Introduction
With the discovery and large-scale development of unconventional natural gas such as tight sandstone gas (simplified as tight gas), coalbed methane, and shale gas, not only has the quantity of natural gas resources increased and the exploration and development methods of natural gas changed, but also profound changes have been made in the geological theory and the understanding of natural gas [1⇓⇓⇓⇓⇓⇓⇓⇓-10]. In 1821, shale gas was first discovered in the Devonian of the Appalachian Basin in the eastern United States. In 1920, guided by White's theory of anticline oil and gas reservoirs, tight sandstone gas was first discovered in the Lower Silurian of the Appalachian Basin. In 1927, the Blanco tight sandstone gas was discovered in the Upper Cretaceous of the San Juan Basin, and industrial exploitation was achieved in the 1950s [11]. The discovery of unconventional natural gas reservoirs has promoted the overall development of the entire oil and gas industry. Currently, the geological theory and technical system of unconventional natural gas have been basically formed, including unconventional natural gas geology, reservoir stimulation technology, etc. So far, most scholars be-lieve that shale gas and tight sandstone gas belong to unconventional natural gas, and there are various views on the accumulation and distribution patterns of shale gas and tight sandstone gas. There is a consensus that shale gas reservoirs are distributed continuously, while there are increasingly different views on whether tight sandstone gas reservoirs are distributed continuously. There are obvious issues worth discussing and discussing in terms of understanding. On the basis of elaborating on the potential and annual production of tight sandstone gas and shale gas resources in the United States and China, the authors systematically review the research history of the distribution of tight sandstone gas and shale gas reservoirs, analyze the distribution characteristics and genetic types of shale gas and tight sandstone gas reservoirs, in order to provide technical support for the exploration and development of shale gas and tight sandstone gas reservoirs.
1. Tight sandstone gas and shale gas becoming important areas for reserve growth
Tight sandstone gas and shale gas are the two main exploration and development fields in current natural gas resources, and will also be important storage targets for conventional natural gas resources for a considerable period in the future. The global tight sandstone gas resource is about 210×1012 m3, and the remaining technically recoverable resource is about 81×1012 m3 [12]. In 2013, the United States discovered over 900 tight sandstone gas fields in 23 oil and gas basins, with a recoverable resource of 13×1012 m3 and a remaining proven recoverable resource of over 5×1012 m3. The United States achieved continuous growth in tight sandstone gas reserves and production from the 1970s to the 1990s [13]. According to statistics, before 2008, the production of tight sandstone gas in the United States accounted for 20% to 35% of its total production. After 2008, with the rapid development of shale gas, the production of tight sandstone gas gradually decreased, currently accounting for only about 8% of its total natural gas production (Fig. 1a ). Since 1973, driven by the strategy of energy independence, the United States has successfully completed the shale gas revolution, pushing shale gas exploration and extraction into a stage of rapid scale-development. The International Energy Agency (IEA) predicted in 2015 that the global shale gas technology recoverable resources were 220×10 12 m3, while the US shale gas technology recoverable resources were 18.8×1012 m3, ranking fourth in the world [14]. Since 2008, the United States has discovered shale gas in nearly 30 shale formations in major basins such as Appalachia, Fortwater, Williston, West Gulf of Mexico, Acoma, Louisiana, and Permia. According to statistics, from 2000 to 2008, the proportion of shale gas production in the United States to total gas production was 5% to 17%, and the annual shale gas production was (277-932)×108 m3. Since 2008, the proportion of shale gas production in the total production in the United States has jumped from 17% to 80%, and the annual shale gas production has rapidly increased from 932×108 m3 to 8 310×108 m3 [15] (Fig. 1b ).
China has abundant resources of tight sandstone gas and shale gas, with a wide range of exploration and development fields. According to the statistics, the recoverable resources of tight sandstone gas, shale gas, and coalbed methane in China are 42.1×1012 m3, accounting for 50% of the total natural gas resources. In addition to the United States, China has achieved large-scale commercial development of tight sandstone gas and shale gas. In 1971, tight sandstone gas was discovered in Zhongba, Chuanxi Depression, Sichuan Basin. By 2010, the tight sandstone gas production had reached 160×108 m3 in China, accounting for over 16% of the total natural gas production of the country [16]. Presently, tight sandstone gas reservoirs discovered in China are distributed all over the onshore and offshore oil and gas-bearing basins, with three major tight sandstone gas production areas established in the Upper Paleozoic of the Ordos Basin, the Mesozoic of the Sichuan Basin and the Cenozoic of the Tarim Basin [17⇓-19]. In 2023, the tight sandstone gas production was 650×108 m3 in China, accounting for more than 28% of the national natural gas production (Fig. 2a ).
Fig. 2. The tight gas and shale gas production over the years and their proportion in natural gas production in China. |
In 1965, gas-bearing shale formations were discovered in the Weiyuan area of the Sichuan Basin. In 2010, industrial shale gas production breakthrough was achieved in the Upper Ordovician Wufeng Fromation-Lower Silurian Longmaxi Formation of the Weiyuan area in the Sichuan Basin. In 2012, China began producing shale gas. Marine shale gas has been discovered successively in the Lower Cambrian Qiongzhusi Formation, Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation, Upper Ordovician Ulalike Formation, and Permian Wujiaping Formation in the Sichuan Basin, East and West Chongqing, North Yunnan, and the western edge of Ordos Basin. By the end of 2023, 9 shale gas fields from the marine Wufeng Formation to the Longmaxi Formation have been discovered and proven in the Sichuan Basin Qianbei region. A batch of shale gas-bearing areas have been discovered in the western edge of the Yichang and Ordos basins, with a cumulative proven shale gas initially-in-place of nearly 3.0×1012 m3. In 2023, shale gas production of 250×108 m3 has been achieved [20]. Among them, the largest shale gas field in China, Fuling shale gas field, has also become the largest shale gas field in the world except for North America. The cumulative proven gas initially-in-place is nearly 9 000×108 m3, and the cumulative production of shale gas has exceeded 600×108 m3. Currently, the annual production is about 100×108 m3. The Weiyuan shale gas field is the earliest discovered shale gas field in China, with a cumulative proven reserves of 4 600×108 m3 and a cumulative production of shale gas exceeding 300×108 m3. The annual production in 2023 is 40.58×108 m3. The Weirong shale gas field is the first deep shale gas field discovered in China with proven gas initially-in-place exceeding 100 billion cubic meters. The main production layer of the gas field is buried at a depth of over 3 700 m, and the confirmed shale gas initially-in-place has been submitted as 1 247×108 m3. The annual production of shale gas is about 10.0×108 m3. The Changning shale gas field was discovered in 2011 and is the first natural gas field on the outer edge of the Sichuan Basin. It has a cumulative proven reserves of 4 600×108m3 and a cumulative shale gas production of 100×108m3. The annual production in 2023 was 52.13×108m3. The Luzhou shale gas field is a trillion-cubic-meter deep to ultra-deep shale gas field discovered in China. The tested shale gas production of Well Lu 203 is 137.9×104 m3/d (approximately 1 099 t oil equivalent), and the proven geological reserves of shale gas are 5 138×108 m3 and the predicted geological reserves are 7 695×108 m3. The annual production in 2023 is 24.58×108 m3. The annual production of the Yuxi shale gas field is 10.87×108 m3. The Qijiang shale gas field is the first deep to ultra-deep large-scale shale gas field discovered in the complex structural zone at the basin edge of China, with a burial depth of 4 000 m to 5 000 m. The proven shale gas initially-in-place is 1 459.68×108 m3, and it is preliminarily confirmed that it has the potential to build a production capacity of 10×108 m3. The Sun shale gas field is a large, fully assembled shallow shale gas field with a main burial depth of less than 2 000 m. The proven gas initially-in-place is 1 359.5×108 m3, with a production capacity of 8.0×108 m3 built in 2020 and 6.07×108 m3 in 2023. Exploration has shown that the shale gas resources are abundant in China, with the characteristics of multi-layers and large-scale distribution of sweet spots. By the end of 2023, the cumulative shale gas production had exceeded 1 400×108 m3 [21], and the annual shale gas production accounts for more than 11% of the national natural gas production (Fig. 2b ).
2. Research evolution of the distribution of tight sandstone gas and shale gas
2.1. The emergence of the concept of continuous accumulation of tight sandstone gas and shale gas
In the 1970s, American scholars classified tight sandstone gas, coalbed methane, and shale gas that were on the sub-economic and economic edge as unconventional gas. After the early concept of tight sandstone gas reservoirs, some scholars proposed concepts such as basin center gas reservoirs and continuous gas reservoirs [22⇓⇓⇓⇓⇓-28]. Schmoker [2-3] and Gautier et al. [5] classified tight sandstone gas reservoirs as unconventional natural gas when evaluating unconventional natural gas resources and considered unconventional natural gas as a continuous reservoir formation. After Law et al. [10] formally proposed the concept of unconventional natural gas, they classified tight sandstone gas and tight carbonate gas with low porosity, low permeability, and high extraction difficulty as unconventional gas, and clearly pointed out that unconventional oil and gas are oil and gas resources that could not be developed using traditional technologies under existing economic conditions. Unconventional oil and gas can be subdivided into 9 types: heavy oil, tight oil, oil shale oil, oil sand oil, shale oil, tight gas, coalbed methane, shale gas, and hydrates. Among them, unconventional gas, tight gas, and shale gas are the main types.
China has also been involved in the study of unconventional oil and gas at an early stage and has noticed the continuous accumulation characteristics of reservoir formation [23⇓⇓⇓⇓-28]. Zou et al. [25] and Yang et al. [26] point out that unconventional oil and gas have two key indicators: (1) large-scale continuous distribution with unclear trap boundaries; (2) no natural production and not obvious Darcy seepage. The study of the distribution patterns of tight sandstone gas reservoirs and shale gas reservoirs suggests that both are continuous accumulation reservoirs. Jia et al. [27-28] pointed out that the basic geological characteristics of unconventional oil and gas reservoirs, mainly tight sandstone gas reservoirs and shale gas reservoirs, are as follows: (1) Continuous accumulation, large-scale distribution, without obvious oil, gas, and water trap interfaces; (2) Unconventional reservoirs are tight and have developed micro- and nano-scale pore throat systems, making them an artificial oil and gas reservoir; (3) The coexistence of unconventional oil and gas in various phases, including solid, liquid, gas, free, adsorbed, etc.; (4) Unconventional oil and gas are formed near source or intra-source enrichment, and near-source accumulation includes tight sandstone gas reservoirs. In summary, it can be concluded that in the early stages, both tight sandstone gas reservoirs and shale gas reservoirs were considered as continuous gas reservoirs.
2.2. Quasi-continuous or discontinuous distribution and trap accumulation of tight sandstone gas
Zhao [22] believes that unconventional oil and gas do not always accumulate in complete continuity. Some can be continuous, some quasi-continuous or discontinuous, forming reservoirs outside the source, accumulating near the source, and accumulating within the source. Shale gas and coalbed methane belong to continuous accumulation. Most tight sandstone gas reservoirs are discontinuous, with only a few appearing to be quasi-continuous. Kang's research [29-30] indicates that unconventional oil and gas are widely distributed continuously or quasi-continuously.
A large number of tight sandstone gas fields, such as Sulige, Daniudi, Guang'an, and Hechuan, discovered in the Carboniferous-Permian of the Ordos Basin and the Xujiahe Formation of the Triassic in the Sichuan Basin and the Lianggaoshan Formation of the Jurassic, exhibit the characteristics of non-continuous distribution of natural gas reservoirs in China [19,31]. There are three types of reservoirs: lithological, anticlinal, and syncline reservoirs. Jiao Fangzheng [32] clearly points out that unconventional oil and gas only include shale oil, shale gas, and coalbed methane. These types of oil and gas reservoirs have integrated sources and reservoirs and continuously accumulate in situ, while heavy oil, oil sands, tight oil, tight sandstone gas, and natural gas hydrates still belong to the conventional oil and gas category. Generally, they follow the mechanism of trap formation and accumulation process with respect to traditional petroleum geological theory, which means that these types of oil and gas reservoirs are discontinuous reservoir formations.
3. Shale gas reservoirs are continuous accumulation
Fig. 3. Section of continuous reservoir formations for Wufeng Formation-Longmaxi Formation shale gas reservoirs in Sichuan Basin (modified from Reference [19]). O2—3—Middle - Upper Ordovician; O3w—Wufeng Formation; S1l—Longmaxi Formation; S1sn—Shiniulan Formation; S1x—Xiaoheba Formation; S2h—Hanjiadian Formation; P—Permian; T—Triassic. |
Fig. 4. Cross section of Barnett shale gas reservoir in Fortwater Basin (modified from Reference [38]). |
Shale gas can be classified into two categories based on whether it is cut by faults and the relationship between fault displacement and gas layer thickness: (1) Continuity: shale gas layers without developed faults, such as Weirong shale gas field (Fig. 3a ) and Barnett shale gas reservoir (Fig. 4 ). The gas layer has developed faults, but the fault displacement is smaller than the thickness of the gas layer and does not damage the continuity of shale gas, i.e., the Changning shale gas field (Fig. 3b ). (2) Intermittency: Shale gas layers are cut by faults with a displacement greater than the thickness of the gas layer, causing the shale gas layer to be interrupted and distributed in an intermittent manner, i.e., the Fuling shale gas field and the Taiyang shale gas field (Fig. 3c , 3d).
4. Trap types and distribution of tight sandstone gas reservoirs
As is known to all, only reservoirs with uniform pore structures can accommodate uniformly continuous fluid. In geological engineering, sandstone with an effective permeability below 0.1×10-3 μm2 (absolute permeability less than 1×10-3 μm2) and a porosity less than 10% is called tight sandstone [39]. Tight sandstone is characterized by shallow water bodies and unstable sedimentary environments, with multiple sources and significant variations in particle size. The main tight sandstones in the Ordos Basin are the continental braided river delta deposits of the Lower Shihezi Formation in the Permian, with multiple sources of sand supply, strong heterogeneity, and complex pore throat microstructures [19]. Dai et al. [40] and Jiao [32] believe that tight sandstone gas reservoirs are discontinuous.
The gas reservoirs of 24 large tight sandstone gas fields in the Ordos Basin, Sichuan Basin and Tarim Basin [19] and some overseas [41-42] tight sandstone gas fields are not continuous. For example, in the middle of the Ordos Basin, the Upper Paleozoic tight sandstone gas reservoirs of Sulige Gas Field, Jingbian Gas Field, Yulin Gas Field and Shenmu Gas Field from west to east are not continuous [19] (Fig. 5 ).
Fig. 5. Section of tight sandstone gas reservoir in the Upper Paleozoic in Sulige gas field to Shenmu gas field in the central part of Ordos Basin (modified according to Reference [19]). |
According to the trap types that control tight sandstone gas reservoirs, tight sandstone gas reservoirs can be divided into three types: lithological, anticlinal, and syncline.
4.1. Lithological tight sandstone gas reservoir
The tight sandstone gas reservoirs of the Upper Paleozoic in the Dongsheng gas field in the northern part of the Ordos Basin, the Mizhi gas field in the southern part, the Zizhou gas field, and the Daji gas field are lithological gas reservoirs (Fig. 6 ). In contrast, the tight sandstone gas reservoirs in the Hechuan gas field in the Sichuan Basin are anticlinal tight sandstone gas reservoirs (Fig. 7a ). Due to the formation of gas bearing tight sandstone lenses in both anticlines and synclines, they are actually lithological traps. Millson et al. [41] believe that the Barik Formation tight sandstone gas reservoir in the Kazan gas field of the Oman Ghaba Salt Basin is a stratigraphic structural gas reservoir, which is actually a lithological gas reservoir under the background of an anticline structure (Fig. 7b ).
Fig. 6. Lithological gas reservoir sections of tight sandstone fields in the northern and eastern Upper Paleozoic of the Ordos Basin. |
Fig. 7. Cross sections of lithological tight sandstone gas reservoirs in the Sichuan Basin of China and the Ghaba Salt Basin of Oman ( |
Lithological tight sandstone gas reservoirs are the main type of tight sandstone gas reservoirs, often formed in structurally stable basins and regions, such as the Ordos Basin and Sichuan Basin. The internal structure of the Yishan Slope in the Ordos Basin is gentle with few faults, and most of China's lithological tight sandstone gas reservoirs are distributed in the Central Sichuan Uplift in the Sichuan Basin [40].
4.2. Anticlinal tight sandstone gas reservoir
Dina 2 gas field, Kelasu gas field, Dabei gas field (Fig. 8 ) and Barik Formation tight sandstone gas reservoir (Fig. 7b ) [41] in Kuqa depression of Tarim Basin, NW China are all anticlinal tight sandstone gas reservoirs.
Fig. 8. Cross sections of anticlinal tight sandstone gas reservoirs in Tarim Basin (modified according to Reference [19]). T—Triassic; J—Jurassic; K—Cretaceous; K1bx—Basigai Formation; K1bs—Bashkirchik Formation; E1-2km—Kumglimu Group; E2—3s—Suweiyi Formation; N1j—Jidi Formation; N1-2k—Kangcun Formation; N2k—Kuqa Formation. |
Anticlinal tight sandstone gas reservoirs are often formed in basins and regions with tectonic activity. Due to the high horizontal pressure intensity, folds are often formed, which is favorable for the formation of anticlinal tight sandstone gas reservoirs. For example, Kuqa Depression in Tarim Basin is a foreland basin with active tectonic movement, forming a series of anticlinal tight sandstone gas reservoirs [40].
4.3. Synclinal tight sandstone gas reservoir
The tight sandstone gas reservoir in Liuyangpu, Ordos Basin [19], and the tight sandstone gas reservoir in the Mesayerde Formation of the Cretaceous in the Pishens Basin, United States [42] are formed in a syncline (Fig. 9 ). In 1921, Emmons pointed out that tight sandstone gas reservoirs "have a lot of accumulation in synclines" [43], while Masters [44] referred to tight sandstone gas distributed in the central part of the basin as deep basin gas. Chinese scholars also hold a similar view and believe that tight sandstone gas in the Upper Paleozoic of the Ordos Basin is deep basin gas [45⇓-47].
Fig. 9. Cross sections of synclinal tight sandstone gas reservoirs in Liuyangpu in Ordos Basin and Mesayerde Formation in Piceance Basin. |
Synclinal tight sandstone gas reservoirs, like anticlinal types, often form in structurally active basins and regions. Synclinal tight sandstone gas reservoirs (deep basin gas) in the United States are distributed in the Piceance Basin, San Juan Basin, and Denver Basin. However, the scale of the Liuyangpu syncline tight sandstone gas reservoir in the Ordos Basin is relatively small, located at the junction of the tectonic activity zone and the stable zone.
5. The genetic types of tight sandstone gas
According to the δ13C1—4 values of tight sandstone gas in the Ordos Basin, Sichuan Basin, Tarim Basin, Egypt's Obayied subbasin, Oman Jaba Salt Basin and the Appalachian Basin in the United States (Table 1 ), the δ13C1—3 values are put into the δ13C1-δ13C2-δ13C3 coal derived gas and oil-type gas identification diagram (Fig. 10 ). From Fig. 10 , it can be seen that the tight sandstone gas in the three basins of China is all coal-derived gas. The tight sandstone gas in the Khatatba Formation of the Middle Jurassic in the Abayied sub-basin of Egypt is also mainly coal-derived gas. Its source rock is mainly coal-bearing shale, and the kerogen is a mixture of types II and III or Type III [48]. The main source of tight sandstone gas (deep basin gas) in the Rocky Mountains Basin group in the United States comes from Cretaceous coal seams and Type III kerogen mudstone with rich organic carbon content in coal measures [46,49]. Law [50] believes that the gas source of tight sandstone gas (deep basin gas) in the Dalu River Basin comes from coal seams and humic carbonaceous shale of the Lance, Almond, and Rock Springs formations of the Upper Cretaceous. From Fig. 10 , it can be seen that the tight sandstone gas in the Barik Formation of the Oman Ghaba Salt Basin and the Clinton Medina Formation of the Silurian in the Appalachian Gas Field of the Appalachian Basin in the United States are oil-type gas [51-52].
Table 1. Gas compositions and carbon isotopic compositions of tight sandstone |
| Country | Basin | Gas field | Well | Layer | Gas composition/% | δ13C/‰ | Type | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CH4 | C2H6 | C3H8 | C4H10 | CO2 | N2 | CH4 | C2H6 | C3H8 | C4H10 | CO2 | |||||||||||||||||||||
| China | Ordos | Sugeli | E58 | P2x | 89.60 | 3.93 | 0.82 | 0.15 | 0.07 | 4.64 | −31.9 | −23.6 | −23.4 | Coal-derived gas | |||||||||||||||||
| Su172 | P1s | 94.12 | 3.02 | 0.50 | 0.07 | 0.06 | 2.08 | −27.3 | −23.0 | −26.1 | |||||||||||||||||||||
| Tao5 | P2x | 90.90 | 4.69 | 0.83 | 0.23 | 0.76 | 2.10 | −36.5 | −23.2 | −24.5 | −22.3 | ||||||||||||||||||||
| Dongsheng | J26 | P2x | 93.66 | 3.59 | 0.81 | 0.30 | 0.35 | 1.16 | −32.0 | −25.4 | −24.8 | −23.8 | −9.9 | ||||||||||||||||||
| J55 | P1s | 83.48 | 7.14 | 1.86 | 0.56 | 0.03 | 6.76 | −36.2 | −24.8 | −26.4 | −28.8 | ||||||||||||||||||||
| J66 | P1x | 88.27 | 7.28 | 2.36 | 1.02 | 0 | 0.18 | -32.4 | -26.3 | -20.7 | |||||||||||||||||||||
| Ushenqi | Zhao4 | P2x | 90.70 | 5.46 | 1.09 | 0.46 | 0.45 | 0.81 | −31.3 | −23.7 | −23.0 | −22.5 | |||||||||||||||||||
| Zhaotan 1 | O1m54—6 | 82.16 | 0.70 | 0.01 | 0.04 | 0.01 | 0.06 | −37.5 | −27.8 | −24.3 | −20.3 | ||||||||||||||||||||
| Shaan167 | P2x | 92.33 | 4.21 | 0.74 | 0.25 | 0.35 | 1.91 | −33.8 | −23.5 | −23.4 | −22.0 | ||||||||||||||||||||
| Daniudi | D10 | P1s2 | 81.15 | 4.01 | 0.85 | 0.59 | 1.12 | 9.71 | −36.0 | −24.0 | −23.5 | ||||||||||||||||||||
| DP14 | P1x1 | 87.91 | 8.07 | 2.32 | 0.77 | 0.42 | 0 | −37.4 | −25.7 | −25.3 | |||||||||||||||||||||
| DK30 | P1x3 | 94.36 | 3.88 | 0.80 | 0.28 | 0.42 | 0 | −34.3 | −25.9 | −25.3 | |||||||||||||||||||||
| Yulin | Shaan118 | P1s2 | 92.60 | 4.32 | 0.93 | 0.30 | 1.04 | 0.23 | −30.3 | −24.0 | −22.31 | −21.7 | −4.4 | ||||||||||||||||||
| Yu 27-11 | P1s2 | 92.47 | 4.24 | 0.91 | 0.33 | 1.64 | 0.24 | −29.8 | −25.2 | −23.7 | −22.8 | −7.4 | |||||||||||||||||||
| Yu 42-2 | P1s2 | 94.03 | 3.28 | 0.52 | 0.15 | 1.65 | 0.29 | −31.0 | −25.5 | −24.1 | −22.5 | −4.2 | |||||||||||||||||||
| Shenmu | Shen 24 | P1t | −31.5 | −25.0 | −23.2 | ||||||||||||||||||||||||||
| Shuang 72 | P1t | −40.7 | −25.6 | −25.1 | −25.8 | ||||||||||||||||||||||||||
| Shen 26 | P1s1 | 85.30 | 7.37 | 2.48 | 0.48 | 0.50 | 2.61 | −35.8 | −23.8 | −24.1 | −24.0 | ||||||||||||||||||||
| Linxing | LX-105-2D | P2x | 95.28 | 2.77 | 0.74 | 0.19 | 0 | 0.87 | −30.3 | ||||||||||||||||||||||
| LX-101 | P2x | 97.14 | 1.17 | 0.20 | 0.09 | 0.03 | 1.32 | −37.5 | −27.1 | −24.0 | |||||||||||||||||||||
| Zizhou | Zhou 28-43 | P1s | 90.44 | 5.42 | 1.54 | 0.65 | −30.2 | −22.7 | −22.2 | −20.2 | |||||||||||||||||||||
| Zhou16-19 | P1s | 91.53 | 1.16 | 0.39 | −34.5 | −24.3 | −21.7 | −21.7 | |||||||||||||||||||||||
| Zhou 25-38 | P1s | 94.67 | 2.87 | 0.42 | 0.13 | 1.40 | 0.38 | −32.6 | −25.7 | −23.3 | −22.9 | ||||||||||||||||||||
| Mizhi | Qishen1 | P2x | −29.2 | −22.4 | −23.0 | ||||||||||||||||||||||||||
| Mi10 | P2s | 96.14 | 1.96 | 0.39 | 0.14 | 0.60 | 0.62 | −34.5 | −27.5 | −24.4 | −23.9 | ||||||||||||||||||||
| Liuyangpu | Dingbei 26 | P1s2 | 92.89 | 1.61 | 0.24 | 0.03 | 4.22 | 0.99 | −28.6 | −24.2 | −24.0 | ||||||||||||||||||||
| Liuping 4T | P1t2 | 96.71 | 1.60 | 0.23 | 0 | 0.09 | 0.77 | −30.6 | −25.3 | −28.0 | |||||||||||||||||||||
| Sichuan | Xinchang | XC134 | J2s | −32.7 | −25.7 | −23.6 | −18.9 | ||||||||||||||||||||||||
| XC134-2 | J2s | 93.08 | 5.02 | 0.82 | 0.40 | 0.44 | 0.16 | −36.7 | −24.4 | −23.4 | −19.3 | −11.3 | |||||||||||||||||||
| X882 | T3x4 | 93.41 | 3.78 | 0.93 | 0.46 | 0.46 | 0.85 | −34.3 | −23.1 | −21.4 | −20.0 | ||||||||||||||||||||
| Qiongxi | QX14 | T3x2 | 96.50 | 1.57 | 0.12 | 0.03 | 1.55 | 0.23 | −30.5 | −24.1 | −23.8 | −5.0 | |||||||||||||||||||
| Pingluo2 | J2s | 93.55 | 4.01 | 0.57 | 0.20 | 0.02 | 1.62 | −39.2 | −25.5 | −21.9 | −21.2 | ||||||||||||||||||||
| Pingluo 3 | T3x | 97.14 | 1.98 | 0.24 | 0.08 | 0.06 | 0.50 | −33.3 | −21.7 | −21.2 | −20.3 | −4.0 | |||||||||||||||||||
| Hechuan | Hechuan5 | T3x2 | 88.75 | 5.25 | 0.98 | 0.47 | 0.19 | 3.79 | −37.9 | −24.9 | −22.1 | −21.6 | |||||||||||||||||||
| Hechuan 1 | T3x2 | 87.57 | 7.40 | 2.68 | 1.04 | 0.04 | 0.46 | −42.8 | −26.6 | −22.7 | −22.2 | ||||||||||||||||||||
| Tongnan101 | T3x2 | 86.18 | 8.42 | 2.77 | 1.04 | 0.29 | 0.86 | −42.0 | −27.2 | −24.7 | −24.3 | −8.7 | |||||||||||||||||||
| Guang’an | Guang’an 11 | T3x6 | −37.1 | −27.4 | −22.7 | −23.6 | |||||||||||||||||||||||||
| Guang’an 14 | T3x6 | 88.83 | 5.76 | 1.32 | 0.46 | −42.0 | −25.9 | −21.7 | −20.7 | ||||||||||||||||||||||
| Guang’an 21 | T3x4 | 88.98 | 6.16 | 2.51 | 1.17 | 0.29 | 0.40 | −40.2 | −27.6 | −26.4 | −24.6 | −7.9 | |||||||||||||||||||
| Bajiaochang | Jiao 6 | Jt4 | −36.5 | −26.0 | |||||||||||||||||||||||||||
| Jiao33 | T3x6 | 91.41 | 4.92 | 1.54 | 0.57 | 0.27 | 0 | −39.5 | −25.7 | −24.4 | −23.4 | −9.8 | |||||||||||||||||||
| Chengdu | Mapeng 46 | J3p | 94.60 | 3.05 | 0.68 | 0.27 | 0.03 | 1.22 | −31.1 | −25.4 | −21.0 | ||||||||||||||||||||
| Mapeng 13 | J3p | 93.53 | 4.14 | 0.92 | 0.33 | 0. | 0.90 | −33.5 | −25.3 | −19.4 | |||||||||||||||||||||
| Shifang10 | J3p2 | 95.81 | 2.27 | 0.49 | 0.21 | 0.09 | 1.04 | −32.1 | −25.0 | −22.5 | −21.6 | ||||||||||||||||||||
| Zhongjiang | JS21-6HF | J2s | −30.4 | −25.3 | −22.7 | ||||||||||||||||||||||||||
| JS24-3H | J2s | −38.6 | −26.2 | −22.9 | |||||||||||||||||||||||||||
| GS301 | J2x | −35.2 | −24.3 | −22.3 | |||||||||||||||||||||||||||
| Luodai | L75 | J3p | 89.69 | 5.98 | 1.85 | 0.77 | 0 | 1.24 | −32.5 | −23.7 | −20.9 | −20.0 | |||||||||||||||||||
| LS24D | J3sn | 92.43 | 4.03 | 0.95 | 0.23 | 0 | 1.81 | −36.3 | −23.6 | −19.6 | −21.0 | ||||||||||||||||||||
| L7 | J3p | 93.82 | 3.12 | 0.63 | 0.15 | 0.12 | 1.81 | −35.3 | −23.7 | −21.0 | −20.0 | ||||||||||||||||||||
| Tarim | Kelasu | Keshen105 | K1bs | 95.94 | 0.47 | 0.03 | 0.01 | 2.36 | 1.14 | −25.7 | −13.8 | Coal-derived gas | |||||||||||||||||||
| Bozi3 | K1bs | 86.64 | 6.53 | 1.65 | 0.36 | 0.26 | 3.11 | −35.6 | −25.1 | −23.2 | −22.9 | ||||||||||||||||||||
| Keshen 13 | K1bs | 94.00 | 1.77 | 0.22 | 0.10 | 1.14 | 2.15 | −30.3 | −18.5 | −18.9 | |||||||||||||||||||||
| Dina2 | DN204 | E1−2km | 86.90 | 7.40 | 0.92 | 0.62 | 0.89 | 2.95 | −34 | −23.1 | −20.8 | −20.4 | −12.4 | ||||||||||||||||||
| DN2 | N1j | 87.93 | 7.25 | 1.40 | 0.59 | 0.81 | 1.55 | −36.9 | −21.3 | −24.4 | −24.7 | −15.7 | |||||||||||||||||||
| DN202 | E2—3s | 88.28 | 7.27 | 1.54 | 0.62 | 0.45 | 1.49 | −34.7 | −23.3 | −21.0 | −21.1 | −17.6 | |||||||||||||||||||
| Dabei | Dabei 104 | K1bs | 95.60 | 0.19 | 0.01 | 0.01 | 1.67 | 2.02 | −26.7 | −19.2 | |||||||||||||||||||||
| Dabei 1 | K1bs | 94.29 | 3.43 | 0.41 | 0.11 | 0.37 | 1.20 | −33.1 | −21.4 | ||||||||||||||||||||||
| Dabei 2 | K1bs | 95.26 | 2.25 | 0.38 | 0.53 | 0.39 | 1.19 | −30.8 | −21.5 | −19.8 | |||||||||||||||||||||
| Zhongqiu | Zhongqiu 101 | K1bs | 90.93 | 4.73 | 1.00 | 0.39 | 0.76 | 1.70 | −32.3 | −20.3 | −18.6 | −20.3 | |||||||||||||||||||
| Zhongqiu 1 | K1bs | −32.6 | −22.3 | −20.7 | −20.6 | ||||||||||||||||||||||||||
| Yudong | Yudong 5 | E | 89.15 | 5.51 | 1.14 | 0.48 | 0.11 | 2.98 | −33.1 | −22.5 | −20.7 | −20.9 | |||||||||||||||||||
| Yudong 1 | E | 89.95 | 5.51 | 1.14 | 0.46 | 0.1 | 2.18 | −35.0 | −22.5 | −21.5 | −22.6 | ||||||||||||||||||||
| Yudong 4 | E | 90.26 | 5.46 | 1.10 | 0.49 | 0.09 | 2.03 | −33.5 | −23.5 | −21.1 | −21.7 | ||||||||||||||||||||
| Country | Basin | Gas field | Well | Layer | Gas composition/% | δ13C/‰ | Type | ||||||||||||||||||||||||
| CH4 | C2H6 | C3H8 | C4H10 | CO2 | N2 | CH4 | C2H6 | C3H8 | C4H10 | CO2 | |||||||||||||||||||||
| China | Tarim | Kekeya | Ke8001 | N1x8 | 87.34 | 6.40 | 2.28 | 1.22 | 0.07 | 1.84 | −34.2 | −25.7 | −23.2 | −23.2 | Coal- derived gas | ||||||||||||||||
| Ke18 | N1x | 84.05 | 8.99 | 1.93 | 0.73 | 3.98 | −38.5 | −26.4 | −25.1 | ||||||||||||||||||||||
| Ke7 | N2x | 79.46 | 9.65 | 3.05 | 1.40 | 0.22 | 5.61 | −38.4 | −26.3 | −24.8 | −26.0 | ||||||||||||||||||||
| Egypt | Obayied sub-basin | Oba2-2A | 77.05 | 8.03 | 2.61 | 9.74 | 1.53 | −38.2 | −28.3 | −26.3 | Coal- derived gas | ||||||||||||||||||||
| Oba2-2C | J2 | 73.80 | 8.90 | 4.10 | 7.90 | 1.18 | −38.2 | −28.3 | −26.1 | ||||||||||||||||||||||
| Oba4-1A | 74.05 | 9.12 | 4.30 | 8.91 | 1.38 | −38.3 | −28.5 | −25.9 | |||||||||||||||||||||||
| Oba2-3 | Khatatba | 68.60 | 13.70 | 6.50 | 4.70 | 0.93 | −43.7 | −31.0 | −26.5 | ||||||||||||||||||||||
| ObaD16 | 73.60 | 8.20 | 4.00 | 7.50 | 1.00 | −37.5 | −27.8 | −25.4 | |||||||||||||||||||||||
| ObaD17 | 78.30 | 7.50 | 2.70 | 8.10 | 1.40 | −37.0 | −26.9 | −24.7 | |||||||||||||||||||||||
| ObaD17 | 78.20 | 7.40 | 2.70 | 8.10 | 0.78 | −37.0 | −26.9 | −24.7 | |||||||||||||||||||||||
| Oman | Ghaba Salt Basin | Khazzan | MKM-1 | −38.4 | −29.0 | −26.0 | Oil- type gas | ||||||||||||||||||||||||
| MKM-3 | −38.4 | −30.0 | −26.5 | ||||||||||||||||||||||||||||
| KZN-1 | −39.4 | −31.0 | −28.0 | ||||||||||||||||||||||||||||
| Saih Rawl | SR-29 | −42.3 | −32.0 | −30.0 | |||||||||||||||||||||||||||
| USA | Appalachia | LSRA | Patterson2 | S | 78.03 | 9.70 | 4.82 | 1.93 | 4.55 | −42.0 | −35.2 | −32.34 | −30.7 | Oil- type gas | |||||||||||||||||
| Bruno1 | S | 85.62 | 6.18 | 2.56 | 1.09 | 3.91 | −39.2 | −33.8 | −31.1 | ||||||||||||||||||||||
| G. Johnson2 | S | 88.10 | 5.30 | 2.16 | 1.08 | 2.63 | −38.1 | −34.6 | −30.8 | −29.5 | |||||||||||||||||||||
| Hissa2 | S | 76.38 | 10.98 | 6.07 | 3.07 | 2.01 | −39.8 | −35.2 | −31.2 | ||||||||||||||||||||||
| Detweiler1 | S | 88.17 | 5.58 | 1.93 | 0.79 | 3.04 | −38.8 | −35.1 | −30.9 | ||||||||||||||||||||||
| D. French2 | S | 87.48 | 5.59 | 2.12 | 0.96 | 3.24 | −38.8 | −35.3 | −31.1 | ||||||||||||||||||||||
| H. Griffin3 | S | 88.19 | 5.17 | 1.87 | 0.77 | 3.54 | −38.8 | −35.6 | −31.3 | −29.8 | |||||||||||||||||||||
| Clemens2 | S | 90.64 | 4.48 | 1.32 | 0.49 | 2.67 | −37.4 | −34.7 | −30.4 | ||||||||||||||||||||||
| Krantz2 | S | 89.34 | 5.11 | 1.65 | 0.62 | 2.84 | −37.5 | −35.3 | −30.9 | ||||||||||||||||||||||
| Governor1 | S | 90.33 | 4.64 | 1.47 | 0.58 | 2.50 | −37.2 | −34.9 | −30.6 | ||||||||||||||||||||||
| Oris8 | S | 89.94 | 4.58 | 1.35 | 0.58 | 3.08 | −36.9 | −35.3 | −30.6 | ||||||||||||||||||||||
| Gibson2l | S | 91.74 | 3.67 | 0.87 | 0.38 | 2.99 | −35.6 | −36.0 | −30.7 | −29.2 | |||||||||||||||||||||
| Brown5 | S | 94.36 | 2.37 | 0.15 | 0.039 | 2.92 | −34.7 | −39.8 | −40.2 | ||||||||||||||||||||||
| Velasaris1 | S | 94.25 | 2.26 | 0.14 | 0.032 | 3.17 | −34.2 | −41.1 | −42.9 | −38.9 | |||||||||||||||||||||
Fig. 10. Identification diagram of the origin of tight sandstone gas (modified according to Reference [51]). |
6. Conclusions
Before 2008, tight sandstone gas in the United States accounted for 20% to 35% of the country’s total production, but by 2023, it only accounted for about 8% of the country’s production. From 2000 to 2008, shale gas in the United States accounted for 5% to 17% of the total production of the country, and by 2023, the production reached 8310×108 m3, accounting for about 80% of the total gas production of the country. In 2010, the tight sandstone gas production of China was 160×108 m3, accounting for over 16% of the country’s total natural gas production. In 2023, the production was 650×108 m3, accounting for over 28% of the country’s total natural gas production. In 2012, China began producing shale gas, and in 2023, the shale gas production was 250×108 m3 in China, accounting for approximately 11% of the country’s total natural gas production.
The distribution of shale gas reservoirs is continuous. According to the relationship between presence of faults, fault displacement and gas layer thickness in shale gas reservoirs, continuous shale gas reservoirs can be classified into continuity and intermittency. The distribution of tight sandstone gas reservoirs is not a continuous type of reservoir formation. They can be divided into three types according to the different types of traps that control the formation of tight sandstone gas reservoirs: lithological, anticlinal, and synclinal.
The key to determining the continuous distribution is that shale gas reservoirs are characterized by the integration of source and reservoir, with deep sedimentary water in the source rock, stable and in a reducing environment, rich in organic matter, and uniform storage spaces for organic and inorganic matter pores. Tight sandstone reservoirs are non-uniform reservoirs, therefore they cannot form continuous gas reservoirs.
The tight sandstone gas in the Ordos Basin, Sichuan Basin, Tarim Basin of China and the Obayied subbasin of Egypt is coal-derived gas, while the tight sandstone gas in America's Appalachian Basin and Oman Jaba Salt Basin is oil-type gas.