CN-121976780-A - Underground in-situ high-temperature gas fracturing and supporting integrated system and operation method thereof

CN121976780ACN 121976780 ACN121976780 ACN 121976780ACN-121976780-A

Abstract

The invention provides an underground in-situ high-temperature gas fracturing and supporting integrated system and an operation method thereof, and relates to the technical fields of unconventional natural gas exploitation and coal mine gas control. The system includes a surface monitoring supply unit, an integrated downhole tool string, and a composite umbilical. Firstly, high-temperature inert gas generated by chemical reaction is utilized to carry out thermal shock embrittlement on the coal body, then the coal body is modulated into pressure pulse waves to carry out brittle motion fatigue crack extension, and simultaneously, a thermal expansion polymer propping agent accurately triggered by temperature is synchronously injected, so that the time-space synchronization of fracturing and supporting is realized. The invention solves the problems of limited complexity and difficult proppant migration of the traditional gas fracturing cracks by a continuous process of high-temperature embrittlement, fatigue expansion and intelligent support and by means of distributed optical fiber sensor real-time monitoring and closed-loop regulation, can efficiently form a complex crack network with durable diversion capability, and remarkably improves the gas extraction efficiency and the coalbed methane recovery efficiency of the hypotonic coalbed.

Inventors

HOU PENG
ZHANG HUIXIN
LIU QUANSHENG
ZHANG CHUANJIU

Assignees

武汉大学

Dates

Publication Date: 20260505
Application Date: 20260327

Claims (10)

1. The underground in-situ high-temperature gas fracturing and supporting integrated system is characterized by comprising a ground monitoring supply unit, an integrated underground operation tool string and a composite pipe cable for connecting the ground monitoring supply unit and the integrated underground operation tool string; The ground monitoring supply unit conveys a liquid chemical thermal reactant and a thermal expansion polymer propping agent to the integrated underground operation tool string through the composite pipe cable, wherein a distributed optical fiber sensor is arranged in the composite pipe cable and is used for monitoring temperature field change and sound wave events in real time; the integrated downhole tool string includes: The high-temperature gas in-situ generation modulation cabin is used for providing a place for the chemical reaction of the liquid chemical thermal reactant and modulating high-temperature inert gas generated after the chemical reaction into high-temperature pulse gas; The propping agent composite injection module is used for mixing the thermal expansion polymer propping agent and the high-temperature pulse gas to form mixed fluid, and injecting the mixed fluid into a target coal seam; The ground monitoring supply unit outputs a control instruction to the integrated underground operation tool string based on the temperature field change and the sound wave event so as to dynamically adjust the temperature of the high-temperature inert gas, the pulse parameters of the high-temperature pulse gas, the concentration of the thermal expansion polymer propping agent and the injection temperature of the mixed fluid.
2. The underground in-situ high-temperature gas fracturing and supporting integrated system according to claim 1 is characterized in that the number of the liquid chemical heat reactants is two, the high-temperature gas in-situ generation modulation cabin comprises a high-efficiency cyclone mixer, an adiabatic reaction chamber and a high-frequency pulse modulation valve, the high-efficiency cyclone mixer is used for uniformly mixing the two liquid chemical heat reactants, chemical reaction is carried out in the adiabatic reaction chamber after uniform mixing, high-temperature inert gas is generated, and the high-frequency pulse modulation valve is used for modulating the high-temperature inert gas into high-temperature pulse gas with specific frequency and amplitude, so that pressure pulse waves are formed.
3. The integrated downhole in-situ high-temperature gas fracturing and supporting system according to claim 2, wherein the thermal expansion polymer propping agent is a microsphere with a core-shell structure, the shell of the microsphere with the core-shell structure is a thermosetting resin coating, and the inner core is a thermoplastic polymer material.
4. A downhole in situ high temperature gas frac support integrated system according to claim 3, wherein the proppant composite injection module comprises: the venturi gas-solid mixer is used for sucking the thermal expansion polymer propping agent according to the set concentration by utilizing the negative pressure generated by the pressure pulse wave and uniformly mixing the pressure pulse wave and the thermal expansion polymer propping agent; And the temperature field regulating ring surrounds the outlet of the Venturi type gas-solid mixer and is used for regulating the outlet temperature of the uniformly mixed pressure pulse wave and the thermal expansion polymer propping agent to the glass transition temperature of the thermosetting resin coating according to the control instruction.
5. The downhole in-situ high temperature gas frac support integrated system of claim 2, wherein the pressure pulse wave has a frequency in the range of 0.5Hz to 10Hz and a temperature in the range of 200 ℃ to 500 ℃.
6. The downhole in situ high temperature gas frac support integrated system of claim 4, wherein the composite umbilical comprises a central tube and an outer tube with an annulus therebetween for transporting a liquid chemical thermal reactant, the annulus for transporting a thermally expanding polymeric proppant to the integrated downhole tool string via an inert gas.
7. The downhole in-situ high temperature gas fracturing support integrated system of claim 6, wherein the distributed fiber optic sensor comprises a distributed fiber optic temperature sensing unit and a distributed fiber optic acoustic sensing unit, the distributed fiber optic being disposed on a wall of an annulus passage.
8. The downhole in-situ high-temperature gas fracturing support integrated system of claim 1, wherein the integrated downhole tool string further comprises a downhole integrated control module and a multifunctional nozzle and monitoring module, wherein the downhole integrated control module is used for receiving the control instruction; The multifunctional nozzle and monitoring module comprises: The switchable nozzle is used for converting the mixed fluid into high-energy jet flow with a specific shape and directly acting on a coal stratum so as to realize a differentiated fracturing target; The underground high-definition camera is used for providing direct optical images of a well bore and a near-well crack area so as to perform real-time visual diagnosis; And a miniature acoustic transceiver for actively transmitting acoustic signals to the formation and receiving reflected, refracted and scattered signals therefrom for detecting invisible information of formations and fractures surrounding the wellbore.
9. The downhole in-situ high temperature gas fracturing support integrated system of claim 1, wherein the surface monitor supply unit is built with a thermal-force coupled fracture propagation model and proppant migration optimization algorithm by which control instructions are output to the integrated downhole operation tool string based on the temperature field changes and acoustic events.
10. A method of in situ frac support continuous operation employing a downhole in situ high temperature gas frac support integrated system according to any of claims 1-9, the method comprising: lowering the integrated underground operation tool string to a target coal seam design fracturing section and anchoring; generating a modulation cabin in situ through the high-temperature gas, and generating high-temperature inert gas to perform thermal shock embrittlement on the coal; Generating pressure pulse waves through a high-frequency pulse modulation valve, and simultaneously injecting a thermal expansion polymer propping agent into the propping agent composite injection module to perform cooperative operation of brittle fatigue crack expansion and support; Based on the temperature field change and the acoustic wave event, outputting a control instruction to the integrated underground operation tool string to dynamically adjust the temperature of the high-temperature inert gas, the pulse parameters of the high-temperature pulse gas, the concentration of the thermal expansion polymer propping agent and the injection temperature of the mixed fluid; after the operation of the current design fracturing segment is completed, temporary plugging steering is carried out, and the integrated underground operation tool string is moved to the next design fracturing segment for continuous operation.

Description

Underground in-situ high-temperature gas fracturing and supporting integrated system and operation method thereof Technical Field The invention relates to the technical field of unconventional natural gas exploitation and coal mine gas control, in particular to an underground in-situ high-temperature gas fracturing and supporting integrated system and an operation method thereof. Background Economic development of hypotonic coal seams relies on the formation of complex fracture networks with long term conductivity. Current anhydrous fracturing techniques, such as liquid CO 2 or nitrogen fracturing, rely primarily on hydrostatic or phase change pressures of the fluid, with the following bottlenecks: 1. The fracturing mechanism is single, the network fracture complexity is limited, the traditional cold gas fracturing mainly comprises tensile failure, a large number of closed natural cracks and layers in coal and rock are difficult to activate efficiently, and the improvement of the physical properties of coal is not deep. 2. The support efficiency is low, the long-term diversion capability is insufficient, the density of the conventional propping agent (quartz sand and ceramsite) is high, the suspension migration capability in low-viscosity gas is poor, the propping agent is extremely easy to deposit and accumulate near a shaft section of a crack, a supporting blank is formed in the depth of the crack, and the rigid propping agent is in risk of being embedded into a coal wall to be broken under the closing stress. 3. The equipment and the process are discrete, the synergy is poor, the fracturing and the propping are usually two independent working stages, even different equipment and fluids are used, the construction period is long, the cost is high, and the propping agent distribution cannot be matched with the fracture form in real time. In recent years, heat stimulated fracturing and new proppant concepts have been proposed separately. For example, electrical heating or steam is used to heat the reservoir to create thermal stresses, but the heating range is limited and the energy consumption is high. In addition, expandable resin-coated proppants have been proposed, but the expansion depends on the formation temperature, the reaction time is long and uncontrollable, and synchronous fixed-point support in the fracturing process cannot be realized. Therefore, the prior art lacks a systematic solution which can carry out collaborative operation on three mechanisms of thermal energy fracturing (non-combustion), fatigue damage and intelligent support in the same time and space through integrated equipment, so that the transformation efficiency and long-term effect of the low permeability coal seam are difficult to be obviously improved. Disclosure of Invention The invention aims to provide an underground in-situ high-temperature gas fracturing and supporting integrated system and an operation method thereof, which are used for overcoming the defects of fracturing and supporting dislocation, crack complexity and insufficient long-term diversion capability in the prior art, realizing rapid thermal shock and embrittlement of high-temperature gas (non-combustion) on coal and fatigue crack expansion under alternating load through an integrated underground operation tool string, synchronously injecting a temperature-triggered thermal expansion polymer proppant, realizing self-adaptive expansion and anchoring in cracks, and finally forming a complex and durable high-efficiency seepage channel with diversion capability. In order to achieve the above object, in a first aspect, the present invention provides an in-situ high temperature gas fracturing support integrated system downhole, comprising a ground monitoring supply unit, an integrated downhole operation tool string, and a composite pipe cable connecting the ground monitoring supply unit and the integrated downhole operation tool string; the ground monitoring supply unit conveys a liquid chemical thermal reactant and a thermal expansion polymer propping agent to the integrated underground operation tool string through a composite pipe cable, wherein a distributed optical fiber sensor is arranged in the composite pipe cable and is used for monitoring temperature field change and sound wave events in real time; the integrated downhole tool string includes: The high-temperature gas in-situ generation modulation cabin is used for providing a place for the chemical reaction of the liquid chemical thermal reactant and modulating high-temperature inert gas generated after the chemical reaction into high-temperature pulse gas; The propping agent composite injection module is used for mixing the thermal expansion polymer propping agent with the high-temperature pulse gas to form mixed fluid and injecting the mixed fluid into the target coal seam; The ground monitoring supply unit outputs control instructions to the integrated underground operation tool string based on the