木里低阻水合物响应机理数值模拟分析研究

At present, it is found that the natural gas hydrate in Qilian mountain Muli area is mainly composed of fissure type and pore type. Due to its relatively low abundance, causing a unique physical phenomenon of low resistance hydrate, and its well logging identification and saturation calculation are difficult. It is of great significance to clarify the formation mechanism of this phenomenon for well logging identification and reserves estimation of low resistivity hydrate reservoirs in Muli area. A lot of experimental results show that hydrate experiment will trigger a variety of conditions to promote the hydrate formation at the same time, making the laboratory macro measuring resistivity rise rapidly, and low resistance phenomenon is difficult to observe. This application based on digital rock technology, a simulated annealing algorithm with enhanced constraint proposed by applicants was adopted. The formation process of the hydrate was simulated by changing the formation conditions, generation mode, reservoir conditions and termination conditions. According to the numerical simulation results of the finite element method, the influence of single factor variable and Multiple factors interact on the macroscopic physical properties of the rock is revealed. Finding the cause mode of low resistance hydrate reservoirs, and tested with the actual log data of the low resistance hydrate reservoir in Muli area, the nonlinear characteristic and law of Archie’s formula of hydrate reservoir are analyzed. So as to put forward a new hydrate reservoir conductivity model, realize the low resistance hydrate reservoir electric diagnosis, then it provides theoretical guidance and realization method for the identification and reserves estimation of low resistance hydrate in Qilian mountain Muli area.

目前已发现祁连山木里水合物主要以裂隙型和孔隙型两种状态产出，因其赋存丰度较低，导致出现低阻水合物这一独特物理现象，其测井识别与饱和度计算困难。厘清该现象的成因机理对木里低阻水合物储层测井识别与储量估计具有重要意义。大量的实验研究结果表明，水合物实验会同时触发多种条件促进水合物生成，使得实验室内宏观测量的电阻率迅速升高，难以观测到低阻现象。本申请基于数字岩心技术，采用申请者提出的增强约束模拟退火算法，通过改变生成条件、生成模式、储层条件及终止条件等模拟水合物的生成过程，依据有限元数值模拟结果，揭示单因素变量及多因素相互作用对电学宏观物理特性的影响规律，寻找造成低阻水合物的成因模式，将其与木里低阻水合物储层实际测井数据进行交互检验，分析水合物储层非阿尔奇特征，从而提出新的水合物储层导电模型，实现低阻水合物电性诊断，进而为祁连山木里低阻水合物的测井识别与储量估计提供理论指导与实现方法。

祁连山木里地区水合物储层矿物组分及孔隙结构等特征极为复杂，储层岩石致密，硬度高，孔隙度小且伴有裂缝发育，导致木里地区水合物储层测井响应特征发生了明显变化，甚至没有出现作为水合物储层主要识别标志之一的电阻率明显增大特征，而是呈现出独特的与低阻油气层类似的低阻特征，导致该地区水合物储层识别及饱和度计算等都面临着较多的难题。首先，根据木里水合物储层储集空间类型，系统地梳理并分析了孔隙型与裂缝型水合物储层的测井响应特征，对储层岩性、物性、孔隙结构及空间分布、水合物及流体分布等特征进行了研究，对水合物储层特征及“四性”关系特征进行了总结；其次，以水合物生成过程特征及实验室水合物生成分布原位观测结果为基础，提出了水合物分布数值模拟方法，实现了水合物生成过程分布数值模拟及理想水合物分布及不同胶结方式水合物数值模拟；然后，通过对比实验室水合物沉积物与理想水合物数字岩心电性差异，有效地识别了水合物生成过程中的微观分布模式变化规律，并由水合物沉积物电性非阿尔奇特征，提出了饱和度指数是水合物饱和度函数的推断，认为其数值与水合物生成程度及分布模式有关，构建了新的水合物饱和度计算模型。更重要的是，采用岩电实验与数字岩心技术相结合的方法，从储层内在因素角度开展了储层导电机理研究，分析了岩石物性与孔隙结构、矿物组成、地层水矿化度、水合物微观分布模式等因素对岩石电性的影响规律，明确了岩石电性特征的主要影响因素及低阻成因。最后，在研究区水合物储层特征及导电机理研究结果基础之上，建立了适用于研究区储层的孔隙度、渗透率及束缚水饱和度参数评价模型。综合考虑泥质、束缚水与可动水的导电作用，提出了新的水合物饱和度计算模型，相比于常规饱和度模型，有效地实现了低阻水合物测井识别与精细定量评价。此外，基于水合物沉积物非阿尔奇特征，构建了动态饱和度指数水合物计算模型，实际应用结果表明该模型能够提高水合物饱和度的计算精度。