Ordos is famous for its rich coal resources, with proven reserves of 230 billion tons, accounting for about 1/6 of the total reserves in China, and 1/2 in Inner Mongolia Autonomous Region. If calculated by underground 1500m, the total reserves are about 1 trillion t (Wang Zailan, 2005).

(A) Ordos coalfield distribution

Ordos coalfield, which spans five provinces (regions) of Shaanxi, Gansu, Ningxia, Shaanxi and Mongolia, is the largest multi-stage coalfield in China, and can be roughly divided into seven coal-bearing regions by region:

1. Coal-bearing area in the eastern edge of Ordos

Located at the junction of Shanxi and Shaanxi provinces, it is basically distributed along the Yellow River, reaching the junction of Shanxi, Shaanxi and Mongolia in the north and near Yumenkou in the south. The eastern boundary is roughly on Pianguan-Lishi-Puxian line, which is equivalent to the outcrop position of coal seam. The western boundary is on Yumenkou-Suide-Jiaxian-Shenmu line, and the coal seam is 2000m deep. It is 450 kilometers long from north to south and 50 ~ 100 kilometers wide from east to west. Geographical coordinates are north latitude11015' ~1130', and north latitude is 35 55' ~ 39 36'. It includes 8 mining areas/coal-producing areas, namely Hejin, Baode, Pianguan, Lishi, Liulin and Xiangning, in Fugu and Wubao of Shaanxi and Hedong coalfields of Shanxi, with coal-bearing area of18813.7km2. The main coal-bearing strata are Carboniferous-Permian Taiyuan Formation and Shanxi Formation. The coals of Taiyuan Formation and Shanxi Formation range from long flame coal to anthracite.

Predict the reliable level resources11941.200 million t, the possible level is 37.242 billion t, the inferred level is 3.9045438+0 billion t, the buried depth is 1000m, and the shallow resources are 62.609 billion t, of which the reliable level is 60/.

2. Coal-bearing area in northern Ordos

Located in the southwest of Inner Mongolia and the north of Ordos Plateau. North to the southern edge of the Yellow River Hetao, east to the south corner of the Yellow River at the junction of Shanxi and Mongolia, west to the western foot of Helan Mountain, and south to the junction of Mongolia and Shaanxi. Geographical coordinates are10640' ~1130' east longitude and 37 38' ~ 40 65438+ north latitude. Including Zhungeer, Dongsheng coalfield and Wulange coal-producing area, with a coal-bearing area of 62368.5km2.

The coal-bearing strata in this area are Carboniferous-Permian Taiyuan Formation, Shanxi Formation and Middle Jurassic Yan 'an Formation. Taiyuan formation is medium ash and ultra-low sulfur coal; Shanxi formation is medium ash and ultra-low sulfur coal; Taiyuan formation is divided into coal with medium ash and medium sulfur; Yan 'an Formation is a high-quality non-stick coal with low ash and ultra-low sulfur.

It is predicted that the reliability level of resources in the whole region is 262.73 billion t, the possible level is 679.468 billion t, the buried depth is less than 1000m, and the resources amount is 98.583 billion t, of which the reliability level is 951.1.400 million t..

3. Coal-bearing areas in northern Shaanxi

Located in the middle of northern Shaanxi, bordering Shaanxi and Mongolia in the northwest and coal-bearing area in the north of Ordos, it reaches the recoverable boundary of middle Jurassic Yan 'an Formation and late Triassic Wayaobao Formation in the southeast, and spans Shenmu, Yulin, Hengshan, Jingbian, Dingbian, Wuqi, Zichang, Ansai, Yan 'an and Fuxian. Geographical coordinates: east longitude10715' ~1045', north latitude 36 05' ~ 39 16'. This area includes six coal-producing areas, Xinmin, Shenbei, Shen Yu, Yuheng, Anbian and Dingbian, as well as Zichang and Niuwu coal-producing areas of Zichang Triassic coalfield, with a coal-bearing area of 28,765.1km2.

The coal-bearing strata are middle Jurassic Yan 'an Formation and late Triassic Wayaobao Formation. Among them, Yan 'an Formation coal is non-stick coal and long flame coal with ultra-low phosphorus and medium and high calorific value.

There are 10 prediction areas in the whole region, and the predicted reliable horizontal resources are 85.31800 million t, the possible level is120.7 billion t, the buried depth is 1000m, and the shallow resources are 25.243 billion t, of which the reliable level is 24.036 billion t.

4. Western Ordos coal-bearing area

Located in Guyuan, Lingwu and Yanchi areas in the east of Gansu and southeast of Ningxia, the geographical coordinates are: east longitude 106 25' ~ 108 40' and north latitude 35 25' ~ 38 20', including Huating coalfield in Gansu and Anguo-Xiamen, Qingyang, Shajingzi, Guyuan and Yanchi.

The coal-bearing strata are Carboniferous-Permian Shanxi Formation and Middle Jurassic Yan 'an Formation. Shanxi Group coal is medium ash and ultra-low sulfur gas coal. Most of the coal in Yan 'an Formation is medium-low ash and low sulfur long flame coal.

The predicted resource reliability level18196.5 million t, possible level 68.558 billion t, inferred level1686.3 million t, buried depth less than10.0000 m, and resource amount 2185.4 million t.

5. Table Mountain and Helan Mountain coal-bearing areas

Located in the north of Ningxia, it crosses Zhuozi Mountain and Alashan Zuo Qi in the north and Weizhou in the south, and is distributed along the banks of the Yellow River, including Mengcheng, Weizhou, Shigouyi, Hengcheng, Shitanjing, Shizuishan, Alashan Zuo Qi and Zhuozi Mountain in Inner Mongolia. Geographical coordinates: east longitude105 46' ~1071',north latitude 37 07' ~ 39 52'. The coal-bearing area is 4752.28 square kilometers.

The coal-bearing strata are Carboniferous-Permian Taiyuan Formation, Shanxi Formation and Middle Jurassic Yan 'an Formation. Carboniferous-Permian coal is mainly coking coal and lean coal. Taiyuan Formation coal is medium ash, medium sulfur, low phosphorus, high calorific value power coal and coking coal. Shanxi group coal is mainly medium ash and ultra-low sulfur coal. The coal in Yan 'an Formation is bituminous coal and anthracite with low-ultra-low ash, ultra-low sulfur and high calorific value. Rujigou high-quality anthracite enjoys a good reputation at home and abroad, and is an ultra-high-quality anthracite base.

The reliability level of predicted resources in the whole region is 29.632 billion t, the possible level is 36.5438+84.9 billion t, the inferred level is 65.438+0.1.10.400 billion t, 1000m, and the depth predicted resources are 20.898 billion t, of which the reliability level/kloc-0.

6. Weibei coal-bearing area

Located on the north bank of Weihe River, northeast of Guanzhong Plain. It is adjacent to the Yellow River in the east and Xiangning coal-producing area in Shanxi at the southern end of Ordos coal-bearing area, reaching the outcrop line of Carboniferous-Permian coal-bearing strata in the south and west, and the buried depth of Taiyuan Formation in the north is-1300m. The coal-bearing area is 200km long from east to west, 30 ~ 55 km wide from north to south, and the coal-bearing area is 80 10.6km2, spanning Hancheng, Chengcheng, Heyang, Baishui, Pucheng, Luochuan, Huanglong, Yichuan, Yijun, Tongchuan, Huangling and Xunyi 12 cities (counties). Geographical coordinates: east longitude 107 55' ~ 109 35', north latitude 39 45' ~ 36 05'. Weibei coal-bearing area, namely the Carboniferous-Permian coalfield in Weibei, is divided into Hancheng, Hecheng, Bai Pu and Tongchuan from east to west. The coal-bearing strata are Carboniferous-Permian Taiyuan Formation and Shanxi Formation.

19 Predicted Resources Reliability Level105.57 million t, Possible Level10/3.05 million t, Inferred Level194.63 million t, Buried Depth 1000m, Shallow Resources/kloc-

7. Huanglong coal-bearing area

Located in the central and western Shaanxi, the southern edge of Ordos Basin. It starts from the Shaanxi-Gansu border in the north, reaches the denudation outcrop line of the middle Jurassic Yan 'an Formation in the south, reaches Hulu River in the east, and reaches the Xiakou of Longxian County in the west, spanning Huangling, Xunyi, Binxian, Yongshou, Linyou, Fengxiang, Qianyang and Longxian County, with geographical coordinates of 106 35' ~ 109 65438. Huanglong coal-bearing area is Huanglong coalfield. From east to west, there are five mining areas and coal-producing areas, namely Huangling, Jiaoping, Xunyao, Chang Bin and Yonglong, with a coal-bearing area of 5230.5km2

The coal-bearing strata are middle Jurassic Yan 'an Formation, and the coal is mostly low ash, low sulfur and low phosphorus long flame coal, non-sticky coal and weakly sticky coal.

In the 10 prediction area, the predicted reliable level resources are 4.064 billion t, the possible level is 2.770 billion t, the inferred level is 3.036 billion t, the buried depth is 1000m, and the predicted resources are 6.834 billion t, of which the reliable level is 4.064 billion t.

(2) Distribution of Ordos coal mining area

The coal mining areas of Ordos energy base are mainly distributed in Weibei coal mining areas such as Hancheng-Tongchuan-Chang Bin-Huangling in Shaanxi, Shenfu in Shaanxi and Dongsheng in Inner Mongolia, Huating in Pingliang, Gansu, Lingwu, Shizuishan and Shitanjing in Ningxia, and Shiguai coal mining areas in Wuda, Wuhai and Baotou in Inner Mongolia. Among them, Jurassic coal mining areas are mainly distributed in Jiaoping, Chang Bin, Huangling, Shenbei, Xinmin and Shen Yu mining areas in northern Shaanxi and Dongsheng mining area in western Mongolia. These mining areas are rich in reserves, excellent in coal quality, shallow and stable in coal seam and simple in structure, which are the main coal development areas in China at the beginning of 2 1 century.

(C) Ordos coal resources development status

The coal resources in this area are highly developed, and the five provinces across the basin have developed and utilized the coal in this area to varying degrees. There are six major coal mining areas with a coal production capacity of over 2 million t/a, of which the Carboniferous wells in Ningxia are 5.89 million t/a, Uda is 2.89 million t/a and Shizuishan is 2.7 million t/a; 52 10000 t/a in Tongchuan, Shaanxi, and 3.65 million t/a in Hancheng ... There are more than 70 coal enterprises in Shaanxi Province, but more than half of them are small coal mines. Longdong area in Gansu Province is located in the middle and west of Ordos Basin, and the coal output reached 365,438+560,000 t in 2000. At present, the coalfields that have been developed and utilized mainly include Huating Coalfield in Huating County and Ankou Xinyao Coalfield in Chongxin-Huating County. In 2002, the output of the two coalfields reached 8.23 million tons. There are more than 0/00 coal enterprises in Ningxia, mainly small coal mines, accounting for more than 90%. In 2002, the coal output reached 153 10000 t, and there were 40 large and medium-sized enterprises located in Ordos Basin, Inner Mongolia. In 20065438, the output was 367 10000t (Li Xinyu, 2005).

Second, the present situation of petroleum resources development

Ordos basin is a large comprehensive energy basin, rich in oil, natural gas, coal, coalbed methane and sandstone-type uranium deposits. The total oil resources in the basin are 8.588 billion t, of which the recoverable reserves are about 2.4 billion t, and the proven degree is only 20%. The total natural gas resources are 10.70 trillion cubic meters, and the proven reserves are1.10.80 billion cubic meters. The proven reserves of Sulige, Wushenqi, Jingbian and Yulin world-class gas fields exceed 1000 billion m3.

(1) exploration history

Oil exploration in the basin has a long history, and Yanchang oil mine in northern Shaanxi is the earliest oilfield discovered and put into development in China. Since the first onshore oil well (Yan 1 well) was drilled in Yanchang County in 1907, oil exploration has gone through 95 years and can be divided into 6 development stages.

1. Preliminary exploration stage (1907 ~ 1949)

This stage lasted for 42 years, and experienced the official camp (1907 ~191year) and Sino-US joint venture (1914 ~/kloc) in the late Qing Dynasty. Many geologists at home and abroad have carried out petroleum geological survey in the basin, but the work is sporadic, mainly confined to the shallow oil layer distribution area in northern Shaanxi. A total of 52 shallow wells were drilled, with footage of 65,438+299,400 meters and oil production of 6,035 tons. ..

2. Regional exploration stage (1950 ~ 1960)

After the founding of New China, the Party and the government attached great importance to oil exploration in Shaanxi-Gansu-Ningxia region, focused on the whole basin, made overall planning and implemented by stages, and invested a lot of manpower and material resources. 94 geological teams and 68 geophysical teams (including earthquake, gravity and magnetism, electrical method and earth current) have been set up successively to carry out regional geological and geophysical surveys, detailed surveys and detailed surveys of the whole basin. Well Lang 9 drilled 423 faces of Shiqianfeng Formation at 1954, with a well depth of 2,646 meters. The Yanchang Formation drilled the oil layer 168 meters .../the Yanchang Well drilled at kloc-0/955/and drilled to 306 meters of Ordovician, thus establishing a relatively complete stratigraphic profile in the east of the basin. Through the above work, the basin outline, stratigraphic distribution and source-reservoir-cap combination have been basically identified, and 265 local structures and 404 surface oil seedlings have been found around the basin, which has made great progress in understanding the oil-bearing prospect of the basin. 1959 drilled Chang 8 oil layer in the second member of Yanchang Formation in Majiatan structure for the first time, with an initial crude oil production of 0.507m3/d; 1960 obtained industrial oil flow in Yan 5 reservoir of Yan' an Formation in Lizhuangzi structure, which achieved a breakthrough in oil exploration in the west of the basin.

3. Exploration stage of structural reservoir in the western margin of the basin (196 1 ~ 1969)

In 1960s, the focus of petroleum exploration shifted from Triassic to Jurassic, and a number of new oil fields were discovered in Lingwu, Yanchi and Dingbian areas with structural oil and gas reservoirs as the exploration target.

In 1965, new reservoirs of Yan 6 ~ 8 were discovered in Lizhuangzi structure, and industrial oil flows of daily output 19m3 and 20m3 were obtained in Tan Li 8 15 well, respectively, which opened up a new situation of oil exploration in the basin.

1966 Well Matan 5 located in Majiatan structure adopts fracturing technology for the first time to obtain industrial oil flow, which opens up a new way for reforming low permeability reservoirs of Yanchang Formation and increasing single well production.

1967 ~ 1969 further develops southward, and oil flow is obtained from 1967 Lijialiang structure; Mafang and Dashuikeng oilfields were discovered in 1968, and Wangjiachang and Dadong oilfields were discovered in 1969.

In addition, the Third General Survey Brigade of the Ministry of Geology also found good oil-bearing marks when drilling Qingshen Well, Zhenshen Well, Huashen Well, Shenzhi Well and Wushen Well in Qingyang, Huachi and Wuqi areas in the hinterland of the basin. Among them, the reservoir of Yanchang Formation in Qingshen 1 Well has been fractured, with a daily oil production of 3.1t. New oil-bearing areas have been discovered.

4. Exploration stage of Jurassic palaeogeomorphic reservoir in the south of the basin (1970 ~ 1979)

1970, the Ministry of Petroleum deployed 18 regional exploration wells in the southern part of the basin. Oil layers were found in 9 wells drilled in Qingyang, Huachi and Wuqi areas, and industrial oil flows were obtained in 6 wells, showing a good oil exploration prospect in the southern part of the basin.

In order to speed up the pace of oil exploration in Ordos Basin in an all-round way,1September, 1970, the State Council and the Central Military Commission decided to set up Changqing Oil Exploration Headquarters to launch a large-scale oil battle with Longdong, Lingyan and northern Shaanxi as the targets within 65,438+10,000 km2 in the south of the basin. In accordance with the deployment principle of "regional expansion, key breakthrough and regional annihilation", campaigns have been set up from regional reconnaissance, encircling Maling, expanding Huachi, developing Wuqi, attacking Jiyuan, drilling two rivers and marching into Dingbian. , completed diamond oil exploration wells 1.252 wells, with footage 1.983m, 520 wells obtained industrial oil flow, with a success rate of 4 1.5%, and established the Jurassic system. Prove or control Maling, Cheng Hao, Huachi, Nanliang, Wuqi, Zhiluo, Xiasiwan, Donghongzhuang, Hongjingzi, Mafang, Dashuikeng, Lizhuangzi, Majiatan and Baiyanjing oilfields 14. 26 new reservoirs such as Yuancheng, Youfangzhuang and Wangwazi were discovered. The newly-increased oil-bearing area is 483.8km2, and the proven petroleum geological reserves are 9 1 7 1 0,000t, laying the foundation for an annual output of 65438+300,000t. ..

5. Triassic delta reservoir exploration stage in the east of the basin (1980 ~ 1994)

Exploration of Triassic Yanchang Formation began with scientific and technological research. Based on the study of sedimentary system, sand body distribution, reservoir evolution and oil and gas enrichment law of Yanchang Formation, the strategic policy of "exploring delta in the east and underwater fan in the west" is put forward. First, dissect the Ansai Delta as a whole, invest 7 1 10,000 yuan in five years, drill 126 wells, and discover Wang Yao and Wang Yao in Ansai Oilfield. In addition, the Jurassic oil-bearing area is 206km2, the proven geological reserves are1.0561.000000 t, and the recoverable reserves are 2 1.227 million t, making it the first large oil field of 100 million tons in the basin. Together with other areas, the cumulative oil-bearing area of 15 is 409.8km2, and the proven geological reserves are 209.23 million t.

6. Pioneering development stage of petroleum exploration (1995 ~ 2005)

In the past seven years, petroleum exploration has been based on the principle of "taking economic benefits as the center and commercial reserves as the goal, and exploring Jurassic based on Triassic; Based on the development strategy of "focusing on the whole basin and attacking northern Shaanxi", great progress has been made in oil exploration in northern Shaanxi and Longdong. The oil-bearing area is 14 1 1.9km2, and the proven geological oil reserves are 703.56 million tons, accounting for 70% of the proven oil reserves over the years, which is the fastest growth period of oil reserves in the basin.

Among them, the exploration in northern Shaanxi is guided by the theory of delta reservoir formation, and Jing 'an Oilfield has been proved, with a proven petroleum geological reserve of 263.35 million tons, which is the second large oil field of 100 million tons in the basin. The second exploration in Ansai Oilfield has achieved fruitful results, with the newly-increased proven oil reserves of 265.438+005 billion t, twice as much as the last proven reserves. New oilfields such as Xifeng, Wu 6 well area of Nanliang Oilfield and Zhenbei have been discovered in Longdong area. The oil-bearing area of old oilfields such as Huachi has been further expanded, and the proven reserves have been greatly increased. In particular, the discovery of Xifeng oilfield has created a new situation in the exploration of ultra-low permeability reservoirs.

(2) Development process

1. Initial stage (1907 ~ 1969)

Ordos basin has a long history of oil development. From 1907 to 1949, the industrial oil flow was discovered from Yan 1 well. Yanchang Oilfield, although oil development experienced the oil officialdom in the late Qing Dynasty (1907 ~ 19 13), the Ministry of Industry of the Republic of China, and the Resources Committee (/kloc After 938 open hole completion, Yongping Oilfield, which was put into development with a monthly output exceeding 10 t.. 1954, was shallow buried, with poor physical properties and high water cut. The buried depth is only 200 ~ 500m, the well spacing is 50 ~100m, and the initial well is completed in open hole, with an average daily oil production of 0.096t.. ..

2. Initial stage (1970 ~ 1979)

The development of 1970 lizhuangzi oilfield and 1973 maling oilfield has opened the curtain of modern oil development in the basin. In the development of Maling Oilfield, the new technologies of fracturing stimulation, early water injection and pumping oil production were adopted, and the crude oil output increased steadily. The crude oil output in Ordos Basin has increased from 70,000 t/year to1130,000 t/year, breaking through the million-ton mark.

3. Stable phase (1980 ~ 1990)

In 1980s, crude oil production in the basin was in a period of steady development. 1980, the crude oil output rose to 14 10000 t, but after that, although Huachi, Yuancheng, Youfangzhuang and Fanjiachuan oilfields were put into development, the increase was not significant, and the crude oil output in the basin was stable at (160 ~1.

4. Great development stage (199 1 ~ 2005)

In 1990s, with the production of Ansai and Jing 'an oilfields, the crude oil output in Ordos Basin entered a period of rapid growth, reaching a new level every year, with199/kloc-0 exceeding 2 million tons per year,/kloc-0 exceeding 3 million tons in 1996, and/kloc-0 exceeding 4.76 million tons in 1997.

(3) the degree of development

By the end of 2005, 47 oilfields, including Ansai, Jing 'an, Maling and Huachi, have been discovered in Ordos Basin, with proven oil-bearing area of 2720.3km2, proven petroleum geological reserves of 65.438+345.3 million tons, recoverable reserves of 240.5438+3. 1 100 million tons ... 40 oilfields have been developed, with geological reserves of 76,952/. Recoverable reserves1.5821.7000 t, remaining geological reserves 575 1 100 million t, recoverable reserves 88267 1 10000 t, and total oil wells 1.9039.

Figure 3- 1 Histogram of Oil Production in Ordos Basin over the Years

(4) The present situation and characteristics of oil exploitation.

Since the reform and opening up, under the guidance of the "multi-level development" policy of the former Ministry of Petroleum Industry, with the success of exploration in the northern Ansai oil region, the crude oil exploitation scope in Ordos Basin has expanded rapidly, and the output has increased year by year, of which the annual output of crude oil in Yan 'an City has reached nearly 2 million tons.

1. There are many levels of development, and the management level and technical level are uneven.

At present, there are three levels of simultaneous development in Ordos Basin: Changqing Oilfield, Yanchang Petroleum Administration Bureau and County Petroleum Drilling and Production Company (existing in northern Shaanxi). Among them, except for centralized export of crude oil and centralized treatment and reinjection of sewage, almost all of Changqing Oilfield adopts single well or centralized discharge of sewage. Yanchang Yanchang Oil Well is centralized exported, oily wastewater is dehydrated at the oil selection station, and the discharged oily wastewater is discharged after simple oil separation treatment. Due to the complicated source of its developers, it is difficult for county oil drilling and production companies to unify their operation processes. Most of them use very rough and backward dehydration technology, and the oil concentration in the dehydrated water is very high.

The most chaotic area of petroleum development and management is Yulin area in Yan 'an, northern Shaanxi. This area is also the birthplace of China's oil industry. Since 1993, due to chaotic management, some county-level governments have issued oil exploration licenses illegally and ultra vires, resulting in the formation of various forms of county drilling and production companies and individual oil producers in addition to the state-owned Changqing Petroleum Exploration and Development Bureau and Yanchang Oil Mine. Northern Shaanxi has become the only area in China where people are engaged in oil exploitation. See table 3- 1 for the oil recovery rates of different enterprises.

Table 3- 1 Recovery ratio of different enterprises in northern Shaanxi

It can be seen from Table 3- 1 that both Changqing Oilfield Company and Yanchang Oilfield are exploiting low permeability oil in the same area. Due to the small scale of civil exploitation and low level of mining technology, the average oil recovery rate is 8%. The primary recovery rate of Changqing Oilfield Company is 20.5%. After water flooding and other technologies, the cumulative recovery rate of secondary oil recovery can reach 30%, that is, the local and individual recovery rates are only 26.67% of the total recovery rate of Changqing Oilfield Company. In other words, 73.33% of the resources are not utilized, resulting in the waste and destruction of valuable oil resources.

2. The oilfield has low permeability and large area.

Jurassic Yanchang series and Triassic Yanchang series are mainly exploited in Ordos basin. These two oilfields are rare ultra-low permeability oilfields in the world, with an average permeability of only 0.49 MD, which determines that the single well production in this area is low, the water content of oil produced by oil wells fluctuates greatly, and the water content of oil produced increases with the development of mining time. In addition, the oil field is large, and the oil wells are scattered in various valleys, ditches and hills, which causes a wide range of oil pollution and is difficult to control.

3. Soil erosion is serious, and non-point source pollution is widespread.

Ordos basin oil-producing area belongs to hilly and gully region of loess plateau, with poor vegetation and serious soil erosion. Petroleum non-point source pollution will cause serious pollution to the water environment in this area.