Method for Determining Effective Drainage Radius Based on Gas Emission Characteristics of Perforated Boreholes

Abstract

The invention discloses a calculation method for measuring an effective extracting radius based on crossing hole gas emission characteristics. The method comprises the following steps: 1) constructing a crossing hole; 2) drawing boring gas emission quantity change curve according to test data; 3) performing fitting analysis on boring natural gas emission time-varying curve, and determining a gas emission quantity attenuation coefficient; 4) performing integral computation on total gas emission quantity in effective boring gas emission time; 5) determining the residual gas content in a limit extracting radius area; 6) resolving the limit extracting radius; 7) determining an effective influencing radius of boring gas natural emission according to gas pressure boundary indicators, namely the crossing-hole effective extracting radius. According to the method disclosed by the invention, on one hand, only a single crossing hole needs to be constructed, and the effective extracting radius is calculated through theoretical analysis by taking a boundary gas pressure critical value as a determination index; on the other hand, later data processing is simpler and rapider, and the effective extracting radius can be obtained without an extraction system.

Description

technical field [0001] The invention belongs to the technical field of coal mine safety in the aspects of gas drainage and prevention of coal and gas outburst, and in particular relates to a calculation method for determining the effective drainage radius based on the characteristics of gas gushing out through a layer-crossing borehole. Background technique [0002] When coal mines use boreholes to pre-extract coal seam gas, under the joint action of coal seam gas pressure and hole bottom negative pressure, the gas in the coal body around the borehole continuously enters the borehole and is pumped away, forming a similar circle with the centerline of the borehole as the axis. The size of the drainage influence circle is called the drainage influence radius, which refers to the distance between the boundary point and the center of the drainage borehole when the original gas pressure and gas content of the coal seam are affected and begin to decline within a specified period of...

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Problems solved by technology

Compared with the single-hole test method, the above-mentioned measurement method has a large amount of drilling and requires more equipment, and the sealing effect directly affects the reliability of the test results, and this type of method is based on observation and comparison, and the observation hole cannot be guaranteed to be accurate. Arranged on the effective sampling boundary, thus greatly affecting the accuracy of the determination

[0004] It is still a difficult problem to obtain the effective drainage radius of boreholes through theoretical analysis and numerical simulation methods, mainly because the establishment of mathematical models of gas flow around coal seam boreholes is relatively complicated. ; The gas pressure distribution in the radial flow field is in line with the gas pressure distribution around the layer-crossing drilling. Based on Darcy's law, the differential equation of the gas flow around the layer-crossing drilling can be deduced, and the radial gas flow field definite solution can be obtained through a series of mathematical treatments. The approximate analytic solution of the method is used to derive the calculation formula of the effective radius of influence of the drilled hole, and the effective radius of influence is obtained by combining the gas flow observation data of the drilled hole on site. However, this process is relatively complicated and many parameters need to be measured. In engineering applications not easy enough

Because the coal seam gas pressure testing technology still has many deficiencies, it is difficult to avoid the errors caused by the gas pressure testing problems in these methods of measuring the drilling gas pressure as a reference index, such as the pressure drop method and the content index method

The computer simulation method often needs to set boundary conditions based on many assumptions, establish a gas flow field model around the borehole, and perform programming simulation to determine the effective drainage radius. However, these assumptions are too idealized and have a large deviation from the actual situation.

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