Carbonate Facies Discrimination, a Different Look to AVO Attributes

A new method of carbonate facies prediction is developed based on principal theory of seismic amplitude variation with offset, AVO. It is revealed in theory that all rock samples with similar Poisson’s ratio must align themselves along a straight line in I and G attribute space regardless of sample porosity. Thus, a group of facies with different amounts of Poisson’s ratio must generate a set of parallel lines in AVO attribute space which might be used to separate them. This was then inspected on ultrasound velocity measurements of core samples from a carbonate reservoir South -West Iran with promising results.Grainstones and packstones that are classified as structurally grain supported material are distributed along parallel lines in I and G plane and away from mud supported wackstone / mudstones. This distinct behavior might be used to separate carbonate facies based on rock’s clay content. As I and G are interface attributes, facies predicted in this way belong to the interval immediately below top reservoir interface. This is helpful especially where reservoir thickness is below seismic resolution and interval dependent attributes such as acoustic impedances fail to resolve different lithologies.