Layered pressure control combined drainage device for double coal seams that are prone to powder and sand discharge

Abstract

The invention relates to a layered pressure control combined drainage-production device for double coal-beds prone to dust and sand spraying. Two drainage pumps are generally combined and used for simultaneous mining of two coal-beds. In case of the coal-beds prone to dust and sand spraying, coal dust and sand enter a suction inlet of the upper drainage pump easily, failure rate of the drainage pump is increased, and workover cycle is shortened. The layered pressure control combined drainage-production device for double coal-beds prone to dust and sand spraying comprises a drainage pump, an oil tube and a sucker rod. The oil tube comprises an upper oil tube and a lower oil tube. A centralizer is disposed on the outer wall of the upper oil tube. The device is characterized in that the drainage pump is a pump for separated zone operation, and a packer and an auxiliary communicating tube are disposed on the lower oil tube. By the use of the pump for separated zone operation, combined mining of the double coal-beds is achieved, the device is more applicable to double coal-beds prone to dust and sand spraying, the failure rate of the pump for separated zone operation is decreased and pump maintenance cycle is prolonged.

Description

technical field [0001] The invention belongs to the technical field of coal bed gas drainage and production, and relates to a layered pressure control combined drainage device for double coal seams that are prone to powder and sand discharge. Background technique [0002] In the process of drainage and gas production of CBM wells, the change of coal reservoir stress is a complicated process. As the depressurization continues, there will be a stress difference effect. When the effective stress increases to a certain value, the permeability of the coal reservoir will drop to a state where it is difficult for the coal seam water to flow. During single coal seam drainage, the pressure can be avoided by reasonably controlling the drainage speed and the position of the dynamic liquid surface. The difference effect will damage the coal reservoir, but in the actual development, the coalbed methane well often encounters two coal seams. If the pressure gradient of the coal reservoir ...

AI Technical Summary

Problems solved by technology

When the effective stress increases to a certain value, the permeability of the coal reservoir will drop to a state where it is difficult for the coal seam water to flow. During single coal seam drainage, the pressure can be avoided by reasonably controlling the drainage speed and the position of the dynamic liquid surface. The difference effect will damage the coal reservoir, but in the actual development, the coalbed methane well often encounters two coal seams. If the pressure gradient of the coal reservoir is inconsistent or the distance between the coal seams is large, the upper coal seam usually produces gas first. As the liquid level drops, the coal seam below begins to produce gas. It is difficult to ensure that the two coal seam production layers desorb and produce gas at the same time. Particle-embedded coal seams and faster fracture closure rate lead to a rapid decline in coal seam permeability and seriously affect gas production

At the same time, for coal seams that are prone to powder and sand discharge, the suction port of the upper extraction pump is easy to enter coal powder and sand particles, which will shorten the pump inspection period of CBM wells

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