Aerated underbalanced drilling method for coal-bed gas

Abstract

The invention relates to an aerated underbalanced drilling method for coal-bed gas, which comprises the following steps of: drilling a vertical well; drilling a horizontal well with a vertical channel and a horizontal channel; drilling a drilling vertical shaft in the horizontal channel and injecting drilling fluid into the drilling vertical shaft simultaneously to wash away rock debris and the like until the horizontal channel is communicated with the lower end of the vertical well; injecting gas into the vertical well while drilling the drilling vertical shaft and making the gas mixed with the drilling fluid injected from the horizontal well to obtain first gas-fluid two-phase flow; stopping injecting the drilling fluid from the horizontal well during preparation work of drilling a next drilling vertical shaft and injecting the drilling fluid into the vertical well while keeping injecting the gas into the vertical well to form second gas-fluid two-phase flow; after finishing the preparation work, stopping injecting the drilling fluid into the vertical well and injecting the drilling fluid from the horizontal well in the process of drilling the next drilling vertical shaft; and repeating the steps after finishing drilling operation until the drilling process of the coal-bed gas horizontal well is finished. The method can effectively prevent the rock debris from sinking to bury a drilling tool when the pump of the horizontal well is stopped.

Description

technical field [0001] The invention relates to an air-inflated underbalanced drilling method for coalbed methane, that is, a vertical well is drilled first, and then a horizontal well is drilled at a conventional distance from the vertical well, for example, 100-350 meters apart. Background technique [0002] In coalbed methane aerated underbalanced drilling engineering, usually a vertical well is drilled at the position where coalbed methane is to be exploited, and then a multi-lateral horizontal well is drilled at a conventional distance from the vertical well, such as about 100-350 meters. When starting to drill a horizontal well, first drill down from the ground in the vertical direction. After reaching a certain depth, the deflection gradually transitions to extend along the horizontal direction towards the vertical well. When the horizontal well is connected to the vertical well, continue to the target coal seam. Drilling and forming a multi-branch horizontal well, wh...

AI Technical Summary

Problems solved by technology

During the pump stop period, there is no drilling fluid flow in the horizontal channel of the horizontal well, which will cause cuttings that cannot be washed away by the drilling fluid and sink to landfill the drilling tool, affecting the next drilling work

If there are too many rock cuttings that sink down before the pump is turned on again, these rock cuttings will accumulate, and the rock cuttings cannot be washed away when the pump is turned on again, causing the drilling tool to be buried and stuck drill

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