Sandstone detection using three‐term amplitude variation with offset projection: A case study

Abstract

Seismic amplitude variation with offset projection is widely used in the oil and gas industry to extract information contained in amplitude variation with offset responses.Traditional two-term amplitude variation with offset projection, based only on intercept (A) and gradient (B), has been used in various ways, including hydrocarbon detection and the estimation of target properties such as water saturation. Three-term amplitude variation with offset projection, in which A, B and curvature (C) are blended using two projection angles (χ and ψ), can also be used for the same purposes and has some advantages over the two-term methods. The effectiveness of the three-term amplitude variation with offset projection in the detection of sandstone has been investigated using field data. A sandstone detection workflow is proposed, which includes (1) defining the target attribute, (2) optimizing projection angle in the χ-ψ analysis plane painted with the target attribute and (3) confirming/refining the selected projection angle using the two-term amplitude variation with offset projection-C cross-plot. The impact of anisotropy is taken into consideration, and the sandstone index is introduced as the target attribute. The sandstone detection workflow was applied for both synthetic and field data, which illustrates that three-term methods offer an important perspective on noise in the amplitude variation with offset attributes: Noise in the third term is correlated with noise in the other terms so that including C can actually suppress noise to some extent, even if C looks unusable. Moreover, two-term amplitude variation with offset projections are a subset of three-term amplitude variation with offset projections; therefore, if C adds no information, this fact is revealed as the worst-case outcome in the three-term analysis; inclusion of C will never degrade results and there is no reason to exclude C a priori.