ABSTRACT

Estimation of Petrophysical exponents greatly affect the estimation of reservoir productivity. It is importance to accurately evaluate these exponents. This dissertation therefore was set out to estimate petrophysical exponents: cementation factor (m), and apparent formation water resistivity (Rw). Pickett’s and Buckle’s plots were utilized in this research. Quick look analysis is performed on well intervals within the five major depositional belts of the Niger Delta region. This work delineated thirty (30) potential reservoirs within twenty (20) oil wells which cut across the Niger Delta Basin. These reservoirs ranged in thickness between 9ft (2.74m) to 120ft (36.58m). The depth range of the reservoirs are 6223.5ft (1896.93 m) to 12365.83ft (3851.40 m). At these depths, sands encountered are intercalated with Shale of volume, 7% to 38.5%. The porosity values for the reservoirs are between 21.8% to 41.6%. These are regarded as good quality reservoirs. Water saturation calculated from Archie’s equation varies from 0.057 – 0.736. This corresponds to average hydrocarbon saturation range between 0.264 – 0.942. Porosity exponent or cementation factor (m) estimated from Pickett’s plot was between 1.74 to 3.39 compared to Archie’s constant of 2. Apparent formation water resistivity (Rw) values obtained from Pickett’s plot range between 0.201 – 0.208 as compared to Archie’s 0.2. Water saturation calculated from Pickett’s plot varies from 0.107 – 0.911. This corresponds to average hydrocarbon saturation range between 0.089 – 0.893. The Water saturation calculated from Archie’s equation are lower compared to water saturation calculated using Pickett’s plot. Volumetric estimations of Original Oil in Place (OOIP) were done within these intervals in bbl of oil using parameters from the known equations of Archie and its modified counterparts (Pickett’s plot). OOIP estimates for Archie with porosity exponent of 2 range from 445.259bbl to1598.999bbl. For Pickett's plot, the porosity exponent between 1.74 to 3.39, the estimated OOIP is between 115.259bl to 1434.299bbl for the same interval. The reservoir volume yielded differences in estimate of OOIP from 5% to 86.28%, between Archie’s equation and Pickett’s plot. The variation of the porosity exponent across the study area is attributed to the fact that porosity exponent varies considerably from interval to interval. This is due to the effect of grain and pore form, grain type, pore system, and overburden pressure. The Buckle's plot demonstrates this impact.This study has therefore shown the importance of using in-situ logs for estimation of porosity exponent and apparent formation water resistivity. These are very useful parameters for estimation of water saturation, formation factor and reserves.