Resource evaluation of Jilin Meihe oil shale mineral-bearing area

The Meihe oil shale mineral-bearing area is located in Hongmei Town, Meihekou City, Jilin Province. The geographical coordinates are 126°43'～126°54' east longitude and 42°56'～43°00' north latitude. Roads and railways extend in all directions. , convenient transportation.

1. Geological background

(1) Structural characteristics

1. Regional structural background

The Meihe oil shale mineral-bearing area belongs to Dunzhou Mi Basin, the huge Tanlu Fault Zone in eastern China, is divided into two branches after the lower Liaohe River fault depression. The east branch is the Fushun Mishan Fault and the west branch is the Yilan-Yitong Fault. The basic structural framework of the fault zone is a strike-slip-rift type, which is controlled by two opposing deep faults to form a group of rift basins of varying sizes. Initial rifting occurred during the late Mesozoic, and the Upper Jurassic-Cretaceous system was deposited. After the Cretaceous, the depositional scope expanded, forming a red clastic rock system about 400 to 1100m thick. During the Cenozoic Era, faulting activity entered its peak stage, forming a series of faulted basin groups with the Cretaceous basin base.

2. Basin structural framework

Basin structural framework is a comprehensive form of the configuration and superposition of structural properties at different stages of basin formation and evolution. It includes the evolutionary structural traces of early basement structures-syn-sedimentary structures-late structural deformation (or stress field conversion).

(1) Preliminary structure of the basin. From the geological map of the Meihe Basin, it can be seen that the faults F01 and F02 of the basin's early structures trend NE40°~60°, which are late Mesozoic faults and control the sedimentation and distribution of the Cretaceous. The basement is Pre-Sinian metamorphic rock series.

(2) Basin synsedimentary structure. The synsedimentary faults of the basin are the opposite-dipping tensile faults F1 and F2 at the basin edge, forming a NE-trending narrow rift-rift (graben) form, with the Cretaceous as the basement. It controls the sedimentation of the coal measures of the Paleogene Meihe Formation and is a synsedimentary fault. The NW side of the fault depression has a small sedimentation amplitude, while the SE side has a large sedimentation amplitude, forming a semi-graben structural framework. The intensity of fault activity along the strike (i.e. fault throw) is different, which directly controls the sedimentary thickness and coal-bearing properties of the Meihe Formation.

(3) Tectonic deformation after the basin formation period. After the sedimentation of the basin ended, it experienced a tectonic movement. The initial strike extensional normal fault F3 divides the basin into two belt-shaped fault blocks in the north and south. The coal series in the ascending plate of the north limb has been denuded and the coal seams are shallowly buried, and has been explored and developed. The descending plate of the south limb and the contemporaneous fault F1 on the southern edge form a new The graben, coal, oil shale and overlying strata are completely preserved. Later NW-trending strike-slip faults (K1, K2, K3, K4) cut the NE-trending narrow graben into different fault blocks, which gradually subsided in a stepped manner along the SW-NE direction of the basin, controlling the burial depth of coal measures and coal seams. Changing trends.

(2) Stratigraphic characteristics

The Meihe oil shale ore-bearing area is a Paleogene fault-depression type coal-accumulating basin, and the basin base is pre-Sinian Anshan Group metamorphic rocks and Cretaceous purple , purple-red mixed with gray-green coarse clastic rock series; the basin is filled with coal- and oil-bearing shale formations of the Paleogene Meihe Formation, overlying the Neogene.

1. Pre-Sinian System

The Pre-Sinian System is mainly distributed at the base and both sides of the basin. It is mainly Anshan Group metamorphic rock, composed of biotite plagioclase gneiss, mixed It is composed of lithified plagioclase gneiss, granitic gneiss, etc., and its thickness is unknown.

2. Cretaceous

The Cretaceous is an intermountain basin accumulation under a semi-arid climate. The lower part of the lithology is mainly purple sandstone, shale, and conglomerate. In Dongyujing One area is exposed; the middle part is mainly gray-green clastic rock, containing animal fossils such as Cyienatani Gralau; the upper part is composed of purple, brown and gray-green coarse sandstone and gravelly coarse sandstone, and the gravels are mostly irregular and angular. , muddy or calcareous cement. It is in unconformable contact with the underlying Pre-Sinian system and is about 400m thick.

3. Paleogene

Paleogene Meihe Formation, from bottom to top is the bottom sandy conglomerate section (E2-3m1), and the lower coal-bearing section (E2-3m2). Deep lacustrine mudstone section (E2-3m3), upper coal-bearing section (E2-3m4), green rock section (E2-3m5). The average thickness of the Meihe Formation is 1160m, and it is in unconformable contact with the underlying strata.

The fossils produced in the Paleogene Meihe Formation mainly include Taxodium cf dubi-um (Sternb) Heer, Sequoia Chinensis Endo, Phyllites sp (cf Aluno sp), Metasequoia dis-tich, Cerc-idi-phyllum articm. The Paleogene Meihe Formation is a coal-bearing stratum in the Meihe Basin. The Meihe Formation coal-bearing rock series is composed of continental clastic rocks, coal seams and oil shale. The coal-bearing rock series sediments of the Meihe Formation can be divided into five sedimentary combinations from bottom to top, which are described as follows:

(1) Bottom sandy conglomerate section (E2-3m1). Overall, it is a set of alluvial fan deposits, composed of sandy conglomerate and conglomerate with poor sorting and grinding degrees. Mainly distributed along the basin edge fault zone, it is loosely cemented and contains water. A small range of peat swamp facies (generally lenticular coal seams) develops in the inter-fan valley, with a thickness of 100-150m.

(2) Lower coal-bearing section (E2-3m2). Mainly coal-bearing clastic rock deposits. It consists of shallow lake facies and fan delta alluvial fan deposits, followed by fan delta and shallow lake facies deposits from the basin edge to the inside of the basin. The main lithology is gray brown to gray black intercalated fine-grained sandstone, and the basin edge zone changes into sandy conglomerate. With continuous filling, an extensive fan delta plain and a vast peat swamp environment with shallow lakes are formed. It contains 1 to 5 coal layers, and the main coal seam is the 12th layer, which is a very thick coal seam that develops in the entire area, with a maximum thickness of 45m. The thickness of the formation is 100~180m.

(3) Deep lacustrine mudstone (oil shale) section (E2-3m3). It is mainly composed of extremely thick layers of deep lacustrine mudstone, mostly brown, gray-brown, chocolate and other pure mudstones containing oil and widely distributed. Below this section is a high-quality oil shale deposit with an oil content as high as 11.40%. The formation thickness of this section is 80 to 440m.

(4) Upper coal-bearing section (E2-3m4). It is mainly the basin filling and contraction stage, with coastal shallow lake facies, delta and fan delta deposits, mainly sandstone, siltstone and mudstone deposits. There are 9 coal-bearing layers (layer groups), of which the 4th to 7th layers are partially mineable and distributed on the south side of the basin. The formation thickness is 250~280m.

(5) Green rock section ((E2-3m5). Green, gray-green mudstone, tuff intercalated with thin layers of gray-white fine sandstone, horizontal bedding developed, thickness 0-400m.

4. Quaternary Series

Distributed throughout the area, the minimum thickness is 8.45m, the maximum thickness is 35.96m, and the general thickness is 15-25m. It is composed of humus soil, sandy clay and quicksand at the bottom. It is in unconformable contact with the underlying strata.

2. Characteristics and distribution of oil shale

(1) Characteristics of oil shale

Oil shale is deep. Gray - gray-black, shell-shaped fracture, soft, flake-shaped, powdery gray-brown, streaks brown, tan, smoke when burned, strong smell of asphalt, and those with high oil content burn when exposed to fire. Testing of shale samples showed that the oil shale in Wells Three and Four has an oil content of up to 11.40%, and the oil content of eight samples ranged from 4.7% to 11.40% (the oil content of the samples taken for this evaluation was 7.78%).

(2) Oil shale formation environment

1. Oil shale mineralization era

The oil shale layers in the Meihe oil shale mineral-bearing area are Paleogene Meihe Formation deep lacustrine mudstones Section (E2-3m3), after various explorations, it is believed that the bottom of the oil-bearing shale series (the roof of the 12th coal seam in the lower coal section) is a high-quality oil shale section, with lithology of brown, gray-brown, and gray-black. Mudstone. It is dense and massive, producing animal fossils and a small amount of plant fossils. Its physical characteristics are type I oil source rocks.

2. Sedimentary sequence and comparison.

The sedimentary sequence from bottom to top is: during the initial rifting period of the basin, the coarse clastic rock section at the bottom of the Meihe Formation in the low-stand system tract was deposited (SE1); during the basin expansion period, the coal-bearing section under the transgressive system tract was deposited (SE2); During the maximum expansion period, the brown mudstone section (oil shale section) of the high-water system tract was deposited (SE3); during the contraction period of the basin, the coal section of the receding system tract was deposited (SE4). The Meihe Basin has a unique sedimentary sequence. After the maximum expansion period of the basin, , has been deposited in the brown mudstone section of the high-water system tract, and the upper coal-bearing section is missing. The thickness of No. 76-5 hole is 500m, and the thickness of No. ZK13 hole is 433m.

3. Depositional rules, genetic types and depositional environment of mineral deposits

The ore-bearing area goes from the initial rift to the maximum expansion period, which is the best coal-forming period, forming thick to extra-thick coal seams ( 12th coal seam). After coal accumulation, it developed into a deep lake environment during the basin's maximum expansion period. It is known from the oil shale sedimentary sequence in the basin that the oil shale was deposited after the deposition of the 12th coal seam, and is the direct roof of the coal seam, forming a coal-oil shale deposition model. Analysis of the sedimentary environment shows that oil shale was formed when a peat swamp environment was transformed into a deeper water body. A huge thick layer of brown oil-bearing shale section is formed, with a general thickness of 80-120m and a maximum thickness of 450m. The bottom 10-20m thick is high-quality oil shale, which has extensive prospecting significance. Such as Fushun Basin, Shulan Basin, etc.

(3) Oil shale distribution characteristics

From the geological map of the Meihe oil shale ore-bearing area, it is known that the graben formed by faults F1 and F2 in the later period of the basin is the coal-bearing section. , oil shale section occurs, covering an area of ??about 20 to 25km2. The oil shale layer is the roof of the 12th coal seam that is widely developed and stable in the basin (Figure 5-10).

Figure 5-10 3-3' geological section of Meihe oil shale mineralization area

3. Oil shale resource evaluation

(1) Exploration work Extent analysis

1. Geological exploration work

The Meihe Basin is located in Hongmei Town, Meihekou City, Jilin Province. It starts from Dubadan in the west and ends at Wurenban Village in the east. It is long and narrow in the NE direction. Shape basin, 15km long from northeast to south-west, 2km wide from southeast to northwest, with an area of ??about 32km2. In the 1960s, coal prospecting was carried out. In 1964, the Changsheng, Zhongyaobao and Dongxia precision survey reports were submitted, and wells were built successively. Four pairs, Meihe No. 1, No. 2, No. 3 and No. 4, have been mining coal to this day. The target layer for exploration and development at that time was the No. 12 (Jie No. 13) coal seam in the lower coal section of the Meihe Formation in the Paleogene. The associated mineral deposit, oil shale, was not comprehensively explored and was omitted. However, in the drilling data, the oil shale on the roof of the 12 coal seams is described, indicating the characteristics or mark depth and thickness of the oil shale judged by naked eyes.

From 1980 to 1990, the "Meihe Basin Analysis" report completed and submitted by the Changchun Scientific Research Institute of Dongmei Geology also discussed the coal seam deposition environment and resource prediction, and did not include oil shale as the target layer. Conduct research.

In 2003, Jilin Coalfield Changchun Exploration and Design Research Institute studied the Meihe Basin and the formation rules of oil shale, gathered various information, and proposed the "Changsheng-Dongxia Coal and Oil Shale Model of the Meihe Basin" "Census Design" began comprehensive prospecting work. In 2004, two boreholes were constructed, and coal and oil shale layers were discovered, making new progress. However, the focus was still on finding coal, and no special oil shale exploration work was carried out.

2. Exploration degree and accuracy

Previous geological exploration research work shows that no special exploration work has been carried out for oil shale in the Meihe Basin. The level of understanding of oil shale deposits is very low. Measured by the exploration stage, it is only a preliminary level. Because there is no real thickness and grade data of oil shale deposits. It is only based on the mineralization model of the coal-oil shale associated combination to understand the origin and distribution of the deposits to provide a basis for prospecting predictions.

(2) Resource Forecast

This time, the oil shale resource forecast for the Meihe oil shale mineral-bearing area is divided into two blocks. The thickness of one block is 10.56~262.71m, and there is no corresponding oil content test data. Samples were taken from the gangue pile and tested, and the oil content was 5%~11.40%. The thickness of the second block is 14.90-61.44m, and the oil content determined by naked eye is relatively low, ranging from 3.5% to 5%. The thickness is conservative when predicting. The arithmetic average of the minimum thickness of boreholes in the two blocks is 12.73m. The oil content is a thickness-weighted average of 4.83% (refer to the oil content of the sampling test in this evaluation of 7.78%). The boundary of the prediction area is composed of oil-bearing shale. The stratigraphy is determined. The area is calculated from the plan view and multiplied by the effective area coefficient of the ore body (oil shale occurrence area in the exploration area/exploration area area). Since the oil shale layer inclination angle is greater than 15°, the inclination angle must be used to correct the oil shale area to 11.48km2. , the weight is analogous to the weight data of other oil shale ore-bearing areas of 2.00t/m3. The potential oil shale resources in the Meihe oil shale ore-bearing area are 292.19 million t, and the potential technical recoverable resources of oil shale are 87.66 million t; The potential resources of shale oil are 14.11 million tons, the potential technically recoverable resources of shale oil are 4.23 million tons, and the potential recoverable resources of shale oil are 3.18 million tons.