Rashid, F, Glover, PWJ orcid.org/0000-0003-1715-5474, Lorinczi, P et al. (2 more authors) (2017) Microstructural controls on reservoir quality in tight oil carbonate reservoir rocks. Journal of Petroleum Science and Engineering, 156. pp. 814-826. ISSN 0920-4105
Abstract
In carbonate reservoir rocks the complex interaction between the petrophysical properties corresponds to the various depositional microstructures which are modified by various diagenetic processes 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 dp smaller than 1 μm and a nanoporous pore-throat size), (ii) matrix composed of micro-intercrystalline pores (1<dp<10 μm with a corresponding micron-scale pore-throat distribution), and (iii) meso-intragranular and moldic pores (dp>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‾⁴mD/psi and -4 ×10‾⁵mD/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.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2017 Elsevier B.V. This is an author produced version of a paper published in the Journal of Petroleum Science and Engineering. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | Tight carbonate reservoirs; Permeability; Porosity; Pore-throat size; Stylolites; Effective stress |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Institute for Applied Geosciences (IAG) (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 27 Jun 2017 10:37 |
Last Modified: | 24 Jun 2018 00:38 |
Status: | Published |
Publisher: | Elsevier |
Identification Number: | 10.1016/j.petrol.2017.06.056 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:118288 |