| Yitong Basin is a part of north in Tanlu fault zone,Source rocks has a large thickness and the quality is very well,the development of reservoir is very well, transpression in late of basin evolvement make Yitong basin to becoming a lot of hydrocarbon resources basin, potential exploration is abundance. Preliminary study indicates there is a very complex petroleum accumulation history that reservoirs in the Yitong Basin experience multi-stage hydrocarbon charging from multiple sources and late adjustment and reconstruction due to the multi-stage tectonics, especially the difference subsidence and tectonic uplift. Oil and gas exploration degree of YiTong basin is low, which has the good exploration prospects. The complex tectonic belt, bedrock buried hill and the southeast margin of fan bodies are the three key factors in the future exploration. But because of the limiting factor of the overall degree of prospecting, geological condition is complex, three-dimensional seismic quality is not well enough. In order to control the basin sedimentary characteristics and hydrocarbon accumulation factors, the corresponding engineering supporting technology still need to continue to research, especially in the complex structure, seismic data which can not meet the needs of reservoir prediction. Its structure characteristics, sedimentary and hydrocarbon accumulation mechanism, such as favorable exploration zone optimization needs to be studied further.This paper applys a new technology, which is based on theories about oil geology, well drilling, geophysics, logging geology and a lot of laboratory tests. Using prestack depth migration procession technology, structure fine interpretation technology, reservoir prediction technology, deposit seismic facies identification technology, fluid inclusion analysis technology, highlightly expound structure, deposit and features of hydrocarbon accumulation. The mainly conclusions are below:Conclusion one:Changing subducted direction of Pacific Plates changes the nature of fault in the northwestern Yitong Basin, left-handed transtension changes right-handed transcompress and forms complex tectonic zone. Under the regional pressure torsion stress, YiTong fracture in Neogene in the northwest edge is right strike-slip, extrusion properties of thrust. Main evidence are:1)The core data show that formation complex; crumpled compression is obviously; part of the core data shows that strata broken, almost close to vertical. Squeezed make the geosphere formed multiple small folds, and develop phase of the small fault, has the mutual interleaving phenomenon. It shows that the northwest of the strata has undergone strong tectonic activities, and extrusion effect is obvious.2) Basin field geological outcrops appear a large number of compression in the surface of the fold which is formed by the structure;3) The new3-D seismic data, combining with drilling data, the comprehensive analysis that the reverse fault exactly exist. It formed a complex tectonic belt in the northwest. Complex tectonic belt of small fault nose strcture is usually formed by the deformation of mudstone. U style tectonic block is detenting tectonic block in strike-slipping. From the view of the distance of strike-slipping, if the distance closing the northwest is the more larger, the strike-slipping of tectonic block near by the basin is the more smaller; Different district of bordering fault has different structure style, and uplift tectonic action still is continued, it is favour of the generation of hydrocarbon,hydrocarbon expulsion and the migration and accumulation of hydrocarbon,it makes the complex tectonic zone became the location of hydrocarbon accumulation.Conclusion two:The development of reservoir in the northwestern is very well, the fast accumulation of fans (it shows thick lay, fast nipped wedge on seismic section) have a very poor separation and physical property; the remaining developped fans(on seismic section,it displays thin fans having a long distance,often have foreset structure or downlap structure)have a relatively good physical property,and the scale of fans is more larger, the physical property of reservoir is more better; the process of recognize the fan body, the results of predictted inversion and attribute can only reference, artificial identification of seismic facies, sedimentary structure is very important. Basin internal fan is superimposed with each other, reservoir developed, but the complex tectonic belt exist undevelopment reservoir zone. The palaeogeomorphology controls the location of fans development and the extending direction, nowdays the valley of the northeast of Dahei mountain in northwestern Yitong basin often is the provenance entrance controlling fans of the northwestern basin,large fault often controls the throughgoing direction of fans, the growth fault within the basin controls sand body throughgoing, the layer’s thickness is the thicker (old below-lying), the reservoir is the more developped; the compression action causes reservoir’s physical property becoming poor, the affection is mutually related the layer’s deformation.Conclusion three:The conditions for oil/gas accumulation are very beneficial. Fiist, hydrocarbon generation depression near the northwestern basin, source rocks is adequate, second, complex tectonic zone is forming by uplift tectonic action, it is the location for hydrocarbon migration, and it has a good accumulation condition; oil/gas accumulation is controlled by maturity for source rocks, radius for efficient hydrocarbon supply and the feature of reservoir development; Otherwides, stress release zone has a bad saving condition, example the intersections of No.2fault and the northwestern fault, it is the entrance for large supply, mudstone development isn’t good, fault development is good, actually, the saving conditions for this locations through drilling data is not good; The relationship between uplift tectonic action and hydrocarbon migration is intimate, the time of changing subducted direction of Pacific Plates is about40Ma, using inclusion technologe confirm the earliest time for hydrocarbon migration, it is about37-40Ma, it illustrates that the relationship uplift tectonic action with hydrocarbon migration is intimate. Subaqueous fan body in the nearshore has basic petroleum geological conditions to form large area of fault-lithological oil reservoir, structural-lithologic oil reservoir. The main reason is:the larger the nearshore subaqueous fan body are in a favorable tectonic facies belt, with abundant oil sources and the widespread distribution of subaqueous fan sand body which match to the oil sources, and in the near northeast updip direction-southwest to the development of the two groups of reverse fault crosscutting northwest the fan body of content source direction. The extrusion of basin evolution period, the fault sealing ability is good, from the backer of hydrocarbon-generating sag of the accumulation of oil and gas accumulation and hydrocarbon concentration plays an important role in shade, oil and gas mainly in the nearshore subaqueous fan sedimentary system of fan and outer fan facies formed in the large area of the distribution of fault-lithological, structural-lithologic oil and gas reservoirs.Conclusion four:The northwestern bain is the complex tectonic zone having a lot of gas/oil, but different section have different areas and horizons. At Moliqing fault depression, source rocks’s maturity is not high, but ridus supplying efficient hydrocarbon is larger, so the main layer is di-segment under the basin, it develops the pattern of self-generating and self-preserving reservoirs; river forks in the road fault depression have a large sedimentation, and rocks’s maturity is high, except for Shuangyang formation, Sheling formation and Yongji formation all develop efficient source rocks, oil and gas reservoirs all present, it have a lot of objective intervals, the potential for exploration is good; At Luxiang fault depression, it’s maturity betweens two parties, limited by the data, the level of exploration is low, but Shuangyang formation and Sheling formation are main layers. We think Moliqing rift in the preservation condition is good primary hydrocarbon accumulation. Oil source mainly comes from the shuangyang group of hydrocarbon source rocks, came from the northwest edge of the door body, cutting by a series of fault which is parallel to the boundary faults, in the complex tectonic belt, especially the front of the complex tectonic belt, forming fault-lithological reservoirs, sag of internal development of a large area of lithologic reservoirs, preservation conditions is good, oil content is abundant; Vertical, double two sections of oil content is better than double three sections, the main relation is the angle of underpart of reverse fault is big, sealing ability is better than the upper.According to the analysis of the typical petroleum pools and formation water salinity, it incorporateds result of adamantine index and conservation condition from petroleum inclusions, which reveal that conservation condition is better in the foot walls of majority faults than hanging walls and the northwest part is better than the southeast of Yitong basin. A series of uplifted structures in the southeast experiences strong reconstruction, especially at the top part, hydrocarbon migrated from faults suffers water flushing and biodegradation which slightly affect the Shuangyang reservoirs in depp part. Majority limbs of the uplift tectonic zones located at downthrown block of faults have good conservation condition and oil-bearing condition. According to above researches, conservation and reconstruction type reservoirs can be discriminated as two models. Conservation type reservoirs will become the main objects of exploration.Major innovation points of this paper are:(1) Resuming the forming process on complerx tectonic zone in northwestern basin and building up tectonic style at different sections;(2) Analysing fans through-going and controlling factor, in the light of palaeotectonics, nowdays physiognomy, the feature of fault controlling sand body, combining the feature of facies and drilling data, synthesizing and predicting fans through-going, repairing the failing on seismic data can’t meeting reservoir prediction;(3) Researching the hydrocarbon migration and accumulation models of complex tectonic zone in the northwestern Yitong basin, the action of tectonic controlling the oil/gas, pointing out beneficial exploration area. |
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