| Songliao Basin is a typical continental sedimentary basin in the world,which has deposited the most typical continental cretaceous strata in the world and is one of the important oil-producing areas in China.At present,the exploration and development of oil and gas resources in Songliao Basin is mainly concentrated in shallow strata with a depth of 3000 meters.However,in recent years,the exploration and development of deep energy resources in Songliao Basin has received increasing attention,and the exploration and development of deep unconventional energy resources still lacks the support of reservoir forming theory,exploration technology and practice.With the development of Earth system science,people have realized more and more that the formation of energy resources,the change of environment and climate,and even the evolution of the earth have their roots in the deep,that is,the shallow geological evolution is closely related to the dynamic process of the earth's interior.Therefore,it is of great significance to study the basic scientific problems of the connection between deep structural evolution characteristics and shallow response in Songliao Basin to realize the breakthrough of deep energy resources in Songliao Basin.Deep seismic reflection profile detection technology has been recognized by the international geoscience community as a high technology to detect the fine structure of the lithosphere.It plays an important role in the study of the intracontinental lithospheric fine structure,revealing the surface shell rock deformation and structural traces,as well as the important relationship between regional tectonic events and the deep middle and lower crust and even the upper mantle of lithosphere.Its data acquisition and processing basically follow the theory,technology and equipment in petroleum seismic exploration,and adopt the collection method of large charge,long offset and long recording time,as well as the data processing process of high amplitude preservation and high fidelity.Based on the recent acquisition of a internal deep seismic reflection profile Songliao Basin,whick start form the Qinggang County in Heilongjiang Province,south to Zhangzhou County,and passes through the deep scientific drilling project of Songliao Basin—Well SK2,the data collection parameters,original features,data processing and attribute extraction process of the reflection profile were analyzed to analyze the fine lithospheric structure in northern Songliao Basin,the dynamic environment of the basin and the well-seismic response characteristics of the deep oil and gas prospect.The original shot provides the most realistic underground structure information,and the knowledge of its reflection and noise characteristics can improve the authenticity and reliability of the interpretation results of structural information.In view of the recently acquired deep seismic reflection profile of "Well SK2",this paper selects typical shots of different structural units to describe reflection features and noise evaluation,which lays a foundation for later data processing and further interpretation.After repeated observations,the single shot reflection characteristics of different tectonic units in the section are obviously different.The most notable feature is that the shots in the Xujiaweizi fault depression area where Well SK2 is located shows obvious strong middle crust reflection,the Moho offset and mantle reflection dipping north,which are completely different from the shots of the north side Zhonghe fault depression area.At present,the interpretation of deep seismic reflection profiles mainly relies on the qualitative structural interpretation of the interface reflection information reflected by the migrated profiles,but lacks the quantitative attribute constraint of the upper and lower lithology of the interface.The profile of Well SK2 has a high signal-to-noise ratio,and the reflection of Moho is clear and continuous.In this paper,AVO analysis technology and Q value inversion technology from the petroleum industry are introduced to extract and describe the attributes of deep seismic reflection data,so as to improve the utilization of profile data.Among them,the AVO analysis technique is used to describe the variation of amplitude of the Moho reflection with the offset in the profile.The results showed that the fault depression in the south side of the section developed,and the amplitude decreased with offset was smaller than that in the north side of the Minshui region.The area near the Moho surface in fault area has a large ratio of compression to shear wave velocity.Meantime,the spectral ratio method was used to calculate the variation trend of the average Q value of the whole crust and the lower crust within the profile range.The results showed that the average compression wave Q value of the crust within the profile range was 306,which was smaller than the global average model,and the fault depression region had a smaller Q value than the fault uplift region.According to the preliminary analysis,the larger ratio of compression to shear wave velocity of Moho in the fault depression area corresponds to the smaller Q value,which may reflect the higher ductility of rocks in the middle and lower crust of the fault depression area.Based on the comprehensive cognition of the single-shot reflex characteristics and attribute characteristics of the “Well SK2” section,this paper combines the deep seismic reflection profiles of the east-west direction across the northern Songliao Basin to describe the fine structure of the lithosphere,and the tectonic characteristics of the three tectonic domains in the north and periphery of Songliao Basin under the action of Paleo-Asian Ocean,Mongolian-Okhotsk ocean and Paleo-Pacific ocean are discussed comprehensively,and the influence of the three tectonic domains on the formation process of Songliao Basin is considered.The results show that the reflection of cretaceous sedimentary cover in the north of Songliao Basin is distinct from that of deep reflection,with strong reflection amplitude and high continuity.An obvious differences can be observed between upper crust with middle and lower crust.In upper crust,the sedimentary shows strong reflection and igneous rock,crystalline rock show weak reflection.On the lower part of the crust on the east-west section is given priority to with oblique reflection,and visible in north and south to section 5-6 s range is obvious strong reflection area,considering the lower part of the earth's crust tend to a series of the north and south decollements;The strong slant reflection of the middle and lower crust and the transparent reflection area alternate with each other.The location of the transparent reflection area is mostly corresponding to the fault depression area.Multiple lenticular short and strong reflection near the horizontal can be seen in many places;On the whole,the Moho is gentle,but there are obvious amplitude differences.There are many areas with the transparent Moho reflection or the Moho offset,among which the transparent Moho reflection area corresponds to the transparent lower crustal reflection area and the fault depression development area.The time difference between the two ways of Moho offset travel time is within 0.2-0.4s and the corresponding depth difference is within 2km.Meantime,obvious mantle reflection can be observed in both sections,most of which are inclined mantle reflection,with strong near-horizontal mantle reflection locally.Considering two section,and in the north of Songliao Basin in Daqing area as the center,middle and lower crust and mantle reflection dipping to Daqing direction,reflects the deep in the north of Songliao Basin in the role of three tectonic domain successively,presents the characteristics of the multidirectional converge to Daqing as the center.It is inferred that there may be signs of early basement convergence and convergence in Songliao Basin,which experienced later extension,sedimentation and basin-forming processes,and fault depression strata are more likely to be distributed above the basement convergence areaIn order to discuss the characteristics of deep oil and gas reservoirs in the north of Songliao Basin,this paper discusses log and seismic response of Shahezi formation reservoirs based on the latest achievements of Well SK2.The shahezi formation in the adjacent area of songke no.2 well is mainly composed of mud shale,and the whole formation is in dustpan shape.This paper divides it into four sequences,the top sequence and the bottom sequence have strong reflection,and their porosity and vertical and horizontal wave velocity logging curves have a large amplitude of variation,and the gas logging shows a good prospect for oil and gas.Found under Well SK2 and other areas of strong continuity better reflection,inferring the for residues in the upper Paleozoic strata in the deep part of Songliao Basin,the Q value of seismic trace inversion speculation within the scope of strong reflection and below 1.5 s for low Q value,conforms to the sediment properties characteristics of observed strong reflection may correspond to the top of the upper Paleozoic strata interface. |
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