Yunnan-Guizhou-Guangxi area is an important area of carbonate oil and gas exploration in southern China, covering an area of nearly 400,000 square kilometers. Among them, Nanpanjiang River Basin is the key area for visual interpretation of this satellite film.
I. Geological survey
This area is adjacent to Jiangnan Uplift in the east, separated from Gukangdian Uplift in the north-south direction by Xiaojiang Fault Zone in the west, connected to Nanhuatai Block in the south and Qianzhong Uplift in the north, facing Sichuan Basin (Block). It is a wide coverage area of Triassic in the combination zone of various structural units, with negative tectonic movement as the main development history. The tectonic lines in this area are criss-crossed, but the northeast formation and northwest formation are the most prominent. 1: The mosaic of 500,000 satellite photos (photo1) clearly shows the structural lines of north-south strike and east-west strike, such as Puding-Huishui Belt running through east and west, Guiding-Donglan Belt running through north and south, etc. These phenomena also record the complex geological and historical processes in this area.
Photo 1 satellite mosaic map of Nanpanjiang area (Nanpanjiang area is obviously divided into three areas: A, B and C in shadow structure)
To the north of Ceheng-Luodian fault zone in this area, the metamorphic basement belongs to Yangtze type, which is composed of slate or phyllite of pre-Sinian Kunyang Group (or Banxi Group) and only exposed in the northeast and southwest of the interpretation area. Above the unconformity surface, the Sinian and Lower Paleozoic are clastic rocks containing carbonate rocks, with a thickness of 3000 ~ 4000 meters, which are exposed in the west and some high anticline cores. To the south of the fault zone, the caprock lacks Ordovician and Silurian, and the lithology tends to transition to Nanhua type.
In the late Paleozoic, the central Guizhou and the south of the Yangtze River rose greatly and surfaced, becoming an important provenance. In this area, the uplift or some high anticline zones are overlapped, especially in Puan-northern Long Yin and Luodian. After the Wu Dong Movement, the tectonic pattern changed. In the early Mesozoic, the sea water in this area became deeper. In Triassic, a remarkable phase change belt was formed along Fuquan-Anshun-Ceheng-Qiubei, which meandered in an "S" shape for more than 500 kilometers, and beaded reefs developed along this belt. The sandstone-mudstone facies area in the southeast of the belt is dominated by turbidite deposits (Figure 2), with a thickness of 3,000 ~ 4,000 m, and the shallow platform facies carbonate distribution area in the northwest with a thickness of about 3,000 m. The movement of Indosinian and Yanshanian caused the caprock formed under the control of Caledonian and Hercynian paleotectonic frameworks to fold and fracture, which laid the foundation for the current structural layout.
Fig. 2 Trough structure in Middle Triassic turbidite in Lucheng, Guangxi.
Second, the image characteristics of multi-band satellite movies and their geological significance
Geological bodies with a certain depth on the surface or underground have different characteristics in radiation and reflection of electromagnetic waves in different spectral ranges. Recorded on satellite film through certain geometric tone anomalies. People use the comparative analysis of various images and their combinations recorded in the multi-band (MSS) satellite photos to reveal the attributes and essence of geological bodies, so as to achieve the purpose of understanding geological bodies. The hue and combination of different geometric shapes in satellite photos is the first reflection of geomorphic landscape, but geomorphic landscape is directly related to strata, rock mass and geological structure. Therefore, the analysis and study of various image features is an important link in geological interpretation. Based on the 7-band mosaic map of 1:500000, this paper discusses the characteristics and geological significance of each image from three elements: color, shape and shadow.
(1) The comprehensive characteristics of the image are the reflection of the regional geological profile.
On the 7-band mosaic, this area is dominated by gray and light gray tones, with dark gray, black gray and a small amount of white tones. On the whole, the color tone darkens from southeast to northwest, and the strip, line and block images composed of black, black gray and light gray become the macro characteristics of satellite images in this area. According to TINT, this area is connected by Luxi-Ceheng-Luodian and Ceheng-Puding, and can be roughly divided into three parts: southeast (a), northeast (b) and southwest (c) (photo 1).
Southeast: composed of gray and light gray tones, with a rough fine dendritic shadow structure, interspersed with a small amount of black-gray block tones. Block tones are mostly diamond or oval. Due to the large color difference and clear boundary (Photo 3), according to the field investigation, a large area of light-colored thick shadow lines is a reflection of the extremely thick sandstone mudstone and its surface folds in Banna Formation and Mu Lan Formation of Middle Triassic. Black-gray rhombic block belongs to Carboniferous and Permian limestone, which is limited by faults and is found in Lingyun and Bama, Guangxi. The gray oval block is a uplift structure with Devonian and Cambrian dolomite or dolomitic limestone as the core, belonging to Longlin-Xilin anticlinorium belt in Guangxi. The great color difference between the two is related to the color, composition and structure of the rock itself, but the landform is also a factor that cannot be ignored. Due to the special karst landform of carbonate rocks in the interpretation area, isolated columnar hills are formed, all of which are above the minimum resolution (79m×79m) required by MSS. The contrast between its settlement and the gently inclined sandstone and mudstone landforms of Banna Formation and Donglan Formation (photo 4) just constitutes the diffusion conditions of electromagnetic waves on the surface. Due to the diffusion of electromagnetic waves, a large part of energy is lost, so it must be reflected as dark tone on MSS positive film.
Photo 3 Block image structure
The dark color is limestone of different ages, and the light gray dendritic system is sandstone and mudstone of Middle Triassic.
Photo 4 Landform Profile of Lingyun West.
On the right is the Middle Triassic sandstone and mudstone landform, and on the left is the C-P karst landform.
Northeast China: The huge annular and banded structure composed of gray and dark gray tones is the main image feature of this area. The gray stripes and massive rough shadows on the northeast edge are pre-Sinian metamorphic rocks on the southwest edge of Jiangnan uplift. Huge annual rings are distributed in Duyun and Luodian (Figure 5). According to the ground data, it is the southerly part of the Giant Nose Uplift extending northward to this area, with an area exceeding 1 10,000 square kilometers. Its core is composed of CAMBRIAN-SILURIAN, and the southern margin is gradually Devonian, Carboniferous and Permian. Guiding-Changming-Zhang Bu banded image, which runs through the north and south, is more than 150km long and is divided into two parts, with a large uplift in the east. The belts are composed of Triassic folds and faults, which are clearly visible in all belts of MSS. It is worth pointing out that the annular body does not include the whole giant nose bulge, but only most of it. Whether this has a deeper geological background needs further study.
Southwest: It is composed of gray, light gray and a small amount of dark gray tones, with a shell-like structure and unique shape and orientation. To the east of Pu 'an, it is dark in color and exquisite in structure, and it is arranged in strips in the northeast direction; The western part of Pu 'an is light in color, with a rhombic or rectangular patchy structure extending north and south. Through comparative analysis, the former is a special Triassic fold combination with triangular plane shape formed on the background of large-scale Devonian, Carboniferous and Permian folds (photo 6), which is obviously controlled by more than two sets of faults in the abdomen. The latter is a huge diamond-shaped block, which consists of Carboniferous-Permian, mainly Triassic, and is unevenly surrounded by pre-Sinian, Cambrian and Silurian. A small amount of Paleogene red beds controlled by ne-trending faults are scattered in the southeast (photo 7). In fact, this area is already on the eastern edge of Kangdian uplift, which is very old and has a long history of activity. So faults and folds are particularly developed.
Photo 5 Block and ring image structure
Photo 6 Dendritic and Shell Shadow Structure
Fig. 7 Block and shadow structure
(2) Geological significance of special images
Remote sensing image is a reduced comprehensive landscape, which contains many direct or indirect geological elements. These geological elements often appear in the background color through a certain tone, thus forming various geometric tone anomalies. These abnormal tones are important clues to understand various geological phenomena. In order to establish a natural relationship between an image and geological concepts, according to the geological conditions and image characteristics of this area, the structure is the main content, which is preliminarily divided into linear, circular, block and strip images.
1. linear image and its geological significance
A linear image is a tone anomaly that extends into a straight line or is close to a straight line. Because MSS has a good resolution for ground linear bodies with a width exceeding 15m, the linear information in satellite images is particularly rich. Its composition has the following three ways:
(1) The sudden appearance of shades in the background color or the mutual appearance of shades in the extension direction. Such images are thin and clear, and often reflect torsional faults, such as the Lizhou-Yuhong fault in Guangxi (see table 1).
Table 1 Summary of Fault Elements
sequential
Note: * strike/dip ∠ dip.
Photo 8 In Yuhong Tea Factory, Guangxi, a 25 strike fault passes through, and the stratum is strongly squeezed and broken in scales.
Photo 9 The Yu Xia-Luliang fault shows a huge fault zone at Xiadian, which is filled with calcite (white calcite mass).
Photo 10 The thin limestone of Middle Triassic in Lucheng, Longlin was strongly compressed and developed into a fault.
Photo 1 1 The cliff formed by Longlin Xiang Bo fault zone is composed of Permian limestone, and its top is Triassic silty mudstone.
(2) The continuous extension of special shadow lines in a certain direction. Because of its long extension and spanning different lithologic units, the width and tone depth of linear images are also different. It has been proved that this is a reflection of the ground fault zone. The NE-trending fault zone from Bao 'ai in Yunnan to Yuhong in Guangxi to Dushan in Guangxi is a typical example. The belt is 250 kilometers long and developed in silty mudstone and siltstone of Middle Triassic. Due to compression, the stratum is broken and locally scaly, and cleavage is extremely developed nearby (photo 8). The crushing bandwidth can reach 400 ~ 500 m, which is the main factor controlling the terrain here. Rivers and mountains extend in the direction of 25 ~ 30. The fault is located in the south of leye county City, resulting in highly fractured limestone, locally mylonite, and serious calcite along the line, with a width exceeding 50m. This is a clockwise compression-torsion fault. As for the reason of different widths, it is the landform difference caused by different lithology. Besides the above reasons, the color difference is also related to hydrophilicity.
(3) the boundary of the plate tone. The clarity of a uniform plate tone boundary or the intersection of two plate tones varies with the color difference, but it is usually not obvious, and it is a ground fissure with different coverage. For example, the NW-trending fault of Lvliang-Yu Xia is most clearly displayed in ms4, MS5, especially in band 5. Its northeast side is a plate-like dark gray tone, and its southwest side is a plate-like light gray tone. Image intermittent extension 190km. The result of measurement at the outcrop point of Lixia is a large fault zone represented by landform, and the southeast section controls the water system. The survey point happens to be the lithofacies change zone of Middle Triassic. Light gray is changed to light green sandy and silty mudstone mixed with sandstone, and the vegetation is mainly weeds; The dark series is a mixture of limestone and dolomite with thick slope sediments. Shrub is the main vegetation, mixed with thatch. The normal stratum occurrence is 25 ∠19. Due to fracture, breccia can be seen everywhere, and calcitization is also very serious (table 1, photo 9).
Of course, not all linear images are direct reflections of ground faults, but the actual geological and non-geological significance is much broader. Such as stratigraphic boundaries, fold axes, water boundaries, artificial buildings, etc.
2. Circular image and its geological significance
Divided into two categories: round and round.
1) Circular image: refers to uniform and smooth circular and near-circular tone abnormality or special shadow structure abnormality. According to the field investigation, it has both geological and non-geological significance.
(1) Geological significance: 1. Trap structure composed of two kinds of rocks. The greater the difference between rocks, the more obvious the abnormal tone or shadow structure. The former, such as Longfengqiu anticline in Bama, Guangxi, is the core of Triassic sandstone-mudstone trap, and limestone of Lower Carboniferous and Permian is exposed. Because limestone has much deeper tone characteristics than mudstone, it constitutes a dark gray tone anomaly (photo 3). The latter, such as Zhemiao anticline in Tianlinxi, Guangxi, is trapped by Mu Lan Formation of Middle Triassic, and the core of Banna Formation is sandstone and mudstone. However, the sandstone of Mu Lan Formation is thick and hard and has strong weathering resistance. The sandstone of Banna Formation is thin and loose, with weak weathering resistance, showing different geomorphological features, which constitutes the difference of schlieren structure. Second, the intrusive reflection. In the sedimentary rock distribution area, intrusive rocks have unique production characteristics. Due to the composition, structure, structure and other reasons, it is often light gray or white, and even the concealed rock mass has different degrees of reflection. For example, Dachang, Nandan, Guangxi, has a round light gray tone anomaly with blurred edges, which is confirmed to be a concealed granite body by drilling.
(2) Non-geological significance: it is mostly caused by water, vegetation or pure geomorphic factors. On the south side of Jiuzhou, Guangxi, all MSS bands have a dark circular fine-grained shadow pattern with abnormal structure. The observation results show that the sandstone of Mu Lan Formation of Middle Triassic is mixed with mudstone, and its occurrence is changeable. On the ground boundary of circular anomaly, there is no abrupt change of geological phenomenon, mainly the difference of vegetation distribution. The abnormal tone area is dark green and dark green dense miscellaneous wood forest area, mainly broad-leaved forest such as chestnut, maple and camellia oleifera. Non-abnormal areas are scattered small pine trees with clear boundaries.
2) Ring image: Trapped image with dark tone or bright tone and a circle or approximate circle between dark tone and bright tone. There are single rings and multiple rings. Single-ring images often reflect intrusions with obvious alteration halos or zones, such as Nandan-Hechi granite body. The rock mass itself is gray or light gray, while the external alteration zone is dark, so the image becomes a dark ring. When the core of a gentle trap structure composed of two or more different lithology exposes an old group (anticline) or covers a new group (direction), the image is also annular. The multi-lithologic combination image is multi-annular.
3. Block image and its geological significance
Refers to the giant regular or irregular block image with the same shadow structure or uniform tone on satellite film. It is not only a reflection of landform and landscape, but also a comprehensive reflection of geological structure information at a certain depth on the surface and underground. Geometrically, the block image of this area can be divided into two types: ellipse and polygon. The former is blocky images such as Qiannan and Longlin. The latter has massive images such as Niushoushan, Luoping and Xuanwei.
(1) Block image in southern Guizhou: surrounded by strip-shaped images, it is oval, and its long axis is in the north-south direction, reaching 120km, with an area of 10000 square kilometers, with a grid-like shadow structure of alternating light and dark. The Bouguer gravity map shows a relatively negative anomaly. Geological data show that during the Devonian-Carboniferous period, this area was a negative tectonic belt dominated by subsidence, and the thickness of Devonian and Carboniferous was only close to more than 4,000 meters (generally only about 2,000 meters), but the current surface is a positive box-shaped fold group located on the south-dipping nose-shaped uplift slope.
(2) Block image of Niushou Mountain: a light variegated structure rhomboid bounded by two sets of linear images in the northeast and northwest directions. The long diagonal line extends about 240 kilometers to the northeast, covering an area of nearly 10,000 square kilometers. There is also a hidden ring in the core, which consists of pre-Sinian metamorphic rocks. Cambrian, Silurian and Devonian are in the south and north in turn. According to geological data, the linear images in NE and NW directions are obviously fault zones. Therefore, although the image of Niushoushan block is an ancient uplift, it is still a dynamic structural block in Indosinian-Yanshan period according to the current structure.
4. Strip image and its geological significance
Refers to the image features that are composed of light and dark tones and extend in parallel straight lines or curves. In many cases, it is a complex of linear images. Although the shape is complex, its geological significance is far less extensive than that of linear images. Mainly reflected in the region:
(1) fault zone. For example, the Rudong-Guiding banded image is composed of different lithologic combinations of Carboniferous-Permian and Triassic cut by more than two (NW-trending) faults, which is about 150km long and extends to the north, far from Guiding. The zones of MSS4 and 5 are white or light gray, and the deepening of MSS6 and 7 is uneven. This fault zone is hydrophilic except that the rock itself has different characteristics in different zones.
(2) Fold zone. It is a linear fold of multi-lithologic combination, which is the image feature after denudation. Guiding-Changming-Zhang Bu N-S banded body is a compact syncline composed of Carboniferous, Permian and Triassic. In addition, large-scale gentle fold groups can also form banded or annular image features after different degrees of erosion.
The above is a preliminary summary of the special images directly related to the structure of this area, which is currently in practice and needs to be continuously expanded and enriched.
Third, the analysis of geological interpretation effect
The ultimate goal of satellite interpretation is to understand geological phenomena and grasp geological laws, so as to evaluate oil and gas exploration prospects. To achieve this goal, apart from the professional level of interpreters, the quality of satellite movies is also closely related to the methods used in interpretation. As for the use value of satellite films in a region, in addition to the above factors, it depends on the interpretation effect.
Through brief field observation and comparative analysis of known data, the visual interpretation effect of1:500,000 false color composite film is good. Especially the fault structure (see figure 1), the author made field observation on more than 30 linear images interpreted by the laboratory. The results show that most of these linear images are reflections of ground faults, deformation and compression zones or hidden faults (Table 1).
Of course, not all ground fractures are reflected in satellite photos or can be directly interpreted, which depends on the resolution of satellite photos and the ability of naked eyes to distinguish the gray level recorded in satellite photos. In addition, because of its wide field of vision, satellite film has unique advantages in determining the spatial extension of faults and their relationship. For example, Ziyun-Du 'an has always been regarded as a big fault, but the satellite mosaic clearly reflects that it is composed of three different groups of faults. That is, the northern section is a part of Shuicheng-Ziyun-Donglan fault, the middle section is a part of Ceheng-Luodian fault, and the southern section is a part of Guiyang-Nandan (340) or Qingzhen-Nandan (330) fault. These three faults not only have different orientations, but also have different formation times (discussed later). Another example is that the Sejong-Maitreya belt is not a fault. Its southwest section is a part of the Mile-Shizong-Qingzhen fault zone, and its north section is composed of Luoping-Panxian fault zone.
Building blocks and satellite plates have more special reflection ability. Because of its macroscopic nature, it completely replaces the purpose of the whole working process from point to line and from line to surface; Because of its authenticity, it fills the distortion phenomenon caused by the limitation of accuracy and human observation in the above process. In the contrast of vast space, through different structural combinations in the plane and related factors in the vertical direction, the unique tonal landscape and its relationship are reflected, which is a comprehensive image of underground massive structures on the surface. This can't be reflected and expressed by various geological maps in the past.
As for the interpretation effect of local structure, it depends on the lithologic differences between the strata that make up the local structure. If the lithology difference is large, the color difference on the satellite film is large, which is easy to be recognized by the naked eye and the interpretation effect is good. In the southeast of this area, the interpretation effect of local structures is far less than that of other places in this area, because most local structures in this area are composed of single sandstone and mudstone in Middle Triassic. The gray difference of this kind of sandstone and mudstone on satellite photos is much lower than the resolution of naked eyes.
The figure11:500,000 false color composite sheet has more fractures and higher accuracy than the regional figure1:200,000.
Four. Regional structural model and selection of favorable structural zones for oil and gas exploration
Through the geological interpretation of satellite photos, this paper attempts to combine various isolated geological structural phenomena or some special landforms with geological significance into a whole through analysis. This whole can not cut off the geological history, but also can be explained by a unified tectonic stress field, so it is called "model". The greatest significance of this model is to predict geological structures and related geological phenomena, thus providing a basis for the final evaluation of oil and gas exploration prospects.
According to the statistical results on the interpretation map, there are as many as 15 groups of faults. From the satellite photos, some are clear, some are intermittent and vague. Those that are clear are mostly large faults exposed on the surface. Concealed, many systems are concealed linear structures or semi-concealed faults. These faults divide the crust in this area into many huge blocks, which are embedded in the shallow tectonic zones with unique folds, thus increasing the structural complexity in this area. However, through the analysis of the structural combination relationship, it can still be seen that there are at least three obvious structural development periods and corresponding folds and faults in this area. That is, the east-west fold structure and its supporting "X"-shaped (340 and 40) faults; The NE-trending fold structure and the vertical (320) extensional fault zone are dominated by the N-trending fold structure, accompanied by NW-trending folds and related fault zones (Table 2 and Figure 7).
Table 2 Structural zones and their characteristics
6 ~ 7 east-west structural zones can be explained on the mosaic map. The Zhehai-Puding-Huishui and Guiyang-Qingzhen belts in the north are relatively large, with a width of about 10km. Their images are blurred, which may be a reflection of hidden structures. Regional data show that the east-west structure appeared in the Xuefeng period of Proterozoic, and the Caledonian period played an important role in making the Yunnan-Guizhou-Guangxi uplift land-forming. A group of "X" faults with 340 and 40 directions are the inevitable products of north-south compression (Figure 2). It is worth pointing out that although the east-west structure developed in Proterozoic, it was still reflected in Yanshan period. According to the change of X-shaped fracture orientation, the compressive stress in the north-south direction is intermittent, and the orientation of stress axis changes (Figure 3).
Fig. 2 Under the horizontal compression in the north-south direction, apart from the east-west folds, a pair of torsional faults were formed.
Fig. 3 With the development of geological history, the compressive stress in the north-south direction deflects eastward, and the orientation of a pair of torsional faults also changes slightly.
North-east (35 ~ 40) fold structures and compressional faults are mainly developed in the west of this area. The main body of the fold is composed of Sinian-Devonian system, which is a part of Cathaysian tectonic system (Figure 4). From the sedimentary point of view, it began to develop at the beginning of Hercynian tectonic cycle. The NW-trending (365,438+00 ~ 320) extensional faults perpendicular to it gradually caused NW-trending trough depressions in the basement of this area, which controlled the late Paleozoic sedimentation. Therefore, the distribution characteristics of northeast sedimentary facies belt in this area have been changed. For example, the sedimentary thickness of Shuicheng-Ziyun-Namo Devonian-Carboniferous narrow facies belt is 3000 ~ 4000 meters ... which is an important background condition of regional tectonic model so far.
Fig. 4 Under the action of counterclockwise torsional stress, NE folds or compressive cracks are formed, and tensile cracks perpendicular to them are produced at the same time.
Fig. 5 A series of torsional fractures of the yoke are formed under the east-west compressive stress.
At the end of Hercynian, this area was horizontally squeezed from east to west, and gradually strengthened in the process of geological development, reaching its peak in Indosinian-Yanshan period, thus laying the outline of the current regional structure in this area. A pair of X-shaped faults in the north-south fold belt, northwest and northeast are important products (Figure 5). The above structural zones are also clearly reflected on the geological map of Kunming Sheet (G-48) (photo 12). Careful analysis of the pictures shows that the hidden structures proposed in the interpretation of satellite photos have different degrees of reflection. It is mainly divided into three groups: east-west, northeast and northwest. The north-south structural belt is naturally more striking (Figure 6), among which two groups of composite structural belts with * * * yoke properties are the most prominent, namely, northeast (65 ~ 70) and northwest (310). Shuicheng-Guanling-Ziyun and Qujing-Brown-Xiuwen are particularly typical. On the surface, this area is a fold pattern mainly controlled by the east-west compressive stress of Indosinian-Yanshan period. Shuicheng-Guanling-Ziyun left oblique fold belt, one of the X-shaped faults, is the result of anticlockwise twisting. In essence, however, this group of fold belts was formed under the background and control of the NW-trending extensional rift belt developed in the late Caledonian or early Hercynian. In other words, the structural belt reflects the structural elements of the early stage (hidden faults) to a great extent. The northward branch of the northwest section of the belt is a direct reflection of the previous faults on the surface. From the satellite photos, the included angle between them is about 10. * * The finishing touch of the yoke-Brown-Xiuwen structural belt was only formed in the early structural belt (NE40), which was covered with the NE-trending torsional fault of Indosinian-Yanshan period. As for the north-south structural belt, like the northeast and northwest structural belts, it belongs to Indosinian-Yanshan period, so it is obvious on both geological maps and satellite photos.
The geological map of Kunming in photo 12 reflects the plane relationship between tectonic zones.
Fig. 6 Schematic diagram of structural outline compiled according to geological map of Kunming.
Fig. 7 Structural morphology and combination formed by east-west compression under the control of F1and F2 hidden faults.
To sum up, the structural model of this area is Indosinian-Yanshan period, which was formed by east-west compression (with signs of clockwise twisting) under the background of east-west and northeast fold belts and northwest extension rift belts. Due to the east-west compression and the north-south extension, a plough-like fault depression was formed in the south of the intersection faults of Shuiling-Guanling-Ziyun and Mile-Qingzhen, which made the thickness of Triassic reach 4200 ~ 5000 meters ... The corresponding north side is located in the southern margin of the central Guizhou uplift. Because the uplift in central Guizhou has been rising and expanding in the corresponding period, it has produced the force of pushing south and limited the northward movement caused by tension, so the settlement is not obvious. In the same way, the vertical movement of the block cut by the previous "X" fracture is also different. Some sink, some rise. The former is like Luoping and Qiannan fault block. In Luoping fault block, the thickness of Upper Permian is only more than 2000 meters, but when crossing the eastern and northern boundaries (faults), the thickness quickly decreases to 442 meters and 500 meters. The latter has Niushoushan fault block, which is in a relatively rising state for a long time, which is of course related to its structural position on the eastern edge of Kangdian ancient uplift. Because the faults that constitute the fault block are multi-stage and have different combination orientations, they are reflected on the satellite images and become block images with different geometric shapes. On the other hand, in the process of geological history development, there are boundary conditions independent of regional tectonic stress field, so local and unique tectonic combination forms can be formed. Reflected in satellite photos, it forms a unique shadow pattern and becomes an important symbol of understanding underground geological structures. The Sino-British tectonic group between Xuanwei and Puding is a typical example (Figures 6 and 7). It is a special structural combination consisting of Maping limestone mixed with dolomite in Upper Carboniferous, triangular anticline with the bottom facing west, nearly north-south syncline in Middle and Lower Triassic and arc anticline in Middle and Upper Carboniferous. Obviously, this is a structural feature formed by east-west extrusion under the control of a pair of "X"-shaped faults in the northwest and northeast directions. Therefore, the hidden structure (fault block or fault) is completely possible, which can be identified by analyzing the special landform of the surface and some fold combinations of the cover.
Photo 13 Xilin, Middle Triassic thin limestone forms an east-west box anticline, and the upper part is the shape of its core section.
It must be pointed out that the above-mentioned tectonic development processes are interrelated in time and space, while others are long-term. As mentioned above, although the east-west structure developed in Proterozoic, it still existed at least in Mesozoic. Xilin's compact box folding is one of the products (photo 13). Of course, it is not that the compressive stress in the north-south direction has always played a leading role, but that different geological periods have different reflections, as do the structural stress or other properties in the east-west direction. Therefore, when analyzing specific geological problems, we must have a clear concept of time and space.
For the selection of favorable structural zones in oil and gas exploration, due to the depth of work, some superficial views are put forward only from the perspective of regional structure for reference in comprehensive evaluation.
According to the analysis of regional data, Dengying Formation of Upper Sinian is an important gas-producing layer in Sichuan Basin. This formation is also dolomite in this area, with a thickness of about 500m, and the total thickness of Lower Paleozoic is greater than1200 m. The reservoir-cap assemblage of Lower Paleozoic can be formed from Upper Sinian to Silurian, and the east-west structural belt developed earliest in this area, forming the eastern structural period of Hugary. Therefore, the east-west direction and its related trap structures are favorable places for oil and gas accumulation in the Lower Paleozoic. Although there is slight metamorphism in the Lower Paleozoic south of Ceheng-Luodian fault zone, low anticlines such as Ningnan-Nayong-Weicheng, Xuanwei-Liuzhi-Duyun front fold belt in the north are still favorable structural belts for oil and gas exploration in the lower assemblage, especially large dome anticlines such as Longli. The Upper Paleozoic reservoir-cap assemblage composed of Devonian to Triassic is widely distributed in this area, with a thickness of about 6000 meters ... especially in the vast areas south of Shuicheng-Guanling-Ziyun and Mile-Qingzhen cross-faults. The trap structures in this area are the first NE structural belt and the second N-S fold belt, which are subjected to counterclockwise torsional stress. Therefore, the NE-trending and NS-trending anticlines are favorable places for oil and gas exploration in the upper assemblage. The above two tectonic belts are superimposed (compounded), and the anticline structure with good preservation conditions is especially valuable for exploration.
Verb (abbreviation of verb) brief conclusion and suggestion
Since satellite remote sensing images have been used for geological interpretation in different regions, they have continuously enriched the content of translation and made many achievements. Therefore, the significance of geological interpretation of remote sensing images is enhanced, and many problems are exposed at the same time. Some can be solved in the application of image processing system, and some need to be discussed later. Therefore, it is too early to draw a proper conclusion about the application of remote sensing technology in geology. Nevertheless, the visualization, authenticity and macroscopic characteristics of satellite photos are still one of the effective methods for geologists to study, discuss and even solve regional geological problems.
(1) Because of the resolution of satellite photos and the above characteristics, it is more suitable for the interpretation and research of regional tectonics or tectonic group combination. It has a unique interpretation effect on regional large faults and intrusive rocks. As for the in-depth interpretation of local structures, it must be supplemented by aerial remote sensing data or computer identification methods.
(2) Through the combination analysis of ground feature information in vertical and horizontal directions and the combination study of ground structural morphology, various concealed structures can be inferred and explained. Thus, to a certain extent, we have deepened our understanding of the characteristics and laws of regional geological structures and provided important background conditions for oil and gas exploration.
(3) Because it is difficult for naked eyes to distinguish the tiny gray differences recorded by different strata with similar lithology in satellite photos, the intuitive interpretation effect of stratum lithology is not ideal, which also affects the in-depth study of local structures.
(4) In order to facilitate field verification and make the interpretation results have practical value, the interpretation results should be converted into1:50,000 or1:65438+100,000 topographic maps, and then other processing should be carried out. Therefore, topographic map should be one of the contents of data preparation before work in interpretation area.