Seismic-Airborne TEM Joint Inversion and Surface Consistent Refraction Analysis: New Technologies for Complex Near Surface Corrections

Abstract

AbstractWe describe two novel technologies developed for seismic characterization of the complex near surface in Saudi Arabia. Current exploration efforts in the Arabian Peninsula are directed at the identification of low-relief structures and stratigraphic traps where most of the major structures (giant and supergiant reservoirs) have been already identified and are under production. The near surface in arid environments such as Saudi Arabia is affected by anomalies caused by karsting, sand dunes and wadis that introduce severe distortions in seismic wave propagation into the subsurface. These distortions cause apparent false structures in the final stacked image that can be erroneously drilled. Two technologies were recently developed by Saudi Aramco to be able to obtain reliable seismic images of deep and low-relief reservoirs. The technologies consist of helicopter-borne transient electromagnetics (HTEM) in joint inversion with seismic, and a novel surface consistent solution for statics using refracted waves named pQC (from the QC analysis of first break (FB) traveltimes: picks). The TEM technology is based on the transmission of a primary electromagnetic signal through a large moment magnetic dipole source and the reception of a secondary magnetic field deriving from the interaction of the primary field with the earth. The acquisition is performed with a helicopter allowing to acquire data with exceptional spatial density and speed. The velocity modeling of the near surface is obtained by in-house developed joint inversion algorithms allowing to integrate the high resolution TEM information into the velocity reconstruction of the near surface. The pQC technology consists of a surface consistent statics solution using refraction data. The high-resolution time delays are calculated by means of cross-correlation of early arrival waveforms that are inverted for surface consistent time delays. This method provides detailed images of the near surface time corrections in a fraction of the time needed by conventional workflows currently used in the seismic industry. The two newly developed technologies are applied to a complex wadi structure in central Saudi Arabia where conventional seismic data analysis approaches fail. The 3D TEM seismic joint inversion solves the long wavelength of the wadi structure while the high-resolution/medium wavelength time correction is obtained by pQC. The combined time corrections of the near surface enable accurate imaging of deep structures important for reserves evaluation. The joint inversion technology with airborne TEM acquisition systems and the surface consistent refraction analysis (pQC) provide innovative solutions for imaging low-relief structures in exploration and field development applications.