Low Frequency Seismic Technology: A New Era for Reservoir Solutions

Abstract

The hydrocarbon bearing strata, due to attenuation of seismic waves, appear as zones of low frequency shadows and its application as a direct hydrocarbon indicator for several years. Traditionally the limited low frequency seismic impedance component can be estimated by interpolation of filtered well logs when performing acoustic inversion and modeling for reservoir characterization. However, sparse wells or low accurate log data can't satisfy with the accuracy of seismic inversion. Breakthrough of low frequency passive seismic survey with low frequency emissions, large offset and high density came from the Pilot experiments between BGP and Shell in western China in 2009 and the innovation of BGP self-developed KZ28LFV3 low frequency vibroseis and its seismic acquisition design was successful to narrow this gap by designing to acquire 1.5 – 3Hz low frequency content. Specific low frequency seismic data processing focused on low-frequency compensation by retaining broad signal band and source wavelet constraint which can effectively preserve the relative amplitude of the broadband seismic data with high S/N ratio. Between February and June, 2013, BGP successfully conducted the first production application of low frequency, high density, broadband, wide-azimuth vibroseis survey on pre-salt carbonate reservoir in the H block of PreCaspian basin in Kazakhstan. Subsequently, standard amplitude-preserved data processing was applied. The resulted seismic data demonstrated high quality imaging of the boundaries of salt domes and subtle geologic geometries within the carbonate reservoir. Obvious low frequency shadows presented beneath oil zones, which were absent in conventional seismic dataset. This technology was successful applied to Taibei depression of Tuha basin in the western China in 2013. In the basin, technical challenges to seismic acquisition were that the less seismic wave propagates can penetrate through the reservoir zones due to thick high attenuation coal beds above the reservoirs. The revolutionary solution was achieved by designing to add 1–3Hz low frequency contents during vibroseis survey so that the seismic energy underneath thick coal-beds can be effectively compensated. The high quality of seismic imaging on geological geometries within the reservoir was finalized by specific amplitude-preserved processing and inversion.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015