Investigating the Near Surface Loess Gravel Layer and Correcting the Static Shift of 3-D MT Data with TEM Data

The Kedong foreland thrust zone is located in the Tarim basin, western China. It shows high potential as an oil resource, but available seismic data are poor due to the serious static shift that results from the uneven, thick loess in the near-surface layer. In an effort to learn more about oil reserves in this basin, 3-D MT and TEM (Transient Electromagnetic Method) surveys were conducted during the 3-D seismic acquisition. The TEM method is relatively inexpensive, and has high resolution in the detection of shallow structures. We programmed the software of TEM data inversion and obtained the sectional resistivity data. By means of comparison with deep microlog data, we correlate the rock’s lithology with its resistivity. The distribution of the loess layer is described in detail, and the thickness is also predicted to have an error less than 10 m compared with the microlog data. The near-surface lithology model is built accordingly, and it provides reference for the building of near-surface velocity models and the static corrections of seismic data. Because TEM have no static shift, they can help the static corrections of 3-D MT data; in other words, they limit the distortion during the 3D MT datainversion.