Controlling Of Multiple-phase Tectonics On Petroleum Accumulation In The Junggar Basin-Implications For Deep-seated Petroleum Exploration

Junggar basin is rich in oil and gas resources,and is one of the four petroleum basins with the equivalent of more than 10 billion tons of onshore oil and gas resources in China.After 70-year constant exploration and development,deeper hydrocarbon exploration has become an inevitable trend for resource development.Junggar Basin has developed into a huge composite basin superimposed by different prototype basins vertically as a result of multistage tectonic events,the Hercynian movement,the Indosinian movement,the Yanshan movement and the Himalayan movement,since the late Paleozoic.Meanwhile multistage complex tectonic events has complicated the hydrocarbon accumulation process,contributing to some key geological problems in the deep layer oil and gas exploration:(1)sharp divergences about the sedimentary basin types and formation mechanisms during different evolutionary phases,and the structural features of superimposed structural layers;(2)weak research in the macroscopic controlling mechanism of superposed and rebuilt process on reservoir formation and petroleum distribution;(3)lack of a clear understanding of the distribution and accumulation of deep reservoirs,as well as the deep favorable exploration zone.This paper combines the newly deep drilling data,2 D seismic lines across the basin,high-precision 3 D seismic data in key exploration area and the predecessor research results to carry out a comprehensive study in the structural geometry and kinematics of Junggar Basin,development characteristics and evolution of the prototype basins and control action of the multistage superposed and rebuilt process on reservoir forming.Identify fault traces,regional unconformity interfaces and growth strata,and draw up the formation thickness maps,based on the seismic data interpretation system through Land Mark.Apply 2 D-Move to deduce tectonic deformations at different stages by the balanced cross-sections.Model the burial history and thermal history of the key hydrocarbon-generation sags using Basin Mod soft.(1)The tectonic evolution stages of the Junggar Basin are ascertained,based on the identification of regional tectonic unconformities.The Junggar Basin has undergone multi-stage tectonic superimposed and reworking since the Permian.We suggest that the basin has undergone five extension-to-compression tectonic cycles bounded by regional tectonic unconformities.In each tectonic cycle,the stress regime transformed from early extension or stability to late compression.Interpretation of seismic reflection profiles and structural restoration of balanced profile reveal that the Junggar Basin has experienced seven obvious regional tectonic deformations,two stages of extension five stages of regional compression.The two extension regional tectonic deformations were related to post-orogenic stress relaxation of Early Permian and Early Jurassic.The Early Permian extensional deformation was strong and resulted in extensive graben-horst and half-graben structures within the basin.The Early Jurassic extensional deformation was weak and only gave rise to local normal faulting in south part of the basin,displacement and distance these normal faults are relatively smaller than that of Early Permian.The five shortening tectonic deformations were closely related to the regional collision/accretionary orogenic events of late Permian,latest Late Triassic,Late Jurassic,Late Cretaceous and Late Cenozoic,respectively.The sedimentary basin was superimposed and reworked by episodic late Paleozoic to Cenozoic tectonic events,giving rise to the uplift and erosion at the basin margins while folding or tilting within the basin.At present,the basin presents a wedge-shaped geometry,with thickest strata in the south and thinnest strata in the north.(2)The basin's archetypes and subsidence mechanisms in different evolution stages are determined.Under the controls of five-stage periodic extension-to-compression tectonic cycles,the Junggar basin has undergone five stages of tectonic-sedimentary evolution since the Permian.Five-stage periodic extension-to-compression tectonic cycles gives rise to the transition of the basin prototype(from extensional rifting or stable depression to compressional foreland or depression),the extent of the lake(from early expansion and transgression to late shrinking and regression),and sedimentary characteristics(from a normal fining-upward sequence in the lower layer to a reversed coarsening-upward sequence in the upper layer.(a)The Junggar Basin initially developed from several continental rifts into a superimposed basin in the early Permian.At the beginning of the middle Permian,the basin developed into a post-rifting depression basin.The basin inverted during the late Permian compressional uplifting.(b)During the Early to early Late Triassic,the Junggar Basin was a stable depression under a tectonic quiescence setting.In the Late Triassic,all the orogenic belts surrounding the basin were reactivated because of the far-field effect of the Qiangtang collision,and the basin developed into a weak compressive intra-continental foreland composite basin.(c)Early to early Middle Jurassic Junngar Basin was a weak extensional depression.During the late Middle to Late Jurassic,the basin was intensely deformed by a significant compressional and formed a composite basin composed by two foreland basins.(d)The Early Cretaceous tectonic quiesence and Late Cretaceous compression led to the transformation of basin prototype from early neutral depression to late compressional depression.(e)The Junggar Basin was a neutral depression during the Paleogene,and a rejuvenated foreland basin formed along the northern flank of the Tian Shan during the Neogene to Quaternary.The Junggar Basin is a superimposed basin,with different tectonic-sedimentary evolution stages and different basin prototypes.(3)Multi-stage of tectonic superposition and reworking in the Junggar basin play an important role both on essential accumulating elements(source,reservoir,seal,trap,migration,circle,transport and preservation),processes(generation,expulsion,migration and accumulation),and complexity of early-formed reservoirs.Fist,under the geological background of multi-stage tectonic superimposed and reworking,and superimposition of various types of sedimentary basins,multiple sets of source-reservoir-cap assemblages,multiple types of traps and multiple sets of composite oil-gas migration systems have been formed in Junggar basin.Secondly,multi-stage tectonic superimposed and reworking caused to multi-stage and multi-area hydrocarbon generation and expulsion,multi-stage and multi-direction oil and gas migration and multi-stage accumulation in the Junggar basin.Finally,subsequent tectonics can adjust,modify,or destroy the early-formed reservoirs.(4)Favorable zone for deep-seated(buried more than 4500-meter-depth)oil and gas exploration are proposed.Preferential accumulation sites,which locate close to the hydrocarbon generation center,or at the favorable oil-gas migration paths,are prospective deep-seated petroleum exploration targets.(1)Carboniferous structural-lithologic traps in the structural highs surrounding or plunging into the generating sags,(2)lower�middle Permian anticlinal traps beneath the Kebai and Wuxia Fault Belts at the northwestern margin and the middle Permian lithologic-stratigraphic traps in slope areas of migrating sags,and(3)Jurassic-Lower Cretaceous anticlines beneath the Huo-Ma-Tu Fault and Fukang Fault Belt in the southern fold-thrust belt,and stratigraphic or lithologic traps in the northern foreslope areas in the southern Junggar foreland basin.