Simulation study on borehole stability of branch horizontal wells in coal bed

By applying branch horizontal well techniques to the development of coal-bed methane (CBM) reservoirs, the perwell yield and the degree of reserves recovery will be increased, good economic results will be obtained. The key technology to drillbranch wells is how to make sure the mechanics integrality, waterpower integrality, and reentering ability in the joint of embranchment.According to the mechanical properties of coal bed, a finite element model for studying branch wells is set up by use of the finiteelement mechanics theories. The hole stability of coal-bed branch horizontal wells is analyzed. Results show that horizontal wells havestress concentration in hole connecting sections and the concentration gets more serious as the pressure difference increases when theangle between the horizontal well hole and the main well hole is 15°. It is possible to result in failure and damage to the connectingsections, as the pressure difference increases. By comparing the different results when the angles are 60º and 15º respectively, it isfound that the hole gets more stable when the angle increases. The result is of great significance to the protection of reservoir drilling,completion, production and design of CBM wells, it can be further applied.