I. Geological background
Structural characteristics of (1)
Danzhou mining area in Hainan belongs to Leiqiong new depression in Huaxia fold belt of South China platform, that is, the south wing of the southern depression in Beibu Gulf depression area of Beibu Gulf Basin. The latest stratum forming its basement is Upper Cretaceous. Due to the imbalance of fault activity, the ups and downs vary from place to place, thus forming Yunlong uplift, Lingao uplift, Changpo sag, Chengmai sag, Fushan sag and Haikou sag.
In the north of the mining area, there are 14 1 line, 153 line, 148 line, 164 line, Zhonghe, Xinying and Wangwu, etc. Due to the little influence of late tectonic movement, the strata of Changpo Formation are a very gentle east-west syncline structure. The two wings of the syncline have an inclination of about 5, and the center is roughly located in the area from Line 4 143 to Line 6 186 and 134. It is wide in the south and narrow in the north, with asymmetrical shape, and some small faults can be seen.
According to the drilling data, the small faults of Changpo Formation are mainly distributed in the area from Changpo to Dongcheng Highway in the south wing of syncline. There are 7 drilling controllers, numbered as F 1 ~ F7. On the plane, it is roughly arranged in parallel with the east and west, and tends to converge to the west, like a broom; On the profile, the F2 fault has a zigzag structure. These faults are all normal faults. Fault occurrence: strike northeast nearly east-west, dip 40 ~ 50, and extend 0.4 1 ~ 5.90 km. Vertical fault distance: according to the thickness of the missing coal seam and stratum near the fault plane controlled by drilling, it is estimated that the maximum is 26 meters, and the minimum is 4 ~ 8 meters, and it tends to become smaller and sharper to the depth. Structural breccia, slip surface, scratches and steep dip angle of strata can be seen at the fault. No fault plane passes through Luo Fu Formation, which is caused by the tectonic movement from the deposition of Changpo Formation to the end of Miocene before the deposition of Luo Fu Formation. The above faults partially cause coal seam and stratum losses, and have no influence on coal quality (Figure 6- 13).
Figure 6- 13 Section A-B of Changpo Exploration Area in Danzhou, Hainan
(2) Stratigraphic characteristics
Except for the Cretaceous outcrop at the edge of the basin, the surface of the basin is covered by Quaternary. According to the drilling results, the strata from old to new are as follows:
1. Upper Cretaceous Baowanqun (K2bw)
The lower part is purplish gray, bluish gray conglomerate, glutenite and gravelly coarse sandstone, the middle part is interbedded with bluish gray or purplish gray, purplish red fine sandstone and siltstone and silty mudstone, and the upper part is interbedded with gray, yellow, purplish red conglomerate, gravelly coarse sandstone, bluish gray or purplish gray medium sandstone, with incomplete stratigraphic exposure and a thickness of more than 2,000m. ..
2. Paleogene
It is composed of red clastic rocks and mudstone in continental lacustrine facies, the lower part is interbedded with brick-red coarse sandstone, glutenite and siltstone, with a thickness of 40 ~ 250 m, and the middle part is low-oil shale with gray ~ dark gray siltstone and glutenite. The normal phase of low-oil shale is transformed into argillaceous rock, with an oil content of 1 ~ 3% and a thickness of 30 ~ 150m. The upper part is brownish red siltstone, mixed with coarse sandstone, mudstone and thin gypsum, with a thickness of 1 15 ~ 170 m. All the above sections are in integrated contact, with a total thickness of 185 ~ 570 m.
3. Neogene
(1) Miocene Xiayang Formation (N 1x): It is a coastal deposit, mainly composed of gray-white-greenish gray sandstone, mixed with sandy mudstone and argillaceous siltstone. The unconformity surface covers Upper Cretaceous or Paleogene, and its thickness is123 ~ 211m.
(2) Miocene Jiaowei Formation (N 1j): shallow-sea facies deposit. The upper part is gray siltstone and mudstone mixed with green sandstone; The lower part is grayish white sandstone or grayish green argillaceous siltstone, and sandstone and sandy mudstone are interbedded, with a thickness of 84 ~ 179m.
(3) Miocene Changpo Formation (N2 1cp): It is composed of combustible organic rocks in lacustrine facies, with the top eroded, and the maximum visible thickness of the borehole is 365m. According to lithology, the main mining area can be divided into five sections, which are described as follows from bottom to top:
The first section (N2 1cpa): gray semi-cemented conglomerate, glutenite mixed with a small amount of clayey sandstone. The thickness is 0 ~ 67m.
Section 2 (N2 1cpb): The lower part is interbedded with medium coarse sand and variegated massive claystone, sandy claystone or claystone with unequal thickness; The upper part is dominated by mottled massive clay and sandy clay. It belongs to lakeside-shallow lake subfacies deposit with a thickness of 22 ~155m.
The third section (N2 1cpc): blue-gray massive calcareous claystone, silty claystone mixed with argillaceous sandy limestone or calcareous sandstone, locally mixed with siderite sandstone lens. See snail fossils, belonging to lacustrine sediments, with a thickness of 2 ~ 25m.
The fourth stage (N2 1cpd): The middle stage is mainly composed of 35 layers of grayish brown oil shale and lignite, and gradually transforms from the upper part to the lower part into brownish gray-gray massive carbonaceous clay, blue gray massive clay and fine sand clay. Horizontal bedding is developed in the middle, with microwave-like and lenticular bedding in some areas, common syngenetic mud gravel and breccia structures, and the top and bottom gradually become massive structures with occasional cracks. Calcium is often distributed in calcium-bearing oil shale in the form of uniform particles (biogenesis), and a few are dispersed in blue-gray clay and sandy clay at the top and bottom in irregular blocks and veins (natural genesis). A large number of ostracods, fish, snails, plant fragments, algae and other fossils are produced in the middle of this section. This section belongs to shallow lake swamp facies deposit. The thickness is120 ~ 205 m.
The fifth stage (N2 1cpe): light gray and blue gray massive clay, silty clay mixed with clayey medium-fine silty sand, belonging to shallow lake-lakeside deposit. The maximum visible thickness of borehole is 95m.
(4) Pliocene Luo Fu Formation (N 12 1f): littoral and shallow marine facies deposit, mainly composed of light gray clay coarse sand layer and clay gravel layer. This group is parallel to the angular tail group and unconformity, with a thickness of 238 ~ 441m.
(5) Pliocene Wanglougang Formation (N22w): shallow sea and bay facies deposits, mainly yellowish brown-brownish red bioclastic glutenite and shell limestone. Integrated contact with Frodo Formation, 92 ~ 290 meters thick.
(6) Lower Pleistocene Zhanjiang Formation (Q 1z): fluvial facies and delta facies deposits, often connected with bedrock slope eluvial layer. It consists of brownish yellow gravel layer, feldspar timely medium coarse sand layer and variegated sandy clay. The thickness is 2 ~ 75m.
(7) Middle Pleistocene Beihai Formation (Q2b): It is medium-coarse sand deposited on marine terraces and sand dikes with good sorting and roundness. It contains ilmenite and zircon with a thickness of 2 ~ 1 10m.
(8) Holocene (Q4): gravel, sand, clay, silt, etc. Deposited in rivers and coastal areas. Generally, there are small and scattered peat soil, and sphalerite and zircon are found in coastal areas.
Second, the characteristics and distribution of oil shale
(A) the characteristics of oil shale
Oil shale in Changpo mining area is thick layered, and several to dozens of samples are collected from each borehole. Quality statistics method: the average ash, calorific value, oil content and thickness (sample length) of a single hole are calculated by weighted average, and the rest are calculated by arithmetic average; The average value of the whole layer is calculated according to the arithmetic average value of drilling holes.
Low-temperature dry distillation: the analysis results of 225 layers of oil shale in the table are arithmetically average, with oil content of 5. 10%, water content 12.58%, semi-coke of 79.70% and gas loss of 5.22%;
Calorific value: There are 225 grades of oil shale in the table, and the total average weighted by the reserves of I and II layers is 5.57MJ/kg.
Industrial analysis: the sample is nearly half done, and the analysis result of oil shale in the table is 103. The arithmetic average is moisture 6.0 1%, ash 69.79%, volatile 24. 15%, fixed carbon 3.32%.
Humic acid analysis: 52 samples were taken, and all layers of oil shale were distributed. Average free humic acid on dry basis: the first layer:16.27% (grade 6); The second floor is 2.73% (Grade 5); The third layer is 1.60%( 1 layer). The weighted average of three-layer oil shale reserves is 3.8 1%.
Total sulfur analysis: the arithmetic average of 46 samples in the table is 3.05%. The change rule is that the oil shale with good quality (high calorific value and high oil content) has higher carbon content, nitrogen content and total sulfur content, but lower hydrogen content and oxygen content.
(2) Formation environment of oil shale
Oil shale in Changpo sag is mainly formed in Changpo Formation. The sedimentary evolution characteristics of Changpo Formation are as follows: in the early stage, it was a continental lake basin in arid climate, a set of piedmont facies deposits mixed with coarse and fine clastic facies were rapidly transported and deposited, and shallow lake-lakeside facies deposits were deposited locally. In the middle period of Changpo Formation, the lake basin sank relatively and the terrain became more and more gentle. This period can be divided into three periods: early and late periods are dominated by lacustrine deposits, with a small amount of lakeside deposits. In the middle period, the terrain is very flat, the climate is warm and humid, and the lake basin is still sinking, but the sinking speed is slow. At this time, the lakes alternate in depth and oscillate frequently, forming a peat swamp facies environment rich in plants and fish, forming lignite and oil shale; In a small decline, a shallow lake-swamp environment rich in fish, ostracods and a small amount of algae was formed, and oil shale was deposited. The sedimentary syngenetic minerals in this period are characterized by a large number of siderite and pyrite. In the late Changpo Formation, the lake became shallow and mottled clastic deposits appeared again. Then, due to crustal movement, the lake basin disappeared and the Changpo area rose to denudation area. Later, the earth's crust sank again, which caused seawater immersion and accepted the marine mud and sand deposits of Luo Fu Formation in the early Pliocene.
(3) Distribution characteristics of oil shale
This area is a concealed Neogene continental basin, with axial east-west, steep north and gentle south, and asymmetrical shape. The sedimentary environment is stable, the occurrence is gentle and the structure is simple. The ore beds are mainly distributed in the south wing of the basin, with monoclinic structure and an inclination of about 5 to the north. The oil shale coal seam is very stable along the strike and naturally pinches out to the east and west ends; It gradually thickens to the north along the trend, spreads to the depth and pinches out (Figure 6- 14).
Figure 6- 14 Profile of Line 6 in Changpo Exploration Area, Danzhou City, Hainan Province
Upper coal seam (Ⅰ): It includes 1 oil shale and 23 ~ 20 coal seams, with a distribution area of 28.60km2, with oil shale and lignite interbedded, with No.23 coal as the roof and slightly higher locally, and No.20 coal as the floor. The buried depth of the roof is 34 ~ 282m, and the elevation of the floor is-18 ~-262m. The thickness of oil shale is 0.70 ~ 1 1.27m, with an average thickness of 6.08m The ore in this layer has stable thickness and the best quality.
China coal (Ⅱ): it is mainly the second layer oil shale, sandwiched with 19 ~ 5 coal seams, with a recoverable area of 42.05km2, a roof buried depth of 30 ~ 305m and a floor elevation of-18 ~-355m. The thickness of oil shale is 0.70 ~ 73.30 m, with an average thickness of 44.53m, and the thickness of this layer of ore is stable.
Lower coal seam (Ⅲ): area 14.50km2, distributed between lines 4 ~ 8. The south and north borders are also smaller than the upper two floors. The buried depth of the top plate is 69 ~ 354m, and the elevation of the bottom plate is-38 ~-342m. The thickness of oil shale is 0.70 ~ 12.89 m, with an average thickness of 4.59m, and the ore thickness of this layer is stable.
The contour map of oil shale cumulative thickness shows that the cumulative thickness of three layers of oil shale is thick in the middle and thin around. The thickness of the middle part is 50 ~ 70m, accounting for more than 2/3 of the total oil shale area, and the thinnest edge is 0.7m.
The oil content in the middle is also relatively high, basically ranging from 4.5% to 5%, and gradually decreases around (Figure 6- 15).
Three. Evaluation of oil shale resources
(1) Analysis of the degree of exploration work
197 1 In the second half of the year, drilling survey was carried out by the fourth detachment of the comprehensive team of the Oceanic Administration until the end of 1975, which lasted more than four years, and finally reached the level of detailed investigation, and 225 geological exploration holes were completed. Footage 504 19.5 1m (see mine hole 20 1 oil shale exploration area 4225) The analysis data include: low temperature dry distillation sample 6 104, industrial analysis 2099, calorific value 5566, elemental analysis 196, and total sulfur 66.
Figure 6- 15 Oil-bearing contour map of the first oil shale in Changpo exploration area of Danzhou mining area, Hainan Province
The exploration grid of line 4 ~ 9 in the southern mine field of this area is about 500× 250 ~ 500m, and the rest is about 1000×500m. Because of the gentle occurrence of oil shale, simple structure and thick coal seam, A-level reserves are found in the exploration grid of 500× 250 ~ 500m, B-level reserves are found in the section of 1000×500m, and C-level reserves are found in the section delineated by the insertion method. The coal seams in the north, east, west and three sides are pointed out, the thickness becomes thinner, the quality becomes worse, and it is reduced to C-level reserves.
(2) Resource evaluation
1. Resource evaluation
According to the new evaluation standard of oil shale, the oil shale resource reserve in Changpo mining area was re-approved and estimated. The oil shale resource reserve in the mining area was 2617.67 million t, of which the proven oil shale resource reserve was 2617.67 million t and the technically recoverable oil shale resource reserve was 243.33 million t; The reserves of shale oil resources in the mining area are 6,543,800+0,274,200 tons, of which the proven reserves of shale oil are 6,543,800+0,274,200 tons, and the technically recoverable reserves of shale oil are 6,543,800 tons. The recoverable reserves of shale oil in the mining area are 906 1 10,000 tons, of which the recoverable reserves of shale oil are 906 1 10,000 tons.
In this evaluation, 265,438+382.4 million tons of proven oil shale resources were obtained in Changpo oil shale exploration area in Danzhou, Hainan.
2. Resource forecast
According to the drilling data, there is no oil shale seam in the borehole outside the ore body boundary, and the seam is strictly controlled by drilling, so it is impossible to extrapolate and predict.