RE:The purple outline around well 6-2 Good question, and that's the billion dollar question, and that's what these wells and seismic the seismic are trying to start to answer. To calculate the volume the formations will be analyzed for hydrocarbon content and porosity (among other formation characteristics) of the formations to determine pore volume for a given formation. The different formation depths containing hydrocarbons will have their porosity determined and then you can multiply that pore volume by the depth of the formation and the area.
The logs and cores determine the porosity, seismic doesn't tell you that. And the cores and logs will also help determine the stratigraphic formations. The seismic will determine the depths of the different formations and the wells will help determine which formations are at what depths between the wells. The seismic will then be used to fill in the depths between wells. As more wells are drilled and more seismic conducted, the estimated volumes become more accurate.