Types, Concentration, Diffusion and Spatial Structure Evolution of Natural Gas Resource Flow in China

Jan., 2016 Journal of Resources and Ecology Vol. 7 No.1 J. Resour. Ecol. 2016 7(1) 012-020 DOI: 10.5814/j.issn.1674-764x.2016.01.002 www.jorae.cn Types, Concentration, Diffusion and Spatial Structure Evolution of Natural Gas Resource Flow in China WANG Yiqiang 1,2, ZHAO Yuan 2,3*, XU Xin 2 1 School of Geography and Tourism, Qufu Normal University, Rizhao 276826, China; 2 School of Geographic Science, Nanjing Normal University, Nanjing 210023, China; 3 Jinling College, Nanjing Normal University, Nanjing 210046, China; Abstract: This paper analyzed the development of different types of natural gas flow zones in China, and then divided all provinces into four flow types: non-flow zones, output centers, input centers and exchanging centers. Next, we analyzed the concentration and diffusion characteristics, current spatial pattern and evolution of source and terminal regions of natural gas resource flows. The numbers of non-flow zones, output centers, input centers and exchanging centers all stabilized during the Eleventh Five-Year Plan period. The number of output centers is small but the quantity of flow is large. The number of input centers is large and they are widely distributed. Generally speaking, it presents a significant characteristic of centralized output and dispersed input in geographic space. The current situation for China s natural gas output source has random distribution characteristics, but the terminal regions of natural gas flow have strong positive spatial correlation, presenting a significant spatial agglomeration pattern. Shandong, Jiangsu, Zhejiang and Shanghai have a high-high agglomeration mode, but Yunnan, Sichuan, Tibet, Qinghai and Gansu have a low-low agglomeration mode. Spatial pattern changes in China s natural gas output zones had three different stages: relatively stable from 2001 2003; moved northwestward, expanded in space, and widely dispersed during 2004 2006; and transferred to the east, spatially contracted and significantly concentrated during 2007 2011. Spatial pattern changes in China s natural gas input zones have two stages: expanded in east-west direction while contracted in north-south direction during 2001 2005; and relatively stable in spatial structure with intensification from 2006 2011. Key words: natural gas resources; flow types; concentration and diffusion; China 1 Introduction Since entering the 21st century, China s natural gas industry has had a leap-forward development in exploration, production and resource utilization. During this period, natural gas flow between different regions has become increasingly frequent, just as the space phenomenon generated by coal and oil flow (Shen et al. 2012). Chinese and international researchers have done multi-angle studies of carbon-based energy resource flow. Economic geography focuses on energy flow process characteristics such as flux and flow direction, investigating the spatial structure of energy source regions, terminal regions and transshipment regions, and analyzing energy flow field characteristics and channel network structure (Zhao and Hao 2006; Cheng et al. 2008; Wang et al. 2009; Xu et al. 2008). Transport geography focuses on the inner structure, spatial arrangement, and chronological order of the unified transport network composed of various transport modes, revealing its inner mechanism and forecasting future trends (Yang and Zhao 2012; Satar and Peoples 2010; Fujii et al. 2002). Logistics science focuses on current characteristics, system construction and optimization of energy logistics network system from the Received: 2015-06-16 Accepted: 2015-10-26 Foundation: National Natural Science Foundation of China (41371518). *Corresponding author: ZHAO Yuan. Email: zhaoyuan@njnu.edu.cn. Citation: WANG Yiqiang et al. 2016. Types, Concentration, Diffusion and Spatial Structure Evolution of Natural Gas Resource Flow in China, Journal of Resources and Ecology. 7(1): 12 20.

WANG Yiqiang, et al.: Types, Concentration, Diffusion and Spatial Structure Evolution of Natural Gas Resource Flow in China 13 from the view of logistics facility, flux, flow direction, flow path and relationship between logistics elements (Wang et al. 2011; Cheng and Duran 2004; Warell 2005). Natural gas flow is an important component of carbon-based energy resource flow. However, research has focused largely on regional gas resource allocation and transportation system optimization (Ai et al. 2011; Li and Zhang 2012; Peng et al. 2012; Dang and Li 2013). With the scale of China s natural gas resource flow, spatial scale and effect range expansion, delving into macroscopic flow characteristics and trends in natural gas resources has become the premise of resource allocation and route optimization. Point to point linear pipeline transportation is the notable characteristic of natural gas transportation. The nodes of the production and consumption are usually natural gas fields, gas power plants and heating plants and other consumer terminals or terminal cities. Because of limited statistical data, researchers have been unable to do micro scale studies node to node. Here, we focus on the geographical distribution of natural gas flux in order to determine the direction of natural gas flow in China. This work does not involve natural gas transportation channels and refers to the existing achievements of oil, coal and other fossil energy flow, and takes natural gas resource flow regions as abstract nodes of internal homogenization. We analyzed natural gas resource passage or transfer relationships between different areas to grasp China s natural gas flow direction, flow rate and basic elements. The purpose is to provide a scientific basis for further research on optimization schemes of natural gas resource flow. Essential data included natural gas input values (including the value of imports from other provinces and countries) and output values (including the value of exports to other provinces and countries) in provinces in the 21 st century. 2 Materials and methods 2.1 Spatial clustering analysis Spatial clustering analysis takes space correlation measurement as the core. Spatial clustering analysis can find the spatial association mode and reveal spatial dependence and heterogeneity through the description and visualization of spatial distribution patterns. It puts forward different spatial structures and other modes of spatial instability (Goodchild and Maguire 1999). This paper will employ Moran s I and Local Moran s I (LISA) to measure the global spatial autocorrelation and local spatial autocorrelation of study subjects. Moran s I is the earliest method applied to global clustering tests, which examine the similarity (positive spatial correlation), dissimilarity (negative spatial autocorrelation) and mutual independence of surrounding areas (Wang 2006). Moran s I is a global statistical index; however, it is difficult to detect the spatial association mode of local regions. Local spatial autocorrelation analysis can measure local spatial association and spatial differences between a region and surrounding areas and identify spatial agglomeration and spatial isolation. Local Moran s I (LISA) defined by Anselin and Florax (1995) is generally used to detect aggregation of the local space and analyze instability. 2.2 Standard distance and standard deviation ellipse The standard distance and standard deviation ellipse reflect the overall characteristics of China s natural gas resources flow spatial distribution from multiple angles. Standard distance reflects the average range of the flux factor s spatial distribution of natural gas source regions or terminal regions. Standard deviation ellipse reflects the spatial distribution of natural gas source regions or terminal regions, and recognizes change trends, their centers and moving directions. The specific calculation method follows Lauren and Mark (2010), Wong (1999) and Gong (2002). Data is from the China Energy Statistics Yearbook (no data or analysis for Hong Kong, Macao and Taiwan). Spatial data is from the National Fundamental Geographic Database, including China provincial administrative zoning map and government coordinates. 3 Flow types of natural gas resources in China 3.1 Flow types Because of the influence of regional resource endowments the flow functions undertaken by different regions in the process of natural gas resource flow differ. This paper divided all provinces with natural gas flow into four types, referring to Zhao and Hao (2006) who classified oil resource flow. The four types include output centers, input centers, exchanging centers and non-flow zones. Natural gas surplus regions that export resources to other areas are called output centers. Natural gas loss regions that import resources from other areas are called input centers. Regions both outputting resources and inputting resources are called exchanging centers. Regions which neither output resources nor input resources are called non-flow zones. Early in China s Reform and Opening Up phase, gas transportation was only in a few provinces. For example, there were two gas output regions including Tianjin and Sichuan, only four gas input regions including Beijing, Hebei, Guizhou and Yunnan in 1985, and all of the above areas were one-way flow. Natural gas flow between provinces was at a small scale in that period. With growing demand for natural gas caused by national economic development and more gas exploration and production, gas transportation in different provinces became grew. The number of no gas communication provinces constantly reduced and the number tended to be stable in the Eleventh Five Year period (maintained at 2 3). Several areas of large natural gas production undertake resource output function, which belong to output centers. The number was stable at about 5 7 after the 1990s. Changes in the number of input centers and non-flow

14 Journal of Resources and Ecology Vol. 7 No. 1, 2016 zones are opposite. Most of the region belonging to nonflow zones gradually transformed into input centers, especially in southern provinces. The number of exchanging centers is growing, maintained at 5 7 at present. Overall, different types of gas resources flow are in a relatively stable state in the Eleventh Five Year period and China natural gas flow pattern has primarily formed (Table 1). Table 1 Number of different flow types of natural gas resources in China from 1985 to 2011. Year Non-flow zones Output centers Input centers Exchanging centers 1985 23 2 4 0 1995 20 5 3 2 2000 17 7 4 3 2001 17 6 5 3 2002 14 7 6 4 2003 12 7 8 4 2004 7 6 13 5 2005 4 6 17 4 2006 3 8 17 3 2007 3 6 16 6 2008 2 7 17 5 2009 3 7 16 5 2010 2 5 17 7 2011 3 5 18 5 Data source: Energy Statistics Division, National Bureau of Statistics 1986-2012. 3.2 Flow functions There were three provinces with no gas communication in 2011: Tibet, Jilin and Heilongjiang. Natural gas supply bases are mainly distributed in western China, including Inner Mongolia, Sichuan, Shaanxi, Qinghai and Xinjiang Table 2 Regional natural gas flow types in 2011. (larger output centers) (Table 2). Sichuan and Inner Mongolia have been production bases of natural gas, whose supply quantity was large and stable in China. Before 2003, Sichuan natural gas supply was located in the top four. Inner Mongolia has had rapid growth of output since 2008, ranked second in the country. Xinjiang in 2006 and Shaanxi in 2011 emerged as the largest gas output areas respectively, which had a decisive influence on changes in natural gas source regions. Recently, Qinghai s natural gas output undergone obvious growth and grown into a relatively large output base. Input centers of natural gas resource flow is mainly concentrated in 18 provinces, located in the east of the line formed by Inner Mongolia, Shaanxi and Sichuan. Some provinces whose gas consumption is totally dependent on external resources almost has no natural gas production and their self-sufficiency rate is 0. These provinces include Anhui, Zhejiang, Fujian, Hunan, Hubei, Guizhou, Guangxi, Ningxia, and Beijing. Natural gas production is very low in nine provinces where the self-sufficiency rate is less than 10%, including Jiangsu, Shanghai and Shandong. However, these provinces have a large population, developed economy and large gas consumption, thus must input a large number of external resources to make up for the consumption gap. Shanxi, Chongqing, Tianjin, Guangdong and Hainan belong to exchanging centers, whose geographical positions are generally located in the connection of massive resource production and consumption areas. Above five provinces are also big resource producers and play a role in resource distribution. Shanxi transits natural gas from Shaanxi to Beijing; Chongqing is located in the center of Sichuan natural gas area getting into southern provinces; Guangdong and Hainan is the main hub of China s natural gas imports and exports; and Tianjin plays the role of communication in the Region Degree of self-sufficiency (%) Flow type Region Degree of self-sufficiency (%) Flow type Beijing 0.00 Shandong 10.14 Zhejiang 0.00 Liaoning 18.54 Anhui 0.00 Jiangxi 29.18 Fujian 0.00 Hebei 34.95 Hubei 0.00 Inner Mongolia 610.32 Hunan 0.00 Shaanxi 435.68 Guangxi 0.00 Xinjiang 247.74 input centers Ningxia 0.00 Qinghai 202.84 Guizhou 0.00 Sichuan 156.16 Jiangsu 0.58 Guangdong 111.74 Yunnan 1.67 Chongqing 99.40 Gansu 5.21 Shanxi 85.37 Shanghai 5.44 Tianjin 72.61 Henan 9.11 Data source: Energy Statistics Division, National Bureau of Statistics 2012. Hainan 3.99 Input centers Output centers Exchanging centers

WANG Yiqiang, et al.: Types, Concentration, Diffusion and Spatial Structure Evolution of Natural Gas Resource Flow in China 15 Bohai rim. Overall, there are a small number of natural gas output regions with big flow and a large number of natural gas input regions with a wide distribution, which shows the significant features of centralized output and dispersed input over geographical space. 4 Agglomeration and dispersion characteristics Natural gas source regions are mainly concentrated in western China; on the contrary, terminal regions are located in mid-eastern China. However, there are some agglomeration tendencies in space for both flow types. 4.1 Analysis of Moran s I Taking provinces as the study units, there will be a source region for a resource output province, and a terminal region for a resource input province. Before computing Moran s I, we first did a logarithmic transformation (normal transformation) for the flux of natural gas in provinces in order to make the frequency follow a normal distribution (Table 3). When investigating the time series of Moran s I in source regions and terminal regions we found that except for 2003 2005, Moran s I in source regions are negative and close to 0. This indicates that natural gas output in China is relatively dispersed in geographical space. However, except for 2007, Moran s I in terminal regions are all positive and suggests that the spatial distribution of terminal regions has a certain clustering property. Investigating the time series of Moran s I in terminal regions, the values overall present a process that decreases in advance and then increases. This shows that the agglomeration of natural gas terminal regions is strengthening gradually in China. In 2011, Moran s I in terminal regions was 0.3229. Carrying out the test of the approximate normal distribution, the value of z is 3.2679, which is greater than the critical value 2.576 of normal distribution 99% confidence interval. This suggests that the spatial distribution of terminal regions has a strong positive autocorrelation and represents a remarkable spatial clustering model. Table 3 Moran s I evolution of source and terminal regions for natural gas flow in China. Year Source regions Terminal regions 2001 0.1108 0.2152 2002 0.0202 0.18 2003 0.175 0.1628 2004 0.2359 0.0034 2005 0.1067 0.1668 2006 0.0799 0.0936 2007 0.0833 0.0352 2008 0.0649 0.0811 2009 0.0271 0.0799 2010 0.0577 0.2862 2011 0.0202 0.3229 Data source: Energy Statistics Division, National Bureau of Statistics 2002-2012. 4.2 Analysis of LISA Moran s I of natural gas terminal regions in 2011 indicates a strong positive correlation in their total space distribution. However, Moran s I is unable to express the type of clustering. This paper used Geodata to construct spatial weight (Queen Adjacency) and draw a distribution map of LISA (Fig. 1) based on Z tests (P 0.05) in order to reveal local agglomeration of natural gas terminal regions. There is a very obvious high-high agglomeration (hot spot) in coastal areas of eastern China, including two provinces and one city in the Yangtze River Delta and Shandong (Fig. 1). Anhui becomes a notable low-high concentration area because the import of natural gas in Anhui is less and Anhui borders Shandong, Jiangsu and Zhejiang whose correlation type are high-high. There is a wide range of lowlow concentrations (cold spot) in the whole study area. The concentration region is located mainly in southwestern China, including Yunnan, Sichuan, Tibet, Qinghai and Gansu. In addition, Heilongjiang also shows the low-low Fig. 1 Moran significance maps for terminal regions of natural gas flow in 2011.

16 Journal of Resources and Ecology Vol. 7 No. 1, 2016 concentration feature because it is adjacent to Inner Mongolia and Jilin (low natural gas input). There are two main reasons for the regional agglomeration of cold spots. First, natural gas reserves in Tibet, Yunnan and Gansu are small but their economic development levels are low and demand for natural gas is relatively small; the corresponding inflow is small. Second, Sichuan, Qinghai and Heilongjiang have a certain scale of natural gas production. Qinghai and Sichuan are resource output centers, and in Heilongjiang natural gas production and consumption is balanced. As a result, natural gas input is relatively small. In conclusion, natural gas terminal regions in China totally perform the characteristic of high value concentration in coastal eastern China but low value concentration in southwestern and northwestern China. 5 Spatial pattern evolution Spatial clustering is only suitable for analysis of clustering and dispersion of natural gas source regions and terminal regions, but not the dynamic evolution of spatial patterns. Therefore, standard distance and standard deviation ellipse for space structure analysis and variation were adopted to reveal the evolution of spatial patterns of natural gas source regions and terminal regions in China. 5.1 Spatial pattern evolution of source regions 5.1.1 Gravity movement trajectory As shown in Figure 2, gravity centre movement for natural gas source regions was located between 102.37 109.77 E and 25.27 36.93 N, including Sichuan, Chongqing, Guangxi, Guizhou, Ningxia, Gansu and Qinghai. Compared with the Chinese mainland geometry center (103.83 E, 36 N), the gravity centre moving track of source regions shows a tendency far from the geometric center and moving closer to it. The offset between gravity centre and geometry center in 2004 was the largest. The deviation in the east-west direction was 5.94 and 10.73 in the north-south direction. By 2011, the deviation in the east-west direction reduced to 1.24, and to 0.93 in the north-south direction. From the time series, the gravity centre moving track of source regions has an obvious feature of periodicity. It moved mainly southeastward from 2001 to 2004, and the space location shifted from northern Chongqing in 2001 to northern Guangxi in 2004. It moved northwestward in turn from 2004 to 2008, and finally eastward after 2008. The gravity centre of source regions moved southeastward from 2003 to 2004 because the amount of natural gas exports in Hainan increased rapidly with no significant changes in output for other source regions. The gravity centre of source regions moved northwestward because Xinjiang natural gas was supplied to Shanghai and other parts of eastern China in 2004 as the east-west gas pipeline came into operation. However, Hainan gas exports continuously reduced at the same time. For example, the moving distance and speed of source regions gravity centre northwestward movement was maximized from 2005 to 2006. At the same time, Xinjiang natural gas output grew from 50.18 10 8 m 3 in 2005 to 102.54 10 8 m 3 in 2006, but Hainan natural gas exports fell rapidly from 215.1 10 8 m 3 in 2005 to 26.97 10 8 m 3 in 2006. This caused the gravity center of natural gas source regions to move northwestward quickly. The gravity centre of source regions moved eastward from 2009 to 2011, a major reason for which was that the output of natural gas grew rapidly in Shaanxi and Inner Mongolia, and in Xinjiang natural gas output decreased over the three years; thus it caused a move eastward. 5.1.2 Standard distance and standard deviational ellipse Space distribution and density of source regions experienced three stages of development (Table 4). Stage 1: standard distance change was smaller, density rose slightly and spatial distribution and gravity center changes were Fig. 2 Discrete trends in the spatial structure of source regions of natural gas flow in China.

WANG Yiqiang, et al.: Types, Concentration, Diffusion and Spatial Structure Evolution of Natural Gas Resource Flow in China 17 Table 4 SD and SDE parameters of natural gas flow source regions in China. Year Standard distance (km) Density (10 4 m 3 km -2 ) Standard deviation for x-axis (km) Standard deviation for y-axis (km) Angle of rotation ( ) 2001 934.80 0.50 1137.51 673.61 146.70 2002 918.82 0.67 1089.57 708.03 137.19 2003 974.74 0.78 1201.48 675.78 157.74 2004 910.51 1.98 1193.02 484.50 169.30 2005 1235.67 1.35 1589.35 726.44 153.17 2006 1317.84 0.86 1669.34 828.69 131.90 2007 1313.62 1.12 1685.64 780.91 128.88 2008 1211.29 1.47 1528.03 774.33 121.17 2009 1169.89 1.62 1420.30 848.54 118.31 2010 1184.84 1.77 1392.38 932.18 119.69 2011 1068.94 2.20 1201.47 917.45 109.30 Data source: Energy Statistics Division, National Bureau of Statistics 2002-2012. relatively stable from 2001 to 2003. Stage 2: standard distance was rising, density was constantly reducing, and source regions presented a trend of decentralization in spatial expansion from 2004 to 2006 because Hainan natural gas exports reached the highest value and Xinjiang natural gas output had rapid growth. The absolute distance between the two zones increases the spatial distribution of the whole source system and leads to a reduction in density. Stage 3: standard distance decreased continuously, density was constantly increasing, and source regions presented a trend of concentration in space shrinkage from 2007 to 2011 because Hainan natural gas export was relatively small and stable (maintained at around 20 10 8 m 3 ) and no longer in the main position in major source regions. Xinjiang natural gas output was flat-to-lower, and fell to 140.37 10 8 m 3 in 2011. However, Shaanxi and Inner Mongolia natural gas output growth was obvious and reached 210.42 10 8 m 3 and 208.26 10 8 m 3 respectively in 2011, exceeding that of Xinjiang. At present, the source system represents a situation of tripartite confrontation by Xinjiang, Inner Mongolia and Shaanxi. The three regions are more concentrated in distribution and this causes concentration in spatial shrinkage. From the perspective of the angle of rotation, there was a trend of increasing-decreasing. The angle of rotation was 146.7 in 2001 and increased to 169.3 in 2004. At this stage, Hainan, Sichuan and Chongqing had the largest resource output and showed a space state of southeast-northwest direction. Since 2005, the angle of rotation has continuously decreased because Hainan natural gas exports decreased significantly after peaking and Xinjiang, Shaanxi and Inner Mongolia have emerged successively. The angle of rotation was constantly decreasing, which caused the space state into a south-north direction. From the perspective of the long axis and the short axis, standard deviations of the x-axis are greater than the y-axis. Thus, east-west is greater than north-south in the spatial distribution of source regions, illustrating that the absolute number gap of natural gas output in the east-west direction is less than that of the north-south direction. This also reflects spatial differences in the geological distribution of natural gas in China. That is, bad natural gas resource endowment in southern China is the main reason for the entire spatial pattern. With internal change in the long axis and short axis, both were relatively small from 2001 to 2003, indicating that the space range of the source regions was relative stable. Both the long axis and short axis had an increasing trend from 2004 2006, indicating that the spatial distribution in the east-west direction and north-south direction were decentralized. The long axis was constantly decreasing and the short axis was increasing from 2007 2011, indicating that the spatial pattern of source regions began to polarize in an east-west direction but continued to diversify in a north-south direction. 5.2 Spatial pattern evolution of terminal regions 5.2.1 Gravity movement trajectory As shown in Figure 3, the gravity centre moving track of natural gas terminal regions was located at 112.83 115.64 E and 32.2 36.2 N, including Southeast Shanxi, Henan and Northwest Anhui. Compared with the continental geometry center, the gravity centre of terminal regions is located to the east. The maximum deviation in the east-west direction is 11.81, and 3.8 in the north-south direction. The gravity centre moving track of terminal regions shows a tendency to move in a northwest-southeast direction. The gravity centre of terminal regions moves southeastward quickly, gradually away from the geometric center because natural gas inputs of coastal areas in eastern China, especially the Yangtze River Delta region, have grown rapidly because of the east-west gas pipeline and zhong wu line. However, there are twists and turns in the process of gravity centre movement for terminal regions. The second Shan Jing gas pipeline project was put into operation in 2005 and caused Beijing natural gas inputs to increase and the gravity center of natural gas terminal regions to move northeast-

18 Journal of Resources and Ecology Vol. 7 No. 1, 2016 Fig. 3 Discrete trend changes in the spatial structure of terminal regions of natural gas flow in China. ward. Beijing natural gas input increased rapidly in Chongqing City in 2008, but Guangdong natural gas input reduced and caused the gravity center to move northward. Overall, movement of the natural gas gravity center was influenced by the construction of natural gas pipelines from 2003 to 2007 and the traffic directive was strong. After 2008, China s main pipeline network of natural gas, LNG-receiving devices and related pipelines and infrastructure was gradually perfected; this weakened the traffic directive. At this stage, the rigid demand of coastal areas of southeastern China for natural gas consumption became the main cause of the shift of the gravity center southward. 5.2.2 Standard distance and standard deviational ellipse The space distribution and density of terminal regions has experienced two stages of development (Table 5). Both standard distance and intensity were relatively small from 2001 to 2004. The standard distance was about 900 km, and the intensity was slightly greater than 0.4 104 m 3 /km 2. The spatial distribution and gravity center change were relatively stable. The standard distance dropped to 800 km, but the Table 5 SD and SDE parameters of terminal regions of natural gas flow in China. Year Standard distance (km) Density (10 4 m 3 km -2 ) Standard deviation for x-axis (km) density was constantly increasing from 2005 to 2011. Terminal regions presented a trend of concentration in space shrinkage. The reasons are as follows: since the east-west gas pipeline began operation the main pipeline network of natural gas, LNG-receiving devices and related pipelines and infrastructure has improved. The need for natural gas, especially in coastal areas of eastern China, has been effectively alleviated. With rapid growth in natural gas consumption in central and eastern China, natural gas input is increasing. The spatial range of terminal regions overall in central and eastern China will not change greatly and the natural gas density of terminal regions is continuously intensive. There were two stages regarding the angle of rotation. In 2001 2005 the angle of rotation was generally about 40 ; and in 2006 2011 the angle of rotation was reduced to 10. From 2001 2005, natural gas was mainly imported into Beijing, Tianjin, Hebei, Liaoning, Chongqing, Yunnan and Guizhou. The spatial structure of terminal regions was northeast-southwest. During this stage, Gansu natural gas Standard deviation for y-axis (km) Angle of rotation ( ) 2001 898.51 0.47 238.54 1248.10 35.38 2002 876.74 0.41 346.74 1190.43 37.36 2003 866.06 0.41 437.31 1144.07 40.63 2004 919.57 0.43 741.66 1068.25 15.30 2005 780.73 0.71 654.17 889.46 47.64 2006 808.65 0.95 728.20 881.80 12.54 2007 827.40 1.60 636.81 981.66 7.50 2008 772.22 2.23 624.50 895.90 14.43 2009 755.03 2.70 592.62 888.22 6.25 2010 837.83 2.95 609.00 1016.38 11.66 2011 824.71 3.65 605.88 996.59 12.72 Data source: Energy Statistics Division, National Bureau of Statistics 2002-2012.

WANG Yiqiang, et al.: Types, Concentration, Diffusion and Spatial Structure Evolution of Natural Gas Resource Flow in China 19 input increased significantly and promoted a spatial structure westward expansion. From 2006 2011, major terminal regions quickly turned into Beijing, Anhui and coastal areas throughout the east, especially the Yangtze River Delta region. There was also some growth of natural gas inputs in central China; the spatial structure became a north-south direction and gradually tended to be stable. From the perspective of the long axis and short axis, the standard deviations for the y-axis are greater than the x-axis. North-south is greater than east-west in the spatial distribution of terminal regions, illustrating that the absolute gap of natural gas output in the north-south direction is less than that in east-west direction. This also reflects the spatial difference of China s economic development. The gap in the level of national economic development in the east-west direction is greater than the gap in the north-south direction. With internal change in the long axis and short axis, the long axis constantly decreased and the short axis increased from 2001 to 2005, indicating that the space pattern of terminal regions began to polarize in a north-south direction, but continued to diversify in an east-west direction. The changes in the long axis and short axis were relatively stable state from 2006 to 2011, indicating that the spatial structure was in a stable developmental stage spatially. 6 Conclusion and discussion The abundance and development order of natural gas resources are major factors accounting for the spatial pattern of source regions of natural gas resources flow in China. In mid-western China there are four national natural gas bases, including the Tarim gas field, Qinghai gas field, Southwest gas field and Changqing gas field. Offshore natural gas production at a large scale is done at the South China Sea gas field represented by the Pearl River Mouth Basin and Qiongdongnan Basin. These five gas fields are the main bases of natural gas production and supply, of which the Southwest gas field is exploited first, followed by South China Sea gas field, Tarim gas field and Changqing gas field, and the Qinghai gas field. The development of new gas fields would drive massive resource outputs (transferred to other provinces or exported to other countries) that have shaped the history and current pattern of source regions of natural gas resource flow. Terminal region spatial patterns change with the evolution consumption patterns. Before 2003, the consumption of natural gas was mainly concentrated in several large resource production areas such as Xinjiang, Chongqing, Sichuan, and Heilongjiang. Developing the natural gas industry in such areas relies on the advantages of resources, which have huge consumption. At the same time, some provinces access to natural gas resources has geographical advantages. For instance, Yunnan and Guizhou usually access natural gas resources from Chongqing and Sichuan, and Beijing and Hebei from Tianjin. At this stage the geographical location is the main cause of natural gas resource flow. Since 2004, China has built an arterial network of oil and gas pipelines with a clear hierarchy due to natural gas infrastructure construction, such as the Sichuan to East Gas Pipeline Project and East-West Gas Pipeline Project. Therefore, natural gas resource consumption gradually spread to developed areas of mid-eastern China from resource production areas. With continuous improvement of the level of economic development in mid-eastern China and transformation of economic development, China natural gas consumption has exceeded the supply of domestic resources. Importing natural gas becomes a powerful prospect. There is strong traffic and economic directives in natural gas resource flow leading the formation mechanism of resource flow. Traffic and economic directives are complementary, showing that regional traffic conditions and natural gas economies promote each other. The arterial network construction of gas pipeline facilities in southeastern China and optimization layout of LNG infrastructure should be strengthened. The spatial pattern evolution of natural gas resources flow suggests that southern China (located east of Chongqing) will become the new center of China natural gas consumption. Because natural gas resource flow has strong traffic directives, pipeline infrastructure networks between southern China and gas production areas in Shaanxi, Inner Mongolia, Sichuan and Chongqing should be improved. According to the distribution pattern of the existing natural gas pipeline, on top of Jiangsu, Anhui, Hubei and Jiangxi, the gas arterial network is deficient or absent in other parts of southern China. For instance, a second east-west gas pipeline runs from Jiangxi to Zhejiang, which only protects gas consumption in Hangzhou and other small and medium-sized cities located along the pipeline. Fujian is completely isolated from the national natural gas arterial network. Guangdong, excluding the Pearl River Delta, cannot be effectively protected and other coastal cities in the province have no pipes. This shows the natural gas pipeline infrastructure construction in southeastern China is lagging behind, particularly in areas ranging from Hangzhou, to the south by the Pearl River Delta. There is an urgent need to plan and construct gas arterial networks, represented by the Sichuan to East Gas Pipeline Project and East-West Gas Pipeline Project, extending to coastal areas in southeastern China. The optimization of LNG terminals, pipelines and infrastructure is also required. Further work should take natural gas fields as source regions of resource flow and consumer terminals represented by gas powers as terminal regions. With a gradual increase in the amount of overseas imports of liquefied natural gas, the disturbance of LNG to China s natural gas resource flow is gradually increasing. However, we did not consider overseas production regions of LNG in the source system. Future work should concentrate on strengthening the analysis of the impact of the international LNG market to China nat-

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