Simulation of gas kick with high HeS content in deep well

The phase transition, from asubcriticalstate to a gaseousstate, of the natural gas with high H₂S content and thesolubility of the H₂S component in the drilling fluid will make the multiphase flow behavior very different from the pure natural gas-drilling fluid two-phase flow under the gas kick condition in a deep well. With consideration of the phase transition and thesolubility of the H₂S component in the natural gas, a multiphase flow model is established. Thesimulation analysis results indicate that, for a typical case of a well depth of 4 325 m, the density of the 100%-H₂S natural gas can be 4 times higher than that of the 0%-H₂S natural gas, and thesolubility of the 100%-H₂S natural gas is 130 times higher than that of the 0%-H₂S natural gas. These will make the detection of the gas invasion more difficult. While the invasion gas moves up along the wellbore to a certain position, the phase transition and the release of the dissolved gas may cause a rapid volume expansion, increasing the blowout risk. The calculation results alsoshow that the risks of a gas kick can be reduced by increasing the wellhead back pressure.     

Prediction of natural gas hydrate formation region in wellbore during deep water gas well testing

Wellbore temperature field equations are established with considerations of the enthalpy changes of the natural gas during the deep-water gas well testing. A prediction method for the natural gas hydrate formation region during the deep-water gas well testing is proposed, which combines the wellbore temperature field equations, the phase equilibrium conditions of the natural gas hydrate formation and the calculation methods for the pressure field. Through the sensitivity analysis of the parameters that affect the hydrate formation region, it can be concluded that during the deep-water gas well testing, with the reduction of the gas production rate and the decrease of the geothermal gradient, along with the increase of the depth of water, the hydrate formation region in the wellbore enlarges, the hydrate formation regions differ with different component contents of natural gases, as compared with the pure methane gas, with the increase of ethane and propane, the hydrate formation region expands, the admixture of inhibitors, the type and the concentrations of which can be optimized through the method proposed in the paper, will reduce the hydrate formation region, the throttling effect will lead to the abrupt changes of temperature and pressure, which results in a variation of the hydrate formation region, if the throttling occurs in the shallow part of the wellbore, the temperature will drop too much, which enlarges the hydrate formation region, otherwise, if the throttling occurs in the deep part of the wellbore, the hydrate formation region will be reduced due to the decrease of the pressure.     

THE WALL EFFECT ON VENTILATED CAVITATING FLOWS IN CLOSED CAVITATION TUNNELS

For ventilated cavitating flows in a closed water tunnel, the wall effect may exert an important influence on cavity shape and hydrodynamics, An isotropic mixture multiphase model was established to study the wall effect based on the RANS equations, coupled with a natural cavitation model and the RNG k-ε turbulent model. The governing equations were discretized using the finite volume method and solved by the Gauss-Seidel linear equation solver on the basis of a segregation algorithm. The algebraic multigrid approach was carried through to accelerate the convergence of solution. The steady ventilated cavitating flows in water tunnels of different diameter were simulated for a conceptual underwater vehicle model which had a disk cavitator. It is found that the choked cavitation number derived is close to the approximate solution of natural cavitating flow for a 3-D disk. The critical ventilation rate falls with decreasing diameter of the water tunnel. However, the cavity size and drag coeflicient are rising with the decrease in tunnel diameter for the same ventilation rate, and the cavity size will be much different in water tunnels of different diameter even for the same ventilated cavitation number.     

LIQUID-GAS TWO PHASE FLOW RATES METERING BY DUAL PRESSURE DIFFERENTIAL MEASUREMENTS

The measurement of the overall mass flow rates in a two phase, gas/liquid pipeline is considered on the basis of dual pressure differential measurements for a combined contraction/frictional pipe type of flow meter and a numerical model to predict overall mass flow rates from pressure differentials measured from this type of flow meter is presented. The experiments generally conform with the predictions of the flow rates prediction model. Whilst the practicability of such metering of two phase flows is clearly demonstrated, application of the method would require careful calibration to allow for the influence of nozzle coefficients, pipe Reynolds number and void fraction upon the one dimensional compressible flow equations through wall friction factor and interphase slip effects.     

NUMERICAL STUDIES FOR GAS SOLID TWO PHASE STEADY MIXED CONVECTION PROBLEMS WITH PHASE CHANGE

A mathematical model for describing gas solid two phase steady mixed convection with phase change has beendeveloped and numerical calculation methods presented.A melting liquid droplet failing a counter gas currenl expe-riences three processes,cooling of liquid droplet,solidification and cooling of the solid particle.The turbulent modelused for Rayleigh number greater than 10~6 is a two equation(k—ε)model of turbulence.For phase change,animproved enthalpy method with varied time step is proposed.The gas particle two phase flow is described by usingEulerian-Lagrangian approach.Modified SIMPLE algorithm and Runge-Kutta method are used in interative calcu-lation.As an example of calculation,the flow in a special 2-dimensional axi-symmetrical prilling tower of diameter20 m and height 50 m has been performed.Buoyancy effect is important for moving droplet with phase change.The model to be developed and analysis of results obtained in this paper are useful for engineering design in indus-try.     

THEORETICAL AND EXPERIMENTAL STUDY ON THE CONICAL SWIRLING WATER JET FLOW

This paper is concerned with theoretical and experimental study on theconical swirling water jet flow.Based upon the theoretical analysis,the experiment on thestructural characteristics of swirling water jet flow including the velocity and pressure dis-tribution laws,on which the parameters of the jet,nozzle and directional blades havemore or less influence,was carried out in CSSRC by using a 3-D LDV in order to optimizea new high-efficiency jet instead of swirling drilling bit for rock-breaking and continuouslydrilling,and to meet the demand of radial horizontal drilling technology.Meanwhile basedon the experimental results,the numerical simulation was conducted for the conicalswirling water jet in the immersed well-bottom flow by solving the RANS equations in the3-D body-fitted coordinate system with the k-ε turbulence model.The numerical resultsare consistent with the experimental data,and lead to some conclusions which are impor-tant for applying the conical swirling water jet to the petroleum drill     

WELL TESTING ANALYSIS FOR HORIZONTAL WELL WITH CONSIDERATION OF THRESHOLD PRESSURE GRADIENT IN TIGHT GAS RESERVOIRS

A fundamental solution for homogeneous reservoir in infinite space is derived by using the point source function with the consideration of the threshold pressure gradient. The fundamental solution of the continuous point source function is then derived based on the Green function. Various boundary conditions of the reservoirs are considered for this case and the corresponding solutions are obtained through the mirror image reflection and the principle of superimposition. The line source solution is obtained by integration. Subsequently, the horizontal-well bottom hole pressure response function for a non-linear gas flow in the homogeneous gas reservoir is obtained, and the response curve of the dimensionless bottom hole pressure and the derivative for a horizontal well in the homogeneous gas reservoir are obtained. In the end, the sensitivities of the relevant parameters are analyzed. The well test model presented in this paper can be used as the basis of the horizontal well test analysis for tight gas reservoirs.     

Acoustics of a viscoelastic medium with encapsulated bubbles

In this paper,a modified Rayleigh-Lamb equation is derived that takes into account the radial vibrations of a gas bubble coated with a viscoelastic shell and located in an elastic medium.For small oscillations of inclusion,the problem of heat exchange between a gas,a liquid phase,a viscoelastic shell,and an elastic medium is solved.The energy integral is determined.In the case of small disturbances,the dispersion relation is found from the Rayleigh-Lamb equations,energy,and the known wave equation for the bubbly medium.An analytical expression of the equilibrium speed of sound is written out and its dependence on the size of the viscoelastic shell and the disturbance frequency is established.An example of a mixture of polydimethylsiloxane with air bubbles coated with a rubber shell illustrates the influence of the elasticity of the carrier medium and the shell of the bubbles on the dependence of the phase velocity and attenuation coefficient on the perturbation frequency.For a mixture of water with air bubbles coated with a rubber shell,the influence of the dependences of the shear modulus and viscosity of butyl rubber on the frequency of disturbances at different temperature on the dispersion curves is shown.A comparison of the theory with experimental data is given.     

Experimental and numerical simulations of bottom hole temperature and pressure distributions of supercritical CO2 jet for well-drilling

The supercritical carbon dioxide （SC-CO2） drilling is a novel drilling technique developed in recent years. A detailed study of temperature and pressure distributions of the SC-CO2 jet on the bottom of a well is essensial to the SC-CO2 drilling. In this paper, the distributions of pressure and temperature on the bottom of the hole during the SC-CO2 jet drilling are simulated experimentally and numerically, and the impacts of the nozzle diameter, the jet length, and the inlet pressure of the SC-CO2 jet are analyzed. It is shown that, the bottom hole temperature and pressure increase with the increase of the nozzle diameter, and the bottom hole temperature reduces and the pressure increases first and then decreases with the increase of the jet length, indicating that the jet length has an optimum value. The increase of the inlet pressure can increase the temperature and pressure on the bottom, which has a positive effect on the drilling rate.     

A THREE-SEGMENT HYDRAULIC MODEL FOR ANNULAR CUTTINGS TRANSPORT WITH FOAM IN HORIZONTAL DRILLING

Through mechanical analysis, an improved hydraulic model for annular cuttings transport with foam was established for horizontal drilling. Based on the two critical inclination angles, the entire well was divided into three segments. The Bagnold stress, generalized power law rheological model and modified hindered particle settling velocity in foam fluid were adopted in the model to improve the simulation accuracy. The proposed model allows more precise prediction of cuttings transport property in the whole range of well inclination angle. Model performance was examined via case study and experimental data. Simulation results given by the propulsion iteration and trial-and-error method agree well with in-situ horizontal well drilling practice for the case study, and the comparison between the model prediction and Capo’s experimental data shows satisfactory agreement.     

井筒环雾流传热模型及其在深水气井水合物生成风险分析中的应用

该文采用Hewitt流型判别法,表明深水含水气井测试时井筒内多为环雾流,考虑了气核与液膜间速度及热力学性质差异,建立了环雾流传热模型,与南海某深水气井实测数据对比,模型预测误差在5%以内。计算表明,忽略含水影响的气体单相模型在含水量大于0.1%时,泥线以上井筒压力和温度预测误差均超过10%,应用该研究建立的环雾流模型则可以得到更准确的结果。含水会使泥线以上一定范围内井段井筒温度显著降低,压力损失增大。产气量较低时,含水量对水合物生成风险基本无影响;产气量较高时,含水量会使得水合物生成区域下界下移,水合物生成区域增大,并使过冷度增大,更容易诱导水合物生成,水合物生成风险增大,需要增加水合物抑制剂用量,并加深注入位置。产水会使无水合物生成所对应的临界产气量增大,需要调整水合物抑制剂用量和注入位置。     

How does oil and gas behave when released in deepwater?

Deepwater oil and gas releases have come to greater attention of the scientists as well as general public in the recent past, especially after the Deepwater Horizon spill in Gulf of Mexico in 2010. In this short paper we show the general behavior of an oil and gas spill in deepwater. A model, CDOG, developed by Zheng et al. (2003) and had undergone successive improvements is used for the simulations to illustrate the oil behavior. The impact of the oil droplet sizes are demonstrated. Although cases are not specific to a particular spill, through the use of a state-of-the-art model, we show the key parameters that affect the behavior of oil. In this paper we show oil and gas behavior that has not been clearly explained in previous papers and address newly found concerns brought on by the recent awareness. This paper also shows how the oil behavior changes when additives like dispersants are applied. Results of the simulations reveal that the “underwater plumes” with low concentrations of oil can be formed and stay submerged for long periods of time when very small (less than 0.5 mm in diameter) oil droplets are present.     

高压气提水泵耗气量与提水量关系试验研究

在我国一些偏远地区还存在着结构性缺水的问题,设计出利用河流中本身蕴藏的水力能实现泵水功能的装置,是解决这一问题的途径之一。试验的研究对象是一套提水装置,它可将自然界的低落差水力能转换成高压气体,然后再用产生的高压气体实现将水提到更高扬程的目的。通过对试验数据以及观察到的现象的分析,探究了耗气量与提水量之间的关系,并考虑进气管直径、回水高度、淹没比、泵管外径等因素的影响,得到了耗气量与提水量的相互作用规律,为该装置的实际工程应用提供科学试验依据。     

考虑表面扩散的页岩气渗透率两区复合解析模型

页岩气是一种以吸附态和游离态为主,赋存于纳米级多孔介质中的一种非常规气藏,其渗流特征较常规气藏存在较大的差异。前人研究表明,页岩气运移过程存在多种渗流机理,主要包括:达西渗流、滑脱效应和扩散。虽然前人对自由气扩散的渗流机理模型进行了大量的研究,但是大多没有考虑吸附气表面扩散对渗流的影响。针对以往研究的不足,该文采用两区复合概念模型,建立了考虑吸附气表面扩散、达西渗流和滑脱效应的气体渗流模型,将吸附气和自由气运动关系利用修正的滑脱速度边界条件进行耦合,采用等值渗流阻力法对气体在纳米孔隙介质中渗流的关键参数―渗透率―进行了深入研究,获得了适用于任意克努森数范围的页岩气渗透率解析模型。通过对不同尺度、不同压力下的储层在考虑表面扩散等多重机制下的渗透率进行了计算并发现:吸附气表面扩散是页岩气渗流的重要机理,其对渗透率的贡献会对页岩气藏储层评价和开发方案制定以及增产改造施工设计产生重要影响。     

佛山水道水流水质模型研究与应用

根据感潮网河区的水力、水质特性,利用一维感潮河网区水流水质数学模型,加入顺逆调节因子,将顺、逆流向的离散方程统一到同一方程中,研究分析佛山水道各种引水方案对佛山水系水流的影响和对佛山水道水环境改善的效果,为佛山水道引水工程的进一步设计提供依据。模型通过相应的同步潮流观测水位资料进行了率定,精度符合要求。     

Distribution features of cuttings bed and sensitivity analysis of major drilling parameters for cuttings transport in gas drilling horizontal wells

In the current engineering methods for the gas horizontal drilling, the distribution features of cuttings bed remain an issue to be cleared, and the gas horizontal drilling is still in early stages of development. For on-site drilling, a 3-D transient model is established in this paper to simulate the distribution features and the transport mechanism of the cuttings bed, based on the gas-solid two-phase flow theory. The effects of major drilling parameters, such as the gas velocity, the drill pipe rotation, the cutting size and the eccentricity, on the cuttings transport efficiency are analyzed. The major findings of this study include that the cuttings begin to settle down and build up a fixed cuttings bed, in the most evident regions in front and behind the connector, the dominant parameter of the wellbore cleaning is the gas velocity, and, as the cutting size is increased, the thickness of the cuttings bed developed in the wellbore increases significantly. In addition, the eccentricity has some influence on the cuttings transport, and the drill pipe rotation has little effect on the cuttings transport.     

二维溃坝洪水波演进的数值模拟

采用基于MacCormack预测-校正技术的隐式数值格式求解控制水流运动的二维浅水方程，建立了模拟大坝瞬间全溃或局部溃倒所致的洪水演进过程数学模型．应用该模型对矩形明渠中缓、急流过渡的水面曲线进行了数值计算，并与理论解进行了比较。最后用该模型预测了矩形河道中大坝瞬间局部溃倒时下游有多个障碍物的洪水演进过程，算例说明该数学模型对模拟溃坝洪水波很有效。     

考虑变井筒存储的凝析气压力动态分析

许多因素影响凝析气井压力动态，以前的试井分析方法虽然考虑了井筒存储的影响，但没有考虑变井筒存储的影响。然而由于凝析气自身的特性，井筒存储的变化对压力及压力导数动态有显著的影响，如不考虑此因素将会对凝析气压力动态分析结果产生较大的影响。文中针对凝析气井测试的特点，对Xu ＆ Lee的凝析气井试井分析数学模型进行修正，建立了考虑表皮效应及变井筒存储的凝析气井试井解释数学模型，对其进行求解，分析研究了各参数对压力和压力导数动态的影响，并形成了新的理论图版。