The conversion of kerogen to oil/gas will build up overpressure. Overpressure is caused by conversion of solid kerogen to fluid hydrocarbons in a relatively fixed pore space. The excess pressure caused by kerogen maturity does have impact on the seismic elastic properties. The wave propagation, velocities, anisotropy and AVO effects by kerogen maturation have been obtained as a function of initial kerogen content (immature), excess pore pressure (mature) for Bakken shale from Williston basin, USA. Our analysis show that more matured shales are brittle and suitable for hydraulic fracturing for maximum production