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Shale gas refers to the mature dark shale or high carbon shale rich in organic matter due to the adsorption of organic matter or the existence of cracks and matrix pores in the rock, so that it stores and preserves the natural gas of biological origin, pyrolysis origin and mixed origin with certain commercial value.
[1]
Shale gas occurs in reservoir rock series dominated by organic-rich shale
Unconventional gas
. It is a continuously generated biochemical gas, thermogenic gas, or a mixture of the two, which can exist in the free state in natural cracks and pores, and exist in the adsorbed state in kerogen, kerogen, kerogen, kerogen and kerogen.
clay
On the surface of the particles, a very small amount is stored in the dissolved state in kerogen and asphaltene, and the proportion of free gas is generally 20% to 85%.
[2]
- Chinese name
- Shale gas
- Foreign name
- Shale Gas
- phylum
- Energy and chemical industry
- China's reserves
- 36.1 trillion cubic meters
- specificity
- Self-generating and self-storage characteristics
- causation
- Thermal cracking and biogenesis
catalogue
- 1Resource introduction
- 2Resource characteristics
- 3Formation reason
- 4Formation condition
- 5Accumulation factor
- 6Reservoir forming process
- 7Research process
- 8Resource distribution
- ▪World reserves and distribution
- ▪Distribution of China's reserves
Shale gas is contained in
page
rock
layer
In terms of natural gas resources available for exploitation, China has large recoverable reserves of shale gas. The formation and enrichment of shale gas has its own unique characteristics, and it is usually distributed in the shale with large thickness and wide distribution in the basin
Source rock
In the stratum. a
Conventional natural gas
In contrast, shale gas development has a long mining life and
Production cycle
The advantage of long shale gas is that most of the producing shale gas has a wide distribution range, large thickness, and generally contains gas, which makes shale gas Wells can produce gas at a stable rate for a long time.
[3]
Shale gas exists in organic-rich mud shale and its interlayers. It is a kind of unconventional natural gas with adsorption and free state as its main mode of existence, and its composition is mainly methane. It is a clean and efficient energy resource and chemical raw material, mainly used in residential gas, urban heating, power generation, automobile fuel and chemical production, and has a wide range of uses. Shale gas generally does not need drainage in the production process, the production cycle is long, generally 30 to 50 years, the success rate of exploration and development is high, and it has a high industrial economic value.
[4]
According to the forecast, the resource volume of China's major basins and regions is about 36 trillion cubic meters, with huge economic value and broad resource prospects.
[5]
On the afternoon of December 24, 2021, the 2022 National Energy Work Conference was held in Beijing. The meeting pointed out that in terms of oil and gas, increasing oil and gas exploration and development, it is expected that the annual crude oil production of 199 million tons, three consecutive years of recovery, natural gas production of about 206 billion square meters, five consecutive years of increase of more than 10 billion square meters, shale oil production of 2.4 million tons, shale gas production of 23 billion square meters, coal bed gas utilization of 7.7 billion square meters, continue to maintain a good growth momentum.
[20]
Shale gas, like deep basin gas and coalbed methane, is a "continuous" accumulation of unconventional gas.
[1]
Shale gas generation model
Shale lithology is mostly asphaltic or rich in organic matter dark, black mud shale and high carbon mud shale, rock composition generally includes 30% to 50% clay minerals, 15% to 25% silty (quartz particles) and 4% to 30% organic matter. It is precisely because of such characteristics of shale that natural gas in shale has a variety of existing modes, mainly including two forms, namely free state (a large amount of existence in shale pores and fractures) and adsorbed state (a large amount of existence in clay minerals, organic matter, kerogen particles and pore surface). The natural gas in the adsorbed state accounts for more than 20% (BarnettShale) to 85% (LewisShale) of the total natural gas occurrence.
[1]
Previous studies on the genesis of shale gas in the five major shale gas basins in the United States show that shale gas can evolve through the following two ways.
[6]
1, thermal cracking gas (naturally generated)
Formation path diagram
The extraction of shale gas
2. Biogenic gas
It generally refers to the gas directly degraded by bacteria in the biochemical stage of shale rock, and also the biogas transformed by gas accumulation in the later period. For example, the Antrim shale gas in the Michigan basin of the United States is the thermal degradation gas generated during the maturation of kerogen and the biogenic gas generated during the metabolic activities of methanogens, mainly the latter. The reason may be that the well-developed fracture system not only allowed natural gas and the original formation water carrying a large number of bacteria to enter the Antrim shale, but also the atmospheric precipitation from the aquifer in the overlying Pleistocene glacial drift invaded at the same time, which was conducive to the formation of bacterial methane.
[1]
1. Sedimentary environment
Fast deposition conditions and better closed reduction environment are important conditions for the formation of black shale. The faster sedimentation rate can enable the organic-rich shale to be deposited in large quantities before being destroyed by oxidation, while the water hypoxia can inhibit the activity of microorganisms and reduce the destruction of organic matter. For example, the organic-rich black shale of the Barnett Formation in the Fort Worth basin is deposited in the deep water (120-215 m) focontinental basin, with anoxic-anaerobic characteristics below the storm wave base and low oxygen zone (OMZ), and limited communication with the open sea.
[1]
2. Effective thickness
Widely distributed shale is an important condition for shale gas formation. At the same time, the effective sediment thickness is a prerequisite to ensure sufficient organic matter and sufficient storage space. The greater the thickness of shale, the stronger the capping ability of shale, which is conducive to gas preservation and thus conducive to shale gas accumulation. The net shale thickness of the five major shale gas exploration and production areas in the United States is 9.14 to 91.44 meters, of which the average thickness of Barnett shale and Lewis shale with high gas production is more than 30.48 meters.
[1]
3. Total Organic Carbon Content (TOC)
Total organic carbon content is an important index to evaluate the abundance of source rocks, and also an important parameter to measure the intensity and quantity of hydrocarbon generation. The organic carbon content varies with the lithology. For clay-rich shale, the organic carbon content is the highest due to the large adsorption capacity. Therefore, the lower limit of organic carbon content of mud shale as a potential source rock is higher, and when the source rock has better organic matter type and higher thermal evolution degree, the corresponding lower limit of organic carbon content is lower. The lower limit standard of organic carbon content in argillaceous oil source rocks is the same at home and abroad, which is 0.4% ~ 0.6%, while the lower limit standard of organic carbon content in argillaceous gas source rocks is different. A large number of research results show that gaseous hydrocarbon molecules are small, soluble in water, easy to migrate, the lower limit of organic carbon content of gas source rock is much lower than that of oil source rock. The total organic carbon content of the five shale gas systems in the United States is high, and the distribution range is large (0.5% ~ 25%), which can be divided into two categories. The TOC content of the Antrim shale and the New Albany shale is high, and the distribution is generally between 0.3% ~ 25%. The TOC content of Ohio shales, Barnett shales and Lewis shales ranges from 0.45% to 4.7%.
[1]
4. Kerogen type and maturity
In different sedimentary environments, kerogen formed from different sources of organic matter has obvious differences in its composition, properties and hydrocarbon generation potential. Therefore, the study of the type (property) of kerogen is an important content of oil and gas geochemistry, and also the basis of evaluating the potential of kerogen for oil generation and gas generation. Kerogen type is a parameter to measure the hydrocarbon production capacity of organic matter, and different types of kerogen also determine whether the product is mainly oil or gas. In general, type I kerogen and type II kerogen mainly produce oil, and type III kerogen mainly produces gas. Looking at the types of shale kerogen in shale gas basins in the United States, mainly type I kerogen and type II kerogen, and some type III kerogen, and different types of kerogen shale have generated a considerable amount of gas, it is reasonable to believe that kerogen type is not the key factor in determining gas production. The abundance of dispersed organic matter and the type of hydrocarbon parent material in sedimentary rocks are the material basis of hydrocarbon generation, and the maturity of organic matter is the key to hydrocarbon generation. Only when kerogen reaches a certain maturity can it begin to produce and expel hydrocarbons in large quantities. Different types of kerogen produce different amounts of hydrocarbon in different stages of thermal evolution. At the low maturity stage (0.4% ~ 0.6%), organic matter can be transformed into hydrocarbons. The thermal maturity distribution of shale in the five major shale basins in the United States ranges from 0.4% to 2.0%, indicating that shale gas is generated in the whole process of hydrocarbon generation from organic matter. As maturity increases, the early crude oil begins to crack into gas. The large gas content of the Barnett shale in the United States is mainly due to the hydrocarbon generation volume (the result of abundance of organic matter, hydrocarbon generation potential and shale thickness), maturity, and the continuous cracking gas of some liquid hydrocarbons. The less mature the Barnett shale, the lower its gas production, probably because there is less gas and the flow of residual hydrocarbons clogs the pores. The pyrolysis of kerogen and oil in many high maturity Barnett shale areas has greatly increased the gas production, resulting in large gas flow in shale gas Wells. Therefore, maturity is a key geochemical parameter to evaluate the similarity of high flow shale gas.
[1]
1. Porosity
In conventional reservoirs, porosity is an important aspect to describe reservoir characteristics. The same is true of shale reservoirs. As a reservoir, shales often show low porosity (<10%), but can also have large porosity and store large amounts of free gas in these pores, even in older formations, free gas can fill up to 50% of the porosity. The free gas content is closely related to the pore volume. In general, the larger the pore volume, the greater the free gas content.
[1]
2. Crack development
The mineral composition of shale is relatively complex, with high quartz content, mostly in the form of clay grains, and often in the form of laminae, while the shale with high organic matter and quartz content is more brittle, easy to form natural cracks and induced cracks under the action of external forces, which is conducive to natural gas seepage, indicating that lithology and rock mineral composition are the main internal factors controlling the development degree of cracks.
[1]
Due to the characteristics of low porosity and low permeability of shale, gas production is not high, and those open rectangular natural fractures make up for this deficiency, greatly improving shale gas production. The seepage capacity of shale is improved by fracture, which is not only a reservoir space, but also a seepage channel, and a necessary way for shale gas to flow into the bottom of the well from the matrix pores. Not all high-quality source rocks can form fractured hydrocarbon reservoirs with economic exploitation value, only those fragile shale with low Poisson ratio, high elastic modulus and rich in organic matter are the primary exploration targets for shale gas resources.
[1]
3. Organic carbon content
In fractured shale gas systems, there is a linear relationship between the gas adsorption capacity of shale and the total organic carbon content of shale.
[1]
Under the same pressure, the methane adsorption capacity of shales with higher total organic carbon content is significantly higher than that of shales with lower total organic carbon content. In addition to being adsorbed on the surface of organic matter, shale gas can also be adsorbed on the surface of clay (dry). At close to the same organic carbon content and pressure, the amount of gas adsorbed by shales with high clay content is higher than that of shales with low clay content. And as the pressure increases, so does the gap.
[1]
4. Formation pressure
Formation pressure is also one of the factors affecting shale gas production. The research shows that formation pressure has a positive correlation with adsorbed gas, and the higher the formation pressure, the greater the adsorption capacity of shale, the higher the adsorbed gas content. The free gas content also increases with the increase of pressure, and the relationship between the two is basically linear. It is worth noting that before the pressure of 6.89MPa, the adsorption gas content increases significantly with the pressure, but after it, the increase is not obvious, similar to the conventional tight gas reservoir. Of course, the pressure gradient in different regions will also be different due to the difference in organic matter content and the storage capacity of surrounding rock.
[1]
In addition to the above factors, the type and maturity of organic matter will also affect the content of shale gas.
[1]
Shale gas has experienced complex and variable accumulation process, and is an important component and typical representative of natural gas accumulation mechanism sequence. According to different accumulation conditions, shale gas accumulation can be characterized by typical adsorption mechanism, piston migration and accumulation mechanism or displacement migration and accumulation mechanism. According to the different accumulation mechanism, the gas accumulation process can be divided into three main stages, and the first two stages are the shale gas accumulation process.
[7]
Reservoir forming process
The second stage is the formation and discharge of natural gas. This stage is at the peak of gas generation, which is similar to the formation mechanism of root gas. As a large amount of natural gas is generated, organic carbon in shale cannot completely adsorb it, so unadsorbed natural gas accumulates in the shale in a free state. With the continuous formation of shale gas, a large amount of free gas gathered will expand and form a high pressure until the rock formation cracks and produces micro-cracks. The cracks, or pores, created at this time are so small that shale gas cannot flow freely through the shale. Under the action of strong hydrocarbon generation, that is, gas expansion force, shale gas is expelled and promoted from the high pressure area at the bottom to the relatively low pressure area at the upper part along the upward tilt of the structure, so that the formation is in the state of containing gas in a large area. The natural gas generated at this stage is not subject to buoyancy and exhibits a piston-type migration and accumulation characteristic (Figure B).
[7]
The third stage is the displacement and migration of natural gas. If the natural gas generation continues to increase and there is a suitable reservoir outside the shale, the natural gas will migrate from the shale to the reservoir in a displacement manner along the fracture under buoyancy, thus forming a conventional gas reservoir (Figure C).
[7]
In the process of shale gas accumulation, adsorption mechanism and piston migration and accumulation mechanism work together to control the spatial proportion of adsorbed and free gas in shale gas reservoir. Therefore, the accumulation mechanism of shale gas is essentially the dynamic balance between the occurrence states of natural gas in shale pores. The existence of adsorbed natural gas in shale is determined by the characteristics of the rock contained in it, and has no direct relationship with the preservation conditions, so there is no special requirement for the preservation conditions after the formation of shale gas. The gas anomalies detected in Marine strata in Sichuan Basin also confirm that even multi-stage tectonic movements do not have much influence on shale gas reservoirs.
[7]
Chinese scholars started the study of shale gas relatively late. The earliest report on shale gas in China appeared in the 4th issue of "Foreign Logging Technology" in 1996. But it was not until 2002 that many scholars in China began to pay attention to shale gas after the classic article "Fractured Shale-Gas systems", which was translated by Li Darong and others from J.B.Curtis, was published.
[7]
Professor Zhang Jinchuan directs the drilling of Pengshui, the first shale gas well
In April 2012, the daily output of shale gas from Wufeng Formation and Longmaxi Formation of Well Ning 201-H1 in Changning area was 15×10
4
Cubic meters, achieving a breakthrough in the commercial development of shale gas exploration in China. In November of the same year, Sinopec achieved a daily output of 20.3×10 shale gas in the Wufeng Formation and Longmaxi Formation in Jiaoshiba area, Fuling, southeast Sichuan
4
Cubic meter.
[8]
In 2014, it submitted China's first proven geological reserves of shale gas 1067.5×10
8
Cubic meter. By the end of 2017, Fuling shale gas field has accumulated proven geological reserves of more than 6000×10
8
Cubic meter. Accumulated shale gas production capacity of 100×10
8
Cubic meters, shale gas annual output of 60.4×10
8
Cubic meter.
[8]
Through exploration and development practice, Chinese scholars have successively proposed the "dual enrichment" law of Marine shale gas in complex structural areas, and the "tectonic sweet spot" and "continuous sweet spot" shale gas enrichment modes. The exploration and evaluation technology system of Marine shale gas selection and target optimization is becoming more and more mature. The development techniques of shale gas reservoir description, productivity evaluation and development parameter optimization have been preliminarily formed. The technologies and processes of optimal and rapid drilling of horizontal Wells, pump-plug cluster perforation stage fracturing, synchronous fracturing, and zipper fracturing are becoming more and more mature, and have the technical ability to develop shallow Marine shale gas at 3500 meters. The operation mode of mountain well factory is formed, which greatly improves the construction efficiency. Compared with single platform and single drilling, the drilling and well construction cycle is shortened by more than 30%. A clean production technology system for recycling and harmless treatment of waste residue, waste liquid and waste gas has been formed. In the development of key fracturing equipment, the formation of 3000 type fracturing truck with independent intellectual property rights, the establishment of domestic high-power fracturing unit research and development, testing, manufacturing system and application specifications; The self-developed open-hole packer, bridge plug and other downhole fracturing tools have achieved industrial mass production. Taking the exploration and development of Fuling shale gas field as an example, more than 100 technical standards and norms have been formed, and 39 national patents have been authorized, including 12 invention patents. China's scientific and technological progress in the field of shale gas has been highly concerned and recognized by the global industry. In 2014, the Fifth World Shale Oil and Gas Summit awarded Chinese enterprises the "Shale Oil and Gas International Pioneer Award", and in 2018, the project "Efficient Exploration and development of Fuling Large Marine shale Gas Field" won the first prize of National scientific and Technological Progress.
[8]
In October 2022, Jiaoye 18-S12HF well in Fuling shale Gas Field, Jianghan Oilfield, Sinopec was successfully completed with a drilling depth of 7,161 meters, including a horizontal section length of 4,286 meters.
Major breakthroughs have been made in the drilling of ultra-long horizontal Wells for shale gas
[25]
.
Global shale gas resources are very rich and widely distributed, according to the United States National Petroleum Council (NPC) statistics, as of the end of 2009, the global shale gas resources of about 456.2 trillion cubic meters, accounting for nearly 50% of the global unconventional gas resources, comparable to conventional natural gas, shale gas resource potential may even be significantly greater than conventional natural gas. It is mainly distributed in North America, Central Asia and China, the Middle East and North Africa, Pacific countries, Latin America, and other regions (see table below).
[3]
|
Estimated shale gas resources in major regions of the world
|
||
|
district
|
Resources/trillion cubic meters
|
Global proportion /%
|
|
North America
|
108.79
|
23.8
|
|
Central Asia and China
|
99.9
|
21.9
|
|
Middle East and North Africa
|
72.15
|
15.8
|
|
Pacific countries
|
65.5
|
14.4
|
|
Latin America
|
59.95
|
13.1
|
|
Other regions
|
49.94
|
11
|
Among them, North America has the most, but its abundance is low, and the proportion of technical recoverable resources in the total resources is low. At the same time, shale gas reservoirs are characterized by low porosity and low permeability, which makes it difficult to exploit and requires high-level drilling and completion technology. in
21st century
At the beginning of shale gas exploitation, horizontal drilling technology and water-based hydraulic fracturing technology are used to improve oil recovery.
[7]
The 48 states of the United States are widely distributed in organic shale and have rich shale gas resources. According to the estimates of the National Oil and Gas Resources Board, the total amount of shale gas resources in the United States is about 14.2 trillion to 19.8 trillion cubic meters, and the recoverable resources are about 3.62 trillion cubic meters. By the end of 2008, the proved shale gas reserves in the United States were 928.9 billion cubic meters.
[3]
European shale gas reserves of up to 15 trillion cubic meters, Sweden's alum schist, northern Germany, the Netherlands and southern England's Porcedonian schist, and so on, are similar to American shale. The shale in Europe is mainly black or dark brown, indicating that the formation of the rock was rich in organic material from organisms growing in the soil, and much of this organic material became shale gas. If confirmed, the shale deposits could change the fate of European countries that have long relied on Russian gas. At present, the EU member states get a quarter of their gas supply from Russia. Latin American shale gas resources are mainly concentrated in Argentina, Mexico and Brazil.
[3]
China is rich in shale gas resources, but the development is still in the initial stage. The state is actively promoting the development and utilization of shale gas.
[9]
In 2018, the working group for Mineral Resources Protection Supervision of the Ministry of Natural Resources revealed that from September 2014 to April 2018, in less than four years, the cumulative new proved geological reserves of shale gas in China exceeded trillion cubic meters, the production capacity reached 13.5 billion cubic meters, and the cumulative gas production was 22.580 billion cubic meters. From September 2014 to April 2018, in less than four years, the four integrated shale gas fields of Fuling, Weiyuan, Changning and Weirong in the Sichuan Basin have been proved, with the cumulative new proved geological reserves of shale gas exceeding trillion cubic meters, the production capacity reaching 13.5 billion cubic meters, and the cumulative gas production reaching 22.580 billion cubic meters.
[10]
Although shale gas exploration in China is still in its infancy, the preliminary comparison of reservoir formation conditions shows that many basins in China have similar geological conditions to shale gas reservoirs in the eastern region of the United States, so the exploration potential is huge. China's shale gas development areas can be divided into four regions roughly corresponding to the plate, namely, the southern region, the central and eastern regions, the northwest region and the Qinghai-Tibet region, which have good shale gas exploration prospects (see figure).
[7]
There are 8 sets of source rocks mainly composed of black shale in the Yangtze platform area of South China: Upper Sinian Doushantuo Formation, Lower Cambrian Qiongzhusi Formation, Upper Ordovician Wufeng Formation - Lower Silurian Longmaxi Formation, Middle Devonian Luofu Formation, Lower Carboniferous Hezhou Formation, Lower Permian Qixia Formation, Upper Permian Longtan and Dalong Formation, and Lower Triassic Qinglong Formation. The above formations have wide distribution, shallow burial, large thickness, rich organic matter, high maturity, and superior shale gas accumulation conditions, so they are favorable areas for shale gas development and have great exploration potential. The Sichuan Basin has experienced complex tectonic changes during the evolution of cratonic and foreland basins, forming structural evolution characteristics and geological conditions similar to those of typical shale gas basins in the United States. Its lower Paleozoic source rocks are characterized by wide distribution, large thickness, high maturity, microfracture development, and strong hydrocarbon generation by organic matter, and there is a large amount of evidence showing that there is abundant shale gas in the basin. For example, the black graptolite shale of the Lower Silurian Longmaxi Formation is the most developed in this basin, and the analysis and test data of the newly drilled shale gas shallow well in the southern Changning structure also confirm that the Longmaxi Formation has the favorable conditions for forming shale gas reservoirs. The shale gas resources of Longmaxi Formation in Sichuan Basin and adjacent areas are estimated to be 4.0×10 by volumetric method
8
~ 12.4 x 10
8
Cubic meters, showing the huge exploration potential of shale gas in this area; In 2009, Yuye 1, the first shale gas strategic survey well drilled in Pengshui, Chongqing, showed a good shale gas display. The later experimental analysis results of Yuye 1 well also showed that the high steep structural belt with complex geological conditions in southeast Chongqing has good geological conditions for shale gas accumulation. At the same time, it also indicates that the upper Yangtze and even the whole Yangzi area may be a favorable potential area for shale gas development. Therefore, in general, the Lower Cambrian Series and Lower Silurian Series shale in eastern and southern Sichuan (including southwest Sichuan) have the greatest potential, while the West Oroq-East Chongqing region and even the whole Middle and Lower Yangtze region are important areas for shale gas distribution.
[7]
The shale gas in the central and eastern regions may be distributed at the bottom of the main oil and gas reservoirs, from the Mesozoic to the Paleozoic. The Cretaceous shales in Songliao Basin, Triassic in Ordos Basin and shallowly buried paleogene shales in Bohai Bay Basin are all conducive to the development of shale gas. Among them, the Mesozoic shale in Ordos Basin is buried less than 3 kilometers deep, the thickness is more than 5 meters, and the organic carbon mass fraction is more than 2%, which is very favorable to the development of shale gas. Constrained by the characteristics of present basins, the Jurassic, Triassic and shallowly buried Paleozoic mud shales in the northwestern region have large thickness and organic carbon content, and have shale gas exploration potential. The meso-Paleozoic mud shale strata in Qinghai-Tibet area have large thickness, high organic matter content and moderate thermal evolution of organic matter, which also have shale gas exploration potential.
On August 24, 2018, natural gas resources within Earth's shale formations were comparable to recoverable reserves of conventional natural gas. "Although China's shale gas development started late, it is the third country to form a scale and industry after the United States and Canada, and the output can reach 10 billion cubic meters of energy in the near future." Zhang Dawei, one of the earliest experts on shale gas in China and director of the Mineral Resources Reserve Review Center of the Ministry of Land and Resources, said so.
[11]
In June 2022, the Ministry of Lithology of China tested 530,000 cubic meters of shale gas per day at Xinye 1 well in Qijiang, Chongqing.
[21]
In July 2022, Sinopec Jianghan Oilfield news, Hubei Enshi Hongxing area shale gas reserves declaration through the review of SINOPEC, the implementation of the control reserves of 62.1 billion cubic meters, the completion of the annual reserves of 124% of the task, marking the Permian shale gas exploration and evaluation in the area again made important progress.
[22]
On October 19, 2022, the reporter learned from the press Office of Sinopec that the Jinshi 103HF exploration well deployed by the Southwest Petroleum Bureau of Sinopec in the Sichuan Basin achieved high and stable production industrial gas flow, with a daily output of 258,600 cubic meters of natural gas, and the evaluation and implementation of geological resources of 387.8 billion cubic meters. This is the first major breakthrough in shale gas exploration in the Cambrian Qiongzhusi formation in China, opening up a new position of shale gas storage on a large scale, which is of great significance for promoting shale gas exploration and development in Sichuan Basin.
[23]
On November 24, 2022, SINOPEC news, submitted by Sinopec Exploration Branch and Southwest Petroleum Bureau, the first proved geological reserves of the Qijiang shale gas field of 145.968 billion cubic meters were approved by the expert group of the Ministry of Natural Resources, marking the birth of another large shale gas field of more than 100 billion cubic meters.
[26]
There are five conditions in the core area for economic development of shale gas, which usually refers to effective shale with TOC value greater than 2%, in the gas window, and brittle mineral content greater than 40%. The effective shale thickness is about 30 to 50 meters. The effective shale is more than 30 meters in continuous development, intermittent development or TOC value is less than 2%, and the cumulative thickness is more than 50 meters to meet the requirements of commercial development.
[12]
Shale gas development
Compared with conventional natural gas, shale gas reservoirs are generally characterized by low porosity and low permeability, and the permeability is usually less than 1×10
3 -
μm,
porosity
The highest is only 4%~5%, the airflow resistance is larger than that of conventional natural gas, and the reservoir hydraulic fracturing can be exploited. The use of hydraulic fracturing and horizontal well technology can greatly improve the production of shale gas reservoirs in shale reservoirs.
[13]
1. Vertical well technology
Vertical well is the main means of shale gas exploitation in early stage. When drilling shallow Wells less than 1000 meters, the underbalance rotary punching method with faster drilling speed is generally used, which can effectively reduce the damage to the formation. When drilling 1,000 to 2,500 meters deep, the light drilling fluid while drilling conventional rotary drilling method.
[14]
2. Horizontal well technology
With the great success of seven horizontal test Wells in the Barnett shale formation in the Fort Worth Basin of Texas in 2002, horizontal Wells were vigorously promoted in the industry and quickly became the main drilling method for shale gas production.
[14]
Horizontal Wells improve the possibility of contact with fractures in the shale and increase the contact area with gas in the reservoir. Meanwhile, horizontal Wells reduce surface facilities, have a large mining extension range, and avoid interference from adverse surface conditions. The output is 3 to 5 times that of vertical Wells.
[13]
At present, the main horizontal well drilling technologies in China include controlled pressure drilling, low pressure underbalanced air drilling and rotary steerable drilling. Controlled pressure drilling technology can overcome the problem of wall collapse well. The application of low pressure underbalanced air drilling technology is mature, rotary steering drilling technology, good hole purification effect, high accuracy of well trajectory control, strong displacement extension ability, is an important direction of the development of horizontal drilling technology. Domestic shale gas horizontal well completion technology has been developed to a certain extent, the main completion technology includes: hydraulic jet perforation completion, combined bridge plug completion, mechanical combination completion technology. Combined bridge plug completion is the most commonly used and time-consuming method for shale gas completion. In casing Wells, the combined bridge plug is used to separate each section for perforation and fracturing. For example, the hydraulic jet perforation completion is to shoot the fluid at high speed through the casing and rock, without using the packer and bridge plug, which can shorten the completion time. The mechanical combination completion uses a special sliding sleeve mechanism and inflatable packers for limited-flow fracturing in horizontal open hole sections. Cementing and fracturing can be performed in a single string trip.
[9]
Compared with vertical Wells, although the construction cost of horizontal Wells is higher, because it can significantly increase the contact area with fractures in the shale rock, effectively improve the flow state of shale gas in the reservoir, and increase the gas output rate, the initial production rate of horizontal Wells is 2 to 3 times higher than that of vertical Wells in terms of controlled reserves and final evaluation of recoverable reserves.
[14]
3. Fracturing stimulation technology
Due to the ultra-low permeability and low porosity of shale gas reservoirs, horizontal Wells need to undergo multistage large-scale hydraulic fracturing to ensure the economic production of shale gas reservoirs. Fracturing stimulation technology is one of the core technologies for the successful development of shale gas.
[13]
According to the fracturing medium, it can be divided into foam fracturing and hydraulic fracturing.
1. Foam fracturing. The fracturing method using liquid nitrogen or carbon dioxide foam as fracturing agent is generally used in shale reservoirs with shallow burial depth and low formation pressure. It has the advantages of high fracture-forming efficiency, low filtration loss, strong sand carrying and flowback capacity, low friction coefficient, and little damage to the reservoir. However, it requires high injection pressure, simple fracture form, difficult to provide more channels for gas migration, and expensive.
[14]
2. Hydraulic fracturing. With water as fracturing agent, it is often used in reservoirs with large buried depth and high formation pressure, and the demand for proppant is less, there is no need for surfactants and stabilizers, and there is little need for pump to pressurize, so the cost is low. Hydraulic fracturing (FRacking) is a clean fracturing technique that cleans cracks and increases the permeability of the reservoir to a certain extent.
[14]
According to the fracturing method, it can be divided into the following types.
1. Horizontal well staged fracturing. In other words, multi-stage fracturing operations are carried out on relatively long horizontal Wells to form multiple hydraulic fractures and effectively increase the fracture network to increase gas production. Staged fracturing can reduce costs, especially when combined with pre-fluid drilling, which minimizes time and costs for mobilization, dissolution, material handling, preparation time, and downtime between pumping operations.
[14]
2. Repeat fracturing. Over time and with the release of pressure, the proppant sustained fractures formed during the initial fracture will gradually close, resulting in a significant reduction in shale gas production. Refracturing is the re-fracturing of shale reservoirs to restore production capacity.
[14]
3. Simultaneous fracturing. Synchronous fracturing is usually performed by two or more Wells at the same time or interactively. It uses the principle that fracturing fluid and proppant travel the shortest distance between two Wells under high pressure to increase fracture density and area, so as to achieve the purpose of stimulation.
[14]
The horizontal well development experience accumulated in the conventional oil and gas field for several decades in China has also accelerated the current domestic shale gas technology development process. Horizontal well hydraulic fracturing technology is widely used in conventional oil and gas development in China, especially multistage fracturing technology, repeated fracturing technology, water fracturing technology, there are many successful applications.
[13]
China has made certain breakthroughs in horizontal well staged fracturing technology, and has formed three major technologies, namely double-seal single-card staged fracturing, hydraulic sandblasting staged fracturing and packer sliding sleeve staged fracturing for horizontal Wells in low permeability oil and gas fields. Four supporting technologies, including self-turning high-efficiency acidizing/acid pressing, chemical temporary plug staged fracturing, hydraulic fracture monitoring and evaluation and horizontal well workover operation, were improved in carbonate reservoir, and a set of fracture and well pattern optimization design methods were established. China has realized 7 horizontal well stage fracturing technology in Changqing, and introduced and absorbed 10 or more long well stage fracturing technology in Sichuan province.
[13]
Although adsorption and free phase gas exist simultaneously, shale gas development does not require it
Drain water
Reduce the pressure. Due to the production of free phase natural gas in shale, the pressure can be reduced naturally, which leads to the ionization of adsorbed phase and a small amount of dissolved phase natural gas, so as to further improve the natural gas production capacity and achieve the purpose of long-term stable production. Because the productivity and recovery efficiency of gas with low porosity and permeability are also low, the ultimate recovery efficiency of rock gas depends on effective fracturing measures. Fracturing technology and production technology have a direct impact on the economic benefits of shale gas Wells.
[15]
Some experts have mentioned
Root-marginal gas
J.a.mcasters (1979) proposed the idea of deep basin gas, established the gas-water inversion model, and described the broad prospect of natural gas exploration and development. Due to the difficulty of identification, P.R.Ose et al. (1986) proposed Basin-centergas, and B.E.Rao et al. 's research idea improved the identification method of this type of gas reservoir from "regional gas-water inversion" to "no edge water". Thus, the tedious identification process is simplified and the identification time of this kind of gas reservoir is advanced to a large extent. Because the determination of the "boundless bottom water" is still more drilling geological data, it is still not the best solution.
[15]
China's first shale gas horizontal well was successfully tested in Weiyuan gas field
Based on the dynamic principle of natural gas accumulation, the gas reservoir identification technology is advanced to a single well profile, that is, whether the gas bearing characteristics of the bottom sandstone are present and developed (completely different from the gas bearing patterns and characteristics of the top sandstone in conventional traps)
Wildcat well
Rather than pre-exploration or even development Wells, the earliest and fastest identification of gas reservoir types can be achieved. Only the gas content at the bottom of the sandstone can explain the continuity of natural gas in reservoir formation, and further explain the mechanism characteristics of natural gas accumulation, so as to determine the accumulation mechanism types of natural gas, that is, the existence of deep basin gas, central basin gas, marginal gas and even synclinal gas or full basin gas, and determine the accumulation, enrichment and distribution characteristics of natural gas.
[15]
1. Foreign development status
The world's shale gas research and exploration and development began in the United States, and the United States and Canada are currently the two major countries in the scale of shale gas development.
[3]
Shale gas is distributed in North America
Cratonic basin
Foreland basin
Jurassic system
, Devonian system,
Mississippi
The system is rich in shale gas resources of various origin and maturity.
[7]
In other countries in the world, with the deepening of shale gas exploration and development, the depth of shale gas exploration and development in North America has reached 2000 ~ 4000 meters, and the maximum is close to 6000 meters. At present, in addition to the United States and Canada, Australia, Germany, France, Sweden, Poland and other countries have also started shale gas research and exploration and development. Large oil and gas companies in many countries are looking for shale gas around the world, such as Australia, China, South Africa and Europe. Europe now has about 30-50 onshore RIGS, compared with at least 1,500 in the United States. The difference in the number of RIGS makes a qualitative difference in the production process, because shale gas needs to be continuously produced once it is produced. The initial gas production of a shale gas well is very high, and if it is not exploited quickly, 70% to 90% of the production will be lost.
[3]
The United States has entered the stage of large-scale production of shale gas, and the transaction of shale gas assets is extremely active. From January 2009 to April 2010, shale gas related M&A deals in the United States totaled $50.033 billion.
[3]
In the United States, the number of companies involved in shale gas exploration and development increased from 23 in 2005, 64 in 2007, and more than 100 in 2009. Production increased from 34 billion cubic meters in 2007 to 95 billion cubic meters in 2009, exceeding the country's annual production of conventional natural gas (83 billion cubic meters). In 2009, the United States surpassed Russia for the first time to become the world's largest producer of natural gas, thanks to a 10 percent increase in shale gas production as a percentage of total natural gas production. In its 2009 World Energy Outlook report, the International Energy Agency said the United States expects shale gas production to increase to 20 percent of its total domestic natural gas production by 2020. The US government's emphasis on shale gas development has provided a strong impetus for the development of shale gas. In addition to national policy support, the U.S. government has provided significant funding to encourage unconventional gas research and development efforts, including grants, loans and loan guarantees, training grants, research grants, and direct investment in exploration. The U.S. Energy Act of 2004 mandates an annual investment of $45 million for 10 years in unconventional gas research. According to the U.S. Energy Information Administration (EIA), shale gas production will increase significantly over the next two decades, and shale gas production will account for the United States by 2030
Natural gas
24.3% of total production.
[3]
At the beginning of this century, American companies combined horizontal Wells and fault technologies to crush the hard rock layer and extract shale gas, which greatly broke through the technical difficulties of shale gas. Fierce competition in the US oil industry forced some innovative, small energy companies to move to high technology, and their technology was bought by the big oil companies, so that shale gas was truly commercialized, and now the world's most advanced shale gas extraction technology is in the United States.
[3]
The general process of shale gas development in the United States: obtaining mineral rights → obtaining licenses → drilling → hydraulic fracturing → construction → production → improving recovery and repair techniques → gas well abandonment and reclamation.
[3]
The rapid development of unconventional gas in North America is mainly due to technological breakthroughs. Advances in horizontal drilling and hydraulic fracturing technology have improved reservoir contact, and advances in equipment technology have reduced unit production costs, especially in low-cost shallow Wells, which have made important contributions to the commercial exploitation of shale gas. Shale gas technology in the United States and Canada has matured and entered the stage of large-scale production.
[3]
2. Domestic development status
Changning block of Changning - Weiyuan shale gas Demonstration zone
From November 13 to 16, 2012, the four-day China International Shale Gas Conference 2012 was held in Chongqing, with the theme of "Promoting investment and cooperation to promote the commercial development of China's shale gas industry". More than 200 shale gas resource developers, buyers, traders, technical support providers, oilfield service and equipment suppliers, leading shale gas industry research experts and government advisors from around the world attended the conference. At the meeting, Li Yuxi, a researcher at the Strategic Research Center of Oil and gas Resources of the Ministry of Land and Resources, revealed that a number of policies to support shale gas industrialization are in the pipeline. This series of support policies mainly include: first, the market-oriented pricing policy of shale gas, while the use of shale gas can be flexible; Second, the regulatory system emphasizes first-level management, and is actually divided into two and three levels of supervision, that is, the supervision system that allows provinces and levels to participate in the management, so that the entire regulatory process extends down to shale gas Wells; Third, the tax will leave most of the profits and taxes to the localities, so as to benefit both enterprises and localities.
[16]
Although the industry's attention to China's shale gas continues to heat up, the industry experts participating in the "2012 China Shale Gas Development Forum" believe that China's shale gas development still faces some problems to be solved, including technical preparation, resource reserves evaluation, policy research to development models, etc., need to learn from the successful experience of the United States, can not rush to success.
[16]
Wang Yan, deputy director of the China Geological Survey, pointed out at the "2019 National Geological Survey Work Conference" on the same day that last year, the Yiyangye 2 well in Yichang, the middle reaches of the Yangtze River, obtained high-yield industrial gas flow, realizing the strategic expansion of China's shale gas exploration and development from the upper reaches of the Yangtze River to the middle reaches.
[17]
According to the China Geological Survey, there are high production shale gas flows in the Sinian, Cambrian and Silurian geological strata in western Hubei. First, the lower Sinean Eyang Page 2 well has a high output of 55,300 cubic meters/day and an open flow rate of 198,200 cubic meters/day, which is the oldest shale gas reservoir in the world so far, providing a new set of layers for China's shale gas exploration to the deep. Second, the central Cambrian Yiye 1 well obtained a production of 60,200 cubic meters/day, open flow 123,800 cubic meters/day of high-yield industrial air flow, Yiyang page 1 well obtained a production of 78,300 cubic meters/day, open flow 288,500 cubic meters/day of high-yield industrial air flow, is the first time outside the Sichuan Basin to obtain industrial air flow in this layer, opening up a new exploration area. Third, the upper part
Silurian system
The 500-meter horizontal section of well Eyiye 2 produced 31,500 cubic meters/day of industrial air flow with an open flow rate of 57,600 cubic meters/day, which realized the expansion of the main shale gas development system in China from the upper reaches of the Yangtze River to the middle reaches.
[17]
China Geological Survey pointed out that the shale gas survey in western Hubei has innovated the theory and exploration technology of shale gas accumulation. In response to world-class problems such as old formation age, difficult reservoir reconstruction, low formation pressure, and difficult gas recovery, three major technical systems have been innovated to form constituency evaluation, drilling engineering and fracturing gas testing. Among them, the three technologies of complex zone selection evaluation, reservoir fracturing reconstruction and fracturing gas test have reached the international leading level.
[17]
Shale gas resource potential evaluation shows that the shale gas geological resources in western Hubei area of China reach 11.68 trillion cubic meters, with an annual capacity of 10 billion cubic meters of resource base. Kang Yuzhu, academician of the Chinese Academy of Engineering, and other 11 experts believe that the results of the shale gas investigation in western Hubei are a strategic breakthrough and have a landmark leading role, and the results have generally reached the international advanced level, and some have reached the international leading level.
The Shale Gas Development Plan (2016-2020) released by the National Energy Administration proposes to innovate the system and mechanism, attract all kinds of social capital, and expand shale gas investment. Through technology research, policy support and market competition, the production of shale gas has been greatly increased, and shale gas has become an important part of China's natural gas supply.
[18]
The plan pointed out that with the shift of China's economic growth, as well as the deep decline in the price of traditional fossil energy such as oil and coal, the competitiveness of natural gas has declined, and the growth rate of consumption has slowed down significantly. Domestic natural gas production has grown steadily, and a series of long-term natural gas import agreements have been signed between China and Russia, which will significantly increase the supply capacity of natural gas in the future. According to the current energy consumption structure, the supply of natural gas during the 13th Five-Year Plan period is generally sufficient. Shale gas is more expensive to develop than conventional natural gas, and it is more difficult to develop the market.
[18]
In terms of development goals, the plan is clear, improve and mature the exploration and development technology of 3,500 meters shallow Marine shale gas, break through the exploration and development technology of 3,500 meters deep sea shale gas, continental and Marine and land transition shale gas; With the policy support in place and the smooth development of the market, we will strive to achieve 30 billion cubic meters of shale gas production in 2020.
[18]
The plan also looks forward to the 2030 development goals: During the "14th Five-Year Plan" and "15th Five-Year Plan" period, China's shale gas industry will accelerate the development, a number of new large shale gas fields will be discovered, and large-scale and effective development will be achieved, and shale gas production will reach 80 billion to 100 billion cubic meters by 2030.
[18]
The plan is clear, encouraging the combination of independent development and foreign cooperation, actively introducing advanced and applicable technologies, supporting joint venture and cooperative development by various investors, and striving to increase investment in exploration and development. At the same time, improve the entry and exit mechanism of shale gas blocks, increase investment subjects, strengthen market competition, promote the upgrading of engineering technology, accelerate cost reduction, and improve the economy of shale gas development. In addition, in view of the immature engineering technology, high exploration and development costs, and low economic benefits in the initial stage of shale gas development, relevant support policies should be improved to ensure the sustainable development of the industry.
[18]
In October 2022,
The Jinshi 103HF exploration well deployed by the Southwest Petroleum Bureau of Sinopec in the Sichuan Basin achieved high and stable production of industrial gas flow, with a daily output of 258,600 cubic meters of natural gas and an estimated geological resource of 387.8 billion cubic meters.
This is the first major breakthrough of shale gas exploration in the Cambrian Qiongzhusi formation in China, and opens up a new position of shale gas storage on a large scale
[24]
.
In November 2022, it was learned from the Press Office of Sinopec that the exploration and development of the Qijiang shale gas field in Sichuan Basin achieved a major breakthrough. The first proved geological reserves of the Qijiang shale gas field submitted by Sinopec Exploration Branch and Southwest Petroleum Bureau were 145.968 billion cubic meters. The reserves were approved by the expert group of the Ministry of Natural Resources. It marks the birth of another large integrated shale gas field of more than 100 billion cubic meters in China. Among them, Xishui County in Guizhou Province added 35.50 square kilometers of proved gas bearing area, and added 33.048 billion cubic meters of proved geological reserves.
[27]
The first is the formulation of China's shale gas resources strategic investigation and exploration and development of medium and long term development plan. On the basis of careful analysis of the world shale gas exploration and development situation and China's current situation, the scientific evaluation and analysis of China's shale gas resource potential, the proved reserves of shale gas trend prediction research, the strategic investigation of China's shale gas resources and exploration and development objectives, priorities and development stages of scientific planning, clear development positioning. To formulate medium - and long-term development plans for shale gas resources strategic survey and exploration and development.
[19]
Shale gas development
The third is to improve and innovate the management system of shale gas mining rights. According to the characteristics of wide distribution of shale gas and strong flexibility of exploration and development, the establishment system of shale gas mining rights in China is deeply studied. Drawing on the management experience of coal-bed methane mining rights, a special registration system for shale gas blocks will be established to implement national management. Qualified local enterprises and private capital are allowed to participate in shale gas exploration and development through joint ventures, shares and other ways, and can also invest independently and directly engage in shale gas exploration and development.
[19]
Fourth, speed up the development of shale gas technical standards and norms. Strengthen government guidance, relying on the implementation of major projects of shale gas resource strategic survey and pilot exploration and development zones, accelerate the construction of technical standards and norms for shale gas resource strategic survey and exploration and development, and promote information sharing and standardized management.
[19]
In addition, we should pay close attention to the development trend of shale gas in the world, and establish and improve the international cooperation and exchange mechanism of shale gas. Strengthen the cooperation and development with foreign powerful companies, introduce advanced concepts and development technology, explore and innovate the core technology suitable for China's shale gas development through the introduction and digestion of shale gas development technology, and lay the technical foundation for China's shale gas large-scale development.
[19]
1. Shale gas is a clean and efficient energy source
With the development of social economy, energy conservation and emission reduction have become a common concern of the world, which requires increasing the use of clean and efficient energy. Shale gas is a natural gas with methane as its main component and in the form of unconventional natural gas. As a clean and efficient energy resource and chemical raw material, shale gas can be widely used in residential gas, heating, power generation, automotive fuel and chemical production.
[5]
2. Shale gas reserves are particularly abundant
Especially rich reserves is one of the important reasons for the utilization and development of shale gas. China's shale gas resources are very rich, the amount of resources is in the forefront of the world, the economic value is huge, and the resource prospects are broad (see figure).
The exploration and development of shale gas in China is in the initial stage. However, with the development of mining technology, shale gas will play a very important role in the energy supply structure of our country.
[5]
3. Help to improve China's energy consumption structure
For a long time, China has been taking coal as the main energy. Natural gas in the proportion of primary energy is still too low, now vigorously develop natural gas is an inevitable choice for China to ensure energy supply and develop low carbon economy.
[5]
It is estimated that with the adjustment of China's energy structure and utilization mode, the proportion of natural gas in China's energy consumption structure will increase to more than 10% in 2020. Compared with coal, natural gas is cleaner, so the country will further promote the use of natural gas in the future. However, the growth potential of conventional natural gas is always limited, which requires more exploration and development of unconventional natural gas such as shale gas.
[5]
Accelerating the exploration, development and utilization of shale gas has many values. It plays an important role in meeting the huge demand for clean energy in social and economic development, controlling greenhouse gas emissions, and building resource-saving and environment-friendly production and consumption modes. It also has important practical significance in improving residents' energy consumption environment and improving the level of ecological civilization.
[5]
4. Increase the chips for ensuring national energy security
China's dependence on foreign oil and natural gas
In recent years, the growth rate of domestic natural gas consumption demand has exceeded that of coal and oil, the external dependence has risen rapidly, and the gap between supply and demand has become increasingly large (see figure), especially the short-term imbalance between supply and demand, which has affected the safety of urban gas supply and the improvement of people's living environment. However, only relying on the increase of conventional natural gas can not effectively alleviate the contradiction between supply and demand, and it is urgent to increase the exploration and exploitation of shale gas, increase the output of shale gas in China, and form an effective supplement to conventional natural gas.
[5]
The development of shale gas is not only the extraction of natural gas from shale rocks, but also the development of natural gas in the operation area while maintaining the coordination with the surrounding environment, facilities and other resources. Shale gas development is a systematic project, and every technology is important. Domestic shale gas development is faced with many problems due to its late start and lack of experience.
[7]
1. Theoretical and development technical issues
First of all, China is still weak in the basic theory and experimental research of shale gas, especially the experimental testing and selection evaluation in the early stage of exploitation. Many researches in China are limited to the macroscopic comparison of geochemical and geological data of typical shale basins in China and the United States, but the microscopic mechanism of shale gas accumulation and rock characteristics of shale have not been simulated and deeply studied. At the same time, the heterogeneity and anisotropy of shale are much stronger than that of sandstone, so the method suitable for domestic resource evaluation is still being explored.
[7]
Secondly, shale gas reservoirs have poor physical properties, extremely low permeability, and high technical requirements for later development. The exploration practice in the United States shows that the breakthrough of development technology, such as horizontal drilling, hydraulic multi-stage fracturing, repeated fracturing, synchronous fracturing and comprehensive fracture monitoring, plays an extremely important role in the rapid development of the shale gas industry. Moreover, shale gas in China is generally buried deep, which further aggravates the difficulty of its development. For example, the Lower Cambrian shale gas reservoirs in Sichuan Basin are generally buried 2~3.5 kilometers deep, while the five major shale systems in the United States are buried 0.8~2.6 kilometers deep. Therefore, China is faced with the problem of deep shale gas development.
[7]
2. Risks and economic benefits
Shale gas belongs to unconventional low-grade natural gas, which has a long development cycle, big investment and big risk. Unconventional shale gas is booming in the short term in conventional coal-bed methane. Therefore, the possibility of large-scale shale gas development investment in China is not large, and shale gas still has a long way to go from rapid development.
[7]
3. Resource and environmental protection issues
Although shale gas extraction has brought huge economic benefits, its potential environmental impact is more worrying. On the one hand, the exploitation of shale gas needs to consume a large amount of fresh water resources, which may threaten the sustainable utilization of local and regional water resources. On the other hand, the environmental pollution caused by noise, waste water containing harmful chemical substances and waste gas in the process of shale gas exploitation, as well as the great loss caused by mining accidents; At the same time, shale gas development also needs related infrastructure, such as water conservancy, roads, etc. These unfavorable factors restrict the rapid development of shale gas.
[7]
Due to the discovery and exploitation of shale gas in the United States, its basic research work is relatively complete, and the future focus will be focused on the field of shale gas development technology, that is, increasing production capacity. However, shale gas in China, which is in the initial stage of development, is facing many challenges, such as: low degree of theoretical research and exploration investigation, unbroken development technology bottleneck, high early-stage risk investment, slow return, etc. In this context, there will be the following development trend.
[7]
1. The geological theory of shale gas and its resource evaluation system are the key research contents in China in the future. The current research in China is mainly focused on explaining the geological characteristics of shale gas reservoirs, comparing the geological conditions of shale gas basins in China and the United States, and predicting the distribution of favorable shale gas resources in China. With the completion of shale gas exploration Wells in the early stage, a lot of first-hand information will be obtained, and how to make good use of these data to correctly evaluate the shale gas exploration potential in the study area will be an urgent problem to be solved. In view of the current research relies heavily on organic geochemistry, rock mineralogy and other data, lack of experimental testing and micro-mechanism research, therefore, in the future period of time, domestic research institutions will gradually pay attention to and solve these problems, laying the foundation for the later development of shale gas.
[7]
2, shale gas related development technology is the bottleneck that China must break through. The exploration practice in the United States has proved that technological progress is the key to the successful development of shale gas. Although China has the key technologies for shale gas extraction, such as horizontal well technology and hydraulic fracturing technology, due to the lack of in-depth understanding of the mechanical characteristics of shale gas rocks, there is still a gap between China and the United States in production simulation, fracturing and other production stimulation and development measures. Therefore, with the deepening of research, it is necessary to continuously improve the technical means to successfully exploit shale gas resources.
[7]
3. In the context of Sino-foreign cooperation, combining reality and adhering to innovation will be the inevitable trend of future development. At present, the relevant domestic research is still very weak, if we want to develop and utilize shale gas resources as soon as possible, we must cooperate with foreign companies with mature theory, rich experience and advanced technology to jointly develop shale gas resources. At the same time, it is necessary to combine the actual situation of sedimentary strata and structural characteristics in China to form a set of exploration and development technology suitable for China's geological characteristics to promote the development of shale gas in China.
[7]
4, After 7 years of investigation and repeated research, the scope involves Yunnan, Guizhou, Guangxi, Hunan, Hubei, Sichuan, Chongqing, Shaanxi and other provinces and regions, and finally locked the advantage area in the southeast of Chongqing, and determined a starting point from the Qijiang through Wansheng, Nanchuan, Wulong, Pengshui, Qianjiang, Youyang, Xiushan development route; In other words, China's shale gas development will start from Qijiang to the whole country.
[7]
5. In view of the huge potential of shale gas resources and its important strategic position in unconventional energy, the state will gradually increase its support. The important role that the successful exploitation of shale gas in the United States has played in easing its domestic energy tensions has given China a new dawn in resource replacement. China's shale gas resources are rich and promising, and once the production capacity is formed, it is bound to ease the pressure on domestic energy.
[7]
