CN115012882A - Method for intermittently and auxiliarily exploiting natural gas hydrate through microwave heating - Google Patents
Method for intermittently and auxiliarily exploiting natural gas hydrate through microwave heating Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 85
- NMJORVOYSJLJGU-UHFFFAOYSA-N methane clathrate Chemical compound C.C.C.C.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O NMJORVOYSJLJGU-UHFFFAOYSA-N 0.000 title claims abstract description 48
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- 230000009471 action Effects 0.000 claims abstract description 57
- 238000004519 manufacturing process Methods 0.000 claims abstract description 50
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 48
- 230000035515 penetration Effects 0.000 claims abstract description 47
- 239000007789 gas Substances 0.000 claims abstract description 37
- 150000004677 hydrates Chemical class 0.000 claims abstract description 14
- 230000005284 excitation Effects 0.000 claims abstract description 7
- 238000005065 mining Methods 0.000 claims description 45
- 230000008569 process Effects 0.000 claims description 16
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims description 12
- 238000000354 decomposition reaction Methods 0.000 claims description 12
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Natural products C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 11
- 239000003345 natural gas Substances 0.000 claims description 7
- -1 natural gas hydrates Chemical class 0.000 claims description 7
- 229910002092 carbon dioxide Inorganic materials 0.000 claims description 6
- 239000001569 carbon dioxide Substances 0.000 claims description 6
- 239000003112 inhibitor Substances 0.000 claims description 5
- 239000007787 solid Substances 0.000 claims description 5
- 238000005243 fluidization Methods 0.000 claims description 4
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- RZVAJINKPMORJF-UHFFFAOYSA-N Acetaminophen Chemical compound CC(=O)NC1=CC=C(O)C=C1 RZVAJINKPMORJF-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- VTVVPPOHYJJIJR-UHFFFAOYSA-N carbon dioxide;hydrate Chemical compound O.O=C=O VTVVPPOHYJJIJR-UHFFFAOYSA-N 0.000 description 1
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/01—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells specially adapted for obtaining from underwater installations
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- E—FIXED CONSTRUCTIONS
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- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B41/00—Equipment or details not covered by groups E21B15/00 - E21B40/00
- E21B41/0099—Equipment or details not covered by groups E21B15/00 - E21B40/00 specially adapted for drilling for or production of natural hydrate or clathrate gas reservoirs; Drilling through or monitoring of formations containing gas hydrates or clathrates
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- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/24—Enhanced recovery methods for obtaining hydrocarbons using heat, e.g. steam injection
- E21B43/2401—Enhanced recovery methods for obtaining hydrocarbons using heat, e.g. steam injection by means of electricity
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Abstract
The invention provides a method for exploiting natural gas hydrate with assistance of intermittent microwave heating, belonging to the field of natural gas hydrate exploitation 1 Microwave thermal excitation of frequency; detecting the water saturation at the position of the microwave transmitting antenna under the well of the production well in real time, and when the water saturation reaches Sw max When the suction pump is started, the suction pump is automatically started; when the water saturation decreases to Sw min When the suction pump is closed; therefore, the penetration depth of the microwave in the reservoir is not limited due to the production of a large amount of free water, and the microwave power is automatically adjusted according to the monitored microwave absorption rate alpha; when f is 1 After the hydrates in the direct action area of the frequency microwaves are completely decomposed, when the temperature of the reservoir is gradually increased to 42 ℃, the microwave frequency is automatically reduced to f 2 Thereby improving the microwave penetrationThe penetration depth is increased, and the microwave action range is enlarged; repeating the steps until the gas production is finished. The invention can optimize the auxiliary action of the microwave, improve the production efficiency and reduce the exploitation cost.
Description
Technical Field
The invention belongs to the field of natural gas hydrate exploitation, and particularly relates to a method for intermittently and secondarily exploiting natural gas hydrates through microwave heating.
Background
Natural gas hydrates are non-stoichiometric solid complexes of water and small molecule gases produced under low temperature, high pressure conditions. As a clean energy with huge reserves, how to efficiently extract natural gas hydrate from sea areas and frozen soil areas is one of the current research hotspots. According to the stable existing condition of the hydrate, the mining mode mainly comprises the following steps: a pressure reduction method, a thermal excitation method, an inhibitor method, a carbon dioxide substitution method, a solid fluidization method, and the like. The depressurization method is simple to operate and good in economic benefit, is repeatedly applied to trial production of the sea natural gas hydrate, but the single depressurization method is difficult to meet the heat requirement in the later stage of hydrate decomposition; the thermal excitation method has good effect, high gas production rate and high cost, and the traditional heating mode has heat loss; the inhibitor method can change the phase equilibrium condition of the hydrate, but the chemical reagent has high cost and may cause the pollution of stratum environment; the carbon dioxide hydrate generated by the carbon dioxide replacement method is more stable than the methane hydrate, and the method can store the greenhouse gas carbon dioxide to reduce the greenhouse effect, but the current conversion efficiency is lower. The above single exploitation methods have advantages and disadvantages, and thus the combination of multiple methods is considered as the most promising exploitation method of natural gas hydrates. The heat shock can provide energy required by the decomposition and heat absorption of the hydrate, wherein the microwave is used as an electromagnetic wave with the frequency of 300MHz to 300GHz, so that the uniform and rapid heating of the polar molecular hydrate can be realized, and the advantages of small heat loss and rapid action make the hydrate one of the favorable auxiliary exploitation methods in the exploitation of the natural gas hydrate.
The natural gas hydrate can be decomposed quickly and efficiently by microwave heating. However, as the amount of free water produced during the hydrate decomposition process increases, the microwave penetration depth decreases significantly. In this case, Microwave energy is more used to raise the temperature of the reservoir and water than to Hydrate Dissociation, heating the heat transfer by penetrating volume heating to the thermal gradient ("experimental study of Methane Hydrate Dissociation behaviour in Microwave-excited loose deposits", journal of energy, 2011, vol.25, No. 1, pages 33-41, see He, s.; Liang, d.; Li, d.; Ma, l.experimental Investigation on the Dissociation condition of the Methane Gas Hydrate of Methane Hydrate moisture in open semiconductor Microwave insulation.energy & functional 2011,25(1), 33-41. htt:// doi.org/10.1021/ef 1011116). Due to the limitation of the penetration depth of the microwave, after the hydrate in the direct action range of the microwave is decomposed, the microwave energy is used for heating the reservoir, and continuous microwave continuous heating inevitably causes the loss of the microwave energy. In the rapid decomposition period of the hydrate, the rapid temperature rise may be caused by continuous microwave action, and the accident potential such as stratum collapse is caused by the stratum pressure surge caused by continuous and rapid gas production. Therefore, a reasonable optimization of the microwave thermal shock protocol is necessary.
Disclosure of Invention
Aiming at the technical problems of the existing natural gas hydrate development method, the invention aims to provide a method for intermittently and secondarily exploiting natural gas hydrate through microwave heating, so that the exploitation of the natural gas hydrate is automatically regulated, optimized and secondarily assisted through microwave heating, the exploitation efficiency and the energy utilization rate are improved aiming at the actual working condition in the well, and the accident potential caused by high temperature and high pressure is avoided.
The technical scheme adopted by the invention for realizing the purpose is as follows: a method for intermittently heating and assisting in exploiting natural gas hydrates by microwaves comprises the following steps:
s10, exploiting the hydrate in the exploitation area by using the existing natural gas hydrate exploitation method and simultaneously applying f 1 Auxiliary mining is carried out by microwave with frequency;
s20, detecting the water saturation Sw of the hydrate at the position of the microwave transmitting antenna under the mining well in real time, and when the detected water saturation Sw is reached max When the hydrate is decomposed, the suction pump is automatically started to absorb water produced by the decomposition of the hydrate into a water production pipeline; when the water saturation decreases to Sw min When the suction pump is closed; in the process, the microwave absorptivity alpha needs to be monitored in real time, and the microwave transmitting power is automatically adjusted according to the monitored microwave absorptivity alpha, so that the microwave absorptivity alpha is always kept to be more than 60 percent, wherein the expression of the microwave absorptivity alpha is (A-B)/B, A represents the microwave transmitting power, and B represents the microwave reflecting power;
wherein Sw max And Sw min The determination process of (2) is: determining frequency f at different water saturations Sw 1 Microwave penetration depth Dp' 1 ，Dp′ 1 Down to frequency f 1 Maximum penetration depth Dp of microwave 1 1/3 the corresponding water saturation Sw value is Sw max ，Dp′ 1 Down to frequency f 1 Maximum penetration depth Dp of microwave 1 2/3, the corresponding water saturation Sw value is Sw min Wherein the frequency f 1 Maximum penetration depth Dp of microwave 1 I.e. frequency f 1 Maximum value of the direct microwave action region;
s30, repeating the step S20 till f 1 Maximum penetration depth D of microwave action at frequency P1 The hydrates in the region are all decomposed;
s40, when f 1 Maximum penetration depth D of microwave action at frequency P1 After the hydrates in the region are completely decomposed, the microwave energy is completely used for increasing the temperature of the reservoir, and when the temperature of the reservoir is gradually increased to 42 ℃, the frequency of the microwave is from f 1 Is automatically lowered to f 2 Completing a mining stage;
s50, using the result value of the microwave frequency obtained in the last mining stageRepeating the steps S10 to S40 for the initial value of the microwave frequency of the next mining stage until the gas production is finished or the lowest microwave frequency f is reached min ，f min 300 MHz; in the process, if the microwave frequency is the lowest microwave frequency f min If gas production is not finished, then according to reservoir temp. T max 42 ℃ and T min And (4) automatically controlling the starting and stopping of a microwave heating program at 8 ℃, and mining in an automatic intermittent microwave heating mode until the mining is finished.
Before step S10, determining the range of the microwave direct acting area according to the reservoir thickness H, and presetting a microwave heating program which is configured to divide microwave heating into five exploitation stages, wherein the initial value of the microwave frequency of the first exploitation stage is set as f 1 The microwave frequency is reduced to f at the completion of the first mining stage 2 Using the result value of the microwave frequency obtained from the previous mining stage as the initial value of the microwave frequency of the next mining stage, the initial value of the microwave frequency of each stage being from f 1 Updated to successively decreasing f 2 、f 3 、f 4 、f 5 Until the gas production is finished, if the frequency is not reduced to five set frequencies in sequence, the gas production is finished, and the rest set frequencies are not started, wherein the frequency f 1 Maximum penetration depth Dp of microwave 1 ，Dp 1 0.01 × H, frequency f 2 Maximum penetration depth Dp of microwave 2 ，Dp 2 0.03 × H, frequency f 3 Maximum penetration depth Dp of microwave 3 ，Dp 3 0.125 × H, frequency f 4 Maximum penetration depth Dp of microwave 4 ，Dp 4 0.08 × H, frequency f 5 Maximum penetration depth Dp of microwave 5 ，Dp 5 0.25H, and frequency f of microwave 1 The value range of (1) is 3.68 GHz-36.7 GHz, and the microwave action range is 0.01 m-0.1 m; frequency f of microwave 2 The value range of (1) is 1.84 GHz-3.68 GHz, and the microwave action range is 0.1 m-0.2 m; frequency f of microwave 3 The value range of (A) is 0.74 GHz-1.84 GHz, and the microwave action range is 0.2 m-0.5; frequency f of microwave 4 The value range of (1) is 0.37 GHz-0.74 GHz, and the action range is 0.5 m-1 m; frequency f of microwave 5 The value range of (1) is 0.3 GHz-0.37 GHz, the action range is 1 m-1.23 m, if Dp 1 、Dp 2 、Dp 3 、Dp 4 、Dp 5 If the calculation result is not in the value of each microwave action range, according to the reservoir thickness H, Dp 1 、Dp 2 、Dp 3 、Dp 4 、Dp 5 If the calculation result is not in the range of each microwave action, the corresponding frequency is replaced by the recommended microwave frequency, and the recommended frequencies of the five microwave frequencies are f 1 ＝5GHz、f 2 ＝2.45GHz、f 3 ＝918MHz、f 4 ＝416MHz、f 5 ＝300MHz。
Further, the microwave emission power range in the intermittent microwave heating assisted natural gas hydrate exploitation method is 100W-8 KW.
The natural gas hydrate mining method in step S10 includes a depressurization method, a thermal excitation method, an inhibitor method, a carbon dioxide displacement method, a solid fluidization method, or a natural gas hydrate mining method combining several methods.
Through the design scheme, the invention can bring the following beneficial effects: the method for intermittently heating and assisting in exploiting the natural gas hydrate can automatically regulate and control the microwave frequency, the microwave transmitting power and the microwave action state according to the underground working condition, and can be matched with the use of the suction pump, so that the direct decomposition of the hydrate area by the microwave can be furthest enhanced, the gas production rate is improved, the utilization rate of microwave energy is enhanced, and the exploitation cost of the hydrate is saved.
Drawings
FIG. 1 is a flow chart of a method for intermittent microwave heating assisted production of natural gas hydrates in an embodiment of the present invention;
FIG. 2 is a schematic diagram of sea area natural gas hydrate exploitation by the intermittent microwave heating-assisted natural gas hydrate exploitation method provided by the invention;
FIG. 3 is a schematic diagram of methane hydrate in a mining laboratory by using the intermittent microwave heating-assisted natural gas hydrate mining method provided by the invention;
in the figure: 1-microwave generating device, 2-gas flowmeter, 3-computer control end, 4-gas collection device, 5-blowout preventer, 6-packer, 7-gas separator, 8-open hole horizontal well, 9-microwave transmitting antenna, 10-suction pump, 11-temperature sensor, 12-microwave direct action hydrate area, 1201-f 1 Direct range of action of microwaves of frequency 1202-f 2 Direct range of action of microwaves of frequency, 1203-f 3 The method comprises the following steps of (1) directly acting microwave range of frequency, 13-non-microwave directly acting hydrate region, 14-microwave power supply, 15-microwave head, 1501-magnetron, 1502-circulator, 1503-directional coupler, 16-three-pin tuner, 17-waveguide, 18-horn antenna, 19-sapphire glass, 20-high-pressure reaction kettle, 21-backpressure valve, 22-ball valve, 23-flowmeter, 24-computer, 25-drying tube, 26-gas cylinder, 27-microwave leakage instrument, 28-water load and 29-reservoir.
Detailed Description
As shown in fig. 1, the method for intermittently heating and assisting in exploiting the natural gas hydrate provided by the invention can optimize the assisting effect of microwaves, improve the production efficiency and reduce the exploitation cost; before mining, presetting a microwave heating program, wherein the microwave heating program is configured to: determining the range of the microwave direct action area according to the thickness H of the reservoir, dividing the microwave heating auxiliary mining process into five mining stages corresponding to different microwave frequency actions, and setting the initial value of the microwave frequency of the first mining stage as f 1 Frequency of microwaves from f at the completion of the first mining stage 1 Is automatically lowered to f 2 Using the result value of the microwave frequency obtained from the previous mining stage as the initial value of the microwave frequency of the next mining stage, the initial value of the microwave frequency of each stage being from f 1 Updated to successively smaller f 2 、f 3 、f 4 、f 5 Until the end of gas production, wherein the frequency f 1 Maximum penetration depth Dp of microwave 1 ，Dp 1 0.01 × H, frequency f 2 Maximum penetration depth Dp of microwave 2 ，Dp 2 0.03 × H, frequency f 3 Maximum penetration depth Dp of microwave 3 ，Dp 3 0.125 × H, frequency f 4 Maximum penetration depth Dp of microwave 4 ，Dp 4 0.08 × H, frequency f 5 Maximum penetration depth Dp of microwave 5 ，Dp 5 If the frequency is not sequentially reduced to the set five frequencies, the gas production is finished, and the rest set frequencies are not started;
the method comprises the following steps:
s10, exploiting the hydrate in the exploitation area by using the existing natural gas hydrate exploitation method and simultaneously applying f 1 Auxiliary mining is carried out by microwave with frequency;
s20, detecting the water saturation Sw of the hydrate at the position of the microwave transmitting antenna under the mining well in real time, and when the detected water saturation Sw is reached max When the hydrate saturation is reduced to Sw, a suction pump is automatically started to absorb water produced by hydrate decomposition into a water production pipeline min When the pumping pump is turned off, the penetration depth of the microwaves in the reservoir is not limited due to the production of a large amount of free water; in the process, the microwave absorptivity alpha needs to be monitored in real time, the expression of the microwave absorptivity alpha is (A-B)/B, A represents microwave transmitting power, and B represents microwave reflecting power; automatically adjusting the microwave transmitting power according to the monitored microwave absorptivity alpha, so that the microwave absorptivity alpha is always kept to be more than 60%; when the microwave absorption rate alpha is very small, the majority of microwaves are reflected, and the actually absorbed microwaves are very few, so that the microwave energy is wasted;
said Sw max And Sw min The determination process of (2) is: determining frequency f at different water saturations Sw 1 Microwave penetration depth Dp' 1 ，Dp′ 1 Down to frequency f 1 Maximum penetration depth Dp of microwave 1 1/3, the corresponding water saturation Sw value is Sw max ，Dp′ 1 Down to frequency f 1 Maximum penetration depth Dp of microwave 1 2/3, the corresponding water saturation Sw value is Sw min Wherein the frequency f 1 Maximum penetration depth Dp of microwave 1 I.e. frequency f 1 Maximum value of the direct microwave action region;
s30, repeating the step S20 till f 1 Maximum penetration depth D of microwave action at frequency P1 The hydrates in the region are all decomposed;
S40. when f is 1 Maximum penetration depth D of microwave action at frequency P1 After the hydrates in the region are completely decomposed, the microwave energy is completely used for increasing the temperature of the reservoir, and when the temperature of the reservoir is gradually increased to 42 ℃, the frequency of the microwave is from f 1 Is automatically lowered to f 2 Completing a mining stage;
s50, using the result value of the microwave frequency obtained in the last mining stage as the initial value of the microwave frequency of the next mining stage, repeating the steps S10 to S40 until the gas production is finished or the lowest microwave frequency f is reached min ，f min 300 MHz; in the process, if the microwave frequency is the lowest microwave frequency f min If gas production is not finished, then according to reservoir temp. T max 42 ℃ and T min And (4) automatically controlling the starting and stopping of the microwave heating program at 8 ℃, and mining in an automatic intermittent microwave heating mode until the mining is finished.
The process of calculating the required microwave frequency from the microwave penetration depth is as follows:
wherein ε' represents a relative dielectric constant; theta v Represents the liquid water volume distribution, i.e. the water saturation Sw; tan δ represents a dielectric loss tangent, δ represents a dielectric loss angle, ε' represents an imaginary part of a relative dielectric constant, and f represents a frequency of a microwave; dp represents the microwave penetration depth; c represents the speed of light in vacuum;
determining f from reservoir thickness conditions 1 Maximum Dp of direct microwave action region of frequency 1 (f 1 The maximum value of the direct microwave action region of the frequency is the frequency f 1 Maximum penetration depth Dp of microwave 1 ) When epsilon ' is the minimum value of 4.09, the reservoir property estimates that the dielectric parameters of the gas hydrate are epsilon ″ (58) and tan delta (0.0642), where the dielectric parameters of the gas hydrate are known (58) and tan delta (0.0642) (all reservoirs are currently calculated according to the two values), epsilon ' is the minimum value of 4.09 because the water saturation Sw is 0, epsilon ' is the minimum value of 4.09 according to the formula (1), and the microwave penetration depth is the maximum value D P1 Is known and the frequency f of the microwave can be calculated 1 And (4) taking values.
Determining the range Dp, Dp of the microwave direct action region according to the reservoir thickness H 1 ＝0.01*H，Dp 2 ＝0.03*H，Dp 3 ＝0.125*H，Dp 4 ＝0.08*H，Dp 5 0.25 × H. If the Dp calculation result is not within the microwave action range, see table 1, selecting the corresponding recommended frequency: frequency f of microwaves 1 ＝5GHz、f 2 ＝2.45GHz、f 3 ＝918MHz、f 4 ＝416MHz、f 5 300 MHz. Namely: if Dp 2 If the value of (b) is not in the range of 0.01 to 0.1m, the corresponding f 1 Taking 5 GHz; dp 2 If the value of (d) is not in the range of 0.1 to 0.2m, the corresponding f 2 Taking 2.45 GHz; dp 3 If the value of (d) is not in the range of 0.2 to 0.5m, the corresponding f 3 Taking 918 MHz; dp 4 If the value of (d) is not in the range of 0.5 to 1m, the corresponding f 4 Taking 416 MHz; dp 5 If the value of (b) is not in the range of 1 to 1.23m, the corresponding f 5 Take 300 MHz.
TABLE 1
| Frequency f of microwaves | Range of frequency values | Range of action Dp |
| f 1 | 3.68GHz～36.7GHz | 0.01～0.1m |
| f 2 | 1.84GHz～3.68GHz | 0.1～0.2m |
| f 3 | 0.74GHz～1.84GHz | 0.2～0.5m |
| f 4 | 0.37GHz～0.74GHz | 0.5～1m |
| f 5 | 0.3GHz～0.37GHz | 1～1.23m |
The microwave emission power range in the intermittent microwave heating-assisted natural gas hydrate exploitation method is 100W-8 KW.
The natural gas hydrate mining method in step S10 includes a depressurization method, a thermal excitation method, an inhibitor method, a carbon dioxide displacement method, a solid fluidization method, or a natural gas hydrate mining method combining several methods.
In order to more clearly illustrate the invention, the invention is further described below in connection with preferred embodiments. It is to be understood by persons skilled in the art that the following detailed description is illustrative and not restrictive, and is not to be taken as limiting the scope of the invention. Unless defined otherwise, technical or scientific terms used herein shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention belongs. Well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention. All devices mentioned in the embodiments of the present invention belong to the prior art, and therefore, the corresponding positional relationship and connection relationship are not described in detail.
Example 1
Fig. 2 shows a schematic diagram of exploiting sea natural gas hydrate by using the intermittent microwave heating assisted natural gas hydrate exploiting method provided by the invention. The hydrate reservoir region is located in 263m sediment with the seawater depth of less than 1200m, the reservoir thickness is 5m, and the reservoir range is 100m x 100 m.
Determining the range of a microwave direct action area Dp according to the thickness H of the reservoir layer being 5m 1 ＝0.05m，Dp 2 ＝0.15m，Dp 3 ＝0.4m，Dp 4 ＝0.4m，Dp 5 1.25m, wherein Dp 5 1.25m is not in Dp 5 Is selected, thereby selecting the recommended frequency f 5 300MHz, corresponding Dp 5 1.23 m. That is, the frequency of example 1 is selected to be f 1 ＝10GHz，f 2 ＝2.45GHz，f 3 ＝918MHz，f 4 ＝416MHz，f 5 ＝300MHz。
The method for intermittently heating and assisting in exploiting the natural gas hydrate by the aid of the microwaves comprises the following steps of:
step S10, drilling a vertical well and a horizontal branch well (an open hole horizontal well 8) in the hydrate exploitation area, and installing a blowout preventer 5, a packer 6 and a gas separator 7 on the vertical well section in the hydrate exploitation area; laying a microwave transmitting antenna 9, a suction pump 10 and a temperature sensor 11 in a horizontal branch well (an open hole horizontal well 8); the microwave generating device 1 is positioned on a drilling ship, microwaves are transmitted to a microwave transmitting antenna 9 in an open hole horizontal well 8 through a microwave transmission line and are transmitted to a hydrate reservoir, the microwaves can be radiated in a hydrate area 12 directly acted by the microwaves and cannot be radiated to a non-microwave hydrate area 13 directly acted by the microwaves; the gas flow meter 2 and the gas collection device 4 are located on the drilling vessel, collect methane gas and monitor production changes; the computer control end 3 monitors the underground working condition and automatically controls the microwave generating device 1, the microwave transmitting antenna 9 and the suction according to the underground environmentAnd (3) a pump 10 whereby the hydrates are rapidly broken down under microwave assistance. Production of gas hydrates in a reservoir zone using a depressurization method, with simultaneous application of f 1 Frequency of 10GHz microwave thermal activation, first stage around producing well 1 The direct action range of the microwave of the frequency is Dp 1 0.04m, i.e. f in the figure 1 Direct range of action 1201, f of microwaves of frequency 1 Hydrate in the direct action range 1201 of microwave of frequency is directly under the assistance of microwave with 30000m 3 Decomposing gas production at a rate of one day;
step S20, when the water saturation detector at the downhole microwave transmitting antenna 9 detects that the water saturation reaches Sw max When the concentration is 56%, automatically starting a suction pump 10 around a microwave transmitting antenna 9, and absorbing water generated by the decomposition of the hydrate into a water production pipeline; when the water saturation at the microwave transmitting antenna 9 under the well is reduced to Sw min At 14%, the action of the suction pump 10 is stopped, so that the penetration depth of the microwaves in the reservoir is not limited by the production of a large amount of free water;
in the process, the microwave transmitting power is automatically adjusted according to the monitored microwave absorptivity alpha, so that the microwave absorptivity alpha is always kept to be more than 60 percent;
step S30, repeating step S20 until f 1 Maximum penetration depth Dp of microwaves at a frequency of 10GHz 1 The hydrates within 0.04m are all decomposed;
step S40, when f 1 Maximum penetration depth Dp of microwaves at a frequency of 10GHz 1 The total decomposition of hydrates in 0.04m, and the microwave energy is all used to raise the reservoir temperature, so that the temperature monitored by the temperature sensor 11 will rise significantly, when the reservoir temperature reaches 42 ℃, the microwave frequency f 1 Automatic lowering to f at 10GHz 2 2.45GHz, thereby increasing the microwave penetration depth Dp 2 To 0.15m, increasing the farther area of the microwave pair production well (f) 2 Microwave direct range of frequencies 1202) decomposition of hydrates;
step S50, repeating the steps S10 to S40, the microwave action frequency f 1 Decrease to f in 10GHz order 2 ＝2.45GHz，f 3 ＝918MHz，f 4 ＝416MHz，f 5 Gas production is still not finished at 300 MHz. During this time, the microwave direct effect hydrate region 12 gradually increases to Dp 2 ＝0.15m、Dp 3 ＝0.40m、Dp 4 ＝0.88m，Dp 5 ＝1.23m，f 3 The microwave direct effect range 1203 of the frequency, see fig. 2, the non-microwave direct effect hydrate region 13 gradually decreases; in the process, when the frequency is the lowest microwave frequency f 5 When the temperature of the reservoir stratum is not higher than 42 ℃, the microwave thermal shock action is automatically turned off, and when the temperature of the reservoir stratum is not higher than 8 ℃, the microwave thermal shock action is automatically turned on, so that the production is carried out in an automatic intermittent heating mode until the production is finished.
According to the embodiment 1, the method for exploiting the natural gas hydrate by using the intermittent microwave heating assistance not only guarantees the production safety during the exploitation of the hydrate, but also guarantees the high-speed gas production rate during the microwave action, improves the utilization rate of microwave energy and saves the exploitation cost. Table 2 shows the microwave frequency for batch microwave heating assisted production of natural gas hydrates for example 1. The frequencies are selected because the frequencies are commonly used in industrial and civil fields and have small influence on communication transmission.
TABLE 2
| Frequency of microwaves | Frequency (GHz) |
| f 1 | 10 |
| f 2 | 2.45 |
| f 3 | 0.918 |
| f 4 | 0.416 |
| f 5 | 0.300 |
Example 2
As shown in fig. 3, in this example, the method for assisting in producing natural gas hydrate by intermittent microwave heating was implemented in a laboratory reaction kettle, the reservoir thickness in the reaction kettle was 0.064m, and the range Dp of the microwave direct action region was determined according to the reservoir thickness H of 0.064m 1 ＝0.00064m，Dp 2 ＝0.00192m，Dp 3 ＝0.00512m，Dp 4 ＝0.009856m，Dp 5 No value is within the range of the frequency action range corresponding to the value of 0.016m, so that the recommended frequency f is selected 1 ＝5GHz，f 2 ＝2.45GHz，f 3 ＝918MHz，f 4 ＝416MHz，f 5 ＝300MHz；
The method specifically comprises the following steps:
step S10, synthesizing methane hydrate in a reservoir 29 of the high-pressure reaction kettle 20, sealing the high-pressure reaction kettle 20 by using sapphire glass 19, communicating a microwave power supply 14, a microwave head 15 (the microwave head 15 is integrated by a magnetron 1501, a circulator 1502 and a directional coupler 1503), a three-pin tuner 16, a waveguide 17, a horn antenna 18 and a water load 28 in a microwave action device, a gas production line, a back pressure valve 21, a ball valve 22, a flow meter 23, a drying pipe 25 and a gas bottle 26, and opening a computer 24 for recording; extracting hydrate in the extraction area by using a depressurization method, wherein the thickness of a reservoir is 0.064m, and applying f 1 Starting a microwave leakage instrument 27 to monitor whether microwave leakage exists or not under the microwave heat excitation action of the frequency of 5GHz, and decomposing and generating gas by directly using hydrates around the exploitation well under the microwave auxiliary action, wherein the gas generation rate can reach 4.298SL/min at most;
step S20, when the microwave transmitting antenna in the reservoir 29The water saturation detector at 9 detects that the water saturation reaches Sw max When the concentration is 64%, automatically starting a suction pump 10 around a microwave transmitting antenna 9, and absorbing water generated by the decomposition of the hydrate into a water production pipeline; when the water saturation around the producing well is reduced to Sw min 15%, the action of the suction pump 10 is stopped, so that the penetration depth of the microwaves in the reservoir 29 is not limited by the production of a large amount of free water; in the process, the microwave transmitting power is automatically adjusted according to the monitored microwave absorptivity alpha, so that the microwave absorptivity alpha is always kept to be more than 60 percent;
step S30, repeating step S20 till f 1 The hydrates in the 5GHz action area are all decomposed;
step S40, when f 1 After the hydrates acted on by the microwaves with the frequency of 5GHz are completely decomposed, the microwave energy is completely used for increasing the temperature of the reservoir 29, and when the four temperature sensors 11 monitor that the reservoir temperature gradually rises to 42 ℃ respectively corresponding to T1, T2, T3 and T4 in the figure, the microwave frequency is automatically reduced to f 2 ＝2.45GHz；
Step S50, repeating steps S10 to S40, at f 2 The hydrate in 2.45GHz is completely decomposed, the gas production is finished, and the other three set frequencies are not started.
The intermittent microwave heating assists in exploiting methane hydrate in a laboratory, the total gas production time is 11.25min, and the total gas production rate is 12.7L. The energy efficiency ratio of the method is respectively improved by 68.76 percent and 59.32 percent under the action of single pressure reduction or single continuous microwave heat shock. Meanwhile, under the method, no mining accident is caused due to overhigh temperature and pressure.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (6)
1. A method for intermittently heating and assisting in exploiting natural gas hydrates by microwaves comprises the following steps:
s10, exploiting the hydrate in the exploitation area by using the existing natural gas hydrate exploitation method and simultaneously applying f 1 Auxiliary mining is carried out by microwave with frequency;
s20, detecting the water saturation Sw of the hydrate at the position of the microwave transmitting antenna under the mining well in real time, and when the detected water saturation Sw is reached max When the method is used, the suction pump is automatically started to absorb the water generated by the decomposition of the hydrate into a water production pipeline, and the water saturation is reduced to Sw min When the suction pump is closed; in the process, the microwave absorptivity alpha needs to be monitored in real time, and the microwave transmitting power is automatically adjusted according to the monitored microwave absorptivity alpha, so that the microwave absorptivity alpha is always kept to be more than 60%;
s30, repeating the step S20 till f 1 Maximum penetration depth D of microwave action at frequency P1 The hydrates in the region are all decomposed;
s40, when f 1 Maximum penetration depth D of microwave action at frequency P1 After the hydrate in the region is completely decomposed, microwave energy is completely used for raising the temperature of the reservoir, and when the temperature of the reservoir is gradually raised to 42 ℃, the frequency of the microwave is from f 1 Is automatically lowered to f 2 Completing a mining stage;
s50, using the result value of the microwave frequency obtained from the last exploitation stage as the initial value of the microwave frequency of the next exploitation stage, repeating the steps S10 to S40 until the gas production is finished or the lowest microwave frequency f is reached min ，f min 300 MHz; in the process, if the microwave frequency is the lowest microwave frequency f min When gas production is not finished, and according to the reservoir temperature T max 42 ℃ and T min And (4) automatically controlling the starting and stopping of the microwave heating program at 8 ℃, and mining in an automatic intermittent microwave heating mode until the mining is finished.
Before step S10, a microwave heating program is preset, the microwave heating program being configured to: determining the range of the microwave direct action area according to the thickness H of the reservoir, dividing the microwave heating auxiliary mining process into five mining stages corresponding to different microwave frequency actions, wherein the first stage isThe initial value of the microwave frequency is set to f in the mining stage 1 Frequency of microwaves from f at the completion of the first mining stage 1 Is automatically lowered to f 2 Using the result value of the microwave frequency obtained from the previous mining stage as the initial value of the microwave frequency of the next mining stage, the initial value of the microwave frequency of each stage being from f 1 Updated to successively decreasing f 2 、f 3 、f 4 、f 5 Until the gas production is finished, if the gas production is finished when the gas production is reduced to a certain microwave frequency, the microwave heating program is automatically stopped, the rest microwave frequencies are not started, wherein the frequency f 1 Maximum penetration depth Dp of microwave 1 ，Dp 1 0.01 × H, frequency f 2 Maximum penetration depth Dp of microwave 2 ，Dp 2 0.03 × H, frequency f 3 Maximum penetration depth Dp of microwave 3 ，Dp 3 0.125 × H, frequency f 4 Maximum penetration depth Dp of microwave 4 ，Dp 4 0.08 × H, frequency f 5 Maximum penetration depth Dp of microwave 5 ，Dp 5 ＝0.25*H。
2. The intermittent microwave heating assisted natural gas hydrate production method as claimed in claim 1, wherein: said Sw max And Sw min The determination process of (2) is: determining frequency f at different water saturations Sw 1 Microwave penetration depth Dp' 1 ，Dp′ 1 Down to frequency f 1 Maximum penetration depth Dp of microwave 1 1/3, the corresponding water saturation Sw value is Sw max ，Dp′ 1 Down to frequency f 1 Maximum penetration depth Dp of microwave 1 2/3, the corresponding water saturation Sw value is Sw min Wherein the frequency f 1 Maximum penetration depth Dp of microwave 1 I.e. frequency f 1 Is the maximum of the direct microwave action region.
3. The intermittent microwave heating assisted natural gas hydrate production method as claimed in claim 1, wherein: frequency f of microwave 1 The value range of (A) is 3.68 GHz-36.7 GHz, and the microwave action rangeThe circumference is 0.01 m-0.1 m; frequency f of microwave 2 The value range of (1) is 1.84 GHz-3.68 GHz, and the microwave action range is 0.1 m-0.2 m; frequency f of microwave 3 The value range of (A) is 0.74 GHz-1.84 GHz, and the microwave action range is 0.2 m-0.5; frequency f of microwave 4 The value range of (A) is 0.37 GHz-0.74 GHz, and the action range is 0.5 m-1 m; frequency f of microwave 5 The value range of (1) is 0.3 GHz-0.37 GHz, the action range is 1 m-1.23 m, if according to the reservoir thickness H, Dp 1 、Dp 2 、Dp 3 、Dp 4 、Dp 5 If the calculation result is not in the value of each microwave action range, replacing the corresponding frequency by the recommended microwave frequency, wherein the recommended frequencies of the five microwave frequencies are f 1 ＝5GHz、f 2 ＝2.45GHz、f 3 ＝918MHz、f 4 ＝416MHz、f 5 ＝300MHz。
4. The intermittent microwave heating assisted natural gas hydrate production method as claimed in claim 1, wherein: the microwave emission power range in the intermittent microwave heating-assisted natural gas hydrate exploitation method is 100W-8 KW.
5. The batch-type microwave heating assisted natural gas hydrate production method according to claim 1, characterized by comprising: the expression of the microwave absorptivity alpha is (A-B)/B, wherein A represents microwave transmitting power, and B represents microwave reflecting power.
6. The intermittent microwave heating assisted natural gas hydrate production method as claimed in claim 1, wherein: the natural gas hydrate mining method in step S10 includes a depressurization method, a thermal excitation method, an inhibitor method, a carbon dioxide displacement method, a solid fluidization method, or a natural gas hydrate mining method combining several methods.
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| US5082054A (en) * | 1990-02-12 | 1992-01-21 | Kiamanesh Anoosh I | In-situ tuned microwave oil extraction process |
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