English abstract
In Oman, the first commercial quantity of hydrocarbon was discovered in the early 1960s. Almost all of the large petrolecam accumulation structures have been anled: hence, the majority of the new field discoveries will be concentrated on low rebe subde structures. The purpose of this study is to contact a prospectivity study within the middle part of Block 5 in North Oman for both Nath and Sha aiba reservoirs The study is camed out to understand the extent and tracation of the Natih reservoir units A B and C members) along with the identification of structural and stratigraphic tapping in Nath and Shuaiba reservoirs to add future drilable prospects for Daleel Petroleum LLC (Block 5 current operator) This has been achieved by examining the data of ten wells and a 3D seismic cube for the study area for subsequent integration and analyses with the aid of Petrel, Rose and Associates Toolbox and Techlog software. Analyses started by the well log analysis process where standard wel logs were used to recognize the formation "well tops. This was followed by generating a NW-SE trend well correlation. Then a seismic-well tie process was done for subsequent seismic-interpretation process for Upper Shu'alba Member and Nanh D Member reflectors in order to generate timedomain maps for Upper Shu'aiba Member and Natih A Member (time-shifted Natih Dhorizon). The extraction of seismic surface attributes was done and followed by a Lault-interpretation process to observe the Upper Shuaiba Member and Natih A Member faulting system. After that, the truncation process for the time-domain maps for upper Natih units (A, B and C members) was done. In addition the generation of the velocity-domain maps using the interval velocity lavered-cake model were done in order to produce depth-domain maps for Upper Shuaiba and Natih A members Nine leads were identified (structural and stratigraphic structural) on the Natih reservoir, whereas the Upper Shu'aiba reservoir showed no formation of closing structures. The evaluation of the prospectively of the identified Natih A leads were done by calculating volume in-place, assigning risk factors for subsequent estimation of the Geological Chance of Success (GCOS) and calculation of expected volume that can be exploited Natih A structural leads are very small in size with low volumes in place which are associated with 26% GCOS and lower espected volumes. However, Nath A stratigraphic structural leads are very large in size with high volumes in place and are associated with 10% GCOS with lower expected voltmes. This prospectivity study resulted in high risk and reservoir-presence uncertainty with Nath A stratigraphic structural leads because of low seconic resolution close to the truncation zone. Although the seismically defined Natih A leads are well preserved under thick Figa Formation they are considered to be economical for drilling de to their small size. PSDM Pre-Stack-Depth-Migration seismic processing would be a useful tool in the study area to get better resolution of the structural leads in term of their size. This tool would also confirm the presence of stratigraphic structural leads in the westward truncation zone.
