The Analysis of China’s Water Environmental Protection in Exploiting Shale Gas

In recent years, under pressures of the global energy crisis and climate change, shale gas(SG) was widely concerned as a relatively clean source of energy. One of the widely used technologies to exploit SG is hydraulic fracturing, which consumes a large amount of fresh water, pollutes water environment, and destroys ecological environment. China, which has the world's largest amount of SG, has begun to carry out researches and tests on SG exploitation by learning the technology and experience from developed countries. However, the imbalance between supply and demand of freshwater became the biggest constraint; water pollution situation and potential geological disaster risk put forward higher requirements for pollution prevention in exploiting SG. Water pollution could be effectively prevented by taking technological innovation, environmental supervision, environmental risks prevention and other measures in exploiting SG. KEYWORD: Shale gas; Water environment; Protection International Conference on Industrial Technology and Management Science (ITMS 2015) © 2015. The authors Published by Atlantis Press 1133 successfully completed a number of SG well drilling, cementing and fracturing operation and accumulated a preliminary experience. Overall, the exploration and exploitation of SG in China is still in its infancy. Exploration and core exploitation technologies are immature, especially that the environmental impact on the exploitation of SG is hard to eliminate [6,7]. Hydraulic fracturing technology is the most common and effective means of exploiting SG. However, hydraulic fracturing technology is a double-edged sword, and consumes a lot of freshwater resources. Taking American Barnett Shale for example, the average water consumption of drilling wells is 180 cubic meters per well, and fracturing operations is 13,650 cubic meters per well [8] . Since water is injected into the shale, which is much deeper than underground aquifers, and a lot of water is absorbed mainly by rocks, and can’t be recycled. Therefore, the key to successful exploitation of SG is to obtain enough water for drilling wells and fracturing operations. 3 THE MAIN ENVIRONMENTAL PROBLEMS IN CHINA’S EXPLOITATION OF SG 3.1 The imbalance between supply and demand of freshwater constraints the exploitation of SG The imbalance between supply and demand of freshwater has becoming increasingly serious in China. The total amount of freshwater resources is 2.8 trillion cubic meters, accounting for 6% of global freshwater resources, ranking fourth in the world. But there is only 1.1 trillion cubic meters of available freshwater resources, deducting flood runoff that is difficult to use and groundwater scattered in remote areas. According to statistics of Chinese 600 cities, over half of the cities are lack of water in varying degrees, and more than 110 cities are in serious water shortages. Coastal cities are no exception, and even more serious. It is predicted that without controlling, China’s water demand will reach to 818 billion cubic meters in 2030, and water shortage will be 201 billion cubic meters. When Chinese population reach to1.6 billion in 2030, the per-capita share of freshwater resources will fall to 1750 cubic meters, which is close to the international standards of water stress[9,10]. China’s natural environment for exploiting SG is harsher than America. Data show that SG reserves of China are mainly distributed in the Sichuan Basin and Tarim Basin, and mostly buried in the underground between 4000 to 6000 meters. These places are mostly mountainous or deserts, which are inaccessible, and in severe water shortages. In the Yangtze River basin where the water is relatively plentiful, SG is found only in Sichuan and Jianghan Basin. In the northwest and north China, SG reserves are abundant, while local freshwater resources are very tight. Considering the recent drought-prone in southwestern region, large-scale exploitation of SG may make the local situation worse in water shortages[11]. If 1.5 billion m 3 of SG in the Sichuan Basinwere exploited by drilling 1000 wells, which would take 24 hours uninterrupted work with all drilling wells for four years. Then 171 million m 3 of water would be used, which was equivalent to 1.1 percent of the mineable groundwater resources in the Sichuan Basin. Although 171 million m 3 of water accounts for a small proportion of freshwater resources, there are regional and seasonal water shortage problems in this region. Thus, the exploitation of SG will further exacerbate the imbalance between supply and demand of freshwater in China. Meanwhile improper wastewater treatments easily pollute the water environment. These will seriously affect the safety of China’s industrial and agricultural water supply and household water. Therefore, it is a challenge to obtain adequate water supply in the process of exploiting SG, and without confliction between the residents’ drinking water and industrial and agricultural water. 3.2 Water pollution situation puts forward higher requirements on the exploitation of SG The exploitation of SG primarily uses hydraulic fracturing method, and hydraulic breaker requires a lot of water, in which chemicals are added, including crosslinking agents, demulsifiers, and stabilizers. Hydraulic fracturing and SG production process will produce wastewater, including fracturing waste fluid and wastewater. These two kinds of wastewater contain potentially harmful contaminants, including salts, organic hydrocarbons, inorganic and organic additives, and naturally radioactive material. Especially, the chemical composition of the fracturing fluid will cause potential impact on groundwater. Taking fracturing waste fluid for example, a single horizontal SG wells generally consume 7,600-19,000 cubic meters of freshwater, and 15%-80% of fracturing waste fluid is discharged into the ground after fracturing operation. For contacting with the strata, the fracturing waste fluid has higher levels of metal ions, organic matter, chloride, and other pollutants. There is a risk of environmental contamination for improper disposal. Therefore, this technique will waste freshwater, and contaminate groundwater. Water pollution reduces the water function, exacerbates the imbalance between supply and demand of freshwater, and bring a negative impact on the implementation of the sustainable development strategy[12].