A method, apparatus, and program product utilize a buffer defined relative to a wellbore trajectory to generate a work zone around a wellbore for use in connection with formation modeling. In some embodiments, for example, a closed curve such as a non-rectangular, polygonal work zone may be defined around a wellbore based upon a buffer that extends generally transverse to the trajectory of a length of a wellbore a predetermined distance. In addition, boundaries may be defined in a work zone to effectively split the work zone into multiple closed curves or polygons in response to user editing, e.g., to create one or more subsurface layers in the work zone. In such instances, points defining a subsurface layer may be shared by adjacent layers such that editing of such points will affect each of the layers sharing such points.