I. Overview of regional geological background
Liaohe basin and its adjacent areas refer to parts of central, northwestern, southeastern Inner Mongolia and western Jilin, covering an area of more than 200,000 square kilometers. Geomorphologically, it is the south extension of Songliao Plain. Qianshan Mountain and Yiwulu Mountain are in the east and west, respectively, and the terrain fluctuates greatly, generally about 500 meters. The middle part is alluvial plain, which is the main body of Liaohe basin, with an altitude of 0 ~ 9m, high in the north and low in the south, and slightly inclined to Liaodong Bay.
From the geotectonic point of view, the scope discussed in this paper is near the junction zone between the northeastern part of the Sino-Korean fault block and the eastern part of the Tianshan-Daxinganling fault fold belt, while the Liaohe Basin belongs to the northeastern edge of the Lu Yi fault block in the Sino-Korean fault block area and the western side of the northern extension of the Tanlu fault zone. In addition to Proterozoic Liaohe Group, there are a large number of Archean Anshan Group deep metamorphic rock series in the west of the basin. Liaohe basin, like Bohai Bay basin, is the product of Yanshan movement and faulting. From the analysis of petroleum geological characteristics, the former is a long and narrow extension of the latter in the northeast, with its own structural characteristics of two depressions and one uplift. According to the isotopic age of the granite gneiss drilled by Well Qi 1 1 in the western depression of the basin, its value is 1787Ma, which is equivalent to Proterozoic granite gneiss exposed in the eastern part of the basin (1768Ma). Therefore, it is considered that the ancient basement of this basin belongs to Yuanguyu. From the main part of the basin, the Sinian system is covered with a small amount of Paleozoic strata, mainly CAMBRIAN and Ordovician carbonate strata. According to the data of Well 3 of Sanjiebao Structural Street in the eastern depression of the basin, the thickness of Paleozoic is 730m ... The Upper Paleozoic is only found in outcrops around the basin. As for Mesozoic, it is mainly Upper Jurassic-Lower Cretaceous. This rock series is mainly distributed in the two sides of the western depression, the east side of the eastern depression and the northern part of the basin, except for sporadic distribution in the depression. Due to the differences in the development time and space of the above rock series, the tertiary in Liaohe area is in direct contact with Sinian system, Sinian limestone and various metamorphic rocks before Paleozoic. This provides good conditions for the formation of buried hill oil and gas reservoirs in this area.
Secondly, the selection, matching and processing of remote sensing data
(a) Selection and matching of image data
In order to study the macroscopic and microscopic characteristics of some image anomalies and their changing rules in different phases and bands, and to determine their geological significance, the interpretation work uses other image data with higher resolution, different phases, different bands and different scales besides MSS standard false color composite film. Such as 1: 10000 or 1: 200000 TM image, 1: 10000, 1: 500000,1:200000.
(2) Image data processing and its effect analysis
This area is a plain area with developed water system and abundant surface water. Not only the lake is dotted with aquatic vegetation, but also there is a thick Quaternary cover. In order to understand underground geological information, it is necessary to eliminate the interference of ground information as much as possible and extract or greatly enhance underground information. Image processing in southern Liaoning and other covered areas shows that local image enhancement processing and its supporting multi-functional combined processing method are effective methods to provide deep geological information, especially combined functional processing.
The so-called combined image processing is to combine several independent image processing functions such as linear expansion, histogram adjustment, local enhancement and color gradation coloring.
From the preliminary geological interpretation, the application effect of the image in this area is good, mainly in understanding the ups and downs of Paleogene basement, the geological structure of basement and the analogy with the image characteristics of known oil fields. Basement undulation and regional geological outline are mainly reflected in synthetic images, which reflect the basic morphology of central uplift and depression on both sides of Liaohe Basin with different tones and colorful texture structures, and show the amplitude and variation characteristics of uplift and depression with electromagnetic wave reflection intensity (Plate III-2). For example, the size, shape and extension direction of the central uplift zone are consistent with gravity data, and the fracture structures reflected by most linear images have been confirmed by drilling data. It is worth pointing out that some pre-Paleozoic buried hill heads in the western depression are also clearly displayed in the joint processing images, such as Shu Qi and Xinglongtai buried hill belts (Figure 1R- 17). This is an effect that the standard false color composite image characterized by comprehensive information cannot achieve.
Comparable analysis and prediction of new oil and gas fields are carried out between the regional tensile images and the image characteristics of known oil fields, and encouraging results are obtained. Judging from the image characteristics of known oil fields in southern Liaoning, almost all of them are characterized by uniform light tones. Without knowing the oilfield information, this feature has been preliminarily verified in the prediction. Therefore, it is considered that the ground effect of underground oil and gas is obviously reflected in the sub-regional processing images.
Three. Geological analysis of image characteristics
Tone characteristics and macro-geological analysis of (1) image
Base structure reflected by 1. image
Basement structure mainly refers to the structure and composition of the basin during the Cenozoic sedimentary period. The interpretation of coverage area shows that the information reflecting basement structure mainly comes from the combined processed images of self-defense films, especially in Liaohe area. It is characterized by a clear tan texture structure on a dark green background, and the overall tone characteristics are obviously deepened from north to south. Most geological and geophysical data show that Tan structure reflects the normal structure (uplift, bulge or buried hill) of the basin basement, and its structural morphological combination reflects the above normal structural characteristics. The dark green tone mainly reflects the negative structural (sag) belt with large thickness developed in Tertiary. The image characteristics and interpretation analysis also show that the Liaohe basin has three characteristics as a whole, namely, the central uplift and two depression zones on the east and west sides. The two depressions on the east and west sides gradually narrowed from south to north, while the central uplift belt tilted from north to south, and was cut down by the NW-trending fault south of the Goldman Sachs-Shaling line, thus merging the above three vertical structural belts into a large southern Liaoning depression. According to the characteristics of the image, the negative structural unit in southern Liaoning sag is consistent with the giant ring structure in the southern half that has been submerged under the seawater in Liaodong Bay, which is reflected in a dark blue tone. According to the analysis of hue and texture structure of synthetic images, their basic composition and fluctuation are not exactly the same (see table 1).
Figure 1 Geological Interpretation Map of Comprehensive Processing of Satellite Images of Liaohe Fault Depression
1- Pre-Cretaceous continuous outcrop distribution area; 2- Pre-Sinian latent uplift area; 3- Paleozoic and some Mesozoic basement distribution areas; 4- Slope or basement dominated by Mesozoic; 5- local uplift; 6- local depression; 7— obvious linear structure; 8— obvious linear structure; 9— Setting the annular structure related to the oil field; 10- lakes and water systems
Table 1 Comparison table of images and interpretation characteristics of each structural unit
2. The geological significance of the giant ring image.
Macroring image refers to the dark green image area in the picture. Compared with the periphery, it is characterized by a much deeper tone, although it also shows a transitional relationship, but the outline is clear. The image range is equivalent to the whole southern Liaoning area south of Shaling-Goldman Sachs-Goubangzi arc. Due to the influence of seawater, the southern part of the annular image is not clearly displayed. According to the calculation, the long radius is 37.5km, and the land part of the annular image is about 4000km2 (plate ⅲ and interpretation map).
Fig. 2 Isobathymetric map of Moho in Bohai Sea.
According to the analysis of the corresponding geological and geophysical data, the giant ring image is consistent with the uplift of the upper mantle in this area. The contour map of 3 1km trap in the crust reflects the uplift area of the upper mantle, which is oval in shape and extends in the northeast direction, with the east boundary around Yingkou-Shenyang line and the west boundary around Jinzhou. The southern half of the oval uplift has entered the sea, while the northern part is roughly equivalent to a dark semicircle image (Figure 2). Therefore, it is speculated that the appearance of this dark image is related to the uplift of the upper mantle. Secondly, historical data show that the Lower Liaohe River area was invaded by seawater in the early Quaternary, leaving a certain thickness of marine sediments. Although the thickness is not large, there are some differences in composition and structure between marine sediments and terrestrial sediments, which can be distinguished from the records in visible light band. In addition, this area is the main part of Liaohe Depression, and it is the main gathering place of Tertiary (S3+S4 is about 2000~3500m thick, and S 1+S2 is about 800 ~ 1500m thick) and Quaternary sediments. The shrinkage rate of Tertiary and Quaternary sediments during diagenesis is much larger than that of solidified rocks around the basin. Therefore, during the NEO period, this area often presents negative topography and becomes the detention place of surface water and groundwater, thus forming a low reflection area of MSS7 band electromagnetic waves on the surface.
(B) the structural characteristics reflected in the image
1. Interpretation of linear structure
Linear image is one of the basic elements of image characteristics. A preliminary analysis of the image data in Liaohe area shows that most of the linear (including banded) images with different lengths, scales and performance degrees are the reflection of underground faults with different depths, ages and scales. For example, L4-6 linear image, located on the east side of the picture, is a light-colored multi-ring texture structure with striking linear dark tones. Especially at the southern end, the multi-ring texture structure on the east side is suddenly interrupted, showing the discontinuous characteristics of the image. Compared with the Paleogene bottom boundary structural map, the ne-trending faults in Long 1 Well Hejie 6 are reflected. Another example is the L4-4 linear image located on the west side of the above picture, which also shows a multi-ring texture structure in the form of directional combination with dark linear characteristics. The extension direction of the multi-ring texture structure in the middle section is consistent with the linear image; In some places, the outer edge of the multi-ring texture structure coincides with the linear image. According to the analysis of the existing data, it is consistent with the NNE fault structure passing through the east side of Ci 10 well and Wan 1 well. This shows that the linear images in southern Liaoning are closely related to the hidden faults.
By comparison, the azimuth frequency of linear images on various images in this area is basically the same. According to statistics, there are nearly 1000 linear and banded images in this area, most of which are reflected by faults. From the distribution direction, there are mainly four groups: northeast, northwest, north and south, and near east and west, especially the northeast and northwest groups. Compared with the previous data, an obvious feature is that the NW-trending fault structures are greatly increased (Ⅲ-1,ⅵ-2 plates), and the control of this group of faults on the oilfield structural pattern can not be ignored.
(1) NE-trending fault structures are characterized by wide bands and dense distribution, mainly dark colors, and sometimes they are beaded combinations of NE-trending light-colored multi-ring structures, all of which are relatively large, mainly reflecting basement fractures. Of course, the basement fault can leave traces on the surface through various channels, which shows that it has a certain control effect on the overlying strata. This influence or control can cause the difference in the thickness distribution of the original sediments, and can also be reflected in the diagenetic process or the displacement of the sediments after diagenesis. For example, the Shenyang-Yingkou fault (L4-6), with a strike of 34 and an extension of more than 350 kilometers, is a part of the northern extension of the Tan-Lu fault zone (also known as Yilan-Yitong fault). The southern section is a light-colored broadband image on the satellite film, which controls the overall flow direction of Hunhe River and Liaohe River in this area. The northern section passes through the exposed area of bedrock along the eastern edge of the basin, with striking light-colored linear images. According to the survey data of vertical deformation of the earth (Ying Shaofen, 1986), the fault zone is currently in a negative deformation state, indicating that there is still some active energy in modern times.
(2) NW (including NW) fault. This group of faults has obvious linear characteristics on satellite photos, but the number and scale are not as good as those of NE-trending faults. For example, the large earthen bag-Huangshatuo linear structure (L 14-0 1) with a length of more than 100km obliquely cuts the whole Liaohe Depression and extends to the Yiwulu Mountain in the northwest, controlling the distribution of its topography and water system; In the southeast of Goldman Sachs, the southwest is dark and the northeast is bright. According to the study of Quaternary sediments, the dark tone in the southwest of linear images is the distribution area of marine sediments, and the light tone in the northeast is the distribution area of river sediments. Therefore, the fault controlled at least part of Quaternary sedimentation. In the granite exposed area north of Beizhen, northwest China, the measured fault occurrence is SW 312 ∠ 74 ~ 80. From the combined image of this area, the fault obliquely cuts the end of the south extension of the central uplift, making the south wall descend and disappear. From this point of view, this group of faults developed later than the NE-trending faults.
(3) The satellite image shows an east-west fault structure, and the fault image is broadband, with blurred boundaries and intermittent extension. For example, the Lingyuan-Jinzhou West Fault (ⅵ-2 plate) presents many parallel lines on satellite images, which appear and disappear, passing through several mountains and intermountain basins in the middle, and tends to extend to the depression. Another feature is that it is often divided by linear structures in the northeast or northwest direction. Therefore, this is a group of ancient structural lines or faults, a large-scale compressive zone or a residual section of an ancient fold zone.
(4) The number of north-south fault structures is small, which shows regional color difference in satellite images. For example, Liaohekou West Fault (Figure 1L 1-0 1), from the false color image, the east side of the linear image is dark gray and the west side is light gray, and the linear boundary of the two color regions is the reflection of this linear structure. Of course, there are also broadband images, such as the abnormal image of the north-south dark zone in Shuangliao-Faku. The anomalies on the magnetic map were interpreted as Hercynian rift zone, which was later filled with magma.
From the analysis of the characteristics of the above four groups of main faults, the NE-trending fault is the largest, most numerous and most influential fault structure in this area, followed by the NW-trending fault. As mentioned earlier, although the scale of NW-trending fault is small, it has a great effect on the transformation of the basin in the later period, especially on the accumulation and preservation of oil and gas, which deserves attention. According to the analysis of the new-old relationship formed by the four groups of faults, the east-west and north-south faults formed the earliest, and had the least influence on the caprock (mainly tertiary and quaternary), while the northwest fault group developed the latest.
2. Geological characteristics reflected by ring image.
Annular image refers to the image anomaly with annular, circular or block geometry on the image. It is composed of different shades or texture structures, and can also be reflected by the abnormal distribution of water system. Many facts show that it is a reflection of massive geological structures on the surface, crust or deeper, such as uplift, depression or various volcanic mechanisms. Because of their shape, structure and composition, there are many differences compared with the surrounding media, and this difference has become a distinguishing sign in geological interpretation.
The so-called distinguishing marks in geological interpretation have obvious relativity, especially the meaning change of hue often depends on different geological and geographical backgrounds. For example, the characteristics of light-colored images are mostly negative structural units, that is, Mesozoic and Cenozoic sedimentary depressions, which are reflected from a wide range of regional geology. However, if the contrast background is limited to the basin, the light-colored image features may reflect the local positive structure. The key to the above changes is that the contrast space has changed; The second is to highlight water media and vegetation factors related to water.
(1) The light-colored ring image is located in the Lower Liaohe area, which mainly reflects normal structures (uplift, bulge, buried hill, etc.). ). For example, on the standard image, the rectangular light-colored image extending northeast from the east side of Taian reflects the main body of the central uplift zone, and its geometric shape is very similar to the gravity height of Bouguer gravity anomaly map. The light-colored image anomaly in the form of texture structure on the composite image is consistent with gravity not only in the overall shape extending in the northeast, but also in the local fluctuation. In addition, there is a large-area (384km2) elliptical ring image composed of light-colored foliated structures on the image of the outcrop area in the north of Jinzhou, which is a reflection of large granite bodies, and so on.
(2) If there is no human interference, the dark ring image is mainly a reflection of negative (sag and graben) structures, such as Damintun sag. Damintun sag is a Cenozoic sag with its long axis extending northeast, and its gravity is in a low value area. On the image, it shows an obvious dark ring image, and its shape is basically the same as that of the depression.
Four, the image characteristics of known oil fields and the preliminary prediction of favorable oil and gas-bearing areas
1. Image characteristics of known oil fields
Some areas in the northwest and east of Xialiaohe (southern Liaoning) sag are one of the areas with high exploration degree. At present, there are Goldman Sachs, Shuguang, Huanxiling, Xinglongtai and Shuangtaizi oilfields in the northwest, and Rehetai, Louyu and Jindai oilfields in the east. These oil fields have obvious and obvious light-colored circular or massive image characteristics on standard false-color images, and have similar characteristics reflecting positive geological structures like the above-mentioned light-colored circular images. The analysis shows that although the oil layer is buried deep in the abdomen, in the long geological history, due to the high pressure of the oil layer, trace hydrocarbons can continuously leak to the surface or the air through the caprock. Some of them are absorbed by the surface soil and undergo biochemical changes, gradually changing the original properties of the soil, causing plants growing on it to metamorphose or form special vegetation communities, thus causing ground effects and so on. In addition, there may be other genetic relationships, such as Shuguang Oilfield, Jindai Oilfield and Lou Yu Oilfield, which are all closely related to the abnormal light or white images in thermal infrared (wavelength 0.4 ~ 12.5μ m) images. The characteristics of this light-colored image are related to geothermal energy. Therefore, it can be said that all the major oil fields listed above are in abnormal areas higher than the average geothermal value (Figures 3r- 10, r- 12, R- 13). According to the research, the two main factors controlling the ground temperature are the nature and fluctuation of the basement structure of the basin, because different basements show different thermal conductivity, and the fluctuation reflects the distance between the heat source and the surface; The second is hydrogeological conditions, which mainly reflect the degree of exchange between surface water and groundwater. If the exchange degree is high or the drainage area is flooded, the ground temperature is easy to be lost, which is not conducive to preservation. Of course, the thickness of caprock is also a necessary condition for the generation and change of geothermal ground effect. Judging from the spatial characteristics of annular or massive images displayed by remote sensing images including TM-6, it is indeed closely related to known oil fields. According to statistics, there are 20 annular or massive images interpreted by * * * in southern Liaoning, of which 14 is related to known oil fields, and the coincidence rate is 70%. The Shaling macrocyclic image in the eastern depression consists of seven secondary cyclic images, four of which are related to Rehetai Oilfield and Jindai Oilfield, such as R- 18, R-20, R-2 1 and R- 16 (Figure 2). In the western depression, R- 16 is related to Xinglongtai Oilfield, R- 15 and R-23 are related to Huanxiling Oilfield, and R-06, 07 and 08 are related to Goldman Sachs Oilfield, and so on. Therefore, as far as Liaohe area is concerned, no matter what kind of image and how to process it, it is closely related to the known oil fields, and this relationship is one of the important basis for predicting oil fields. Whatever the reason, the above image characteristics of the known oil fields in Liaohe area are obviously credible.
Fig. 3 Interpretation diagram of TM6 thermal anomaly
1- obvious thermal anomaly area; 2- obvious thermal anomaly area; 3- negative thermal anomaly area; 4-Open fracture; 5— The obvious boundary between outcrop area and west slope; 6- swamp
2. Preliminary prediction of favorable oil-bearing areas
According to the known characteristics of oilfield images and the abnormal performance of remote sensing information, combined with the basic petroleum geological conditions obtained by geophysical exploration and drilling in this area, the following favorable and relatively favorable oil-bearing areas are predicted.
(1) Favorable oil-gas bearing area
① In Shaling area, the thermal infrared image shows a striking light-colored abnormal area from Shaling to the east of Huangshatuo, extending to the northeast, with a wide and round southwest end and a narrow and long northeast end. In the light-colored anomaly area, there are two prominent white anomalies, one near Well Xiao 4 in Huangshatuo and the other near Well Nordic 1 in Shaling.
This area also appears as an oval light red abnormal area in the partitioned image, and its major axis and minor axis are 20km and 12km respectively. Although there are some blocky structures with different light and dark in the image of this light red anomaly area, it still belongs to a whole, in which well Ou/Kloc-0 and well Xiao 4 have good oil display, and industrial oil flow can be seen in some areas. Therefore, it is reasonable to treat thermal infrared and light red image anomalies as a whole that is beneficial to oil and gas exploration.
② The area west of Rongxing Reservoir, especially the area near Shuangtaizi Estuary (near Waijiang River), is a thermal anomaly area disturbed by surface water network. In terms of landform, it is a relatively high place on the beach. On the sub-region processing map, there are two annular or rectangular light-colored image anomalies in this region, which have shadow characteristics. Although the image obviously reflects the characteristics disturbed by surface factors, it is similar to the known oilfield image characteristics, and it is speculated that it is a favorable oil-gas bearing area.
③ Nanpigang area is the meandering area closest to Daling River and Shuangtaizi River, with vertical and horizontal water networks and well-developed vegetation. Therefore, there is no abnormality on the thermal infrared image, but on the standard image, it shows that the rectangular light-colored image with north-south distribution is abnormal, with the major axis of about 16km and the minor axis of about 9km. The abnormal north is covered with reeds, and industrial oil flow has been seen, and the south extends to the beach. From the overall image characteristics, since the industrial oil flow has been obtained in the north, the south should also be a favorable oil-bearing area.
(2) Favorable oil-gas bearing areas
Favorable oil and gas-bearing areas refer to areas with large surface interference, weak reflection of underground geological information and inconspicuous image characteristics, which still have annular or circular image characteristics compared with known oilfield image characteristics. For example:
(1) The area to the south of North Xiaoliushu is the tidal flat between Daling River and Xiaolinghe River estuary, and part of it is Yantian. On the thermal infrared image, it shows an abnormal area extending in the east-west direction with obvious characteristics. There are two kinds of images on TM sub-regional processing map: circular and circular. Vegetation (mainly reeds) is developed in the north, and the image is spotted. Macroscopically, it is located on the west side of the great ring in southern Liaoning, which is a favorable oil and gas exploration area.
② In the area north of Rongxing Reservoir and west of Tianzhuangtai, the area is white in thermal infrared image, and no large-scale thermal anomaly is found. However, there are three annular images with different sizes in TM sub-regional processing images, which are represented as shadows. Although the underground structure reflected by the image information is complex, it is similar to the image characteristics of known oil fields, and it is speculated that it is a favorable oil-bearing area.
In addition, the central beach of Shuangtaizi estuary (the northern extension of Gaizhou beach) may be related to the underground normal structure, and if the petroleum geological conditions are good, it is also one of the better prospects.
Verb (abbreviation of verb) abstract
From the preliminary results of image processing, interpretation and analysis, the application potential of remote sensing information in Liaohe area is great, mainly in the following aspects:
(1) The work in the Quaternary coverage area of Liaohe River shows that the quality of the original remote sensing image can be greatly improved by choosing an appropriate image processing method suitable for the surface conditions in this area, and various hidden geological information reflected by factors such as micro-geomorphology change, water system characteristics, humidity and vegetation can be obtained, thus playing a positive role in supplementing and modifying the original geological data.
(2) Through geological interpretation, we have a new understanding of the NW-trending fault structure in Liaohe Basin and its peripheral areas: NE-trending fault is the dominant factor in the formation of the basin, and NW-trending fault is not as good as NE-trending fault in quantity and scale, but it is one of the main factors affecting oil and gas accumulation and migration.
(3) Using the image characteristics of known oil fields to simulate, analyze and predict new oil and gas fields also has broad prospects.
(4) Make full use of the favorable conditions for exploration in this area, so that all kinds of petroleum geological data reflected by remote sensing information can be verified in time, thus accurately establishing remote sensing petroleum geological interpretation marks and deepening the application of remote sensing technology in oil and gas exploration in covered areas.
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