Constitutive model for mechanical properties of highly porous organic-rich chalks from central Israel

O. Shitrit, Y. O. Rosenberg, Y. H. Hatzor, I. Reznik, S. Nguyen, Shimon Feinstein, H. J. Vinegar

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

We report the effects of porosity and total organic carbon (TOC) content on the mechanical behavior of organic-rich chalks, based on laboratory measurements. The organic-rich chalks are from the Senonian Ghareb and Mishash formations. This deposit is an immature oil-prone source rock, about 300 meters thick, situated at shallow depths (several hundreds of meters) in the Shefela basin in central Israel. The study is based on core data collected from the Zoharim borehole. Three main phases comprise the bulk volume of this rock: 1) carbonate mineralogical phase (predominantly calcite); 2) pores (mostly saturated with brine); and 3) solid organic phase (type IIS kerogen). The mechanical effects of porosity (23-45%) and TOC (4-19%) are evaluated based on bulk incompressibilities vs. volumetric fractions analysis. Volumetric fractions of mineralogical and organic phases were obtained by porosity, density and TOC measurements. Saturated rock bulk moduli were measured through ultrasonic velocity measurements. Saturated rock bulk moduli correlate best with the sum of kerogen and pore volume fractions, rather than each of them separately. The volumetric fractions were also used to define the range of bulk modulus of the organic-rich chalk, using the Hashin-Shtrikman upper and lower bounds. Based on Marion's Bounding Average Method (BAM), the normalized stiffness factor of the chalk averaged at w=0.197, indicating a soft pore geometry. Using the average normalized stiffness factor, the BAM predictions showed excellent match with the saturated rock bulk modulus and the sum of kerogen and pore volume fractions. Based on our findings, it is inferred that kerogen grains do not support the solid skeleton but are distributed between the minerals grains. We also propose here a straightforward approach for calculating the Hashin-Shtrikman bounds, based on TOC and porosity measurements. The mechanical effects of porosity and TOC indicated here are very important for the understanding of the influence of immature kerogen presence in highly porous chalks, as the Ghareb and Mishash formations.

Original languageEnglish
Title of host publication13th ISRM International Congress of Rock Mechanics
Editors Hassani, Hadjigeorgiou, Archibald
PublisherInternational Society for Rock Mechanics
Volume2015- May
ISBN (Electronic)9781926872254
StatePublished - 1 Jan 2015
Event13th ISRM International Congress of Rock Mechanics 2015 - Montreal, Canada
Duration: 10 May 201513 May 2015

Conference

Conference13th ISRM International Congress of Rock Mechanics 2015
Country/TerritoryCanada
CityMontreal
Period10/05/1513/05/15

Keywords

  • Elastic moduli
  • Incompressibility
  • Kerogen
  • Organic-rich chalk
  • Porosity
  • Total Organic Carbon (TOC)

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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