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Question: Are there any widely accepted published values (or ranges) that classifies a rock as having “low” “medium” “high” -strength, -hardness, -toughness, and -consolidation (cementation or cohesion?)?

UCS Background Material: I have come across some papers that have defined what is considered to be “low”, “medium”, “high” strength rocks as characterized by unconfined (uniaxial) compressive strength (UCS). This is what I have found:

  • “Due to the unique properties of these quartz arenite sandstone reservoirs high compressive strengths up to 25,000 psi are common,…” (emphasis is mine) (1)

  • “In order to define the effect of formation compressive strength on perforator penetration and hole character, various formations in the low-, medium-, and high- strength ranges were acquired for laboratory shot tests.” (emphasis is mine) (2).

The author then lists the rocks tested: low ~ 2000 psi UCS ( Austin chalk), medium ~ 5000 to 7000 psi UCS (Idiana limestone and Berea sandstone), High ~ 11,000+ psi UCS (Carthage limestone)

  • Ultrahigh-strength formations….Oman formations in which UCS varies from 20,000 to 55,000 psi.” (emphasis is mine) (3)

Hardness Background Material: I have seen a paper that has defined the inter-relationship between hardness (using the Brinell hardness number (BHN)) and consolidation, reference 4.

  • Loosely consolidated material (BHN 2-4 kg/mm2)

  • Friable-to-consolidated material (BHN 10-15 kg/mm2)

Consolidation Background Material: Reference 5 defines what is “unconsolidated” (damp sand), “weakly consolidated” (Saltwash south), and “strongly consolidated” Castlegate, Berea, etc., qualitatively.

  • “unconsolidated” = essentially no cohesion e.g. cohesive forces due to friction, granular interlocking and capillary forces.
  • “weakly consolidated” = can be failed by forces one can generate with their fingers
  • “strongly consolidated” = requires a tool such as an hammer to fail the rock

References:

  1. Blosser, W. R. (1995, January 1). An Assessment of Perforating Performance for High Compressive Strength Non-Homogeneous Sandstones. Society of Petroleum Engineers. doi:10.2118/30082-MS
  2. Thompson, G. D. (1962, January 1). Effects of Formation Compressive Strength on Perforator Performance. American Petroleum Institute.
  3. Mustafa, H. D., Briner, A. P., Jumaat, M. S., Grove, B. M., Atwood, D. C., & Judd, T. C. (2012, January 1). Ultrastrong Formations: Perforating Challenges, Limits, and Optimization. Society of Petroleum Engineers. doi:10.2118/159771-MS
  4. Vriezen, P. B., Spijker, A., & van der Vlis, A. C. (1975, January 1). Erosion of Perforation Tunnels in Gas Wells. Society of Petroleum Engineers. doi:10.2118/5661-MS
  5. Walton, I. C., Chang, F. F., & Lopez de Cardenas, J. (2004, January 1). Perforation Morphology and the Onset of Sand Production. Society of Petroleum Engineers. doi:10.2118/90123-MS
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  • $\begingroup$ I think there is no such distincitvely discriminating scheme. However, for consolidation, you mind find it usefull that there is an overconsolidation ratio (OCR) that gives the consolidation with respect to the recent depth of a rock. Moreover, you might look for Brittleness Index. $\endgroup$ – Bendaua Sep 26 '17 at 16:55
  • $\begingroup$ There is a consolidation test, but applied to mass rocks on geology engineering. There is dry and wet triaxial test eg geolabs.co.uk/effective-stress/#tab-id-2 $\endgroup$ – Universal_learner Oct 14 '18 at 8:57

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