Abstract
Three selected reservoirs (XB, XC and XE) from three wells (A, B and C) occurring within the Agbada producing sands in part of the Greater Ughelli Depobelt of the onshore Niger Delta have been studied. The study aims at evaluating the petrophysical characteristics of the sand-bodies and also identifies the various flow units present within each reservoir. Petrophysical parameters were used as input data to generate the Stratigraphic Modified Lorenzo Plots (SMLP). This model uses a graphical method to quantitatively determine flow units and to understand the flow and storage capacities of sedimentary rocks. Results of the analysis shows that average porosity and permeability range is between 7-28.8% and 1.20-529 mD, indicating poor to very good reservoir quality in different parts of the field. Generally, porosity and permeability decrease with increasing depth in the field reflecting burial diagenetic porosity loss in response to increasing thermal exposure with depth. Porosity and permeability change laterally across the field from west to east. Increase in porosity and permeability towards the eastern part of the field reflects lateral change in facies. Well C has the best porosity (28%) and permeability (529 mD), lowest water saturation (0.01), hence, highest hydrocarbon prospect. The stratigraphic Modified Lorenzo Plots (SMLP) revealed a total of seventy five (75) Flow Units (FU) in the three studied reservoirs. Each reservoir displays similar flow pattern relative to others suggesting that facies (rock properties) have a strong control on flow in each reservoir. Generally, poor quality units occur towards the bottom of each reservoir in a well and good quality units towards the top. The dominant flow units in the three reservoirs fall within the high storage and flow (normal flow unit) unit category, suggesting that the dominant depositional setting (shallow marine shoreface/beach/barrier) and facies type beside diagenetic effects play significant role in fluid dynamic behaviour of any rock body. Depositional environments and subsequent diagenesis are the primary factors controlling porosity distribution, pore connectivity and fluid flow in the three studied reservoirs.
Highlights
The study area falls within the onshore portion of the Niger Delta sedimentary basin in the Greater Ughelli depobelt
Petrophysical evaluation of three reservoirs (XB, XC and XE) carried out shows average porosity and permeability range to be between 7-28.8% and permeability 1.20-529 mD (Table 1)
Well A occurred towards the basin-ward side of the field and may indicate that there is a shift from lower marine mud/silt dominated environment to the shoreface/coastal environment where porosity is high
Summary
The study area falls within the onshore portion of the Niger Delta sedimentary basin in the Greater Ughelli depobelt. The Agbada stratigraphic unit forms the hub of oil and gas accumulation in the basin. Extensive studies have been carried out that gave insight into the gross depositional setting of the foreset beds of the Agbada reservoirs (Amajor and Agbaire, 1989; Reijers, 2011; Arochukwu, 2014). Efforts have been concentrated on developing and producing from proven reserves in the various oilfields. This provided more job opportunities for reservoir engineers, production engineers, development geologists and petrophysicists than exploration geoscientists. Petrophysical parameters serve as input data that help in building these models that have given much insight into reservoir condition and improved oil and gas production
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