CN103090571B - Method of circular mining geothermal resources - Google Patents

Abstract

The invention relates to a method for cyclically exploiting geothermal resources, comprising the following steps: 1) determining a region with a relatively high geothermal gradient; 2) determining a reservoir in the region with a relatively high geothermal gradient; The main extension direction of the reservoir is used to determine the well positions of two wells and carry out drilling. One well is in the relatively low part of the reservoir, which is the water inlet well; the other well is in the relatively high part of the reservoir, which is the water outlet well; Both the water inlet well and the water outlet well are drilled to the reservoir, and then perforated in the same reservoir section to obtain a reservoir channel, so that the water inlet well communicates with the water outlet well through the reservoir channel; 5 ) on the ground, inject surface fresh water from the water inlet well, and the surface fresh water passes through the reservoir channel to obtain heated hot water, and the heated hot water flows into the water outlet well, and then sent to the outlet well head.

Description

A method for recycling geothermal resources

technical field

The invention relates to a method for circularly exploiting geothermal resources.

Background technique

"Geothermal" refers to the abbreviation of thermal energy resources buried in the ground that can be economically utilized by human beings. The earth's thermal field is also called the earth's temperature field or geothermal field. It is the earth's physical field together with the earth's electric field, gravity field, and magnetic field. The geothermal field represents the distribution of temperature in the layers of the Earth's interior. The temperature distribution and thermal field characteristics of each circle of the earth are different. Generally speaking, the thermal field refers to the part that can be directly measured in the upper layer of the earth.

As a new energy source, geothermal resources have already attracted the attention of countries all over the world. Geothermal resources are a kind of precious natural resources. It has been estimated that the total amount of underground thermal energy is about 170 million times the energy that may be released by all coal reserves. Geothermal resources can not only provide heat energy, but also provide water supply and mineral resources, such as extraction of useful elements and compounds. my country is rich in geothermal resources and is one of the earliest developed countries in the world.

At present, my country's heat consumption is mainly reflected in the following aspects, namely, industrial heating, industrial and agricultural heat, household heating, bathing, greenhouse planting, breeding, etc. my country's current heat supply is mainly coal, electricity and some geothermal heat. In addition to hydropower, wind power, and solar power, electricity is mainly coal power.

According to the statistics of the Ministry of Construction in 2010, the current national heating energy consumption is about 250 million tons of coal throughout the year, accounting for 10% of the total energy consumption of the whole society. According to information from the 2010 annual meeting of the "Clean and Efficient Coal-fired Power Generation Technology Cooperation Network", coal used for power generation and heating in my country currently accounts for about 50% of the country's total coal production. Because coal is a highly polluting energy source, about 90% of the country's SO2 emissions are generated by coal power, and 80% of CO2 emissions are emitted by coal power. While bringing convenience to people's production and life, it also produces relatively large pollution, which brings harm to people's lives and health. At the same time, coal-fired boilers are high-pressure vessels, and improper use will cause dangers such as explosions.

According to the current level of development and utilization, the total amount of geothermal water that can be developed and utilized in the country is about 6.845 billion cubic meters per year, which is equivalent to the calorific value of 32.848 million tons of standard coal per year. However, less than 20% are now exploited. Even so, due to long-term blind mining, the use is unreasonable, the comprehensive utilization is low, and the waste is relatively serious. In some places, due to lack of management, the layout of wells is unreasonable, the density is too high, and the mining is excessive, resulting in a sharp drop in the groundwater level. A large amount of geothermal water is discharged into the environment randomly, which will cause the pollution of surface water and underground fresh water.

The earth we live in is a huge low-heat reservoir. Only a 10-kilometer-thick underground layer can store 1.05×1026 joules of heat, which is equivalent to the heat released by 9.95×1015 standard coal. According to SEMHACH, a company engaged in geothermal energy research and development, the reserves of geothermal energy exceed those of coal and oil.

Geothermal resources are a part of mineral resources. Compared with traditional fossil energy such as coal, oil and natural gas, geothermal energy has the advantages of cleanness, environmental protection, direct use on site, relatively low cost, and stable prices. Due to the huge amount of natural heat stored in the earth—geothermal energy, which has little negative impact on the environment, it has been recognized as a renewable and clean energy by all countries in the world, and it has been listed as one of the new energy sources for key research and development by various countries.

The current geothermal utilization includes two ways of power generation and heat utilization. Geothermal resources can be divided into three types according to the temperature of the medium: high temperature (greater than 150°C), medium temperature (90-150°C), and low temperature (less than 90°C) systems. Most of the medium and low temperature geothermal systems adopt direct utilization methods (such as: heating, bath therapy, use in industry and agriculture, etc.) and ground source heat pump heating and cooling for development and utilization; high temperature geothermal systems are used for power generation, and the installed capacity of geothermal power generation It has reached 10 million kilowatts. It can be said that geothermal is currently the most realistic and competitive new energy after wind energy.

According to data from the Ministry of Land and Resources, according to preliminary estimates, the geothermal energy stored within 2,000 meters from the surface of the country's major sedimentary basins is equivalent to the heat of 250 billion tons of standard coal. There are 103 geothermal fields nationwide that have been formally surveyed and approved by the land department, and the submitted recoverable geothermal resources are 332.83 million cubic meters per year; 214 geothermal fields have been preliminarily evaluated. According to the current level of development and utilization, the total amount of geothermal water that can be developed and utilized in the country is about 6.845 billion cubic meters per year, which is equivalent to the calorific value of 32.848 million tons of standard coal per year. However, less than 20% of them are utilized now, and the prospect of development and utilization is broad.

Current technology faces two problems:

One is the use of coal to generate serious pollution, and the cost is relatively high. The total annual coal consumption (including coal power generation and heating) is 1 billion tons, conservatively calculated at 500 yuan per ton, which is 500 billion yuan;

The second is that the use of geothermal heat is only to obtain hot water from the ground, and although the amount of underground hot water is relatively large, it is also limited.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for circularly exploiting geothermal resources that saves a large amount of coal resources.

The technical scheme of the present invention to solve the above-mentioned technical problems is as follows: a method for circularly exploiting geothermal resources, comprising the following steps:

1) Identify an area with a relatively high geothermal gradient;

Collect past geothermal data in this area, especially the temperature data actually measured by drilling wells, so as to determine the geothermal gradient in this area. Underground, if the geothermal gradient is 4°C/100 meters, and the surface temperature is usually 15°C, it can reach 95°C for two kilometers and 135°C for three kilometers. Specifically:

(1) Measure the terrestrial heat flow value in this area.

The terrestrial heat flow value is a comprehensive parameter, and it is the only physical quantity that can be directly measured on the surface to reflect the thermal status of the deep crust.

(2) Measure the geothermal gradient in the area. The underground temperature is obtained by direct measurement of the ground temperature of the borehole and the mine. After the well is drilled, the temperature corresponding to different depths is measured using the geophysical logging in the geophysical well logging. The temperature increased every 100 meters is the ground temperature. gradient.

Geothermal gradient is also called "geothermal gradient". A parameter that represents the degree to which the temperature in the Earth's interior is unevenly distributed. Generally, the deeper the buried depth, the higher the temperature value, which is expressed by the number of degrees Celsius increased per 100 meters of vertical depth. The geothermal gradient is different in different places, usually (1-3) ℃/100 meters, and the volcanic activity area is higher.

2) Identify reservoirs in areas where said geothermal gradient is relatively high.

3) Determine the well positions of two wells in the main extension direction of the reservoir and carry out drilling. One well is in the relatively low part of the reservoir, which is the water inlet well; the other well is in the relatively high part of the reservoir, which is out of the well;

4) Drill both the water inlet well and the water outlet well to the reservoir, and then perforate in the same reservoir section to obtain a reservoir channel, so that the water inlet well passes through the reservoir channel and the outlet well Well connected;

5) On the ground, inject surface fresh water from the water inlet well, and the surface fresh water passes through the reservoir channel to obtain heated hot water, and the heated hot water flows into the water outlet well, and then sent to the outlet well head.

The beneficial effects of the present invention are:

1. Treat the underground as a heat store, that is, a heating furnace, so that it can heat the cold water instead of simply extracting its hot water.

1. Solve the problem that wells can be drilled anywhere, but where the ground temperature is high, the wells can be drilled shallower, and where the ground temperature is low, the wells should be drilled deeper.

3. How much water enters the stratum, how much water is taken out, not at all taken, and the balance of the groundwater level is maintained.

4. Save a large amount of coal resources, 250 million tons of coal can be saved every year, conservatively calculated at 500 yuan per ton, it is 125 billion yuan; at the same time, it greatly reduces CO2 emissions and reduces many environmental pollutions. Because the amount of CO2 produced per ton of standard coal combustion is about 2.6 tons of CO2 in industrial boilers, saving 250 million tons of coal can reduce 650 million tons of CO2 emissions.

5. It can be implemented in places with sedimentary basins, and the area of sedimentary basins in my country is nearly 6 million square kilometers, which avoids the limitations of the current exploitation of geothermal energy.

6. Save groundwater resources and prevent water level drop caused by excessive exploitation. More than 50 cities in 19 provinces in my country have experienced different degrees of land subsidence, and they are mainly concentrated in the Yangtze River Delta region.

7. The hot water coming out of the ground contains more minerals. These minerals and trace elements have certain beauty and skin care effects, can improve the skin and promote blood circulation, and the calcium, magnesium, sodium, hydrogen carbonate, hydrogen sulfide and other minerals in these waters can change the pH value of the skin, thereby softening the skin horny. Therefore, commonly used for bathing can benefit people's health.

8. It can be used in many places such as industry, agriculture, residents, and greenhouses. Has been widely used in industrial and agricultural production and medical and health fields. In industry, it is mainly used for power generation, textile, printing and dyeing, papermaking, brewing, leather processing, etc.; in agriculture, it is mainly used for heat preservation seedlings, greenhouse cultivation, artificial hatching and adjustment of irrigation water temperature.

On the basis of the above technical solutions, the present invention can also be improved as follows.

Further, in step 2), the reservoir is a sandstone layer in the continental formation, and a carbonate cave and/or fracture in the marine formation.

Further, in step 2), the specific steps for determining the reservoir are:

2.1) Choose places that have been sedimentary basins in geological history;

Due to the exploration and development of energy geology (oil, natural gas, coal and unconventional natural gas), the distribution range of sedimentary basins has been basically clear. If it is not clear, non-seismic geophysical and geochemical techniques such as gravity, magnetism, electrical, and geochemical techniques can be used for identification and delineation.

2.2) In the sedimentary basin, use seismic methods to predict the location of the reservoir;

Seismic mainly uses the reflection wave method to identify the reservoir, because the reservoir usually contains water, which can cause changes in its amplitude, frequency, and wavelength. In addition, seismic waves travel at different speeds in different rocks, so that mud, shale, sand, and conglomerate can be distinguished in continental strata; limestone and dolomite can be distinguished in marine strata.

2.3) According to the reservoir predicted by the seismic method, identify the thickness, range, void and permeability of the reservoir, and select the reservoir that meets the requirements;

In general, the thickness of the reservoir is selected to be 20-50 meters; the distribution is stable, and the general area is greater than 100 square kilometers; the permeability is better, generally the porosity is greater than 25%, and the permeability is greater than 200 mD; the connectivity is better ; The sealing of the top and bottom plates is better. Under this premise, the higher the geothermal gradient, the better; because the geothermal gradient is high, and under the same water temperature conditions, the wells will be drilled shallow, which will save costs.

Further, in step 3), the specific steps of drilling are: use a 311mm drill bit to drill the surface layer, and then use a 215mm drill bit to drill down to the reservoir, and then run the casing, and then Cement the well with cement slurry.

Further, the drilled surface depth is 300-500 meters.

Further, the following steps are also included between the steps of drilling the surface layer and then drilling down: in order to prevent the surface layer from collapsing, the surface layer casing is lowered, and then the well is cemented with cement slurry.

Further, the thickness of the surface casing is 240mm.

Further, the thickness of the sleeve is 140mm.

Further, after the well is drilled to the reservoir, the following step is also included before the casing is run: performing geophysical logging. On the one hand, it is to measure the thickness and permeability of the reservoir; on the other hand, it is to measure the well temperature and determine the geothermal gradient.

The purpose is to see whether the measured results are the same as those measured before drilling (referring to the measured results obtained when a good reservoir process is determined), whether it is higher or lower. This determines the depth and cost of drilling wells in this area in the future.

Further, in step 4), the process conditions for perforating are as follows: choose 102-type guns equipped with 127 bullets for concentrated energy perforation, 60° phase angle helical perforation, hole density 24 holes/m, and emissivity not less than 98%.

Before perforating, the casing and cement sheath (the layer cemented with cement slurry is called the cement sheath) wrap the formation and coal seam. Only after perforating, the perforating bullets penetrate the casing and cement sheath to form holes. , when it hits the reservoir, the reservoir can be connected with the water inlet well and the water outlet well.

Further, the depths of the water inlet well and the water outlet well are both 2000-3000 meters.

Furthermore, the distance from the water inlet well to the water outlet well is 300-500 meters.

Further, the reservoir channel has a width of 20-50 meters.

Further, the temperature of the heated hot water is 95-135°C.

Further, a water pump is installed in the outlet well to pump hot water to the mouth of the outlet well.

Further, when the surface fresh water passes through the reservoir channel, it also includes the step of fracturing. The fracturing is pressurized from the surface, and the fracturing fluid and proppant are pressed into the reservoir through the holes opened, and the reservoir is fractured. That is to say, the main fracture is generated, and the fracturing fluid carries the proppant into the formation, and can reach a range of 200-300 meters along the direction of the main fracture; wherein, the amount of the fracturing fluid is 1200-1500 m3, and the amount of proppant is 60-80 m3. square.

Further, the fracturing equipment for fracturing is a fracturing unit with a size of more than 1000 and good performance.

Further, the fracturing fluid is active water or clear water, and the proppant is quartz sand.

Further, KCL with a volume percentage of 1-3% is added to the clear water, and the purpose of adding KCL is to increase the viscosity of the fracturing fluid and facilitate the carrying of quartz sand.

Further, the pressure from the ground surface is 30-40 MPa.

Further, the displacement of the fracturing fluid and proppant pressed into the reservoir is 3-5 cubic meters per minute.

For the hot water obtained by the above method, first verify the physical and chemical properties of the water. Wells are drilled to produce water, and water samples are taken every day for laboratory analysis. If it is used for heating, check to see if there are any components that corrode pipelines, such as high sulfur content; if it is used for bathing, check to see if there are any elements that are harmful to the human body. After the verification is completed, it will be transported to the destination through pipelines or water tank trucks.

Description of drawings

Fig. 1 is the structural representation of drilling two vertical wells in the method for circularly exploiting geothermal resources of the present invention;

In the accompanying drawings, the list of parts represented by each label is as follows:

1. Inlet well, 2. Outlet well, 3. Reservoir, 4. Suction pump.

Detailed ways

The principles and features of the present invention are described below in conjunction with the accompanying drawings, and the examples given are only used to explain the present invention, and are not intended to limit the scope of the present invention.

First make sure you have found a good reservoir

If a good reservoir is found, the specific steps are as follows: determine a well location on the reservoir that meets the requirements, generally refer to the outcrop data around the basin, combined with non-seismic geophysical and chemical exploration data, especially seismic and previous well drilling data in the area, And after the comprehensive geological condition analysis, the well location is determined, and the drilling is carried out. Generally, coal field or oil drilling rigs are used for drilling. The purpose is to confirm whether the reservoir determined by seismic as the main method exists, and if so, to determine whether the reservoir is good or not.

After a well is drilled, water is produced in the well, and the daily water production is more than 100 cubic meters, and the continuous water production is more than 3 months, which is determined to be a good reservoir.

Then two vertical wells are drilled, as shown in Figure 1, that is, one well is in a relatively low part of the reservoir for water inflow; the other well is in a relatively high part for water outflow. After drilling, the reliability of the seismic data was confirmed. Then, two wells can be deployed along the main extension of the reservoir. Wherein, one is in the low position, is water inlet well 1; Because, according to the subsurface pressure system and the distribution of potential energy, it is usually water that migrates to high places.

The two wells drilled need to be perforated in the third section of the same reservoir, and the 20-50-meter-thick reservoir channel is perforated. The surface fresh water enters the formation from the perforation of the water inlet well 1 after the surface is pressurized. Entering the formation, passing through the reservoir 3 channel of 300-500 meters (that is, the distance between the water inlet well 1 and the water outlet well 2), at a temperature of 95-135 ° C, it will be heated quickly. When the outlet well 2 is perforated, the temperature can basically reach 95-135° C., and the water is pumped to the wellhead through the water pump 4 installed in the outlet well. Then, it is transported to the destination through pipelines or water tank trucks.

If the water isn't flowing, you need to frack it. Clean water is used as the fracturing fluid, quartz sand is used as the proppant, with a certain displacement and a certain sand ratio.

The fracturing equipment should be above 1000 fracturing units with good performance, and the fracturing fluid should be active water or clear water (add 1-3% KCL by mass). Usually, the amount of fracturing fluid is 1200-1500 cubic meters, the quartz sand is 60-80 cubic meters, the displacement is 3-5 cubic meters per minute, and the pressure is increased to 30-40 MPa.

If the reservoir is found, but the reservoir is not very good, a horizontal well can also be used to replace the reservoir. That is to drill two wells, one vertical well, one horizontal well, and the two wells are connected. The specific steps are:

First drill a vertical well with a vertical depth of about 2500m at a higher position, and the vertical wellhead is 900m away from the horizontal wellhead. Then drill a horizontal well at the lower part. The horizontal well is drilled with a 311mm drill bit, and a 240mm casing is drilled to a depth of about 250m, and the cement slurry is returned to the ground. 2. Spud the cement plug and enter the new stratum to start deflection at the depth of 1800m. Combined dynamic drilling tools, the dogleg angle of the deflection section is designed to be 4.5°/30m, and the profile is designed as a single arc profile. °, horizontal displacement 500m, vertical depth 2800m). Lower the 140mm casing down to the top of the reservoir. During use, the tap water injected is heated at the horizontal well, and the heated tap water is taken out from the vertical well.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (21)

1. A method for recycling geothermal resources, characterized in that it may further comprise the steps: 1) Identify an area with a relatively high geothermal gradient; 2) identifying reservoirs in areas where said geothermal gradient is relatively high; The specific steps for determining the reservoir are: 2.1) Choose a place that has been a sedimentary basin in geological history; 2.2) In the sedimentary basin, use seismic method to predict the position of the reservoir; 2.3) According to the reservoir predicted by the seismic method, the thickness, range, void and permeability of the reservoir are identified, and the reservoir meeting the requirements is determined; The reservoir thickness of the reservoir meeting the requirements is 20-50 meters, the reservoir area is greater than 100 square meters, the porosity of the reservoir is greater than 25%, and the permeability of the reservoir is greater than 200 mD; 3) Determine the well positions of two wells in the main extension direction of the reservoir and carry out drilling, one well is in the relatively low part of the reservoir, which is the water inlet well; the other well is in the relatively high part of the reservoir, which is out of the well; 4) Drill both the water inlet well and the water outlet well to the reservoir, and then perforate in the same reservoir section to obtain a reservoir channel, so that the water inlet well passes through the reservoir channel and the outlet well Well connected; 5) On the ground, inject surface fresh water from the water inlet well, and the surface fresh water passes through the reservoir channel to obtain heated hot water, and the heated hot water flows into the water outlet well, and then sent to the outlet well head; the surface fresh water When passing through the reservoir channel, it also includes the step of fracturing. The fracturing is pressurized from the surface, and the fracturing fluid and proppant are pressed into the reservoir through the holes opened, and the reservoir ruptures to generate the main fracture. , the fracturing fluid carries the proppant into the formation, and reaches the range of 200-300 meters along the direction of the main fracture; Wherein, the dosage of the fracturing fluid is 1200-1500 cubic meters, and the dosage of the proppant is 60-80 cubic meters. 2. The method for circularly exploiting geothermal resources according to claim 1, characterized in that: in step 2), the reservoir is a sandstone layer in the continental strata, and a carbonate cave and/or in the marine strata or cracks. 3. The method for circularly exploiting geothermal resources according to claim 1, characterized in that: the seismic method is a reflected wave method. 4. The method for circularly exploiting geothermal resources according to claim 1, characterized in that: in step 3), the specific steps of the drilling are: use a 311mm drill bit to drill the surface layer, then use a 215mm drill bit, and then go to the Drill down, drill to the reservoir, run down the casing, and then cement the well with cement slurry. 5. The method for circularly exploiting geothermal resources according to claim 4, characterized in that: the surface depth of the drilling is 300-500 meters. 6. The method for circularly exploiting geothermal resources according to claim 4, characterized in that: between the step of drilling the surface layer and then drilling down, the following steps are further included: in order to prevent the surface layer from collapsing, the surface layer casing is lowered, Then cement the well with cement slurry. 7. The method for circularly exploiting geothermal resources according to claim 6, characterized in that: the thickness of the surface casing is 240 mm. 8. The method for circularly exploiting geothermal resources according to claim 4, characterized in that: the thickness of the casing is 140mm. 9. The method for circularly exploiting geothermal resources according to claim 4, characterized in that: after drilling to the reservoir and before running the casing, the method further includes the following step: performing geophysical logging. 10. The method for circular exploitation of geothermal resources according to claim 9, characterized in that: the geophysical logging is to measure the thickness and permeability of the reservoir on the one hand; to measure the well temperature on the other hand to determine temperature gradient. 11. The method for circularly exploiting geothermal resources according to any one of claims 1 to 10, characterized in that: in step 4), the process conditions for perforating are: select 102-type gun with 127 bullets to gather energy Perforation, 60° phase angle helical holes, hole density 24 holes/m, emissivity not less than 98%. 12. The method for circularly exploiting geothermal resources according to any one of claims 1 to 10, characterized in that: the depths of the water inlet well and the water outlet well are both 2000-3000 meters. 13. The method for circularly exploiting geothermal resources according to any one of claims 1-10, characterized in that the distance from the water inlet well to the water outlet well is 300-500 meters. 14. The method for circularly exploiting geothermal resources according to any one of claims 1 to 10, characterized in that: the reservoir channel has a thickness of 20 to 50 meters. 15. The method for circularly exploiting geothermal resources according to any one of claims 1-10, characterized in that: the temperature of the heated hot water is 95-135°C. 16. The method for circularly exploiting geothermal resources according to any one of claims 1 to 10, characterized in that: a water pump is installed in the outlet well to pump hot water to the mouth of the outlet well. 17. The method for cyclically exploiting geothermal resources according to claim 1, characterized in that: the fracturing equipment for fracturing is a fracturing unit of size 1000 or above with good performance. 18. The method for circularly exploiting geothermal resources according to claim 1, characterized in that: the fracturing fluid is activated water or clear water, and the proppant is quartz sand. 19. The method for circularly exploiting geothermal resources according to claim 18, characterized in that: 1-3% by volume of KCL is added to the clear water. 20. The method for circularly exploiting geothermal resources according to claim 1, characterized in that: the pressure from the ground surface is 30-40 MPa. 21. The method for circularly exploiting geothermal resources according to claim 1, characterized in that: the displacement of the fracturing fluid and proppant pressed into the reservoir is 3-5 cubic meters per minute.