| A large number of faults formed by the multi-phase tectonic activities of the Shunbei Oilfield in the Tarim Basin control the Ordovician carbonate fracture reservoir formation and hydrocarbon accumulation.The accurate identification of faults on seismic data is the basis for the evaluation of Ordovician fault-dissolving reservoirs.The igneous rocks widely developed in the Permian in the study area have affected the accurate identification of Ordovician faults.The strong shielding and absorption of seismic waves by igneous rocks caused poor seismic data,which made it difficult to accurately identify small and medium-sized faults and restricted the discovery of fault-dissolved reservoirs.The lithological and thickness variations of igneous rocks affect the accuracy of the seismic data velocity field,which may cause a large number of pseudo-faults that do not exist in the seismic data,which increases the exploration risk of fault-dissolved reservoirs.Based on the research of faults fine imaging technology and quantitative analysis of pseudo-faults technology in Shunbei Oilfield the analysis of the impact of fault grading and segmentation on oil and gas enrichment is carried.The main research and results of this paper are as follows(1)Because of the shielding and attenuation of seismic waves by igneous rocks,the characteristics of the small and medium scale faults in the original seismic data is very difficult to accurately identify.Through the research on the identification model of faults seismic section,the forward simulation of the response characteristics of different scale faults in the seismic section provides a basis for the interpretation of the fault profile.The plane identification method of different scale faults is used to improve the resolution of the original seismic data.Combined with the faults-sensitive property optimization,the plane-distribution features of faults of different scales are clearly characterized.The fine interpretation of the Ordovician fault in the north block of the Shun 8 North block is completed by the joint interpretation of the profile and plane-distribution.(2)The Permian igneous rock affects the accuracy of the migration velocity field and causes pseudo-faults in the seismic data.The accurate description of the lithofacies distribution of the Permian igneous rocks and the establishment of the igneous rock geological distribution model are the basis for the accurate identification of pseudo-faults in the work area.Firstly,the electrical characteristics of different igneous rocks are analyzed by logging curve intersection,and the corresponding igneous rock seismic facies are calibrated with the logging.Secondly,the igneous rock eruption periods are identified by the normal sedimentary rocks in the logging records and the unconformity wave impedance interface in the seismic and logging data.Finally,the RMS values of the igneous rocks are extracted in stages,and the seismic facies characteristics of various igneous rocks are combined to characterize the distribution of the lithofacies of the Permian igneous rocks.(3)The study of the causes of pseudo faults and its main controlling factors are the basis for the accurate identification of pseudo-faults.Based on the establishment of the geological distribution model of the igneous rock in the Shun 8 North,the effects of the migration velocity error,thickness variation and faults spatial position of the high-velocity igneous rock on the fault imaging are analyzed,and the spatial relationship between the pseudo-faults and the high velocity igneous rock is analyzed.(4)Replacing the background velocity of the dacite in the seismic of Shun 8North block with the average logging velocity of dacite in Shunbei 1 block,through the forward modeling,to study on the pseudo throw of the target layer which is influenced by the change of thickness and migration velocity error of high-velocity igneous rock.Establish the quantitative calculation formula of the vertical faults throws of the pseudo faults,and identify the truth of faults which underlying the dacite boundary and the sharp contour of the superimposed thickness of dacite.The faults that were pseudo-quantitative after quantification were eliminated,and the identification of true faults in the study area is completed.(5)Based on the real fault identification,according to the development of the fault zone and the mechanical characteristics of the fault zone,the criteria for classification and segmentation of the fault zone are proposed.The differences in reservoir development and oil and gas enrichment caused by faults levels and faults segmentation in Shunbei 1 block are analyzed.Through the fracture characteristics and the seismic fracture-cavity analogy,the oil and gas enrichment evaluation of the fault zone in the Shun 8 North is realized,which provides a basis for the exploration and evaluation of well deployment.The main innovations of this paper are reflected as follows(1)A technique for judging the location of pseudo faults based on the superimposed thickness of high velocity igneous rocks is proposed for the first time.Starting from the establishment of the geological model of igneous rock distribution in the study area,the cause of formation of the Ordovician pseudo faults was analyzed by forward modeling.It can be seen that the plane distribution of the pseudo faults has a similar morphology on the boundary of the superimposed thickness of dacite and the contoured area of the contour.The technique can quickly identify the pseudo faults position in many faults of the Ordovician target layer and screen out the real faults that are not affected by igneous rocks.(2)A pseudo faults identification technique(invention patent)based on quantitative analysis of wave equation of fault throws is proposed for the first time.Firstly,the fitting relationship between the faults throws of the pseudo fault under different migration velocity error and the thickness of the overlying Permian dacite is quantitatively established.Secondly,the logging velocity of the high velocity igneous in the adjacent area is introduced to calculate the migration error of the seismic data in the work area.The deviation velocity error range of the igneous rock section is taken,and the maximum pseudo-offset value of the Ordovician fault is calculated by calculating the boundary thickness of the high velocity dacite.When the target faults is greater than the maximum pseudo value in the original seismic data,it can be identified as the true fault.The paper establishes a set of geophysical techniques suitable for improving the imaging quality of seismic data and detecting multi-scale faults in Shunbei Oilfield.And for the first time,even in the absence of well logging data and the inability to obtain accurate seismic velocity,a set of technical methods for effectively discriminating pseudo faults underlying igneous rocks is proposed.Based on this,the fine interpretation of Ordovician faults and the evaluation of oil and gas enrichment in faulted control reservoir of the Shun 8 North block is carried out,which provides the geological and the geophysical basis for the selection of Ordovician oil and gas exploration targets in Shunbei Oilfield. |
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