The Study About Seismic Phase And Sedimentary Phase Of T₃x² Formation In LNS Of Middle Sichuan

The LNS structure is a local anticline. In general, the characteristics of the study area is gentle fold, little major fault, and more minor fault. Drilling work of the study area began in 1950s, and now 11 wells were tested in Xujiahe formation of Upper Triassic. The tested 5 wells were more than million level, indicating that it had a certain value in LNS area. In this paper, the principle of sedimentary petrology, X ray fluorescence spectrometry, well logging and seismic phase analysis was applied, and the method of combination of field outcrops and advanced test means was adopted. Compared with other methods, which were used by predecessors, X ray fluorescence spectrometer was used in the identification of sedimentary environment for the first time. Seismic phase and sedimentary phase were analyzed in T3X2 formation after sedimentary environment was determined, according to the well logging and 3D seismic data.Based on the 3D seismic data, firstly, we interpret the 3D seismic data, and demarcate geologic horizon accurately, find the fault location in the bottom of T3X3 and T3x1 formation; we should find out the reflection horizon’s structural configuration details, size and high position in the Xujiahe formation. Then we use small fault interpretation technique and coherence technology for detection of fault distribution in the fracture development zone, especially the distribution of small faults. Secondly, in order to investigate the sedimentary facies of controversial formation and sedimentary environment in the Upper Triassic of the Central Part in Sichuan Basin, samples were collected in four representative zones from Xujiahe formation in Sichuan Basin. The method of X ray fluorescence spectrometry were used to analyze the element contents and its’change characteristics of the deposition from target formation. Finally, under the guidance of the sedimentary environment, the characteristics of seismic reflection are divided into different seismic facies with sedimentary facies of single well, and seismic facies are transformed into sedimentary facies according to data of drilling and logging.In this paper, the results obtained are as follows.The method of XRF was firstly used to identify sedimentary environment in T3X2 formation of LNS area. First of all, the uncontested formation of T3X3 and T3X4 was analyzed by sedimentary geochemistry. The experimental results are consistent with previous research, which shows that this method is reliable. Secondly, the controversial T3X2 formation was analyzed by that way, which provides a feasible method to solve controversial formation and motivates the breadth and depth of application in geology.In addition, the method of XRF also coincides with previous research in geologic climate and changes of element contents near the surface of hard ground, which illustrates further the reliability of this method. The relative error between this method and conventional chemical analysis is less than 3%. The method of X ray fluorescence spectrometry is simple and feasible, which provides a half-quantitative analysis method for the study of sedimentary phase and shows it has high accuracy. The target formation about time-depth relation was calibrated accurately with seismic synthetic records. Horizon interpretation about the top and internal of T3x2 formation was finished respectively, which laid the foundation for the analysis of seismic phase. Fault interpretation was cross validated through the pickup of section and coherent detection, which makes the results more accurate and reliable.Tectonic map shows that the number of T3x1 formation’ fault is the most and structure is more complex. In summary, the shallower stratum is, the less fault is. The fold changed or superimposed and structure became more complicated under later stress.The data of drilling, logging, 3D seismic was used to study seismic and sedimentary phase, because study area was lack of core and outcrop. The target formation is divided into two sections to make 2 map of seismic and sedimentary phase. And the sedimentary phase of the study area is mainly delta and lake.