关井期间连续气侵气泡在井筒的动态运移分析

在停止循环状态关井条件下,由于井筒储集效应的影响,地层气会继续侵入井筒,侵入气体沿静止钻井液向上滑脱运移,井口回压与井底压力随之增加,威胁井控安全,因而,有必要研究关井条件下,气泡在井筒内滑脱上升时引起的井口和井底压力波动规律.考虑井筒储集效应,建立了关井期间井底压力和井口压力的计算模型,并对模拟井关井过程中气泡沿井筒运移特性进行了分析.模拟分析结果表明:不同气侵量下,随着关井时间的延长,井底压力和井口压力增加,渗透率低的地层井底压力较高,井口套压稳定的速度较快;当井筒气侵量一定时,随着关井时间的延长,井底压力和井口压力增加,渗透率高的地层井底压力、井口套压较高.     

考虑完井液存在的气井环空带压计算模型研究

准确预测套管内环空压力上升规律有助于指导现场在压力值达到破坏井筒完整性前采取措施,可有效降低环空带压对注采井安全生产带来的威胁.本文考虑气体在完井液中体积变化及运移规律,建立了完井液存在条件下环空压力计算模型,通过对比实例带压井的环控压力计算值与实际值,验证了模型的准确性.同时,计算分析了完井液液柱高度、完井液压缩系数及水泥环渗透率对最大环空压力值与其变化规律的影响,计算结果表明:较大的水泥环渗透率和较小的完井液压缩系数将会增大环空压力的上升速度,而完井液液柱高度不但对环控压力上升速度产生影响,较小的液柱高度还将导致最大环空压力增加.因此,增加完井液压缩性能、适当降低完井液柱高度、提高固井质量以降低气体在水泥环中的窜流是延缓环空带压的有效措施.     

控压钻井井底气侵停止与否实时判别方法研究

实时判别井底气侵停止与否是控压钻井井控方法的关键,直接关系到基于立压控制法循环排气或常规关井等后续作业的选取.综合考虑气体运移膨胀和气体溶解的因素,指出出入口流量一致并不等同于井底气侵停止,两者存在时间先后关系.基于快速施加井口回压控制方法,建立了控压钻井井筒与地层耦合的多相变质量流动模型,采用有限差分法迭代求解,模型计算值与实验测量值吻合较好.模拟结果表明,出口流量有无明显拐点是区分出入口流量一致和井底气侵停止时间先后的标志.一旦井底气侵停止,立管压力的二阶导数会迅速降至0点附近且趋于稳定.根据上述参数变化特征,提出了基于出入口流量和立管压力实时监测的井底气侵停止与否实时判别方法.该研究对于完善控压钻井井控理论具有重要的指导意义.     

川渝裂缝性地层自动压井环空多相压力波速特性研究北大核心CSCD

考虑虚拟质量力、环空沿程压力、气液相间阻力、气体滑脱、环空空隙率等因素,基于小扰动理论,提出了裂缝性地层自动压井环空多相压力波速数学模型,结合半显式差分方法,以彭州PZ-5-3D井(垂深5827 m)为实例,对模型编程求解.结果表明:裂缝性地层出气具有段塞流特点,随空隙率增大,压力波速呈现先减小后增大趋势;空隙率在0%至16%区间,压力波速以液弹为主,压力波速呈急剧下降趋势;空隙率在16%至40%区间,压力波速趋于平缓恒定值;空隙率在42%至100%区间,压力波速呈现增大趋势,压力波速以气弹为主;随环空井深减小,环空空隙率减小,压力波速整体呈现减小趋势;随压井循环排气井口回压增大,压力波速整体呈现增大趋势;环空空隙率在0%至13%区间内,气体滑脱速度对压力波速影响不大;环空空隙率在13%至85%区间内,随气体滑脱速度增大,压力波速呈现减小趋势;节流阀调阀时间间隔与井底压力响应时间具有跟随性,随井底压力响应时间增大,调阀时间间隔增大.     

CO_2驱分层注气井注入系统数学模型及其应用

CO_2驱分层注气是控制CO_2气窜和提高开发效果的有效手段.确定合理的分层注气参数是CO_2驱分层注气现场试验的关键环节.本文在CO_2驱单管分层注气和同心双管分层工艺的基础上,通过分析注入CO_2在地面管道、井筒、气嘴及地层中的流动规律,分别建立了两种注气工艺注入系统的数学模型,利用节点系统分析方法对数学模型进行求解和敏感性分析,能够确定不同注气工艺条件下各层合理的注气压力和注气量.以吉林油田CO_2驱注气井为例,结合实际地层参数,确定了各层合理的注气参数,为CO_2驱分层注气的现场实施提供理论依据和指导.     

稠油油藏高温盐析调剖的孔渗表征方法研究

深层高温油藏在开采过程中,由于近井地带压力变化剧烈,地层水蒸发致使结晶盐析出,进而导致储层孔隙度、渗透率降低.为研究稠油油藏高温盐析调剖的孔渗变化规律,根据盐类溶解/沉淀原理及储层孔隙度渗透率关系和填砂管模型高温盐析实验结果,建立了考虑地层水蒸发、水中氯化钠析出和储层孔渗变化的综合盐析模型.研究结果表明:随着堵剂注入量增加,封堵率快速上升并趋于稳定;实验温度在200~500℃之间氯化钠堵剂具有较好的封堵效果;盐析调堵方法可以有效封堵储层气窜通道,改良吸气剖面,提高周期采油量.最后用实验结果对数学模型进行拟合修正,得到稠油油藏高温盐析调剖的孔渗表征方法.     

考虑钻具接头影响的环空压耗计算

控压钻井是针对"窄安全压力窗口"现象所引起的勘探开发过程中的钻井难题所提出的,井筒压力分布的准确预测是保证控压钻井顺利实施的前提,为提高井筒压力的预测精度需准确计算环空摩阻压耗,应用量纲分析理论,综合考虑钻具接头、钻具旋转的影响,修正了环空摩阻压耗计算模型,提高了井筒压力的预测精度.模型研究表明:随着钻井液排量的增加,钻井液从层流变为紊流,局部摩阻压耗明显增加;且井越深,接头的累计压耗越大,接头对总摩阻压耗的贡献增加.随着钻具旋转速度的增加,环空压耗的增加或减少取决于惯性力与剪切稀释的共同作用.     

基于格子boltzmann方法固井环空介观微间隙气体窜槽研究

固井环空微间隙气体窜槽现象直接影响固井质量与油田生产,准确地描述固井环空微间隙气体窜槽的流动规律是有效控制气体窜槽的核心与"瓶颈"问题.从微观粒子运动角度出发,基于格子Boltzmann方法建立了固井环空微间隙气体粒子流动模型.选取大庆油田某区块计算模拟不同环空压差下微间隙内气体粒子流动速度分布规律,计算结果揭示了固井气窜气体粒子在微环间隙内流动的本质,为后续固井气窜问题的研究开辟新的思路.     

基于多指标正交方案设计的二氧化碳利用及封存参数优化

针对大民屯凹陷JG-2块高凝油油藏长期水驱导致的开发矛盾突出,增产难度大等问题,评价高含水条件下注CO_2的利用及封存效果.为寻找适合工区的最佳注气方式,结合室内实验及数值模拟技术,探讨了不同含水及不同续驱手段下的驱替效果,进而结合正交试验设计原理,将采出程度、CO_2滞留率、换油率及地层压力作为综合指标,对水气交替驱续驱过程中的注气时间、注气周期、注气速度、段塞比及气油比等5个因素进行了主控评价及优化研究.结果表明,注CO_2水气交替驱续驱适应区块开发条件,注气速度、注气时间及气油比是影响续驱进程的主要因素.获取最佳CO_2利用及封存参数:注气年限20 a,注气周期8 mon,注气速度0.5×10~4m~3·d~(-1),段塞比2:1,气油比1500m~3·m~(-3).     

储气库油侵气窜压差界限研究

针对储气库开采过程中油侵气窜的问题,以喇嘛甸北部为研究对象,对储气库油气界面的运移进行监测,分别通过物理模拟方法和数值模拟方法研究油侵气窜与油气区压差的关系,进而得到生产过程中油区气区之间的合理压差.物理模拟研究表明,当油气区压差超过一定值时,油气界面会发生运移,压差越大,油气界面运移距离越远;数值模拟研究表明,储气库油侵气窜压差界限为±0.5MPa;通过矿场监测论证,最终确认上述压差界限的合理性.     

Multiphase transient flow model in wellbore annuli during gas kick in deepwater drilling based on oil-based mud

Transient-state gas and oil-based mud (OBM) two-phase flow in wellbore annuli will occur during gas kick. The phase behavior of influx gas and OBM will make the gas kick during OBM drilling more complicated. There are three possible cases in an annulus: only liquid flow in the entire annulus, gas and liquid two-phase flow in part of the annulus, and gas and liquid two-phase flow in the entire annulus. First, the phase behaviors of gas and OBM in wellbore annuli are studied based on the phase behavior of methane and diesel. A multiphase transient-flow model in annuli during gas kick based on OBM is then established based on gas–liquid two-phase flow theory and on flash theory in annuli. The influences of phase behavior in annuli and annular geometry are taken into account. The local flow parameters are predicted by the hydrodynamic models and the local thermodynamic parameters are predicted by the heat-transfer models in the corresponding flow pattern. The proposed model has a better performance, compared with two other models, against the published experimental data. Finally, the variation of pit gain, well-bottom hole pressure, and gas void fraction are obtained, leading to a better understanding of the occurrence and evolution mechanism of gas kick during deepwater drilling.     

气体钻井钻柱气固耦合横向振动数学模型的建立与控制

根据钻柱力学和动量守恒基本理论,建立了考虑气体钻井液对钻柱内外耦合影响时的钻柱横向振动模型,此模型与一般的梁式结构的振动模型不同,它包含了钻柱轴力、钻柱内注入压力、环空压力和钻柱内气体对钻柱振动的影响.同时给出边界条件和初始条件.通过把系统外激励函数当作控制变量,利用Banach空间几何性质证明了此系统存在唯一最优控制元.     

隔水管注气双梯度钻井井筒参数计算研究北大核心CSCD

基于隔水管注气双梯度钻井过程中隔水管环空多相流特性,建立了隔水管注气双梯度钻井环空多相流模型,采用有限差分法对模型进行求解,结合墨西哥湾某口深水井现场数据,分析了钻井参数对井底压力和环空压力的影响,并对注气流量的影响因素进行讨论.研究结果表明:隔水管注气双梯度钻井井底压力比常规钻井更低,更适用于海底窄密度窗口钻井;隔水管注气双梯度钻井在钻井过程中注气流量的大小对井底压力和环空压力影响较大;水深和钻井液密度是影响注气流量的两个重要因素.在隔水管注气双梯度钻井参数设计时,应选择合适的注气流量,且钻井液密度不宜过大,以确保隔水管注气双梯度钻井安全.该研究对隔水管注气双梯度钻井设计及现场作业具有指导意义.     

Influence of nonisothermal effects on gas production in northern regions

The influence of mathematical model parameters on the dynamics of pressure and temperature fields at nonisothermal gas filtration is investigated in a numerical experiment. A nonlinear system of partial differential equations obtained from the energy and mass conservation laws and the Darcy law are used to describe the process, and physical and caloric equations of state are used as closing relations. The boundary conditions correspond to a given pressure drop at the bottomhole. It is shown that the influence of the temperature field on such integral characteristics as cumulative gas production is most pronounced at moderate pressure drops. The size of the zone of possible hydrate formation in a gas reservoir is determined in a particular example.     

Flow Structure behind a Shock Wave in a Channel with Periodically Arranged Obstacles

We study the propagation of a pressure wave in a rectangular channel with periodically arranged obstacles and show that a flow corresponding to a discontinuity structure may exist in such a channel. The discontinuity structure is a complex consisting of a leading shock wave and a zone in which pressure relaxation occurs. The pressure at the end of the relaxation zone can be much higher than the pressure immediately behind the gas-dynamic shock. We derive an approximate formula that relates the gas parameters behind the discontinuity structure to the average velocity of the structure. The calculations of the pressure, velocity, and density of the gas behind the structure that are based on the average velocity of the structure agree well with the results of gas-dynamic calculations. The approximate dependences obtained allow us to estimate the minimum pressure at which there exists a flow with a discontinuity structure. This estimate is confirmed by gas-dynamic calculations.     

Thermodynamic equilibrium studies of nanocrystallite SrTiO3 grain boundaries by high temperature photoelectron spectroscopy

Nanostructured strontium titanate (SrTiO₃) thin films are studied by high temperature photoelectron spectroscopy and thermal gravimetric analysis. The results indicate that ion migration and redistribution as well as transformation between lattice oxygen and gas phase oxygen take place near the grain boundaries during thermodynamic equilibrium process, which lead to obvious variation of the surface composition with temperature. The lattice oxygen ions migrate from bulk to grain surface with temperature rising up; meanwhile Ti ions also migrate to grain surface and combine with oxygen ions forming Ti-0 complex. An opposite process takes place during temperature falling down, but the latter process is much slower than the former one. A primary model is proposed to explain this phenomenon.     

突出矿井瓦斯抽放限制影响因素的AHP-熵权法评价模型

为提高煤与瓦斯突出矿井瓦斯抽放效果,建立了3个一级指标、14个二级指标的突出矿井瓦斯抽放限制影响因素评价指标体系,利用AHP和熵权法分别确定指标因子主、客观权重.通过实地调研分析和反馈验证了AHP-熵权法的可行性和正确性,利用加权平均法确定评价模型的综合权重.研究表明:封孔方式、钻孔半径、抽放时间、煤体裂隙发育程度和抽放负压是目前影响煤矿瓦斯抽放效果的主控因素.     

蒸汽沉淀化学反应方程混合元法的离散格式研究

蒸汽沉淀化学反应过程有着极其广泛的应用,其数学模型归结为一个包含流速场,温度场,压力场和气体溶质场的非线性偏微分方程组．用混合有限元方法研究蒸汽沉淀化学反应方程组,导出其半离散化和全离散化的混合元格式,并证明这些格式的解的存在性和收敛性(误差估计)．用混合元法处理究蒸汽沉淀化学反应方程组,可以同时求出流速场,温度场,压力场和气体溶质场的数值解. 因此该研究既具有重要的理论意义,又具有广泛的应用前景．     

A direct method for determining the mass of gases in ICF shell

In the present paper, the defects of dew point method for measuring the mass of gas filled in ICF shells are analyzed. An accurate state equation for gas D2 is deduced from Benedict-Webb-Rubin (BWR) equation and experimental data in planar phase. A direct method to determine gas mass in ICF shells via measuring the temperature and pressure outside the shells and solving the equation of state by numerical method is proposed. It overcomes the theoretical defects of dew point method and the complexities of equipment. In the present method, the state equation can be improved by more accurately measuring P-V-T values of gas D2, so the measuring precision of the mass of gas in the shells can also be improved. The present method is effective for treating mix gases filled in the shells as well. The errors between the computational results and experimental data are very small. Some cases in the filling process are predicted, and the proper temperature and pressure for filling gases effectively are also suggested.