深水钻井天然气水合物生成预测研究

发布时间：2018-06-17 20:07

本文选题：深水钻井 + 天然气水合物　；参考：《西南石油大学》2017年硕士论文

【摘要】：随着我国经济的飞速发展和对能源需求的日益增加,深水油气的勘探和开发将成为确保我国能源安全的重要举措。在深水油气开发中,受水深和海洋环境的影响,泥线附近温度较低,溢流气体容易在海底井口、防喷器、节流管线等部位生成水合物,从而造成防喷器无法正常操作或者堵塞节流管汇,影响正常压井作业,给深水钻井带来诸多安全隐患。因此,研究深水钻井中水合物的生成规律,预测水合物的生成和分解对井筒压力控制的影响,对确保深水钻井的安全高效具有重要的理论及实践意义。本文在广泛调研国内外水合物生成条件预测方法的基础上,建立了天然气水合物相平衡模型。基于质量守恒、动量守恒、能量守恒定律及传热学理论,考虑海水、地层、环空的传热特征及不同工况下溢流气体相态变化的影响,建立了深水钻井过程中无溢流循环、溢流循环、关井和压井4种工况的井筒温度压力预测模型。结合辅助方程、定解条件,采用有限差分法对模型进行了离散和求解,对深水钻井无溢流循环、溢流循环、关井和压井工况下水合物的生成情况进行了预测,分析了排量、关井时间、循环时间、抑制剂和隔水管保温层等因素对水合物生成的影响,模拟了溢流工况和压井工况下环空气相体积分数、井底压力、泥浆池增量、节流阀压力等参数的变化规律,研究了水合物相态变化对井筒多相流动规律的影响。建立了关井水击压力数学模型,计算了水击波速和水击压力,采用分子动力学方法对比分析了给定温度压力和给定温度但压力波动两种情况下的水合物生成情况。在理论研究的基础上,编制了深水钻井不同工况下天然气水合物生成预测软件及溢流和压井过程中水合物对井筒压力影响软件。计算结果表明:在溢流工况下,水合物生成较少,水合物相变对流体流动规律影响不大。关井工况下,泥线附近温度快速降低,导致水合物生成;关井引起的压力波动提高了水合物的成核速率,导致水合物生成;压井工况下,溢流气体进入节流管线后会生成少量水合物,同时随着压井的进行,泥线附近已生成的水合物会开始分解,节流阀压力也会在水合物分解后会出现第二次上升的过程,给压井施工带来困难。深水钻井中,可以采取增大循环排量、减少关井时间、加入水合物抑制剂或使用隔水管保温层等措施抑制水合物的生成。本文研究成果可用于预测深水钻井中天然气水合物的生成情况,分析水合物相变对井筒多相流动规律的影响,为深水钻井水合物的预防和合理井控措施的制定提供理论支持。
[Abstract]:With the rapid development of China's economy and the increasing demand for energy, the exploration and development of deep-water oil and gas will become an important measure to ensure the energy security in China. In deep water oil and gas development, due to the influence of water depth and marine environment, the temperature near the mud line is relatively low, and the overflow gas can easily form hydrates at the bottom wellhead, blowout preventer, throttling pipeline, etc. As a result, the blowout preventer can not operate normally or clog the throttling manifold, which affects the normal well killing operation and brings many safety risks to deep water drilling. Therefore, it is of great theoretical and practical significance to study the rules of hydrate formation in deep water drilling and to predict the influence of hydrate formation and decomposition on wellbore pressure control to ensure the safety and efficiency of deep water drilling. A phase equilibrium model of natural gas hydrate is established on the basis of extensive investigation of the prediction methods of hydrate formation conditions at home and abroad. Based on the conservation of mass, momentum, energy conservation and heat transfer theory, considering the heat transfer characteristics of sea water, formation and annulus, and the influence of the phase change of overflow gas under different working conditions, the non-overflow circulation in deep water drilling is established, which is based on the conservation of mass, the conservation of momentum, the conservation of energy and the theory of heat transfer. The wellbore temperature and pressure prediction model of overflow circulation, shut-in and dead well. Combined with auxiliary equation and solution condition, the model is discretized and solved by using finite difference method. The formation of hydrate in deepwater drilling without overflow circulation, shut-in and dead well is predicted, and the displacement is analyzed. The effects of shutoff time, circulation time, inhibitor and insulation layer of riser on hydrate formation are simulated. The volume fraction of annular air phase, bottom hole pressure, mud pool increment are simulated under overflow and well killing conditions. The influence of gas hydrate phase change on wellbore multiphase flow is studied by the variation of throttle valve pressure and other parameters. The mathematical model of water hammer pressure in closed well is established, the wave velocity and water hammer pressure are calculated, and the formation of hydrates under two conditions of given temperature pressure and given temperature but pressure fluctuation is compared and analyzed by molecular dynamics method. On the basis of theoretical research, the software for predicting the formation of natural gas hydrate under different conditions of deep water drilling and the influence software of hydrate on wellbore pressure during overflow and well killing are developed. The results show that under the overflow condition, the hydrate formation is less, and the hydrate phase transition has little effect on the fluid flow law. Under shut-in condition, the temperature near the mud line decreases rapidly, which leads to the formation of hydrate. The pressure fluctuation caused by shut-in increases the rate of hydrate nucleation and results in hydrate formation. When the overflow gas enters the throttling pipeline, a small amount of hydrates will be formed. At the same time, the hydrates formed near the mud line will begin to decompose, and the throttle pressure will rise for a second time after the hydrates decompose. It brings difficulties to the well-killing operation. In deep water drilling, measures such as increasing circulating discharge, reducing shutoff time, adding hydrate inhibitor or using insulation layer of riser to restrain hydrate formation can be taken. The research results in this paper can be used to predict the formation of natural gas hydrate in deep water drilling, and to analyze the influence of hydrate phase transition on well bore multiphase flow, and to provide theoretical support for the prevention of hydrate in deep water drilling and the formulation of reasonable well control measures.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE52

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