilting and extinction stage (N-Q). The most intense period of activities is the Middle Jurassic. Dur-ing the Early Jurassic, the Chepaizi-Mosuowan paleo-structure was a low amplitude uplift. Because of the subsequent strong uplifting during Middle-Late Jurassic, the Middle and Upper Jurassic were eroded. With the evolution of the Chepaizi-Mosuowan paleo-uplift, the sedimentary pattern of the basin changed, and the paleo-uplift separated the northern depositional systems from those in the south side. As a result, the basin tectonics controlled the distribution and evolution of the depositional systems. During Early Jurassic, while the paleo-uplift was low, its controlling effect on depositional systems was limited and sediments coming from the northwest could reach the central and southern parts of the basin. With the strong uplifting of the Chepaizi-Mosuowan paleo-structure during Middle-Late Jurassic, sediments from the northwest provenance could only deposit in the northern graben of the paleo-uplift. The intense erosion of the Middle-Upper Jurassic also changed the former sedimentary center of the basin into a source area, supplying sediments for grabens on both sides of the paleo-uplift. In the Cretaceous, regional subsidence caused the paleo-uplift to be buried again and subsequently sediments accumulated on top of it. The depositional facies are dominated by fluvial in the Early Cretaceous and shallow lacustrine to deltaic in the Late Cretaceous. In the history of the long-lasting development of this paleo-uplift, large-scale erosions of the paleohigh not only provided sufficient sediments to the center of the Junggar Basin, but also created favorable conditions for the formation of various subtle traps such as lithologic and stratigraphic traps.

Temporal and Spatial Evolution Analysis:The Early Paleozoic Paleo-Uplifts in the Tarim Basin

ABSTRACT： Twenty unconformities, primarily superimposed types, were identified based on inter pretation of a 46 000 km seismic profile combined with data from over 40 drilling wells. These respec tively correspond to the main tectonic evolution stages and the boundaries between those stages. Re construction of the original depths of eroded strata was conducted for the Middle Caledonian, Early Hercynian, Late Hercynian, Indosinian, Early Yanshanian and Late Yanshanian unconformities using the virtual extrapolation of seismic reflection. Eroded strata thicknesses were also calculated for indi vidual periods and intervals. Based on the reconstructed data, in combination with data from research on sedimentary facies, a paleogeomorphological profile was constructed for different tectonic evolution stages of the basin during the Early Paleozoic. The profile indicates the presence of obvious regularity in the temporal and spatial evolution of these unconformities. Based on the characteristics of paleouplift evolution and postlayering reconstruction, the paleouplifts were divided into inherited （e.g., Tazhong （塔中）, residual （e.g., North Tarim） and active （e.g., Southwest Tarim and Bachu （巴楚） types. The huge North Tarim uplift represents a typical form of residual paleouplift. The Paleozoic strata in the upper layers of the uplift is in poor condition for reservoir accumulation and preservation; however, the Upper MesozoicCenozoic structural layer can form a secondary reservoir that is rela tively rich in oil and gas. Furthermore, the flank slope area of the uplift is always a key source for oil and gas collection and the most advantageous position for the formation of the original reservoir. The Tazhong paleouplift has been stable since its formation in the Late Ordovician, where petroleum accumulation has been distributed not only in the uplift, but also in the deep and slope belts of the uplift. Important breakthroughs in petroleum exploration of the slope break in the North Tazhong area datingback to the Paleozoic have further confirmed the enrichment of oil and gas in this type of uplift. The Southwest Tarim paleouplift is a buried type, which has given it favorable properties for hydrocarbon migration over a long time. An open question is whether the large amount of oil and gas accumulated here was transported to the current Bachu uplift.

Controlling factors of Dengying Formation reservoirs in the central Sichuan paleo-uplift

Macroscopic and microscopic characteristics revealed that the Dengying Formation reservoir in the central Sichuan paleo-uplift belonged to the compound genetic reservoir of the mound-shoal facies and karst.Development of the reservoir was controlled by the mound-shoal facies,and dissolution-enlarged or added pores(vugs)due to superimposed karstification modification were favorable reservoir spaces.The karst of the Dengying Formation in Tongwan stage was the stratabound-weathered crust karst of the early diagenesis stage,the extensive superimposition of mound-shoal facies and regional karstification in the central Sichuan paleo-uplift area was the key to develop the large-scale continuous Dengying Formation reservoirs.Due to differences in the development degree of mound-shoal facies and in the intensity of karst modification,the reservoir development degree varied in different zones in the paleouplift area.The NS-extending zone on the western side of the Gaoshiti-Moxi area was the sweet spot for reservoir development.Effective identification of mound-shoal facies and fine depiction of karst landform was the key for reservoir prediction of the Dengying Formation to discovery the superimposed area of the mound-shoal facies and the karst monadnock-karst steep slope which similar to Moxi-Gaoshiti area.

四川盆地乐山——龙女寺古隆起震旦系气藏形成机制

以四川盆地乐山—龙女寺古隆起区古老的震旦系深层碳酸盐岩气藏为研究对象,通过系统分析气藏形成的各种特征,包括气藏类型、流体性质、天然气成因与来源、油气充注期次与成藏演化等,研究了气藏的形成模式机制。结果表明,四川盆地震旦系灯影组发育构造、岩性、地层—岩性等多类型气藏,不同气藏流体的性质存在差异。天然气为震旦系烃源岩与寒武系烃源岩混源气,不同气藏混源比例存在差异。气藏的形成经历了"三阶段":古油藏生成、原油发生裂解、气藏调整与定型;具"三机制":古油藏裂解异位聚集、古油藏裂解原位(就近)聚集、晚期干气聚集。对于类似于研究区这种高演化阶段的深层碳酸盐岩气藏,古油藏裂解原位聚集机制可能是气藏形成与保存的最有利模式,最近勘探取得重大突破的川中地区灯影组大型气藏即属于这种模式机制。