Microstructural controls on reservoir quality in tight oil carbonate reservoir rocks
File(s)
Accepted version
Author(s)
Rashid, F
Glover, PWJ
Lorinczi, P
Hussein, D
Lawrence, JA
Type
Journal Article
Abstract
In carbonate reservoir rocks the complex interaction between the petrophysical properties corresponds to the various depositional microstructures which are modified by various diagenetic process es that ultimately define the reservoir quality, and pose challenges to the prediction of permeability. The permeability heterogeneity in the carbonate oil reservoirs of northern Iraq varies widely and is thought to be controlled by a number of different factors. In this work, controls of matrix permeability for the Cretaceous Kometan formation selected from five oil fields in Kirkuk embayment zone have been investigated. Helium porosity, helium pulse decay permeability, brine permeability, Nuclear Magnetic Resonance (NMR), Mercury Injection Capillary pressure (MICP), Scanning Electronic Microscopy (SEM), X-Ray diffraction (XRD), and photomicrography of thin section have been used to investigate the effect of microstructure on the variation of permeability in the Kometan Formation. The formation has porosities and permeabilities which range from 0.5 ± 0.5% to 29 ± 0.5% and from 0.65 ± 0.08 μD to 700 ± 0.08 μD respectively. Three types of pore systems have been investigated using pore type, pore size and pore-throat size as characterizing parameters. We have recognized three microstructural types: (i) matrix composed of nano-intercrystalline pores (pore diameter d p smaller than 1 μm and a nanoporous pore-throat size), (ii) matrix composed of micro-intercrystalline pores (1 < d p < 10 μm with a corresponding micron-scale pore-throat distribution), and (iii) meso-intragranular and moldic pores (d p > 10 μm) also with microporous pore-throat radii. The nano-intercrystalline pore system is common across northern Iraq and represents the effective pore system type in the reservoirs of the Kirkuk embayment zone. For these tight carbonate reservoirs, the mineralogy, especially of quartz and clay minerals (illite and smectite), has little relationship with the measured Klinkenberg-corrected permeability. Consequently, mineralogy is not a useful controlling factor for permeability. Diagenetic processes have altered the depositional texture significantly, resulting in changes to the pore size and pore-throat size distribution and affecting the permeability. In addition the matrix permeability is sensitive to stress, with permeability decreases between −4 × 10 −4 mD/psi and −4 × 10 −5 mD/psi in the effective stress range from 0 psi to 4000 psi. It has been found that of the three microstructure pore types the nano-intercrystalline pore system is more sensitive to increasing effective stress compared to the micro-intercrystalline and meso-intragranular pore systems. Laboratory experiments have shown that stylolisation resulting from regional fluid movements has also affected matrix permeability, with the stylolites acting as barriers to fluid flow and considered to be an important source of tightness of the Kometan formation in the Kirkuk embayment fields.
Date Issued
2017-07-01
Date Acceptance
2017-06-21
Citation
Journal of Petroleum Science and Engineering, 2017, 156 (1), pp.814-826
ISSN
0920-4105
Publisher
Elsevier
Start Page
814
End Page
826
Journal / Book Title
Journal of Petroleum Science and Engineering
Volume
156
Issue
1
Copyright Statement
© 2017 Elsevier B.V. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/
Identifier
https://www.sciencedirect.com/science/article/pii/S0920410517305466
Subjects
Science & Technology
Technology
Energy & Fuels
Engineering, Petroleum
Engineering
Tight carbonate reservoirs
Permeability
Porosity
Pore-throat size
Stylolites
Effective stress
HETEROGENEOUS CARBONATES
PETROPHYSICAL PROPERTIES
OUTCROP ANALOG
PARIS BASIN
PORE-SIZE
PERMEABILITY
POROSITY
DIAGENESIS
SANDSTONE
EVOLUTION
Energy
0403 Geology
0904 Chemical Engineering
0914 Resources Engineering and Extractive Metallurgy
Publication Status
Published
Date Publish Online
2017-06-24