Pre-Khuff Imaging in Qatar: What Does It Take?
van der Molen, Matthijs *1; Strijbos, Floris 2; Duijndam, Bart 2; Zeylmaker, Lammert 2; Yahaya Joe, Osman 3
(1) Qatar Shell Upstream International, Doha, Qatar. (2) Shell Global Solutions International, Rijswijk, Netherlands. (3) Qatar Petroleum, Doha, Qatar.
Qatar Shell Upstream International B.V. (QSUI) is an unincorporated Joint Venture formed by Shell (75%), PetroChina (25%) and the State of Qatar and is exploring its Block D acreage for pre-Khuff hydrocarbons. This paper highlights QSUI’s approach to rapidly addressing the geophysical issues associated with pre-Khuff exploration.
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 suffers from multiples which can be as strong as, or even stronger than 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. The key exploration challenge facing QSUI is to be able to remove, or at least sufficiently reduce the multiples from the strong carbonate overburden interfaces to see the relatively weak primary reflections from the deep pre-Khuff clastics.
In order to identify and understand the main generators of coherent seismic noises and their characteristics, QSUI undertook seismic modeling using VSP data, legacy shot records and full-waveform synthetic modeling. Results of this work fed into reprocessing of existing seismic and into the design of a new 3D Ocean Bottom Cable (OBC) seismic survey to be acquired in 2011/2012. The expectation is that the new acquisition together with state-of-the-art processing algorithms will significantly improve the pre-Khuff imaging and allow QSUI to select optimal exploration well locations.
Preparations for the 3D OBC survey and acquisition in shallow waters over the offshore part of the survey highlighted the criticality of accurate bathymetry data. Traditional methods of ship-based multi-beam echo-sounder surveying, or aeroplane-based LiDAR measurements would have taken valuable time and incurred significant HSSE exposure and cost. As a result, QSUI deployed a new technology of satellite-based bathymetry estimation with significant cost and operational benefits. This is the first time such technology has been used in Qatar and calibration of the resulting data set demonstrated that results are of sufficient quality for the design and operational planning of the seismic survey.
AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain