What is that hydrodynamic you mentioned and what is its significance?
Natural percolation of water from the SE to NW, which (in some formations) provides a slight water drive on closed structures, and even distorts oil pools around a structure. At the same time, that can provide some pressure maintenance in the reservoir as well.
In some instances, salt layers in the rock (there are several widespread evaporite beds of significance in the Williston Basin--in the Spearfish, Charles, Prairie, Interlake, and Ashern Formations to name a few) will be dissolved, and the collapse of overlying sediments can create a trap for oil. The Northeast corner of the Basin is an angular unconformity, and the water that makes it that far can exit into shallower formations.
Although the amount of water present in the Bakken/Three Forks varies, that dynamic may be providing an assist in some instances by pushing oil and gas toward the wellbore. In other cases where laterals got 'more wet' by going into areas of the formation with higher water saturation, the 'hills and valleys' created by the variation in depth of the lateral create situations in the wellbore where water causes production problems, creating water flows in the wellbore contrary to the flow of oil and gas out of the well.