多孔介质中天然气水合物二维开采实验模拟研究

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	多孔介质中天然气水合物二维开采实验模拟研究
其他题名	Experimental Study of Production of Natural Gas Hydrate in Porous Media with the 2D Experimental System
	杜燕
导师	冯自平
	2008-06-02
学位授予单位	中国科学院广州能源研究所
学位授予地点	广州能源研究所
学位名称	博士
关键词	天然气水合物电容降压注化学剂二维数值模拟
摘要	天然气水合物（Natural Gas Hydrates，NGH）作为潜力巨大的优质、洁净替代能源，其开采技术的研究具有重要的理论和实践意义。本论文综合运用机理分析、室内实验和数值模拟技术，系统研究了多孔介质中NGH的合成与分解规律，通过分析降压开采、注化学剂开采过程中的压力、温度、产量等参数的变化规律，研究不同开采方式的开采机理、开采动态及影响开发效果的主要因素，对不同开采技术进行综合评价。研制成功一套水合物二维开采实验模拟系统。该系统由供液、供气、生成与开采模拟、环境模拟、回压控制、温度压力流量计量、数据采集处理7个功能模块组成，同时采用电容测量方式对合成与分解过程进行监测。可进行多孔介质中NGH的合成和降压、加热、注化学剂等各种开采实验。水合物定容生成与分解实验中温度和压力的变化特性验证了系统的有效性。水合物生成速度相比与文献介绍极大增加，诱导时间最短缩至5分钟。重复实验往往会加长生成时间，说明水的记忆效应并不是对于所有实验系统存在的普遍现象。此外，实验表现出来的特殊的压力变化曲线和规律还表明晶核形成对水合物晶体的生成并非绝对重要。体积、面积较大的模型生成实验重复性好、规律性强。在生成过程中，随水合物饱和度的增加，水量的不断减少，电容量总体减小趋势明显。电容测试方法在水合物实验方面有一定的可行性，尤其对于研究多孔介质中水合物生成分解过程中各相的流动特性极有意义。在本实验条件下，NGH降压开采是一种比较好的方法，产气速度较高且主要受压降速度的控制，且不需要昂贵的注热、注化学剂等投入。降压开采过程可以归结为两方面的控制因素，流动与动力学。对于第一种二维模型，NGH饱和度低，流动阻力小，开采过程属动力学控制；第二种二维模型，在NGH饱和度较高时，流动阻力较大，开采过程受动力学与流动共同控制。较小的分解压差都会造成极大的降温，在井底地层中极易再次形成水合物，会大大减小流向井底的气流，造成开采量减小。考虑到自然界NGH藏的低传热特性，控制降压速度对保证生产至关重要。另外，还可以考虑注热、注化学剂等其他辅助强化措施。降压开采模拟中分解速率常数和渗透率是影响产气动态的两个重要方面。在实验条件下，分解速度常数越大，产气量峰值越大，分解时间越短。绝对渗透率的变化对结果影响不大。在本实验研究条件下，化学剂注入浓度越高、注入速度越快，开采效率越高；注入浓度与注入速度都相同时，三井开采比单井开采效率高；注入浓度、注入速度与开采井网布置方式相比，前者对开采效率的影响大，但对于自然界NGH藏注化学剂开采而言，科学的井网布置对开采极其重要。温度场随时间的变化趋势直接反映化学剂在平面上分解前沿的推进过程。化学剂在二维面上的波及范围有限，致使大量NGH剩余难以产出,表明采用单一的注化学剂开采方式并不可行。实际开采中，可采用“化学剂溶液段塞＋常温水驱替”方式或者转而采用降压方式开采。考虑注化学剂开采与降压开采相结合的开采模式，将注化学剂开采作为降压开采的辅助强化措施。
其他摘要	As a greatly potential alternative energy resource, natural gas hydrates (NGH) is of high quality and burns clean. The production technologies of NGH have the great significance in view of theory and practice. Through mechanisms analysis, experiments and numerical simulation technology studied systematically, the law of formation and decomposition of NGH in porous medium and two production methods of depressurization and chemical inhibitor stimulation were discussed in this paper. By the analysis of variation of parameters, including temperature, pressure and gas production rate, a comprehensive understanding about production mechanism, dynamic characteristics and influencing factors was achieved, and furthermore, the all-round evaluation about these methods were developed. A set of Two-dimensional experimental system for the production of NGH in porous media was designed. The system consists of seven modules, which are water supplying, gas supplying, formation and decomposition simulating, environment simulating, backpressure regulating, pressure、temperature and flow flux metering, data acquiring. Capacity technology was also used to measure the phase development in the process of NGH formation and dissociation. The system can be used in NGH formation experiment in porous media and in diverse decomposition experiments as well, such as depressurization, thermal stimulation and chemicals injection. The changing tendency of temperature and pressure in the NGH formation and dissociation prove the experimental apparatus and method are reliable. The formation rates of NGH are much higher than those reported by other researchers and induction time decreased to five minutes at most. Annealing process would lengthen the formation and the first experiment is always the most timesaving, which suggests that memory effects does not exist widely. Special development curves of pressure show that nucleation is not always essential for the complete growth of hydrate crystals. Experiments displayed similar reproducibility and development law in the vessel with the larger volume or larger surface area. Water content is the most important influential factor in the capacity measurement. In the formation experiment, capacity becomes lower as water volume decreased because of formation of NGH. The validity of the capacity technology used in NGH is proved, especially its significance in investigating the flowing characteristics of the gas and water in formation and dissociation in porous media. In the condition of this experiment, depressurization is an effective method of NGH production, because of its high gas production rate that is mainly controlled by depressurizing rate and steady low water production rate. Moreover, it costs less unnecessary to stimulate continuously. Flow and dissociation mechanism are the most important controlling factors in depressurization. The conclusion can be made that hydrate dissociation process is kinetic-controlled for the first kind of 2D simulators with low NGH saturation and high permeability and flow-controlled for the second kind simulator with high NGH saturation and lower permeability. Great temperature decrease can be gained by minimum pressure drop which most be likely to induce the reformation of NGH in the sediment at the well bottom. As a result, gas flux towards the well decrease, which consequently reduce the exploitation quantity. Consideration of the heat transfer characteristics of natural NGH reservoir, it is important to control the depressurize rate for the exploitation of NGH successfully. In addition, it is considered to heat injection or inhibitor injection as auxiliary strengthening measures. Decomposition rate constant and permeability are two most important factors that influence the gas production performance in simulation. For the laboratory-scale reservoir, the peak value of gas production rate increases and the decomposition time shortens with the increase of decomposition rate constant. The variation of absolute permeability almost has no effects on the production behavior. Under the condition of this experiment, the production efficiency by chemicals injection (the volume of the output gas under the standard condition in a time unit when a mass unit of chemical inhibitor is injected) is increasing with the solution concentration and the injection rate. Multi-well production has higher efficiency than that of single-well production with the identical concentration and injection rate. Compared with the well-layout of NGH production, solution concentration and injection rate have the greater impacts on the production efficiency. But truthfully, it is not the case for the naturally occurring hydrate reservoirs. The variations of temperature field with the time elapsing reflect directly the advancement of hydrate dissociation front. The fact that limited sweep region of chemical inhibitor cause a large quantity of NGH production failed, which indicates that chemical inhibitor method used alone for NGH production is unfeasible. In the real exploitation of natural NGH reservoir, the method of “chemical inhibitor solution slug and ambient temperature water displacement” can be applied, or with depressurization method combined. This model should be proposed for NGH production that to combine depressurization with inhibitor injection simulation, considering the latter as the strengthening measure of the former.
页数	127
语种	中文
文献类型	学位论文
条目标识符	http://ir.giec.ac.cn/handle/344007/4061
专题	中国科学院广州能源研究所
推荐引用方式 GB/T 7714	杜燕. 多孔介质中天然气水合物二维开采实验模拟研究[D]. 广州能源研究所. 中国科学院广州能源研究所,2008.

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