【作者】 赵江鹏；

【导师】 孙友宏；

【作者基本信息】 吉林大学 ， 地质工程， 2011， 博士

【摘要】 我国是世界上第三冻土大国,多年冻土面积达215万平方公里,占国土总面积的22.3%。我国冻土区主要分布于东北大兴安岭地区和青藏高原,并零星分布在一些高山上。初步调查研究成果显示我国冻土区尤其是羌塘盆地、祁连山、风火山和漠河盆地等具备较好的天然气水合物成矿条件和找矿前景。钻探取心是获得天然气水合物岩心最直接手段,也是验证其他方法(如地球物理方法)调查结果的最可靠方法和开展天然气水合物开发工作的必要前提。通过对天然气水合物岩心的分析,可以评估资源量、规模和性质等地质参数,这对于开发天然气水合物都具有十分重要的意义。鉴于天然气水合物热物理性质及赋存地质条件的特殊性,国外在陆地冻土区一般采用分解抑制法钻进。同时,为取得原状岩心样品,在钻遇天然气水合物层取样时,采用特殊的取样钻具,国内外采用的取样钻具以保压取样器为主。保压取样器机械保压机构一般采用球阀或板阀,当取样器的设计压力达到一定程度后,如果想再要增加压力,取样器的材料和和密封性能将需要做很大的提高,而且这并不容易做到。本论文设计并加工了一套适合低温泥浆制冷的泥浆制冷系统,并在前人的研究基础之上,对孔底冷冻取样器主要从孔底冷冻方式、孔底冷冻过程和储冷机构三个方面进行研究。依据天然气水合物钻探取心施工工艺要求,首先总体设计了泥浆制冷系统工作原理和工作流程。考虑泥浆特性、泥浆流量、运行温度和运行压力等因素,对泥浆制冷系统换热器进行选型,并采用平均温差法对其具体参数设计计算；载冷剂箱是泥浆制冷系统中重要装置之一,载冷剂箱应保证系统运行时所需载冷剂循环量,载冷剂箱应容纳足够多载冷剂,以携带足够的冷量防止制冷机组频繁启动,达到保护制冷机组各部件的作用,因此,根据其功能要求设计计算载冷剂箱容积。根据设计的泥浆制冷系统组成,选择所需设备；然后,进行室内试验,检验泥浆制冷系统在设计条件下,换热器泥浆进出口温度差是否能够达到设计要求,并验证设计换热器所选取的经验关联式的可靠性；之后,依托2009年在祁连山木里地区天然气水合物钻探取心工程项目,检验该套泥浆制冷系统是否能够满足天然气水合物钻探取心工艺要求：结合2010年在东北漠河盆地的天然气水合物钻探施工,在第一套泥浆制冷系统的基础上,再加工了一套泥浆制冷系统并进行野外试验。试验证明,该系统原理可靠,成功将泥浆温度控制在低温范围之内,满足了天然气水合物钻探取心对泥浆温度要求,达到了设计要求和预期效果。根据泥浆制冷系统在野外试验过程中出现的问题,对其进行改进。首先对比研究了三种管路连接方式,比较其各自特点；根据野外出现的泥浆堵塞现象,增设泥浆制冷系统预防泥浆堵塞功能；从强化传热过程的三个途径对该换热器展开分析并改进,并从流量匹配角度对该换热器进行优化分析；最后根据以上分析结果,设计了采用螺纹管作为内管、具有流量匹配功能和预防泥浆堵塞功能的泥浆制冷系统。孔底冷冻取样器采用干冰为冷源,酒精为载冷剂和催化剂。首先分析了孔底冷冻取样器的特点：然后在对CO2温压特性分析的基础上,研究了孔底冷冻取样器的孔底冷冻方式。其次,数值模拟了取样器冷冻机构在孔底的冷冻过程,分析孔底冷冻过程中,岩心冷冻所需时间及冷冻机构各部分的温度分布。最后,通过数值模拟,分析目前储冷机构的保冷效果,根据模拟结果分析储冷机构所存在问题并进行改进。本论文的研究可为我国在陆地冻土区正在进行的天然气水合物调查研究和勘探开发提供技术支撑,以及在未来海洋天然气水合物钻探开采中提供技术参考。更多还原

【Abstract】 China is the third in the world with a permafrost area of 2.15 million square meters, which is mainly distributed in the Daxing"anling region and Qing-Tibet Plateau, while a few in the high mountains. The permafrost area accounts for 22.3% of total land area in China. The previous studies have showed that it has perfect conditions and great prospecting potential for gas hydrate in the Qiangtang Basin, Qilian Mountain region, Fenghuo Mountain region and Mohe Basin.Core drilling is not only the most direct method used to identify gas hydrate, it is also a necessary means to verify the findings of other methods (e.g.. geophysical methods) and a prerequisite for the development and utilization of gas hydrate. By means of the gas hydrate core sample analysis, it could be assessed the reservoirs, scale and other geological parameters, which are of great significance for gas hydrate exploration and exploitation.In view of the thermophysical properties and the geological conditions of occurrence, the decomposition inhibition method is commonly used in permafrost gas hydrate drilling operation. The essentials of decomposing inhibition method involves low-temperature mud is chilled by mud cooling system to prevent the temperature of the gas hydrate strata and core sample from increasing, maintaining the gas hydrates at the equilibrium state of inhibition, and maintaining borehole stability. Meanwhile, in order to obtain undisturbed core samples, a special core sampler should be used when encounter the gas hydrate strata. At present, the pressure-tight core barrel is the main truth-preserving core sampling, and its operating principle is that maintaining pressure inhibits the gas hydrates dissociating by mechanical operating mechanism. It demands high intensity for core barrel especially, the higher intensity and tightness for ball valve. If the tightness of ball valve has a small drop; the core will not preserve its primitive pressure, and lead to sample failure. When the design pressure of sampling device arrives at a high value, it is very difficult to raise the tight pressure for designing core barrel, and it must greatly improve the leak tightness and intensity of material.A down-hole freezing method for gas hydrate core drilling is proposed by Jilin University. It involves that a low-temperature mud chilled by mud cooling system cycles in drilling well during the running of drilling occurrence, and a down-hole freezing core sampler (FCS) is used for gas hydrate core sample in the coring operation.Mud cooling and FCS are two key technologies in the down-hole freezing core drilling method. A mud cooling system suited for low-temperature mud is designed and developed. And. based on previous studies, a research on FCS will be studied, which involved the down-hole freezing way. the processing of down hole freezing and cold-store mechanism.According to the requirement of gas hydrate core drilling, firstly, a mud cooling system is designed, of which involves the process and principle. Considering the mud properties, mud flow, operating temperature, operating pressure and other factors, the heat exchanger for mud cooling system is selected, and the design and calculation for its specific parameters is carried out on request. The secondary refrigerant tank is one of the important devices for mud cooling system. The secondary refrigerant tank should ensure the amount of refrigerant circulation when the system is running, and the secondary refrigerant tank should contain enough refrigerant in order to carry enough cooling energy, to prevent the refrigeration units frequently start, so as to protect various components of the refrigeration units. The secondary refrigerant tank is a place where the air and impurities are carried out by refrigerant cycling and separated. Therefore, the secondary refrigerant tank volume calculation is also important, according to its functional requirement, the design calculation for the secondary refrigerant tank volume has been carried out.According to the composition of mud cooling system, the other necessary devices are selected. And then the laboratory experiments are carried out to test whether the temperature difference between the mud import and export of the heat exchanger can meet the design requirement when it is in the designed flow conditions. Then, according to gas hydrate drilling in the Muli Basin in the Qilian region in 2009. The system has been tested that whether it can meet the technological requirements of gas hydrate core drilling or not. Combined the gas hydrate core drilling in 2010 in Mohe Basin, and based on the first set of mud cooling system, a new mud cooling system has been developed, and field experiments are conducted.According to the problems occurred during the field experiments, the mud cooling system is improved. First, three possible piping connections are explored, and a comparative study of their own characteristics are conducted. According to mud clogging problem found in field experiments, its anti-blocking function is designed. The heat transfer efficiency of heat exchanger plays a great role on the heat transfer efficiency of the mud cooling system, enhancing the heat transfer efficiency can increase the heat transfer efficiency of the system. Finally, based on the analysis above, a new mud cooling system is designed, of which screwed pipe instead of smooth pipe in the heat exchanger is used. The mud cooling system have two special functions, one is the velocity of flow adapted and another is mud could prevent from blocking during the running.The FCS uses dry ice as freezing source, uses alcohol as refrigerant and catalyst. Firstly, the characteristics of the FCS is analyzed based on the analysis of cot characteristics of temperature and pressure, the freezing way of the FCS in the bottom of the hole is also analyzed. Second, the freezing process of sampler freezing institution is simulated when coring in the 200m deep in the hole. Finally, the insulated effect of cold-store mechanism is carried out by means of simulation and the cold-store mechanism is improved.This study could provide a technical support for the terrestrial permafrost gas hydrate exploration and exploitation, also provide a technical reference for seabed gas hydrate drilling in the future.更多还原