Simulation study on wellbore instability of horizontal wellbore in deep interbedded gangue combined coal rock

doi:10.16265/j.cnki.issn1003-3033.2025.11.1468

Abstract

Abstract:

To address wellbore instability caused by differences in the physical-mechanical properties of coal-rock and gangue seams, this study established a numerical model for borehole collapse in deep horizontal wells with composite coal-rock layers. The model leveraged triaxial compression test data on coal-rock and gangue mechanics, integrating composite material failure criteria with poroelastic coupling equations. This model was used to simulate how coal-gangue configurations affect peripheral collapse pressure in horizontal wells and analyze the influence of interface positioning and dip angles on collapse pressure distribution. The results show that significant differences in mineral composition ratios between coal and gangue create compromised cementation strength at interfaces, where coal samples fracture more readily due to lower strength. Disparities in physical-mechanical properties and weak interfacial bonding cause pronounced pressure discontinuity at contacts when drilling traverses varied composites. While interface position dictates coal-gangue collapse pressure differentials, dip angle variations not only modulate peak collapse pressure magnitudes but also trigger migration of extreme-value locations along the borehole wall.

Key words: interbedded gangue combined coal rock, contact surface, horizontal well, wellbore stability, collapse pressure

CLC Number:

X936

WANG Heyuan, FENG Fuping, ZHANG Jianwei, HAN Xu, ZHANG Yuhao, YANG Donglin. Simulation study on wellbore instability of horizontal wellbore in deep interbedded gangue combined coal rock[J]. China Safety Science Journal, 2025, 35(11): 122-130.

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参数	数值
最大水平地应力/MPa	64.83
最小水平地应力/MPa	54.75
上覆岩层压力/MPa	69.24
地层压力/MPa	41.16
煤岩密度/(g·cm³)	1.54
煤岩渗透率/μm²	0.047×10^-3
煤岩孔隙度/%	6.09
煤岩黏聚力/MPa	2.92
煤岩内摩擦角/(°)	8.51
煤岩杨氏模量/GPa	2.8
煤岩泊松比	0.31
夹矸密度/(g·cm³)	2.53
夹矸渗透率//μm²	0.012×10^-3
夹矸孔隙度/%	4.8
夹矸黏聚力/MPa	11.633
夹矸内摩擦角/(°)	30.69
夹矸杨氏模量/GPa	7.3
夹矸泊松比	0.16
接触面黏聚力/MPa	0
钻井液黏度/(mPa·s)	20