Systematic AVO response with depth

Danielle Boyd

danielle@sep.stanford.edu

ABSTRACT

Well logs reaching several kilometers into the surface of the earth show that the P-wave reflection coefficient changes behavior with depth. I examined one particular well log, reaching approximately 5 km below the surface of the earth and assumed to be saturated with water. Simple two-layer models consisting of an upper layer of saturated sand and a lower layer of shale were constructed for three different depths to study the AVO response. Studying how the amplitude variation with offset (AVO) response changes with depth for brine and gas saturated sand shows that the well log exhibits all three classes of reflectivity. The shallow portions of the well display typical Class III reflections. The deepest sections exhibit Class I behavior. Near 2.4 km, the well log comes to a crossover point and displays Class II reflection behavior.