TAXONOMY, PALYNOFACIES AND SEQUENCE STRATIGRAPHIC CHARACTERIZATION OF ORE-1, ORE-2 AND ORE-3 WELLS, ORE FIELD WESTERN NIGER DELTA BASIN, NIGERIA

Abstract

Taxonomy, palynofacies and sequence stratigraphic studies were carried out on sediments retrived from Ore-1, 2 and 3 wells. Ore-1, 2 and 3 wells are located on latitudes 6º 03ʹ 40ʹʹ N, 6º 03ʹ 40ʹʹ N and 6º 03ʹ 17ʹʹ N and longitudes 5º 35ʹ 44ʹʹ E, 6º 03ʹ 17ʹʹ E and 5º 37ʹ 22ʹʹ E respectively in the onshore part of the western Niger Delta.The study aims at the identification, description and classification of palynofacies assemblages and paleoenvironment under which they were deposited.One hundred and forty-three ditch cutting samples were analysed between the intervals of 9700 ft - 10350 ft in Ore-1, 9800 ft – 10575 ft in Ore-2 and 9700 ft – 10475 ft in Ore-3. The acid method for samples preparation were employed for the recovery of palynofacies assemblages present in the three wells. Palynofacies data were integrated with the gamma ray log data for paleoenvironmental, paleoclimatic and sequence stratigraphic study. A total of 501 palynomorphs were recorded in Ore-1, 1191 in Ore-2 and 678 in Ore-3. The assemblages were dominated by freshwater palynomorphs of Botryoccocusbraunii.Palynomaceralsanalysis of the three wells reveal over 90% of palynomaceral 1 (PM1), 80%ofpalynomaceral 2 (PM2), less than 5% of palynomrphs and low percentage of palynomaceral 3 and 4.Threepalynostratigraphic interval zones were established in Ore-1 well and four zones inOre-2 and 3 wells. The zones in Ore-1 well consists of Verrucatosporitesusmensis- Ctenolophoniditescoastatus, Pachydermitesdeiderixi - Grismdalapolygonalis and Spinicolpitesechinatus - Proxapertitescursuszones. Ore-2 has Verrucatosporitesusmensis - Pachydermitesdeiderixi,Retibrevitricolporitesprotrudens–Grimsdaleapolygonalis, Pradapolisflexibillis - Proxapertites cursus and Longapertites sp.–Ctenolophoniditescoastatuszones. Ore-3 comprises of Verrucatosporitessp. - Grimsdaleapolygonalis, Doualaditeslaevigatus–Ctenolophoniditescoastatus,Pradapolisflexibillis – Psilatricolporitescrassus and Retimonocolpitesssp. -Racmonocolpiteshianszones. The studied intervals were dated middle (38 to 47.8 Ma)tolate Eocene (33.9 to38 Ma) based on the stratigraphic age range of marker species. The lithology of the wells consists ofalternation of course, medium to fine grainedsandstone units and shale beds. The shale and sand ratio in Ore-1 averages 66.2:33.8%, Ore-2 recorded 57.3:42.7% and Ore-3 average 45.8:54.2%. Integration of textural characteristics, gamma ray log and palynofacies assemblages revealed that the sediments from Ore-wells were deposited in upper to lower delta-plain environment. The studied interval comprises of one depositional system which consists of the lowstand systems tract (LST) at the base, transgressive systems tract in the middle (TST) and the highstand systems tract at the top (HST). The maximum flooding surface (MFS) has been dated 38.6 Ma - 41 Ma while the sequence boundaries (SB) dated 44.4 Ma. The sandstone and shale units of the systems tracts are prospective hydrocarbon source, reservoir and seal rocks. Integration ofseismic data analysis, sedimentology, porosity and permeability studies are recommended for better understanding of the hydrocarbon system within the wells.