Online Journal for E&P Geoscientists

Shrivastava, Chandramani ^*1; Bildstein, Joe²; Al-Alawi, Abdullah³, Busaidi, Hafidh¹
(1) Wireline, Schlumberger, Muscat (MCT), Oman. (2) Gas Directorate, PDO, Muscat (MCT), Oman. (3) DCS, Schlumberger, Muscat (MCT), Oman.

The geological complexities of the clastic reservoirs in Northern Oman pose difficult challenges in understanding the distribution of reservoir facies for proper delineation of the gas bearing formations. The latest borehole imager helped a great deal in overcoming the limitation of traditional imaging in high salinity mud and detailed sedimentological interpretation could be performed to understand the architecture of the reservoir.

Proper uunderstanding of the reservoir sand distribution and their genetic relationship in one of the bigger clastic reservoirs of Northern Oman is not available. The high salinity mud environment downhole was affecting the data quality of borehole images for detailed sedimentological description and the structural elements that offset the reservoir sand bodies. The latest borehole imager with improved signal to noise ratio and tolerance to high mud salinity (~300,000 ppm) acquired good quality images to help in interpretation of sandstone reservoirs.

The detailed analysis of borehole images in the sands of the field suggested the presence of a fault that juxtaposed the sands of probable aeolian environment against the fluvial sands. The reservoir properties and their distribution are different for these sands, which were earlier interpreted to be the part of the same fluvial stacking. The earlier understanding of these sands was not able to explain the variations in the dynamic response of the reservoir.

Different architectural elements were identified as dunes and inter-dunes of aeolian deposition where high-angle cross-bedded sands could provide a good permeability zone. Similarly the different fluvial elements were also identified on borehole images. A comprehensive sedimentological evolution was understood in terms of depositional environments, and the impact of faulting was understood with the help of nearby well data.

The integrated interpretation in the framework of geological evolution and distribution of sand bodies affected by the faulting explained the different flow units for production.