The Common Reflecting Element (CRE) method (non-uniform asymmetric multifold system)

Abstract

It is known that a stack of traces of multiple coverage gather is usually accompanied by loss of resolution. Resolution could be essentially improved if sources and receivers are distributed on the free surface in such a manner that all traces in a gather correspond to one specular point. The corresponding method, called the Common Reflecting Element (CRE) method, is presented in this paper. The CRE method includes (1) a special binomial asymmetrical distribution of source-receiver pairs along a spread; (2) a special dynamic correction, called the Oblique Spherical Correction (OSC), depending on local characteristics of a medium and wavefront, emitted by a fictitious source located at the CRP on a reflector; (3) a special procedure of generating synthetic traces of so called corrected quasi-focusing gather, corresponding to binomial root distribution of the paris and to the OCS, if sources and receivers had been distributed in the field arbitrarily and if the parameters of the binomial root distribution and of the OCS are known; (4) a special procedure of search of synthetic traces of an optimal corrected quasi-focusing gather, if sources and geophones had been distributed in the field arbitrarily and if only sets of possible values of the parameters of the binomial distributions and of the OSC are known. The comparison of distribution of sources and receivers and of NMO, calculated by ray tracing program, with the binomial distribution and the OSC, shows high accuracy of the obtained formulas in CRE. Modelling testing of the principal blocks of the proposed procedures indicated that they should operate well.