Excel worksheet for comparing AVO of various lithology

AVO Curves

AVO curves represent the characteristic of seismic reflections from near to far offset, or angles, and are commonly used to evaluate whether a seismic data set can be used to extract certain information such as reservoir distribution, or more important, the hydrocarbon distribution. Many commercial exploration softwares have this kind of tool. CREWES, for example, provides a free reflectivity explorer for this purpose (http://www.crewes.org/ResearchLinks/ExplorerPrograms/ReflEx/REcrewes2_1.html)

MS Excel spreadsheet, in fact, can be used to do similar task, even more. The famous Aki-Richard AVO equation can be written in the Excel worksheet to model AVO curves of various lithology pairs. The figure below shows the comparison of AVO curves generated for shale-coal (MODEL1), shale-gas sand (MODEL2), and shale-wet sand (MODEL3) pairs. Different pairs of lithology can be simply modeled by replacing the elastic properties (Vp, Vs, and Rhob). The figure easily describes that the reflection from coal will be dominating, but looking at the slopes of the reflection curves, coal and gas sand should be able to be distinguished from the seismic stacks or seismic gathers. Therefore, ones can proceed to utilize the seismic data for advanced seismic analysis such as AVO analysis or prestack seismic inversion. The worksheet clearly shows the importance of having this kind of tool for an effective decision in reservoir/hydrocarbon distribution studies.

With the advent of tables, iphones, or ipads, this worksheet can be used for quick and mobile interpretation. The figure below shows the same worksheet displayed on a Samsung tab by Polaris office.