煤层割理结构及其对井壁稳定的影响研究

doi:10.13809/j.cnki.cn32-1825/te.2020.04.007

Abstract

Abstract:

In order to illustrate the influences of the in-situ stress heterogeneity and cleat angle on wellbore stability of coal seam, the following researches have been done. The basic physical properties, mechanical parameters, macro and micro structure of cleats and in-situ stress states of coal and rock in an area have been acquired. Based on the discrete element numerical simulation method, comprehensive evaluation and analysis of the in-situ stress heterogeneity and cleat angles on wellbore stability in coal seam has been conducted by two kinds of evaluation method i.e. the maximal displacement and normalized the plastic area radius. The results of the numerical simulation show that under the condition of isotropic in-situ stress, cleat angle has little influence on the borehole stability. With the increases of the heterogeneity of in-situ stress, the influence of cleat angle on borehole stability is becoming more and more obvious. The maximum displacement around the well increases first and then decreases with the increase of the cleat angle from 0° to 90°. Meanwhile, with the increase of in-situ stress heterogeneity, the anisotropy of the radius of the circumferential plastic area caused by the change of cleat angle becomes more obvious. Therefore, the influence of cleat angle on wellbore stability should not be ignored in coal and rock strata with great difference in in-situ stress. The research results can provide reference for the drilling plan design of vertical and horizontal wells of coal seam in the study area.

Key words: coal seams, borehole stability, in-situ stress, heterogeneity, cleat angle

CLC Number:

TE122

WANG Yuepeng,SUN Zhengcai,LIU Xiangjun,LIANG Lixi. Study on cleat structure and its influence on wellbore stability in coal seams[J].Reservoir Evaluation and Development, 2020, 10(4): 45-52.

Figures/Tables 8

Fig. 1

Fig. 2

Table 1

Mechanical strength parameters of coal and rock"

模拟参数	煤岩	面割理	端割理
密度 $ρ$ /（kg·m^-3）	1.36×10³
体积模量 $K$ /MPa	5.11×10³
剪切模量 $G$ /MPa	2.36×10³
内聚力 $C$ /MPa	7	0	0
内摩擦角 $?$ /（゜）	29.63	26.00	26.00
抗拉强度 $σ$ /MPa	2.0	0	0
法向刚度/MPa		2.0×10⁴	2.0×10⁴
切向刚度/MPa		1.0×10⁴	1.0×10⁴

Table 1

Fig. 3

Fig. 4

Fig. 5

Fig. 6

Fig. 7

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Study on cleat structure and its influence on wellbore stability in coal seams

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