天然气水合物钻井液冰阀速生机理研究

发布时间：2018-03-11 05:16

本文选题：天然气水合物　切入点：冰阀式保压取心器　出处：《吉林大学》2017年硕士论文　论文类型：学位论文

【摘要】：化石能源是支撑国民经济发展的重要物质基础,天然气水合物作为一种潜在的新型洁净化石能源被广泛关注,并对海底滑坡、全球变暖等有重要影响。从2002年开始,我国全面开展天然气水合物资源调查工作。并且将天然气水合物的勘探开发技术列为国家科学和技术发展重点研究项目。取心技术是资源勘探调查研究的关键技术方法。国内外多用保压取心技术提取天然气水合物岩心。自国际深海钻探(DSDP)首次开始应用保压取心钻具以来,各类保压取心器的保压取心成功率均较低,究其原因主要是目前的天然气水合物保压取心器均采用球阀、板阀等机械阀门作为密封机构,在水合物取样钻进过程中,由于井内环境恶劣,钻井液中夹杂的大量固相颗粒会磨蚀阀门密封表面,造成密封失效,还会经常出现岩心未能正常提升造成岩心屑卡堵,阀门不能正常关闭的问题。针对现有取心器存在的问题,提出利用冰封保压的方式对天然气水合物取样器进行密封保压。与常规取心器相比,采用冰封保压具有以下优点:无需球阀等运动部件;无精密配合表面要求;无橡胶等密封元件。因此结构相对简单,不会出现卡堵、冲蚀等问题造成保压取心失效。本文结合数值模拟和室内试验,对天然气水合物钻井液冰阀速生机理进行了研究,开展的主要研究内容和取得的主要进展如下:1、基于Ansys Fluent软件,将固液相变、热对流、热传导等多种复杂物理过程考虑在内,构建了一系列带底端盖冰阀管形成冰阀过程的生长模型,数值模拟与室内试验结果对比表明:影响带底端盖冰阀管形成冰阀速率的主要原因是钻井液与冷却液的热交换速度。因此冰阀管材料导热系数大小对冰阀生成速率影响较小,冷却液温度和冷却液流速对冰阀生成速率影响较大,并且形成冰阀长度越长,消耗时间越多,因此在实际钻进中,在保证承压的前提下应优先考虑较短的冰阀。2、针对实际应用中冰阀管底端口无底端盖的情况,采用数值模拟方法对冰阀形成过程及其影响因素开展了研究,数值模拟结果表明,减慢冰阀生成速率的主要因素是钻井液的自然对流,由于自然对流的影响,生成相同长度冰阀消耗时间比带底端盖的冰阀管平均慢6min左右。3、为了在现场应用中加快冰阀的形成,缩短冰封保压取样冷冻时间,采用数值模拟结合室内试验的方法开展了肋片加速形成冰阀的研究。数值模拟和室内试验结果均表明,在冰阀管底端布置肋片可有效阻止冰阀管内钻井液与孔底钻井液发生自然对流,加速冰阀的形成。数值模拟结果表明:与无底端盖冰阀管结构相比,采用肋片结构最快可使冰阀生成时间缩短6.5min;肋片层数对形成冰阀速率影响较大,肋片层数越多,形成冰阀速率越高;肋片层间隙与肋片材料对形成冰阀速率影响较小;肋片厚度为0.9mm比肋片厚度大于0.9mm的冰阀管管内钻井液完全形成冰阀速率更快。
[Abstract]:Fossil energy is an important material foundation to support the development of national economy. As a potential new clean fossil energy, natural gas hydrate has been widely concerned, and has an important impact on submarine landslide, global warming and so on. Since 2002, The investigation of natural gas hydrate resources has been carried out in an all-round way in China, and the exploration and development technology of natural gas hydrate has been listed as the key research project of national science and technology development. Coring technology is the key technology in the investigation and research of natural gas hydrate exploration. Methods of extraction of natural gas hydrate cores by multiple pressure keeping coring techniques at home and abroad. Since DSDP was first used in deep sea drilling, The success rate of pressure-retaining coring is low in all kinds of pressure-keeping coring devices. The main reason is that the current gas hydrate pressure-keeping coring devices use mechanical valves such as ball valves, plate valves and other mechanical valves as sealing mechanisms, which are used in the process of hydrate sampling and drilling. Due to the bad environment in the well, a large number of solid particles in the drilling fluid will erode the sealing surface of the valve, resulting in the failure of sealing, and the failure of the core to raise normally, which will result in the blockage of the core chips. In view of the problems existing in the existing coring devices, it is proposed to seal the gas hydrate sampler by using the method of ice sealing and keeping pressure, compared with the conventional coring device. The use of ice to keep pressure has the following advantages: no ball valve and other moving parts; no precise matching surface requirements; no rubber and other sealing elements. In this paper, the mechanism of ice valve rapid growth of natural gas hydrate drilling fluid is studied in combination with numerical simulation and laboratory test. The main research contents and progress are as follows: 1, based on Ansys Fluent software. In this paper, a series of growth models of ice valve tube with bottom end cover are constructed by taking into account many complex physical processes, such as solid-liquid phase transition, thermal convection, heat conduction and so on. The results of numerical simulation and laboratory test show that the main reason that affects the ice valve formation rate is the heat exchange velocity between drilling fluid and coolant, so the heat conductivity of ice valve material has little effect on the ice valve formation rate. The temperature of the coolant and the velocity of the coolant have great influence on the formation rate of the ice valve, and the longer the length of the ice valve is, the longer the time is, so in the actual drilling, Under the premise of guaranteeing the pressure, the short ice valve should be given priority. In view of the situation that there is no bottom end cover at the bottom end of the ice valve pipe in practical application, the forming process of the ice valve and its influencing factors are studied by using the numerical simulation method. The numerical simulation results show that, The main factor of slowing the ice valve formation rate is the natural convection of drilling fluid. Due to the influence of natural convection, the average time to produce the ice valve of the same length is about 6 minutes slower than that of the ice valve tube with the bottom cover. In order to speed up the ice valve formation in the field application, In order to shorten the freezing time of frozen ice seal, the method of numerical simulation combined with indoor test was used to study the accelerated formation of ice valve. The results of both numerical simulation and indoor test show that, The arrangement of ribs at the bottom of the ice valve tube can effectively prevent the natural convection between the drilling fluid in the ice valve tube and the drilling fluid at the hole bottom and accelerate the formation of the ice valve. The numerical simulation results show that compared with the structure of the ice valve tube without the bottom end cap, The formation time of ice valve can be shortened by 6.5 mins as soon as the rib structure is adopted, the number of rib layers has a greater influence on the rate of ice valve formation, the more the number of rib layers, the higher the rate of ice valve formation, and the smaller the influence of the gap of rib layer and the material of rib sheet on the rate of ice valve formation. The ribbed blade thickness of 0.9 mm is faster than that of the ice valve pipe in which the ribbed blade thickness is greater than 0.9 mm.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P634.6;P618.13

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