Study On Seismic Velocity Inversion Of Permian Igneous In GL And FY Areas

The Halahatang region has a good geological background for the formation of large oil and gas field,and it is the main block for increasing production and reserves of black oil.It has been drilled thick and widely distributed igneous with violently varying lithology and velocity in Permian.The unclear understanding of igneous lithology and velocity will seriously affect the “beads” migration imaging and the variable-velocity mapping of low-amplitude structure traps.It is very important to conduct the elaborate lithology identification and high precision velocity modeling for igneous in Halahatang area.The paper aims at the GL and FY work areas of Halahatang region,comprehensives logging data,seismic data and geological data,and combines seismic forward,seismic attribute and seismic facies,different seismic inversion methods are carried out to study the lithology identification and fine velocity modeling of igneous,such as constrained sparse pulse inversion,acoustic reconstruction inversion and geostatistical inversion.Firstly,the lithology and distribution characteristics of igneous in FY and GL areas have been studied in this paper.The logging data of the GL and FY study areas were collected and analyzed.The vertical distribution and the logging response of igneous in the work area were studied through comprehensive strata log diagram,GR-DT crossplot and SP-GR crossplot,which lays the foundation for seismic velocity inversion.And through seismic attribute optimization,this paper optimized the average absolute amplitude attribute,energy half-time attribute,correlation length attribute and so on,and in combination with the seismic facies,the distribution characteristics of the igneous in the two work areas are studied,which can guide and verify the igneous seismic velocity inversion.Secondly,prior to the velocity inversion,the influence of the velocity error of the igneous velocity on the Ordovician "bead" imaging is analyzed qualitatively to recognize the necessity of the high precision velocity modeling of igneous in Halahatang region.For this problem,through seismic forward,the paper get the following conclusions: To a certain extent,when the velocity of igneous decreases,the "bead" imaging is clear and concentrated,but it will seriously affect the recognition of "bead" boundaries and reduce the ability to distinguish beads;When the igneous velocity increases,seismic energy around the "bead" becomes weaker and dispersed,the influence of interference wave is bigger,and the "bead" imaging is not clear,which has great influence on the identification and location of "bead".Therefore,the accuracy of igneous velocity is of great significance for Ordovician “bead” imaging in Halahatang region.Finally,lithology identification and velocity modeling of igneous in GL and FY areas are studied by seismic inversion.For the GL work area with few wells and complex seismic facies,we use the CSSI that respect the seismic data to conduct the study of igneous lithology identification and velocity modeling,by comparing the seismic attributes and seismic facies of GL work area,the lithology characterization was scientifically reasonable,and velocity modeling precision is controlled within 2% at the key wells locations.In the FY area,there are 9 wells,and the Permian igneous seismic facies is mainly characterized by parallel facies,which has better stratification in the longitudinal direction.Therefore,the CSSI,acoustic curve reconstruction inversion and geostatistical inversion are conducted and compared to research the igneous in the FY area.By comparing the seismic attributes and seismic facies of FY area,the lithologic and velocity distribution law of the igneous obtained from geostatistical inversion are more scientific and rational,and the description of the igneous is richer and more delicate.The igneous rock distribution law in the FY working area is farther understood.At the same time,the velocity modeling precision was high,the error of key wells was controlled within 2%.The fineness of the igneous velocity model in the FY work area was greatly improved.