Disclosure of Invention
In order to solve the problems, the invention provides a method for co-production of deep multi-thin layer coal bed gas and coal bed gasification, which comprises the following steps:
s100, drilling three gas production wells and one gasification well, wherein the three gas production wells penetrate through each thin coal seam, the three gas production wells form a triangle, and the gasification well is positioned in the middle of the triangle;
s200, drilling a branch well system on one side of the gas production well far away from the gasification well, wherein the branch well system corresponds to the gas production well one by one and comprises a main well and a plurality of branch wells with different heights, the branch wells are horizontal wells, and the tail ends of the branch wells point to the gasification well;
S300, dividing a thin coal layer with the same or similar stratum pressure into a exploitation section, wherein a branch well corresponds to the lower part of each exploitation section;
S400, perforating and fracturing all thin coal layers of the bottommost exploitation section simultaneously by three gas production wells, and then exploiting coalbed methane of the bottommost exploitation section simultaneously;
The bottom branch wells of the three branch well systems are all used as injection wells when gas is produced, gasifying agents are injected, the gasifying wells are production wells for coal bed gasification, heat is provided for the production sections above the gasifying wells, and the production of the coal bed gas is promoted;
according to S400, mining coal bed gas and gasifying the coal bed in each mining section from bottom to top;
S500, after coal bed gas exploitation is finished, taking any one gas production well as an injection well, taking a gasification well as a production well, performing coal bed gasification on the bottommost thin coal bed, and then taking the gasification well as the injection well, and taking the other two gas production wells as production wells, and continuously gasifying the bottommost thin coal bed;
and (S500) carrying out coal seam gasification on a plurality of thin coal layers from bottom to top.
The multi-thin-layer coalbed methane reservoir has obvious property differences, the multi-thin-layer coalbed methane reservoir is mainly controlled by reservoir pressure and reservoir permeability, the permeability is related to geological structures, coal structures, stratum pressure and the like, and for the same region of land, the coal reservoir pressure is a main control influencing factor of coalbed methane layered combined mining, under normal pressure gradient, the greater the burial depth of the coal layer is, the greater the coal reservoir pressure is, the most representative reservoir pressure is selected to divide the multi-thin-layer reservoir, all the thin-layer reservoirs are divided into a plurality of mining sections according to the sequence from bottom to top, each mining section comprises a plurality of thin coal layers, the stratum pressure of the coal layers in the same mining section is the same or similar, so that centralized mining is facilitated, and compared with single thin coal layer mining, the gas production method can improve the gas production amount of the gas well. Different perforating and fracturing operations (different operating parameters and fracturing fluid compositions) are implemented on different exploitation sections with larger pressure differences.
In order to further improve the gas yield, the invention combines coal bed gas exploitation and coal bed gasification, one branch well corresponds to the lower part of one exploitation section, when the branch well is matched with the gasification well to gasify the coal bed, a large amount of heat is generated, the heat rises to the upper exploitation section where the coal bed gas is exploited, and after the thin coal layer of the exploitation section is heated, the desorption of methane is facilitated, thereby improving the yield of the coal bed gas.
And after the coal bed gas is extracted in each extraction section, underground gasification can be performed according to the coal bed conditions. At this time, the gas production well and the gasification well alternately function as an injection well and a production well, gasifying underground coal. And the triangular arrangement form of the three gas production wells is matched, so that coal bed gas and underground gasification are conveniently exploited to the maximum extent, and coal bed gas and coal resources are fully utilized.
Optionally, in step S100, the gas producing wells and the gasification wells are vertical wells, the three gas producing wells form an equilateral triangle, the distances between the gasification well and each gas producing well are equal on the cross section of the equilateral triangle, the bottom depths of the three gas producing wells are the same, and the bottom of the gasification well is lower than the bottom of the gas producing well.
Optionally, in step S200, the main well of the branch well system is a vertical well, the side wall of the main well is connected with a plurality of branch wells, the plurality of branch wells are sequentially arranged from top to bottom, the branch wells are all horizontal wells, and the tail ends of the horizontal sections of the branch wells extend towards the corresponding gas production well.
Optionally, in step S300, the horizontal section of the branch well is lower than the bottom of the corresponding production section;
The depth of the horizontal section of the bottommost branch well of the branch well system is larger than the depth of the bottom end of the gas production well, and the bottom end of the gasification well and the horizontal sections of the three bottommost branch wells are in the same depth, so that the gas produced by the gasification of the branch wells can be received correspondingly.
Optionally, in step S400, taking a production well as an example, the production of coal-bed gas is specifically:
S401, perforating on the side wall of the bottommost thin coal seam of the bottommost mining section corresponding to the gas production well, fracturing the bottommost thin coal seam, temporarily discharging liquid, and then sealing the bottommost thin coal seam;
S402, perforating on the side wall of the secondary bottom thin coal layer of the gas production well corresponding to the bottommost mining section, fracturing the secondary bottom thin coal layer, temporarily stopping draining liquid, and then sealing the secondary bottom thin coal layer;
According to S401-402, perforating and fracturing are sequentially carried out on each thin coal layer of the bottommost exploitation section from bottom to top, and liquid is discharged uniformly after the thin coal layers of the exploitation section are all fractured;
and S403, after the liquid is discharged, uniformly mining the coalbed methane for all the thin coal layers of the bottommost mining section by using the prior art.
Further optionally, if the distance between two adjacent thin coal seams is not greater than 20 meters, a temporary plugging mode of throwing balls is adopted, namely, a temporary plugging ball which is soluble is thrown into the gas production well at the end stage of fracturing of the lower coal seam, and under the pressure of fracturing fluid, the temporary plugging ball plugs the perforation holes of the lower coal seam, so that the side wall of the gas production well corresponding to the lower coal seam is plugged.
Further optionally, if the distance between two adjacent thin coal seams is greater than 20 meters, a soluble bridge plug is lowered into the gas production well to seal the cross section of the production well between the upper and lower thin coal seams.
Optionally, in step S401 or S402, perforating is performed on a sidewall of the bottom of the gasification well corresponding to the bottommost branch well, and perforating directions are towards the three gas production wells.
Optionally, at the same time of implementing step S403, respectively introducing gas injection pipes into the three branch well systems, wherein the bottom end of each gas injection pipe reaches one end of the corresponding bottommost branch well close to the gasification well, introducing a production pipe into the gasification well, and the bottom end opening of the production pipe corresponds to the depth of the bottommost branch well for collecting mixed gas produced by gasification.
Optionally, step S500 specifically includes:
s501, respectively marking three gas production wells as a first gas production well, a second gas production well and a third gas production well according to the clockwise direction, taking the first gas production well as an injection well, taking a gasification well as a production well, and gasifying the first gas production well to the bottommost coal bed of the gasification well;
And S502, when the gasification high-temperature zone between the first production well and the gasification well is expanded to the front edge of the gas cooling zone, taking the gasification well as an injection well, taking the second production well and the third production well as production wells, and continuously gasifying the bottommost coal bed between the gasification well and the second production well and between the gasification well and the third production well.
Detailed Description
The embodiment provides a method for co-production of deep multi-thin layer coal bed gas and coal bed gasification, as shown in fig. 1-2, which comprises the following steps:
s100, drilling three gas production wells 1 and one gasification well 2, wherein the three gas production wells enclose a triangle, the gasification well is positioned in the middle of the triangle, and the gas production wells and the gasification well penetrate through each thin coal seam;
s200, drilling a branch well system 5 on one side of the gas production well far away from the gasification well, wherein the branch well system corresponds to the gas production well one by one and comprises a main well 3 and a plurality of branch wells 4 with different heights, the branch wells are horizontal wells, and the tail ends of the branch wells point to the gasification well;
S300, dividing a thin coal layer with the same or similar stratum pressure into a exploitation section, wherein the depth of a branch well corresponds to the lower part of each exploitation section;
S400, perforating and fracturing all thin coal layers of the bottommost exploitation section simultaneously by three gas production wells, and then exploiting coalbed methane of the bottommost exploitation section simultaneously;
The bottom branch wells of the three branch well systems are all used as injection wells when gas is produced, gasifying agents are injected, the gasifying wells are production wells for coal bed gasification, heat is provided for the production sections above the gasifying wells, and the production of the coal bed gas is promoted;
according to S400, mining coal bed gas and gasifying the coal bed in each mining section from bottom to top;
S500, after coal bed gas exploitation is finished, taking any one gas production well as an injection well, taking a gasification well as a production well, performing coal bed gasification on the bottommost thin coal bed, and then taking the gasification well as the injection well, and taking the other two gas production wells as production wells, and continuously gasifying the bottommost thin coal bed;
and (S500) carrying out coal seam gasification on a plurality of thin coal layers from bottom to top.
Optionally, in step S100, three gas producing wells and one gasification well are drilled downwards from the ground according to geological exploration information, the gas producing wells and the gasification well are all vertical wells and penetrate through each thin coal seam overlapped up and down, the three gas producing wells form an equilateral triangle, the distances between the gasification well and each gas producing well are equal on the cross section of the equilateral triangle, the bottom depths of the three gas producing wells are the same, and the bottom ends of the gasification wells are lower than the bottom ends of the gas producing wells.
And respectively setting casings into the gas production well, and performing well cementation and well completion operations according to the prior art. And (3) a sleeve and/or a screen pipe is/are put into the gasification well, so that the side wall of the gasification well can be communicated with each thin coal seam, and well cementation and well completion operations are carried out according to the prior art.
Optionally, in step S200, a set of branch well systems, gas production wells and gasification wells corresponding to each other are sequentially arranged along a straight line, and three gas production wells correspond to three straight lines, and the three straight lines intersect at the gasification well;
the main well of branch well system is the vertical well, and the lateral wall of main well connects a plurality of branch well, and a plurality of branch well from top to bottom sets gradually, and the branch well is the horizontal well, and the branch well includes deflecting section and horizontal segment, and the main well lateral wall is connected at the top of every branch well, sets up one section again and deflects the section, then drills and establishes the horizontal segment, and the horizontal segment end extends towards corresponding gas recovery well direction.
The branch wells of the same branch well system can be parallel to each other, and the upper and lower positions can be corresponding. According to the characteristics of a thin coal seam where the horizontal section of the branch well is positioned and the requirements of the coal seam gasification, the position of the tail end of the branch well is reasonably set, and the tail end of the branch well does not reach the position of the corresponding gas production well in general, namely the gas production well is positioned between the tail end of the branch well and the gasification well. And during subsequent gasification, the coal bed between the tail end of the gasification combustion branch well and the gasification well is gasified, and a high-temperature zone of coal bed gasification is just below a mining section of the coal bed gas which is being mined by the corresponding gas production well, so that heat can be conveniently and directly lifted and transferred to the coal bed of the mining section which is being mined. And after the coal bed in the mining section is heated, desorption of methane is facilitated, so that the yield of coal bed gas is improved.
Optionally, in step S300, the depth of the horizontal section of the branch well is greater than the bottom of the corresponding exploitation section, that is, the horizontal section of the branch well is lower than the bottom of the corresponding exploitation section, and the distance between the horizontal section and the bottom of the exploitation section in the vertical direction is determined by comprehensive assessment according to the safety requirements of coal bed gas exploitation and underground gasification and the transfer efficiency of gasification heat. The branch well is drilled, run, well cementation and well completion by adopting the prior art, and a screen pipe is preferably used, so that reliable support and connection of the branch well and the main well are conveniently provided.
Further optionally, the depth of the horizontal section of the bottommost branch well of the branch well system is greater than the depth of the bottom end of the gas production well, and the bottom ends of the gasification wells and the horizontal sections of the three bottommost branch wells are at the same depth, so that the gas produced by gasification of the branch wells can be received correspondingly.
Optionally, in step S400, taking a production well as an example, the production of coal-bed gas is specifically:
S401, perforating on the side wall of the bottommost thin coal seam of the bottommost mining section corresponding to the gas production well, fracturing the bottommost thin coal seam, temporarily discharging liquid, and then sealing the bottommost thin coal seam;
S402, perforating on the side wall of the secondary bottom thin coal layer of the gas production well corresponding to the bottommost mining section, fracturing the secondary bottom thin coal layer, temporarily stopping draining liquid, and then sealing the secondary bottom thin coal layer;
According to S401-402, perforating and fracturing are sequentially carried out on each thin coal layer of the bottommost exploitation section from bottom to top, and liquid is discharged uniformly after the thin coal layers of the exploitation section are all fractured;
and S403, after the liquid is discharged, uniformly mining the coalbed methane for all the thin coal layers of the bottommost mining section by using the prior art.
Further optionally, if the distance between two adjacent thin coal seams is not greater than 20 meters, a temporary plugging mode of throwing balls is adopted, namely, a temporary plugging ball which is soluble is thrown into the gas production well at the end stage of fracturing of the lower coal seam, and under the pressure of fracturing fluid, the temporary plugging ball plugs the perforation holes of the lower coal seam, so that the side wall of the gas production well corresponding to the lower coal seam is plugged.
Further optionally, if the distance between two adjacent thin coal seams is greater than 20 meters, a soluble bridge plug is lowered into the gas production well to seal the cross section of the production well between the upper and lower thin coal seams.
According to the invention, the thin coal layers in the same exploitation section are subjected to perforation and fracturing respectively, then liquid is discharged uniformly, and coalbed methane of all the coal layers in the exploitation section is exploited in a combined way, so that the gas yield in unit time can be greatly improved, and the exploitation cost is reduced. The three gas production wells operate simultaneously on the same thin coal seam of the same mining section according to the method.
Optionally, in step S401 or S402, perforating is performed on a sidewall of the bottom of the gasification well corresponding to the bottommost branch well, and perforating directions are towards the three gas production wells, so that the gasification well can receive the gas obtained by gasification from the three bottommost branch wells.
Optionally, at the same time of implementing step S403, gas injection pipes are respectively introduced into the three branch well systems, the bottom end of each gas injection pipe reaches one end of the corresponding bottommost branch well close to the gasification well, the top of the gas injection pipe is positioned at the ground wellhead of the main well and is connected with a gasification agent supply device, the gasification agent is supplied to the bottommost branch well of the three branch well systems and is ignited, a production pipe is introduced into the gasification well, and the bottom end opening of the production pipe corresponds to the depth of the bottommost branch well and is used for collecting mixed gas produced by gasification.
According to the steps S401-S403 and the operations of the branch well and the gasification well in the three steps, the coalbed methane of each exploitation section is exploited sequentially from bottom to top, and the coalbed below the corresponding exploitation section is gasified sequentially from bottom to top.
For example, when the secondary bottom mining section is mined, the depth of the branch well corresponding to the secondary bottom mining section is in the range of the bottommost mining section, and the branch well may correspond to any thin coal seam of the bottommost mining section, so long as the gasification of the thin coal seam below and the mining of the coal seam gas of the secondary bottom mining section above can be safely performed.
Preferably, after the gasification of the corresponding coal seam is completed in each branch well, cement is poured from the main well, cement flows into the branch well which has just completed gasification, flows into the coal seam along the branch well, and fills the cavity formed after the gasification of the coal seam. The flow rate of cement is controlled (the flow rate is not too fast and flows down along the side wall of the main well, which is not connected with the branch well), or a line is led in the main well, the bottom of the line corresponds to the branch well which is at the bottom and is used for independently injecting cement, so that the cement can only flow into the branch well at the bottom and is used for completing the gasification task, and cannot flow into the unvaporized branch well above.
Optionally, step S500 specifically includes:
s501, respectively marking three gas production wells as a first gas production well, a second gas production well and a third gas production well according to the clockwise direction, taking the first gas production well as an injection well, taking a gasification well as a production well, and gasifying the first gas production well to the bottommost coal bed of the gasification well;
And S502, when the gasification high-temperature zone between the first production well and the gasification well is expanded to the front edge of the gas cooling zone, taking the gasification well as an injection well, taking the second production well and the third production well as production wells, and continuously gasifying the bottommost coal bed between the gasification well and the second production well and between the gasification well and the third production well.
Further optionally, in step S501, an injection pipe is introduced into the first gas production well, the bottom end of the injection pipe reaches the bottom-most coal seam corresponding to the first gas production well, a production pipe is introduced into the gasification well, the bottom end opening of the production pipe corresponds to the depth of the bottom end of the injection pipe, the injection pipe inputs gasification agent and ignites, and mixed gas produced by gasification is discharged from the gasification well.
The bottommost coal seam in step S501 refers to the coal seam with the deepest depth reached by the bottom of the production well, but not the coal seam corresponding to the bottommost branch well, which is lower than the bottom of the production well.
The gasification high temperature area is a high temperature area where coal is burnt, and coal gas (namely CH4、CO、H2) formed by the reaction of water vapor and coal flows to the extraction well through the carbonization area and is extracted through the extraction well.
The front edge of the gas cooling area is 2/3 of the distance between the adjacent injection well and the extraction well, the gasification high-temperature area gradually moves from the injection well to the extraction well, when the distance between the edge of the gasification high-temperature area closest to the extraction well and the injection well reaches 2/3 of the distance between the adjacent injection well and the extraction well, the first gas production well is closed, the gasification well is used as the injection well, the second gas production well and the third gas production well are used as the extraction well, and the bottom coal seam is continuously gasified.
The gas cooling area is approximately a carbonization area, coal in the area is heated, chemical reaction possibly occurs, but the coal is not combusted, and gas generated after coal combustion can be cooled in the process of passing through the gas cooling area, so that the gas pressure of a production well is reduced, and the production of the gas is facilitated. Therefore, a part of coal bed is always reserved between the extraction well and the injection well as a gas cooling area.
In step S502, the coal seam between the gasification well and the second gas production well, and between the gasification well and the third gas production well can be gasified at the same time, so that the underground coal seam resource can be more fully utilized.
According to S500, the coal seam gasification is carried out on a plurality of thin coal seams from bottom to top, namely if the coal seam condition is good, all the thin coal seams can be gasified one by one in sequence, meanwhile, the whole deep coal seam area does not collapse, and if the coal seam condition is bad, the thin coal seams can be gasified at intervals, so that the whole deep coal seam area is ensured not to collapse.
Further optionally, in step S500, after the first gas production well gasifies a certain coal seam, a pipeline is lowered into the first gas production well for inputting cement to seal an internal space of the first gas production well corresponding to the coal seam immediately after gasification, so that a gasifying agent is prevented from entering the lower coal seam when the upper coal seam is gasified subsequently;
And in the same way, after the second gas production well and the third gas production well gasify a certain coal seam, respectively lowering pipelines into the second gas production well and the third gas production well for inputting cement so as to block the inner space of the coal seam just gasified corresponding to the second gas production well and the third gas production well, and prevent gasifying agents from entering the coal seam below when the upper coal seam is gasified subsequently.