This work presents a numerical study of a W-type index chalcogenide fiber design for Mid-Infrared (MIR) supercontinuum (SC) generation beyond 10μm. Our fiber design consists of a Ge15Sb15Se70 glass core, a Ge20Se80 glass inner cladding and a Ge20Sb5Se75 glass outer cladding. These chalcogenide materials have the advantages to broaden the spectrum to 12μm, due to their low material absorption. The optical mode distribution of the chalcogenide fiber is simulated by a finite element method based on edge elements. With a 6 μm core diameter and a 12 μm inner cladding diameter, the proposed fiber design exhibits flat anomalous dispersion in the wavelength range (4.3-6.5μm), with a peak of about 7ps/(nm.km). The position of the second zero-dispersion wavelength (ZDW) can be easily and precisely controlled by the inner cladding size and should be shifted to around 7μm for a 18 μm inner cladding diameter. This design is more suitable for a pump wavelength at 6.3μm which is in the anomalous dispersion regime between two ZDWs and can broaden the spectrum due to the soliton dynamics. Our fiber design modelling shows that the nonlinear parameter at 6.3μm is 0.1225W−1 m−1, when using a nonlinear refractive index nNL=3.44 ×10−18 m2W−1, and the chromatic dispersion is D = 3.24ps/(nm.km). Compared to previously reported step-index fibers, the proposed W-type index chalcogenide structure ensures single mode propagation, which improves the nonlinearity, flattened dispersion profile and reduces the losses, due to a tight confinement of the mode within the core.