Integrated mineralogical and petrophysical evaluation of reservoir quality: an implication to exploration risk assessment in Odie field, offshore, Niger Delta.

Abstract

To reduce the risks involved in a successful hydrocarbon production in established oil fields, it is necessary to evaluate the quality of the heterogeneous sandstone reservoirs in the paralic sequence in the Niger Delta. As a result, the objective of this study is to assess and characterize the effects of mineralogy, reservoir quality, and diagenetic processes on selected reservoir samples from one appraisal well in the Odie oil field. On three (3) reservoirs that have been defined across the well, methods such as a petrographic study using both thin section and scanning electron microscope investigations and petrophysical analysis using suites of wireline logs have been successfully applied and integrated. According to established classification systems for rocks, the detrital mineralogy of the Odie reservoir sandstone samples is petrologically categorized as subarkose, quartz arenite, lithic arkose, and litharenite lithofacies. In both polycrystalline and monocrystalline samples, quartz grains are the most prevalent detrital component. Feldspars, particularly K-feldspar, micas, detrital and authigenic clays, and carbonatic detritus are next in abundance. The sandstones have admixtures of granules and pebbles with a range of sorting qualities, from moderately well sorted to poorly sorted. They range in grain size from fine to coarse. Authigenic syntaxial quartz overgrowths and K-Feldspar overgrowths were only occasionally to very rarely found in the sands units, with authigenic opaques appearing to be the most significant diagenetic phase seen. Although very delicate grains, like splayed mica laths, do show some evidence of crushing, all of the samples appear to have undergone relatively little compaction with point grain contacts throughout. Additionally, there seems to be some evidence of grain dissolution (primarily clay clasts with some feldspars), which suggests that porosity is enhanced by dissolution. Due to the unconsolidated nature of the sand section within the studied well (Odie-2), SEM analysis of the sediments revealed that the optical porosity is composed of well-connected intergranular macropores (27.1% to 44.0%), minor microporosity, and intragranular secondary pores (trace to 1%), with total porosity values ranging from 23.1% to as high as 45%. Effective porosity values show a minimum porosity value of 22% and a maximum porosity value of 31%, which shows that the reservoirs within the Odie field range from good, very good, to excellent porosity. This comparison to porosity estimation from well logs suggests a good match. The distribution of permeability within the field varies from good to very good to excellent reservoir permeability quality standards. Water saturation levels in all reservoirs have been calculated, and it has been determined that the Odie field contains hydrocarbons and should be developed accordingly in order to produce hydrocarbons. Key words: Reservoir quality, mineralogy, petrophysics, exploration risks, Niger delta.

Publication Info:

Author: Akporjevwe Godwin Umukoro, Yinka Ayodeji Olayinka, Olutayo Yusuf Lawal and Richmond U. Ideozu

Volume: 0

Issue: May

Published By: N/A, 2025-04-03