약한 층리면이 발달된 셰일층의 방향성 시추공의 안정성 분석
A Stability Analysis of Directional Drilling on the Shales With Weak Bedding Planes
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초록
본 연구에서는 약한 층리면이 발달된 셰일층에서 방향성 시추시 발생할 수 있는 안정성 문제를 분석하였다. 분석을 위해 대체로 지질학적 특성과 암석역학적 자료가 잘 알려진 캐나다 북동 브리티시 콜롬비아 지역의 셰일층을 선택하였다. 연구 결과 약한 층리면이 발달되어 있는 셰일층의 경우에는 붕괴 시 비대칭적 붕괴가 일어나는 것을 알 수 있었다. 또한, 약한 층리면이 발달한 경우에는 시추공이 층리면에 대해 수직에 가까울수록 더욱 안정적인 것을 알 수 있었다. 이러한 경우 최적의 방향성 시추궤도의 선정은 시추이수의 비중을 높이지 않고서도 안정적 시추를 가능케 함을 알 수 있었다. 이 연구 방법 및 결과는 향후 지질학적으로 이 연구지역과 유사한 퇴적특성을 지닌 셰일층에서의 방향성 시추 안정성 평가에 활용할 수 있을 것이다.
Abstract
In this paper, directional wellbore stability analysis is carried out for the shales in which weak bedding planes are developed. Shale layers in Northeastern British Columbia area has been selected for the wellbore stability analysis due to well-known geological and geomechanical properties. In the case of shale layer with weak bedding planes, it was found that breakouts around the wellbore developed asymmetrically. It was also found that wellbore is more stable with the trajectory almost perpendicular to the weak bedding planes. In this case, less mud weight can be applied to achieve more stable directional wellbore with this trajectory. It is expected that the methodologies and results in this paper can be beneficial to wellbore stability analyses for shale layers with similar geological and geomechanical setting to this research area.
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