Prediction of transient pressure change during natural gas hydrate formation

Abstract

The increasing demand for fossil fuels and diminishing natural energy reserves have necessitated the exploration of gas hydrates. Gas hydrates find importance in oil and gas industries where the formation and dissociation of gas hydrate become important. Thus, the proper understanding of formation, decomposition and properties of gas hydrates is a required. In this work, a macroscopic kinetic model is analyzed and modified to predict the pressure change with time during the hydrate formation based on the chemical affinity of compounds. With the help of experimental data, the degree of parity of the modified and unmodified models are explained. The dependency of the chemical affinity of the gas hydrate reformers is explained based on the kinetic model validation with the experimental results. The modified model predict the transient pressure during gas hydrate formation with an average absolute error of 3.6%.     

Predicting the conditions for gas hydrate formation

Gas hydrate is a crystalline mixture obtained from gas molecules trapped in the cavity of hydrogen bonding water. To date, an essential step in the development of natural gas industry has been the acquisition of knowledge in the operation and handling of gas under high pressure without hydrate formation. Since there are several ways to predict hydrate formation, this study investigates predicting hydrate formation using the Katz method. In addition, several new models for accurate estimation of gas hydrate formation conditions will be provided. These models are based on artificial neural network (ANN) requirements. To create the model, predictive experimental data published in books and journals, as well as data extracted from Katz graph (Katz chart), estimate the formation conditions of gas hydrate. We validate the model created with the use of various statistical parameters such as mean squared error (MSE) and R²-value. The result of these parameters in models created to predict the formation of hydrates accurately and efficiently is evaluated. In this study, our goals are to use an artificial intelligence neural network to predict the formation of gas hydrates.     

OCEANIC METHANE HYDRATE: THE CHARACTER OF THE BLAKE RIDGE HYDRATE STABILITY ZONE, AND THE POTENTIAL FOR METHANE EXTRACTION

Oceanic methane hydrates are mineral deposits formed from a crystalline "ice" of methane and water in sea-floor sediments (buried to less than about 1 km) in water depths greater than about 500 m; economic hydrate deposits are probably restricted to water depths of between 1.5 km and 4 km. Gas hydrates increase a sediment's strength both by "freezing" the sediment and by filling the pore spaces in a manner similar to water-ice in permafrost. Concentrated hydrate deposits may be underlain by significant volumes of methane gas, and these localities are the most favourable sites for methane gas extraction operations. Seismic reflection records indicate that trapped gas may blow-out naturally, causing large-scale seafloor collapse.
In this paper, we consider both the physical properties and the structural integrity of the hydrate stability zone and the associated free gas deposits, with special reference to the Blake Ridge area, SE US offshore, in order to help establish a suitable framework for the safe, efficient, and economic recovery of methane from oceanic gas hydrates. We also consider the potential effects of the extraction of methane from hydrate (such as induced sea-floor faulting, gas venting, and gas-pocket collapse). We assess the ambient pressure effect on the production of methane by hydrate dissociation, and attempt to predict the likelihood of spontaneous gas flow in a production situation.     

中国天然气水合物赋存特征

中国陆上冻土区和海域深水区都拥有丰富的天然气水合物（以下简称水合物）资源，二者虽在同盆共生、运聚机理上有相似之处，但差异也十分明显。为了给地质—工程—环境一体化开发水合物提供准确的基础地质数据，从构造与沉积、地温、热流、地球化学、地球物理响应、赋存类型、孔渗、力学强度、饱和度等9个方面，对比分析、总结了二者在分布规律与赋存特征上的差异性。研究结果表明：①陆上冻土区水合物主要赋存于中生代地层，以热成因气为主，受断层裂隙构造控制，具有较好的圈闭条件，其储层温度、地温梯度、热流、压力表现为“四低”特征，水合物多数分布在砂岩孔隙和泥页岩裂隙中；②陆上冻土区水合物测井响应总体显示“两高两低”特征（高电阻率、高波速、低自然伽马、低密度），储层岩石力学强度高，具有低孔隙度、低渗透率和低水合物饱和度特征；③海域水合物主要赋存于新生代第四纪地层，热成因或生物成因气皆有，受泥底辟、气烟囱、断层裂隙控制，无明显圈闭，其储层温度、地温梯度、热流和压力表现为“四高”特征；④海域水合物多数分布在富含有孔虫的黏土质粉砂和粉砂质黏土中，地震反射波显示明显的BSR特征，测井响应则总体表现为“两高”特征（高视电阻率、高波速），其储层沉积物力学强度低，具有高孔隙度、低渗透率和相对较高的水合物饱和度。结论认为：①海域是中国水合物富集的主要区域，后续应突破海域水合物甜点识别与评价技术，统筹考虑整个水合物油气系统的资源禀赋特征；②应重点攻关水合物储层精细表征技术和富集矿体—储层系统的精细刻画，加强海陆联合和全球比对研究。