(China Petroleum and Natural Gas Co., Ltd. Beijing 100086)
About the author: Fei, male, born in 1946, Manchu, graduated from China Geo University in 1965, mainly engaged in the research and management of oil, natural gas and coalbed methane exploration and development.
Based on the ten years' experience of coalbed methane exploration in China Petroleum and Natural Gas Co., Ltd., this paper systematically summarizes the new knowledge and technology of China Petroleum in the field of coalbed methane exploration, and has made important exploration achievements by using these knowledge and technology, discovered three gas fields and reserved a large number of favorable target areas. China Petroleum will increase the input of coalbed methane during the 11th Five-Year Plan period to promote the early industrialization of coalbed methane.
Keywords: new discoveries and new fields of coalbed methane geological theory
Practice and strategy of exploration and development of petroleum coalbed methane in China
Fei, Li Jingming, Zhao Peihua,
(China Oil and Gas Company Limited, Beijing 100086)
According to the ten years' experience of coalbed methane exploration in China Petroleum and Natural Gas Co., Ltd., some new knowledge and technologies of coalbed methane exploration in China Petroleum and Natural Gas Co., Ltd. are systematically summarized. China Petroleum has made great achievements in coalbed methane exploration by using these knowledge and technologies, discovered three coalbed methane fields and reserved a number of favorable coalbed methane prospect areas. During the 11th Five-Year Plan period, China Petroleum will double its investment in coalbed methane, so as to realize the successful development of coalbed methane industry in China at an early date.
Key words: CBM geological theory; New discovery; frontier
order
Coalbed methane is mainly methane, which is a clean natural gas resource. Coalbed methane is an unconventional natural gas, which mainly exists in coal seams in the form of adsorption. Coalbed methane exploration can reduce the disaster of coal mining and slow down the pollution to the atmosphere. More importantly, coalbed methane is a reserve resource of natural gas. China Petroleum and Natural Gas Co., Ltd. set up a CBM exploration project management department in the exploration division of the former new area of 1994, which is responsible for CBM exploration. In the past ten years, the Ninth Five-Year Plan Company has organized scientific research on coalbed methane and a large number of coalbed methane exploration and development projects. More than 250 people have participated in the project, and regional evaluation research has been carried out with a view to the whole country. The project has invested 450 million yuan and drilled 80 wells, opening up three experimental areas: Dacheng in Hebei, Jincheng in Shanxi and Daning. A large number of favorable coalbed methane blocks have been obtained and a number of outstanding technical achievements have been made. During the Eleventh Five-Year Plan period, the company will further increase investment, promote the early industrialization of coalbed methane and realize the diversification strategy of energy resources of the joint-stock company.
1 China has a breakthrough understanding of coalbed methane geological theory.
Combined with the geological characteristics of coalbed methane in China, coalbed methane reservoirs are divided into four types: confined water plugging type, pressure plugging type, roof water network microfiltration type and structural plugging type. It is pointed out that the preservation condition of confined water sealing gas reservoir is good, which is beneficial to drainage and depressurization, and coalbed methane is the most abundant and is the main exploration target.
According to the hydrocarbon generation mechanism of coal thermal evolution, it can be divided into five types: regional magmatic thermal metamorphism, local thermodynamic metamorphism, deep-water alternating thermal metamorphism, regional compaction metamorphism and tectonic stress metamorphism. It is pointed out that the regional magmatic thermal metamorphic coal seam is well developed, with good physical properties and superior high-yield conditions, which is the focus of exploration.
The genetic types of coalbed methane can be divided into four types from the edge of the basin to the abdomen: methane weathering zone, biodegradation zone, saturated adsorption zone and low desorption zone. It is pointed out that the biodegradation zone is shallow buried, there is little water and atmosphere in mining, the methane gas in the methane weathering zone is extremely low, the coal seam in the low desorption zone is deeply buried, the physical properties are poor, the gas saturation is low and the desorption rate is low, and the saturated adsorption zone is a favorable part for high yield and enrichment.
There are five main types of transformation after coalbed methane accumulation: hydrodynamic scrubbing, coal seam mineralization, structural pulverized coal, diagenetic compaction and structural deformation differential aggregation. Generally speaking, the upward confined water with structural deformation differential accumulation has good sealing conditions, sufficient gas supply to the downward part and superior high-yield enrichment conditions, which is the focus of exploration.
2. The matching technology of coalbed methane exploration has been formed.
Twenty-two special exploration technologies for coalbed methane have been organized successively, and the following six have reached the international leading level.
2. 1 rope-type fully-enclosed rapid coring technology for coal seam
In order to accurately calculate the gas content in coal seam and improve the recovery ratio of coal seam coring, a rope coring tool (large diameter) and its supporting equipment were developed, including coring bit, outer pipe, inner pipe assembly, semi-closed core pipe, suspension mechanism, spring clamping and positioning mechanism, cutting and clamping mechanism, single-acting mechanism, alarm device, differential mechanism, inner and outer pipe centralizers, fishers and rope hoisting system, with a diameter greater than 65438+. The field coring of 30 wells shows that the average recovery rate is over 98%, the original structure of coal core is maintained and the coring speed is fast. It only takes 8 ~ 10 minutes for a 700-meter well depth, and the measured gas content is reliable. It is 20 times faster than the conventional coring speed, and this technology has won the national invention patent.
2.2 Injection/Pressure Drop Well Testing Technology
According to the characteristics of soft coal seam, low pressure, low permeability, gas and water, the advanced foreign injection pump with high pressure and low displacement (the highest injection pressure is 4 1MPa and the lowest injection displacement is 2m3/h) is introduced, and it is equipped with an advanced and reliable surface drainage system. The test technology suitable for different test areas is established, and the special interpretation system software is developed. Through the field test and comparison of more than 50 layers, the interpretation accuracy of parameters such as coal seam permeability is high.
2.3 Gravity potential monitoring technology for coal seam fracturing cracks
According to the inelastic characteristics of coal seam, the indoor mathematical model and physical model test are established, and the monitoring equipment and interpretation software of coal seam fracturing by gravity potential method are developed, which can directly and dynamically monitor and quantitatively explain the extension direction and length of coal seam fracturing cracks on site. Through the field test and comparison of more than 60 layers, the monitoring results of fracturing cracks are accurate, which solves the problem that the horizontal fractures of coal seam fracturing can not be evaluated intuitively and quantitatively in the past. This technology has obtained the national invention patent.
2.4 Cross-well seismic acoustic tomography (CT) technology
According to the characteristics of low P-wave velocity in coal seam and further reduction of P-wave velocity after fracturing, cross-well seismic acoustic tomography technology is used to describe the change characteristics of coal seam physical properties on acoustic profile, so as to evaluate the cross-well communication after fracturing. Through field test and comparison, the results of cross-well test are clear and reliable, which solves the problem that it is impossible to evaluate coal seam fractures intuitively and quantitatively in the past.
2.5 CBM logging evaluation technology
According to the geological characteristics of coalbed methane in the experimental area, a series of coalbed methane logging evaluation software has been developed, which can quantitatively explain parameters such as gas content, caprock, industrial analysis and rock mechanics. Compared with the indoor test results of more than 200 samples from 28 wells, the gas content error is less than 6%, and the cost of each well can be saved by using this technology.
2.6 coalbed methane reservoir simulation technology
Advanced numerical simulation software for coalbed methane and comet coalbed methane reservoirs is introduced from abroad, and developed and applied according to the characteristics of coalbed methane in China. It can be used for three-dimensional two-phase coal reservoir production fitting and reservoir parameter sensitivity analysis of various completion methods and mining methods, and can predict gas production rate, single well and well group productivity, reasonable well spacing, well pattern geometry and well pattern optimization within 20 years, and evaluate gas reservoir development level and production effect in the experimental area. It has been fully applied in Jincheng area of Qinshui basin and Daning-Jixian area of Ordos basin.
Using geological theory and exploration technology, the exploration benefit is remarkable.
3. 1 adhere to the four-level evaluation research and achieve remarkable results.
Regional evaluation: the prospective resources of coalbed methane in 68 coal-accumulating units in 39 coal-bearing basins in China are estimated to be 27.3× 65438+300 ~1500m under the burial depth of 300~65438 (the prospective resources of coalbed methane in the US 18 basin are only1/kloc-0. Among them, the favorable exploration area in great basin is 7.6× 104km2, and the prospective resources of coalbed methane are19×10/2m3.
Zoning evaluation: Eight favorable electoral districts, namely, the central and eastern Ordos Basin, Qinshui, Jizhong-Jidong, Luxi-Puyang, Yuxi, Huainan-Huaibei and Liupanshui, are selected, with an exploration area of 4× 104km2 and a prospective coalbed methane resource of 7./kloc-0 /×1.
Target evaluation: A number of favorable exploration targets, such as Jincheng in Qinshui basin, Daning-Jixian in Ordos basin, Hancheng, Gemudi and Northwest in Liupanshui area of Wushenqi, have been screened out, with an exploration area of 2× 104km2 and prospective coalbed methane resources of 4.4×10/2m3.
Block evaluation: Take the proven controlled reserves of Jincheng target Fanzhuang and Zheng Zhuang blocks and the controlled reserves of Daning-Jixian target Wucheng block.
3.2 Qinshui gas field, the first large-scale coalbed methane field in China, was discovered.
1 June, 1997,1The drilling depth is 705m, and 6 layers 12m are drilled in the main target layers of Permian Shanxi Formation and Carboniferous Taiyuan Formation, showing that the coalbed methane is good during drilling. 1February, 1998, the gas test of No.3 coal in this well was started, and the daily gas production was stable above 2700m3, with a maximum daily gas production of 4050m3. It was the first time that a stable industrial gas flow of coalbed methane was obtained in this area.
1 From April to August, 1998, a total of 1- 1, 1-2, 1-3, 1-4 and/kloc-were drilled near Jinshijing. From April 1999 to February 19, this well group carried out regional drainage and depressurization gas production, and the daily gas production of 4 wells was stable at 2400~3500m3.
At the same time of gas testing in 1 well group, 2, 3, 4, 5 and 6 wells were drilled in Fanzhuang and Zheng Zhuang blocks respectively. After gas testing, the daily gas production of a single well is 2,700 ~ 4,400 m3, with a maximum of 9780m3. The average daily gas production of 3 # coal and 15 # single well is predicted by using coalbed methane reservoir simulation software.
In 200 1 year, the proven gas-bearing area of Fan Zhuang block is 182.22km2, and the geological reserve of coalbed methane is 352.26x108m3; . The gas-bearing area of Zheng Zhuang block is 447. 1km2, and the geological reserve of coalbed methane is 911.2×108m3. The total gas-bearing potential resource area in this registration area is 1090km2, and the total resource amount is 2656x108m3.
Whether conventional drilling or pinnate horizontal drilling technology is adopted, the development of coalbed methane in this area has good economic benefits. Shaanxi-Beijing and the West-East Gas Pipeline are close to this area, which will bring immeasurable benefits to changing the environment of Beijing and the eastern coastal cities.
3.3 A large coalbed methane field was first discovered in the eastern margin of Ordos.
The cumulative thickness of No.6 coal seams of Shanxi Formation and Taiyuan Formation drilled by Jishi 1 well in Daning-Jixian area of Ordos Basin is17.4m, of which No.5 coal seam is 5.4m thick and No.8 coal seam is 8.8m thick, and the coal seam pressure coefficient is1.1~1. The average gas content of 5 # coal is 20.7m3/t, the gas saturation is 9 1%, the average gas content of 8 # coal is 13.8m3/t, the gas saturation is 77%, and the self-overflow water volume of 5 # coal during drilling is 10m3/d, and the main geological parameters are close to the high-yield and rich areas in the American Black Warrior Basin. Among them, the total thickness of coal seam in Jishi 4 well is 7 layers and 22.8m, and the coal seam permeability is as high as 82× 10-3μm2. The thickness of No.5 coal in Well Jishi 5 is 6.8m, the gas content is as high as 23.2m3/t, the gas saturation is 95%, and the daily gas production is 6629m3. At present, it is preliminarily controlled that the buried depth of coal seam in this area is 500 ~ 1200m, the gas-bearing area of coalbed methane is 885km2, and the controlled reserves are 800× 108m3.
4 China CBM development and utilization prospects
2 1 century is the century of natural gas, and the development of natural gas in China will develop rapidly in the coming decades. The west-to-east gas transmission is a rare historical opportunity for the development of coalbed methane industry. The West-to-East Gas Transmission Project will cross many oil and gas basins and coal-bearing basins in China. According to the estimation of gas supply capacity and design life of "West-to-East Gas Transmission Project", the geological reserves of natural gas of1012m3 are needed as a guarantee, but the current proven geological reserves of conventional natural gas are only about 7000× 108m3, so it is urgent to replenish gas sources. As an unconventional natural gas, more than 95% of coalbed methane can be completely combined with methane. At the same time, the area where the "West-to-East Gas Transmission" pipeline passes is also rich in coalbed methane resources. The total resources of coalbed methane enrichment zones such as Tabei, Ordos Basin, Qinshui Basin, the eastern foot of Taihang Mountain, western Henan, Xuhuai and Huainan are close to14×101.2m3, and the Qinshui large-scale coalbed methane field through which the pipeline passes has obtained proven reserves of coalbed methane. In a short time,
China's coalbed methane industry, like other countries, will develop simultaneously with underground drainage and surface drainage. On the one hand, we will continue to improve underground drainage technology and improve drainage efficiency; On the other hand, vigorously carry out ground drainage tests. China's underground coalbed methane drainage has a history of more than 50 years, and the drainage technology is mature. With the strengthening of environmental awareness, more CBM utilization facilities have been completed and put into operation, and the state and enterprises pay more attention to safety in production. It is predicted that in the next 10 year, underground coalbed methane drainage will develop greatly, and the amount of underground coalbed methane drainage will reach 10 billion m3 in 2005 and 10 year.
The ground development test of coalbed methane in China has changed from single well test to well group test, and some coalbed methane development projects have shown the prospect of commercial development. The development of coalbed methane in China should adopt the principle of combining old areas with key breakthroughs. First of all, make supplementary exploration in Ordos and Qinshui basins with good resource conditions and high exploration degree, and concentrate on development, so that the coalbed methane production capacity has been greatly improved in the near future and a breakthrough has been made in development and utilization.
According to the current forecast of the development speed and policy orientation of coalbed methane in China, the output of coalbed methane in China will increase in three stages: slow, rapid and stable. It is estimated that by 20 1000 ~ 2000, China will have proven (1000) × 108m3 of coalbed methane available reserves, and build 3 ~ 5 demonstration bases for coalbed methane development, so that the coalbed methane output will reach (20 ~). It is predicted that the year 2000 ~ 20 10 will be the great development stage of coalbed methane in China, which is equivalent to the level of the United States in 1980s. Because of the low production and long life of coalbed methane wells, it is necessary to have preferential policies to encourage coalbed methane exploration and development, so that China's coalbed methane exploration and development has made great progress at this stage. The amount of coalbed methane resources available for exploration in North China is equivalent to the sum of San Juan and Darth Vader Basin in the United States, but the geological conditions are complex and exploration is difficult. It is predicted that by 20 10, the national coalbed methane output will reach 20× 108m3, and the controlled reserves will be 1500× 108m3. It is predicted that in 20 10-2020, with the maturity of coalbed methane exploration and development technology, the exploration scope will be further expanded to South China, Northeast China and Northwest China, and the coalbed methane output is expected to reach 150× 108m3 in 2020. By 2025, 5-6 CBM production bases will be built, and the CBM output will reach 200× 108m3, forming a perfect CBM industrial system.
5 China petroleum coalbed methane development strategy
During the 11th Five-Year Plan period, China Petroleum will base itself on the coal-bearing basins in the central and eastern regions, and form a coalbed methane production capacity of 30× 108m3 within five years. In order to achieve this goal, we should do a good job in the following aspects.
5. 1 Increase investment in coalbed methane science and technology.
China is rich in coalbed methane resources, and the gap between supply and demand of clean gas energy is large, so it is urgent and necessary to develop and utilize coalbed methane. Compared with the United States, coalbed methane reservoirs in China are characterized by low permeability, low saturation and low reservoir pressure. The geological conditions of coalbed methane are complex and it is difficult to mine. China Petroleum will further increase its scientific and technological investment in coalbed methane. On the one hand, it will strengthen the basic theoretical research of coalbed methane reservoir formation theory and economic evaluation, and pay attention to the systematicness of coalbed methane science; On the other hand, increase investment in key research and demonstration projects of coalbed methane to create scientific and technological support for breakthroughs in coalbed methane development.
5.2 According to the characteristics and distribution of coalbed methane resources in China, select favorable development blocks.
China has a large amount of coalbed methane resources, which has obvious characteristics of regional enrichment and time domain enrichment. On the basis of comprehensive evaluation of coalbed methane resources in China, the development prospect is classified and evaluated by gas-bearing zones, and 10 favorable target areas are determined as the optimal blocks for coalbed methane development, and the favorable blocks for coalbed methane development in Qinshui basin, eastern margin of Ordos basin, Huaibei area and western low-rank coal areas can be regarded as the key work areas for recent exploration and development.
5.3 Develop a complete and scientific development plan for coalbed methane.
Adhere to the overall planning and coordinated development of the upstream and downstream of coalbed methane, combine evaluation with exploration, combine key breakthroughs with scale development, and develop from shallow to deep, from easy to difficult and rolling; Adhere to the principle of surface scale development, promote underground drainage in coal mines, and simultaneously develop surface and underground drainage, and establish a comprehensive development model of mineral resources of "gas extraction first and coal mining later".
5.4 China Petroleum will incorporate the development and utilization of coalbed methane into the company's medium and long-term energy development plan, and attach importance to related infrastructure construction.
China's CBM infrastructure is weak, especially there is no long-distance CBM pipeline network. China Petroleum will incorporate pipeline construction into the company's infrastructure development plan, invest appropriate funds in infrastructure construction in a planned way, and implement it by stages to accelerate the formation and development of coalbed methane industry in China.
refer to
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