I. Selection of test sections
1. Hydrogeological conditions in the test area
(1) Anyang experimental area
1) Groundwater burial conditions and water abundance: The experimental area is located in the southwest of Anyang City and belongs to the alluvial and diluvial fan of Anyang River. The alluvial-diluvial fan of Anyanghe River was formed in the middle and late Pleistocene and late Holocene, and it has an obvious binary structure with fine upper part and thick lower part. Surrounded by mountains and hills on three sides, it is open to the east and is dustpan-shaped, with good sealing conditions, forming a complete hydrogeological unit.
The terrain of the experimental area is flat, and the surface layer is mostly silt, which is beneficial to the recharge of atmospheric precipitation. The water-bearing medium is composed of middle-upper Pleistocene sandy pebble layer (Figure 4- 1). Shallow groundwater (more than 100m) is mainly mined in the experimental area, which occurs in the loose fissure water storage medium of the alluvial-diluvial fan of Anyang River, and the bottom is a partition composed of mud gravel or clay of Lower Pleistocene.
The main water storage media in the experimental area are middle-upper Pleistocene alluvial gravel and semi-cemented calcium gravel layer (Figure 4-2). Here, the roof of the gravel layer is buried at a depth of 26.4m, slightly inclined to the east, with a thickness of about 32m, mainly composed of limestone, followed by timely sandstone, with a particle size of 0.2-5cm and a maximum of 10cm, with good roundness, poor sorting, sand content of about10%-30%, and clay lenses locally sandwiched. The daily inflow of a single well is about 5000m3/5m, the buried depth of water level is 37.5m, and the thickness of water-bearing medium is 21m.. The permeability coefficient is greater than 200m/day.
Figure 4- 1 Hydrogeological Profile of Anyang Experimental Area
Figure 4-2 Histogram of Stratum Structure of Sanfenzhuang Pumping Well in Anyang City
2) Chemical characteristics of groundwater: The chemical type of groundwater in the experimental area is HCO3, and the salinity is generally less than 1g/L, so it is fresh water.
(2) Zhengzhou High-tech Zone Experimental Zone
1) Groundwater burial conditions and water abundance: The experimental area is located in Huicheng Community in the northeast of Zhengzhou High-tech Development Zone, and the aquifer is Quaternary Holocene and Upper Pleistocene, alluvial and diluvial, followed by Middle Pleistocene. Groundwater above 150 ~ 200 m can be divided into shallow groundwater and middle groundwater, which have certain hydraulic connection, and the actual exploitation is mostly mixed intake. Shallow groundwater is shallow. In the experimental area, the bottom plate of shallow aquifer is about 70m deep and 30m thick. At present, the area has changed from an agricultural area in previous years to a new industrial area. The water supply source of this city is the groundwater in the Jiuwutan water source area of the Yellow River. In addition, the cultivated land in this area is reduced, the exploitation of middle and deep groundwater is restricted, and the intensity of groundwater exploitation is low. In addition, the experimental area is adjacent to the stone Buddha grit chamber in the east, and the surface water has a strong recharge effect on the shallow underground, and the groundwater level has an obvious upward trend.
The water in the middle and deep layers mainly consists of alluvial deposits in the middle and lower Pleistocene in Quaternary and upper lake deposits in Neogene. The buried depth of the roof of the middle-deep aquifer group in the experimental area is about 90m, and the middle-deep water is the main exploitation layer for urban water supply at present, with the well depth of about 100 ~ 300m, and the lithology of the aquifer is medium sand, fine sand and coarse sand. The total thickness of the shallow aquifer at 200m is about 50m.
According to the existing drilling and pumping data (Figure 4-3), the mixed water level of shallow and middle-deep layers is generally around 30m. The actual pumping depth is 20m, the water output of a single well is 70m3/h, and the permeability coefficient is generally 8 ~10m/d. According to the evaluation results of groundwater resources in Zhengzhou, the exploitable modulus of groundwater in high-tech zone is 13.42× 104m3/km2 per year, and the current exploitation utilization rate is only 46%, which has the ability to expand exploitation. The mixed water temperature of shallow and middle layers in the experimental area is 65438 07℃.
2) Chemical characteristics of groundwater: the hydrochemical type of shallow groundwater in the experimental area is HCO 3-Ca Mg, with salinity of 604.28mg/L and total hardness of 428 mg/L; The middle and deep layers are HCO3-Ca-Na type, with salinity of 453.33mg/L and total hardness of 273.5428 mg/L.
(3) Zhengdong New Area Experimental Area
1) Groundwater burial conditions and water abundance: The experimental area is located in the alluvial plain of the Yellow River, with silty soil on the surface, and the burial depth is10.6m. According to the drilling data (Figure 4-4), there are five aquifers above 90m * * *, with a total thickness of about 44m, and the lithology is mainly medium fine sand and silty fine sand. The measured water level drops by 9.6m, the single well water yield is 5 1 m3/h, the permeability coefficient is 4.04m/d, and the water temperature 15.9℃.
2) Chemical characteristics of groundwater: the chemical type of groundwater in the experimental area is HCO 3- calcium sodium type, with salinity of 1407mg/L and total hardness of 630 mg/L. ..
(4) Dongguo Experimental Zone, Xinxiang City
1) Groundwater burial conditions and water abundance: The experimental area is located in the north of the productive canal in the north of Xinxiang City, and the landform is the ancient floodplain. The lithology of shallow stratum is silty clay, with 3 ~ 4 layers of fine sand at a depth of 40 ~ 60m, with a total thickness of 30 ~ 40m. The water inflow of a single well at a depth of 5m is 500 ~ 1000m3/d, the permeability coefficient is 10 ~ 15m/d, and the water level is about/kloc-0.
2) Chemical characteristics of groundwater: the chemical type of groundwater is HCO 3- calcium, sodium and magnesium, the salinity is 1 183.2mg/L, and the total hardness is 572.5 mg/L. ..
(5) Xinxiang Nanlubao Experimental Area
1) Groundwater burial conditions and water abundance: The experimental area is located in Lubao, southwest of Fengquan District, Xinxiang City. Shallow lithology is silty clay and fine sand. There are two aquifers in the depth of 45m, with a total thickness of 22m, and the water-bearing medium is fine sand. The buried depth of water level is 1 1m, the measured water inflow of a 2.95m deep single well is 37. 19m3/d, the permeability coefficient is 12.3m/d, and the water temperature is 16.0℃.
2) Chemical characteristics of groundwater: the chemical type of groundwater is HCO 3 Cl-Mg Ca Na type, with salinity of 999.66mg/L and total hardness of 547.5 mg/L. ..
Figure 4-3 Formation Structure of Oil and Water Wells in Zhengzhou High-tech Zone
2. Layout of test site
Five groups of pumping and recharging test points are located in alluvial fan, piedmont alluvial plain and alluvial plain respectively, representing the pumping and recharging capacity of alluvial gravel, alluvial lake, alluvial coarse sand, medium sand and fine sand aquifers (Table 4- 1). Pumping and recharging methods include primary pumping and secondary pumping (Figure 4-5). For example, the Dongguo experiment in Xinxiang City used one pumping. During the test, the water that exceeds the recharge capacity of the recharge well is recharged to the pumping well.
Figure 4-4 Pumping and injection wells and stratum structure in Zhengzhou New Area
Table 4- 1 Basic information of test wells
Figure 4-5 Layout of Dongguo Water Injection Test Site in Xinxiang
Urban shallow geothermal energy in Henan Province
Second, the test method and quality
1. detection method
The pumping test adopts single hole steady flow method and hole group unsteady flow method respectively. In the recharge test, the self-flow recharge mode is adopted, and the water level in the recharge hole is kept stable during recharge, and the water injection quantity is measured.
(1) observation content and accuracy
During the test, the water level of the pumping hole and observation well, the water output, water temperature and air temperature of the pumping hole, the recharge quantity and water level of the water injection hole were observed.
The main observation tools are double parallel lines and water level gauge, and the observation accuracy: the water level reading of pumping hole is cm, and the water level reading of observation well is mm; The pumping quantity and the return quantity are measured by water meter, and the reading reaches 0.1m3; ; The reading of water temperature and air temperature is 0.5℃.
(2) Observation method
1) Single-hole steady-flow pumping test: Single-hole steady-flow pumping test carries out a steady-flow pumping with maximum depth reduction. During the pumping test, the observation time of dynamic water level and water output is every 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes and 30 minutes after the pumping starts. Observe the water temperature and air temperature synchronously every 2 hours. The stable duration of pumping shall not be less than 8 hours. After stopping pumping, observe the recovery of water level, and the observation frequency is consistent with that at the beginning of pumping until the water level tends to be stable or the static water level before pumping.
2) Unsteady flow pumping test of hole group: During the pumping process, the water output of pumping holes remains stable. The frequency of water level observation is 1, 2, 3, 4, 6, 8, 10, 15, 20, 25, 30, 40, 50, 60, 80, 100,/kloc. After pumping, observe the recovery water level of pumping holes and observation wells, and the observation frequency is consistent with that at the beginning of pumping, until the water level tends to be stable or the static water level before pumping.
3) Recharge test: Natural gravity recharge method is adopted. Adjust the recharge amount in time when recharging. Considering the actual rise of water level in the process of recharge, the buried depth of water level in recharge hole is generally stable at 2 ~ 4m m. The observation method and frequency are the same as the steady flow pumping test.
(3) collecting water samples
Before the end of the pumping test, take a complete water quality analysis sample, fill in the water sample record card, and send the water sample to the laboratory for testing.
The analysis items include sand content, color, smell and taste, turbidity, visible matter, pH value, chloride ion, sulfate, bicarbonate, carbonate, hydroxide, potassium ion, sodium ion, calcium ion, magnesium ion, total hardness, total dissolved solids, ammonium ion, total iron, phosphorus, nitrate, nitrite, fluoride and permanganate index.
Step 2 test quality
1) The technical standards for pumping recharge test mainly include: Code for Hydrogeological Investigation of Water Supply (GB50027-200 1), Technical Code for Exploration and Evaluation of Shallow Geothermal Energy, Code for Collection, Preservation and Inspection of Water Samples, and Technical Code for Engineering of Ground Source Heat Pump System (GB50366-2005).
2) In order to ensure the test quality, the personnel involved in observation should be trained in observation technology before pumping, and the format and requirements of observation records should be unified;
3) Before pumping, all equipment is ready, drainage works are completed, and observation tools and personnel are in place.
4) The survey line adopts high-quality double-stranded parallel lines with small flexibility to reduce the observation error.
5) The observers and measuring tools in the same observation well are fixed, and the observation data are filled in timely, accurately, clearly and completely.
6) Organize the observation data in time, solve the problems found in time, and ensure the integrity of the data.
Third, the test results
1. Parameter calculation method and results
According to the data of single-hole steady-flow pumping test, the permeability coefficient k of aquifer is calculated according to the following formula.
Urban shallow geothermal energy in Henan Province
According to the test data of the water injection hole, the permeability coefficient k is approximately calculated by the following formula.
Urban shallow geothermal energy in Henan Province
Calculate unit pumping quantity q or unit reinjection quantity q according to the following formula:
Q pumping = q pumping/s; Q = q /S
Where: k is the permeability coefficient in m/day; Q is the stable water production or water injection, in cubic meters per day (m3/d); H is the thickness of the phreatic aquifer, in meters (m); S is the depth or increase of water level, in meters (m); R is the influence radius, taking the empirical value, and the unit is m; R is the filter radius in m; L is the length of the test section or filter, in meters.
The calculation results are shown in Table 4-2. See Table 4-3 for some collected reinjection test results.
Table 4-2 Summary of Test Results of Pumping and Recharge
Table 4-3 Collection Results of Recharge Test
2. Analysis of the influencing factors of recharge.
The amount of recharge is affected by many factors, such as the structure and quality of the well, hydrogeological conditions and so on.
The lithology of aquifer is the basic factor to determine the recharge. As can be seen from Table 4-2, the ratio of permeability coefficient obtained from pumping and water injection tests of different aquifers is: the aquifer dominated by coarse sand and gravel is 65,438+0.96 ~ 2.865,438+0, and the aquifer dominated by medium sand and fine sand is 3.28 ~ 8.50. The results show that the coarser the aquifer particles are, the closer the pumping and recharge capacity is, that is, the coarser the aquifer particles are, the easier it is to recharge.
The buried depth of water level has obvious influence on the total recharge, and the recharge is proportional to the buried depth of water level. Comparing the two groups of reinjection tests in Zhengzhou High-tech Zone and Zhengdong New Zone, it is found that the aquifer lithology is similar and the aquifer permeability is similar. The buried depth of static water level in Zhengzhou High-tech Zone is 34m, that in Zhengdong New Zone is only 10.6m, that in Zhengzhou High-tech Zone is 42m3/h, and that in Zhengdong New Zone is only12.56m3/h. ..
The structure of the filter tube has a direct impact on the amount of recharge. In the section with similar aquifer lithology, the reinjection amount of steel bridge filter tube well is obviously greater than that of cement filter tube well (Table 4-3).
It is found that the unit recharge quantity in gravel aquifer area is greater than 70% of the unit pumping quantity; In coarse sand and medium sand aquifer areas, the unit recharge is about 70% ~ 40% of the unit water output; In the medium-fine sand aquifer area, the unit recharge is about 50% ~ 30% of the unit water output; In areas with fine sand and silt aquifers, the unit recharge is less than 30% of the unit water output.
3. Determine the proportion of pumping wells and recharging wells.
The ratio of unit pumping volume to unit reinjection volume can be used as the main basis for determining the number of reinjection wells. According to the above test results, considering the possible blockage of recharge wells in the long-term recharge process, when the buried depth of groundwater level is greater than 10m, the proportion of pumping wells in geothermal air-conditioning wells is determined as shown in Table 4-4.
4. Influence of geothermal air conditioning well operation on groundwater environment
Influence of (1) on groundwater temperature
In the study area, the water temperature of the geothermal air-conditioning well pumping well is generally around 16 ~ 20℃, and the water temperature of the return pipeline is generally around 10 ~ 15℃, which is 2 ~ 7℃ lower than the groundwater temperature of the pumping well, and the cooling period is generally around 18 ~ 25℃, which is higher than the groundwater temperature of the pumping well/kloc. According to the monitoring of groundwater temperature in geothermal air conditioning wells (Figure 4-6 and Figure 4-7), the operation of geothermal air conditioning has obvious phased influence on groundwater temperature.
Table 4-4 Determination of the proportion of pumping wells and recharging wells in geothermal air conditioning wells
Figure 4-6 Dynamic Curve of Groundwater Depth and Water Temperature of Pumping Wells in Zhengzhou Children's Hospital
Figure 4-7 Dynamic Curve of Groundwater Depth and Water Temperature in Recharge Well of Songyang Middle School in Zhengzhou City
The temperature of reinjection water in cooling period is generally between 19 ~ 30℃, and the highest temperature can reach 35℃. The temperature of reinjection water in heating period is generally around 8 ~ 15℃. Due to the influence of reinjection temperature, the groundwater temperature rises slightly in the cooling period and decreases slightly in the heating period, but in a complete cooling and heating cycle, the reinjection of geothermal air conditioning wells has no obvious influence on the overall sustainability of groundwater temperature. The multi-year temperature dynamic curve (Figure 4-8 to Figure 4- 13) also shows that the operation of geothermal air conditioning in the study area has not caused the continuous increase or decrease of groundwater or soil temperature. No obvious thermal pollution was observed.
Figure 4-8 Dynamic Curve of Water Temperature of Recharge Well in Wenfeng Times Square, Anyang City
Figure 4-9 Dynamic Curve of Water Temperature of Recharge Well in Anyang No.5 Middle School
Figure 4- 10 Dynamic Curve of Water Temperature in Recharge Well of Cotton Research Institute, Chinese Academy of Agricultural Sciences
Fig. 4- 1 1 dynamic curve of water temperature of recharge well in Anyang Radio and Television Bureau
② Influence on groundwater quality
According to the water quality sampling analysis of geothermal air conditioning wells in Zhengzhou Children's Hospital before operation (May 5), during operation (August 2 1 day) and after operation (1October 29 10) (Table 4-5) and the water quality sampling analysis of some pumping wells and recharging wells in Anyang City during operation (Table 4-6 Through comparison, it is found that shallow geothermal energy has little influence on groundwater quality in the process of development and utilization; The element zinc in the recharge well increased obviously. The main reason is that zinc is easily oxidized into zinc ions and enters the water. Therefore, it is recommended not to use galvanized steel pipes.
Figure 4- 12 Dynamic Curve of Water Temperature of Recharge Well of Anyang Public Security Bureau
Fig. 4- 13 dynamic curve of water temperature in recharge well of Xixiangfeng Hotel in Anyang City
5. Determination of spacing between pumping well and recharging well
The reasonable spacing between pumping wells and recharging wells is based on the principle of no thermal short circuit. The time for reinjection water to reach the pumping well (thermal short-circuit time) can be expressed by the following formula:
Urban shallow geothermal energy in Henan Province
Where n is the effective porosity of the aquifer; π is pi; D is the distance between pumping well and water injection well; B is the thickness of the aquifer; Q is the stable water injection.
According to the above formula, it can be determined that the critical distance of thermal short circuit pumping back into the well is:
Urban shallow geothermal energy in Henan Province
When the distance between the pumping well and the recharging well is less than a reasonable distance (D), thermal short circuit will occur. Take Children's Hospital as an example:
The number of pumping wells and irrigation wells in the geothermal air conditioning project of Children's Hospital is 6, of which the depth of pumping wells is 98m and the depth of recharging wells is 70m. The operation mode of pumping and recharging wells is two pumping and four irrigation, 3 # and 6 # are pumping wells, and the other 4 wells are recharging wells. During operation, the pumping capacity of a single well is 100m3/h, and the reinjection capacity of a single well is 50m3/h. See Figure 4- 14 for the location distribution of pumping wells, irrigation wells and observation wells.
Figure 4- 14 Distribution of Pumping and Irrigation Wells
Table 4-5 Comparison Table of Sewage Quality of Geothermal Air Conditioning Wells in Zhengzhou Children's Hospital at Different Time Periods
According to the operation time of heat pump in cooling period 120d, aquifer thickness 15.9m, porosity of 0.30, and d of 85m, that is, when the recharge amount is 50m3/h (equivalent to the alluvial plain in front of the platform), thermal short circuit will not occur when the distance between pumping wells is more than 85m. If the reinjection amount of a single well reaches 85m3/h (equivalent to the alluvial plain of the Yellow River), thermal short circuit will not occur when the distance between pumping and irrigation wells is greater than11m.
In fact, the distance between No.3 pumping well and No.2 recharging well is 36 meters ... The distance between No.6 pumping well and No.5 recharging well is only 55 meters ... Figure 4-7 shows the water temperature curve of No.6 pumping well when the system is running. Judging from the temperature change, the thermal short circuit obviously occurred, and the highest temperature during the cooling period was 23 ~ 24℃, which was 3 ~ 4℃ higher than the background value (20℃). The lowest temperature in heating period is 17 ~ 16℃, which is about 3 ~ 4℃ lower than the background value.
Generally, when the heat pump unit works normally, the water temperature is required to be between 2℃ and 35℃ to ensure the normal operation of the system. Therefore, although reinjection water causes thermal short circuit, the temperature change is still within the allowable range of heat pump, which can ensure the operating efficiency of the system and meet the requirements of building cooling and heating load. On the other hand, most construction sites in the city can't meet the requirements of pumping and irrigation well spacing calculated theoretically. A large number of observation data also show that thermal short circuit phenomenon is widespread. However, due to the moderate temperature of reinjection water, the operating efficiency of water source heat pump air conditioning system can be guaranteed. The variation of pumping and irrigation temperature fluctuates periodically in heating period and cooling period, which also reflects the regularity of groundwater temperature fluctuation at a certain point within the influence range of hydrodynamic field during the long-term operation of water source heat pump air conditioning system, that is, within the influence range of alternating cold and hot during the long-term operation of water source heat pump air conditioning system, groundwater temperature will not increase or decrease obviously and continuously.
Table 4-6 Comparison Table of Water Quality between Pumping Well and Recharge Well
Therefore, the determination of well spacing of geothermal air conditioning should not only be based on thermal short circuit, but also consider whether the change of water temperature within the influence range of reinjection water can meet the operation requirements of heat pump system, its impact on geological environment and its operation economy. However, if conditions permit, the requirements of well spacing should be met as much as possible to reduce the influence of thermal short circuit and ensure the operating efficiency of the system. In practical engineering, the recharge is quite different from the aquifer thickness. According to the investigation of the operation effect of the existing geothermal air-conditioning system and the results of pumping and irrigation test, it is suggested that the spacing between pumping and irrigation wells in fine-grained stratum should not be less than 40m and the spacing between gravel aquifers should not be less than 80 m, which can be adjusted according to the specific conditions in practical engineering application.