The effect of mineral composition and rock fabric on brittleness index: an example using the Montney Formation, Canada

Son, Junhyun; Lee, Hyun Suk; Kwon, Sanghoon

doi:10.31697/jpsg.2018.1.1.16

J Pet Sediment Geol 1(1):16-31

eISSN: 2635-7704

DOI: https://doi.org/10.31697/jpsg.2018.1.1.16

Article

광물 조성 및 함량과 암석 조직이 취성도 계산에 미치는 영향: 캐나다 몬트니층을 예시로

손준현¹^,²^,³, 이현석¹, 권상훈²^,^*

The effect of mineral composition and rock fabric on brittleness index: an example using the Montney Formation, Canada

Junhyun Son¹^,²^,³, Hyun Suk Lee¹, Sanghoon Kwon²^,^*

Author Information & Copyright ▼

¹한국지질자원연구원 석유해저연구본부

²연세대학교 지구시스템과학과

³포스코대우

¹Korea Institute of Geosciences and Mineral Resources

²Dept. of Earth System Sciences, Yonsei University

³POSCO DAEWOO

^*Corresponding Author : Sanghoon Kwon, Tel: +82-2-2123-5666, E-mail: skwon@yonsei.ac.kr

ⓒ Copyright 2018 Korean Society of Petroleum and Sedimentary Geology. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received: Jun 21, 2018 ; Revised: Jul 16, 2018 ; Accepted: Jul 18, 2018

Published Online: Oct 31, 2018

요약

암석 내에서 균열의 거동에 영향을 미치는 중요한 암석역학의 개념적 특성인 취성을 정량적으로 표현하기 위한 방법인 취성도에 대한 연구를 진행하였다. 일반적으로, 취성이 높은 암석일수록 더 많은 균열이 발달하고 서로 연결된다. 이러한 이유 때문에, 취성은 셰일 및 치밀가스 생산을 위한 수압파쇄 기법 적용의 대상 지층을 선정하기 위한 지표로 사용된다. 취성을 정량적으로 표현하기 위해 다양한 취성도가 사용되고 있으며, 각 취성도 계산에 영향을 미치는 요소를 파악하려는 연구가 수행되어왔다. 본 연구는 광물학 기반의 취성도를 계산하는 데 있어 암석 조직의 영향을 알아보는 것을 목표로, 캐나다 몬트니층에서 취득된 자료들을 기반으로 가장 대표적으로 사용되는 취성도인 탄성계수 기반의 취성도와 광물학 기반의 취성도를 계산하였다. 탄성계수 기반의 취성도는 음파검층, 물리검층 자료로부터 계산된 영률과 포아송비를 이용하여 도출하였으며, 광물학 기반의 취성도는 X-선 회절 분석을 이용한 정량분석 결과를 바탕으로 평가하였다. 두 가지 서로 다른 방법으로 얻은 취성도를 비교한 결과, 하부 몬트니층에서는 석영이 취성도에 주요한 영향을 주는 광물일 가능성이 제시되었다. 그러나 박편 관찰 결과로부터 하부 몬트니층의 강도에 영향을 줄 수 있는 광물이 백운석 및 점토광물로 추정됨을 고려할 때, 본 연구의 결과는 암석의 강도와 취성도가 서로 다른 요인에 의해 영향을 받을 수 있음을 지시하며, 이는 광물학 기반의 취성도를 보다 정확하게 계산하기 위해서 광물 조성 및 함량뿐만 아니라, 엽층리구조에 의한 이방성, 박편관찰을 통한 입자, 교결물질, 기질을 구성하는 광물의 정량분석 등 암석이 가지는 조직에 대한 고려가 수반되어야 함을 제시한다.

ABSTRACT

This study deals with brittleness index, which is a conceptual property that affects fracture behavior in rocks. Generally, more fracture networks are developed in more brittle rocks. For this reason, brittleness has been used as a guide to decide the target formation of hydraulic fracturing stimulation for shale and tight gas productions. Previous studies have been conducted to find out which factors have influences on the estimations of various brittleness indices to represent rock brittleness quantitatively. The objective of this study is to investigate the effect of rock fabric on the estimation of the mineralogy-based brittleness index. Both elastic moduli- and mineralogy-based brittleness indices, which are the most commonly used indices, are obtained using available data from the Montney Formation, Canada. The former index is evaluated using the Young’s modulus and the Poisson’s ratio that are calculated from the sonic and density logs. The latter index is estimated based on the mineral composition from X-ray diffraction quantitative analysis. Comparison between the results from two different methods indicates that quartz might be the controlling mineral on the brittleness index of the lower Montney Formation. Thin section observations, however, show that the strength of the lower Montney Formation might be determined by dolomite and clay considering matrix-supported textures. This means that rock strength and brittleness may not be governed by same controlling factors. This suggests that rock fabrics, such as anisotropy due to the lamination or quantitative analysis of minerals which constitute grain, cement, and matrix through thin section observation, should be considered in addition to the mineral composition in order to evaluate mineralogy-based brittleness index more accurately.

Keywords: 취성도; 몬트니층; 암석 조직

Keywords: brittleness index; Montney Formation; rock fabric

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