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Application of Under-balanced Drilling Technology in CBM Horizontal Well Construction
Pages: 62-64
Year: Issue:  7
Journal: Coal Geology of China

Keyword:  CBMhorizontal wellmulti-branchunder-balanced drillingtechnical measures;
Abstract:  To prevent coal seam reservoir from damage and pollution, the under-balanced drilling technology is widely used in CBM horizontal well construction at present. This operation is after the connection of horizontal well and vertical well in the coal seam;through vertical well gas injection, lowering down multi-phase fluid column hydrostatic pressure in annular space around horizontal and vertical wells and realized under-balanced drilling. The paper has summarized problems existed and means of settlement in CBM un-der-balanced drilling, the one is because of circulation system instability (pressure fluctuation) caused by round trip pump stopping dur-ing drilling process, arising unstable wall and easy to collapse, this can be settled through site continuous gas injection via vertical well, but gas volume should be adjusted properly; the another is when compressor air output unable to adjust, the air output adjustment should be controlled mainly through by-pass valve opening size. The study has accumulated valuable experience for CBM under-bal-anced drilling technology possible applications in the area.
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