A method for intensifying shale gas recovery by freezing and thawing cycles with large temperature difference

Abstract

The invention discloses a method for enhancing shale gas exploitation through a large-temperature-difference freeze-thaw cycle. The method comprises the following steps of firstly, injecting magnetized water into a shale gas exploitation pipe of a shale gas well through pulsation; secondly, driving the magnetized water to move into shale as much as possible through high-pressure nitrogen, and thenconducting liquid-nitrogen freezing and high-temperature nitrogen melting on the magnetized water several times to fully utilize the permeability of the magnetized water, the driving property of thehigh-pressure nitrogen, the expansion force of the frozen magnetized water and an ultra-large-temperature-difference freeze-thaw cycle formed by the liquid nitrogen and the high-temperature nitrogen in order to cause complete cracking of the shale. Moreover, the high-temperature nitrogen can also provide energy for the shale gas to be separated from the shale, correspondingly the cracking effect of the shale can be effectively improved, the crack expansion range of the shale can be effectively expanded, and the shale permeability is increased, so that large-flow, high-concentration and long-time exploitation of the shale gas is improved.

Description

technical field [0001] The invention relates to a method for intensifying the exploitation of shale gas, in particular to a method for intensifying the exploitation of shale gas with a large temperature difference freeze-thaw cycle. Background technique [0002] Shale gas is natural gas extracted from shale formations, and its composition is mainly methane. It is an important unconventional natural gas resource. my country's shale gas resource reserves are abundant. The geological resource potential of shale gas in land areas is 134.42 trillion cubic meters, and the recoverable resource potential is 25.08 trillion cubic meters. The mining life and growth cycle are long. Therefore, the commercial exploitation of shale gas is expected to improve the current situation that my country's conventional natural gas resources cannot be self-sufficient. [0003] The main method of existing shale gas exploitation is to rely on its own desorption. After a period of gas extraction, the ...

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Problems solved by technology

This method has the following problems: ①Although seepage channels are added to allow part of the desorbed shale gas to flow out, it does not fundamentally accelerate the desorption of adsorbed shale gas, and the effect of increasing production is limited; Shale gas distribution areas with water and water shortages cannot be exploited by this technology, and water resources are wasted; ③The maximum fracture initiation pressure for shale hydraulic fracturing is 140MPa, but the number of main cracks formed is limited, and it is difficult to enter the shale. It is difficult to effectively increase the recovery rate in shale due to the tight pores of shale; ④The chemical additives in fracturing fluid enter the groundwater, which seriously damages the ecological environment

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