Controlling Factors on Petrophysical and Acoustic Properties of Bioturbated Carbonates: (Upper Jurassic, Central Saudi Arabia)

Moaz Salih,Hani Al Mukainah,Ammar El Husseiny,Mazin Bashri,Hassan Eltom,John J G Reijmer,Michael A Kaminski

doi:10.3390/app11115019

Moaz Salih, Hani Al Mukainah + Show 5 more

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https://doi.org/10.3390/app11115019

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Abstract

Many of the world’s productive Jurassic reservoirs are intensively bioturbated, including the sediments of the Upper Jurassic Hanifa Formation. Hydrocarbon exploration and production from such reservoirs require a reliable prediction of petrophysical properties (i.e., porosity, permeability, acoustic velocity) by linking and assessment of ichnofabrics and trace fossils and determining their impact on reservoir quality. In this study, we utilized outcrop carbonate samples from the Hanifa Formation to understand the main controlling factors on reservoir quality (porosity and permeability) and acoustic velocity of bioturbated carbonates, by using thin-section petrography, SEM, XRD, CT scan, porosity, permeability, and acoustic velocity measurement. The studied samples are dominated by Thalassinoides burrows that have burrow intensity ranging from ~4% to 27%, with porosity and permeability values ranging from ~1% to 20%, and from 0.002 mD up to 1.9 mD, respectively. Samples with coarse grain-filled burrows have higher porosity (average µ = 14.44% ± 3.25%) and permeability (µ = 0.56 mD ± 0.55) than samples with fine grain-filled burrows (µ = 6.56% ± 3.96%, and 0.07 mD ± 0.16 mD). The acoustic velocity is controlled by an interplay of porosity, bioturbation, and mineralogy. Samples with relatively high porosity and permeability values (>10% and >0.1 mD) have lower velocities (<5 km/s) compared to tight samples with low porosities and permeabilities (<10% and <0.1 mD). The mineralogy of the analyzed samples is dominated by calcite (~94% of total samples) with some quartz content (~6% of total samples). Samples characterized with higher quartz (>10% quartz content) show lower velocities compared to the samples with lower quartz content. Bioturbation intensity, alone, has no control on velocity, but when combined with burrow fill, it can be easier to discriminate between high and low velocity samples. Fine grain-filled burrows have generally lower porosity and higher velocities (µ = 5.46 km/s) compared to coarse grain-filled burrows (µ = 4.52 km/s). Understanding the main controlling factor on petrophysical properties and acoustic velocity of bioturbated strata can enhance our competency in reservoir quality prediction and modeling for these bioturbated units.

Highlights

In many parts of the world, Jurassic strata contain extensive bioturbated intervals that encompass significant hydrocarbon reservoirs such as the Fulmar Formation and BrentGroup, North Sea, UK [1,2]; the Ile Formation, Norway [3]; the Shaqra Group and the Ghawar Field, Saudi Arabia [4,5,6]; and the Vaca Muerta Formation, Argentina [7]
This study aims to determine the main factors that control the reservoir quality and acoustic velocities of the Upper Jurassic bioturbated strata of the Hanifa Formation in Central Saudi Arabia
The Upper Jurassic Hanifa Formation is composed of slightly to intensely bioturbated strata that were deposited within an intra-shelf basin on a shallow-marine carbonate platform

Summary

Introduction

In many parts of the world, Jurassic strata contain extensive bioturbated intervals that encompass significant hydrocarbon reservoirs such as the Fulmar Formation and BrentGroup, North Sea, UK [1,2]; the Ile Formation, Norway [3]; the Shaqra Group and the Ghawar Field, Saudi Arabia [4,5,6]; and the Vaca Muerta Formation, Argentina [7]. Bioturbation is defined as the biogenic (by benthic infauna) transport of sediment particles and pore water which destroys the sediment stratigraphy. These processes impact the physical properties of the sediment such as grain size spectrum, porosity, and permeability [8]. Benthic infauna can significantly modify the original sediments while generating new structures through sediment mixing and redistribution of the grains. Such modification may include sediment removal (bioerosion), sorting (biostratification), emplacement (biodeposition), and compaction [9]. Geochemical signatures of sediments may be modified by burrowing organisms through a combination of organic matter produced by these organisms [6,10]

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