Imaging the Pre-Khuff: Changing the Game with Innovative Seismic Technology

Abstract

AbstractThis paper highlights QSUI's approach to rapidly addressing the geophysical challenges associated with Pre-Khuff exploration. Based on legacy seismic data, significant uncertainty exists in relation to the deep structure of the Qatar Arch, particularly when in neighboring countries the Pre-Khuff has been shown to be structurally different to the overburden. Legacy seismic data shows reflectors below the Khuff which appear to mimic the Khuff and overburden structure. It is well known that seismic data in parts of the Middle East suffer from multiples which can exhibit amplitudes stronger than the primary reflectors. Recent work by QSUI suggests that existing seismic data is dominated by multiples at Pre-Khuff levels which make mapping Pre-Khuff structures challenging. One of the key exploration challenges facing QSUI is the ability to remove the multiples from the strong carbonate overburden interfaces to image the relatively weak primary reflections from the deep Pre-Khuff clastics.In order to identify and understand the main generators of coherent seismic noise, QSUI has undertaken seismic modeling using VSP data, legacy shot records and full-waveform synthetic modeling. Results of this work steered the reprocessing of existing seismic and the design of a 3D Ocean Bottom Cable (OBC) seismic survey. The expectation is that the tailored seismic acquisition together with state-of-the-art processing algorithms will significantly improve the Pre-Khuff imaging and allow QSUI to select optimal well locations.During preparation for the 3D OBC survey it became apparent that the level of potential hazards associated with shallow water acquisition warranted collection of high-accuracy bathymetry data. Traditional methods of ship-based multi-beam echo-sounder surveying, or aeroplane-based LiDAR measurements would have incurred significant HSSE exposure and would not have been available in time to be included in the tender documents for the seismic acquisition. As a result, QSUI deployed a new technology of satellite-based bathymetry estimation with significant operational benefits. This is the first time such technology has been used in the Middle East. Calibration of the resulting data set demonstrated that results are of sufficient quality for the design and operational planning of the seismic survey.