Coal seam well wall stability analysis method under multi-factor coupled effect

An analysis method and stability technology, which are applied in the field of wellbore stability analysis and drilling mud density window calculation, can solve the problems that it is difficult to reflect the real situation of coal seam drilling wellbore stability, and the mud density is difficult to work.

Inactive Publication Date: 2016-03-16
CHINA UNIV OF PETROLEUM (BEIJING) +1
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Problems solved by technology

[0005] In summary, the results obtained from the existing coal seam wellbore stability analysis are difficult to reflect the real situation of coal seam drilling wellbore stability, and the calculated mud density is difficult to be effective in the actual drilling process

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  • Coal seam well wall stability analysis method under multi-factor coupled effect
  • Coal seam well wall stability analysis method under multi-factor coupled effect
  • Coal seam well wall stability analysis method under multi-factor coupled effect

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Embodiment Construction

[0037] A coal seam well wall stability analysis method under the coupling effect of multiple factors proposed by the present invention is described as follows in conjunction with the accompanying drawings, taking the well wall stability analysis of a coal bed methane well as an example.

[0038] According to attached figure 1 As shown, the first to third steps of the method proposed by the present invention are to collect relevant geological data of the target well and conduct indoor experiments on cores to obtain relevant physical and mechanical properties of the target coal seam. This example considers a vertical well in Qinshui Basin, Shanxi, the target reservoir depth is 717.5m, the drill bit size is 219.5mm, the elastic modulus of coal rock is 2.50GPa, Poisson’s ratio is 0.33, the peak cohesion and internal friction angle are respectively is 2.5MPa and 35.0°, the overburden pressure is 18.6MPa, the horizontal maximum and minimum principal stresses are 17.7MPa and 12.9MPa ...

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Abstract

The invention discloses a coal seam well wall stability analysis method under a multi-factor coupled effect and belongs to the technical field of coal seam drilling engineering. A well wall is quite unstable because of low strength, large brittleness and remarkable anisotropism of coal rock. An existing coal seam well wall stability analysis method is incapable of reflecting a coal seam stress-damage-seepage coupling process; the calculated mud density is hard to be effective during a practical drilling process. The invention develops the coal seam well wall stability analysis method under the multi-factor coupled effect based on elastoplasticity of a porous medium, a seepage flow theory and a corresponding finite element numerical method; the method is used for accurately predicting the shape and size of collapsed and damaged coal rock around the well under the coupled effect of a plurality of factors such as stress, damages and seepage, providing a limit of the size of a collapsed area of the well wall according to the practical drilling situation of a target coal seam, and determining a corresponding coal seam drilling safe mud density window. The method disclosed by the invention is high in calculation accuracy and good in prediction effect; a designed drilling mud density plays an effect of stabilizing the well wall during on-site drilling and also plays a reservoir protection effect.

Description

technical field [0001] The invention relates to the technical field of wellbore stability in coalbed methane drilling, in particular to a wellbore stability analysis and a corresponding drilling mud density window calculation method applicable to multi-factor coupling in the coal reservoir drilling process. Background technique [0002] Coal is an organic rock transformed by ancient plant remains buried underground and undergoing long-term biochemical and geological processes. In the formation process of coal rocks, various geological factors lead to the development of a large number of fractures in the coal body, such as the cleat fractures formed by shrinkage internal stress due to the loss of volatile matter and water during coalification, and the shear fractures formed under the action of crustal movement. or tensile cracks. The existence of a large number of various fractures makes the macroscopic properties of coal and rock show low strength, high brittleness, signifi...

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): E21B49/00
CPCE21B49/00E21B49/005
Inventor 邓金根刘伟蔚宝华汪伟杨恒林田中兰
Owner CHINA UNIV OF PETROLEUM (BEIJING)
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