Remote Sensing Techniques and Petroleum Exploration
Combined Image Processing can reveal underground Geological Information
The petroliferous basins in east China are all covered by the Quaternary sediments, thus, the petroleum geological studies are dependent on the expensive geophysical methods. The use of MSS combined image processing can get information of underground geological structures and features, including the extension of depression, second-order structural zones and large local structure, the processing procedure includes four steps such as linear extension photometric adjustment, local strengthening and colour change. The Liaohe Subasin is a typical example.
The Liaohe Subasin, located on the northern coast of liaodong Gulf, is a component of Cenozonic sedimentary basin of Bohai Bay. The onshore area of the subbasin is 12,000 sq km . The basement of subasin consists of pre-Sinian metamophic rocks, with some Palaozoic and Mesozoic sediment in local places. The exploration target is the lower tertiary. The Lower Tetiary contacts directly with pre-Sinian metamorphic rocks, with some areas, and this provids conditions for discovering buried-hill reservoirs. The Upper Tertiary and Quaternary are widespread covers of the area, with thickness of 800-1500m, In the MSS combined processing map, the subbasin is characterized by different color tones and plentiful veins that reflect amplitude and feature changes of rises and sags in the subbasin (Fig. 1) for example, the central Rise.
Figure 1 MSS Pseudocolor Landsat Image for Liaonan Area
The Buried-Hill Belt Arrowed
1-Central Upleft;
2-Eastern Slope in East Depression;
3-Sub-Uplift in West Depression;
4-Main Part of Liaonan sag
Zone in the Liaohe subbasin is very clear in the map, its size, extension direction and high gravity are all identical, and some buried-hill zones to the west are also quite clear. The main part of the subbasin is certainly more distinct in the combined processing map. The faulted depression is in a semi-ring shape of blackish green in the photo, characterized by darker color tones by comparison with that of surrounding. The outline is very clear though there are some transitional solors. The extension of the faulted depression include the whole Liaonan area to the south of the Shaling-> Gaosheng-> Goubangzi arc. The south part of the circular image is indistinct because of the effect of sea water. It is estimated that the long radius of the circular image can reach 37.5 km and the onshore area is about 400 sq km.
Based on the corresponding analysis of geological and geophysical data, the circular image coincides with the upper mantle bulge of the area. The mantle bulge of the area. The mantle bulge can be reflected by the earth crust isopach of 35 km, in a shape of ellipse and extending in direction of NE. The east boundary of the bulge is along Yingkou—Shenyang, and the west boundary is near Jinzhou. The south part of the elliptic rise located in sea waters The position of the west part is corresponding with the dark semi-ring image. Thus, it is concluded that the dark image is related to the upper mantle bulge . Moreover, according to the geochronological data, the Liaohe area was flooded by transgression and became a gulf, and there are some marine sediments. Though the marine sediments is thin, the difference between continental and marine sediments can be distinguished in the records of visible light wavelength. In addition, this area is the main part of Liaohe subasin, being the main depcenter and accumulation position of the Quaternary and Tetiary sediments (2,800-5,000 m thick), the sediments possessed high percentage of contraction during the diagenesis by comparison with the solidified rocks in the surrounded areas of the basin. Thus, the area usually was a negative landform, being a stagnant region of surface water and underground water and underground water that certainly is a low reflection region of MSS.
