Numerical Wavefield Simulation in Deviated Boreholes within Vertical Transversely Isotropic Formations, Part 1: A Monopole Source

The impact of well deviation on wavefields in deviated boreholes within vertical transversely isotropic formations is investigated through numerical simulations. A three-dimensional finite-difference model incorporates a cubic block containing a borehole, with a Kelly source employed as the acoustic monopole source. Findings indicate that at zero well deviation, the wavefield exhibits isotropic characteristics, transitioning to anisotropic behavior as well deviation increases, characterized by a reduction in P-wave velocities along the x-axis while remaining constant along the y-axis. Analysis using slowness-time-coherence analysis reveals that P-wave dispersion decreases with increasing well deviation. Additionally, simulation results for Stoneley waves show significant variations in amplitude and propagation velocity across different well deviation angles, with the most substantial dispersion observed in vertical wells and minimal dispersion in horizontal wells. The alignment of simulated results with field data supports the reliability, indicating that as well deviation increases, P-wave arrival times advance and amplitudes decrease, while Stoneley wave characteristics align with the simulated outcomes. These findings have substantial implications for optimizing logging and completion strategies, thereby enhancing the efficiency of exploration and development efforts in unconventional oil and gas reservoirs.