Abstract:
3-D poststack time-migrated seismic and well-log data containing wireline logs like, gamma ray, caliper, sonic, resistivity and density logs from the TOKS Field in the Niger Delta were used to develop a detailed structural interpretation of the field. The aim of the work is to carry out detailed analysis of the sealing property of faults in “TOKS” Field, with a view to evaluating the reservoir trap integrity. Three wells, “TOKS” 1, 2 and 3, were used for lithologic correlation. Forward modeling was used to generate synthetic seismogram which was used to tie wells to seismic. Time and depth structural map were made to reveal structural orientation. Seismic attributes such as similarity, Energy were generated along with fault enhancement filter. Quantitative and qualitative fault seal analyses were carried out. Qualitative analysis is derived from chimney cube extraction while quantitative analysis was carried out using Shale Gorge ratio and Shale smear factor algorithms.Five reservoirs named R-1, D-2, D-3, F and G, respectively from top to bottom were mapped within the Agbada Formation and they fall in the range of 5970.6ft (1819.6m) to 9949ft (3032.5m). Computed petrophysical parameters from the logs in “TOKS 2” show porosity within the range of 0.147 to 0.207, gross interval 6.50ft (1.9m) to 79.5ft (24.2m), net pay from 1ft (0.3048m) to 56ft (17.1m). The time structural map for the top of the reservoirs reveals three major faults with five secondary antithetic and synthetic faults. The major faults are dipping towards the south. The time structure maps show that 2-way and 3-way fault assisted closure were present in the field. The synthetic seismogram shows a good tie with the seismic data. Seismic interpretation revealed that the hydrocarbon reservoir mapped were close to the crest of each structure. Similarity attributes and chimney cube show the orientation of the faults. Using the quantitative analysis, the result obtained from the shale gouge ratio (SGR) also revealed that the sealing capacity of the shale is very low with SGR value of 5% whereas the threshold value is between 15% and 20%.
The chimney cube analysis corroborate with the SGR result, as it shows the presence of fluids through it.The study results equally reveals that the sealing integrity of the faults is low and they serve as migration pathway for the trapped hydrocarbon in the prospects identified. Therefore these are high risk prospects
