CN114320237B - Novel multi-layer combined mining method for coal bed gas of composite coal gas reservoir - Google Patents
Novel multi-layer combined mining method for coal bed gas of composite coal gas reservoir Download PDFInfo
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Abstract
The invention discloses a novel multi-layer coal bed methane production method of a composite coal gas reservoir, which comprises the following steps: completion of the well; logging; a lower pipe; installing coal bed methane drainage Shi Bei; draining; the invention is suitable for the technical field of coal bed gas extraction, ensures the existence of original cracks to the maximum extent through the use of a novel well structure and improves the well cementation technology, simultaneously encourages the coal bed to collapse to form new secondary cracks, increases the specific surface area and permeability of the coal bed, solves the technical problem of damage to reserve cracks caused by the well formation and well cementation technologies of the traditional coal bed gas well, and improves the yield of the coal bed gas; through well type transformation, more coal beds participate in the production of the coal bed gas, the problem that the coal bed gas production layer of the traditional coal bed gas well is limited (generally 2-3 layers) is solved, the yield of the coal bed is improved, the recovery ratio of the coal bed is improved, the service life of the coal bed gas is prolonged, and the economic benefit is improved.
Description
Technical Field
The invention belongs to the technical field of multi-layer coal bed gas combined mining, and particularly relates to a novel multi-layer combined mining method for coal bed gas of a composite coal-to-gas reservoir.
Background
At present, a coal bed gas multi-layer coal mining technology mainly aims at a dominant coal bed with large coal bed thickness, high coal bed gas content, high coal bed permeability and complete coal body structure, 2-5 layers of coal bed perforation are selected in a vertical well or an inclined well to form a perforation layer, and a fracturing section is formed through staged fracturing; through the multi-layer mining technology, daily gas yield of the coal bed gas can be remarkably improved, recovery ratio of coal bed gas resources is improved, and economic benefit of coal bed gas development is improved. The formation of the coalbed methane reservoir in China has the adverse characteristics of early age, complex structure, low pressure coefficient, low permeability, low water saturation and the like; in southwest areas of China, the characteristics of large number of coal layers and thin coal layers are that the single-layer coal-bed gas resource amount is generally low, and in order to improve single-well productivity, a plurality of coal layers which are adjacent to each other in the longitudinal direction and have similar characteristics are usually combined together to develop in a combined mining mode, but the yield increasing effect is not obvious due to the limited number of layered coal mining layers. Therefore, aiming at the geological condition of the coalbed methane in China, a multi-layer mining technology aiming at the composite coal reservoir is urgently needed, and the yield of the coalbed methane is improved.
However, the conventional well forming and cementing technology of the coal-bed gas well has larger fracture damage to reserves, the original fracture is closed, and the conventional coal-bed gas exploitation generates secondary fractures in a fracturing mode, so that the permeability of a fracturing interval is improved; meanwhile, compared with the overseas technologies, the fracturing technology in China has a larger gap, the number of common fracturing intervals is 2-3, so that a large amount of coalbed methane cannot be mined, the benefit of the coalbed methane industry in China is lower, and the development of the coalbed methane industry is restrained.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a novel multi-layer combined mining method for coal bed gas in a composite coal gas reservoir.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a novel multi-layer coal bed gas production method of a composite coal gas reservoir comprises the following steps:
adopting a two-well structure to design a vertical well, and completing the well according to the design;
after the well is completed, the next casing is opened and well cementation is carried out;
logging after the second completion, and determining a main coal seam, an extended coal seam, an undervoltage coal seam and an overpressure coal seam;
respectively laying pipes (two-open casing) on each layer section of the well, laying a pattern pipe on a main coal seam, an expanded coal seam, laying steel pipes on an underpressure coal seam and an overpressure coal seam, and carrying out layered well cementation on each layer section of the underpressure coal seam and the overpressure coal seam;
installing a coalbed methane drainage device, and lowering a drainage pump to the bottom of the lowest coalbed;
draining at a suitable drain rate;
and the liquid level is reduced to the upper part of the top plate of the first main force producing layer, the casing pressure is controlled to be about 0.05MPa, and the coal bed gas extraction is carried out.
Preferably, the method further comprises:
the yield of the coalbed methane of the first principal coal bed is reduced to a certain extent, the liquid level is slowly reduced to the upper part of the top plate of the next principal producing layer, and the coalbed methane of the next principal coal bed is extracted;
and when the coal bed gas of all the main producing layers is completely extracted and the yield of the coal bed gas is insufficient to support production, carrying out secondary yield increase transformation on the coal bed, wherein the secondary yield increase transformation is changed into thermal yield increase transformation.
Preferably, the logging comprises:
and determining a main coal bed, an extended coal bed, an underpressure coal bed and an overpressure coal bed according to the permeability, the gas content, the gas saturation, the critical desorption pressure, the reservoir pressure gradient, the layer spacing and the coal lithology of the coal bed, and classifying the extended coal bed adjacent to the main coal bed into a main coal bed group.
Preferably, the logging further comprises: the thickness of the coal bed, the gas content of the coal bed, the permeability of the coal bed, the pressure of a coal bed reservoir and the structure of the coal body are taken as main evaluation parameters to evaluate the potential of a producing layer, and the potential is a dominant coal bed; the expanded coal seam is a coal seam near the main coal seam, and the pressure gradient of the reservoir is less than 0.1MPa/100m and greater than 0.05MPa/100 m; the undervoltage coal bed refers to a coal bed with a reservoir pressure gradient of less than 0.05MPa/100 m; the pressure gradient of the overpressure coal seam reservoir is greater than 0.1MPa/100m.
Preferably, each interval of the well is respectively down-pipe, and each interval is subjected to layered well cementation, which comprises the following steps:
the surface layer section, the bottom layer section, the under-pressure layer section, the overpressure layer section and the structural coal layer section are designed to be seamless steel pipe sections, the main force coal layer section is designed to be a pattern pipe section, and the surface layer section, the bottom layer section, the under-pressure layer section, the overpressure layer section and the structural coal layer section are subjected to layered well cementation after being lowered.
Preferably, the method further comprises:
the well cementation material is G-grade cement, the main force coal layer section does not perform well cementation operation, the main force coal layer section is kept in an empty state, any free collapse is realized, pulverized coal flows into a pocket of a drilled hole from a round hole of a perforated pipe, the hole on the perforated pipe is round, the true diameter is 21mm, the round hole adopts a spiral design, the hole center distance on the circumference is 47.1mm/49.1mm, and the axial hole center distance is 44.4mm.
Preferably, the surface layer section is the part above the top plate of the first main force layer group, and the bottom layer section is the part below the bottom plate of the last main force coal layer group.
Preferably, the drainage rate is adjusted according to the production stage and the water content, and the production stage takes a low value.
Preferably, the drainage rate is 1-5m/d.
In summary, due to the adoption of the technical scheme, the beneficial effects of the invention are as follows:
according to the invention, through the use of a novel well type structure, the existence of original cracks is ensured to the greatest extent through the improvement of a well cementation technology, meanwhile, the collapse of the coal bed is encouraged, a novel secondary crack is formed, the specific surface area and the permeability of the coal bed are increased, the technical problem that the well formation and well cementation technology of the traditional coal bed gas well damage the reserved cracks is solved, and the coal bed gas yield is improved; through well type transformation, more coal beds participate in the production of the coal bed gas, the problem that the coal bed gas production layer of the traditional coal bed gas well is limited (generally 2-3 layers) is solved, the yield of the coal bed is improved, the recovery ratio of the coal bed is improved, the service life of the coal bed gas is prolonged, and the economic benefit is improved.
Drawings
FIG. 1 is a flow chart of a novel multi-layer combined production method of coal bed gas in a composite coal gas reservoir;
FIG. 2 is a schematic diagram of a multi-layer gas production-combined borehole well structure in an embodiment of the invention;
reference numerals: 1. a formation; 2. a main coal bed 3, an extended coal bed, a 4 and an under-pressure coal bed; 5. overpressure coal seam; 6. a hole wall; 7. a sleeve; 8. two sleeve pipes are opened; 9. a well cementation section is opened; 10. a second well cementation section; 11. a flower tube; 12. a surface layer section; 13. a bottom layer section; 14. a liquid surface.
Detailed Description
The following is a detailed description of a novel multi-layer combined production method of the coal bed gas in the composite coal gas reservoir with reference to fig. 1. The novel multi-layer combined mining method for the coal bed gas of the composite coal gas reservoir is not limited to the description of the following embodiments.
Example 1:
the embodiment provides a specific implementation mode of a novel multi-layer combined mining method for coal bed gas in a composite coal gas reservoir, which is shown in fig. 1 and comprises the following steps:
adopting a two-well structure to design a vertical well, and completing the well according to the design;
after the well is completed, the next casing is opened and well cementation is carried out;
after the second completion, logging is carried out, and a main coal seam 2, an extended coal seam 3, an underpressure coal seam 4 and an overpressure coal seam 5 are determined;
respectively laying pipes (two-open casing) on each layer section of the well, laying a flowtube on the main coal bed 2, the expanded coal bed 3, laying steel pipes on the underpressure coal bed 4 and the overpressure coal bed 5, and carrying out layered well cementation on each layer section of the underpressure coal bed 4 and the overpressure coal bed 5;
installing a coalbed methane drainage device, and lowering a drainage pump to the bottom of the lowest coalbed;
draining at a suitable drain rate;
the liquid level 14 is lowered to the upper part of the top plate of the first main force producing layer, the casing pressure is controlled to be about 0.05MPa, and the coal bed gas extraction is carried out.
Further, the method further comprises the following steps:
the yield of the coalbed methane of the first main coal bed 2 is reduced to a certain extent, the liquid level 14 is slowly lowered to the upper part of the top plate of the next main production layer, and the coalbed methane of the next main coal bed 2 is extracted;
and when the coal bed gas of all the main producing layers is completely extracted and the yield of the coal bed gas is insufficient to support production, carrying out secondary yield increase transformation on the coal bed, wherein the secondary yield increase transformation is changed into thermal yield increase transformation.
Further, logging, including:
and determining a main coal bed 2, an extended coal bed 3, an underpressure coal bed 4 and an overpressure coal bed 5 according to the permeability, the gas content, the gas saturation, the critical desorption pressure, the reservoir pressure gradient, the layer spacing and the coal lithology of the coal bed, and classifying the extended coal bed 3 adjacent to the main coal bed 2 into a main coal bed group.
Further, logging, further comprising: the thickness of the coal bed, the gas content of the coal bed, the permeability of the coal bed, the pressure of a coal bed reservoir and the structure of the coal body are taken as main evaluation parameters to evaluate the potential of a producing layer, and the potential is greatly taken as a dominant coal bed 2; the extended coal seam 3 is a coal seam near the main coal seam 2, and the pressure gradient of the reservoir is less than 0.1MPa/100m and more than 0.05MPa/100 m; the underpressure coal seam 4 refers to a coal seam with a reservoir pressure gradient of less than 0.05MPa/100 m; the pressure gradient of the reservoir of the overpressure coal bed 5 is greater than 0.1MPa/100m.
Further, each interval of the well is respectively lowered, and each interval is subjected to layered well cementation, and the method comprises the following steps:
the surface layer section 12, the bottom layer section 13, the undervoltage layer section, the overpressure layer section and the structural coal layer section are designed to be seamless steel pipe sections, the main coal layer 2 group section is designed to be a flower pipe 11 section, and the surface layer section 12, the bottom layer section 13, the undervoltage layer section, the overpressure layer section and the structural coal layer section are subjected to layered well cementation after being down.
Further, the method further comprises the following steps:
the well cementation material is G-grade cement, the main coal seam 2 groups are not subjected to well cementation operation, the main coal seam is kept in an empty state, any main coal seam freely collapses, pulverized coal flows into a pocket of a drilled hole from a round hole of the perforated pipe 11, the hole on the perforated pipe 11 is round, the true diameter is 21mm, the round hole adopts a spiral design, the hole center distance on the circumference is 47.1mm/49.1mm, and the axial hole center distance is 44.4mm.
Further, the surface layer section 12 is the upper part of the top plate of the first main force layer group, and the bottom layer section 13 is the lower part of the bottom plate of the last main force coal bed 2 group section.
Further, the liquid discharge rate is adjusted according to the production stage and the water content, and the production stage takes a low value.
Further, the liquid discharge rate is 1-5m/d.
Working principle: as shown in fig. 1;
the key point of increasing the yield of the coalbed methane is to increase the permeability and the specific surface area of the coalbed, reform the reservoir by using a technology of 'compound coal-to-gas reservoir coalbed methane multi-layer mining', increase the number of exposed coalbeds, increase the specific surface area of the coalbed and increase the yield of the coalbed methane;
the fracture damage of the conventional well forming and cementing technology to reserves is large, the original fracture is closed, and the conventional coal bed gas exploitation generates secondary fractures in a fracturing mode, so that the permeability of a fracturing interval is improved;
according to the invention, the existing of the original cracks is ensured to the greatest extent by modifying the well cementation technology, meanwhile, the coal seam is encouraged to collapse, a new secondary crack is formed, the specific surface area and the permeability of the coal seam are increased, and the coal seam gas yield is improved; through the control of the liquid level, the multi-layer coal seam sequentially becomes a main production layer of the coal seam gas, so that the yield of the coal seam is improved, the recovery ratio of the coal seam is improved, the service life of the coal seam gas is prolonged, and the economic benefit is improved.
The method mainly comprises the steps of determining a main coal seam according to logging data and assisted by data analysis means, carrying out production layer combination on the basis of the main coal seam by adopting a segmented consolidation technology, placing a screen pipe on a main coal seam section, and well cementing petroleum pipes in other sections (by using the well cementing technology of a reference well), so that the main coal seam is fully exposed.
The precondition for producing layer combinations is that the physical and fluid properties of each producing layer are similar. Under the condition of multi-coal-bed hypotonic, physical properties of reservoirs are basically similar, but the difference between reservoir pressure and critical desorption pressure is obvious. In the later drainage control process of multi-layer production, critical desorption pressure, interlayer spacing and reservoir pressure gradient become critical parameters for ensuring that each production layer concentrates and produces gas continuously and does not interfere with each other. Comprehensively considering the factors, determining the principle of expansion of the main force producing layer as follows: (1) the main position of the main force producing layer is guaranteed, the downward expansion combination of the producing layers is optimal, the special situation is expanded upwards, and when each producing layer in one producing layer combination starts to produce gas in sequence, the main force producing layer cannot be exposed above the liquid surface so as not to cause damage to the main force producing layer. The crushed coal or the crushed coal are not involved in combination, so that the influence of 'powder injection' on the later engineering of the whole production layer is avoided. (2) The combined reservoirs essentially ensure that the reservoir pressure gradient difference between the extended reservoir and the dominant reservoir is less than 0.1MPa/100m in a fluid pressure system.
For the main force producing layer of the coal bed gas, in the stable production stage, the liquid level is reduced to the upper part of the top plate of the main force producing layer, and the casing pressure is controlled to be about 0.05 MPa. When a plurality of coal bed gas main force producing layers exist, after the productivity of the previous main force producing layer is obviously reduced, the liquid level slowly drops to the upper part of the top plate of the next main force producing layer.
In the coalbed methane gas production process technology, a pump is arranged at the bottom of the lowest coalbed, so that interlayer interference caused by the difference of isothermal adsorption curves of all coalbeds can be basically eliminated, the yield of the coalbed methane well is greatly increased, and the difficulty of the combined production of the development layers of the coalbed methane well is solved.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.
Claims (6)
1. The novel multi-layer combined mining method for the coal bed gas of the composite coal gas reservoir is characterized by comprising the following steps of:
adopting a two-well structure to design a vertical well, and completing the well according to the design;
logging well, and determining a main coal seam, an extended coal seam, an undervoltage coal seam and an overpressure coal seam;
respectively discharging pipes to each layer section of the well, discharging a main coal bed, an expanded coal bed section, discharging a steel pipe to an underpressure coal bed and an overpressure coal bed, and carrying out layered well cementation on each layer section of the underpressure coal bed and the overpressure coal bed;
installing a coalbed methane drainage device, and lowering a drainage pump to the bottom of the lowest coalbed;
draining at a suitable drain rate;
the liquid level is reduced to the upper part of the top plate of the first main force producing layer, the casing pressure is controlled to be about 0.05MPa, and the coal bed gas extraction is carried out;
the well logging system further comprises: the thickness of the coal bed, the gas content of the coal bed, the permeability of the coal bed, the pressure of a coal bed reservoir and the structure of the coal body are taken as main evaluation parameters to evaluate the potential of a producing layer, and the potential is a dominant coal bed; the expanded coal seam is a coal seam near the main coal seam, and the pressure gradient of the reservoir is less than 0.1MPa/100m and greater than 0.05MPa/100 m; the undervoltage coal bed refers to a coal bed with a reservoir pressure gradient of less than 0.05MPa/100 m; the pressure gradient of the overpressure coal seam reservoir is greater than 0.1MPa/100 m;
each layer section of the well is respectively lowered into the pipe, and the layer cementation is carried out on each layer section, comprising the following steps:
designing a surface layer section, a bottom layer section, an under-pressure layer section, an overpressure layer section and a structural coal layer section into seamless steel pipe sections, designing a main-force coal layer section into a pattern pipe section, and carrying out layered well cementation on the surface layer section, the bottom layer section, the under-pressure layer section, the overpressure layer section and the structural coal layer section after pipe descending;
further comprises:
the well cementation material is G-grade cement, the main force coal layer section does not perform well cementation operation, the main force coal layer section is kept in a temporary state, any free collapse is realized, and pulverized coal flows into a pocket of a drilled hole from a round hole of the perforated pipe.
2. The novel multi-layer combined production method of the coal bed gas of the composite coal gas reservoir, which is characterized by further comprising the following steps:
the yield of the coalbed methane of the first principal coal bed is reduced to a certain extent, the liquid level is slowly reduced to the upper part of the top plate of the next principal producing layer, and the coalbed methane of the next principal coal bed is extracted;
and when the coal bed gas of all the main producing layers is completely extracted and the yield of the coal bed gas is insufficient to support production, carrying out secondary yield increase transformation on the coal bed, wherein the secondary yield increase transformation is changed into thermal yield increase transformation.
3. The novel multi-layer combined production method of coal bed gas in a composite coal gas reservoir as claimed in claim 1, wherein the well logging comprises:
and determining a main coal bed, an extended coal bed, an underpressure coal bed and an overpressure coal bed according to the permeability, the gas content, the gas saturation, the critical desorption pressure, the reservoir pressure gradient, the layer spacing and the coal lithology of the coal bed, and classifying the extended coal bed adjacent to the main coal bed into a main coal bed group.
4. The novel multi-layer combined mining method for coal bed gas in a composite coal gas reservoir, as claimed in claim 1, is characterized by comprising the following steps: the surface layer section is the part above the first main force layer group top plate, and the bottom layer section is the part below the last main force coal layer group bottom plate.
5. The novel multi-layer combined mining method for coal bed gas in a composite coal gas reservoir, as claimed in claim 1, is characterized by comprising the following steps: the liquid discharge rate is regulated according to the production stage and the water content, and the production stage takes a low value.
6. The novel multi-layer combined mining method for coal bed gas in a composite coal gas reservoir, as claimed in claim 1, is characterized by comprising the following steps: the liquid discharge rate is 1-5m/d.
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