Numerical analysis on fracture initiation from radial micro‐hole in anisotropy formation

Abstract

Abstract The radial jet drilling (RJD) technology is typically developed to open multiple lateral micro‐holes from a main wellbore to the formation. The multiple groups of 3D numerical models of radial micro‐holes through a main well are built by incorporating the pore hydro‐mechanical coupling effects. A number of sensitivity analyses were conducted on the effects of the radial jetting azimuth, the stress anisotropy, and the elastic anisotropy on the rock fracture initiation of the micro‐holes. As revealed from the results, the fracture initiation from the micro‐hole exhibited the diversified characteristics with the increase in the jetting azimuth of the micro‐hole. On the whole, the fracture initiation point was concentrated at the maximum principal stress. Thus, the jetting azimuth of the nozzle was recommended to be designed in the interval of 0°‐30°. A higher elastic modulus anisotropy ratio K and a lower Poisson's ratio anisotropy ratio K′ caused the significant rigidity characteristics of the rock, which increased the possibility of fracture initiation in the horizontal direction; a lower elastic modulus anisotropy ratio K and a higher Poisson's ratio anisotropy ratio K′ caused the strong rigidity characteristics, so the rock could not easily fracture in the vertical direction. Several suggestions were given that the rock is easy to be broken by selecting a smaller jetting azimuth angle and a more significant in‐situ stress difference. The numerical simulation results agree well with field experiment results, with an average accuracy of 97.17%. The proposed numerical model has a good performance in predicting the fracture initiation pressure of the radial micro‐hole in anisotropy formation.

Keywords

• elastic anisotropy
• radial jet drilling
• radial jetting azimuth
• rock failure
• stress anisotropy