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Site selection principle
In order to realize the geological storage of CO2 in deep saline water, CO2 must be stored underground in the form of supercritical fluid, that is, the storage depth must be greater than 800 m ... Geological storage of CO2 is equivalent to building an underground artificial gas reservoir, and its site selection conditions mainly consider the following factors: it is located in a stable geological structure, where earthquakes, volcanic activities and active faults are not developed, and the possibility of sealed gas leaking to the atmosphere is small; The reservoir has high porosity and permeability and a certain thickness, which can reach the required storage capacity; Cover with airtight cover (Zhang et al., 2005; Sun Shu, 2006; Xu Zhigang et al., 2008; Zhang Sen, 20 10).

Different from natural gas reservoir conditions, the following factors should be considered: the reservoir pressure exceeds the critical value of CO2, CO2 is compressed at this pressure, the density is 600-800 kg/m3, and the buoyancy is lower than that of natural gas but higher than that of crude oil; The lower geothermal gradient and geothermal flow value make CO2 reach a higher density at a smaller depth. The negative impact on human society, natural environment and resources is small (Shen, 2009).

To sum up, there are both reservoirs with good groutability and stable caprocks, the regional geological structure is stable, earthquakes, volcanic activities and active faults are underdeveloped, and unconnected caprocks do not have geological defect risk factors such as cracks, faults and abandoned wells, which can ensure the safe geological storage of CO2 for more than 1000 years, and the ground engineering of grouting site is not affected by adverse geological effects on the surface, with reasonable source-sink matching and relatively low cost. It also meets the requirements of local industrial and agricultural development planning, relevant laws and policies and environmental protection objectives. "Underground determines the ground, and underground gives consideration to the ground" is the basic principle of CO2 geological storage site selection in deep saline water.

(1) The target reservoir is based on the principle that carbon dioxide can be stored for more than 30 years, with a large storage capacity.

As far as the average service life of modern coal-fired power plants is concerned, the reasonable service life of CO2 geological storage site in deep brine layer should be more than 30 years.

The service life of CO2 geological storage site in deep saline aquifer is the time from CO2 injection to closure. Theoretically, the longer it is used, the lower the geological storage cost per unit of carbon dioxide. Therefore, the service life of the site should be fully considered when selecting the site.

Effective storage capacity is defined by applying certain technical conditions (geology and engineering), such as physical conditions of caprock (porosity, permeability, temperature and pressure), burial depth, stability and safety, and development and utilization of other resources (oil, natural gas, coal, geothermal and minerals, etc.). ) in the storage area.

In order to determine the effective storage capacity of the proposed site, it is necessary to collect data through geophysical exploration, drilling, sample collection and testing, perfusion test and monitoring, so as to clarify the geometric shape of the reservoir, the integrity of the trap structure, and the buried depth, thickness, porosity, permeability, heterogeneity, pressure, temperature, rock mineralogy characteristics, fluid flow direction and salinity of the deep saline water layer, and screen potential reservoirs, and determine them through numerical simulation.

(2) Safety principle

Safety principle is an important principle for the location of CO2 geological storage in deep salt water. The impacts of leaked CO2 on the local environment are as follows: First, it may increase the acidity of the receiving water, break the original geochemical and ecological balance, and lead to groundwater pollution; Second, once a strong crustal movement occurs, a large amount of CO2 will leak to the surface, which will cause devastating disasters to nearby areas (Zhou Xitang, 2006) and affect people's health; In addition, it may also induce earthquakes, produce ground deformation and produce geological disasters.

Therefore, in the site selection stage of the project, it is necessary to carry out site geological data collection, remote sensing geological survey, site comprehensive geological survey, geophysical exploration, drilling, grouting test and environmental background monitoring to find out the site historical earthquake, active faults, crustal stability, caprock sealing, and whether there are potential CO2 leakage channels such as abandoned drilling and faults. Clear the basic data such as whether there is a groundwater aquifer in the upper part of the reservoir that can be used for industry and agriculture, the relationship and distance with the main recharge area of available groundwater, the location relationship and distance with surface drinking water sources such as rivers and reservoirs, the distance with fixed settlements, the dominant wind direction relationship with fixed settlements and the distance with other target areas that need special protection. In the site selection stage, the local risk of CO2 geological storage in deep saline water layer caused by geological defects is eliminated.

(3) Economic principles

At present, it is the basic principle to realize the geological storage of CO2 in deep saline water with reasonable technical and economic scheme, less investment and additional consumption of other fossil energy.

Therefore, in the site selection stage, it is necessary to understand the distribution and scale of CO2 sources, the distance of carbon sources, infrastructure (water, electricity, transportation, communication, medical care, etc.). ), understand the price of land acquisition and CO2 injection project construction, demonstrate the mode of transportation, and put forward the best economic plan.

(four) in line with the general construction project environmental protection site selection conditions, not affected by external adverse geological factors.

At present, CO2 geological storage practices mostly treat CO2 as industrial waste. Therefore, CO2 geological storage project belongs to environmental protection project. At the same time, due to the leakage risk of CO2 geological storage, the principle of meeting the environmental protection site selection conditions of general construction projects should be adhered to in the site selection stage.

For example, GB 18598-200 1 Pollution Control Standard for Hazardous Waste Landfill stipulates as follows.

(1) The selection of landfill site should meet the requirements of national and local urban and rural construction master plans, and the site should be in a relatively stable area, which will not be damaged by natural or human factors.

(2) Landfills should not be selected in urban industrial and agricultural development planning areas, agricultural protection areas, nature reserves, scenic spots, cultural relics (archaeological) protection areas, drinking water source protection areas, water supply prospective planning areas, mineral conservation zone and other areas that need special protection.

(3) The distance from the landfill to the airport and military base should be more than 3000 meters.

(4) The boundary of the landfill should be located 800 m away from the residential area, which will not affect the atmospheric environment of the nearby residential area under local meteorological conditions.

(5) The landfill must be located above the elevation line of once-in-a-century flood, and outside the flooded area and protected area of artificial water storage facilities such as reservoirs in the long-term planning.

(6) The distance between the landfill and the surface water area should not be less than150 m.

(7) The geological conditions of the landfill should meet the following requirements: it is located outside the main recharge area of groundwater and drinking water sources; The geological structure is relatively simple and stable, with no faults.

(8) Landfill site selection should avoid the following areas: destructive earthquakes and active tectonic areas; Areas affected by tsunamis and surges; Wetlands and low-lying watersheds; Areas with high ground stress concentration and rapid ground uplift or subsidence rate; Cave development zone; Abandoned mining area or subsidence area; Collapse, rock pile and landslide area; Mountain torrents and debris flow areas; Active dune area; Unstable alluvial fan and gully area; High compressibility silt, peat and soft soil areas and other areas that may endanger the safety of landfills.

(9) The landfill site should be selected in an area with convenient transportation, short transportation distance, low construction and operation costs and the normal operation of the landfill site.

The above-mentioned environmental protection site selection conditions can be used as a reference for the site selection of CO2 geological storage ground engineering in deep saline water layer.