【作者】 李洋辉；

【导师】 宋永臣； Masayuki Hyodo；

【作者基本信息】 大连理工大学 ， 能源与环境工程， 2013， 博士

【摘要】 天然气水合物作为一种重要的新能源,因其在世界范围内分布广、储量大,引起世界各国包括我国政府在内的高度关注。天然气水合物勘探和开发可能会引起海底滑坡、井壁坍塌、工程结构物破坏以及甲烷气体泄漏等灾害。本文针对上述过程涉及的天然气水合物储层力学问题,开展了实验研究及应力应变本构关系研究,以期为天然气水合物安全开采提供理论依据与技术支持。根据天然气水合物稳定存在的低温、高压特点,研制了一套专用的TAW-60低温、高压水合物三轴仪,以及与之配套的压力晶析制样装置。采用混合制样法制备天然气水合物沉积物试样,实验研究了温度、围压、水合物含量等对冻土区天然气水合物沉积物强度及变形特性的影响。首次发现了高围压条件下冻土区天然气水合物沉积物和含冰粉天然气水合物强度降低的现象,获得了冻土区天然气水合物沉积物的剪切强度、黏聚力、内摩擦角等参数,提出了分段线性强度准则和高围压条件下的非线性强度准则,验证了高围压条件下修正Duncan-Chang模型对冻土区天然气水合物沉积物的适用性。利用日本山口大学温控、高压水合物三轴仪,采用原位生成法制备天然气水合物沉积物试样。系统分析了不同荷载条件下,注热开采与降压开采过程对海底天然气水合物储层稳定性的影响。研究表明,当天然气水合物沉积物承受的荷载大于分解后沉积物的强度时,注热开采会导致天然气水合物储层的破坏,降压开采不会导致天然气水合物储层的破坏,而水压回复过程则有可能造成储层的破坏。研究了气饱和天然气水合物沉积物及C02水合物沉积物的强度及变形特性,详细分析了温度、孔隙压力、有效围压、水合物饱和度等对其力学特性的影响,并与水饱和天然气水合物沉积物进行了对比。发现相同条件下气饱和天然气水合物沉积物的强度、刚度、体积变形均大于水饱和天然气水合物沉积物,且气饱和天然气水合物沉积物呈现出更明显的剪胀和应变软化现象。证实了在一定温度、压力条件下,采用C02置换法开采天然气水合物在力学稳定性上是可行的。基于大量实验研究获得的天然气水合物沉积物应力应变规律,在修正剑桥模型(Modified Cam-Clay Model)的基础上,通过引入次加载面(Subloading surface)理论,同时考虑天然气水合物对沉积物剪胀和黏聚力的影响,建立了适用于海底天然气水合物沉积物的新的弹塑性本构模型。更多还原

【Abstract】 Methane hydrate has attracted global attention due to its widespread occurrences and large potential as an energy resource. During the production of methane from hydrates, hydrate dissociation may induce a variety of geological disasters, such as subsea landslides, borehole collapse, destruction of engineering structures and methane gas leakage. In this paper, according to the related mechanical problems during production, the constitutive relationship of methane hydrate-bearing sediments was studied, based on a series of experimental research, in order to provide a theoretical basis and technical support for safe extraction of methane hydrates.A series of triaxial compression tests were conducted to investigate the effects of temperature, confining pressure and hydrate content on the mechanical properties of permafrost-associated methane hydrate-bearing sediments (prepared by mixed volume sample preparation method), using a specifically designed low-temperature high-pressure triaxial testing device (TAW-60). This paper originally discovered that the failure strength of methane hydrate-bearing sediments and methane hydrate containing ice presented a slow descending trend with increase of confining pressure under high confining pressures, obtained the shear strength, cohesion and internal friction angle of methane hydrate-bearing sediments, proposed a piecewise linear strength criterion and a nonlinear strength criterion under high confining pressures, verified the applicability of modified Duncan-Chang model for permafrost-associated methane hydrate-bearing sediments under high confining pressures.The methane hydrate-bearing specimens were also prepared by in situ forming method, using a temperature-controlled high pressure triaxial apparatus of Yamaguchi University. The effects of thermal recovery method and depressurization method on the mechanical properties of methane hydrate-bearing sediments were studied. The results indicate that:the thermal recovery method will cause the failure of methane hydrate-bearing sediments when the axial load is higher than the strength of methane hydrate-bearing sediments after dissociation; the depressurization method will not cause collapse of methane hydrate-bearing sediments during depressurization. However, water pressure recovery may lead to failure under certain conditions. Also, the effects of temperature, pore pressure, effective confining pressure and hydrate saturation on the mechanical properties of gas-saturated methane hydrate and CO2hydrate-bearing sediments were studied, and a comparison was made with water-saturated methane hydrate-bearing sediments. The results indicate that:(1)failure strength, and stiffness of gas-saturated specimens are higher than those of water-saturated specimens, and the gas-saturated specimens present more markedly shear dilation and strain-softening behavior;(2)it is feasible to use CH4-CO2replacement technology for the production of methane from hydrate reservoirs in mechanical considerations.Based on the modified Cam-Clay model, subloading surface theory and obtained experimental data, a new elastoplastic constitutive model for methane hydrate-bearing sediments was proposed, considering the effects of methane hydrate on the cohesion and shear dilation.更多还原