Comparisons between CIGs and CMP gathers for AVO analysis-A case study on gas reservoir

When we delineate oil and gas reservoir in complex structural or lithologic controls. AVO analysis will be applied with either common-image gathers (CIGs) or common-midpoint (CMP) gathers. Different gathers may draw distinct conclusions, thus correct gathers are vital for AVO analysis. Biondi et al.(2004) depicted the differences between CMP gathers and CIGs in the quality and accuracy of seismic imaging. Reshef (2008) discussed the sensitivity of velocity variation both in angle and offset domains and found that interval velocity analysis for prestack depth migration (PSDM) is more sensitive to offset variation than reflection angle in CIGs. Mahmoudian and Margrave (2009) used angle-domain common image gathers (ADCIGs) for AVA analysis and found that they uniquely define ray couples for each point in the subsurface. The purpose of this paper is to delineate and compare the advantages of CIGs and CMP gathers in the offset domain. Comparing velocity model, computational cost and images both for generating CIGs and CMP gathers, we find that CIGs are better than CMP when in large dip angle and more sensitive to velocity variation. While in small dip angle and flat layers, CMP gathers have almost the same image as CIGs but cost-effective in offset domain.