Abstract

Presented are new seismic technologies ANCHAR and SVSL, developed by the VNIIGeosystem Center.

These technologies allow substantially improve the geological efficiency of prospecting and exploration owing to identifying and outlining of oil and gas fields with the use of infra-low frequency seismic waves generated by HC pools and identifying high-fractured zones from scattered seismic waves. Considered are results of applying these technologies in Russia.

Introduction

Seismic data are commonly applied in prospecting oil and gas fields to identify the structural and non-structural traps with possible accumulation of HC. Yet, identifying the presence of HC in these traps and assessing the heterogeneity of oil-saturation of pay zones is a challenge of up-to-date seismic despite a substantial progress in seismic instrumentation and software. Impossibility to solve these problems by using only reflected seismic waves is the reason of numerous failures in prospecting and outlining of HC fields and drilling dry wells in existing HC fields. In order to solve these urgent problems two principally new seismic technologies have been developed and successfully applied by the VNIIgeosystem Centre: a technology for estimating oil-and-gas saturation (ANCHAR) and determining the 3-D distribution of open fracturing (SVSL) of geomedium. The fundamental distinction of these technologies from standard seismic (CDP), where mirror-reflected waves are used, lies in identifying specific types of seismic waves - scattered waves and infra-low frequency waves in the seismic wavefield which are not commonly used in seismic.

ANCHAR Seismic technology ANCHAR is based on the natural phenomenon discovered by the Technology VNIIgeosystem scientists - generation of intrinsic seismic vibrations in the infra-low frequency band by an oil-and-gas pool when subject to the field of elastic waves1. The intensity of such vibrations is much more less than the level of natural seismic background. To identify these weak infra-frequency vibrations generated by a HC pool, special methodical and measuring units shall be applied.

Particularly, one has to apply special-designed sensors featuring a high sensitivity in the infrafrequency band (0.5–7.0 Hz) and provide a long-term recording of signals generated by the HC pool. The preliminary data processing being performed in course of field operations allows promptly implement additional observations to adjust the outline of identified HC field. The results of ultimate processing are presented as prediction maps of field location within the area under study.

The ANCHAR seismic studies have been implemented in Russia mostly in the geologic exploration of Cis-Ural, Volga, and Caspian r

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