A numerical investigation on chalcogenide W-type co-axial optical fiber structures is reported for broadband highly coherent mid-IR supercontinuum generation. The structural parameters of the optical fiber were optimized to achieve small normal dispersion in a broad spectral range of the mid-IR region. The W-type optical fiber structure possesses a flat chromatic dispersion profile with the flatness of the dispersion variation of ±2.45 ps/nm/km within the spectral range of 4.9–12.6 μm. A coherent mid-IR supercontinuum spectrum spanning 2.28 to 15.52 μm at the −40 dB level is obtained using a 4 cm long W-type optical fiber when it pumped by a 200 fs laser pulse with a peak power of 10 kW at 7.0 μm. Broadband coherent mid-infrared supercontinuum sources have potential applications in frequency metrology, nonlinear microscopy, non-destructive testing, optical coherence tomography, and molecular spectroscopy.