CN111827936A - Batch drilling rolling type well group natural gas hydrate exploitation system and method - Google Patents
Batch drilling rolling type well group natural gas hydrate exploitation system and method Download PDFInfo
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- CN111827936A CN111827936A CN202010809797.5A CN202010809797A CN111827936A CN 111827936 A CN111827936 A CN 111827936A CN 202010809797 A CN202010809797 A CN 202010809797A CN 111827936 A CN111827936 A CN 111827936A
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP 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
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP 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
- E21B43/013—Connecting a production flow line to an underwater well head
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP 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
- E21B43/30—Specific pattern of wells, e.g. optimizing the spacing of wells
- E21B43/305—Specific pattern of wells, e.g. optimizing the spacing of wells comprising at least one inclined or horizontal well
Abstract
The invention provides a batch drilling rolling type well group natural gas hydrate exploitation system and a method, wherein the system comprises an acquisition device and a data control device; the method comprises the following steps: (1) identifying a natural gas hydrate enrichment area and evaluating methane reserves in a natural gas hydrate reservoir, then carrying out economic evaluation, selecting a mining area and determining the number of drilled wells; (2) double horizontal wells open circuit circulation batch drilling; (3) fracturing and crack-making yield improvement and sand prevention and yield stabilization; (4) and (3) rolling type well group mining, wherein a well group mining mode with multiple well groups side by side is adopted, an underwater mining pipe network shared by the multiple well groups is established, and a mode of mining while drilling is adopted, so that rolling type development is realized. The method can effectively reduce the drilling and exploitation cost of the natural gas hydrate, effectively improve and stabilize the exploitation yield of the natural gas hydrate, prolong the exploitation life, facilitate the improvement of the exploitation economic benefit of the natural gas hydrate, and provide guarantee for realizing commercial exploitation of the natural gas hydrate.
Description
Technical Field
The invention relates to a system and a method for exploiting natural gas hydrates by batch drilling rolling well groups, belonging to the technical field of exploitation of sea natural gas hydrates.
Background
The world energy structure is shifting to low carbon and the natural gas's share of the world's disposable energy is increasing year by year. The international energy agency predicts that natural gas will replace coal in 2030, becoming the second largest energy source next to oil. Global gas hydrates, which have a carbon equivalent of about 2 times the sum of other fossil energy sources, are likely to be an important source of future natural gas. The resource amount of natural gas hydrate in the sea area of China is about 800 million tons of oil equivalent, the method has wide development prospect, and the acceleration of the realization of the commercial exploitation of the natural gas hydrate is the key to seize the top point of the global energy development strategy in the future.
The efficient exploitation of the sea natural gas hydrate is a worldwide engineering technical problem. At present, the natural gas hydrate mining technology is generally in the theoretical research and stope trial mining stage, an economic and effective commercial mining mode is not formed, and the main mining methods comprise a depressurization method, a heat injection method, a chemical agent injection method and a CO (carbon monoxide) injection method2Displacement methods, solid state fluidization methods, and the like. By combining the current state of the natural gas hydrate production technology, a mode of combining a proper production increasing measure based on a depressurization method is considered as the most potential production technology. Aiming at the marine natural gas hydrate, trial production engineering is firstly developed in Japan and China, and although stable gas production is realized through multiple trial production, the trial production engineering faces a series of problems of low gas production, high cost, poor safety guarantee and the like, and the whole mining engineering is still in a test stage. Patent documents also report on methods for exploiting natural gas hydrates in the sea area. Chinese patent document CN110043229A provides a multi-well group communication convergence mining method for sea natural gas hydrates, comprising the following steps: vertical wellDrilling; constructing a gas collecting chamber at the bottom of a vertical well; drilling a horizontal well: comprises a diameter section, a first deflecting section, a stable deflecting section, a second deflecting section and a horizontal section; running a second production casing in the horizontal well, wherein the end part of the second production casing is in sealed connection with the side wall of the artificially constructed gas collection chamber; performing later-stage well completion reservoir transformation and putting in a sand control screen pipe; drilling a plurality of horizontal wells and sealing the horizontal wells and the vertical wells in a butt joint and communication manner; and (5) pressure reduction and extraction. However, the method has the defects of high butt joint difficulty, long time consumption, high drilling and production cost, incapability of being suitable for future large-area block mining and the like of the horizontal well and the vertical well.
In summary, an economical and efficient natural gas hydrate exploitation method is not available at present, which is a key difficulty in restricting the commercial exploitation process of sea natural gas hydrates. The invention is therefore proposed.
Disclosure of Invention
The invention provides a batch drilling rolling type well group natural gas hydrate exploitation system and method, aiming at the defects of the prior art, in particular to the problems of low yield, short duration and poor economy in the existing natural gas hydrate exploitation process. According to the development requirement of the natural gas hydrate, the system and the method for economically and efficiently exploiting the natural gas hydrate are determined by combining the factors such as the capacity requirement, the cost control and the like, so that the economic benefit of exploiting the natural gas hydrate is effectively improved, and the guarantee is provided for realizing the commercial exploitation of the natural gas hydrate.
The technical scheme of the invention is as follows:
a batch drilling rolling type well group natural gas hydrate exploitation system comprises an acquisition device and a data control device;
the collecting device comprises an underwater pipe network, a main gas pipeline, an offshore floating production and storage Facility (FPSO), two or more detachable interfaces, two or more first electric submersible pumps and two or more second electric submersible pumps; the underwater pipe network comprises two or more branches, each branch is provided with a control valve and a flowmeter, and each branch of the underwater pipe network is connected with a detachable interface; the underwater pipe network is connected with an offshore floating production and storage Facility (FPSO) through a main gas transmission pipeline; the first electric submersible pump and the second electric submersible pump are respectively arranged in the two horizontal well sections;
the data control device comprises an optical cable, a photoelectric demodulator, a signal execution mechanism and a computer terminal; one end of the photoelectric demodulator is connected with the flowmeter through an optical cable, and the other end of the photoelectric demodulator is connected with a computer terminal; and the computer terminal is respectively connected with the control valve, the first electric submersible pump and the second electric submersible pump through the signal execution mechanism.
According to the invention, the first electric submersible pump and the second electric submersible pump are preferably respectively positioned in the horizontal well section at a position 5-10m away from the end point of the horizontal well section.
According to the present invention, preferably, the operation method of the above system is as follows:
one end of the underwater pipe network is connected with seabed well mouths of different well groups through a detachable interface, the other end of the underwater pipe network is connected with an offshore floating production and storage Facility (FPSO) through a main gas pipeline, and natural gas produced by each well group is collected to the main gas pipeline through the underwater pipe network and is finally conveyed to the offshore floating production and storage Facility (FPSO); each branch of the underwater pipe network is provided with a control valve and a flowmeter, the control valve is used for controlling the production start time of the well group so as to control the yield change of the whole well group, and the flowmeter is used for measuring the gas production rate and the water production rate of each well group in real time; gas-liquid flow data acquired by the flow meter are transmitted to the photoelectric demodulator through an optical cable, and are converted into electric signals and then transmitted to the computer terminal; the computer terminal is connected with the signal execution mechanism and controls the opening and closing of the control valve by sending an instruction to the signal execution mechanism, so that the production starting time of different well groups is controlled, and the yield change of the whole well group is controlled; meanwhile, the computer terminal sends an instruction to the signal execution mechanism through analyzing gas-liquid flow change data of different well groups monitored by the flow meter in real time so as to control the power of the first electric submersible pump and the second electric submersible pump at the bottom of the wells of the different well groups.
According to the invention, the method for exploiting the natural gas hydrate by using the system and the batch drilling rolling well group comprises the following steps:
(1) identifying a natural gas hydrate enrichment area and evaluating methane reserves in a natural gas hydrate reservoir, then carrying out economic evaluation, selecting a mining area and determining the total well group number of the drilled wells;
(2) double-horizontal-well open-circuit circulating batch drilling well
In the selected mining area, batch drilling is carried out in a mode of circularly drilling double horizontal wells in an open circuit, and drilling of all well groups of one well group is completed at one time; the double horizontal wells are called a well group, each well group comprises a vertical well section, two horizontal well sections and two deflecting sections, the left and right directions of the lower end of the vertical well section are respectively connected with a first deflecting section and a second deflecting section, the first deflecting section is connected with the first horizontal well section, and the second deflecting section is connected with the second horizontal well section; after completing the drilling work of one well group, sequentially completing the drilling work of the other well groups;
(3) fracturing crack-making yield improvement and sand prevention stable yield
After the well drilling of one well group is completed, fracturing induction crack formation and sand prevention construction are carried out on each horizontal well section, and perforation fracturing is carried out on each horizontal well section by adopting fracturing fluid to form cracks; performing sand prevention construction after fracturing induction crack formation is finished, adopting sand prevention measures of filling cracks with a sieve tube and gravels, and injecting a chemical sand prevention agent into the cracks filled with the crack sieve tube and the gravels to form an artificial well wall and a sand prevention layer around a horizontal well section shaft;
(4) rolling well group mining
Adopting a well group mining mode that a plurality of well groups are arranged side by side, and mining the natural gas hydrate by adopting a depressurization method by controlling the pressure change at the bottom of the well; returning natural gas produced by a plurality of well groups in one well group to the same underwater production pipe network; by adopting a mode of mining and drilling simultaneously, a batch of well groups are in production, and a batch of well groups are in drilling, so that rolling development is realized, and the yield peak value can be ensured to be reached every year;
in the process of exploiting the natural gas hydrate, one end of an underwater pipe network is connected with seabed well mouths of different well groups through detachable interfaces, the other end of the underwater pipe network is connected with an offshore floating production and storage Facility (FPSO) through a main gas pipeline, and natural gas produced by each well group is collected to the main gas pipeline through the underwater pipe network and is finally conveyed to the offshore floating production and storage Facility (FPSO); the computer terminal sends an instruction to the signal execution mechanism to control the starting of the control valves arranged on the underwater pipe network to adjust the production starting time of different well groups, so that the yield change of the whole well group is controlled, the peak value change of the gas production of the whole well group is flattened, the relative stability of the natural gas production of the whole well group is kept, and meanwhile, the gas-liquid flow monitored by the flow meter arranged on the underwater pipe network is transmitted to the computer terminal through an optical cable and a photoelectric demodulator; and the computer terminal analyzes the gas-liquid flow change data of different well groups monitored by the flow meter in real time, sends an instruction to the signal execution mechanism, controls the power of the first electric submersible pump and the second electric submersible pump at the bottom of the different well groups in real time, efficiently pumps hydrate produced at the bottom of the well into an underwater pipe network, and finally reaches an offshore floating production and storage unit (FPSO).
According to the present invention, preferably, in the step (1), the natural gas hydrate-enriched zone identification step is: carrying out sea natural gas hydrate drilling work, and identifying a seabed shallow natural gas hydrate reservoir body according to a Bottom Simulating Reflector (BSR) in seismic data by means of a three-dimensional seismic reflection technology; the distribution range of the natural gas hydrate is described by picking up BSR of the seismic profile, and the saturation of the natural gas hydrate is defined>30% of reservoir thickness>10m, methane reserve>108m3The region of (a) is a natural gas hydrate-rich region.
According to the present invention, preferably, in step (1), the methane reserve in the natural gas hydrate reservoir is calculated as follows:
V＝A·ΔZ·φ·H·E (1)
in the formula (1), V is the methane reserve in the natural gas hydrate reservoir, and m3(ii) a A is the distribution area of the natural gas hydrate, m2(ii) a Δ Z is the average thickness of the natural gas hydrate stability zone, m; phi is the average porosity in the deposit, dimensionless; h is the filling rate of the natural gas hydrate, and has no dimension; and E is the volume ratio of the natural gas hydrate, and a theoretical value of 164 is taken.
According to the present invention, it is preferable that the natural gas hydrate-enriched zone satisfying the development economy requirement in step (1) satisfies the following conditions:
in the formula (2), V is the methane reserve in the natural gas hydrate reservoir, m3；VminEconomic reserve of methane, m, for natural gas hydrates3(ii) a t is the age limit, year; i.e. idIs a discount coefficient; c1Is mobile capital, yuan; n is1Year, the year of exploration; n is2For the construction year, year; n is3For stable production years, years; (C)e)tThe exploration investment cost of the t year is Yuan; (C)z)tThe investment cost of the drilling engineering in the t year is Yuan; (C)d)tInvestment cost of ground system engineering in the t year is Yuan; (C)j)tThe unit operation cost in the t year is Yuan; f. ofk1Influence coefficient of scientific and technological progress on exploration investment; f. ofk2The influence coefficient of the technological progress on the investment of the drilling engineering is shown; f. ofk3The influence coefficient of the scientific and technological progress on the reduction of the operation cost is reduced; vtFor annual mining speed, m3A year; f. ofsThe commodity rate of gas is; p is gas price, yuan/m3；txThe comprehensive tax rate.
According to the present invention, it is preferred that the total number of well groups to be drilled for the gas hydrate production zone selected in step (1) is calculated according to the following formula:
n＝V/(xVo) (3)
in the formula (3), n is the total well group number and has no dimension; x is the producible age of a single well group, year; voFor annual production rate of a single well group, m3A year; v is the methane reserve in the reservoir of natural gas hydrate, m3。
According to the present invention, preferably, in step (2), the number of well groups included in one well group is calculated according to the following formula:
nz＝Vn/Vo(4)
in the formula (4), nzThe number of well groups is one well group, and the number has no dimension; vnFor planned annual production, m3A year; voFor annual production rate of a single well group, m3And (4) a year.
According to the invention, preferably, the starting point of the vertical well section in the step (2) is located at a mud line, and the end point is located 10-20m above the upper end of the hydrate reservoir.
According to the invention, preferably, the first deflecting segment and the second deflecting segment in the step (2) start deflecting at the lowest end of the vertical well section, and the well inclination angle is 80-90 degrees.
According to the invention, preferably, the first horizontal well section and the second horizontal well section in the step (2) are both arranged in the middle of the hydrate reservoir, and the lengths of the first horizontal well section and the second horizontal well section are both 200-1000 m.
According to the invention, the double-horizontal-well open-circuit circulation batch drilling is adopted in the step (2), because a marine riser with the length of thousands of meters is not arranged, according to the basic parameters of the platform such as the operating environment, the operating depth and the variable load, the drilling equipment parameters such as the lifting capacity and the turning capacity and the environmental protection requirement, a more economic drilling platform with the variable load meeting the drilling requirement is optimized, the daily cost of the drilling platform can be reduced, and further, the drilling cost of a single well is effectively reduced, meanwhile, the rock debris generated at the bottom of the open-circuit circulation drilling well directly returns to the seabed along with the drilling fluid through the annular space between a drill rod and a well hole, and the drilling speed; by adopting a batch drilling mode, the drilling work of other well groups is completed immediately after the drilling work of one well group is completed, so that the drilling work of a plurality of well groups of the whole well group is completed at one time under the condition that the movement of a drilling platform is reduced as much as possible, the drilling time loss of the whole well group can be greatly reduced, the single-well drilling time is effectively shortened, and the single-well drilling cost is obviously reduced.
According to the invention, preferably, the fracturing fluid in the step (3) is a fracturing fluid system with little damage to a hydrate reservoir and good compatibility; preferably, the fracturing fluid is clear water, and the discharge capacity of the fracturing fluid is more than 1.5m3Min; the fracturing pressure of the perforation fracturing is greater than the initiation pressure of the stratum, and the safety of the stratum is guaranteed according to the stratumAnd setting the characteristics.
According to the invention, preferably, in the step (3), a fracture support material is injected into the fracture to improve the stability of the fractured fracture, effectively improve the flow conductivity of the fractured fracture, increase the pressure relief area and further obviously improve the yield of the single-well natural gas so as to meet the requirement of the single-well yield development of the natural gas hydrate; the fracture propping material is a material which is easy to carry, not easy to embed and good in propping performance, preferably low-density resin coated sand or fiber composite propping agent, and is a commonly used fracture propping material in the field.
According to the present invention, preferably, the chemical sand control agent in step (3) is a resin or oligomer, which are all chemical sand control agents commonly used in the art.
According to the invention, preferably, in the step (4), the underwater production pipe network is recycled, and the production pipe network of the original production well group is disassembled and installed on the new production well group, so that the production cost is further reduced.
The invention has not been described in detail, but is in accordance with the state of the art.
The invention has the following technical characteristics and beneficial effects:
1. according to the method, the superior natural gas hydrate storage area with high natural gas hydrate saturation, high reservoir permeability, large reserve capacity and good economic benefit can be selected as a mining area through the accurate identification of the natural gas hydrate enrichment area, so that the yield of the single-well natural gas is improved; the open-circuit batch drilling of the horizontal well shortens the single-well drilling time to a great extent, the single-well drilling cost can be effectively reduced by selecting a more economical drilling platform with smaller variable load, and the economic benefit of the natural gas hydrate exploitation can be obviously improved; the yield of the natural gas hydrate can be obviously improved after fracturing, inducing and crack formation and sand prevention of the horizontal well group, the stability of the stratum and the well wall is ensured, and the long-term stable high-yield development is facilitated by matching with a depressurization mining method.
2. The invention adopts a rolling well group exploitation mode to control the exploitation yield change of the well group in real time, and repeatedly utilizes an underwater production pipe network, thereby being beneficial to reducing the production cost, simultaneously ensuring that the annual natural gas yield is in a relatively stable peak value, and being beneficial to realizing the long-term commercial exploitation of the natural gas hydrate.
Drawings
FIG. 1 is a schematic vertical section of a well group according to the present invention.
Fig. 2 is a schematic structural diagram of a system for producing natural gas hydrates by batch-drilling rolling well groups.
FIG. 3 is an enlarged view of the horizontal well segment fracturing and fracture-making and sand-control of the present invention.
Fig. 4 is a schematic diagram of the change of the yield of the natural gas hydrate obtained by the invention.
In the figure: 1 a hydrate reservoir; 2. shallow seabed layer; 3. seawater; 4. sea level; 5. a vertical well section; 6. a first deflecting section; 7. a second deflecting section; 8. a first horizontal well section; 9. a second horizontal well section; 10. a first electrical submersible pump; 11. a second electrical submersible pump; 12. a detachable interface; 13. a control valve; 14. a flow meter; 15. an underwater pipe network; 16. a main gas line; 17. an offshore Floating Production Storage and Offloading (FPSO); 18. an optical cable; 19. a photoelectric demodulator; 20. a signal actuator; 21. a computer terminal; 22. cracking; 23. artificial well wall and sand control layer.
Detailed Description
The present invention will be further described by way of examples, but not limited thereto, with reference to the accompanying drawings. The examples are not exhaustive and are all prior art in the field.
Example 1
As shown in fig. 2, a batch-drilling rolling well group natural gas hydrate exploitation system comprises a well group acquisition device and a data control device;
the well group collecting device comprises an underwater pipe network 15, a main gas pipeline 16, an offshore floating production and storage Facility (FPSO)17, 5 detachable interfaces 12, 5 first electric submersible pumps 10 and 5 second electric submersible pumps 11; the underwater pipe network 15 comprises 5 branches, each branch is provided with a control valve 13 and a flowmeter 14, and each branch of the underwater pipe network 15 is connected with a detachable interface 12; the underwater pipe network 15 is connected with an offshore floating production and storage Facility (FPSO)17 through a main gas pipeline 16; the first electric submersible pump 10 and the second electric submersible pump 11 are respectively positioned in the horizontal well section at a position 5m away from the end point of the horizontal well section.
The data control device comprises an optical cable 18, a photoelectric demodulator 19, a signal execution mechanism 20 and a computer terminal 21; one end of the photoelectric demodulator 19 is connected with the flowmeter 14 through an optical cable 18, and the other end is connected with a computer terminal 21; and the computer terminal 21 is respectively connected with the control valve 13, the first electric submersible pump 10 and the second electric submersible pump 11 through the signal execution mechanism 20.
The working method of the system comprises the following steps:
one end of an underwater pipe network 15 is connected with seabed well mouths of different well groups through a detachable connector 12, the other end of the underwater pipe network is connected with an offshore floating production and storage device (FPSO)17 through a main gas pipeline 16, and natural gas produced by each well group is collected to the main gas pipeline 16 through the underwater pipe network 15 and finally conveyed to the offshore floating production and storage device (FPSO) 17; each branch of the underwater pipe network 15 is provided with a control valve 13 and a flowmeter 14, the control valve 13 is used for controlling the production start time of the well group so as to control the yield change of the whole well group, and the flowmeter 14 is used for measuring the gas production rate and the water production rate of each well group in real time; gas-liquid flow data collected by the flow meter 14 is transmitted to the photoelectric demodulator 19 through the optical cable 18, and is converted into an electric signal and then transmitted to the computer terminal 21; the computer terminal 21 is connected with the signal execution mechanism 20, and the computer terminal 21 controls the opening and closing of the control valve 13 by sending instructions to the signal execution mechanism 20, so that the production starting time of different well groups is controlled, and the production change of the whole well group is controlled; meanwhile, the computer terminal 21 sends an instruction to the signal execution mechanism 20 by analyzing the gas-liquid flow change data of different well groups monitored by the flow meter 14 in real time, so as to control the power of the first electric submersible pump 10 and the second electric submersible pump 11 at the bottom of different well groups.
Example 2
The batch-drilling rolling-type well group natural gas hydrate exploitation system is as described in embodiment 1, except that the first electric submersible pump 10 and the second electric submersible pump 11 are respectively located in the horizontal well section at a distance of 10m from the end point of the horizontal well section.
Example 3
A method for exploiting natural gas hydrates by batch drilling rolling well groups comprises the following steps:
(1) identifying a natural gas hydrate enrichment area and evaluating methane reserves in a natural gas hydrate reservoir, then carrying out economic evaluation, selecting a mining area and determining the total well group number of the drilled wells;
firstly, carrying out sea natural gas hydrate drilling work, and identifying a seabed shallow natural gas hydrate reservoir body according to Bottom modeling Reflector (BSR) in seismic data by means of a three-dimensional seismic reflection technology; the distribution range of the natural gas hydrate is described by picking up BSR of the seismic profile, and the saturation of the natural gas hydrate is defined>30% of reservoir thickness>10m, methane reserve>108m3The region of (a) is a natural gas hydrate-rich region.
The methane reserves in the natural gas hydrate reservoir are calculated as follows:
V＝A·ΔZ·φ·H·E (1)
in the formula (1), V is the methane reserve in the natural gas hydrate reservoir, and m3(ii) a A is the distribution area of the natural gas hydrate, m2(ii) a Δ Z is the average thickness of the natural gas hydrate stability zone, m; phi is the average porosity in the deposit, dimensionless; h is the filling rate of the natural gas hydrate, and has no dimension; and E is the volume ratio of the natural gas hydrate, and a theoretical value of 164 is taken.
And after evaluating the reserves of the natural gas hydrates, judging and selecting the natural gas hydrate enrichment area meeting the development economic requirement as a development block according to the formula (2).
In the formula (2), V is the methane reserve in the natural gas hydrate reservoir, m3；VminEconomic reserve of methane, m, for natural gas hydrates3(ii) a t is the age limit, year; i.e. idIs a discount coefficient; c1Is mobile capital, yuan; n is1Year, the year of exploration; n is2For the construction year, year; n is3For stable productionYear limit, year; (C)e)tThe exploration investment cost of the t year is Yuan; (C)z)tThe investment cost of the drilling engineering in the t year is Yuan; (C)d)tInvestment cost of ground system engineering in the t year is Yuan; (C)j)tThe unit operation cost in the t year is Yuan; f. ofk1Influence coefficient of scientific and technological progress on exploration investment; f. ofk2The influence coefficient of the technological progress on the investment of the drilling engineering is shown; f. ofk3The influence coefficient of the scientific and technological progress on the reduction of the operation cost is reduced; vtFor annual mining speed, m3A year; f. ofsThe commodity rate of gas is; p is gas price, yuan/m3；txThe comprehensive tax rate.
After a natural gas hydrate development block is selected, calculating the total well group number needing to be drilled according to the following formula after the designed annual production speed and production age of a single well:
n＝V/(xVo) (3)
in the formula (3), n is the total well group number and has no dimension; x is the producible age of a single well group, year; voFor annual production rate of a single well group, m3A year; v is the methane reserve in the reservoir of natural gas hydrate, m3。
(2) Double-horizontal-well open-circuit circulating batch drilling well
In the selected mining area, batch drilling is carried out in a mode of circularly drilling double horizontal wells in an open circuit, and drilling of all well groups of one well group is completed at one time; a double horizontal well is called a well group, a schematic diagram of the well group is shown in fig. 1, the well group comprises a vertical well section 5, the left and right directions of the lower end of the vertical well section 5 are respectively connected with a first deflecting section 6 and a second deflecting section 7, the first deflecting section 6 is connected with a first horizontal well section 8, and the second deflecting section 7 is connected with a second horizontal well section 9; one end of the first horizontal well section 8 is connected with the first deflecting section 6, the other end, namely the tail end, is provided with a first electric submersible pump 10, the first electric submersible pump 10 is positioned at a position 10m away from the tail end point of the first horizontal well section 8, one end of the second horizontal well section 9 is connected with the second deflecting section 7, the other end, namely the tail end, is provided with a second electric submersible pump 11, and the second electric submersible pump 11 is positioned at a position 10m away from the tail end point of the second horizontal well section 9; after the drilling work of one well group is finished, the drilling work of the other well groups is finished in sequence, so that the drilling work of a plurality of well groups of the whole well group is finished at one time under the condition that the movement of a drilling platform is reduced as much as possible, the drilling time loss of the whole well group can be greatly reduced, the single-well drilling time is effectively shortened, and the single-well drilling cost is obviously reduced;
the number of well groups contained in a well group is calculated according to the following formula:
nz＝Vn/Vo(4)
in the formula (4), nzThe number of well groups is one well group, and the number has no dimension; vnFor planned annual production, m3A year; voFor annual production rate of a single well group, m3And (4) a year.
The starting point of the vertical well section is positioned at the mud line, and the end point is positioned 10m above the upper end of the hydrate reservoir.
The initial deflecting positions of the first deflecting section and the second deflecting section are the lowest ends of the vertical well sections, and the well angle is 80 degrees.
The first horizontal well section and the second horizontal well section are both arranged in the middle of the hydrate reservoir and are both 200m in length.
(3) Fracturing crack-making yield improvement and sand prevention stable yield
After the well group is drilled, fracturing induction seam making and sand prevention construction are carried out on each horizontal well section, a clear water fracturing fluid system with small damage to a hydrate reservoir and good compatibility is preferably selected according to the reservoir characteristics of a natural gas hydrate exploitation block, and the discharge capacity of the fracturing fluid is 2.0m3Performing perforation fracturing on each horizontal well, ensuring that the fracturing pressure is greater than the initiation pressure of the stratum, and forming cracks 22 around the shaft on the premise of ensuring the safety of the stratum so as to increase the decomposition area of the natural gas hydrate; meanwhile, the low-density resin coated sand which is easy to carry, difficult to embed and good in support property is preferably selected to be injected into the fracturing crack so as to improve the stability of the fracturing crack, effectively improve the flow conductivity of the fracturing crack, increase the pressure relief area and further obviously improve the natural single-well areaAnd (4) gas yield to meet the requirement of single well yield of natural gas hydrate development.
After fracturing induction crack making is completed, sand control process construction is carried out, sand control measures of screen pipe and gravel filling are adopted, resin chemical sand control agents are injected into the fracturing cracks 22, an artificial well wall and a sand control layer 23 are formed around a shaft, sand production is prevented, the stability of the well wall is kept, well blocking caused by a large amount of sand production is avoided, and therefore long-term stable development of the natural gas hydrate is achieved.
(4) Rolling well group mining
And (3) mining by adopting a well group mining mode that a plurality of well groups are arranged side by side according to the number of the well groups in one well group determined in the step (2), arranging a batch-drilling rolling type well group natural gas hydrate mining system in the mined well group, wherein the structural schematic diagram of the system is shown in figure 2, and mining the natural gas hydrate by adopting a depressurization method by controlling the change of bottom hole pressure.
In the process of exploiting the natural gas hydrate, each branch of an underwater pipe network 15 is connected with seabed well mouths of different well groups through a detachable connector 12, the other end of the underwater pipe network is connected with an offshore floating production and storage device (FPSO)17 through a main gas pipeline 16, and the natural gas produced by each well group is collected to the main gas pipeline 16 through the underwater pipe network 15 and finally conveyed to the offshore floating production and storage device (FPSO) 17. The computer terminal 21 sends an instruction to the signal execution mechanism 20 to control the start of the control valve 13 installed on each branch of the underwater pipe network 15 to adjust the production start time of different well groups, so as to control the yield change of the whole well group, smooth the peak value change of the gas production of the whole well group, and keep the relative stability of the natural gas yield of the whole well group. Meanwhile, the gas-liquid flow monitored by the flow meter 14 installed on each branch of the underwater pipe network 15 is transmitted to the computer terminal 21 through the optical cable 18 and the photoelectric demodulator 19. The computer terminal 21 sends an instruction to the signal execution mechanism 20 by analyzing the gas-liquid flow change data of different well groups monitored by the flow meter 14 in real time, controls the power of the first electric submersible pump 10 and the second electric submersible pump 11 at the bottom of different well groups in real time, and pumps hydrate produced at the bottom of the well into the underwater pipe network 15 efficiently, and finally reaches the FPSO 17.
In order to realize the long-term mining requirement, a mode of mining while drilling is adopted: one group of wells are drilled while the other group of wells are produced, when the yield of the production well group is reduced to the critical yield of economic exploitation, the production target is turned to a new group of drilled wells, the underwater production pipe network 15 installed in the original production well group is disassembled at the same time, and the underwater production pipe network is installed to the new group of production wells, so that the recycling of the underwater production pipe network 15 can be realized, the production cost of the natural gas hydrate is further reduced, the long-term rolling type efficient development of the sea natural gas hydrate is realized, and the annual yield can be ensured to reach the peak value of commercial exploitation yield. By adopting the rolling well group production mode, the natural gas production per year can be in a relatively stable peak value to meet the commercial production demand as shown in fig. 4.
Example 4
A method of producing natural gas hydrates from a batch-drilling rolling well cluster, comprising the steps of (1) performing the above-described steps, except that in step (2), the end point of the vertical well section is 20m above the upper end of the hydrate reservoir; the well inclination angle of the first deflecting section and the second deflecting section is 90 degrees; the length of the first horizontal well section and the length of the second horizontal well section are both 1000 meters.
Claims (10)
1. The system for exploiting the natural gas hydrate by the batch drilling rolling well group is characterized by comprising an acquisition device and a data control device;
the collecting device comprises an underwater pipe network, a main gas pipeline, an offshore floating production and storage Facility (FPSO), two or more detachable interfaces, two or more first electric submersible pumps and two or more second electric submersible pumps; the underwater pipe network comprises two or more branches, each branch is provided with a control valve and a flowmeter, and each branch of the underwater pipe network is connected with a detachable interface; the underwater pipe network is connected with an offshore floating production and storage Facility (FPSO) through a main gas transmission pipeline; the first electric submersible pump and the second electric submersible pump are respectively arranged in the two horizontal well sections;
the data control device comprises an optical cable, a photoelectric demodulator, a signal execution mechanism and a computer terminal; one end of the photoelectric demodulator is connected with the flowmeter through an optical cable, and the other end of the photoelectric demodulator is connected with a computer terminal; and the computer terminal is respectively connected with the control valve, the first electric submersible pump and the second electric submersible pump through the signal execution mechanism.
2. The batch-drilling rolling-type well group natural gas hydrate production system according to claim 1, wherein the first electric submersible pump and the second electric submersible pump are respectively positioned in the horizontal well section at a distance of 5-10m from the end point of the horizontal well section.
3. A method for batch drilling rolling well group natural gas hydrate production using the system of claim 1, comprising the steps of:
(1) identifying a natural gas hydrate enrichment area and evaluating methane reserves in a natural gas hydrate reservoir, then carrying out economic evaluation, selecting a mining area and determining the total well group number of the drilled wells;
(2) double-horizontal-well open-circuit circulating batch drilling well
In the selected mining area, batch drilling is carried out in a mode of circularly drilling double horizontal wells in an open circuit, and drilling of all well groups of one well group is completed at one time; the double horizontal wells are called a well group, each well group comprises a vertical well section, two horizontal well sections and two deflecting sections, the left and right directions of the lower end of the vertical well section are respectively connected with a first deflecting section and a second deflecting section, the first deflecting section is connected with the first horizontal well section, and the second deflecting section is connected with the second horizontal well section; after completing the drilling work of one well group, sequentially completing the drilling work of the other well groups;
(3) fracturing crack-making yield improvement and sand prevention stable yield
After the well drilling of one well group is completed, fracturing induction crack formation and sand prevention construction are carried out on each horizontal well section, and perforation fracturing is carried out on each horizontal well section by adopting fracturing fluid to form cracks; performing sand prevention construction after fracturing induction crack formation is finished, adopting sand prevention measures of filling cracks with a sieve tube and gravels, and injecting a chemical sand prevention agent into the cracks filled with the crack sieve tube and the gravels to form an artificial well wall and a sand prevention layer around a horizontal well section shaft;
(4) rolling well group mining
Adopting a well group mining mode that a plurality of well groups are arranged side by side, and mining the natural gas hydrate by adopting a depressurization method by controlling the pressure change at the bottom of the well; returning natural gas produced by a plurality of well groups in one well group to the same underwater production pipe network; the mode of mining and drilling is adopted, a batch of well groups are in production, and a batch of well groups are in drilling, so that rolling development is realized;
in the process of exploiting the natural gas hydrate, one end of an underwater pipe network is connected with seabed well mouths of different well groups through detachable interfaces, the other end of the underwater pipe network is connected with an offshore floating production and storage Facility (FPSO) through a main gas pipeline, and natural gas produced by each well group is collected to the main gas pipeline through the underwater pipe network and is finally conveyed to the offshore floating production and storage Facility (FPSO); the computer terminal sends an instruction to the signal execution mechanism to control the starting of control valves arranged on the underwater pipe network to adjust the production starting time of different well groups, and meanwhile, gas-liquid flow monitored by a flow meter arranged on the underwater pipe network is transmitted to the computer terminal through an optical cable and a photoelectric demodulator; and the computer terminal analyzes the gas-liquid flow change data of different well groups monitored by the flow meter in real time, sends an instruction to the signal execution mechanism, controls the power of the first electric submersible pump and the second electric submersible pump at the bottom of the different well groups in real time, and efficiently pumps hydrate produced at the bottom of the well into an underwater pipe network to finally reach the FPSO.
4. The batch-drilling rolling well group natural gas hydrate exploitation method according to claim 3, wherein in the step (1), the natural gas hydrate enriched zone identification step is: carrying out sea natural gas hydrate drilling work, and identifying a seabed shallow natural gas hydrate reservoir according to Bottom Simulating Reflector (BSR) in seismic data by means of a three-dimensional seismic reflection technology; the distribution range of the natural gas hydrate is described by picking up BSR of the seismic profile, and the saturation of the natural gas hydrate is defined>30% of reservoir thickness>10m, methane reserve>108m3The region (a) is a natural gas hydrate enrichment region;
the methane reserves in the natural gas hydrate reservoir are calculated as follows:
V＝A·ΔZ·φ·H·E (1)
in the formula (1), V is the methane reserve in the natural gas hydrate reservoir, and m3(ii) a A is the distribution area of the natural gas hydrate, m2(ii) a Δ Z is the average thickness of the natural gas hydrate stability zone, m; phi is the average porosity in the deposit, dimensionless; h is the filling rate of the natural gas hydrate, and has no dimension; and E is the volume ratio of the natural gas hydrate, and a theoretical value of 164 is taken.
5. The batch-drilling rolling well group natural gas hydrate exploitation method according to claim 3, wherein in the step (1), the natural gas hydrate enriched zone meeting the development economy requirement needs to meet the following conditions:
in the formula (2), V is the methane reserve in the natural gas hydrate reservoir, m3；VminEconomic reserve of methane, m, for natural gas hydrates3(ii) a t is the age limit, year; i.e. idIs a discount coefficient; c1Is mobile capital, yuan; n is1Year, the year of exploration; n is2For the construction year, year; n is3For stable production years, years; (C)e)tThe exploration investment cost of the t year is Yuan; (C)z)tThe investment cost of the drilling engineering in the t year is Yuan; (C)d)tInvestment cost of ground system engineering in the t year is Yuan; (C)j)tThe unit operation cost in the t year is Yuan; f. ofk1Influence coefficient of scientific and technological progress on exploration investment; f. ofk2The influence coefficient of the technological progress on the investment of the drilling engineering is shown; f. ofk3The influence coefficient of the scientific and technological progress on the reduction of the operation cost is reduced; vtFor annual mining speed, m3A year; f. ofsThe commodity rate of gas is; p is gas price, yuan/m3；txThe comprehensive tax rate.
6. The batch-drilling rolling well group natural gas hydrate production method according to claim 3, wherein in the step (1), the total well group number of the natural gas hydrate production zone selected in the step (1) to be drilled is calculated according to the following formula:
n＝V/(xVo) (3)
in the formula (3), n is the total well group number and has no dimension; x is the producible age of a single well group, year; voFor annual production rate of a single well group, m3A year; v is the methane reserve in the reservoir of natural gas hydrate, m3。
7. A method for producing natural gas hydrates by batch-drilling rolling well groups according to claim 3, wherein in the step (2), the number of well groups included in one well group is calculated according to the following formula:
nz＝Vn/Vo(4)
in the formula (4), nzThe number of well groups is one well group, and the number has no dimension; vnFor planned annual production, m3A year; voFor annual production rate of a single well group, m3And (4) a year.
8. A method for producing natural gas hydrates from a batch-drilling rolling well group according to claim 3, wherein the starting point of the vertical well section in the step (2) is located at a mud line, and the end point is located 10-20m above the upper end of the hydrate reservoir.
9. The batch-drilling rolling well group natural gas hydrate production method according to claim 3, wherein the first deflecting section and the second deflecting section in the step (2) start deflecting at the lowest end of the vertical well section, and the well inclination angle is 80-90 degrees;
the first horizontal well section and the second horizontal well section are both arranged in the middle of the hydrate reservoir, and the lengths of the first horizontal well section and the second horizontal well section are both 200-1000 m.
10. The batch-drilling rolling type well group natural gas hydrate production method according to claim 3, wherein in the step (4), the underwater production pipe network is recycled, and the production pipe network of the original production well group is disassembled and installed on the new production well group.
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| CN115217445A (en) * | 2021-04-16 | 2022-10-21 | 中国石油化工股份有限公司 | Device and method for exploiting natural gas hydrate in U-shaped well |
| CN115306366A (en) * | 2022-09-13 | 2022-11-08 | 中国石油大学(华东) | Efficient yield-increasing exploitation method for natural gas hydrate |
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