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Seismic stratigraphic analysis for hydrocarbon exploration in the Beta Field, Coastal Swamp Depobelt, Niger Delta

Adeleye Mutiu A., Yekeen Kazeem O., Amidu Sikiru A.

Geology, Geophysics and Environment

2020

Vol. 46, no. 4

259--271

Hydrocarbon exploration analysis from a seismic stratigraphic approach was carried out within the Beta Field, Coastal Swamp Depobelt, Niger Delta, to identify system tracts and sequence boundaries that could be associated with potential hydrocarbon accumulation. 3D seismic volume and data from four wells were analyzed. Depositional sequences, system tracts, sequence boundaries, and candidate maximum flooding surfaces were picked from logs, while reflection patterns and terminations were interpreted from seismic sections. Log shapes from gamma rays in combination with seismic facies analysis were interpreted in order to delineate lithology, depositional environments and depositional sequences. Seismic attributes were extracted and were draped on gridded surfaces from the interpreted seismic horizons. These were integrated with structure maps to obtain structural and stratigraphic trends, and possible presence of reservoir sand. Five depositional sequences and nine seismic facies were identified within the field. The depositional sequences were designated Sequences S1 to S5 based on the depth of the occurrences and stacking patterns. This study reveals a progression from fluvial depositional settings to the shelf. The main reservoirs identified are the sand units of the highstand and lowstand within three depositional sequences (S1, S4 and S5) although interbedded sands within the TST of S4 and S5 are also suspected of being potential reservoirs. The channel sand deposits within the study area are suspected to be hydrocarbon bearing as they occurred within the complex fault trapping system popular in the Niger Delta. The application of seismic stratigraphy, as shown in this study, serves to encourage exploration in the Niger Delta where it could be effectively employed for reducing risk in hydrocarbon exploration.

Exclusive governance of the 1st and 2nd order sequence framework by regional extensional tectonics as demonstrated on the Gondwanian Tethyan margin

Krishna J.

Volumina Jurassica

2006

Vol. 4, no. 1

51-51

Krishna et al. (2000) invoked the role of extensional tectonics to explain the explicit discordance of the 1st order MFS of the Jurassic-Cretaceous depositional sequences on the two margins of the Tethys, respectively i. e. above the Late Kimmeridgian Eudoxus Zone on the European Tethyan margin, and above the Middle Oxfordian Schilli Subzone in Kachchh (India). By way of further demonstration of the exclusing role of the regional extensional tectonics is here interpreted the basal SB of the sequence near the Pliensbachian/Toarcian boundary in different basins of the Gondwanian Tethyan margin from East Africa and Madagascar in the west to Indonesia and Australia in the east inclusive of the entire Tethyan margin of the Indian subcontinent. The so determined basal SB is again found unambiguously discordant with the corresponding SB on the European Tethyan margin. The interpretation of the basal SB is based on the presence of tectonically induced marked change of environment and litho-biofacies along with subaerial stratigraphic gap of varying duration between the Triassic-Liassic stratigraphic units below, and Toarcian or younger units above with or without ammonoids in Somalia, Ethiopea, Kenya, Tanzania, Madagascar; Baluchistan, Attock and Hazara regions of Pakistan; Kachachh, Jaisalmer, Malla-Johar and Spiti regions of India; areas of Nepal; Indonesia and Australia. These facies changes and subaerial stratigraphic gaps are also evident in the intra-cratonic non-marine Gondwana basins, as also in the exposed and onshore/offshore well sections on the Indian East coast. Igneous activity is also manifested in a few regions of the Gondwanian Tethyan margin. In the East African countries, Madagascar and Baluchistan the non-marine Triassic sands are uncoformably overlain by marls and limestones with basal Toarcian Bouleiceras. In Kachchh the late Late Bajocian Leptosphinctes bearing sediments are underlain by several hundred meters of sediments before reaching the Precambrian basement. In Spiti the marine ammonoid devoid Liassic limestones are overlain by marls with Early Toarcian Alocolytoceras. In the Indian intra-cratonic non-marine successions too, there is evidenced a large stratigraphic gap between Triassic-Liassic and Late Jurassic - Early Cretaceous stratigraphic units. In the Indian East coast Krishna-Godavari and other basins the non-marine Triassic units are overlain by Late(?) Jurassic - Early Cretaceous marine units. To conclude, the 1st and 2nd order sequence stratigraphic framework on the two margins of the Tethys is exclusively governed by the respective highly differing regional/basinal extensional tectonics and so is highly discordant. In contrast the agreement at the 3rd order is solely guided by the global sea-level changes. Further, the tectonically governed high magnitude and low frequency 1st and 2nd order framework is unable to distort the eustatically guided low magnitude high frequency 3rd order framework.