【作者】 王飞；

【导师】 张卫东； 时贤；

【作者基本信息】 中国石油大学(华东) ， 油气井工程， 2020， 硕士

【摘要】 天然气水合物是一种未来重要的清洁能源,且储量巨大,受到了世界各国的广泛重视。我国于2017年5月对南海神狐海域水合物进行了试采,取得了巨大进展和成功,但是最终的产气量仍难达到商业化开采规模。探索水合物在连续试采中日产量衰减迅速的原因和机理对加快我国水合物的商业化开采进程有着有重要理论和现实意义。针对神狐海域水合物藏未固结或极弱固结特征,以及水合物完全分解后地层骨架变形大的特点,本文从储层堵塞的角度探索水合物生成和分解过程中的物性变化规律,对水合物开发产量衰减进行机理性探索。首先,通过开展人造岩芯的制作装置和制作工艺的设计和优化,得出的人造岩芯配方在粒径级配、密度、孔隙度和胶结强度等物性上十分贴近神狐海域水合物储层的骨架。针对后期实验需求,本文分别侧重可批量制作、与真实地层差异小、限定反应界面设计了三种不同水合物岩芯制作方式,并均得到水合物生成良好的水合物岩芯。利用自主设计的设备对水合物在岩芯内部的合成及分解展开初步的实验模拟研究,从宏观水合物合成及分解气量,分析水合物在岩芯中合成和分解过程中的地层堵塞的因素及机理。为消除不同的岩芯体积和孔隙体积的不同带来的实验误差,本文在处理数据过程中定义了以客观孔隙水能够吸收的甲烷量为标准进行计算得出的标准化参量α和β,其中α用于比较水合物生成差异,β用于比较水合物分解差异。研究表明:水合物在岩芯中生成过程中存在水合物堵塞孔隙抑制水合物进一步生成的现象,使得生成过程具有阶段性。附着在孔隙内壁的水合物增长缩小孔隙尺寸会令水合物稳定性降低,游离水合物黏连堵塞孔喉会阻碍甲烷气向岩芯内运移。岩芯内泥质含量的升高会加剧这两个过程,泥质含量到达20%效果更佳显著。水合物在岩芯内分解过程中存在微粒运移、孔隙堵塞、骨架破坏。整个过程中伴随着泥质颗粒从原位置剥离,运移进而在其他位置堵塞孔隙,不同时期还拥有特殊堵塞物,水合物的分解前期伴随游离水合物和冰颗粒的产生;分解中期在孔隙被泥质堵塞到一定程度时气泡也通过贾敏效应阻碍气水运移;分解后期水合物的分解气压降低导致气泡更难通过孔喉,同时孔隙内流体流速降低造成泥质颗粒更容易沉积聚集。更多还原

【Abstract】 Natural gas hydrate is an important clean energy in the future.Its reserves are hugeand all countries have invested a lot of energy to explore natural gas hydrate at present.In May 2017,China conducted trial mining of the Shenhu area hydrate in the South China Sea with great progress and success,but it is still difficult to make it commercialized.Exploring the reason and mechanism of the rapid decline in daily production of hydrates in the Shenhu Sea for 60 days of continuous trial mining is of great theoretical and practical significance for the commercial exploitation of hydrates in China.Aiming at the characteristics of unconsolidated or very weak consolidation of the hydrate reservoir in the Shenhu area and the disappearance of the formation skeleton after the hydrate is completely decomposed,this paper explores the hydrate formation and decomposition process from the perspective of reservoir blockageandthe design and optimization of the manufacturing device and manufacturing process of the artificial core were carried out.The obtained artificial core formula was very close to the skeleton of the Shenhu Sea hydrate in terms of particle size grading,density,porosity and cementing strength.To meet the needs of later experiments,this article focuses on three different methods for making hydrate cores,which can be produced in batches,have small differences from real formations,and have limited reaction interfaces.All of them can produce good hydrate cores.The self-designed equipment is used to conduct preliminary experimental simulation research on the synthesis and decomposition of hydrates in the core.From the macroscopic hydrate synthesis and decomposition gas volume,the factors and mechanism of blockage during the synthesis and decomposition of hydrates in the core are analyzed.In order to eliminate the experimental errors caused by different core volumes and pore volumes,in this paper,the standardized parametersα and β calculated by taking the amount of methane that can be absorbed by objective pore water as a standard are defined during data processing.α is used to compare differences in hydrate formation,and β is used to compare differences in hydrate decomposition.Studies indicate that: In the process of hydrate formation in the core,there is the phenomenon that hydrate blocks the pores and restrains the further formation of hydrate,which makes the formation process phased.The growth of hydrates attached to the inner wall of pores will reduce the pore size and reduce the stability of hydrates.Free hydrate adhesion will block the pore throat and prevent the migration of methane gas into the core.The increase of the muddy content in the core will aggravate these two processes,and the effect of the muddy content reaching 20% is more significant.It is considered that there are particle migration,pore blockage,and skeleton damage during the hydrate decomposition in the core.With the peeling of muddy particles from the original position during the whole process,the pores will be blocked at other locations.There are also special plugs in different periods.The early decomposition of hydrates is accompanied by the generation of free hydrates and ice particles.When the pores are blocked to a certain extent by mud in the middle of the decomposition,the bubbles also hinder the gas-water movement through the Jiamin effect.In the later stage of decomposition,the reduction of the decomposition pressure of hydrates makes it more difficult for the bubbles to pass through the pore throat,and at the same time,the reduction of the fluid flow velocity in the pores makes the muddy particles easier to deposit and aggregate.更多还原