사암 저류층 특성 변화에 따른 해양전자탐사 반응 분석
An Analysis on mCSEM Responses for Sandstone Reservoirs with Respect to Changes in Petrophysical Properties
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초록
이 연구에서는 사암 저류층의 매개변수 값 변화에 따른 해양전자탐사 자료의 반응 변화를 분석하였다. 수포화도, 공극률, 지층수의 전기비저항과 같은 저류층의 특성에 따라 탐지하고자 하는 탄화수소층의 전기전도도가 달라지며 이는 전자기 반응에 영향을 미치게 된다. 따라서 해양전자탐사자료의 올바른 해석을 하기 위해서는 저류층 특성에 대한 연구가 필수적이다. 반응 변화 연구를 위하여 유한차분법에 기초한 3차원 순방향 모델링알고리즘을 이용하였다. 순수사암 저류층 분석에 많이 이용되는 Archie 공식을 이용하여 순수 사암 저류층의공극률과 수포화도 그리고 지층수의 전기비저항을 고려하여 저류층 전기비저항 값을 계산한다. 계산된 전기비저항을 저류층 수치 모델에 적용하여 반 무한매질에서 전기장의 진폭을 각각 비교 분석하였으며, 반무한 매질의전기장 진폭으로 정규화한 결과로 반응 변화를 살펴본다. 또한 자료에 영향을 미칠 수 있는 탐사 변수인 주파수와 저류층의 매설 깊이의 영향도 분석하였다. 사암 저류층에서 수포화도가 0.2에서 0.5로 증가할 때 해양전자탐사의 반응은 70% 이상 변화하였다.
Abstract
This study makes an analysis on marine controlled-source electromagnetic method (mCSEM) responsesfor various petrophysical properties of sandstone reservoir. It is necessary to consider sensitivity of mCSEM datato petrophysical properties of the reservoir for valid interpretation of mCSEM field data. For computing reservoirresistivity that changes in accordance with reservoir porosity, water saturation and resistivity of formation water,we used Archie’s equation which is widely used for formation evaluation of sandstone reservoir. We obtain andanalyze not only amplitude of electric field but also its normalized amplitude by using a three-dimensional mCSEMmodeling algorithm. Furthermore, we study on relations between operation frequency and buried depth ofhydrocarbon reservoir. The relative difference in mCSEM responses for a sand reservoir is more than 70% whenthe water saturation increases from 0.2 to 0.5.
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