Journal of Petroleum and Sedimentary Geology
Korean Society of Petroleum and Sedimentary Geology
Article

셰일 및 치밀 저류층의 지화학 및 암석물리 특성 연구동향 고찰

이현석1, 홍성경1, 최지영1,*, 안태웅1, 진재화1
Hyun Suk Lee1, Sung Kyung Hong1, Jiyoung Choi1,*, Tae Woong Ahn1, Jae Hwa Jin1
*Corresponding Author : Jiyoung Choi, Tel: +82-42-868-3252, Fax: +82-868-3417, E-mail: jychoi@kigam.re.kr

ⓒ Copyright 2020 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 permit unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received: Jul 03, 2018 ; Revised: Dec 04, 2018 ; Accepted: Dec 11, 2018

Published Online: Dec 01, 2020

요약

바넷셰일에서 가스의 상업적 생산이 1998년 시작된 이후 여러 종류의 비전통 에너지 자원 중 셰일가스에 대한 관심이 고조되었다. 셰일가스의 개발 초기에는 획일적인 수평시추와 다단계 수압파쇄로 대표되는 공장형 생산기법이 우세하였다. 하지만 최근 들어 지속되고 있는 고유가와 유가와 가스가의 비동조화 현상 등으로 인하여 셰일 및 치밀 저류층에 대한 지질학적 이해와 생산기법의 최적화 연구가 활발히 수행되고 있다. 셰일 및 치밀저류층의 생산성 평가를 위해서는 저류층에 배태된 가스량을 정확히 예측해야 한다. 이를 위해서는 자유가스량을 계산할 수 있는 투과도, 공극률, 수포화도가 측정되어야 하며, 탈착될 수 있는 가스량을 예측할 수 있는 총유기탄소량과 흡착성능을 측정해야 한다. 셰일 및 치밀저류층은 통상적인 저류층에 비하여 공극률과 투과도가 매우 낮기 때문에 이를 극복할 수 있는 측정방법이 필요하다. 최근에는 분쇄암석법(GRI법)을 사용하여 공극률과 투과도를 측정하고 있지만, 아직까지 표준방법이 확립되지 못한 실정이다. 공극 내 탄화수소의 체적을 제시하는 수포화도는 셰일 저류층을 대상으로 연구가 많이 미진한 상태이다. 셰일층 내 수포화도의 실측 자체에 많은 어려움이 있고, 기존 저류층에서 사용하던 관계식을 변형하여 적용하는 것에도 제약이 존재한다. 총유기탄소량은 셰일층의 석유과 가스 생성량을 평가하기 위하여 분석해 왔으며, 셰일층 내 잔류되어 있는 가스량을 추정할 수 있는 주요한 특성이다. 흡착가스량은 저류층의 압력에 따라서 셰일층 내에 흡착되는 가스량을 추정하는 것이다. 측정방법은 기존의 석탄층 메탄가스 평가에서 활용되는 방법을 사용하고 있지만, 셰일 및 치밀저류층에 적합한 흡착가스량 평가과정이 필요한 상태이다. 이처럼 셰일 및 치밀저류층이 가진 암석물리적 모호성과 특성분석의 어려움 때문에 표준화된 평가기법은 아직 미정립 상태이다. 향후 다양한 셰일 및 치밀저류층에 대한 연구를 수행하여 통합된 특성화 기법이 도출되어야 한다.

ABSTRACT

Shale reservoirs has drawn great attention among unconventional resources since the first unconventional extraction of gas from Barnett Shale by Mitchell in 1998. In the beginning, carpet drilling and hydraulic fracturing to shale reservoirs made a great benefit without detailed geological understanding. However, the sudden increase of gas supply and international economic crisis resulted in lower gas price relative to oil price, which requires more detailed development optimization and geological characterization on shale reservoirs to reduce operation cost. In order to evaluate the productivity of shale and tight reservoirs, it is necessary to accurately predict the amount of gas stored in the reservoir. To calculate exact volume of gas in reservoirs, we must reliably measure petrophysical parameters such as permeability, porosity, and water saturation to estimate free gas volume, and geochemical parameters such as total organic carbon (TOC) and adsorption capacity to estimate desorbed gas volume. Several measurement techniques have been proposed to overcome the difficulty in very low porosity and permeability of shale and tight reservoirs. Recently, the crushed rock technique have been used for porosity and permeability of shale and tight reservoir are measured, but the standard procedures have not yet been established. Water saturation is another hurdle since actual measurements are extremely difficult and time-consuming. Modified conventional equations have been tried, but there are still various limitations. We also cover currently available techniques and their limitations on TOC, a measure for gas generation potential, and adsorption capacity. Currently, measurement techniqies for petrophysical and geochemical properties of shale and tight reservoirs are not fully established. There should be detailed studies for the accurate estimation of these properties, which can lead successful reservoir characterization.

Keywords: 셰일저류층; 치밀저류층; 암석물리; 석유지화학; 평가모델
Keywords: shale reservoir; tight reservoir; rock physics; petroleum geochemistry; evaluation model

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