Mechanical behaviors of coal surrounding horizontal wellbore during drilling process considering the effects of loading rate, pore pressure and temperature

Abstract Coal is a kind of rock with the characteristics soft structure, developed joints, cleats, cracks, and pores, resulting in that its mechanical behaviors are highly sensitive to stress, pore coalbed methane (CBM, gas) pressure temperature. Thus, due variations temperature caused by drilling operation, coal surrounding wellbore can be easily damaged, which would cause serious instability problems. In this presented work, stress path loading axial unloading confining (LAS-UCP) was first determined based on redistribution horizontal CBM reservoir during process. A series triaxial compression tests LAS-UCP then conducted study effects rate, coal. The results show that: (1) Under path, deformation divided into elastic stage, plastic reduction stage. With decrease rate increases temperature, stage becomes shorter, more significant, slower, shows features plasticity ductility. (2) increasing compressive strength apparent modulus increase linearly, absolute values strain, radial strain volumetric at peak grow gradually, but Poisson’s ratio changes irregular. (3) pressure, strength, have no change rule, gradually. (4) reduce linearly. not only provide guidance for safety operation reservoir, also important significance other engineering constructions related seam.