Though there are many factors offecting the image accuricy of low closure structures

the building up of a real and reasonable variable speed velocity field is the most important one ofter eliminating mis-tie and calibrating and tracing exactly the horizon.A t

0

value can be found at the spill point in iso t

0

map

and the spill point depth can be obtained from base level corrected oil or gas wells.Then the spill point constrained average velocity can be derived.When well control point are rare or distributed unevenly

the seismic stacking derived average velocity should be constraint corrected with spill point average velocity and well point average velocity

then a reasonable varying speed velocity field could be obtained.Structural maps made in this way will have more accurate trap configuration and closure

and could provide more reliable basis for reserve calculation and development well allocation.