Study on Change Rules of Factors Affecting Gas Loss during Coalbed Air Reverse Circulation Sampling

Demin Chen,Wei Long,Rui Zhang,Yanyan Li,Jia Lin

doi:10.1155/2021/5550726

Abstract

The gas loss in sampling is the root of coalbed gas content measurement error. The pressure and particle size have a significant impact on the gas loss. Using the self-developed coal particle pneumatic pipeline transportation experimental system, this study investigated the pressure and particle size changes in the sampling pipeline. It is found that the sampling process can be divided into four stages: no flow field stage, sample outburst stage, stable conveying stage, and tail purging stage. The extreme pressure in the sampling pipeline appears at the sample outburst stage; and the pressure in the pipeline has levelled off after sharp decrease in the stable conveying stage. It is also found that the extreme pressure increases first and then decreases with the increase of particle size. The duration of outburst stage is negatively correlated with particle size, and that of stable conveying stage is positively correlated with particle size. In addition, the results show that the loss rate of 1–3 mm particles is the smallest after the test but that particles less than 1 mm increase by about two times and particles greater than 3 mm decrease by more than three times. The study also shows that the particle size distribution of coal samples is a single peak with left skew distribution, and the gas reverse circulation sampling test does not change the location of the peak but makes it higher and sharper. The single size coal sample is more likely to collide than the mixture. This study can help to advance the understanding of impact factors on gas loss during reverse circulation sampling.

Highlights

Gas content has been recognized as the basic parameter of gas disaster prevention as well as coalbed methane resource development and applications [1,2,3]
Pressure Characteristics in the Pipe during Mixed Coal Sample Tests. e pressure change in the air reverse circulation sampling pipeline is the result of the kinetic energy transfer between gas and particles, as well as the conversion of the gas phase kinetic energy and pressure potential energy
E whole test process can be divided into four stages: no flow stage, sample outburst stage, stable conveying stage, and Sample location: Xintain Colliery

Summary

Introduction

Gas content has been recognized as the basic parameter of gas disaster prevention as well as coalbed methane resource development and applications [1,2,3]. Is gradually led to the development of a method to reverse the amount of gas loss in the sampling process by using these calculation models. These methods are based on the condition of fixed particle size and pressure and do not consider the influence of pressure and particle size change on gas loss during sampling. E air reverse circulation sampling technology is a method that brings the coal sample at the bottom of the hole to the surface from the central channel of the drill pipe with the help of compressed air [23] It is currently the most commonly used sampling method in coal seam gas content measurement. The change rules of pressure and particle size were experimentally studied, aiming to reveal the change rules of pressure and particle size during reverse circulation sampling and provide the basic theory for the establishment of a more accurate gas loss compensation model

Materials and Methods

Pressure Variation during the Process of Sampling

Particle Size Variation during the Process of Sampling

Conclusions