Study on borehole stability under different spatial angles in three-dimensional stress field
LIU Hongtao
HAN Zijun
HAN Zhou
GUO Linfeng
HAN Xiangyang
LIU Qinyu
CHEN Zihan
ZHANG Rongguang
Abstract：In order to explore the influence of different spatial angles on the stability of bore-holes,the mechanical properties of rock masses with different borehole angles were investigated based on uniaxial and triaxial tests.The mechanical calculation models of boreholes with different spatial angles in three-dimensional stress field were established.Based on the Euler transformation,the relationship between the in-situ stress coordinate system,the spatial rectangular coordinate system and the borehole column coordinate system was estab-lished.Combined with the three-dimensional expression form of Mohr-Coulomb strength crite-rion,the implicit equation of plastic zone boundary of borehole surrounding rock under different spatial angles in three-dimensional stress environment was derived.The second invari-ant J 2 of the deviatoric stress tensor of the comprehensive stress index describing the stress distribution characteristics around the borehole was sought.By changing the inclination angle and azimuth angle,the size and shape distribution characteristics of the borehole circumferential deviatoric stress J2 under different schemes were studied,and the distribution range and shape of the plastic zone under different spatial angles were analyzed.The corre-sponding relationship between deviatoric stress J 2 and plastic zone was established,and the es-sence of deformation and failure of surrounding rock was revealed.Based on the theoretical a-nalysis,the engineering application guidance was put forward.The results show that there are different degrees of stress concentration around the borehole under different spatial angles,which leads to great differences in the strength characteristics and acoustic emission character-istics of rock mass.Under different inclination angles and azimuth angles,there are great differences in the degree of deviatoric stress concentration around the borehole.The change of inclination angle and azimuth angle has an important influence on the angle of the maximum concentration position of J 2 around the borehole.The J 2 stress expansion angle under different schemes is completely consistent with the polar angle corresponding to the maximum J 2 around the borehole,and the J2 stress deflection angle is basically stable at 38°-42°.There are great differences in the degree of damage,the maximum size of damage expansion and the fail-ure mode of the plastic zone of the borehole under different well inclination angles and azimuth angles.The morphological evolution law of the deviatoric stress J2 isoline is consistent with the morphological evolution law of the plastic zone.At different spatial angles J 2 and the plastic zone morphology,the asymmetric expansion characteristics of'butterfly single wing expansion'are presented,and the angle difference between the maximum failure position of the plastic zone and the maximum concentration position of the deviatoric stress J 2 under dif-ferent schemes is 3°-5°.The research results have important theoretical significance and refer-ence value for coal seam gas extraction and borehole pressure relief.
Keywords：borehole stress distributionthe stability of surrounding rockplastic zonethe second invariant of deviatoric stress J2coordinate transformationdrilling inclination
Publication Date：2024-09-30
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：18( 925-942 )