Stratigraphic architecture of the mid-Cretaceous reservoirs of the Al Shaheen field, offshore Qatar

Abstract

In the mid- and Lower Cretaceous succession of Block 5 (offshore Qatar) six reservoir zones are distinguished. These reservoir zones differ strongly from each other in lithological and sedimentological facies composition, in stratigraphic architecture and in structural context. Different development strategies, including very long horizontal wells, have been applied to obtain the most optimal production from these reservoirs. The following reservoir units are distinguished. The Kharaib B and C reservoirs are low-angle, carbonate ramp systems that how a layer-cake architecture. In contrast, the overlying Aptian-age Shu’aiba Formation, shows a very high lateral facies variability, due to a platform-to-basin transition. The Shu’aiba platform is incised and overlain by Nahr Umr sands and shales. The producing sands are very thin, below seismic resolution, and show significant lateral facies changes. The Mauddud/Khatiyah carbonates are again characterized by platform-to-basin facies changes. The top of this unit has been strongly affected by local uplift. Detailed geological knowledge of these reservoirs has provided the basis for the successful development of the Al Shaheen field, allowing for optimal well planning, and has provided essential support for geosteering and completion of long horizontal wells. A full-field. high-resolution 3-D seismic data is being acquired to complement the assessment, understanding and development of these producing reservoirs.