(I) tumuji Oil Sands Mine
1. Overview of oil sands
In 1980s, in tumuji, local residents drilled wells and discovered oil sands. In 1990s, a local registered the mining right of 1.94km2 and the geological exploration right of 12.48km2 in the name of mining road sand and clay. In March 2003, Meng Xing-Japan Land and Resources Development Service Center registered a favorable area of 600km2 in the name of "General Survey of Oil-bearing Sandstone and Organic Clay Minerals" according to drilling data. The registered area of Jilin Oilfield in 2003 was 1 478.27km2 (Figure 5- 1). According to the current exploration and research results, Hengyuan Mining Comprehensive Development Company in Zhalaite Banner, Inner Mongolia and the registration area of Meng Xing-US-Japan Land and Resources Development Service Center are the most favorable areas for oil sands.
Figure 5- 1 Tumuji Mineral Rights Registration Map
Before 2002, Jilin Oilfield Company made little investment in the western overlapping zone. The gravity survey of1:200,000 was completed in 1990s. In tumuji area in 2003, two main survey lines and one tie line were 18km, and four geological survey wells (Pu35, Pu36, Pu37 and Pu39) and two oil sands were drilled, of which Pu36 oil sands were 4.6m thick and Pu37 oil sands were 2.0m thick.
In addition, the data of 69 agricultural and pastoral wells were collected in tumuji Reform-through-Labor Farm, of which 12 wells were found in the oil sands, mainly distributed near the oil sands in tumuji.
Daqing Logging Company first completed the three vertical and three horizontal skeleton 1 1 electrical sounding profile in tumuji area, and completed 4 12 electrical sounding points. According to the analysis of the survey results, 64 survey wells were drilled, with an average depth of 50m and a maximum depth of 83m. Shallow exploration of nearly 400km2 was initially completed, and two relatively independent oil sands deposits were discovered, namely, block 5 19 centered on well 5 19, block 4 centered on well 4007 and block 223 centered on well 223.
2. Basic geological characteristics of oil sands
(1) stratigraphic sequence. The strata drilled from top to bottom in this block have Quaternary fluvial facies or alluvial facies sand bodies, which are in abrupt contact with an underlying set of gray-black mudstone. According to the analysis of organic carbon in mudstone core of Well 5 14-2 in Figure 565438, the organic carbon content is 2.74%, which completely corresponds to the mudstone of Nenjiang Formation in Daqing area, and it is confirmed that this set of mudstone was deposited in Nenjiang Formation. Below mudstone is a sedimentary combination of siltstone, fine sandstone and glutenite. Due to the limitation of well depth, no basement was drilled in all wells. However, according to the analysis of existing data, there are a few deposits of Member 2 and Member 3 of Qing in this area under Sarthou Oil Formation, which are the basement below it (Figure 5.2).
This set of sandstone-mudstone assemblage basically inherits the structural characteristics of the underlying basement, and is a stratum with east dip, southeast dip and small dip angle. The main sandstone-mudstone thickens from west to east.
(2) Reservoir characteristics. There are two sets of oil sands in tumuji area, one in Nen 1 member and the other in the upper part of Yao Jia Formation. Oil sands belong to Sarthou oil group.
① Layer group division. According to the sedimentary cycle, rhythm and oil-bearing property of Sarthou oil-bearing formation in block, it can be roughly divided into three sand-bearing formations (Ⅰ, Ⅱ and Ⅲ), and oil sands are mainly distributed in Ⅰ and Ⅱ sand-bearing formations. ② Reservoir lithology and physical properties. Tumuji block 1 sand group is the main oil-bearing horizon, and the main lithology is fine sandstone. According to the analysis of relevant data, the mineral composition is mainly feldspar and detritus, followed by timely, the rock type is lithic feldspathic sandstone, followed by feldspathic lithic sandstone, and the main cement is argillaceous and a small amount of calcium. The rock structure is loose and the cementation is poor. Overall physical properties are good. Sand group 2 is mainly fine sandstone in area 4 in the southwest of the block, but blocks 5 19 and 6 in the north of the block are mainly glutenite. ③ Distribution characteristics of reservoir sand bodies. This block is located in Yingtai sedimentary system, and the source of reservoir mainly comes from the west and northwest. The sand bodies are mainly distributed in strips or lenses, and massive sandstone bodies with large thickness are formed in the east. The sand bodies in the north and northwest of the block are thick, coarse-grained and developed with glutenite. The south side of 5 19 block is an obvious sandstone low value area. The variation trend of sand body thickness is closely related to sedimentary facies belt. On the plane, the development degree of the same set of sand groups varies greatly and changes dramatically. Relatively speaking, the first sand group in the west of the block is relatively stable, but it is partially missing due to Quaternary erosion.
Figure 5-2 Comprehensive Histogram of tumuji Oil Sands Mine
3. The nature of oil sands
Environmental scanning electron microscope analysis technology is a new technology developed in recent years. Oil sands samples can be directly sent to the environmental scanning electron microscope sample room for observation without any treatment, without destroying the original structure of oil sands samples, and can be effectively used to evaluate the microstructure characteristics of oil sands reservoirs and observe the distribution and adhesion of asphaltene and heavy oil in oil sands. Observed by environmental scanning electron microscope, it can be seen that the surface of sand particles is covered with a large number of oil films, oil is filled between particles, and loose sand particles are stuck together by oil films. There are pores, and the oil is gelatinous and layered.
Through the sampling analysis of oil sands, it is found that the crude oil composition of oil sands is close to that of the southern Songliao Basin in the reservoirs with good preservation and sealing conditions. The content of alkane is 38.5% ~ 58.4%, aromatic hydrocarbon 12.4% ~ 22. 1%, asphaltene 1.3% ~ 4%, and non-hydrocarbon+asphaltene 15.5% ~ 42.3%. The quality of crude oil is similar to that of Taobao crude oil, and the content of alkanes and asphaltenes is similar, while the content of aromatics in tumuji oil sands is low. Viscosity, wax content and freezing point are lower than those of the jacket. Due to oxidation, groundwater erosion and bacterial decomposition, the quality of oil products becomes worse, with less light components, higher viscosity, higher specific gravity and higher gum content.
4. Metallogenic conditions
The main oil-bearing layer in this area is the uppermost I sand group in Sarthou, which has the characteristics of continuous distribution, while the II sand group is thick and has good physical properties, but its oil-bearing property is poor, mainly because the overlying mudstone caprock is thin and does not form a good shelter. It can be seen that the oil content of sand group I should be mainly formed by lateral migration. Moreover, the mudstone caprock of Nenjiang Formation distributed in a large area provides a good prerequisite for its long-distance migration.
Well Tu 4- 1 in the southwest of the block is located at the structural high point of Area 4. The mudstone caprock of Nenjiang Formation in the upper part of I sand group is well preserved, with a thickness of nearly 25m. I and II sand groups are well developed, but the coring results show that the oil content is very poor, and only the oil content at the top of I sand group shows about 1m, indicating that the oil supply is seriously insufficient. Well Figure 4- 13, which is only 2 kilometers away from it, is located in the lower part, but it encounters oil sands with a thickness of nearly 4m and good quality. This shows that the law of oil and gas migration and accumulation is: generally from southeast to northwest, first filling the lower sand body, and then continuing to migrate. Therefore, the sand bodies with lower geological position and better reservoir-cap combination have higher oil abundance.
5. Calculation of tumuji oil sands resources on the western slope of Songliao Basin.
According to the geological survey data in tumuji area of Jilin Oilfield, the data of farming and animal husbandry wells and the exploration results of 64 shallow wells in Daqing Logging Company, a normal fault is inferred and the distribution law of oil sands is predicted. The buried depth of oil sands in the northwest of the fault is less than 50m, and the buried depth of oil sands in the southeast of the fault is between 45 ~ 150 m.
(1) calculation parameters. According to the data of general survey wells, agricultural wells and shallow wells in Daqing Logging Company, the distribution map of oil sands is deduced, and the distribution area and average thickness of oil sands with different burial depths are determined. The distribution area of 0 ~ 100 m buried oil sands is 77.9 km2, and the distribution area of 100 ~ 150 m buried oil sands is 5 1km2. The average thickness is 2.1m. The highest oil content in this area can reach 12.6%. Considering the heterogeneity of oil sands in this block, the average oil content is 9. 1%.
(2) Calculation of resources. According to the above parameters, the Cretaceous oil sands resources in tumuji area are evaluated by oil content method (Table 5- 1). The oil sands with a buried depth of 0 ~ 100 m are 32.75110,000 t, and the oil sands with a buried depth of 100 ~ 150 m are 21440,000 t.
Table 5- 1 Calculation Table of Oil Sands Resources in tumuji
(B) Western slope belt oil sands resources
There are few oil display points in Songliao basin. At present, oil sands are only found in tumuji area in the western slope zone. According to the characteristics of crude oil evolution and structural evolution in different areas of Songliao Basin, combined with the data of geological survey wells in tumuji area of Jilin Oilfield, data of farming and animal husbandry wells and the exploration results of 64 shallow wells in Daqing Logging Company, it is considered that the oil sands resources in Songliao Basin are mainly distributed in the western slope zone of Songliao Basin.
The western part of Songliao basin is covered with a gentle slope inclined to the east. Controlled by the shape of basement, the overlying strata are still monoclinic with gentle eastward dip, and the dip angle is small, generally less than 2. The structure is simple, the faults are undeveloped, and the structural lines in the north-south direction are roughly parallel. The basement in the area is very shallow, and there is a basement exposed 4km west of the block, which belongs to Caledonian granite. The eastern part of the block is Yingtai fault depression area (Figure 5-3).
Figure 5-3 Comprehensive Geological Profile of the Western Margin of Songliao Basin
Due to the formation of basement, this block is at the edge of the basin, and the strata from Jurassic to Middle Cretaceous have been eroded for a long time, and the strata are missing. In the middle and late Middle Cretaceous, with the development of Songliao Basin reaching its peak, the range of lake basin reached its maximum, and a set of sandstone and mudstone strata from Qing 2 member to Qing 3 member to Nen 2 member were also deposited in this area. At the end of Nenjiang Formation, with the overall uplift of Songliao Basin, the lake basin shrank, and the area was in a state of denudation again, and only Quaternary modern sediments were deposited on Nenjiang Formation. Due to strong denudation, Nenjiang Formation strata in some areas have also been denuded, thus forming an unconformity surface between Quaternary and underlying strata. The underlying Cretaceous strata overlap the basement layer by layer, forming another unconformity surface.
The modern surface is mainly flat Quaternary sediments, showing the basic topographic characteristics of high in the west and low in the east. In the west, there are mudstone residual hills of Nenjiang Formation and some hilly areas formed by outcrops of basement granite.
1. Controlling factors of oil sands in western slope belt
The main lithology of oil sands in the western slope zone is fine sandstone with poor cementation and loose structure, belonging to delta front deposition, with sheet sand, underwater distributary channel and estuary bar as the main sedimentary microfacies. Its oil-water distribution and oil plumpness are mainly controlled by the following three factors:
Control of (1) sedimentary facies belt. The sedimentary period of Sand Group I, the main oil-bearing layer in this block, is the end of Yao Jia Formation, with lake invasion as the main sedimentary background, and the main sedimentary facies belts are delta front sheet sand and underwater distributary channel facies.
From the analysis of the distribution range and grain size of sand bodies, it can be seen that the hydrodynamic conditions of rivers and lakes are weak during the deposition period of this set of sand bodies, and the sand bodies are generally small in scale, with fine grain size of sandstone, rapid lateral change and complicated deposition between distributary channels, which leads to poor connectivity and continuity of sand bodies and difficult lateral comparison. The reservoir type belongs to lithologic trap reservoir, thus forming a complex oil-water distribution phenomenon on the plane.
(2) Control of reservoir sealing conditions. During the sedimentary period of Nenjiang Formation, the gray-black mudstone deposited at its bottom is the main caprock in this block. From the regional comparison, it can be seen that during the Quaternary sedimentary period, there was a large river with nearly east-west trend, which strongly eroded the mudstone caprock of Nenjiang Formation, and even completely eroded and destroyed Sand Formation I in many areas. Because the oil sands are shallow buried and very loose, and the groundwater erosion is also strong, the oil sands formed in the missing mudstone caprock become denser and the oil quality becomes obviously worse. The oil sands formed by caprocks have good oil quality. The strong erosion in Quaternary made the already complicated distribution of oil sands more complicated.
(3) structural control. In the whole western slope area, only a few low-amplitude structures are developed, so the key to reservoir formation is to block oil and gas, and the development characteristics of faults determine the scale of oil and gas reservoirs. In addition, low-amplitude structure is also the main cycle type of major oil and gas reservoirs.
2. Oil sands accumulation model in western slope belt.
The oil-bearing horizon in the western slope belt is Sarthou oil layer. Although the overlying mudstone of Nenjiang Formation is one of the main source rocks in the basin, it is not the source rock of oil sands in this area because it is located at the edge of the basin, with a high altitude, small sedimentation and shallow burial, far from reaching the threshold depth of oil generation of mudstone of Nenjiang Formation 1000 meters. There is a small amount of Qingshankou Formation mudstone in the lower part of Sarthou oil layer in this block, but the burial depth has not reached the threshold depth of oil generation.
Through the comparative study and comprehensive analysis of oil and source, it is considered that the oil and gas in this area originated from Qingshankou Formation in the central depression, and migrated along the slope, with Yao Jia Formation channel sand as the migration channel, and gathered in Yaojia Formation in tumuji area. The boundary fault of Pinganzhen fault depression began to move after the deposition of Nenjiang Formation, and oil and gas migrated along the fault and accumulated in Nenjiang reservoir. At the end of Mingshui Formation, due to the influence of compressive stress field, the fault sealing was enhanced, and the migrated oil and gas were blocked by the fault and gathered in Yao Jia Formation, which formed the reservoir-forming characteristics that Nenyi Formation dominated in the west and Yao Jia Formation dominated in the east of the fault.
3. Estimation of oil sands resources on the western slope of Songliao Basin.
According to the geological survey data in tumuji area of Jilin Oilfield, the data of farming and animal husbandry wells and the exploration results of 64 shallow wells in Daqing Logging Company, combined with the sedimentary facies and the distribution law of sand bodies, according to the existing actual data in tumuji area, it can be known that the quality and thickness of oil sands in tumuji area are better in the whole western slope area, but slightly worse in other blocks than in tumuji. Comprehensive analysis shows that the oil sands with oil content of 7. 1% and thickness of 2. 1m, 0 ~ 1. 107 km2 have a distribution area of 584km2 and a distribution area of 65438+ with a depth of 100 ~ 300m.
According to the above parameters, the Cretaceous oil sands resources in the western slope area are evaluated (Table 5-2). The geological resources of oil sands with a buried depth of 0 ~ 100~300m are16410.2 million t, and those with a buried depth of 100~300m are 31.10.24 million.
Table 5-2 Estimation Table of Oil Sands Resources on the Western Slope of Songliao Basin (including tumuji Block)