Study Of Geoelectric Structure In Tarim Basin Based On Magnetotelluric Method

Tarim basin is the largest sedimentary basin in China and an important oil-producing region in western China. This paper applies mature analysis and inversion technologies to research the geoelectrical structure of Tarim basin based on832magnetotelluric sounding points.Firstly, we present the necessary issues of MT data interpretation briefly, and show the main technical scheme. The primary problems include:polarization mode estimation, static shift estimation and processing, estimation for the strike direction and dimensionality of geoelectric structures, and selection for modes of1-D and2-D inversion.Secondly, we introduce the distribution of the observed points in Tarim basin and the characteristics of data, and analyses the data quality quantitatively, and also analyses dimensionality of geoelectric structure using the rotation invanriants of magnetotelluric impedance tensor. In addition, this chapter analyses skew of all complete data and emphasizes a long profile crossing through the whole survey area. The result of skew reveals the low dimensional characteristic of Tarim basin, and this technology is efficient for the dividing of structure unit. Based on the above work, this chapter discusses the WAL analysis results in detail, and states that the geoelectrical structure is one-dimension primarily and two-dimension partly with NE direction. Furthermore, and the static shift is not serious. Furthermore, there are two high-dimensional regions according to WAL analysis, which is from Keping uplift to Bachu uplift and the uplift of southern Tarim. The analysis of WAL provides a solid foundation for1-D and2-D inversion. Accordingly, the1-D and2-D inversion in Tarim basin is feasible and reliable.This paper focuses on the models from1-D inversion and2-D inversion. The results of1-D inversion are displayed in form of six scatter diagrams, which indicate a series of characteristics of Tarim basin:firstly, the resistivity of basin margin is higher than central region, as well as the western part is higher than eastern part; secondly, two high resistivity anomalies locate in the basin, including the region from Keping uplift to Bachu uplift, and the uplift of southern Tarim close to Kunlun Mountains folded belt, which is corresponding to the high dimensional areas from WAL analysis; lastly, the Tarim basin is covered by great thick sedimentary layer except a few basin margin, and the thickness of sedimentary layer is various in different regions, such as thickest in Manjiaer depression and thinnest in Bachu uplift.There are15profiles used in2-D inversion, which including four southeastern direction lines, three northeastern direction lines and eight north-south direction lines. The results of2-D inversion indicate a series of characteristics of Tarim basin:the resistivity are higher in upper layer than it in lower layer, and no obvious lateral variation, which indicates this area is a typical sedimentary basin; the basement’s variation of each uplift, depression and slope is very obvious, for example, Bachu uplift is always thin sedimentary layer and high resistivity in every profile, moreover Manjiaer depression is thick sedimentary layer and low resistivity.Lastly, this paper interprets the geoelectrical structure of eastern Tarim especially the structure of Kuluketag-Manjiaer aulacogen. This chapter also summarizes the characteristics of suture zone between southeastern Tarim and Aerjin basin, and the features of Aerjin strike-slip fault belt.