ORGANIC RICHNESS AND PETROLEUM GENERATIVE POTENTIAL OF ENUGU AND MAMU FORMATION, ANAMBRA BASIN, NIGERIA

Abstract

Organic geochemical assessment of Enugu andMamu Formations is aimed at characterizing the organic richness, type and the thermal maturity in order to deduce the hydrocarbon generating potential of the formations. The assessment encompassing Total Organic Carbon (TOC wt.%), Soluble Organic Matter (SOM mg/g) and Hydrogen Index (HI) and Tmax were accomplished through analytical procedure of Walkely Black, Soxhlet extraction and Rock Eval Pyrolysis. Bedding characteristics of the investigated section of the Enugu Formation reveal a coarsening upward sequence with thick dark grey shale at the base grading upward through siltstone into thin texturally matured sandstone. On the other hand, the investigated section of the Mamu Shale is made up of alternating sequence of shale, siltstone and sandstone. Total Organic Carbon values for Enugu Formation ranges from 0.52 to 3.79 wt.% with an average of 1.55 wt.%. Determined TOC value for Mamu Shale ranges from 0.83 to 3.79 wt.% with an average of 2.47 wt.%. The average values for both formations in excess of the 0.5 wt.% threshold is indicative of adequate concentration of organic matter for hydrocarbon generation. Soluble Organic Matter ranges for the two formation (634 to 1251 ppm for Enugu Formation and 725 to 1714 ppm for Mamu Formation) classify them as moderately to fairly rich hydrocarbon source rock. However the low Hydrgen Index (HI) signifies terrestrially sourced sediment input of the organic matter and with a low Tmax value which ranges between 425oC to 435oC, a low thermal maturation is inferred for both Enugu and Mamu Formation.