Remote Sensing Techniques and Petroleum Exploration

Remote Sensing Techniques and Petroleum Exploration

Ye Hefei, Cao Yu
Department of Remote Sensing Geology,
Research Institute of Petroleum Exploration and Development , Beijing , China

Abstract
The paper briefly deals with application and result of remote sensing techniques income inland petroliferous basins in China. Based on some examples, important roles of remote sensing techniques presented, such as in studies of regional geological settings of pre-exploration of petroliferous basins, petroleum geological conditions concerning temporal and spatial regulations and mechanism of basin formation, structural features of basin, distribution of oil-bearing structural zones, analogy and analysis of image characteristics of known oil field as well as prediction of new oil fields. Particularly, starting with the theory of surface inter-growth effects of petroleum micro-seeping, the paper tries to probe the practices of remote sensing techniques in oil discovery and to demonstrate that the application of the techniques in petroleum exploration is very wide and will become an indispensable exploration method.

Introduction
Although the technology is very late to use in the application of the petroleum industry in China, a lot of satisfactory works have been done since we began studying the remote sensing petroleum geology in the Tarim basin of Xinjiang in 1978. We have studied petroleum geology in an area of 3.5 million sq km covering 15 provinces and regions such as the Qinghai, Tibet, Inner Mongolia, Liaoning, Shandong, Shanxi, Jiangsu, Sichuan, Yunnan, Guizhou and Guangxi, concerned various geomorphological features, different tectonic units and sedimentry basins in different time, and gained a great deal of first-hand data related to structural zones and ten thousand faults, and some plays with good prospects and oil-bearing structural zones have been predicted. The practices have proved that the remote sensing techniques play very important roles not only in the studies of petroleum geological conditions of preexploration including researches on regional geological settings of petroliferous basins, structural features, distribution of oil-bearing structural zones, analysis and analogy of image characteristics of known oil-bearing structural zones, analysis and analogy of image characteristics of known oil fields as well as the prediction of new oil fields. Meanwhile, as remote sensing images posses characteristics of realty, microscope and visualization and comparative analysis of multiple temporal phases, the techniques also have wide applications in engineering designing, oil exploration and environmental survey. Here we mainly discuss geological problems in petroleum exploitation.

Roles of Remote Sensing Techniques in Selection of Petroleum Exploration Targets
The selection of effective exploration targets is an important step to achieve success in oil exploration. The selections are dependent on studies of basic petroleum geological conditions. Petroleum geologists generally consider basins to be a basic geological unit of petroleum exploration and their main tasks is to find and determine various sedimentary basins. The remote sensing images have characteristics of realty and macroscope that provide accurate and visual data for directly determining geometric shapes of sedimentary basins. The remote sensing techniques are more effective and useful for understanding and studying those basins in the out-of-the-way mountains and remote deserts, such as the Tarim basin in northwest China.

The Tarim basin, located between the Tianshan Mountains and Kunlan Mountains, is a huge sedimentary basin with an area of 0,56 million sq.km. The surface of the basin is widely covered by the quaternary, and two thirds of that is occupied by deserts. Basin beasement is of the presinian metamorphic rocks, and basin fillings consist of the palaeozoic, meaozoic and Cenozoic sediments with a thikness 0f 15,000m. Based on drilling data, we find that the lithologic features of sediments within the basin are basically same with that of corresponding sediments outside the basin. Commercial oil flows have been found all in the Palaeozoic , Mesozoic and Cenozoic strata. The basin in characterized by even light colour in a standard pseudo-coloured ,mosaic map, with a distinct outline by comparison with the mountains outsied the basin that are characterized by dark colours and complex schieren textures. In addition, three faults (Quiemo,South Quiemo and Arjinfault) developed in direction of NEE in southwest basin, the south Qiemo fault intersect Arjinfault in acute angle, and are especially clear and eye-catching.

According to the statistics, 86 circular structures are interpreted in the west basin, among them, 15 structures coincide with the surface structures and 40 structures are related with concealed structures determined by geophysical methods. The success rate can reach 64%. It is necessary to point out that No. 168 concealed structure that has produced oil was first discovered by the remote sensing data.

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.

Remote Sensing Detection of Oil and Gas
The remote sensing detection of petroleum is based on the characteristic analogy and analysis of remote sensing information from known oil fields. The thinking way is as follows: micro-seeping of hydrocarbon-> ground effect-> remote sensing detection is certainly gainful. The following regulations are concluded from the characteristics of remote sensing images of divers oil fields in east China : special color tones -> spectral and geochemical characteristics --> geomorphological features -- > underground geological structures ---> inexorable relations exis-ting among oil and gas fields. In 1985, we made same prediction on the west slope and NS trend structural zone of the Dongpu sag of zhong-yuan region and some commercial oil flows have been discovered in succession.

Figure 2 Geological Interpretation of the Compositionally Processed Landsat Image for the Liaohe Dpression Legend:
1-Pre-Cretaceous Outcrops;
2-Pre-Sinian Hidden Uplift Area;
3-Paleozoic and Partial Mesozoic Basement;
4-Mesozoic Slope or Basement;
5-Local Uplift;
6-Local Sag;
7-Obvious Linear Structure
8-Linear Structure;
9-Vast Circular Structure; 10-Lake and River
Dongpu sag is a Mesozoic-Cenozoic structural basin with an area of 5,000 sq km . Its main part is located in the contact region of Hebei, Shanxi, Shandong and Henan provinces . The exploration targets are 3,000-5,000 m deep, covered by the quaternary sediments over 130m thick. The east part of the sag is strictly controlled by the Lan-Liao fault. The basement consists of paleozoic and some Archaeozoic metamorphic rocks. Just as gravity and magnetic data revealed, the basement is a NE trend monoclinal structure that was formed by abrupt insertion of Neihuang uplift from NW to SE under thick sediments of Mesozoic and Cenozoic and complicated by late faults. The burial depth of east sag basement can reach 9,000m. But the basement beyond Lan-Liao fault in the east is slightly shallow, and become a component of west end of Luxi uplift. The light color image map in the west side of Lan-Liao fault belt, there is an abnormal zone about 25-30km wide and 200 km long, the abnormal zone is from qixian in Henan province in the south to Lankao and Dongming in the north, extending into shandong province by Nanle and Fanxian. The special image anomaly is similar with the image characteristics of many known oil fields, having same geological backgrounds, thus , it is considered as an important part of ground effect resulted from micro-seeping of hydrocarbon based on analogy and analysis, and predicted as a favourable oil and gas area. The exploration in the recent 3-4 years proves that the predicted area is the region to increase oil reserve in the sag. The area has been put into production.

We made interpretation and analysis for petroleum geological conditions of remote sensing images of Liaohe subasin in 1988 again, the success rate of predictive area, commercial oil flows have been gained. This can prove that the remote sensing detection has bright prospects. Particularly, the microscopic and scientific analysis has been made from geochemical fields of ground effect of hydrocarbon micro-seeping and geophysical fields including ground effect of micro-seeping, this provide reliable evidences for the remote sensing detection. But it is necessary to point out that the above principles are dependent on special geological backgrounds. If the detection is expected to achieve the best results, some detailed petroleum geological conditions and certain geographic environments must be considered.

The above practices indicate that the application of remote sensing techniques in petroleum exploration has bright prospects and will become an indispensable method, shortening period of oil exploration saving exploration investment and raising economic benifit.

References

Ye H. and Qui X., Petroleum Anmalysis of remote Sensing Images in Liaohe Basin and its Vicinities . National resource Remote sensing studies Vol. PP 13, 1990.
Ye H. and Cao X., collections of reports on new Theory, New method , new techniques in Petroleum Exploration. Application of Remote Sensing in petroleum Exploration in Dongpu Sag Ocean Press , Beijing, PP 150, 1989.
Ye Hefei et al, The Initial Application of the satellite Remote Sensing Image for the Investigation and of the structure of the Gas-Oil bearing Field of Mesozoic and Cenozoic of Henan, Proceelings of the Bejing International Symposium on Remote Sensing . 1986.