【作者】 马庆涛；

【导师】 张卫东；

【作者基本信息】 中国石油大学 ， 油气井工程， 2011， 硕士

【摘要】 随着油气能源需求的不断增长和天然气水合物藏勘探的不断深入,商业开发天然气水合物已列入议事日程。由于天然气水合物分解前后,水合物赋存地层的力学性质产生变化,导致水合物钻井中发生井壁破坏的可能性明显增加,因此研究水合物储层的力学性质和井壁稳定性问题很有必要。本论文针对水合物钻井中保持井壁稳定这一技术问题,通过实验和理论研究的方法测定了水合物储层的剪切强度,分析了水合物钻井中保持井壁稳定的温度压力控制,以期对水合物的安全开发提供理论指导和技术支持。文中研究了天然气水合物的储层物理性质,对储层孔隙度、饱和度、渗透率、导热系数和力学性质等进行了系统总结。在调研国内外水合物剪切强度实验的基础上,自主研制了天然气水合物储层剪切强度仪,该仪器可以提供水合物稳定存在的低温高压环境,并在此环境中对水合物填砂模型进行直接剪切,测定了不同水合物饱和度下的剪切强度的变化规律。实验发现水合物储层的内聚力和内摩擦角随着水合物饱和度增加而增加,通过实验曲线的回归,得到了内聚力和内摩擦角随水合物饱和度的变化关系式,为计算水合物层井壁坍塌压力提供了参数。通过研究水合物钻井中保持井壁稳定的方法发现,如何确定并控制钻井液的低温高密度是解决问题的关键,文中在考虑岩屑和地层中水合物分解的情况下,基于质量、动量、能量守恒原理和传热学理论,利用微元分析和有限差分的方法,建立了环空气液两相流体的温度压力分布模型,编程求解模型并进行相关参数的敏感性分析。将求取的环空温度压力值与水合物相态曲线和钻井液安全密度窗口进行对比,提出了保持水合物层井壁稳定的钻井液临界入口温度和水合物分解压力两个关键参数,并给出了计算方法,为水合物钻井中钻井液温度和密度的确定提供了依据。更多还原

【Abstract】 With the growing demand for oil and gas energy and developing of natural gas hydrates exploration, it is planned to exploit gas hydrates commercially. However, as a result of gas hydrates dissociation, the mechanical properties of hydrate formation would change, and this will result to the possibility of borehole damage and reservoir unstable during hydrates drilling process, so it’s necessary to study the mechanical properties and borehole stable problems. Confronted with the problem of maintaining reservoir stability in the process of drilling, this paper measures the shearing strength of reservoir bearing hydrates by theoretical and experimental method, and studied the stability of hydrate reservoir during drilling in order to provide the theoretical guide and technique supports for security of the natural gas hydrates exploration.This paper makes research on the physical properties of hydrates reservoir, and summarizes the porosity, saturation, permeability and mechanical properties, etc of hydrates’reservoir systematically. On the base of investigation of shearing test around the world, the author develops a shear strength measuring apparatus of hydrates reservoir, which could provide the low-temperature and high-pressure conditions of hydrates existing stably, measures the strength of sand models with different saturation, and gets that with the increase of the saturation, the friction cohesion and friction angle will increase too. By regression of experiment curve, this paper gets the relationship of cohesion and friction angle with saturation, and provides parameters for calculating the collapse pressure of reservoir bearing hydrates.The author found that the key to this problem is how to determine and control the drilling fluid to be low-temperature and high-density by studying the method of keeping borehole stable during drilling process. Taking into account of the gas invasion due to rock debris and decomposition of gas hydrates, based on mass, momentum, energy conservation principle and the theory of heat transfer, we established temperature and pressure distribution model of annular air-liquid two-phase flow by using the micro-element analysis and finite difference method, and did sensitivity analysis to each affecting elements. Through the comparison of annular space temperature & pressure and the hydrate phase curve & reasonable drilling fluid density window, we proposed two key parameters of hydrate decomposition pressure and critical inlet temperature of drilling fluids which can keep borehole stable during the hydrate reservoir mining, and gave the calculation methods of these two key parameters.更多还原