含水合物沉积物三轴力学参数演化规律实验

含水合物沉积物三轴力学参数是评价天然气水合物开采过程中储层力学响应机制的重要参数之一。本文通过系列含水合物沉积物室内三轴剪切实验，探讨了天然气水合物饱和度、有效围压等参数对沉积物三轴力学参数的影响规律。特别地，本文将岩土临界状态理论应用于含水合物沉积物剪切过程中发生应变硬化、应变软化破坏的机理分析。结果表明，含水合物沉积物在剪切过程中发生应变硬化破坏还是应变软化破坏，取决于沉积物本身特性、外界加载条件两方面，实验条件下水合物饱和度与有效围压分别是控制含水合物沉积物破坏形态的内因与外因。典型三轴力学参数如峰值模量、轴向应变-侧向应变关系等参数的演化规律随着沉积物破坏模式的不同而迥异，因此含水合物沉积物三轴力学参数定量演化规律建模需要在同一个破坏模式条件内进行。

特别需要指出的是，本文通过实验证明：随着含水合物饱和度的降低，对于同一种含水合物沉积物，会发生峰值模量的“陡降”。这意味着对于实际水合物开采储层而言，随着水合物开采过程的进行，必定存在某一个临界水合物饱和度值，当水合物饱和度值低于该临界饱和度值时，可能导致地层的突发性破坏。因此为了有效支撑水合物试采安全可控，必须针对特定地层开展进一步的三轴剪切实验，为试采过程提供风险提示点。

Advances in Geo-Energy Research， 2018, 2(1): 43-52论文网址： http://www.astp-agr.com/index.php/Index/Index/detail?id=47

Experimental study on evolution behaviors of triaxial-shearing parameters for hydrate-bearing intermediate fine sediment

Yanlong Li, Changling Liu, Lele Liu, Jianye Sun, Haojia Liu, Qingguo Meng

(Published: 2018-02-02)

Corresponding Author and Email: Changling Liu, qdliuchangling@163.com

Citation: Li, Y., Liu, C., Liu, L., Sun, J., Liu, H., Meng, Q. Experimental study on evolution behaviors of triaxial-shearing parameters for hydrate-bearing intermediate fine sediment. Advances in Geo-Energy Research, 2018, 2(1): 43-52, doi: 10.26804/ager.2018.01.04.

Article Type: Original article

Abstract:

Evolution behaviors of triaxial shearing parameters are very important for geo-technical response analysis during the process of extracting natural gas from hydrate-bearing reservoirs. In order to explore the effects of hydrate formation/decomposition on triaxial shearing behaviors of intermediate fine sediment, natural beach sand in Qingdao, China, which was sieved from 0.1 mm to 0.85 mm, was used and a series of triaxial shear tests were carried out in this paper. The principle of critical state was firstly used to explain the mechanism of strain softening and/or hardening failure mode. Moreover, an empirical model was provided for axial-lateral strain and corresponding model parameters calculation. Evolution rules of critical strength parameters were analyzed prominently. The results show that failure mode of sediment is controlled by several parameters, such as effective confining pressure, hydrate saturation, etc. Different axial-lateral strain model coefficients’ effect on strain relationships are different, probing into the physical meaning of each coefficient is essential for further understanding of strain relationships. Complex geotechnical response should be faced with the progress of producing natural gas from hydratebearing reservoir, because of sudden change of failure pattern and formation modulus. Further compressive study on critical condition of failure pattern is needed for proposed promising hydrate-bearing reservoirs.

Keywords: Hydrate-bearing sediments, strain-hardening, strain-softening, triaxial shear strength, intermediate fine sediment.

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