WO2024082412A1 - 一种多分支地热井系统及施工方法 - Google Patents

一种多分支地热井系统及施工方法 Download PDF

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WO2024082412A1
WO2024082412A1 PCT/CN2022/139329 CN2022139329W WO2024082412A1 WO 2024082412 A1 WO2024082412 A1 WO 2024082412A1 CN 2022139329 W CN2022139329 W CN 2022139329W WO 2024082412 A1 WO2024082412 A1 WO 2024082412A1
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heat exchange
well
branch
main well
pipe
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PCT/CN2022/139329
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English (en)
French (fr)
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李龙
王俊逸
鞠贵冬
蒋方明
黄文博
陈娟雯
Original Assignee
双良节能系统股份有限公司
中国科学院广州能源研究所
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Publication of WO2024082412A1 publication Critical patent/WO2024082412A1/zh

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24T—GEOTHERMAL COLLECTORS; GEOTHERMAL SYSTEMS
    • F24T10/00—Geothermal collectors
    • F24T10/20—Geothermal collectors using underground water as working fluid; using working fluid injected directly into the ground, e.g. using injection wells and recovery wells
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24T—GEOTHERMAL COLLECTORS; GEOTHERMAL SYSTEMS
    • F24T10/00—Geothermal collectors
    • F24T2010/50—Component parts, details or accessories
    • F24T2010/53—Methods for installation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/10—Geothermal energy

Definitions

  • the present invention relates to the technical field of geothermal energy development and utilization, and in particular to a multi-branch geothermal well system and a construction method.
  • geothermal energy is basically not affected by geographical location, climate and seasons. It has the characteristics of large reserves, wide distribution, clean and environmentally friendly, stable and reliable. It plays an important role in optimizing energy structure, saving energy and reducing emissions, and improving the environment.
  • the heat exchange surface of the underground well is not large enough and the well depth is limited, which makes the heat extraction of a single well small, resulting in the inability to promote and utilize it on a large scale. Therefore, it is urgent to develop a dry hot rock geothermal heat extraction technology with higher single well heat extraction efficiency and lower cost to solve the above problems.
  • existing geothermal energy utilization and heat transfer enhancement methods include fracturing technology for EGS, convection speed-increasing tube technology for indirect heat exchange, and airflow mixing heat exchange technology.
  • fracturing technology for EGS convection speed-increasing tube technology for indirect heat exchange
  • airflow mixing heat exchange technology airflow mixing heat exchange technology
  • the purpose of the present invention is to provide a multi-branch geothermal well system and construction method, by sharing the main well and adopting a multi-branch structure in the deep layer with high geothermal temperature, so as to increase the heat exchange area and improve the heat extraction of a single well.
  • a multi-branch geothermal well system comprises an above-ground heat exchange unit and an underground heat exchange unit, wherein the underground heat exchange unit comprises a geothermal well and a heat exchange pipe, wherein the heat exchange pipe is disposed in the heat exchange well and is connected to the above-ground heat exchange unit, wherein the geothermal well comprises a main well and a plurality of branch wells, wherein the main well is a vertical well, wherein at least one cementing casing is disposed on the inner wall of the main well and the fixed casing extends along the length direction of the main well, wherein a plurality of branch wells inclined downward are provided on the open hole portion of the main well and/or the fixed casing, wherein the heat exchange pipes are disposed in the plurality of branch wells and the main well, wherein a sealing layer is disposed at the interface between the heat exchange pipe and the branch well and the main well, and wherein the heat exchange pipe is a gravity heat pipe or a coaxial casing.
  • the heat exchange tube located in the main well is connected to the heat exchange tube located in the branch well, and a liquid separator is provided at the connection point, the liquid separator has a liquid separation area, the liquid separation area is provided in the heat exchange tube located in the main well, and the liquid separation area is also connected to the heat exchange tube located in the branch well.
  • the liquid separator includes a liquid separator plate and a liquid storage ring.
  • the liquid storage ring is arranged on the tube wall of the heat exchange tube located in the main well and is surrounded by the tube wall of the heat exchange tube to form a liquid separator area.
  • the liquid separator plate is arranged in the liquid separator area with one end of it fixed on the inner wall of the liquid storage ring, and the other end extends into the heat exchange tube located in the branch well.
  • the heat exchange tube is a gravity heat pipe
  • the liquid storage ring is arranged on the tube wall of the gravity heat pipe located in the main well and is surrounded by the tube wall of the gravity heat pipe to form the liquid separation area.
  • the heat exchange tube is a coaxial sleeve, which includes an inner tube and an outer tube, with a flow gap between the inner tube and the outer tube, and the liquid storage ring is arranged in the flow gap of the coaxial sleeve located in the main well, one end of the liquid storage ring is attached to the outer wall of the inner tube, and the other end is fixed on the inner wall of the outer tube and surrounded by the inner wall of the outer tube to form the liquid separation area.
  • the ground heat exchange unit includes a condenser, a hot working fluid valve, and a cold working fluid valve.
  • the condenser is provided with a hot working fluid port, a cold working fluid port, a cooling water inlet and a cooling water outlet.
  • the heat exchange pipes located in the main well are connected to the hot working fluid port and the cold working fluid port of the condenser through pipelines, and the hot working fluid valve and the cold working fluid valve are respectively provided on the connecting pipelines.
  • the heat exchange tube is a gravity heat pipe
  • the condenser is also provided with a vacuum port and a condensed water outlet.
  • the vacuum port is connected to a vacuum pump through a pipeline and a vacuum valve is provided on the connecting pipeline.
  • a condensed water valve is provided on the pipeline connected to the condensed water outlet.
  • the bottom spacing of the plurality of branch wells is greater than 50 meters, and the fixed casing is arranged in the branch well.
  • the fixed casing is arranged along the inner wall of the branch well and extends along the length direction of the branch well.
  • the present invention also provides a multi-branch geothermal well system construction method for manufacturing a multi-branch geothermal well system as described in any one of the above, the steps are:
  • Drilling is performed at the main well construction location, and at least one fixed casing is used for cementing according to the geological conditions;
  • the main well and branch wells need to drain the heat exchange tubes after the lowering of the tubes is completed, the cold working fluid valve is closed, the hot working fluid valve is opened, the vacuum valve is opened, and the condensate valve is closed.
  • the vacuum pump evacuates the condenser to an absolute pressure of 1 to 3 kPa and maintains it, and 7°C cooling water is introduced to condense the water vapor in the heat exchange tubes into water, and the condensate valve is opened to discharge the water, so as to discharge all the water in the heat exchange tubes.
  • the multi-branch geothermal well system uses a multi-branch structure in the deep layer with high geothermal temperature by sharing the main well, which greatly increases the heat exchange area of the deep geothermal heat of the heat extraction well.
  • an ultra-long gravity heat pipe or coaxial casing into the multi-branch geothermal well, the heat extraction of a single well can be greatly increased, and the heat extraction can be increased by 3 to 5 times under the premise of increasing the project cost by 0.5 to 1 times.
  • FIG1 is a schematic half-section diagram of the internal structure of an underground heat exchange unit
  • FIG2 is a half-section schematic diagram of another internal structure of an underground heat exchange unit
  • FIG3 is a schematic diagram of the structure of the ground heat exchange unit
  • FIG4 is a schematic structural diagram of a liquid dispenser
  • FIG5 is a schematic diagram of the internal structure of the liquid dispenser
  • FIG6 is a top view of a liquid storage ring placed in a gravity heat pipe
  • FIG. 7 is a top view of the liquid storage ring placed in the coaxial sleeve.
  • Liquid separation plate 902. Liquid storage ring.
  • a multi-branch geothermal well system includes an above-ground heat exchange unit and an underground heat exchange unit.
  • the underground heat exchange unit includes a geothermal well and a heat exchange pipe, and the heat exchange pipe is placed in the heat exchange well and communicated with the above-ground heat exchange unit.
  • the geothermal well includes a main well 1 and a plurality of branch wells.
  • the main well 1 is a vertical well.
  • the inner wall of the main well 1 is provided with at least one cementing casing and the fixed casing extends along the length direction of the main well 1.
  • one open casing 2 and two open casings 3 are used for cementing. If the geological conditions are good, only one open cementing can be used. If the geological conditions are poor, three or more open cementing is required.
  • a multi-branch structure is adopted when the main well 1 is located in a deep layer with high geothermal temperature, that is, a plurality of branch wells inclined downward are opened on the open hole part and/or the fixed casing of the main well 1.
  • the branch wells can be cemented with cementing casings.
  • the branch well cementing casing 25 is arranged along the inner wall of the branch well and extends along the length direction of the branch well.
  • the branch well can also be drilled directly in the open hole form, as shown in FIG2.
  • the number of branch wells is selected according to actual needs. In this embodiment, two branch wells are used.
  • One branch well is arranged at the open hole part of the main well 1 as the first branch well 4, and the other branch well is arranged on the fixed casing as the second branch well 5.
  • the bottom spacing of branch wells only needs to be greater than 50 meters. This structure does not require high spacing between branch wells and is more conducive to the layout of multiple branch wells.
  • Heat exchange pipes are arranged in the first branch well 4, the second branch well 5 and the main well 1, and the heat exchange pipes are gravity heat pipes or coaxial sleeves.
  • a plugging layer is arranged at the interface between the heat exchange pipe and the first branch well 4, the second branch well 5 and the main well 1.
  • the heat exchange pipe located in the main well 1 is defined as the heat exchange pipe main pipe 6
  • the heat exchange pipe located in the first branch well 4 is defined as the heat exchange pipe branch pipe 1 7
  • the heat exchange pipe located in the second branch well 5 is defined as the heat exchange pipe branch pipe 2 8.
  • the heat exchange tube main pipe 6, the heat exchange tube branch pipe 1 7 and the heat exchange tube branch pipe 2 8 are connected and a liquid distributor 9 is provided at the connection point.
  • the cold medium flows in along the wall surface at the top of the heat exchange tube main pipe 6, and after being divided by the liquid distributor 9, it enters the heat exchange tube branch pipe 1 7, the heat exchange tube branch pipe 2 8 and the heat exchange tube main pipe 6 in sequence.
  • the liquid distributor 9 has a plurality of liquid distribution areas 10, and the heat exchange tube main pipe 6 is provided with liquid distribution areas 10 at the connection point between the heat exchange tube main pipe 6 and the heat exchange tube branch pipe 1 7, and at the connection point between the heat exchange tube main pipe 6 and the heat exchange tube branch pipe 2 8. Specifically referring to FIGS.
  • the liquid separator 9 includes a liquid separator plate 901 and a liquid storage ring 902.
  • the liquid storage ring 902 is arranged on the tube wall of the heat exchange tube main pipe 6 and is surrounded by the tube wall of the heat exchange tube main pipe 6 to form a liquid separator area 10.
  • the liquid separator plate 901 is arranged in the liquid separator area 10 and one end of the liquid separator plate 901 is fixed on the inner side wall of the liquid storage ring 902, and the other end extends to the heat exchange tube branch pipe 1 7 or the heat exchange tube branch pipe 2 8. Referring to FIG.
  • the liquid storage ring 902 is arranged on the tube wall of the heat exchange tube main pipe 6 and is surrounded by the tube wall of the heat exchange tube main pipe 6 to form a liquid separator area 10.
  • the coaxial sleeve when the heat exchange tube is a coaxial sleeve, the coaxial sleeve includes an inner tube 11 and an outer tube 12, and a flow gap 13 is provided between the inner tube 11 and the outer tube 12.
  • a liquid storage ring 902 is arranged in the flow gap 13, and one end of the liquid storage ring 902 is attached to the outer wall of the inner tube 11, and the other end is fixed on the inner wall of the outer tube 12 and is surrounded by the inner wall of the outer tube 12 to form a liquid separation area 10.
  • the mass of liquid entering each heat exchange tube is distributed, so that the heat extraction capacity of each heat exchange tube can be maximized.
  • the liquid storage ring 902 and the liquid separation plate 901 of appropriate size are calculated, so that the percentage of the heat exchange tube main pipe 6 wall surrounded by the liquid storage ring 902 to the entire heat exchange tube main pipe 6 wall is the same as the proportion of the mass of the inflowing liquid.
  • the ground heat exchange unit includes a condenser 14, a hot medium valve 15, and a cold medium valve 16, wherein the condenser 14 is provided with a hot medium port 17, a cold medium port 18, a cooling water inlet 19, and a cooling water outlet 20, and the heat exchange pipe main 6 is connected to the hot medium port 17 and the cold medium port 18 of the condenser 14 through pipelines, and the connecting pipelines are provided with a hot medium valve 15 and a cold medium valve 16.
  • the cold medium enters from the heat exchange pipe main 6, and enters the heat exchange pipe branch pipe 1 7, the heat exchange pipe branch pipe 2 8, and the heat exchange pipe main 6 in turn through the liquid distributor 9 to exchange heat indirectly with the high-temperature rock formation, and the hot medium after heat exchange returns to the condenser 14 from the hot medium port 17 through the pipeline for heat exchange.
  • the inflowing medium can be water, ammonia, or other low-boiling-point Freon medium, and the outflowing medium can be the gaseous or liquid form of the above medium.
  • the condenser 14 is also provided with a vacuum port 21 and a condensed water outlet 22.
  • the vacuum port 21 is connected to a vacuum pump through a pipeline and a vacuum valve 23 is provided on the connecting pipeline.
  • a condensed water valve 24 is provided on the pipeline connected to the condensed water outlet 22.
  • the vacuum pump evacuates the condenser 14 to an absolute pressure of 1 to 3 KPa and maintains it, and introduces 7°C cooling water.
  • the water vapor in the heat exchange tube branch pipe 1 7, the heat exchange tube branch pipe 2 8 and the heat exchange tube main pipe 6 converges and enters the condenser 14 to condense into water, and the condensed water valve 24 is opened to discharge the water, so as to discharge all the water in the heat exchange tube.
  • S1 Determine the ground construction location of the main well of the geothermal well, the number of branch wells, and the depth of the main well and each branch well.
  • Drilling is performed at the main well construction location, and at least one fixed casing is used for cementing according to the geological conditions.
  • one open casing and two open casing cementing are used.
  • the second branch well can be drilled directly. After the second branch well is drilled, the heat exchange pipe can be lowered and the interface can be sealed.
  • the branch wells can be drilled in an open hole manner or in a cemented manner.
  • the basic drilling principle is that if the branch well currently being drilled is completed in an open hole manner, it is necessary to first lower the heat exchange pipe and then drill the next branch well. If the branch well currently being drilled is completed in a cemented manner, the pipe can be lowered together after the other branch wells are completed.
  • the present invention uses a shared main well and a multi-branch structure in deep layers with high geothermal temperatures, thereby greatly increasing the heat exchange area of the deep geothermal heat in the heating well and significantly improving the heat production of a single heating well. Under the premise of increasing the project cost by 0.5 to 1 times, the heat production can be increased by 3 to 5 times.

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Abstract

一种多分支地热井系统，包括地上换热单元和地下换热单元，地下换热单元包括地热井和换热管，换热管置于地热井内并与地上换热单元连通，地热井包括主井（1）和多个分支井，主井（1）为直井，主井（1）的内壁至少设置有一个固定套管且固定套管沿主井（1）的长度方向延伸，主井（1）的裸眼部分和/或固定套管上开设有多个倾斜向下设置的分支井，多个分支井和主井（1）内设置有换热管，换热管与分支井和主井（1）的接口处设有封堵层，换热管为重力热管或同轴套管。所述系统通过共用主井（1），并在地热温度高的深层采用多分支结构，以此增大换热面积，提高单井采热量。

Description

一种多分支地热井系统及施工方法
本申请要求于2022年10月21日提交中国专利局、申请号为202211296055.2、发明名称为“一种多分支地热井系统及施工方法”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明涉及地热能源开发利用技术领域，具体涉及一种多分支地热井系统及施工方法。
背景技术
地热能作为一种绿色低碳、可循环利用的可再生清洁能源，基本不受地理位置、气候和季节的影响，其具有储量大、分布广、清洁环保、稳定可靠等特点，具有优化能源结构、节能减排和改善环境的重要作用。对于井下间接换热的技术方式，由于井下换热面不够大，井深度有限，使得单井取热量小，导致无法大范围内推广利用。因此，亟需开发一种单井取热效率更高、成本更低的干热岩地热取热技术，以解决上述问题。
为了提高井下间接换热的地热能利用效率和单井取热量，现有地热能利用传热强化的方式有用于EGS的压裂技术、用于间接换热的对流增速管技术和气流掺混换热技术等。但是目前这些技术投资成本高、技术难度大，均处于研发阶段，并没有大规模投入商业化运营。
发明内容
有鉴于此，本发明的目的是提供一种多分支地热井系统及施工方法，通过共用主井，并在地热温度高的深层采用多分支结构，以此增大换热面积，提高单井采热量。
为达到上述目的，本发明采用的技术方案是：
一种多分支地热井系统，包括地上换热单元和地下换热单元，所述地下换热单元包括有地热井和换热管，所述换热管置于所述换热井内并与所述地上换热单元连通，所述地热井包括有主井和多个分支井，所述主井为直井，所述主井的内壁至少设置有一个固井套管且所述固定套管沿所述主井的长度方向延伸，所述主井的裸眼部分和/或所述固定套管上开设有多个 倾斜向下设置的所述分支井，多个所述分支井和所述主井内设置有所述换热管，所述换热管与所述分支井和所述主井的接口处设有封堵层，所述换热管为重力热管或同轴套管。
作为优选的，位于所述主井内的所述换热管和位于所述分支井内的所述换热管连通，且连通处设置有一分液器，所述分液器具有一分液区，所述分液区设置在位于所述主井内的所述换热管内，所述分液区还与位于所述分支井内的所述换热管连通。
作为优选的，所述分液器包括分液板和存液环，所述存液环设置在位于所述主井内的所述换热管的管壁上并与所述换热管的管壁围设形成分液区，所述分液板设置在所述分液区内且其一端固定在所述存液环的内侧壁上，另一端延伸至位于所述分支井的所述换热管内。
作为优选的，所述换热管为重力热管，所述存液环设置在位于所述主井内的所述重力热管的管壁上并与所述重力热管的管壁围设形成所述分液区。
作为优选的，所述换热管为同轴套管，所述同轴套管包括内管和外管，所述内管和所述外管之间具有流动间隙，所述存液环设置在位于所述主井内的所述同轴套管的所述流动间隙内，所述存液环的一端贴附与所述内管的外侧壁设置，另一端固定在所述外管的内侧壁上并与所述外管的内侧壁围设形成所述分液区。
作为优选的，所述地上换热单元包括有冷凝器、热工质阀门、冷工质阀门，所述冷凝器上开设有热工质口、冷工质口、冷却水进口和冷却水出口，位于所述主井内的所述换热管分别通过管道与所述冷凝器的所述热工质口和所述冷工质口连通，且连通管道上分别设置有所述热工质阀门和冷工质阀门。
作为优选的，所述换热管为重力热管，所述冷凝器上还开设有抽真空口和冷凝水出口，所述抽真空口通过管道与一真空泵连通且连接管道上设置一真空阀，所述冷凝水出口连通的管道上设置有一冷凝水阀门。
作为优选的，多个所述分支井的井底间距大于50米，所述分支井内设置有所述固定套管，所述固定套管沿所述分支井的内壁设置且沿所述分支 井的长度方向延伸。
同时，本发明还提供一种多分支地热井系统施工方法，用于制造如上任意一项所述的一种多分支地热井系统，步骤为：
S1、确定地热井的主井地面施工位置、分支井数及主井和各分支井的深度；
S2、在主井施工位置进行钻井，并根据地质情况至少进行使用一个固定套管固井；
S3、选择在主井的裸眼部分和/或固定套管上以裸眼形式和/或固井方式侧钻多个分支井；
S4、当分支井以裸眼形式完钻后，需先对该分支井下换热管并对接口处进行封堵，其后再钻取下一个分支井；当分支井以固井方式完钻后，可直接钻取下一个分支井，待其余分支井全部完钻后再一并下换热管并对接口处进行封堵；
S5、主井洗井，其后对主井下换热管，并将位于主井内的换热管与位于各个分支井内的换热管进行连接；
S6、将位于主井内的换热管通过管道与冷凝器的热工质口和冷工质口连通。
作为优选的，换热管采用重力热管时，主井和分支井在下管完成后需对换热管进行排水，关闭冷工质阀门，打开热工质阀门，打开真空阀，关闭冷凝水阀门，位于主井内的换热管与冷凝器连通后，真空泵将冷凝器内抽真空至绝对压力1～3KPa并保持，通入7℃冷却水，将换热管内的水蒸气冷凝为水，并开启冷凝水阀门排出水，以将换热管内的水全部排出。
与现有技术相比，本发明提供的一种多分支地热井系统通过共用主井，在地热温度高的深层采用多分支结构，大大增加了取热井深层地热的换热面积。通过在多分支地热井中下入超长重力热管或同轴套管，可以大幅提高取热井单井采热量，在工程造价提高0.5～1倍的前提下，实现3～5倍采热量的提升。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对 实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为地下换热单元的一种内部结构半剖面示意图；
图2为地下换热单元的另一种内部结构半剖面示意图；
图3为地上换热单元的结构示意图；
图4为分液器的结构示意图；
图5为分液器的内部结构示意图；
图6为存液环放置在重力热管内的俯视图；
图7为存液环放置在同轴套管内的俯视图。
附图中涉及的附图标记和组成部分说明：
1、主井；2、一开套管；3、二开套管；4、第一分支井；5、第二分支井；6、换热管主管；7、换热管支管一；8、换热管支管二；9、分液器；10、分液区；11、内管；12、外管；13、流动间隙；14、冷凝器；15、热工质阀门；16、冷工质阀门；17、热工质口；18、冷工质口；19、冷却水进口；20、冷却水出口；21、抽真空口；22、冷凝水出口；23、真空阀；24、冷凝水阀门；25、分支井固井套管；
901、分液板；902、存液环。
具体实施方式
下面将通过具体实施方式对本发明的技术方案进行清楚、完整地描述。显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
参见图1所示，一种多分支地热井系统，包括地上换热单元和地下换热单元。其中，地下换热单元包括有地热井和换热管，换热管置于换热井内并与地上换热单元连通。
地热井包括有主井1和多个分支井，主井1为直井，主井1的内壁至少设置有一个固井套管且固定套管沿主井1的长度方向延伸，在本实施例 中使用了一开套管2、二开套管3固井，如果地质情况较好可以仅使用一开固井，如果地质情况较差需进行三开或以上固井。在主井1位于地热温度高的深层采用多分支结构，即在主井1的裸眼部分和/或固定套管上开设有多个倾斜向下设置的分支井，分支井可以采用固井套管固井，分支井固井套管25沿分支井的内壁设置且沿分支井的长度方向延伸，当然分支井也可以直接以裸眼形式完钻即参见图2所示。根据实际需要选择分支井的数量，在本实施例中采用2个分支井，一个分支井设置在主井1的裸眼部分处为第一分支井4，另一个分支井设置在固定套管上为第二分支井5。分支井的井底间距大于50米即可，本结构对分支井之间的间距要求不高，更有利于多分支井的布置。
第一分支井4、第二分支井5和主井1内设置有换热管，换热管为重力热管或同轴套管。换热管与第一分支井4、第二分支井5和主井1的接口处设有封堵层。为了便于描述，将位于主井1内的换热管定义为换热管主管6，将位于第一分支井4内的换热管定义为换热管支管一7，将位于第二分支井5内的换热管定义为换热管支管二8。
换热管主管6、换热管支管一7和换热管支管二8连通且连通处设置有一分液器9。在运行过程中，冷工质沿换热管主管6顶端的壁面流入，经分液器9分流后依次进入换热管支管一7、换热管支管二8以及换热管主管6内。上述分液器9具有多个分液区10，换热管主管6内部位于换热管主管6与换热管支管一7连通处、换热管主管6与换热管支管二8的连通处均设置有分液区10。具体参见图4～图5所示，分液器9包括分液板901和存液环902，存液环902设置在换热管主管6的管壁上并与换热管主管6的管壁围设形成分液区10，分液板901设置在分液区10内且其一端固定在存液环902的内侧壁上，另一端延伸至换热管支管一7或换热管支管二8内。参见图6所示，当换热管为重力热管，存液环902设置在位于换热管主管6的管壁上并与换热管主管6的管壁围设形成分液区10。参见图7所示，当换热管为同轴套管时，同轴套管包括内管11和外管12，内管11和外管12之间具有流动间隙13，存液环902设置在流动间隙13内，存液环902的一端贴附与内管11的外侧壁设置，另一端固定在外管12的 内侧壁上并与外管12的内侧壁围设形成分液区10。
根据地热井各个分支井和主井1的采热能力、换热工质的流动阻力，分配进入各个换热管内的液体质量，从而使得各个换热管的采热能力得到最大程度的发挥。根据换热管支管一7、换热管支管二8和换热管主管6流入液体质量的占比，计算合适尺寸的存液环902和分液板901，使得存液环902围设的换热管主管6管壁占整个换热管主管6管壁的百分比与流入液体质量的占比相同。
再参见图3所示，地上换热单元包括有冷凝器14、热工质阀门15、冷工质阀门16，其中冷凝器14上开设有热工质口17、冷工质口18、冷却水进口19和冷却水出口20，换热管主管6分别通过管道与冷凝器14的热工质口17和冷工质口18连通，且连通管道上分别设置有热工质阀门15和冷工质阀门16。冷工质从换热管主管6内进入，并经分液器9依次进入换热管支管一7、换热管支管二8以及换热管主管6内与高温岩层间接换热，换热后的热工质经管道从热工质口17返回冷凝器14内进行换热。流入的工质可以为水、氨以及其他低沸点氟利昂工质，流出的工质可为上述工质的气态或液态。
在换热管下管施工过程中，换热管内可能存在水，如若换热管采用重力热管时则需要将管内的水排出。因此冷凝器14上还开设有抽真空口21和冷凝水出口22，抽真空口21通过管道与一真空泵连通且连接管道上设置一真空阀23，冷凝水出口22连通的管道上设置有一冷凝水阀门24。关闭冷工质阀门16，打开热工质阀门15，打开真空阀23，关闭冷凝水阀门24，换热管主管6与冷凝器14连通后，真空泵将冷凝器14内抽真空至绝对压力1～3KPa并保持，通入7℃冷却水，换热管支管一7、换热管支管二8和换热管主管6内的水蒸气汇流后进入冷凝器14内冷凝为水，并开启冷凝水阀门24排出水，以将换热管内的水全部排出。
上述多分支地热井系统实际的施工方法为：
S1、确定地热井的主井地面施工位置、分支井数及主井和各分支井的深度。
S2、在主井施工位置进行钻井，并根据地质情况至少进行使用一个固 定套管固井，在本实施例中采用一开套管、二开套管固井。
S3、选择在主井的裸眼部分和以及固定套管上进行侧钻第一分支井和第二分支井二。
S4、当第一分支井采用裸眼形式完钻后，需先对第一分支井下换热管支管一并对接口处进行封堵，其后再以裸眼形式钻取第二分支井并进行下换热管支管二；
当第一分支井采用固井方式完钻后，可直接钻取第二分支井，待第二分支井完钻后可一并下换热管并对接口处进行封堵。
本实施例所提供的地热井中，分支井的钻取方式可采用裸眼形式或固井方式，基本钻取原则为如若当前所钻分支井采用裸眼形式完钻，则需要先下换热管其后再进行下一分支井钻取，如若当前所钻分支井采用固井形式完钻，则可待其他分支井完钻后一同下管。
S5、主井洗井，其后对主井下换热管主管，并将换热管主管与换热管支管一、换热管支管二进行连接。
S6、将换热管主管通过管道与冷凝器的热工质口和冷工质口连通。
本发明通过共用主井，在地热温度高的深层采用多分支结构，大大增加了取热井深层地热的换热面积，大幅提高取热井单井采热量，在工程造价提高0.5～1倍的前提下，实现3～5倍采热量的提升。
对所公开的实施例的上述说明，使本领域专业技术人员能够实现或使用本发明。对这些实施例的多种修改对本领域的专业技术人员来说将是显而易见的，本文中所定义的一般原理可以在不脱离本发明的精神或范围的情况下在其他实施例中实现。因此，本发明将不会被限制于本文所示的这些实施例，而是要符合与本文所公开的原理和新颖特点相一致的最宽的范围。

Claims (10)

  1. 一种多分支地热井系统，包括地上换热单元和地下换热单元，所述地下换热单元包括有地热井和换热管，所述换热管置于所述换热井内并与所述地上换热单元连通，其特征在于：所述地热井包括有主井和多个分支井，所述主井为直井，所述主井的内壁至少设置有一个固井套管且所述固定套管沿所述主井的长度方向延伸，所述主井的裸眼部分和/或所述固定套管上开设有多个倾斜向下设置的所述分支井，多个所述分支井和所述主井内设置有所述换热管，所述换热管与所述分支井和所述主井的接口处设有封堵层，所述换热管为重力热管或同轴套管。
  2. 根据权利要求1所述的一种多分支地热井系统，其特征在于：位于所述主井内的所述换热管和位于所述分支井内的所述换热管连通，且连通处设置有一分液器，所述分液器具有一分液区，所述分液区设置在位于所述主井内的所述换热管内，所述分液区还与位于所述分支井内的所述换热管连通。
  3. 根据权利要求2所述的一种多分支地热井系统，其特征在于：所述分液器包括分液板和存液环，所述存液环设置在位于所述主井内的所述换热管的管壁上并与所述换热管的管壁围设形成分液区，所述分液板设置在所述分液区内且其一端固定在所述存液环的内侧壁上，另一端延伸至位于所述分支井的所述换热管内。
  4. 根据权利要求3所述的一种多分支地热井系统，其特征在于：所述换热管为重力热管，所述存液环设置在位于所述主井内的所述重力热管的管壁上并与所述重力热管的管壁围设形成所述分液区。
  5. 根据权利要求3所述的一种多分支地热井系统，其特征在于：所述换热管为同轴套管，所述同轴套管包括内管和外管，所述内管和所述外管之间具有流动间隙，所述存液环设置在位于所述主井内的所述同轴套管的所述流动间隙内，所述存液环的一端贴附与所述内管的外侧壁设置，另一端固定在所述外管的内侧壁上并与所述外管的内侧壁围设形成所述分液区。
  6. 根据权利要求1所述的一种多分支地热井系统，其特征在于：所述 地上换热单元包括有冷凝器、热工质阀门、冷工质阀门，所述冷凝器上开设有热工质口、冷工质口、冷却水进口和冷却水出口，位于所述主井内的所述换热管分别通过管道与所述冷凝器的所述热工质口和所述冷工质口连通，且连通管道上分别设置有所述热工质阀门和冷工质阀门。
  7. 根据权利要求6所述的一种多分支地热井系统，其特征在于：所述换热管为重力热管，所述冷凝器上还开设有抽真空口和冷凝水出口，所述抽真空口通过管道与一真空泵连通且连接管道上设置一真空阀，所述冷凝水出口连通的管道上设置有一冷凝水阀门。
  8. 根据权利要求1所述的一种多分支地热井系统，其特征在于：多个所述分支井的井底间距大于50米，所述分支井内设置有所述固定套管，所述固定套管沿所述分支井的内壁设置且沿所述分支井的长度方向延伸。
  9. 一种多分支地热井系统施工方法，其特征在于：用于制造权利要求1～8任意一项所述的一种多分支地热井系统，步骤为：
    S1、确定地热井的主井地面施工位置、分支井数及主井和各分支井的深度；
    S2、在主井施工位置进行钻井，并根据地质情况至少进行使用一个固定套管固井；
    S3、选择在主井的裸眼部分和/或固定套管上以裸眼形式和/或固井方式侧钻多个分支井；
    S4、当分支井以裸眼形式完钻后，需先对该分支井下换热管并对接口处进行封堵，其后再钻取下一个分支井；当分支井以固井方式完钻后，可直接钻取下一个分支井，待其余分支井全部完钻后再一并下换热管并对接口处进行封堵；
    S5、主井洗井，其后对主井下换热管，并将位于主井内的换热管与位于各个分支井内的换热管进行连接；
    S6、将位于主井内的换热管通过管道与冷凝器的热工质口和冷工质口连通。
  10. 根据要求9所述的一种多分支地热井系统施工方法，其特征在于：换热管采用重力热管时，主井和分支井在下管完成后需对换热管进行排水， 关闭冷工质阀门，打开热工质阀门，打开真空阀，关闭冷凝水阀门，位于主井内的换热管与冷凝器连通后，真空泵将冷凝器内抽真空至绝对压力1～3KPa并保持，通入7℃冷却水，将换热管内的水蒸气冷凝为水，并开启冷凝水阀门排出水，以将换热管内的水全部排出。
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