Petrographic and Thermal Maturity Investigation of Sediments from IDM 4 and IDM 5 Wells in the Niger Delta Basin, Nigeria.
Abstract
A Palynofacies analysis and thermal maturation study was conducted on wells IDM-4 and IDM-5 in the Niger Delta Basin, located within Latitude 04⁰ 08’ 02’’ N and longitude 06⁰ 08’ 06’’ E for IDM-4, and latitude 04⁰ 08’ 0’’ N and longitude 06⁰ 07’ 06’’ E for IDM-5. The study covered a depth range of 10030 ft to 11700 ft at 30 ft intervals.
Forty-nine ditch cutting samples from IDM-4 and forty-seven samples from IDM-5 were subjected to palynological processing, analysis, and interpretation. Additionally, kerogen analysis was performed on selected samples. The palynofacies analysis employed the simple acid method of sample preparation.
Lithological characterization of the sedimentary succession was determined through physical observation and Gamma Ray log analysis, revealing the presence of fine to medium-sized sandstones and sandy mudstones. The recovered palynomorphs and palynomacerals included biomarkers such as Zonocostites ramonae, Pachydermites diederixii, Sapotaceodaepollenites sp., Psilatricolporites cassus, and Crassoretitriletes vanraadshooveni, among others. These findings were correlated to early-Miocene to middle-Miocene stratigraphic ages.
In IDM-4, two distinct zones were identified: the Pachydermites diederixi zone (7000 ft to 7990 ft) and the Crassoretitrites vanraadshooveni Zone (6030 ft to 7000 ft). In IDM-5, three zones were established: the Polypodiaceoisporites sp. Zone, Magnastriatites howardi Zone, and Pachydermites diederixi Zone.
Based on palynofacies associations, the depositional environment for Pachydermites diederixii in IDM-4 was interpreted as a mangrove swamp, while the Crassoretitrites vanraadshooveni Zone suggested a mangrove-shoreface depositional environment. For IDM-5, the depositional environment ranged predominantly between mangrove and channel environments.
Regarding thermal maturation, intervals at 6050 ft, 6150 ft, 6400-6600 ft, and 6900-6950 ft in IDM-4 indicated the presence of mature liquid oil, while intervals at 6100 ft, 6200-6400 ft, 6600-6900 ft, and 6950-7950 ft indicated the presence of dry gas. In IDM-5, intervals at 10000-10950 ft represented the presence of dry gas, while intervals at 10950-11025 ft and 11450-11700 ft indicated the presence of mature liquid oil.
Petrographic and Thermal Maturity Investigation of Sediments from IDM 4 and IDM 5 Wells in the Niger Delta Basin, Nigeria.