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Recent Significant Gas Discoveries in China: Influence on National Energy Structure and Future Gas Exploration*
By
Chenxia Xie1
Search and Discovery Article #10067 (2004)
*Adapted from poster presentation at AAPG Annual Convention, Dallas, Texas, April 18-21, 2004.
1IHS Energy, Houston, Texas ([email protected])
Significant gas fields were discovered in China in recent years, such as the Kela 2 gas field in the Tarim Basin, Sulige gas field in the Ordos Basin, Luojiazhai gas field in the Sichuan Basin, etc. These new discoveries strengthen the gas supply to “West-Gas-To-East” gas trunkline. Energy growth in China is expected to increase rapidly. As a clean-burning fuel, natural gas is more welcome in energy-hungry China. The new gas discoveries plus already existing important gas fields and the construction of gas pipeline networks throughout the country, support the target of increasing gas percentage from the current less than 3% to 5-8% in primary energy usage in the next ten years.
Most new gas fields have been discovered in the three major gas-bearing basins: Tarim, Ordos, and Sichuan. New gas fields in each basin have their own features. In the Sichuan Basin, new gas discoveries are mainly made in the newly found Triassic oolitic limestone play in the northeastern part of the basin; in the Ordos Basin, the distribution of the Upper Paleozoic deltaic sandbodies controls the accumulation in the large Upper Paleozoic gas field; while in the Tarim Basin, new gas discoveries are concentrated in structure-dominated plays in the Kuche Depression. Since huge resource potential exists in the surrounding areas of these new gas discoveries, it is anticipated that more gas fields will be discovered in the areas with similar tectonic features and sedimentary history.
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IntroductionFigures 1-2China has been growing more and more energy hungry. In 2003, China imported a record high 91 MMt crude oil, superseding Japan as the second oil importer after the United States. Energy growth in China is expected to increase rapidly. Currently coal continues its dominant role in primary energy usage in China, accounting for over 70%, oil being second, while natural gas accounts for only 2.5%, much lower than the world average level of 23%. In the most recent decade, numerous significant gas discoveries were found, and much effort has been made to build up the pipeline networks throughout the country. Gas supply districts are forming with dependence on gas-bearing basins, including Ordos, Tarim, Sichuan, and Qaidam onshore, and Yinggehai, Qiongdongnan, and East China Sea offshore. Gas reserves of the four onshore basins/districts (Figure 1) account for over 70% of China’s total (not including Taiwan) (Zhao et al, 2002) (Figure 2), and they are the subjects of discussion here. The most recent decade is the most important stage for gas reserve growth in China. The gas reserves discovered since 1990 occupy at least 55% of the total in the four major onshore gas-producing basins, up to 93.5% in the Tarim Basin (Zhao et al., 2002). Figures 3-7
Large gas fields are distributed in the Eastern Slope in the Ordos Basin (Figure 3). There exist two groups of gas reservoirs – Upper Paleozoic and Lower Paleozoic, with source rocks of Carboniferous-Permian coal measures and Ordovician Majiagou carbonates. The Lower Paleozoic reservoirs are composed of the altered Ordovician Majiagou carbonates that have been altered through dissolution and/or weathering. Discovered in 1989, Jingbian, the first large gas field of the basin, has been producing gas from Majiagou reservoirs (Kang et al., 2000) (Figures 4 and 5). Of the major fields, it is the only one that produces from Ordovician carbonates. Establishment of the Upper Paleozoic as targets occurred in the middle 1990’s, resulting in the discoveries of the giant Sulige, Changdong, Changbei, Wushenqi, and Shenmu fields. The Upper Paleozoic reservoirs are composed of river-dominated deltaic sandstones (Figures 6 and 7). By end-2000, the proven recoverable gas reserves of the Ordos Basin reached 18,245 bcf, replacing Sichuan Basin to become the basin with the largest gas supply in China (Zhao et al., 2002; Kang et al., 2000; Qi et al., 2001; Liu et al., 2004; Xu and Shen, 1996).
Sichuan Basin (Figure 8) is the area that natural gas was discovered and used earliest in China. Over 100 gas fields have been found, most of them located in the eastern and southern parts of the basin. By end-2000, the proven recoverable gas reserves reached 16,959 bcf, of which 9641 bcf was found from 1991 to 2000, accounting for 56.8% of the total. The newly found reserves are concentrated in the Carboniferous limestone formations in Chuandong (Sichuandong) High Fold Belt in eastern Sichuan Basin (e.g., Figures 9 and 10), up to 7136 bcf, accounting for 74% of the reserves found from 1991 to 2000. The other two big contributors to the newly found reserves are Lower Triassic Feixianguan oolitic limestones, also in Chuandong High Fold Belt (e.g., Figures 11 and 12), and Jurassic sandstones in western Sichuan. The development and distribution of the oolitic limestones are the key trapping factors in the Feixianguan reservoirs (Zhao et al., 2002; Kang et al., 2000; Xu and Shen, 1996; Qiu and Gong, 1999; Zhou, 1996).
Tarim BasinFigures 13-14
Tarim Basin is the largest continental basin in China, with an area of 560,000 km2. Exploration has been quite active since middle 1980’s. Over 20 gas discoveries have been made, especially the discovery of the Kela 2 gas field (Figures 13 and 14), being the largest gas field of the country at the time of its discovery and forming the foundation for the construction of the trunk gas pipeline “West-Gas-To-East”. The gas fields are mainly distributed in the Kuqa Depression and Tabei Uplift in the northern part of the basin. Multiple source rocks and reservoirs exist. Primary reservoirs exist in the Cretaceous-Paleogene sandstone plays. By end-2000, the recoverable gas reserves of the Tarim Basin reached 12,769 bcf, becoming the third largest gas-supply basin in China after Ordos and Sichuan (Zhao et al., 2002, Xu and Shen, 1996; Qiu and Gong, 1999; Jia, 2000.
Figures 15 and 16
Qaidam is the largest biogenic gas accumulation area of China, represented by Sebei 1 and Sebei 2 fields (Figures 15 and 16). By end-2000, the recoverable gas reserves of the basin were 2826 bcf. The biogenic gas fields are mainly situated in the Sanhu Depression, accounting for 91.2% of the gas reserves of the basin. The biogenic gas reservoirs are composed of the Quaternary shaly sandstones deposited in shallow lacustrine environment. Favorable traps are syndepositional anticlines. Main source rocks are Upper Pliocene-Quaternary (Pleistocene) lacustrine dark mudstones and carbonaceous mudstones. The Qaidam Basin supplies gas for Xining and Lanzhou cities via the gas pipeline “Se (Sebei)-Ning (Xining)-Lan (Lanzhou) (Zhao et al. 2002; Xu and Shen, 1996; Qui and Gong, 1999; Shurr and Ridgley, 2002).
Before the 1990’s, natural gas was mainly used as fuel in the nearby areas around gas fields. The discovery of the Jingbian gas field in the Ordos Basin resulted in the construction of the gas trunkline “Shaan (Shaanxi)-Jing (Beijing)”. As more and more gas fields were discovered, gas pipeline networks were built. In the most recent decade, over 10,000 km of gas pipelines have been constructed, including the eastern section of the famous gas trunk “West-Gas-To-East.” Currently there are 3420 km of gas pipelines under construction, including the western section of “West-Gas-To-East.” Plans are to construct over 4,000 km of gas pipelines to form a network in eastern China.
Is a natural gas era coming to China? The answer is “Yes.” Why? 1. China faces a larger and larger gap in the production and consumption of energy. 2. Rapidly growing gas reserves form the foundation for increasing gas usage. 3. Gas pipeline networks have been constructed to make it possible for increasing gas usage. 4. Increasing gas usage is favorable for environment protection. It is believed that the above factors will spur the country’s gas exploration and production and vice versa.
The author is grateful to Keith Ina, Rick Luangkhot, and Tianguang Xu for their great help for illustration preparation, and to Richard Kyle for the text review. Partial data presented here are from IHS Energy’s field database. The author thanks IHS Energy for giving permission to publish it.
ReferencesJia, Chengzao, 2000, Recent Gas Exploration Progress in Tarim Basin, China: AAPG Bulletin, v. 84, p. 1395-1518. Kang, Zhulin, Chengde Fu, Shufen Cui, and Xianyi Yang, 2000, Introduction to Middle to Large Gas Fields in China: Petroleum Industry Press. Liu, Qingsheng, Lungsang Chan, Qingsong Liu, et al., 2004, Relationship between magnetic anomalies and hydrocarbon microseepage above the Jingbian gas field, Ordos basin, China: AAPG Bulletin, v. 88, p. 241-251. Qi, Min, Hua Yang, and Jinhua Fu, 2001, Deep Basin Gas in Ordos, in Deep Basin Gas Accumulation in Eerduosi Basin: Petroleum Industry Press. Qiu, Zhongjian, and Zaisheng Gong, 1999, Petroleum Exploration in China: Petroleum Industry Press. Shurr, George W., and Jennie L. Ridgley, 2002, Unconventional Shallow Biogenic Gas Systems: AAPG Bulletin, v. 86, no. 11, p. 1929-1969. Xu, Yongchang, and Ping Shen, 1996, A Study of Gas Origins in China: AAPG Bulletin, v. 80, no. 10, p. 1604-1614. Zhao, Xianzheng, Jingming Li, Dongxu Li, Shuopeng Ma, et al., 2002, Rapidly Developing Ten Years of China Natural Gas Exploration: Petroleum Industry Press. Zhou, Joe G., 1996, Evaluation of Sichuan Basin in China: AAPG Bulletin, v. 80, p. 985-985 |
