岩石水力破裂數值分析模式建立暨初步物理模型試驗

Establishment of Numerical Analysis Model and Preliminary Lab Test for Hydraulic Fracture of Rock

童舒暘(SHU-YANG TUNG)

指導教授 ： 王泰典

國立臺灣大學/工學院/土木工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202003273

摘要

現地應力量測的重要性與日俱增，亦有許多調查現地應力方法，然而現地情況相當複雜，岩石的異質性或者結構本身的異向性甚至於其他因素皆有可能影響現地應力量測，若要充分了解不同影響因素對於量測的影響，需要建立一個簡單的環境，並且能簡便的控制並更改需要觀察的因子，來研究其對現地應力量測影響。建立一套能夠達成此一目的的程序是初始且至關重要的一環，此亦是本研究的目標。
本研究採用了調查現地應力中一個常見的方法——現地水力破裂試驗(Hydraulic Fracturing, HF)的概念，設計出實驗室規模的實驗。岩石水力破裂試驗相對於其他調查方法，通過水壓力紀錄、孔內影像以及岩石材料性質，更容易推估現地應力方向以及大小，然而水力破裂試驗雖可估算出現地應力情形，然而現地岩層情況太過於複雜，無法準確得知結果屬於鑽孔附近處局域之現地應力，或者其能夠代表全域之現地應力，此亦為水力破裂試驗目前需要改善之處，使估算的精度提升。
為了建立能夠探索現地應力影響因素之研究方法，本研究中採用了一邊長為30公分之立方形試體，於中間製作一鑽孔並封堵住上下兩側，將水注入鑽孔內側以進行實驗室尺度之水力破裂實驗，用以了解所建立之實驗系統能否順利執行水力破裂實驗，並且能夠提供之後的數值模分析模式一個驗證之手段；研究中所使用之數值分析軟體為以離散元素法(Discrete Element Method, DEM)為基礎之顆粒流數值模擬軟體(Particle Flow Code, PFC)，對相同尺寸之模型進行二維下之模擬，確認數值分析模式的可行性，並且探討不同圍壓下裂縫的生衍模式。於研究最後建立包含物理實驗及數值分析的執行步驟、程序，為往後了解現地應力量測影響因素的研究做為基石。

關鍵字

水力破裂物理實驗 ； 水力破裂數值模擬 ； 應力估算 ； 裂縫初生 ； 裂縫生衍 ； PFC 模擬

並列摘要

In-situ stress is an important parameter for civil engineering and will affect the design significantly. There’s different method nowadays of in-situ stress estimation like focal mechanism, inversion of fault slip data, and hydraulic fracturing. However, it’s difficult to estimate the exact in-situ stress. The reason why is that magnitude and orientation of in-situ stress can influence by complex reason, such as heterogeneity of material, structure anisotropy of rock, and terrain. Thus, it’s important to clarify the influence of different reason when conducting the estimation.
Apparently, it’s difficult to clarify the impact of different factors under in-situ condition since the interaction between them. Hence, a simpler situation should be created. A laboratory scale hydraulic fracturing test will be a good solution. By using mortar as experiment material, the control of conditions is possible. Changing different target factors and conducting hydraulic fracturing test could show the influence of corresponding factors through the result. After a series of research, the influence is clarified. But before it, a process of laboratory scale hydraulic fracturing should be established.
In this research, laboratory hydraulic fracturing experiment will be conduct, and fracture will be observed. The fracture initiation and propagation pattern, injection water pressure, and confining stress magnitude will obtain and be record during the physical experiment. After finishing a series of experiment, numerical analysis software PFC (Particle Flow Code) will carry out to simulate the physical experiment for the purpose of obtaining detailed data. A progress including physical experiment, numerical simulation, and calibration of hydraulic fracturing test will then be given.

並列關鍵字

Hydraulic fracturing experiment ； Hydraulic fracturing simulation ； Stress state estimation ； Fracture propagation ； PFC simulation

參考文獻

1. Adachi, J., Siebrits, E., Peirce, A., Desroches J., 2007. Computer simulation of hydraulic fractures. Int. J. Rock Mech. Min. Sci. 44, 739–757.

2. Al-Busaidi A., Hazzard J. F., Young R. P., 2005. Distinct element modeling of hydraulically fractured Lac du Bonnet granite. J. Geophys. Res. 110, B06302.

3. Barth, A., Reinecker, J., Heidback, O., 2008. Stress derivation from earthquake focal mechanisms, World Stress Map Project – Guidelines, 12.

4. Bell, J.S., Gough, D.I., 1979. Northeast-southwest compressive stress in Alberta: evidence from oil wells. Earth Planet Sci. Lett. 45, 475-482.

5. Bock, H., 1993. Measuring in-situ rock stresses by borehole slotting. In: Hudson, J. A., editor. Comprehensive rock engineering—principles, practice projects, vol. 3. Oxford: Pergamon Press, 433-443.