PETROPHYSICAL PROPERTIES DISTRIBUTION AND ASSESSMENT OF THE KOCR-FIELD USING WIRELINE LOGS AND CORE DATA, NIGER DELTA BASIN, NIGERIA.

Abstract

Petrophysical properties distribution and assessment was conducted on an onshore marginal field in Niger Delta with the aim of evaluating the rock and fluid properties to boost hydrocarbon production and exploration in the field. Eight well logs were used for the eight wells in each reservoirs A, B and C, the well log and core data obtained were utilized for this study. Petrophysical properties evaluated are porosity, net to gross, formation factor, irreducible water saturation, permeability, water saturation, hydrocarbon saturation and pay thickness. The well logs suite contained the following logs: Gamma ray log for lithology identification; Resistivity log for fluid type discrimination and determination of water saturation; Density log for porosity determination; and Neutron in combination with density log for hydrocarbon types. A total of three reservoir sands (Sand A, B and C) were identified and correlated across all the eight wells based on gamma ray, resistivity, neutron and density log profiles. The reservoir gross thicknesses ranged from 62.55 to 228.50 ft, shale volume from 7.0 to 24.60%, net to gross from 0.76 to 0.93%, effective porosity from 20.78 to 26.22%, water saturation from 35.80 to 62.30% and permeability ranged from 545.94 to 2821.97 mD. This shows that the reservoirs are of good quality for hydrocarbon production across the field. From the analysis the field indicated that the proportion of void spaces occupied by water is low, thus, indicating high hydrocarbon saturation. Quantitative porosity verification using Pearson Correlation Coefficient and Regression Equations revealed significant similarity in the porosity values obtained from petrophysical well log and core data. Plots on scatter diagrams using porosity values derived from petrophysical log and that from core analysis for the three reservoirs obtained correlation coefficient (r) values of 0.7165, 0.8094, and 0.5025, respectively for reservoirs A, B, and C indicating strong linear relationships. Plots of values of water saturation derived from core analysis and that from petrophysical log for the reservoirs also showed linear trends. Plots of porosity values against permeability values showed fairly strong linear relationships between the two variables in all the reservoirs indicating that the reservoirs are permeable and have pores that are in strong communication. The calculated volumetrics indicates that reservoir sand body A has the highest STOIIP of (3329MMSTB), followed by C with (220MMSTB), and B having the least of (29MMSTB). The petrophysical properties of the reservoirs are enough to permit hydrocarbon production. For optimal hydrocarbon recovery, static modeling report should be considered for best well placement positions in field development since wrong well positioning could easily compromise wells and cause production decline.