Drilling Fluid Density Design Method Considering Uncertainty of In-situ Stress in Coal Seam

Abstract

The invention relates to a drilling fluid density design method with consideration of uncertainty of coal seam ground stress. The drilling fluid density design method comprises the following steps of drilling a target coal seam of an area to be drilled to take out a large rock core, and determining a rock type coefficient and a geological intensity index of the coal rock; carrying out experimental sample machining on the obtained large rock core of the coal seam to manufacture multiple groups of standard columnar coal rock core samples; carrying out a rock mechanics parameter test on the manufactured coal rock cores by utilizing a uniaxial compression test machine, wherein the tested parameters comprise elasticity modulus, Poisson ratio and uniaxial compressive strength of the coal rock; establishing a Hoek-Brown criterion of the coal rock; determining distribution intervals of the horizontal maximum main stress and the horizontal minimum main stress of the coal seam; and giving out a coal seam drilling fluid design density formula according to the established Hoek-Brown criterion of the coal rock. According to the drilling fluid density design method with consideration of the uncertainty of the coal seam ground stress, which is disclosed by the invention, the shortages of a drilling fluid density design with ignorance of the uncertainty of the coal seam ground stress in the prior art are solved, so that the value of the drilling fluid density design is more approximate to the true value.

Description

technical field [0001] The invention belongs to the field of coalbed methane drilling engineering, and in particular relates to a drilling fluid density design method considering the uncertainty of coal seam stress. Background technique [0002] In the process of coalbed methane drilling, the accuracy of drilling fluid density design directly determines the stability of coalbed wellbore, which in turn affects the risk of coalbed methane drilling. At present, scholars at home and abroad have made a series of achievements in the research on the density design of reservoir drilling fluid. Addis, Maloneys et al. used simulation tests to study wellbore stability; Hojka, Maury et al. discussed the influence of temperature on wellbore stability. Deng Jingen, Wei Baohua, Liu Yushi and others considered the high temperature, high pressure, seepage and other conditions of the borehole wall, combined with the Mohr-Coulomb criterion, gave a fixed value solution for the drilling fluid d...

AI Technical Summary

Problems solved by technology

However, these models all have certain shortcomings, that is, they ignore the uncertainty characteristics of reservoir stress, which affects the accuracy of the design value of drilling fluid density to a certain extent.

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