The Palynostratigraphy,Palynofacies and Thermal Maturity of x and y Wells,Niger Delta.Nigeria

Ogunleye, Segun Oyewole (2015)




A palynostratigraphic investigation was carried out on ditch cuttings from Wells X and Y, located within the shallow offshore, Niger Delta. This was with a view to establishing the age as well as attempting the zonation of sections and determining the paleoenvironment and maturity of the sediments penetrated. Sixty (60) samples composited from each of Well X (interval 2105 – 3305 m) and Well Y (interval 1000 – 2220 m) were employed for the study. The samples were prepared for palynological and palynofacies studies using standard extraction technique involving Hydrochloric acid (HCl) and Hydrofluoric acid (HF) treatment. The organic extracts were wet - sieved using 5µm and 10µm polypropylene mesh sieve. Recovered palynomorphs and particulate organic matter were mounted on the glass slide and analysed using a transmitted light LeitzOrtholux II biological microscope. The lithological description of the analysed sections of both wells revealed a clastic sequence composed of alternating sand and shale sequences with accessory shell fragments, carbonaceous detritus, ferruginous materials, mica flakes, pyrites and glauconite. Moderately abundant and diverse pollen and spores, fresh water algae and dinoflagellates were recovered from the studied section of both wells. One floral zone (P800) and three (3) subzones (P860, P850 – P840 and P830) were delineated in both wells based on the recognition of the base continuous occurrence of Nympheaepollis clarus and the quantitative base occurrence of Cyperaceaepollis sp. These bioevents as well as the associated palynomorph assemblage indicated a Late Miocene age for the analysed section of both wells. The organic facies analysis revealed three palynofacies types pointing to three possible paleoenvironments which were the proximal, marginal and distal shelf environment laid down under anoxic, suboxic and oxic condition. On this basis a coastal to marginal marine environment was proposed for the sequence penetrated by the two wells. The thermal maturity deduced from the optical examination of the organic matter revealed that Well X organic matters were immature while those of Well Y were immature to slightly mature (TAI between - 2 and + 2 and SCI between 3 and 5). A strong correlation occured between the two wells studied based on their microfloral and palynofacies contents as well as the thermal maturity. The study concluded that palynoflora and palynofacies analysis played an important role in the hydrocarbon exploration technique, especially in the determination of age, paleoenvironment and thermal maturity of the penetrated strata.