In the history of oil and gas exploration and development in the past 150 years, people have been wondering whether oil and gas resources will be exhausted soon. Practice has proved that oil and gas reserves and production are still increasing every year. Unconventional oil and gas is a hot spot of exploration in recent years and has played an important role in exploration and development.
Unconventional oil and gas and its geological characteristics have long been noticed abroad (Table 1-5), most of which belong to continuous oil and gas. The earliest recognized continuous gas reservoir belongs to tight sandstone gas reservoir, which was discovered in San Juan Basin in the United States on 1927 and put into development in the early 1950s. It was called subtle gas reservoir at that time. In 1950, Silver mentioned two important characteristics of the basin: the lack of edge and bottom water and the common gas in Cretaceous. In 1970s, many researchers explained various mechanisms of this special type of gas reservoir, and put forward the viewpoints of isolated (pore) gas reservoir, stratigraphic-diagenetic gas reservoir, hydrodynamic gas reservoir and water-sealed gas reservoir. From 65438 to 0976, Elm Voss giant deep basin gas reservoir was discovered in Alberta basin in western Canada. From 65438 to 0979, masters put forward the concept of deep basin gas based on the analysis of Elm Worth, milk River and Blanco gas fields. 1986, Rose and others first used the term "basin central gas" when studying Raton basin. Lao et al studied "tight sandstone gas". In 1995, the United States Federal Geological Survey put forward the concept of "continuous oil and gas accumulation" (Schmoker, 2005), emphasizing that continuous gas reservoirs are atmospheric reservoirs that are not strongly affected by water columns, and gas enrichment is not directly related to the buoyancy of water to gas, and is not composed of discrete and countable gas fields delineated downward by the gas-water interface. In 1996, Schmoker formally used the concept of "continuous gas reservoir". In 2006, the United States Federal Geological Survey proposed that deep natural gas, shale gas, tight gas sand, coalbed methane, shallow microbial gas sand and natural gas hydrate (methane hydrate) are six kinds of unconventional natural gas, which are collectively called continuous gas.
The "unconventional" meaning in the concept of unconventional oil and gas refers to some oil and gas that cannot be completely explored, developed and processed by conventional methods and technologies at present. It is mainly divided according to some special standards, such as the maximum matrix permeability, special regulatory status, areas that need special technology or are difficult to enter (such as polar regions or deep waters), but these standards will change with the progress of the oil and gas industry (Schmoker, 2002), and different people have different views on it. The general geological characteristics of continuous oil and gas reservoirs are: lack of obvious caprocks and traps, diffuse oil or gas-rich, widely distributed, low permeability of reservoir matrix, abnormal pressure and close to source rocks; Its exploitation features are: low recovery ratio, lack of real empty wells, development by fracture permeability and relatively high yield "dessert", but occasionally "success or failure theory" appears in drilling (Schmoker et al., 1996). Although all wells drilled into continuous oil (gas) reservoirs will encounter oil (gas) reservoirs, many wells may lack economic value (Schmoker, 2005).
The research and exploration of unconventional oil and gas in China started late. After 1990s, the concepts of deep basin gas (Jin Zhijun et al., 2003), deep basin oil (Hou et al., 2006) and syncline oil (Wu et al., 2007) appeared in China. Zou Cai (2009) put forward the concept of "continuous reservoir (field)" for unconventional resources such as Qinshui coalbed methane, Sichuan shale gas, Sichuan-Shaanxi tight sandstone gas, Songliao and Ordos tight oil, South China Sea gas hydrate, and revealed its migration, seepage and accumulation mechanism.
Since 2 1 century, with the extension of oil exploration from conventional oil and gas reservoirs to unconventional oil and gas reservoirs, unconventional oil and gas geology research has been paid more and more attention. In recent years, remarkable progress has been made in unconventional oil and gas geology research, mainly in the study of spatial microstructure of oil and gas reservoirs, and the scale of reservoir research has expanded from micron level to nanometer level. The research shows that there are mainly three kinds of nano-scale pores in shale: organic matter, intergranular pores and intragranular pores, and the permeability is extremely low.
Second, the strategic position of unconventional oil and gas.
Unconventional oil and gas reservoirs are the main exploration fields in the future. According to the statistics of the US Federal Geological Survey and the US Department of Energy, the total scale of unconventional oil resources in the world is 4495× 108t, of which shale oil is 2770× 108t, natural asphalt is 1067× 108t and heavy oil is 658× 108t. The global unconventional oil production has risen rapidly, nearly doubling from 200 1 in 2008, and has exceeded 6000× 104t (Figure 1-8). According to statistics, the total scale of unconventional natural gas resources in the world is 3922×10/2m3, including 3000×10/2m3 of hydrate, 456×1065438 of shale gas and 02m3 of coalbed methane. The global unconventional natural gas production is rising rapidly, accounting for 18% of the natural gas production (Figure 1-9).
Figure 1-8 Global Unconventional Oil Production Changes
North America is in a leading position in the exploration and development of unconventional oil and gas. The contribution and growth trend of unconventional oil and gas to its oil and gas reserves and output reflect the position of unconventional oil and gas in the future oil and gas strategy. From 2000 to 2008, the discovery of tight sandstone gas and shale gas reservoirs on the North American platform (Table 1-6) was a major breakthrough in global oil and gas continuous acquisition (Hilletal. , 2007). The tight sandstone gas, coalbed methane and shale gas resources in the United States have achieved large-scale commercial production, and the output in 2009 reached 1.890× 1.08 m3, 576× 1.08 m3 and 930× 1.08 m3 respectively (according to the data) Unconventional natural gas production accounted for about 55% of the total natural gas production in the United States that year. Bakken tight sandstone oil in North America has also been developed on a large scale. In 2009, the output of tight oil reached 1230× 104t, an increase of 240× 104t compared with 2008. Eagleford tight limestone oil has also made great discoveries, becoming another hot exploration and development field in North America after shale gas.
Figure 1-9 Global unconventional natural gas production changes
Table1-6 Statistics of shale gas reservoir discovery in North America from 2000 to 2008
Figure1-101998 ~ 2008 Composition of American Natural Gas Production
Natural gas hydrate exists widely all over the world. About 27% of the land and 90% of the marine waters on the earth belong to the potential occurrence areas of natural gas hydrate deposits, and the resources are huge. It is estimated that the natural gas hydrate resources are more than twice that of all known fossil fuel resources, with the advantages of shallow burial, wide distribution and high energy density. At present, it is considered that natural gas hydrate can be mined by thermal shock method, depressurization method and chemical reagent method, so it is known as "energy of the future" and "energy of 2 1 century".
Unconventional oil and gas resources in China are rich, diverse and widely distributed, which will occupy an important position in the future oil and gas industry. According to the results of a new round of resource evaluation, China's shale oil resources are 476× 108t, oil sand resources are 59.7× 108t, and coalbed methane resources are 36.8×10/2m3 (buried depth is less than 2000m). China is rich in unconventional oil and gas resources such as tight oil, tight gas, shale gas, oil shale and heavy oil asphalt.
Third, unconventional oil and gas strategic breakthrough and significance
As we all know, unconventional oil and gas is a resource that cannot be explored and developed by conventional methods and technical means at present. It is characterized by large total resources, high technical requirements and poor physical properties, with general air permeability < 1× 10-3 μ m2 and porosity < 10%. Its resource development needs to have the necessary technical and economic conditions. Only by emancipating the mind can we liberate oil and gas and promote the transformation of unconventional resources into conventional resources.
In recent years, a series of major breakthroughs have been made in global unconventional oil and gas exploration. Tight gas and coalbed methane have become the key areas of global unconventional gas exploration, tight oil has become the highlight of global unconventional oil exploration, and shale gas has become the hot spot of global unconventional gas exploration. Significant progress and strategic breakthroughs have been made in global unconventional oil and gas exploration and development. Especially in North America, natural gas production accounts for 27.2% of the world, making it the largest natural gas producing area in the world. The development of unconventional natural gas in the United States has developed rapidly, and the proportion of unconventional natural gas production has reached 50%. 1970 The total natural gas output in the United States exceeded 6000× 108m3, and reached a peak of 6400× 108m3 in 1973. After 20 years, the output continued to decline, and the total output reached 6000× 108m3 in 2009, mainly due to the contribution of unconventional natural gas (Figure 66 shows that the first breakthrough is tight gas, followed by coalbed methane and shale gas.
Figure 1- 1 1 Changes of natural gas production in the United States over the years
The breakthrough of unconventional oil and gas in the world brings the following important enlightenment: First, unconventional oil and gas development should be carried out in different levels, and industrial experiments should be carried out first; Second, technological breakthrough and large-scale application are important factors to promote the development of unconventional oil and gas; Third, policy support and rising oil and gas prices have provided a strong impetus for unconventional oil and gas development; Fourth, breakthroughs in major fields require long-term basic theoretical research and technical research preparation; Fifth, misunderstanding is a forbidden area for exploration. Only by emancipating the mind can we liberate oil and gas and promote the transformation of unconventional resources into conventional resources. Taking shale gas as an example, the breakthrough of shale gas exploration and development is of great significance in terms of resource increment, reservoir-forming theory and development technology, and has a far-reaching impact on the expansion of exploration field and the development of oil and gas industry: ① It has broken through the restricted area of resources and increased the types and quantity of resources, and conventional exploration regards shale as a non-reservoir and ignores it as an effective resource for integrating sources and reservoirs; (2) It breaks through the traditional theory of reservoir formation and the viewpoint that there is a lower limit for conventional oil and gas reservoirs and traditional traps, and proves that oil and gas reservoirs with nanometer pore throats can also accumulate natural gas; (3) Break through unconventional technologies, upgrade oil and gas exploration and development technologies, promote the development of conventional and unconventional oil and gas development technologies, and promote unconventional resources such as tight oil and gas and shale oil to become conventional resources.
1. Tight gas has become the key field of unconventional gas exploration.
The development of tight gas is the earliest in the world, accounting for about 75% of unconventional natural gas production. At present, the United States has discovered more than 900 tight gas fields in 23 basins, with recoverable resources of13×10/2m3, recoverable reserves of 5× 10 12m3, and more than 65,438+million production wells, with the output in 2009. The rapid development of tight gas mainly benefits from the progress of geological understanding and the breakthrough of fracturing technology.
China has found abundant tight gas resources in Ordos, Sichuan and Turpan-Hami basins, and the current tight gas reserves and production have accounted for about 30% of the country. The evaluation results of China No.7 great basin show that the favorable exploration area of tight gas is 27× 104km2, and the resource amount is about (9 ~12 )×10/2m3, which is an important realistic field of natural gas exploration in the future.
2. tight oil has become the highlight of global unconventional oil exploration.
Bakken tight oil in North America is another hot field abroad after shale gas breakthrough, and tight oil is also called "black gold". The discoverer Findlay won the AAPG Outstanding Explorer Award in 2006. In 2008, Bakken tight oil achieved large-scale development and was identified as one of the top ten discoveries in the world. Reservoirs are silty sandstone and carbonate rocks sandwiched in source rocks. Bakken reservoir area is 7× 104km2, buried depth is 2590~3200m, thickness is 5 ~ 10m, and permeability is (0. 1 ~ 1) × 65438. At present, 19 tight oil basins have been discovered in North America, and the proven recoverable reserves of four main tight oil pay zones, such as Bakken tight sandstone and Eagle Ford tight limestone, are 6.4× 108t, and the output in 2009 is 1230× 100t. The large-scale development of tight oil in North America mainly benefits from the large-scale application of horizontal well staged fracturing technology after 2005. The initial oil production of horizontal wells is 500t/d, and the stable production is 15 ~ 25t/d, which realizes the rapid industrial development.
Tight oil in China is widely distributed, including Jurassic in Sichuan Basin, tight sandstone in Chang 7 member of Ordos Basin, lacustrine carbonate rock of Shahejie Formation in Bohai Bay, Cretaceous marl in Jiuquan Basin and Permian dolomite in Junggar Basin. , has the geological conditions to form a large-scale tight oil.
3. CBM has become an important field of unconventional natural gas exploration.
It is estimated that the total amount of coalbed methane resources in the world is about (91~ 260 )×10/2m3, and the latest statistical result is 256.1×10/2m3 (Oil and Gas Journal Online, In 200 1 year, the coalbed methane resources in the United States are 21.19×10/2m3, and those in Russia are (17 ~113. Major coal-producing countries in the world attach great importance to the development of coalbed methane. At present, among 74 coal-bearing countries in the world, 35 countries have carried out research and development of coalbed methane, and about half of them have carried out special exploration and testing of coalbed methane. The development and utilization of coalbed methane in the United States, Britain, Germany and Russia started earlier. From the late 1970s to the early 1980s, the United States began to exploit surface coalbed methane and achieved success. During the period from 1983 to 1995, the annual output of coalbed methane increased sharply from 1.7× 108m3 to 250× 108m3, and formed rapidly. In 2005, the output has exceeded 500× 108m3, accounting for 8% ~ 10% of the total natural gas production in the United States, making it an important energy resource in the United States. The development speed of coalbed methane industry in the United States has attracted worldwide attention. In Canada, the experiment of coalbed methane mining began with 1978. In 2002, the annual output of coalbed methane was about 1× 108m3, increased to 15.5× 108m3 in 2004, and is expected to reach 207× 108m3 in 2020. Australia produced 12.85× 108m3 coalbed methane every year from 1996 to 2004. The development of coalbed methane in Australia is mainly concentrated in several Permian-Triassic coal-bearing basins in the east, including Sydney, Kennedy, Galilee and Bonn, of which 78% of coalbed methane production comes from Bonn Basin in Queensland.
The development of coalbed methane in China started late. Since 1994 started the special exploration of coalbed methane, only Qinshui basin has realized the industrial output of coalbed methane. At present, China is entering the breakthrough stage of coalbed methane development. In 20 10, China's coalbed methane production capacity will reach 25× 108m3, realizing the rapid development of China's coalbed methane industry. Other countries, such as Czech Republic, Poland, Belgium, Britain, Russia, Ukraine, India and Zimbabwe, also participated in the evaluation and exploration of coalbed methane. Generally speaking, it is not possible to develop coalbed methane on a large scale at present. In 2007, the world's coal-bed methane output was about 700× 108m3, among which the United States, Canada and Australia were the largest coal-bed methane producers in the world, with the United States producing about 540× 108m3, Canada producing nearly 100× 108m3 and Australia producing 50×/08m3.
4. Shale gas has become a hot field of unconventional natural gas exploration.
In recent years, a shale gas "revolution" has been set off around the world. The breakthrough of shale gas lies in increasing the variety and quantity of resources, breaking through the lower limit of conventional reservoirs and the traditional concept of trap accumulation, promoting the development of conventional and unconventional oil and gas development technologies and upgrading the bottleneck technology of oil and gas development. The output of shale gas in North America exceeded 200× 108m3 in 2006 and 900× 108m3 in 2009. The rapid development of shale gas mainly benefits from the breakthrough of horizontal well and fracturing technology after 2003. At present, eight important shale gas producing areas have been formed in North America, such as Barnett, Fayetteville and Haynesville. The proven recoverable reserves are about1×1.01.2m3, and the output in 2009 is 1.000× 1.08 m3. Early drilling confirmed that shale had almost no permeability, and "artificial" permeability was achieved through horizontal well fracturing, forming shale "artificial gas".
There are three types of shale in China: marine shale, transitional marine shale and continental shale, among which marine shale gas is the most realistic, and Paleozoic in southern Sichuan is the core area of recent breakthrough. Important progress has been made in shale gas exploration research in China, such as optimizing the core area through regional research, discovering nano-scale pores in Wei 20 1 well for the first time, and the first batch of shale gas industrialization demonstration zones in China, such as Changning and Zhaotong, established by China Petroleum and Natural Gas Group Corporation, are progressing smoothly and have made important discoveries. However, shale gas in China has the characteristics of high thermal evolution, deep burial, complex ground and lack of water resources, which should be paid special attention to in exploration and development.
In the history of oil and gas exploration, misunderstanding is the forbidden area of exploration. Conventional thinking can not find unconventional oil and gas, and the understanding of continuous oil and gas reservoirs has broken through the conventional discontinuity and exploration forbidden zone.