CN112610191A - Method for exploiting natural gas hydrate reservoir permeable by cover layer by utilizing branch horizontal well - Google Patents
Method for exploiting natural gas hydrate reservoir permeable by cover layer by utilizing branch horizontal well Download PDFInfo
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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
- E21B43/14—Obtaining from a multiple-zone well
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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
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
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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
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/18—Repressuring or vacuum methods
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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
- E21B43/16—Enhanced recovery methods for obtaining hydrocarbons
- E21B43/24—Enhanced recovery methods for obtaining hydrocarbons using heat, e.g. steam injection
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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
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
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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
- E21B43/295—Gasification of minerals, e.g. for producing mixtures of combustible gases
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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 discloses a method for exploiting a cover-layer-permeable natural gas hydrate reservoir by utilizing a branched horizontal well, which belongs to the field of ocean natural gas hydrate exploitation. The multi-branch horizontal well for injecting fluid in the natural gas hydrate reservoir and producing the cover layer can form an upper injection and production system and a lower injection and production system, can effectively prevent methane gas generated by hydrate decomposition from leaking to the seabed through the cover layer, and effectively reduces the environmental pollution risk in natural gas hydrate reservoir exploitation containing the permeable cover layer.
Description
Technical Field
The invention belongs to the field of marine natural gas hydrate exploitation, and particularly relates to a method for exploiting a natural gas hydrate reservoir with a permeable cover layer by using a branch horizontal well.
Background
The natural gas hydrate is an ice-like crystalline compound with a cage-shaped structure formed by natural gas and water under the conditions of low temperature and high pressure, and is mainly found in land frozen soil areas and marine sediments. The natural gas hydrate reserves are huge, and are considered as ideal alternative energy sources in the 21 st century.
26 days 3 and 26 months in 2020, the gas hydrate in the sea area of China is produced by 86.14 million cubic meters in accumulated gas production through the second trial production, and the gas production per day is 2.87 million cubic meters, so that two new world records of 'total gas production amount and daily gas production amount' are created, and a solid foundation is laid for commercial exploitation of the gas hydrate. However, trial production finds that the occurrence environment of natural gas hydrate in the south China sea area is different from that of a conventional gas reservoir, and particularly the cover layer of the natural gas hydrate reservoir has permeability. For the natural gas hydrate reservoir with the permeable cover layer, seawater energy continuously permeates into a hydrate reservoir when the natural gas hydrate reservoir is mined by adopting a general depressurization method, so that the depressurization degree of the hydrate reservoir is limited, and the depressurization mining effect is influenced. When the thermal excitation method, the chemical agent injection method and other methods are adopted, the decomposed methane gas can permeate into the cover layer under the driving of the formation pressure gradient and the pressure of injected fluid, so that the recovery ratio is reduced, a large amount of methane gas can be transported to the seabed, the marine environment is polluted, and even the greenhouse effect is intensified.
Some other methods proposed to date for the production of gas hydrates are also not suitable for the production of gas hydrate reservoirs containing permeable cap layers, such as: patent document No. CN201210171680.4 discloses a method for producing natural gas hydrate, in which a communicating well is drilled in a hydrate reservoir, hot water or a hydrate decomposition promoter is injected from one end of the well head, and the other end is used for gas production, which is not suitable for the production of hydrate reservoirs containing permeable cover layers. Patent document No. CN201810716966.3 discloses a double-communication well structure and method for exploiting marine hydrates, in which two communication wells are arranged at intervals up and down on a hydrate layer to achieve hydrate exploitation, and the permeability of a cover layer is not considered, so that the double-communication well structure and method are not suitable for the exploitation of hydrate reservoirs containing permeable cover layers. Patent document No. CN201911015194.1 discloses a method for producing hydrate based on multilateral well, which deploys horizontal branches in high-temperature and high-pressure gas reservoir and hydrate reservoir, and uses high-temperature fluid in the gas reservoir to promote hydrate decomposition, and is not suitable for producing hydrate reservoir containing permeable cover. Patent document No. CN201910496581.5 discloses a method for increasing natural gas hydrate reservoir recovery by artificially densifying the cap layer by injecting a cement slurry into the permeable cap layer to prevent the migration of methane gas into the atmosphere through the permeable cap layer. However, the permeability of the cover layer is low as a whole, so that the grouting range and effect cannot be guaranteed, the process is complex, and the cost is high.
Disclosure of Invention
In view of the problems in the background art, the invention aims to provide a method for exploiting a natural gas hydrate reservoir with a permeable cover layer by using a branch horizontal well, so as to solve the problems of poor depressurization effect, methane gas leakage and the like in the exploitation of the natural gas hydrate reservoir with the permeable cover layer and realize the efficient and safe development of the natural gas hydrate reservoir with the permeable cover layer.
In order to achieve the purpose, the invention adopts the following technical scheme: a method for exploiting a natural gas hydrate reservoir permeable to a cap layer by using a branched horizontal well is characterized by comprising the following steps of:
when the upper cover layer or the lower cover layer is permeable, the multi-branch horizontal well adopts two branch horizontal wells, the two branch horizontal wells comprise a vertical well section, a first branch horizontal section and a second branch horizontal section, the first branch horizontal section is communicated with the vertical well section through an inclined section, and the first branch horizontal section extends along the horizontal direction and is positioned on the permeable upper cover layer or the permeable lower cover layer; the second branch horizontal section extends along the horizontal direction and is positioned in the natural gas hydrate reservoir stratum; when the upper cover layer is permeable, the distance between the first branch horizontal section in the upper cover layer and the top surface of the natural gas hydrate reservoir is 0.5-3 m, and the distance between the second branch horizontal section in the natural gas hydrate reservoir and the bottom surface of the natural gas hydrate reservoir is 0.5-3 m; when the lower cover layer is permeable, the horizontal section of the first branch in the lower cover layer is 0.5-3 m away from the bottom surface of the natural gas hydrate reservoir, and the horizontal section of the second branch in the natural gas hydrate reservoir is 0.5-3 m away from the top surface of the natural gas hydrate reservoir;
when both the upper cover layer and the lower cover layer can penetrate, the multi-branch horizontal well adopts a three-branch horizontal well, the three-branch horizontal well comprises a vertical well section, a first branch horizontal section, a second branch horizontal section and a third branch horizontal section, the first branch horizontal section, the second branch horizontal section and the third branch horizontal section are communicated with the vertical well section through an inclined section, and the first branch horizontal section, the second branch horizontal section and the third branch horizontal section extend along the horizontal direction and are respectively and correspondingly positioned on the upper cover layer, the natural gas hydrate reservoir layer and the lower cover layer; the first branch horizontal section in the upper cover layer is 0.5-3 m away from the top surface of the natural gas hydrate reservoir stratum, and the second branch horizontal section in the natural gas hydrate reservoir stratum is positioned in the middle of the natural gas hydrate reservoir stratum; the distance between the third branch horizontal section in the lower cover layer and the bottom surface of the natural gas hydrate reservoir is 0.5-3 m;
step 5, setting a packer in an annular space of a casing and an oil pipe of a branch horizontal section of the natural gas hydrate reservoir, sealing the annular space of the casing and the oil pipe, wherein the setting position of the packer is located at the starting point of the branch horizontal section, and the starting point is one end of the branch horizontal section close to the vertical well section;
and 7, after injecting the fluid for 1 to 30 days, starting depressurization production of the branch horizontal section in the cover layer, controlling the production pressure difference to be between 2 and 10MPa, wherein the bottom hole pressure of the branch horizontal section in the cover layer is lower than that of the branch horizontal section in the natural gas hydrate reservoir layer, methane gas and water generated by the decomposition of hydrate in the natural gas hydrate reservoir layer are displaced into the branch horizontal section in the cover layer by the injected fluid, and the methane gas rises along a shaft, so that the exploitation of the natural gas hydrate reservoir permeable by the cover layer is realized.
In step 2, the length of each branch horizontal section in the multi-branch horizontal well is controlled to be 200-2000 m.
As a preferable scheme of the invention, the length of each branch horizontal section in the multi-branch horizontal well is controlled to be more than 500 m.
In step 3, the perforation density is more than 24 holes/m and the perforation depth is more than 0.6m when the casing is perforated and completed.
In a preferred embodiment of the present invention, in step 6, the temperature of the fluid is 50 ℃ or higher.
As a preferable scheme of the invention, in step 6, the displacement is 200m3More than one day.
In step 6, the fluid is hot water, methanol, CO2Fluids and plant flue gases.
Further, the CO is2The fluid is supercritical CO with the temperature of more than 50 ℃ and the pressure of more than 10MPa2Or CO of emulsion2。
Further, the temperature of the factory flue gas is higher than 50 DEG CAnd N in the plant flue gas2And CO2The total content of (A) is more than 90%.
Through the design scheme, the invention can bring the following beneficial effects:
1. the branch horizontal section of the natural gas hydrate reservoir and the branch horizontal section in the cover layer form a single-well injection-production system, and the problem that the natural gas hydrate reservoir in the natural gas hydrate reservoir containing the permeable cover layer is low in pressure reduction and production efficiency is solved.
2. The multi-branch horizontal well for injecting fluid in the natural gas hydrate reservoir and producing the cover layer can form an upper injection and production system and a lower injection and production system, can effectively prevent methane gas generated by hydrate decomposition from leaking to the seabed through the cover layer, and effectively reduces the environmental pollution risk in natural gas hydrate reservoir exploitation containing the permeable cover layer.
3. After the hydrate is decomposed, the reservoir structure of the natural gas hydrate is damaged, sand is easy to generate in a production well distributed on the reservoir of the natural gas hydrate, and the instability of a well wall is easy to induce in the production process.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the invention without limitation and are not intended to limit the invention in any way, and in which:
FIG. 1 is a schematic diagram of a natural gas hydrate reservoir which is permeable to both an upper cover layer and a lower cover layer and is mined by adopting a three-branch horizontal well;
FIG. 2 is a schematic view of a gas hydrate reservoir permeable to the upper cap layer produced using two horizontal wells;
FIG. 3 is a schematic view of a gas hydrate reservoir permeable to the lower cap layer produced using a two-branch horizontal well.
The respective symbols in the figure are as follows: 1-a permeable top cover layer; 2-dense capping layer; 3-a natural gas hydrate reservoir; 4-a permeable lower cap layer; 5-dense lower cap layer; 6-vertical well section; 7-deflecting section; 8-upper cover layer branch horizontal segment; 9-reservoir branch horizontal section; 10-lower cover layer branch horizontal segment; 11-an oil pipe; 12-oil jacket annulus; 13-a packer; 14-direction of injection fluid flow; 15-direction of methane gas flow in the gas reservoir; 16-direction of methane gas flow in the wellbore; 17-perforating; 18-well head; 19-sea level.
Detailed Description
As shown in fig. 1, 2 and 3, the present invention provides a method for exploiting a cap-permeable natural gas hydrate reservoir using a lateral horizontal well, the method comprising the steps of:
when the upper cover layer or the lower cover layer is permeable, the multi-branch horizontal well adopts two branch horizontal wells, the two branch horizontal wells comprise a vertical well section 6, a first branch horizontal section and a second branch horizontal section, the first branch horizontal section and the second branch horizontal section are communicated with the vertical well section 6 through an inclined section 7, and the first branch horizontal section extends along the horizontal direction and is positioned on the permeable upper cover layer or the permeable lower cover layer; the second branch horizontal section extends in the horizontal direction and is located in the natural gas hydrate reservoir 3; when the upper cover layer is permeable, the distance between the first branch horizontal section in the upper cover layer and the top surface of the natural gas hydrate reservoir layer 3 is 0.5-3 m, and the distance between the second branch horizontal section in the natural gas hydrate reservoir layer 3 and the bottom surface of the natural gas hydrate reservoir layer 3 is 0.5-3 m; when the lower cover layer is permeable, the horizontal section of the first branch in the lower cover layer is 0.5-3 m away from the bottom surface of the natural gas hydrate reservoir 3, and the horizontal section of the second branch in the natural gas hydrate reservoir 3 is 0.5-3 m away from the top surface of the natural gas hydrate reservoir 3;
when both the upper cover layer and the lower cover layer can be penetrated, the multi-branch horizontal well adopts a three-branch horizontal well, the three-branch horizontal well comprises a vertical well section 6, a first branch horizontal section, a second branch horizontal section and a third branch horizontal section, the first branch horizontal section, the second branch horizontal section and the third branch horizontal section are communicated with the vertical well section 6 through an inclined section 7, and the first branch horizontal section, the second branch horizontal section and the third branch horizontal section extend along the horizontal direction and are respectively and correspondingly positioned on the upper cover layer, the natural gas hydrate reservoir layer 3 and the lower cover layer; the first branch horizontal section in the upper cover layer is 0.5-3 m away from the top surface of the natural gas hydrate reservoir 3, and the second branch horizontal section in the natural gas hydrate reservoir 3 is positioned in the middle of the natural gas hydrate reservoir 3; the distance between the third branch horizontal section in the lower cover layer and the bottom surface of the natural gas hydrate reservoir stratum 3 is 0.5-3 m;
the longer the branch horizontal section is, the larger the well control mining area is, and in order to improve the mining effect, the length of all the branch horizontal sections is recommended to be controlled to be more than 200 m;
further, the length of each branch horizontal section in the multi-branch horizontal well is controlled to be 200-2000 m.
And 3, completing the well by adopting casing perforation in all the branch horizontal sections of the multi-branch horizontal well to form a perforation 17 for providing a flow channel for fluid, wherein the perforation density is controlled to be 12-36 holes/m, and the perforation depth is controlled to be 0.4-3 m.
And 4, lowering the oil pipe 11 into the branch horizontal section of the natural gas hydrate reservoir stratum 3 through the wellhead 18 above the sea level 19 to a depth of 1/4-1/2 of the total length of the branch horizontal section, so that fluid can flow to the natural gas hydrate reservoir stratum 3.
And 5, setting a packer 13 in an annular space of a casing and an oil pipe 11 of the branch horizontal section of the natural gas hydrate reservoir 3, sealing the annular space of the casing and the oil pipe 11, wherein the annular space between the casing and the oil pipe 11 is an oil casing annular space 12, and setting the packer 13 at a starting point of the branch horizontal section, wherein the starting point is one end of the branch horizontal section close to the vertical well section 6.
And 7, after injecting the fluid for 1 to 30 days, starting depressurization production of the branch horizontal section in the cover layer, controlling the production pressure difference to be between 2 and 10MPa, and displacing methane and water generated by the decomposition of the hydrate in the natural gas hydrate reservoir layer 3 into the branch horizontal section in the cover layer by the injected fluid because the bottom hole pressure of the branch horizontal section in the cover layer is lower than that of the branch horizontal section in the natural gas hydrate reservoir layer 3, wherein the methane gas rises along a shaft, thereby realizing the exploitation of the natural gas hydrate reservoir with the permeable cover layer.
In the step 1, the permeable cover layer is further divided into an upper cover layer located at the upper part of the natural gas hydrate reservoir 3 and a lower cover layer located at the lower part of the natural gas hydrate reservoir 3, the permeability is greater than 1mD, and when the permeability of the cover layer is lower than 1mD, the fluid flow capacity is poor, and the cover layer is considered to be impermeable, namely, the cover layer is a dense cover layer.
In the step 2, the preferable scheme suggests that the length of the branch horizontal section in the multi-branch horizontal well is controlled to be more than 500m under the premise that the drilling capability is ensured, so as to improve the mining effect.
In the step 3, preferably, in the case of casing perforation completion, in order to ensure that the flow channel in the well is unblocked, the perforation density is greater than 24 holes/m, and the perforation depth is greater than 0.6 m.
In the step 4, preferably, when the natural gas hydrate is produced by injection heat, the oil pipe 11 may adopt an oil pipe 11 with a heat insulation function to reduce heat loss in the wellbore.
In the step 6, preferably, the higher the temperature during heat injection exploitation is, the faster the hydrate is decomposed, and the heat injection temperature is recommended to be controlled to be higher than 50 ℃; the larger the injection displacement is, the more favorable the hydrate decomposition is, but the reasonable injection displacement is comprehensively determined according to the working capacity, the reservoir permeability, the injection pressure and the like of the on-site pump, and in order to ensure the exploitation efficiency, the displacement is recommended to be 200m3More than one day; by using CO2When the hydrate is replaced, supercritical CO with the temperature of more than 50 ℃ and the pressure of more than 10MPa can be adopted2Or CO of emulsion2Plant flue gases at temperatures above 50 ℃ may also be used (requirement N)2And CO2Above 90%) to achieve efficient decomposition and production of hydrates.
In the step 7, preferably, when the methane gas production in the middle and later stages of production is reduced, the horizontal branch section in the cap layer can be closed for 1 to 7 days, and then the production is started until the production is finished.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the present invention.
Example 1
The method for exploiting the natural gas hydrate reservoir with the upper cover layer and the lower cover layer both permeable by utilizing the three-branch horizontal well comprises the following steps of:
(1) as shown in fig. 1, a natural gas hydrate reservoir composed of a permeable upper cover layer 1, a permeable lower cover layer 4 and a natural gas hydrate reservoir 3 is selected, and the permeability of each of the permeable upper cover layer 1 and the permeable lower cover layer 4 is greater than 1 mD.
(2) The method comprises the steps of drilling a three-branch horizontal well after target natural gas hydrate is reserved, wherein the three-branch horizontal well comprises a vertical well section 6, a deflecting section 7, an upper cover layer branch horizontal section 8, a reservoir layer branch horizontal section 9 and a lower cover layer branch horizontal section 10, the upper cover layer branch horizontal section 8, the reservoir layer branch horizontal section 9 and the lower cover layer branch horizontal section 10 are distributed in an up-down parallel mode and extend in the horizontal direction, the upper cover layer branch horizontal section 8, the reservoir layer branch horizontal section 9 and the lower cover layer branch horizontal section 10 are respectively communicated with the vertical well section 6 through the deflecting section 7, and the lengths of the upper cover layer branch horizontal section 8, the reservoir layer branch horizontal section 9 and the lower cover layer branch horizontal section 10 are all larger than 200 m. The upper cover layer branch horizontal section 8 is positioned in the permeable upper cover layer 1, the upper cover layer branch horizontal section 8 is 0.5-3 m away from the top surface of the natural gas hydrate reservoir 3, the reservoir layer branch horizontal section 9 is positioned in the middle of the natural gas hydrate reservoir 3, the lower cover layer branch horizontal section 10 is positioned in the permeable lower cover layer 4, and the lower cover layer branch horizontal section 10 is 0.5-3 m away from the bottom surface of the natural gas hydrate reservoir 3.
(3) Perforating and completing the upper cover layer branch horizontal segment 8, the reservoir layer branch horizontal segment 9 and the lower cover layer branch horizontal segment 10 by using a casing pipe to form a perforation 17 for providing a flow channel for fluid; the perforation density is controlled to be 12-36 holes/m, and the perforation depth is controlled to be 0.4-3 m.
(4) And (3) descending an oil pipe 11 into the horizontal section 9 of the reservoir branch through a well head 18, wherein the descending depth is 1/4-1/2 of the total length of the horizontal section of the branch.
(5) Setting a packer 13 in an oil casing annular space 12 of the horizontal section 9 of the reservoir branch, wherein the oil casing annular space 12 is an annular space formed between the oil pipe 11 and the casing pipe, sealing the annular space between the casing pipe and the oil pipe 11, and the setting position of the packer 13 is positioned at the starting point of the horizontal well section.
(6) At the wellhead 18 at a displacement of 100m3A day is 500m3Injecting 30-90 deg.C hot water or hydrate decomposition promoter such as methanol or CO into the oil pipe 11 at a speed of one day2Fluid, promoting hydrate decomposition.
(7) After injecting fluid for 1 to 30 days, the upper cover layer branch horizontal segment 8 in the permeable upper cover layer 1 and the lower cover layer branch horizontal segment 10 in the permeable lower cover layer 4 start to carry out pressure reduction production, and the production pressure difference is 2 to 10 MPa; methane gas in the natural gas hydrate reservoir stratum 3 is displaced by the injection fluid into the upper cover layer branch horizontal section 8 in the permeable upper cover layer 1 and the lower cover layer branch horizontal section 10 in the permeable lower cover layer 4, and flows along the deflecting section 7, the vertical well section 6 and the oil casing annulus 12, so that natural gas hydrate exploitation is realized.
In fig. 1, the direction indicated by the arrow denoted by reference numeral 14 is the injection fluid flow direction; the direction of the arrow indicated by reference numeral 15 is the flow direction of methane gas in the gas reservoir; the direction of the arrow indicated by reference numeral 16 is the direction of flow of methane gas in the wellbore.
Example 2
The method for exploiting the natural gas hydrate reservoir with the permeable upper cover layer and the compact lower cover layer by utilizing two branch horizontal wells comprises the following steps:
(1) as shown in fig. 2, a natural gas hydrate reservoir is selected that is composed of a permeable upper cap layer 1, a dense lower cap layer 5, and a natural gas hydrate reservoir 3. Wherein, the permeability of the permeable upper cover layer 1 is more than 1mD, and the permeability of the compact lower cover layer 5 is less than 1 mD.
(2) Drilling a two-branch horizontal well in a target natural gas hydrate reservoir, wherein the two-branch horizontal well comprises a vertical well section 6, a deflecting section 7, an upper cover layer branch horizontal section 8 and a reservoir layer branch horizontal section 9, the upper cover layer branch horizontal section 8 and the reservoir layer branch horizontal section 9 extend in the horizontal direction and are arranged in parallel, the upper cover layer branch horizontal section 8 and the reservoir layer branch horizontal section 9 are respectively communicated with the vertical well section 6 through the deflecting section 7, and the lengths of the upper cover layer branch horizontal section 8 and the reservoir layer branch horizontal section 9 are both larger than 200 m; the upper cover layer branch horizontal section 8 is positioned in the permeable upper cover layer 1, the upper cover layer branch horizontal section 8 is 0.5-3 m away from the top surface of the natural gas hydrate reservoir 3, and the reservoir branch horizontal section 9 is positioned in the natural gas hydrate reservoir 3 and is 0.5-3 m away from the bottom surface of the natural gas hydrate reservoir 3.
(3) Perforating and completing the casing of the upper cover layer branch horizontal section 8 and the reservoir layer branch horizontal section 9 to form a perforation 17 for providing a flow channel for fluid; the perforation density is controlled to be 12-36 holes/m, and the perforation depth is controlled to be 0.4-3 m.
(4) And (3) descending an oil pipe 11 into the horizontal section 9 of the reservoir branch through a well head 18, wherein the descending depth is 1/4-1/2 of the total length of the horizontal section of the branch.
(5) Setting a packer 13 in an oil casing annular space 12 of the horizontal section 9 of the reservoir branch, wherein the oil casing annular space 12 is an annular space formed between the oil pipe 11 and the casing pipe, sealing the annular space between the casing pipe and the oil pipe 11, and the setting position of the packer 13 is positioned at the starting point of the horizontal well section.
(6) At the wellhead 18 at a displacement of 100m3A day is 500m3Injecting 30-90 deg.C hot water or hydrate decomposition promoter such as methanol or CO into the oil pipe 11 at a speed of one day2Fluid, promoting hydrate decomposition.
(7) After injecting fluid for 1 to 30 days, the upper cover layer branch horizontal section 8 in the permeable upper cover layer 1 starts pressure reduction production, and the production pressure difference is 2 to 10 MPa; methane gas in the natural gas hydrate reservoir stratum 3 is displaced by the injection fluid into the upper cover layer branch horizontal section 8 in the permeable upper cover layer 1 and flows along the deflecting section 7, the vertical well section 6 and the oil casing annulus 12, so that natural gas hydrate exploitation is realized.
In fig. 2, the direction indicated by the arrow denoted by reference numeral 14 is the injection fluid flow direction; the direction of the arrow indicated by reference numeral 15 is the flow direction of methane gas in the gas reservoir; the direction of the arrow indicated by reference numeral 16 is the direction of flow of methane gas in the wellbore.
Example 3
The method for exploiting the natural gas hydrate reservoir with the compact upper cover layer and the permeable lower cover layer by utilizing two branch horizontal wells comprises the following steps:
(1) as shown in fig. 3, a natural gas hydrate reservoir is selected that is composed of a dense overburden 2, a permeable overburden 5, and a natural gas hydrate reservoir 3. Wherein, the permeability of the permeable lower cover layer 5 is more than 1mD, and the permeability of the dense upper cover layer 2 is less than 1 mD.
(2) Drilling a two-branch horizontal well in a target natural gas hydrate reservoir, wherein the two-branch horizontal well comprises a vertical well section 6, a deflecting section 7, a reservoir layer branch horizontal section 9 and a lower cover layer branch horizontal section 10, the reservoir layer branch horizontal section 9 and the lower cover layer branch horizontal section 10 extend in the horizontal direction and are arranged in parallel, the reservoir layer branch horizontal section 9 and the lower cover layer branch horizontal section 10 are respectively communicated with the vertical well section 6 through the deflecting section 7, and the lengths of the reservoir layer branch horizontal section 9 and the lower cover layer branch horizontal section 10 are both larger than 200 m; the reservoir branch horizontal section 9 is positioned in the natural gas hydrate reservoir 3 and is 0.5-3 m away from the top surface of the natural gas hydrate reservoir 3, and the lower cover layer branch horizontal section 10 is positioned in the permeable lower cover layer 5 and is 0.5-3 m away from the bottom surface of the natural gas hydrate reservoir 3.
(3) Perforating and completing the casing of the reservoir branch horizontal section 9 and the lower cover layer branch horizontal section 10 to form a perforation 17 for providing a flow channel for fluid; the perforation density is controlled to be 12-36 holes/m, and the perforation depth is controlled to be 0.4-3 m.
(4) And (3) descending an oil pipe 11 into the horizontal section 9 of the reservoir branch through a well head 18, wherein the descending depth is 1/4-1/2 of the total length of the horizontal section of the branch.
(5) Setting a packer 13 in an oil casing annular space 12 of the horizontal section 9 of the reservoir branch, wherein the oil casing annular space 12 is an annular space formed between the oil pipe 11 and the casing pipe, sealing the annular space between the casing pipe and the oil pipe 11, and the setting position of the packer 13 is positioned at the starting point of the horizontal well section.
(6) At the wellhead 18 at a displacement of 100m3A day is 500m3Injecting 30-90 deg.C hot water or hydrate decomposition promoter such as methanol or CO into the oil pipe 11 at a speed of one day2Fluid, promoting hydrate decomposition.
(7) After injecting fluid for 1-30 days, the branch horizontal section 10 of the lower cover layer positioned in the permeable lower cover layer 5 starts to carry out pressure reduction production, and the production pressure difference is 2-10 MPa. Methane gas in the natural gas hydrate reservoir stratum 3 is displaced by the injection fluid into the lower cover layer branch horizontal section 10 in the permeable lower cover layer 5 and flows along the deflecting section 7, the vertical well section 6 and the oil casing annulus 12, so that natural gas hydrate exploitation is realized.
In fig. 3, the direction indicated by the arrow denoted by reference numeral 14 is the injection fluid flow direction; the direction of the arrow indicated by reference numeral 15 is the flow direction of methane gas in the gas reservoir; the direction of the arrow indicated by reference numeral 16 is the direction of flow of methane gas in the wellbore.
Claims (9)
1. A method for exploiting a natural gas hydrate reservoir permeable to a cap layer by using a branched horizontal well is characterized by comprising the following steps of:
step 1, selecting a natural gas hydrate reservoir with the thickness of more than 20m and the permeability of a permeable cover layer of more than 1mD as a mining object according to regional seismic data and logging data;
step 2, drilling a multi-branch horizontal well in the selected natural gas hydrate reservoir target area, wherein the multi-branch horizontal well is a two-branch horizontal well or a three-branch horizontal well;
when the upper cover layer or the lower cover layer is permeable, the multi-branch horizontal well adopts two branch horizontal wells, the two branch horizontal wells comprise a vertical well section, a first branch horizontal section and a second branch horizontal section, the first branch horizontal section is communicated with the vertical well section through an inclined section, and the first branch horizontal section extends along the horizontal direction and is positioned on the permeable upper cover layer or the permeable lower cover layer; the second branch horizontal section extends along the horizontal direction and is positioned in the natural gas hydrate reservoir stratum; when the upper cover layer is permeable, the distance between the first branch horizontal section in the upper cover layer and the top surface of the natural gas hydrate reservoir is 0.5-3 m, and the distance between the second branch horizontal section in the natural gas hydrate reservoir and the bottom surface of the natural gas hydrate reservoir is 0.5-3 m; when the lower cover layer is permeable, the horizontal section of the first branch in the lower cover layer is 0.5-3 m away from the bottom surface of the natural gas hydrate reservoir, and the horizontal section of the second branch in the natural gas hydrate reservoir is 0.5-3 m away from the top surface of the natural gas hydrate reservoir;
when both the upper cover layer and the lower cover layer can penetrate, the multi-branch horizontal well adopts a three-branch horizontal well, the three-branch horizontal well comprises a vertical well section, a first branch horizontal section, a second branch horizontal section and a third branch horizontal section, the first branch horizontal section, the second branch horizontal section and the third branch horizontal section are communicated with the vertical well section through an inclined section, and the first branch horizontal section, the second branch horizontal section and the third branch horizontal section extend along the horizontal direction and are respectively and correspondingly positioned on the upper cover layer, the natural gas hydrate reservoir layer and the lower cover layer; the first branch horizontal section in the upper cover layer is 0.5-3 m away from the top surface of the natural gas hydrate reservoir stratum, and the second branch horizontal section in the natural gas hydrate reservoir stratum is positioned in the middle of the natural gas hydrate reservoir stratum; the distance between the third branch horizontal section in the lower cover layer and the bottom surface of the natural gas hydrate reservoir is 0.5-3 m;
step 3, completing the well by adopting casing perforation in all branch horizontal sections of the multi-branch horizontal well, wherein the perforation density is controlled to be 12-36 holes/m, and the perforation depth is controlled to be 0.4-3 m;
step 4, lowering an oil pipe into a branch horizontal section of the natural gas hydrate reservoir through a well mouth, wherein the lowering depth is 1/4-1/2 of the total length of the branch horizontal section;
step 5, setting a packer in an annular space of a casing and an oil pipe of a branch horizontal section of the natural gas hydrate reservoir, sealing the annular space of the casing and the oil pipe, wherein the setting position of the packer is located at the starting point of the branch horizontal section, and the starting point is one end of the branch horizontal section close to the vertical well section;
step 6, discharging 100m at the wellhead3A day is 500m3Injecting a fluid for promoting hydrate decomposition into the oil pipe at a speed of one day, wherein the temperature of the fluid is 30-90 ℃;
and 7, after injecting the fluid for 1 to 30 days, starting depressurization production of the branch horizontal section in the cover layer, controlling the production pressure difference to be between 2 and 10MPa, wherein the bottom hole pressure of the branch horizontal section in the cover layer is lower than that of the branch horizontal section in the natural gas hydrate reservoir layer, methane gas and water generated by the decomposition of hydrate in the natural gas hydrate reservoir layer are displaced into the branch horizontal section in the cover layer by the injected fluid, and the methane gas rises along a shaft, so that the exploitation of the natural gas hydrate reservoir permeable by the cover layer is realized.
2. The method of exploiting a cap-permeable natural gas hydrate reservoir with a lateral horizontal well according to claim 1, characterized in that: in step 2, the length of each branch horizontal section in the multi-branch horizontal well is controlled to be 200 m-2000 m.
3. The method of exploiting a cap-permeable natural gas hydrate reservoir with a lateral horizontal well according to claim 2, characterized in that: the length of each branch horizontal section in the multi-branch horizontal well is controlled to be more than 500 m.
4. The method of exploiting a cap-permeable natural gas hydrate reservoir with a lateral horizontal well according to claim 1, characterized in that: in step 3, when the casing is perforated and completed, the perforation density is more than 24 holes/m, and the perforation depth is more than 0.6 m.
5. The method of exploiting a cap-permeable natural gas hydrate reservoir with a lateral horizontal well according to claim 1, characterized in that: in step 6, the temperature of the fluid is 50 ℃ or higher.
6. The method of exploiting a cap-permeable natural gas hydrate reservoir with a lateral horizontal well according to claim 1, characterized in that: in step 6, the displacement is 200m3More than one day.
7. The method of exploiting a cap-permeable natural gas hydrate reservoir with a lateral horizontal well according to claim 1, characterized in that: in step 6, the fluid is hot water, methanol, CO2Fluids and plant flue gases.
8. The method of exploiting a cap-permeable natural gas hydrate reservoir with a lateral horizontal well according to claim 7, wherein: what is needed isCO as described above2The fluid is supercritical CO with the temperature of more than 50 ℃ and the pressure of more than 10MPa2Or CO of emulsion2。
9. The method of exploiting a cap-permeable natural gas hydrate reservoir with a lateral horizontal well according to claim 7, wherein: the plant flue gas is the plant flue gas with the temperature higher than 50 ℃, and N in the plant flue gas2And CO2The total content of (A) is more than 90%.
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