Online Journal for E&P Geoscientists

Harvey, Craig ^*1; Wicker, Jorg ¹; Molinaro, Matteo ¹; Zahran, Mamdouh E.²; Taylor, Andrew ³; Churchill, James ³
(1) Qatar Shell Upstream International, Doha, Qatar. (2) Qatar Petroleum, Doha, Qatar. (3) Ichron Limited, Northwich, United Kingdom.

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. Pre-Khuff clastic reservoirs are well known in Saudi Arabia and Oman but remain relatively under-explored in Qatar. This paper highlights QSUI’s integrated approach to rapidly developing a detailed view of its exploration acreage.

The pre-Khuff plays poses two main challenges; firstly the geophysical challenge of being able to image the deep pre Khuff structure and secondly the geological challenge of being able to realistically predict reservoir and top seal quality.

QSUI has undertaken seismic reprocessing of vintage 2D data. The main seismic data challenge is the presence of severe multiple energy interfering with seismic primaries especially at deeper pre-Khuff levels. State-of-the-art demultiple techniques were applied to attenuate the long, medium and short-period multiples, thereby enabling more reliable velocity picking. Final reprocessing results significantly improve seismic value and show clear improvements in seismic data quality: higher Signal/Noise level with better reflector continuity and elucidation of structural and stratigraphic complexity.

Geological data has been re-assessed and new work undertaken on fault mapping, gravity, stratigraphy, depositional models, reservoir quality and seal integrity of the pre-Khuff. One of the key aspects is to map the continuity of the Palaeozoic stratigraphy and reliably pick the base Hercynian Unconformity. This has been achieved using a combination of palynology and chemical stratigraphy. The latter is valuable in differentiating Berwath, Jubah, Jauf and Tawil successions when they have similar wireline log signatures in a succession of quartzites. The former is particularly valuable for mapping Silurian source facies and in the detailed understanding of the Jauf reservoir intervals and seals.

Revised depositional models, based on core observations, have been used to extend potentially successful play fairways into Qatar. New petrographic analysis programs address the diagenetic controls on reservoir quality and their relationship with depositional environments aiding the prediction of potential net viable reservoirs at depths greater than conventional cementation floors.