Evaluation of oil shale mineral resources in Tanshanling, Gansu Province

Tanshanling Oil Shale Mining Area is located 37 kilometers southwest of Tianzhu County, with an area of 23.75 square kilometers. It starts from Tanshanling in the north, reaches the north slope of Table Mountain in the south, reaches Donglagou-Jinsha Xiakou in the west, and reaches Pianpozi-Wangyaogou in the east. Administrative divisions are under the jurisdiction of Tianzhu Tibetan Autonomous County in Gansu Province. Geographical coordinates are102 40' 30 "east longitude and 36 57' north latitude.

The geomorphological features of Tanshanling oil shale mining area generally belong to alpine areas, and the Jinsha River basin in the middle and east of the mining area is a valley area, with discontinuous first and second terraces on both sides. The terrain of the mining area is complex and the height difference is large.

1969 10 when designing the overall planning of Tianzhu mining area in Gansu province, the tanshanling mining area was divided into 1, 2, 3 and 4 mining fields.

I. Geological background

Tanshanling oil shale ore-bearing area is located in the northern margin of Yongdeng sag in Minhe Basin. The geotectonic position belongs to the eastern and central part of Qilian mountain complex, which is a Mesozoic-Cenozoic continental small fault depression. The fault depression is distributed in a NW-SE belt.

Structural characteristics of (1)

Tanshanling oil shale mining area has a simple structure, which is monocline with an inclination of about 25, and there is no major fault damage and complex fold structure in the mining area.

The lower Jurassic in the northwest of the mining area is NW-trending, with developed fold structures and faults, and the fold structure is NW-SE "S"-shaped. The middle and upper Jurassic strata are monoclinic strata, which are distributed in northwest direction and northeast direction. Cretaceous strata are NW-trending, which is a monoclinal structure inclined to the northeast.

The fault structure in the mining area is not developed. The larger faults are F 1 and F2 faults, which were formed in the Eastern Glaciation and have been active for a long time. They belong to regional large faults and play a major role in controlling the formation and distribution of fault depressions.

The F 1 fault is located in the northeast of the mining area, and the strike of the fault is NW-SE, which tends to NE. It is a high-angle thrust fault extending over 30 kilometers. The F2 fault is located in the western edge of the mining area, striking NW-SE with an inclination of 80. The fault drop is between 30 and 500 m, and the extension length is about 15km. It is also a thrust fault.

(2) Stratigraphic characteristics

The basement of Tanshanling fault basin is mainly composed of Proterozoic metamorphic rocks, Ordovician metamorphic rocks, Devonian purplish red sandstone and siltstone. Sedimentary caprocks are Tandonggou Formation of Lower Jurassic, Yaojie Formation and Xinhe Formation of Middle Jurassic, xiang tang Formation of Upper Jurassic and Hekou Formation of Cretaceous, with the following characteristics:

1. Lower Jurassic Tandonggou Formation

The lower member of this formation is purplish red siltstone, grayish white sandstone and glutenite; The upper member is grayish black and dark gray siltstone, mudstone mixed with thin sandstone, thin coal and 1 ~ 3 coal seam. The stratum thickness is more than 402m, which is exposed in the area of Kestan and Donglagou in the northwest of the mining area, and is in angular unconformity contact with the underlying metamorphic rock series.

2. Yaojie Formation of Middle Jurassic

It is the main coal-bearing and oil shale series in the basin. The lower part is thick coal seam, gray siltstone, dark brown oil shale mixed with gray green marl; The middle and upper part is thick layered light gray green marl; The top is grayish black mudstone and dark gray and grayish green marl. The average stratum thickness is1527.75m, which is incomplete in Tandonggou Formation.

3. Xinhe Formation of Middle Jurassic

The lower part is gray mudstone, dark gray siltstone mixed with fine sandstone and purplish red mudstone, with an average thickness of 24.70 meters; The middle part is dark gray mudstone, siltstone and gray-green marl, with an average thickness of 58.50m, and the upper part is gray-white fine sandstone, dark gray mudstone and siltstone with an average thickness of 2 1.67 m, which is in contact with the underlying Yaojie Formation as a whole.

4. Upper Jurassic xiang tang Formation.

The lithology is mainly purplish red siltstone, with thin layers of gravelly coarse sandstone and grayish white limestone in the middle and lower parts. This group is widely distributed in the whole region. The average thickness is139.86m, which is in pseudo-integrated contact with the underlying Xinhe Formation.

5. Lower Cretaceous Hekou Formation

The lower member of Hekou Formation is light purple thick layered gravelly coarse sandstone, glutenite mixed with gray-green coarse sandstone and thin yellow-red sandstone. The middle section is dark purple thick layered glutenite and conglomerate; The upper member is light purple glutenite, yellow red, earth red sandstone and coarse sandstone. The average formation thickness is1550m. Unconformity contact with the underlying Jurassic.

Second, the characteristics and distribution of oil shale

Yaojie Formation in Tanshanling Oil Shale Mining Area contains four layers of oil shale, and the top two layers of oil shale in Yaojie Formation are mixed with mudstone and marl, with a thickness of 0. 10 ~ 0.5m, and the oil content is less than 3.5%, which cannot reach the industrial exploitation value. The two layers of oil shale with industrial exploitation value are the top oil layer and the bottom oil layer of the upper coal seam.

(A) the characteristics of oil shale

1. Reservoir characteristics

According to the field outcrop and drilling core observation, the oil layer is dark brown and grayish black, with yellowish brown stripes and khaki luster, with an average weight of 2.3t/m3 and developed horizontal bedding. It is grayish brown and papery after weathering.

According to the core sampling analysis of the coal exploration team of Gansu Coalfield Geological Exploration Company 145 (Table 8-9), the first oil layer has a high oil content, with an average oil content of 6.66% and an average ash content of 76.77%, but its calorific value is low, with an average calorific value of only 4.64MJ/kg. The industrial genetic type belongs to oil shale with high ash content and low oil content. By chemical element analysis, the oil layer contains carbon 12.25%, hydrogen 1.78%, oxygen 6.6%, nitrogen 0.27%, sulfur 0.5%, and the nitrogen content is obviously low.

Table 8-9 Table of Reservoir Quality Parameters in Tanshanling Oil Shale Mining Area

The oil layer in the southern mine field is of good quality, with oil content of 7% ~ 9%, while the oil content in the northern mine field is low, with oil content of 6% ~ 7%. The oil content decreases gradually from west to east along the dip angle of strata. The oil content of No.4 mine field is 9.3% in 24 wells, 7.40% in East 18 wells and 5.63% in East 67 wells.

2. Characteristics of the second oil layer

According to the observation of drilling cores and coal gangue mined underground, the second layer of oil is grayish brown and dark brown, with oily luster and yellowish brown stripes, with a weight of 2.30t/cm3. According to the analysis of drilling core, its oil content and calorific value are higher (Table 8- 10), with an average oil content of 7.03% and an average calorific value of 5.22MJ/kg, which is better than that of the first oil layer. The industrial genetic type belongs to oil shale with high ash content and low oil content.

Table 8- 10 Quality Parameter Table of Tanshanling Oil Shale in Mining Area

The chemical element analysis of the second oil layer shows that the carbon content of oil shale is 12.8 1%, the hydrogen content is 1.86%, the oxygen content is 7.3 1%, the nitrogen content is 0.28%, and the sulfur content is 0.65%.

Among the four exploration areas in Tanshanling oil shale oil-bearing area, the oil shale in Well Pad 4 is the best (Table 8- 1 1), with an average oil content of 8.6 1% and an average calorific value of 5.96MJ/Kg, while the oil shale in Well Pad 1 is the worst, with an average oil content of 6.56.

Table 8- 1 1 Quality Parameter Table of Oil Group 2 in Exploration Area of Tanshanling Oil Shale Mining Area

(2) Formation environment of oil shale

The Jurassic in Tanshanling oil shale mining area is the main development period of faulted lake basin, and the middle Jurassic Yaojie Formation is the heyday of lake basin development, which is also the main coal-forming period and oil shale deposition period in Tanshanling mining area.

In the early sedimentary period of Tandonggou Formation, the sedimentary environment was fluvial facies, which was a low water level system tract sedimentary system in the early stage of basin development. The late sedimentary period is lake swamp facies, which is the initial development period of transgressive system tract. The early sedimentary period of Yaojie Formation is lake swamp and peat swamp facies. During this period, the climate was warm and humid, plants flourished, swamp facies distributed in a large area, and organic matter was abundant, forming top coal, upper coal, lower coal and oil shale in Tanshanling mining area, which was the main development period of transgressive system tract. The late sedimentary period of Yaojie Formation is a deep lake-semi-deep lake sedimentary system developed in high water level system tract. Through sampling analysis, the kerogen type indexes of 1 oil layer and 2 oil layer are 87.2 and 3.7 respectively, and the genetic types are sapropelic oil shale and sapropelic-humic oil shale respectively.

The Xinhe Formation of the Middle Jurassic is a fluvial-lacustrine sedimentary system, which reflects that the lake becomes shallower, the lake basin becomes smaller and fluvial facies begins to develop, which is the initial stage of the development of regressive system tract (Figure 8- 12).

Jurassic deposits in Tanshanling mining area constitute a complete transgression-regression cycle. 1 oil layer and oil layer 2 were formed in deep lake-semi-deep lake subfacies of high water level system tract and peat swamp facies of transgressive system tract, respectively, representing two different genetic types of oil shale.

(3) Distribution characteristics of oil shale

1. Oil layer distribution characteristics

The first oil layer is widely distributed in the mining area with stable thickness, with the maximum thickness of 34.50 m (well C22), the minimum thickness of 0.7m, and the average thickness of11.66 m. The thickness of oil shale in No.3 well field in the southwest of the mining area is relatively large, and the thickness of the first oil layer in the north is reduced, and the average thickness of the first oil layer in No.1 well field is reduced to 5.73m (Table 8-65438) The thickness of oil shale in No.3 mine field is 22.88m in 66 wells, 9.24m in east15.84m in south 13 wells and only 5.5 1 m in east 17 wells.

Figure 8- 12 Sedimentary Profile of Tanshanling Oil Shale Mining Area

Table 8- 12 Table of Oil Shale Thickness of Various Fields in Tanshanling Oil Shale Mining Area

The thickness of oil shale is mainly controlled by paleogeomorphological characteristics and sedimentary environment. The thickness of oil shale in bedrock uplift area is generally small. There is an ancient uplift of bedrock between the south of No.2 mine field and the north of No.4 mine field, and the oil shale overlaps and pinches out, most of which are missing. The bedrock in the middle of No.4 mine field is slightly uplifted, and the thickness of oil shale is generally small. The oil layers in the north of No.1 and No.4 mine fields become grayish black siltstone and mudstone, and become thinner and missing. At the southern end of No.2 mine field and the southeast edge of No.4 mine field, the oil layers become gray fine sand and sandstone, the thickness becomes thinner, and even oil shale is missing.

The first oil layer is a single-layer coal seam inclined to the east (Figure 8- 13), and the dip angle is generally10 ~ 25. Oil shale is exposed in the western edge of the mining area, and its burial depth gradually increases eastward, with the maximum burial depth of 820m.

Figure 8- 13 Section of 7-7' Exploration Line in Tanshanling Oil Shale Mining Area

2.2 Reservoir distribution characteristics

According to the thickness and oil content, the second oil layer only partially meets the industrial requirements, and the distribution range of oil shale is small, with the maximum thickness of14.16m (No.6 well), the minimum thickness of 0.87m, and the average thickness of 4.58m The second oil layer is widely distributed in No.3 and No.4 mine fields, which is the most developed area in the Tanshanling oil shale mining area. The average thickness of the second oil layer in No.3 mine field is 6.99m, and the average thickness of the second oil layer in No.4 mine field is 4.89m m. The second oil layer in No.1 mine field is transformed into dark gray mudstone and siltstone with thin oil shale, which has no industrial value.

The second oil layer is exposed in the western edge of the mining area, and the coal seam tends to the northeast, and the dip angle is generally between15 ~ 25. The structure of coal seam is simple, and the buried depth gradually increases from west to east, with the maximum buried depth of 680m m.

Three. Evaluation of oil shale resources

(1) Analysis of the degree of exploration work

1. Exploration work

1954 Team 603 of Northwest Geological Survey conducted a general survey in Tanshanling, and compiled a summary report of the general survey work and a geological map of1:50,000 route. 1September, 1957, Northwest Coal Geological Survey Institute 134 team conducted a comprehensive survey and exploration of the mining area, completed a geological survey of1∶ 25,000, and drilled 33 holes. From August 1958, tanshanling mining area began to turn to fine exploration, and completed the topographic and geological map of 1∶5000 and the geological report of tanshanling coalfield. From the beginning of 1976 to the end of 1979, the No.2, No.3 and No.4 coal fields in Tanshanling were re-explored, and the B+C+D oil shale reserves were submitted to be 238.08 million tons.

2. Degree and accuracy of exploration

Northwest Coalfield Exploration Bureau 134 team used 500m×400m well pattern density to calculate A2 reserves in Tanshanling fine exploration. In the middle of the mine field, 500 m× 700 ~ 800 m is used to calculate A2 horizontal reserves. The well pattern density of 800 m× 1000 ~ 1500 m is used to calculate the B-level reserves. 33 wells have been drilled, covering an area of 654.38+100000 meters, and the structural situation of the mining area and the distribution characteristics of oil shale have been basically found out.

At the beginning of 1976, Gansu Coalfield Geological Exploration Company 145 team re-explored No.2 and No.4 mine fields, and completed 1 16 wells, including 2 special hydrological wells with drilling footage of 49,877.72 meters and well pattern density of 400 meters× 500 meters, but

At the end of exploration, the plugging quality was checked, and the qualified rate was 50%, so the plugging quality was not high. In addition, although there are many wells that encounter oil shale, there are few samples and tests, which affects the accuracy of oil shale quality evaluation. At present, the exploration level has reached the exploration level.

(2) Evaluation of oil shale resources

1. Resource evaluation

After this oil shale resource evaluation, the resource reserves of each oil-bearing grade in Tanshanling oil shale mining area are: 3.5% oil.

Table 8- 13 Table of Changes in Resources and Reserves of Tanshanling Oil Shale Mining Area Unit: 10,000 tons

After this resource evaluation, the proven reserves of oil shale in Tanshanling mining area are 467.96 million tons, the proven reserves of oil shale technology are 209.94 million tons, the proven reserves of shale oil are 35.47 million tons, and the proven reserves of shale oil technology are15.87 million tons.

2. Prediction of oil shale resources

Tanshanling oil shale mining area 1 is located in the east of 1 well field. It is predicted that the average thickness of oil shale is 7.28m and the average oil content is 6.30%. The average weight of Tanshanling oil shale mining area is 2.30t/m3, and the predicted area is 4. 10km2. The potential resources are estimated by volume method. The potential resources of oil shale are 68.6874 million tons, and the potential technical recoverable resources of oil shale are 2232.

No.2 prediction area is located in the east of No.2 mining field to the ancient city. It is bounded by F 1 1 fault in the north, No.2 mine field boundary in the northwest, No.3 prediction area boundary and F2 fault in the southwest, Gu6 Well, Xingu4 Well and Gupu Well 1 in the east, and Liushuxiakou and Gucheng Dongshan Highway in the south, with a predicted area of 46. 14km2. The predicted average thickness of oil shale is 7.68m, the oil content of oil shale in the predicted area is 5. 13%, and the average weight of Tanshanling mining area is 2.30t/m3. It is estimated that the potential resources of oil shale in Prediction Area 2 are 8150,000 t, the potential technically recoverable resources of oil shale are 2,648.75 million t, the potential resources of shale oil are 4180.95 million t, and the potential technically recoverable resources of shale oil are135881000 t. ..

No.3 prediction area is located on the east side of No.4 mine field. The predicted thickness of the first layer is 4. 16m, the oil content is 7. 13%, and the predicted area is 1.4 1km2. The average thickness of the second oil layer is 9.82m, the average oil content is 7.68%, the predicted area is 0.82km2, the average weight of Tanshanling mining area is 2.30t/m3, the potential resources of the first oil layer are13458700t, the potential resources of the second oil layer are18428500t, and the potential resources are 3/kloc-.

After this evaluation, the oil shale resources in Tanshanling are138.353 million tons, of which the proven oil shale resources are 467.96 million tons and the potential oil shale resources are 915.57 million tons; the oil shale technical recoverable resources are 507.5 million tons, of which the proven oil shale technical recoverable resources are 209.94 million tons and the potential oil shale technical recoverable resources are 297.56 million tons. The shale oil reserves are 83.98 million tons, including 35.47 million tons of proven shale oil reserves and 485 1 10,000 tons of potential shale oil resources. The recoverable resources of shale oil technology are 310.64 million tons, of which the recoverable resources of shale oil technology are10.587 million tons and the potential recoverable resources of shale oil are10.577 million tons. The recoverable resources of shale oil are 23.72 million tons, of which the proven recoverable resources of shale oil are 1 1.9 million tons, and the potential recoverable resources of shale oil are1/.82 million tons.