English abstract
The Aptian Lower Shuaiba reservoir is one of the main hydrocarbon reservoirs in
Northern Oman, which has been extensively studied. However, the Shuaiba reservoir in
Natih field in northern Oman is poorly understood. Through the analysis of the available
data, a structure model, depositional and facies model, diagenesis understanding, reservoir
quality, and new opportunities are studied. The project studies both blocks of the Natih
fault, the upthrown and the downthrown blocks.
Different models have been developed to better understand the Shuaiba reservoir
in the Natih field. Starting with the structure model, and based on seismic attributes as well
as seismic cross-sections, the majority of the faults at the Shuaiba level in the upthrown
block are trending NE-SW. In addition, the maximum fault throw in the upthrown block
is 7 m, with an average throw of 3 m. The results of this analysis confirm the efficiency of
Nahr Umr sealing since the average Nahr Umr thickness in the Natih field is 130 m.
Moreover, the Natih fault is a reverse fault that was most likely moving as a strike-slip
fault, with locally being transtensional or transpressional during the Alpine 1 event,
depending on the geometry of the fault trajectory. Next, three facies have been identified
in the upper 35 m of the Shuaiba reservoir. The three facies are oncodidal packstone,
which was most likely deposited in a shoal flank setting; bioclastic mudstone, which was
most likely deposited in an open marine shelf; and bioclastic wackstone, which was most
likely deposited in a shallow marine shelf. However, the diagenesis model shows that early
and late cementation with dissolution has affected the Shuaiba reservoir in the Natih main
field, as well as compaction and fractures. In addition, the diagenesis model shows that the
faulted/fractured areas have been cemented due to the highly saturated salt fluids that went
through the faults/fractures and led to cementation in the surrounding areas.
In terms of the new opportunities, the downthrown block might be a good
opportunity to test. The petrophysical logs show a good reservoir quality with hydrocarbon
saturation. Moreover, seismic attributes are used as hydrocarbon indicators, which show
the probability of the presence of hydrocarbon in the downthrown of the Natih fault. As a
recommendation, the top structure of the Shuaiba reservoir in the downthrown block is
recommended to be drilled.
