A technique facilitates plugging of a wellbore during, for example, a fracturing operation. A frac plug is constructed with an unobstructed internal passage and comprises a seal member combined with a plurality of slips for engaging a surrounding wall, e.g. a surrounding wellbore wall. Additionally, the frac plug comprises a lower sub having raised edges arranged to catch a ball during a flow back stage without blocking flow along the unobstructed internal passage.