Zhangwu Basin is located in the northern part of Liaoning Province and the eastern part of Inner Mongolia Autonomous Region, and belongs to the southeast uplift area of Songliao Basin in structural division, with an area of 1.28× 104km2 and a favorable exploration area of 5069km2.
Coalfield geological exploration has been carried out in this basin since the late 1950s, including1∶ 200,000 electrical and seismic work, and1∶ 200,000 aeromagnetic and gravity magnetic surveys. During the period of 1988, the geological brigade of Liaohe Oilfield Research Institute conducted a general survey of petroleum geology and collected drilling data in the coalfield, and on the basis of analysis and research, made an early resource evaluation in this area. Seismic exploration is carried out in Zhangqiang sag and Baokang sag. The density of seismic network in Zhangqiang sag reaches 1km×2km, and locally reaches 1km× 1km. Changbei anticline completed 60km2 3D seismic exploration. The density of seismic network in Baokang sag has reached 4 km× 4 km ~ 2 km× 2 km, and the degree of seismic exploration is high, but the seismic quality is poor, especially the deep data. An oil field has been found in Zhangqiang sag, with high drilling degree and low drilling degree in Baokang sag. At present, only the well Leshen 1 has been drilled, which completely exposes the strata of the depression and provides geological data for the evaluation of the depression.
This evaluation is undertaken by China Petroleum Liaohe Oilfield Company, and the evaluation unit mainly includes four favorable depressions, such as Zhangqiang, Baokang, Zhalanying and Baogetu. The evaluation series is mainly Mesozoic and Early Cretaceous. Evaluation methods include occurrence method and analogy method. The analogy areas are Lujiapu sag and Zhangqiang sag.
Through this evaluation, it is concluded that the total prospective resources of Zhangwu Basin are 0.9 1× 104t, the total geological resources are 0.80× 104t and the total recoverable resources are 0.3 1× 104t.
Second, the oil and gas geological conditions
(1) Geological survey
The basin belongs to Mesozoic fault basin, with an area of 12800km2 and a favorable exploration area of 5069km2. It has experienced three stages: early Cretaceous fault depression (main basin-forming period), middle-late Cretaceous depression period and the end of Cretaceous basin extinction. The basin consists of ten depressions and three bulges, among which Zhang Qiang, Anle, Zhalanying and Baogetu depressions are favorable and have large areas. Faults and uplifts are alternately distributed, and depressions are highly differentiated.
Zhangqiang sag, located in the southern margin of Songliao basin, is a Mesozoic oil-bearing fault depression and belongs to a secondary negative structural unit of Zhangwu basin. Tumaotai sag in the south, Baokang sag in the north, Shuangliao-Kangping uplift in the east and Sandaotu Sijiazi uplift in the west, with a width of 12 ~ 16 km, a length of 88km and an area of about 65,438+.
The northern Liaoning area where Zhangqiang Depression is located is located at the northern end of North China Platform and the southern part of Jihei Fold System, including Zhangwu Basin, Tieling Basin and part of Kailu Basin. The Paleozoic and Mesozoic-Cenozoic tectonic environments in this area are completely different. In Paleozoic, this area was a part of Tianshan-Meng Xing geosyncline system, and it was an ocean in Lower Paleozoic. As the Siberian plate drifted into contact with the North China plate, the Central Asia-Mongolia Trough closed one after another at the end of Paleozoic, and the two continents merged to form the North Asian continent. The Mesozoic Pacific-Kula plate dived northwest to Eurasia, forming a regional uplift zone and subsidence zone in the northeast direction. In the late Jurassic, this area entered the stage of fault depression, and along the fault system dominated by NEE direction, a group of fault depressions arranged in wild lines were formed. After that, the area was transformed from fault depression to fault depression, and then a large area of uplift and loss deposition appeared.
(2) Source rocks
Characteristics of source rocks in 1 .zhangqiang sag
(1) Geological characteristics of source rocks.
According to the analysis of drilling data and seismic interpretation data, Zhangqiang sag is a fault-subsidence superimposed sag. In the early, middle and late stages of fault depression development, oil-generating strata with different characteristics were formed, namely, Jurassic Jiufotang Formation lacustrine oil-generating strata and Shahai Formation semi-deep lacustrine coal-bearing oil-generating strata.
The source rocks of Jiufotang Formation are the products of the early and middle stages of fault depression, which are distributed all over the region. The source rocks of this group gradually thicken from south to north. The average thickness of the northern Jirgalang sag is 200 ~ 250 m, accounting for 54% of the total thickness of the stratum, and the average thickness of the central Zhanggutai sag is about 150m, accounting for 53% ~ 70% of the total thickness of the stratum. The source rocks of the two depressions are mainly dark gray and gray-black mudstone mixed with shale. The source rocks in Qijiazi Depression in the south are mainly gray, light gray mudstone and sandstone in littoral shallow lake facies with weak oxidation-reduction environment, and the organic carbon content is generally less than 0.5%. The average thickness of source rocks is 100 ~ 150 m, accounting for about 22.5% of the total thickness of the stratum. It is considered that Jirgalang sag is the main oil-generating sag (Jiufotang Formation) with high organic matter abundance.
The source rock of Shahai Formation is the product of the middle and late fault depression, and it is an important coal-bearing source rock in the depression. Source rocks are distributed in the whole region, mainly in Zhanggutai sag and Qijiazi sag. The thickness of source rocks in Jirgalang sag is relatively small, generally about 50m. Oil source rocks are developed in Zhanggutai sag and Qijiazi sag, and the thickness is generally 200 ~ 250 m, accounting for 44% of the total thickness of the stratum. The lithology is mainly dark gray and gray mudstone, mixed with marl and oil shale, which is a shallow-semi deep lacustrine deposit in reducing environment (S-2 = 0.53%).
(2) Rich organic matter.
The abundance of organic matter represents the abundance of organic matter in rocks. Only when rocks have a certain abundance of organic matter can they have the material conditions to become source rocks. Organic carbon content, asphalt "A" content, total hydrocarbon content and hydrocarbon conversion rate are the grading standards for evaluating organic matter abundance of source rocks. It can be seen from Table 8- 15- 1 that all the indexes of source rocks in Fuxin Formation are low. They are 0.373%, 0.0037%, 19.2ppm and 0.665, 438+0% respectively, while the source rocks of the southern Shahai Formation and the northern Jiufotang Formation have the characteristics of high organic carbon content, high asphalt "A" content, high total hydrocarbon content and moderate hydrocarbon conversion degree, and the four indexes of the Shahai Formation are 3.65438 respectively. The four indexes of Jiufotang group were 3.07%, 0.263%, 65,438+0.524 ppm and 3.38% respectively. According to the quality classification standard table of continental lacustrine source rocks in China, Jiufotang Formation in the northern part of the depression is a good source rock, and Shahai Formation is a good source rock.
Table 8- 15- 1 organic matter abundance of source rocks of upper Jurassic Fuxin Formation-Jiufotang Formation in Zhangqiang Depression
Note: Average value of interval values.
(3) Type of organic matter.
Organic matter type is an index to evaluate hydrocarbon generation capacity and quality. The determination of organic matter types in Zhangqiang sag mainly adopts kerogen element analysis, rock pyrolysis angular spectrum and kerogen microscopic examination.
Kerogen element analysis: According to the existing kerogen element analysis data in the depression (Table 8- 15-2), the H/C of Fuxin Formation is low, while that of Shahai Formation is high, with the H/C between 0.8 1 ~ 1.63 and the O/C between 0.04 ~ 0.
Table 8- 15-2 Statistical Table of Kerogen Element Composition of Upper Jurassic in Zhangqiang Depression
Kerogen carbon isotope (δ 13C‰): According to the statistics of only six samples, the δ 13C‰ of Shahejie Formation is generally -23.3 ‰ ~-28.6 ‰, with an average of -25.65 ‰, indicating that the provenance of Shahejie Formation in this depression is type I. ..
Pyrolysis chromatography: According to the analysis results of 82 samples in the depression (Table 8- 15-3), the hydrogen index of the source rocks of Fuxin Formation and Jiufotang Formation is relatively high, and the hydrocarbon generation potential and yield index are similar to the hydrogen index. According to the analysis, the organic matter types of Fuxin Formation and Jiufotang Formation in the south are Type II, and it is presumed that Jiufotang Formation in the north is Type I; The Shahai Formation is mainly Ⅱ1type, and the organic matter type of Shahai Formation in the northern part of Jierhalang sag may become worse.
Table 8- 15-3 Pyrolysis Chromatographic Characteristics of Upper Jurassic Rocks in Zhangqiang Depression
Microscopic examination of kerogen: directly observing the microscopic components of kerogen with a microscope has become one of the effective methods to study kerogen types. According to the maceral composition of kerogen, Fuxin Formation is mainly inertinite formation, belonging to type ⅲ. Shahai Formation is mainly composed of sapropelic formation and crustaceous formation (70%), belonging to type II (mixed type).
(4) Maturity of organic matter.
The maturity of organic matter is a sign of the thermal evolution degree of organic matter in rocks. Commonly used methods include vitrinite reflectance, maximum pyrolysis peak temperature and kerogen composition, among which vitrinite reflectance is the most commonly used and effective index. At present, the Ro value in the oil generation stage is usually set at 0.5% ~ 1.3%, and the Ro value reaches the peak of oil generation around 1.0. It can be seen from Table 8- 15-4 that Fuxin Formation and Shahai Formation have reached the threshold of hydrocarbon generation, and the Ro is 0.62% ~ 0.94%. From the peak temperature Tmax of rock pyrolysis chromatography (Table 8- 15-4), Tmax is mostly between 435℃ and 486℃, reaching. To sum up, Shahejie Formation and Jiufotang Formation in Zhangqiang Depression have entered a mature stage.
Table 8- 15-4 Statistics of vitrinite reflectance of upper Jurassic kerogen in Zhangqiang Depression
According to the burial history map of Shen Qiang 1 well, the source rocks of Jiufotang Formation began to generate hydrocarbons in the late Shahe Formation and all matured in the early Fuxin. The source rocks of Shahai Formation entered the threshold of hydrocarbon generation in the late Fuxin period (Ro=0.65%), and the source rocks of Shahai Formation and Jiufotang Formation entered the mature stage, which are the main source rocks in Zhangqiang Depression.
2. Hydrocarbon source conditions in Baokang sag
(1) Geological characteristics of source rocks.
Baokang sag covers an area of about 1000km2, and consists of two sub-sags, north and south. Zhangjiayao sag in the north has a large area and thick sedimentary rocks, while Xidala sag in the south has a small area. Well Leshen 1 is located in Zhangjiayao sag in the north. According to the drilling lithologic profile, the main source rock is Shahai-Jiufotang Formation, with dark mudstone undeveloped, with Shahai Formation only13m, Jiufotang Formation only 34.5m, and only the brown-gray mudstone at the top of Jiufotang Formation is good, pure and brittle, showing oil in fractures. The dark mudstone of Yao Jia-Qingshankou Formation is 57.5m thick, with an area of 2 1%, the pure mudstone is 28.5m thick, and the single-layer continuous thickness is only 5m ... The dark mudstone of Nenjiang Formation117.5m, with an area of 67.5%, of which the pure mudstone is 85m thick and the maximum continuous thickness of single-layer is 39m. ..
Fig. 8- 15- 1 kerogen element composition map of upper Jurassic in Zhangqiang sag
(2) Abundance and type of organic matter.
Statistics of organic matter abundance in Leshen 1 well show that the organic carbon content of source rocks in Nenjiang Formation and Yao Jia Formation-Qingshankou Formation is relatively high, generally 1.94%- 1.98%, chloroform asphalt "A" is generally 0.043%-0.047%, and total hydrocarbons are generally 6544. The numerical values of Shahai-Jiufotang Formation vary greatly, ranging from extremely poor to excellent source rocks. The highest organic carbon is 4.46%, the worst is 0.678%, the highest chloroform asphalt "A" is 0.8539%, the lowest is 0.0074%, and the highest total hydrocarbon is 5733ppm, the lowest is 27.9ppm. The Nenjiang Formation and Yao Jia-Qingshankou Formation are mainly mixed with sapropelic mud, and the Shahai-Jiufotang Formation is mainly mixed.
(3) Maturity of organic matter
The source rocks in Baokang sag are obviously worse than those in Zhangqiang sag, and the thickness and organic matter abundance of source rocks are not as good as those in Zhangqiang sag, so the oil and gas geological conditions in Anle sag are relatively poor.
(3) Other conditions for reservoir formation
1. Other reservoir-forming conditions in Zhangqiang sag
(1) Reservoir conditions.
The reservoir types in Zhangqiang sag are mainly fan delta, braided river delta, sandstone, glutenite and conglomerate reservoirs of nearshore subaqueous fan sedimentary system. Among them, Jiufotang Formation is dominated by fan delta, Shahai Formation is dominated by fan delta nearshore subaqueous fan, and Fuxin Formation is dominated by braided river delta. At present, reservoirs have been obtained in fan delta and braided river delta reservoirs.
Fig. 8- 15-2 Source Rock Profile of Shen Qiang 1 Well in Zhangqiang Depression
The reservoirs of Shahai Formation in Zhangqiang Depression are mainly gravel sandstone, medium-fine sandstone and partial siltstone, and the rock types are feldspathic sandstone and lithic sandstone with low maturity. The types of reservoir space are pore type, fracture type and mixed type, and the main pore types are intergranular pore, intergranular pore and dissolution pore. Shahai Formation consists of semi-deep lake-deep lake facies, shore-shallow lake facies, swamp facies, fan delta, nearshore subaqueous fan and braided river delta facies. Among them, the fan delta is the most favorable facies belt, and the nearshore subaqueous fan and braided river delta are the more favorable facies belts.
The reservoir properties of Shahejie Formation in Zhangqiang Depression are poor. According to the well, the porosity is generally 5% ~ 2 1%, and the permeability k < 1× 10-3 μ m2, with the maximum value of 1904× 10-3 μ m2.
According to the results of reservoir regional evaluation, the primary reservoirs in this depression are mainly distributed in Shahai Formation, followed by Jiufotang Formation. The second kind of reservoirs are distributed in braided river deltas of Shahai Formation and Fuxin Formation, and the nearshore subaqueous fan sedimentary system is developed. Class III reservoirs are mainly Jiufotang Formation, followed by Shahai Formation, distributed in shallow lake and semi-deep lake facies development areas.
To sum up, Shahai Formation has the best reservoir conditions, and its Class I and Class II areas can be the main target layers for future exploration, Fuxin Formation and Jiufotang Formation are Class II and Class III areas, and those with poor reservoir conditions should be regarded as secondary exploration layers.
(2) Cover and preservation conditions.
From the comparison of wells in the depression, it can be seen that argillaceous siltstone, mudstone and oil shale are developed in the middle and upper part of Fuxin Formation, the top and middle and lower part of Shahai Formation respectively, which are all distributed in the whole region, and the thickness is more than 20m, which is a good cover for the underlying reservoir. In addition, some people think that the oil and gas migration period in this area is Quantou Formation, after which there is no tectonic movement and the preservation conditions are good.
2. Other reservoir-forming conditions in Baokang sag
(1) Reservoir conditions.
The Yuleshan 1 well profile in Baokang sag can be used as a reservoir with a total of 55 sand layers, with a cumulative thickness of 253.6m, accounting for 15.88% of the total sand layer thickness. The lithology of the reservoir is gravelly sandstone, accounting for 47.7% of the total reservoir thickness. The pore type is single, mainly secondary dissolved pores, and the pore individuals are generally small, with low pore surface area ratio, thin throat, poor connectivity, high proportion of small pore throat system, low porosity and low permeability as the main physical characteristics, and extremely poor oil content. Especially, the Shahejie Formation-Jiufotang Formation, the main exploration target layer in the basin, is basically non-reservoir because its porosity is generally less than 10% and permeability is less than 1× 10-3 μm 2.
(2) Trap conditions.
The structural trap conditions in Zhangjiayao sag in the north of Baokang sag are good. * * * Four local traps, with a total area of 125.2km2, were discovered and confirmed, which can be roughly divided into two types according to the plane shape and development characteristics. These structures were cut into multiple fault blocks by several faults. For example, Anjia fault anticline is located in the north of the central fault zone, and it is a complex fault anticline controlled by faults, which strikes northwest and comes from Shahai. The anticline is divided into seven fault blocks with a total area of 64.2km2, of which the trap area of the largest fault block is 28.2km2, and the trap area of the smallest fault block is only1.25km2. There is only a gentle anticline in the northwest of Xidala sag in the south with an area of about 30km2.
(3) Preservation conditions.
Qingshankou Formation in Baokang Depression is a set of purple mudstone and silty mudstone with large thickness and wide distribution, which is a good regional caprock.
Both Baogetu sag and Zhalanyingzi sag are located in the northern part of the basin. There is no drilling at present, and their petroleum geological conditions are not very clear. From the analogy analysis of depressions, it should have similar petroleum geological conditions with Zhangqiang Depression and Anle Depression.
(4) Main geological knowledge
The basin consists of ten depressions and three bulges, among which Zhangqiang, Anle, Zhalanying and Baogetu depressions are large and favorable. Jiufotang Formation and Shahai Formation are the main source rocks. There are two sets of effective hydrocarbon source beds, the thickness of which is generally 400 meters and the maximum thickness is 500 meters.
The reservoirs are relatively developed, and there are many types of reservoirs, and the oil storage properties are mainly mesoporous-low permeability.
The main trap types are anticline, fault anticline, fault nose and fault block, and the traps are relatively developed. Thick mudstone of Qingshankou Formation and Shahai Formation is a regional caprock. The northern sag is basically denuded, while the western sag and Quantou Formation above Fuxin Formation have been denuded. Three sets of reservoir-forming assemblages of Yixian Formation, Jiufotang Formation and Shahai Formation were developed. Shahai is the main reservoir combination, followed by Jiufotang Formation, with good supporting conditions.
Three, resource evaluation methods and parameter system
This evaluation unit mainly includes four favorable depressions, such as Zhang Qiang, Baokang, Zhalanying and Baogetu. The evaluation series is mainly Mesozoic and Early Cretaceous. Evaluation methods include occurrence method and analogy method. The analogy areas are Lujiapu sag and Zhangqiang sag.
(a) Chloroform asphalt "A" method
This method is one of the "residual hydrocarbon methods" and the earliest practical method used in China. This method is suitable for basins with parametric wells. Without parameter wells, it is impossible to determine the "A" content, effective source rock thickness, maturity threshold depth and effective source rock area of chloroform asphalt.
Step: calculating the average value of chloroform asphalt "A" according to the layering system of the conveying and polymerization unit; Using the compensation coefficient of chloroform asphalt "A" to recover the content of chloroform asphalt "A"; The analogy method for calculating each migration and accumulation unit is a method to infer the unknown area from the known area. By analogy with reservoir-forming conditions, the abundance of resource area of evaluation unit can be obtained, and then the resource quantity can be estimated. The resources of the basin are obtained by adding the resources of geological units covering the whole basin.
Use chloroform asphalt "A" method to calculate the resources of Zhangqiang Depression (Table 8- 15-5):
Table 8- 15-5 Calculation Results of Chloroform Asphalt "A" Method in Liaohe Peripheral Basin
(2) Reservoir scale sequence method
Calculate the change rate of reservoir size k with software; Calculate the serial number of the discovered reservoir in the whole reservoir sequence according to K; Calculate the reserves of undiscovered oil fields including the largest oil reservoir; Add up the undiscovered reservoir reserves to get the predicted reserves.
The calculation results of reservoir scale sequence method are shown in the following table 8- 15-6.
(3) Reservoir discovery sequence method
According to the layered system of migration and polymerization unit, the average value of chloroform asphalt "A" is calculated; Using the compensation coefficient of chloroform asphalt "A" to recover the content of chloroform asphalt "A"; Calculate the resources of each migration and accumulation unit, in which the hydrocarbon expulsion coefficient is based on basin simulation, and determine the data scale area model of the reservoir-forming system; Basin resources are obtained by adding the resources of migration units and accumulation units covering the basin.
Only Ludong sag and Zhangqiang sag in Liaohe peripheral basin meet the application conditions of statistical method, and the calculation results of reservoir discovery sequence method (Table 8- 15-6).
Table 8- 15-6 Calculation Results of Statistical Resources in Zhangqiang Depression
(4) analogy method
Analogy is a method to infer unknown area from known area. By analogy with reservoir-forming conditions, we can get the abundance of evaluation unit resource area, and then estimate the resource quantity. The resources of the basin are obtained by adding the resources of geological units covering the whole basin.
In the analogy of reservoir-forming conditions, we adopt two scoring methods: the overall analogy of reservoir-forming conditions of geological units and the combination analogy of reservoir-forming conditions of geological units. There are five factors to be considered: hydrocarbon source conditions, reservoir conditions, trap conditions, preservation conditions and support conditions. Among them, the source conditions are subdivided into such scoring items as the thickness of source rock, maturity, hydrocarbon supply mode, hydrocarbon supply area coefficient, hydrocarbon generation intensity, migration distance, dredging conditions and crude oil leakage. Reservoir conditions are divided into reservoir thickness, reservoir percentage, porosity, permeability and connectivity with hydrocarbon sources. Trap conditions are subdivided into trap type, trap area coefficient and trap amplitude. The preservation conditions are further divided into the thickness of the cap rock, lithology of the cap rock, unconformity above the cap rock, fracture damage degree and other factors. The supporting conditions are subdivided into time matching, migration mode and source-reservoir-cap configuration.
The exploration degree of most depressions in Liaohe peripheral basin is very low, and the parameters required by analogy method are relatively simple and flexible to operate. Therefore, most of the depressions with low exploration degree are calculated by analogy method, and the analogy area is Luxi sag. See table 8- 15-7 and table 8- 15-8 for the calculation parameters.
Table 8- 15-7 Relative Analogy Scoring Table of Zhangqiang Depression and Luxi Depression
Table 8- 15-8 Relative Analogy Scoring Table of Anle, Bogetu, Zhalanyingzi Depression and Zhangqiang Depression
Fourth, the results of resource evaluation.
(1) Evaluation results of oil and gas resources
Through this evaluation, it is concluded that the total prospective resources of Zhangwu Basin are 0.9 1× 104t, the total geological resources are 0.80× 104t and the total recoverable resources are 0.3 1× 104t. See table 8- 15-9 for details.
Table 8- 15-9 Evaluation Results of Oil and Gas Resources in Zhangwu Basin
(2) Distribution of oil and gas resources
Zhangwu Basin is a faulted basin developed in JBOY3 -K2 period, and its overall reservoir-forming conditions are better than other surrounding basins, second only to Kailu Basin. Oil and gas are mainly distributed in Jiufotang Formation and Shahai Formation. Zhangqiang sag is the most favorable sag in the basin, with a certain scale of oil fields (Keerkang oilfield) discovered, and it is also the most favorable sag except Lujiapu sag and Longwangtong sag. In addition, there are Baogetu sag and Zalanying sag in the basin, which have similar reservoir-forming conditions with Zhangqiang sag.
Verb (abbreviation of verb) exploration suggestion
Zhangwu basin is an oil-bearing basin with certain resource scale and exploration prospect. At present, the drilling work in the basin is uneven, and only Zhangqiang sag has a high degree of exploration.
There are some unfavorable factors in exploration: ① Well Leshen 1 located in the north of Zhangqiang Depression, there is no oil and gas display during drilling, and the main source rocks become worse. ② The six depressions in the south of the basin are located in the high uplift area in the early and middle Yanshan period, lacking Fuxin Formation and Quantou Formation strata, with shallow buried source rocks and low maturity, and the preservation conditions are not as favorable as the four depressions in the north. However, in shallow well drilling, the abundance of organic matter in source rocks is high, and there is still hope for oil exploration in deep buried sag areas such as Daleng sag.
Abstract of intransitive verbs
The total prospective resources in Zhangwu Basin are 0.9 1× 1.04t, and the total geological resources are 0.80×1.04t.. Zhangqiang sag is the most favorable sag in the basin, with a certain scale of oil fields (Keerkang oilfield) discovered, and it is also the most favorable sag except Lujiapu sag and Longwangtong sag. In addition, there are Baogetu sag and Zalanying sag in the basin, which have similar reservoir-forming conditions with Zhangqiang sag.