Alternate cooling and heating yield increasing method for gas extraction bored well

Abstract

The invention provides an alternate cooling and heating yield increasing method for a gas extraction bored well. The method comprises the following steps: sequentially feeding a gas extraction pipe and a gas injection pipe into a ground bored well; opening a valve II and injecting a large amount of clear water into the ground bored well through the gas injection pipe so as to enable the water to enter gaps in coal layers at the periphery of the ground bored well; injecting compared air with the pressure of 1-2MPa into the ground bored well through the gas injection pipe and discharging the clear water in the ground bored well through the gas extraction pipe; injecting cold air into the ground bored well through the gas injection pipe; closing the valve II, and keeping for 2-5 days so as to enable the water in the coal layers to be fully iced by cold energy; injecting high-temperature nitrogen gas into the ground bored well through the gas injection pipe so as to enable ices to be thermalized into water vapor and discharging the water vapor through the gas extraction pipe; closing a valve I and the valve II so as to enable ices in the gaps to be fully de-frozen; opening the valve I and the valve II so as to reduce the internal temperature of the ground bored well to normal temperature; injecting compressed air with the pressure of 5-10MPa into the ground bored well through the gas injection pipe so as to discharge water in the bored well; closing the valve II and starting to extract gases in the coal layers.

Description

technical field [0001] The invention relates to a method for increasing production by alternating cooling and heating for gas drainage drilling, and relates to a method for expanding coal body fissures and increasing gas drainage volume. Background technique [0002] In the 1970s, the United States took the lead in the world to carry out the gas extraction project of ground drilling. Due to the good air permeability of coal seams in the United States, the ground pre-extraction of gas has achieved great success. By 2004, the gas production reached 50 billion m 3 ; In addition, countries such as Australia, Germany, the former Soviet Union and the United Kingdom successively used ground drilling technology to extract gas, and achieved good results. In the late 1970s, my country began to carry out ground drilling gas drainage tests. More than 40 ground pre-drainage wells were constructed mainly in Fushun, Yangquan, Jiaozuo and Baisha mining areas, and hydraulic fracturing tests ...

AI Technical Summary

Problems solved by technology

In nearly 20 years of national trials, the overall effect of gas drainage is poor

The experience of gas pre-extraction from surface drilling in the United States shows that the coalbed methane development area generally requires that the permeability of the coal seam is not lower than 9.87×10 -15 m 2 , but in my country, coal-bearing strata have generally experienced strong tectonic movements after coal formation, the endogenous fracture system of the coal seam has been destroyed, and the plasticity has been greatly enhanced, thus becoming a highly plastic structure with low permeability, resulting in generally low coal seam permeability , usually less than 9.87×10 -15 m 2 , so the low permeability of the coal seam is the main reason that limits the effect of gas pre-extraction by ground drilling in my country

[0004] In order to improve the permeability of coal seams, hydraulic fracturing technology is generally used for coal seam anti-permeability treatment, but related research results show that: the cracks produced by hydraulic fracturing mainly expand along the direction perpendicular to the minimum principal stress, and the number of cracks produced is small, making it difficult to form relatively large fractures. Long fractures, failed to produce bulk fracture effect on coal seam storage, and also have the disadvantage of high fracturing fluid pressure

At present, the application effect of this technology in most mining areas in my country is not ideal, and the relevant technical processes need to be further studied. At the same time, it is urgent to develop a new method for increasing the production of surface drilling gas, so as to enrich my country's technical system for efficient extraction of coal seam gas by surface drilling

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