Coalbed methane horizontal well underbalance drilling system and method thereof

Abstract

The invention discloses a coalbed methane horizontal well underbalance drilling system and a method thereof. The coalbed methane horizontal well underbalance drilling system comprises a casing pipe, adrill rod, a fluid director, a top drive, degassing valves, a water-gas mixing supply unit and a three-phase separator. According to stable underbalance drilling, the displacement and the pressure ofcompressed air are adjusted according to the displacement and the pressure of drilling fluid, a certain proportion of compressed air is injected into the drill rod, and the compressed air is separated from a coal seam borehole far away from the position of a drill bit through the set of degassing valves installed on the drill rod and rapidly expands. Expanded air bubbles ascend and continuously expand, the expanded air bubbles can replace or discharge drilling fluid with the same volume, and the density of the compressed air bubbles is far smaller than that of the drilling fluid, so that thedensity of a fluid in an annulus channel is reduced, and the pressure of an annulus liquid column acting on the coal seam borehole is reduced; and in this way, an underbalance or near-balanced drilling state that the pressure of the annulus liquid column acting on the coal seam borehole is smaller than or approximately equal to the coal seam gap pressure is formed.

Description

Technical field [0001] The present invention relates to the technical field of coal-bed methane mining, and more specifically, to a drill pipe that opens and closes downhole degassing valves through pump pressure control by installing a set of drill pipes far away from the drill bit when drilling a horizontal well in a coal seam. An underbalanced drilling system and method for injecting compressed air into an air compressor to realize horizontal wellbore stability in a coal seam. Background technique [0002] In the field of coalbed methane development, there is a horizontal well that is drilled in the coalbed without fracturing to achieve coalbed methane extraction. Since most coal seams are coal seams with low porosity, low permeability and low reservoir pressure, the drilling fluid and pulverized coal generated during drilling enter the coal seam under the action of the annular liquid column pressure and cause blockage. The gas production of horizontal wells has no commercial...

AI Technical Summary

Problems solved by technology

The solid-free clean drilling fluid undoubtedly reduces the intrusion pollution of solid-phase additives on low-pressure coal seams. For coal seams with high permeability and high pore pressure, this method has less pollution to coal seams and can obtain ideal gas production. In the coal seam with low reservoir pressure, the coal powder produced during drilling enters the coal seam with the loss of drilling fluid and blocks the micro cracks in the coal seam, which will cause great damage to the coal seam

Although the micro-bubble solid-free drilling fluid can partially reduce the pressure of the annular fluid column on the coal seam, the leakage of the drilling fluid still causes serious pollution to the coal seam, especially the chemical additives used in the micro-bubble drilling fluid, which cause more serious damage to the coal seam , even causing horizontal wells to fail to produce gas

Although the underbalanced drilling technology of drill pipe gas addition can realize underbalanced drilling for high-rank coal and highly consolidated coal seams, it is not used for most low-rank coal seams and soft and fractured coal seams because these coal seams are easy to drill. Collapse, coupled with the fact that the compressed air bubbles will rapidly expand after flowing out of the drill bit to form a shock wave, causing continuous impact on the coal, making the wellbore of the coal seam that is prone to collapse more unstable, the collapse is more serious, and even the drilling tool is stuck, causing drilling not working

[0005] Injecting compressed air through vertical wells docked at the proximal end is a relatively successful method for realizing underbalanced drilling of horizontal wells in coal seams. However, the cost of this process is relatively large, because the construction cost of a near-end vertical well costs nearly 1.5 million yuan, and the drilling cost increases by nearly 20%

At the same time, its structure is complex and the docking construction is difficult

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