Preprint Article Version 1 This version is not peer-reviewed

Controls of Depositional Environments on Reservoir Quality in Terms of Porosity and Permeability Gabo Field Niger Delta

Version 1 : Received: 24 April 2019 / Approved: 25 April 2019 / Online: 25 April 2019 (11:16:30 CEST)

How to cite: Ideozu, R.; Nduaguibe, T. Controls of Depositional Environments on Reservoir Quality in Terms of Porosity and Permeability Gabo Field Niger Delta. Preprints 2019, 2019040280 (doi: 10.20944/preprints201904.0280.v1). Ideozu, R.; Nduaguibe, T. Controls of Depositional Environments on Reservoir Quality in Terms of Porosity and Permeability Gabo Field Niger Delta. Preprints 2019, 2019040280 (doi: 10.20944/preprints201904.0280.v1).

Abstract

The controls of depositional environments on reservoir quality have been evaluated in terms of porosity and permeability of the Gabo Field, Niger Delta, Nigeria. Data used in this research include Well logs, Core data and photos, and grain size analysis for Wells 51 and 52 in the study area. Standard methods as applicable in petrophysical and sedimentological analysis has been adopted. Thirteen reservoir units have been identified in wells 51 and 52 which had 5 reservoirs cored each. The lithofacies units of the identified reservoirs across the study area, comprise pebbly sands, coarse -, medium -, fine- and very fine-grained sands, sandy mud, silty sands and heteroliths. The heteroliths – very fine-grained silty muds are highly bioturbated. Ophiomorpha and skolithos are the major trace fossils with sedimentary structures (ripple lamination, wavy lenticular and planar beds, cross bedded sands, coarsening and fining upward). The facies associations interpreted for the study area are Channel and Coastal barrier systems and the environment of deposition as distributary channel, upper and lower shoreface. The sedimentary processes that deposited facies ranged from high energy regimes, reworking by waves to low energy with periodic influx of silts and muds. The average porosity and permeability for reservoirs in Well 51 is 16.7% and 1317 Md, reservoirs in Well 52 is 28.2% and 2330Md whereas porosity range for the study area is 2% - 32% and permeability is 1.2 – 10600 Md. The reservoir quality reservoir of the sand units in Well 51 (7, 9 and 13) and Well 52 (5, 7, 9, 11 and 13) is excellent - good, this is because of the dynamics environments of deposition (upper shoreface and distributary channel) as well as the mechanisms that play out during deposition such as bioturbation, sorting, sedimentary structures formed. Whereas the poor quality across the reservoirs especially the lower shoreface and prodelta facies is as result of lack bioturbation, connectivity, multiplicity of burrows that may have been plugged by clay and intercalation of shale and sand (heteroliths). This research has shown that environments of deposition have direct influence the reservoir quality in terms of porosity and permeability.

Subject Areas

Porosity, permeability, skolithos, Ophiomorpha, lithofacies, reservoir, bioturbation, channel and coastal barrier systems.

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