STRATIGRAPHIC INTERPRETATION OF SEISMIC SECTIONS FROM WELLS -‘B’ AND ‘C’, CENTRAL DEPOBELT, NIGER DELTA, NIGERIA

Seismic and sequence stratigraphic approach was applied to sedimentary study of ‘X’ and ‘Y’ fields  in the Central Depobelt of the Niger Delta using 2D seismic section, wire line logs (gamma ray and resistivity) and a high resolution biostratigraphic datasets of well-‘B’ and well-C’. The study observed succession of sediments being deposited progressively basin wards and overlain by thick marine shales and clay deposits.  These thick, sand rich wedges are separated from each other by up-dip extending thinner sediments of fossiliferous marine shales. The extracted seismic horizons showed a more conspicuous and varied seismic pattern which has on one hand, predominantly a smooth texture; high amplitude; with a discontinuous rugged texture; whereas the chaotic seismic pattern was observed to possess a low coherence attribute.  On the other hand, the low amplitude and variable frequency has a less predictable texture than the high-amplitude, continuous, coherent reflection pattern. Four regional transgressive shales, dated by characteristic foraminifera events, which correspond to the downlap surfaces were recognized in the wells analysed. These include; Chiloguembelina cubensis and/or Globorotalia opima opima, Uvigerinellasparsicostata, Spiroplectammina wrightii and Hopkinsina bononiensis. The delineated Maximum Flooding Surfaces (MFSs) in this study are dated 28.1/Ch*1Ma, 31.3/Ru*2Ma, 33.0/Ru*1Maand 34.0/Ru*1Ma for the candidate surfaces. However, the encountered depositional sequences are bounded with sequence boundaries dated 27.3Ma, 29.3Ma, 32.4Ma, 33.3Ma and 35.4Ma respectively. The delineated system tracts within the two wells are Lowstand, Highstand and Transgressive systems tracts with their associated aggradation, progradation and retrogradation stacking patterns.  However, the identified Maximum Flooding Surfaces (MFS) were extrapolated on the seismic sections.  It was observed that on the analysed seismic section, the Maximum Flooding Surface within these wells commonly appear as thick amplitude events that form the upper bounding surfaces of sandy, bright-amplitude intervals.   In all stage boundaries, it coincides with flooding surfaces which occur at the tops of major upward-fining successions in the shelf deposits and ranges conspicuously between 1.9 – 3.0secs within the sections.Seismic and sequence stratigraphic approach was applied to sedimentary study of ‘X’ and ‘Y’ fields in the Central Depobelt of the Niger Delta using 2D seismic section, wire line logs (gamma ray and resistivity) and a high resolution biostratigraphic datasets of well-‘B’ and well-C’. The study observed succession of sediments being deposited progressively basin wards and overlain by thick marine shales and clay deposits. These thick, sand rich wedges are separated from each other by up-dip extending thinner sediments of fossiliferous marine shales. The extracted seismic horizons showed a more conspicuous and varied seismic pattern which has on one hand, predominantly a smooth texture; high amplitude; with a discontinuous rugged texture; whereas the chaotic seismic pattern was observed to possess a low coherence attribute. On the other hand, the low amplitude and variable frequency has a less predictable texture than the high-amplitude, continuous, coherent reflection pattern. Four regional transgressive shales, dated by characteristic foraminifera events, which correspond to the downlap surfaces were recognized in the wells analysed. These include; Chiloguembelina cubensis and/or Globorotalia opima opima, Uvigerinellasparsicostata, Spiroplectammina wrightii and Hopkinsina bononiensis. The delineated Maximum Flooding Surfaces (MFSs) in this study are dated 28.1/Ch*1Ma, 31.3/Ru*2Ma, 33.0/Ru*1Maand 34.0/Ru*1Ma for the candidate surfaces. However, the encountered depositional sequences are bounded with sequence boundaries dated 27.3Ma, 29.3Ma, 32.4Ma, 33.3Ma and 35.4Ma respectively. The delineated system tracts within the two wells are Lowstand, Highstand and Transgressive systems tracts with their associated aggradation, progradation and retrogradation stacking patterns. However, the identified Maximum Flooding Surfaces (MFS) were extrapolated on the seismic sections. It was observed that on the analysed seismic section, the Maximum Flooding Surface within these wells commonly appear as thick amplitude events that form the upper bounding surfaces of sandy, bright-amplitude intervals. In all stage boundaries, it coincides with flooding surfaces which occur at the tops of major upward-fining successions in the shelf deposits and ranges conspicuously between 1.9 – 3.0secs within the sections.