A unified fractional flow framework for predicting the liquid holdup in two-phase pipe flows

Two-phase pipe flow occurs frequently in oil&gas industry,nuclear power plants,and CCUS.Reliable calculations of gas void fraction(or liquid holdup)play a central role in two-phase pipe flow models.In this paper we apply the fractional flow theory to multiphase flow in pipes and present a unified modeling framework for predicting the fluid phase volume fractions over a broad range of pipe flow conditions.Compared to existing methods and correlations,this new framework provides a simple,approximate,and efficient way to estimate the phase volume fraction in two-phase pipe flow without invoking flow patterns.Notably,existing correlations for estimating phase volume fraction can be transformed and expressed under this modeling framework.Different fractional flow models are applicable to different flow conditions,and they demonstrate good agreement against experimental data within 5%errors when compared with an experimental database comprising of 2754 data groups from 14literature sources,covering various pipe geometries,flow patterns,fluid properties and flow inclinations.The gas void fraction predicted by the framework developed in this work can be used as inputs to reliably model the hydraulic and thermal behaviors of two-phase pipe flows.

缝洞型油藏溶洞-裂缝组合体内水驱油模型及实验

根据相似理论设计了满足几何相似、运动相似、动力相似和缝洞特征参数相似的缝洞组合体物理模型和模拟实验,研究了缝洞组合体内流体流动特征、水驱油特征的影响因素以及不同驱替方式的提高采收率特征。模拟实验结果表明:油水密度差异导致的油水置换效应是水驱油主要机理;注水速度对剩余油分布和含水率变化规律无影响;缝洞连接关系是决定无水采收率、极限剩余油和含水率变化规律的主要因素;油水黏度比是影响产油速度、换油率和经济极限剩余油的重要因素;充填疏松时充填作用对剩余油几乎没有影响,充填致密时剩余油包括"阁楼油"和充填孔隙中剩余油两部分;水驱转泡沫驱主要通过启动溶洞顶部"阁楼油"提高采收率,泡沫驱后剩余油位于溶洞中部;水驱转聚合物驱主要通过增加注入水的换油率和采油速度提高经济极限采收率,对水驱极限剩余油无影响。

利用单频双程波动方程计算初至走时及其振幅

通过在频率域双程波动方程模拟算法中加入一个复数频率(实部表示频率,虚部表示衰减因子)压制地震波初至走时之后的能量,从而把初至走时及其振幅的计算问题转换为单一频率波场中最大能量走时和振幅的拾取问题,然后利用单一频率域波场的相位项和振幅项分别计算初至走时及其振幅.本文还提出利用参数分析方法求取最优的复数频率,并给出数值计算例子,将本方法的计算结果与有限差分程函方程初至走时和最大能量走时振幅进行比较,结果表明,该方法具有适应于任意复杂介质和多炮多接收点走时和振幅的计算.

页岩气吸附解吸效应对基质物性影响特征

为了研究页岩气降压开采过程中吸附气解吸作用对基质表观物性(如有效孔隙半径、有效孔隙度、表观渗透率)及气体流动机制的影响,推导了吸附解吸作用下页岩基质孔隙有效半径和表观渗透率动态模型,建立了考虑吸附解吸影响基质表观物性和气体传输机制的页岩气渗流数学模型。采用有限体积法对模型进行求解,利用实验及矿场数据验证了模型的可靠性,最后应用该模型研究了页岩气开采过程中基质物性参数、气体流动机制变化特征以及吸附效应对页岩气开发的影响规律。研究结果表明,页岩气开采过程中基质孔隙有效半径、有效孔隙度和表观渗透率逐渐变大,体积压裂改造区域流动机制由滑脱流转变为过渡流;忽略吸附层影响将导致地质储量和产气量严重高估;随着吸附层厚度增加,累计产气量变化不大,但采收率逐渐降低。

多因素影响的泡沫驱数值模拟方法

基于泡沫封堵规律实验结果和质量守恒定律,建立了综合考虑多孔介质渗透率、发泡剂质量浓度、泡沫干度、油藏温度、含油饱和度、含水饱和度以及渗流速度等多因素影响的泡沫驱数学模型.采用IMPES和Runge Kutta方法对模型进行了求解和验证.利用数值模拟方法研究了泡沫封堵特性和泡沫驱开发效果影响因素的敏感性.研究结果表明：随着转驱时机的推迟,最终采收率先小幅升高后迅速降低;随着泡沫干度增加,最终采收率先增加后降低,泡沫干度为50％～67％时的驱替效果最佳;随着发泡剂质量浓度增加,最终采收率先迅速增加后趋于稳定;随着注入速度增加,最终采收率先增加后降低;各因素对泡沫驱最终采收率影响程度大小为：发泡剂质量浓度＞注入速度＞泡沫干度≈转驱时机.由于该数学模型考虑了众多与实体油藏相关的参数,所以该模拟方法可以更容易、有效地应用于指导泡沫驱矿场试验方案的制定.

天然裂缝多孔介质中流体运移的流线模拟

为了研究天然裂缝在多孔介质中的作用,将嵌入型离散裂缝模型(EDFM)与流线模拟方法相结合,对天然裂缝进行模拟,计算流体在基质和裂缝中的流动轨迹及流动时间。通过分析具有不同裂缝网络的油藏见水时间和驱扫体积的差别,研究裂缝导流能力、裂缝数目和裂缝位置对流体流动轨迹和流动时间的影响。研究表明,在其他条件相同的情况下,与无裂缝均质油藏相比,裂缝性油藏中水驱见水时间会快30%,而驱扫体积会少10%。虽然增加单条裂缝可以加速见水时间,减少驱扫体积,但增加更多裂缝却不一定得到相同效果。水驱效果还跟裂缝的走向和位置有关系,不同的走向和位置可以导致见水时间相差20%,而驱扫体积相差9%。裂缝长度越短,对于流体流动轨迹和流动时间的影响越小。裂缝的位置对驱扫效率影响较大,单条裂缝的位置变动可以导致驱扫体积变化1%。

Shale gas production evaluation framework based on data-driven models

Increasing the production and utilization of shale gas is of great significance for building a clean and low-carbon energy system.Sharp decline of gas production has been widely observed in shale gas reservoirs.How to forecast shale gas production is still challenging due to complex fracture networks,dynamic fracture properties,frac hits,complicated multiphase flow,and multi-scale flow as well as data quality and uncertainty.This work develops an integrated framework for evaluating shale gas well production based on data-driven models.Firstly,a comprehensive dominated-factor system has been established,including geological,drilling,fracturing,and production factors.Data processing and visualization are required to ensure data quality and determine final data set.A shale gas production evaluation model is developed to evaluate shale gas production levels.Finally,the random forest algorithm is used to forecast shale gas production.The prediction accuracy of shale gas production level is higher than 95%based on the shale gas reservoirs in China.Forty-one wells are randomly selected to predict cumulative gas production using the optimal regression model.The proposed shale gas production evaluation frame-work overcomes too many assumptions of analytical or semi-analytical models and avoids huge computation cost and poor generalization for numerical modelling.

On the uncertainty of interwell connectivity estimations from the capacitance-resistance model

The capacitance-resistance model （CRM） is an alternative to conventional reservoir simulation. CRM, a simplification of complex numerical models, uses production and injection rates to infer a reservoir description. There is no prior geologic model. The principal output of CRM fitting is the fraction of injected fluid （usually water） that is produced at a producer at steady-state. These fractions are interwell connectivities. Interwell connectivities are fundamental information needed to manage waterfloods in oil reservoirs. The data-driven CRM is a fast tool to estimate these parameters in mature fields and allows one to make full use of the dynamic data available. This paper considers the problem of setting an upper bound on the uncertainty of interwell connectivities for linear-constrained models. Using analytical bounds and numerical simulations, we derive a consistent upper limit on the uncertainty of interwell connections that can be used to quantify the information content of a given dataset.

Understanding aqueous foam with novel CO2-soluble surfactants for controlling CO2 vertical sweep in sandstone reservoirs

The ability of a novel nonionic CO2 -soluble surfactant to propagate foam in porous media was compared with that of a conventional anionic surfactant（aqueous soluble only）through core floods with Berea sandstone cores.Both simultaneous and alternating injections have been tested.The novel foam outperforms the conventional one with respect to faster foam propagation and higher desaturation rate.Furthermore,the novel injection strategy,CO2 continuous injection with dissolved CO2 -soluble surfactant,has been tested in the laboratory.Strong foam presented without delay.It is the first time the measured surfactant properties have been used to model foam transport on a field scale to extend our findings with the presence of gravity segregation.Different injection strategies have been tested under both constant rate and pressure constraints.It was showed that novel foam outperforms the conventional one in every scenario with much higher sweep efficiency and injectivity as well as more even pressure redistribution.Also,for this novel foam,it is not necessary that constant pressure injection is better,which has been concluded in previous literature for conventional foam.Furthermore,the novel injection strategy,CO2 continuous injection with dissolved CO2 -soluble surfactant,gave the best performance,which could lower the injection and water treatment cost.

Implementation of configuration dependent stiffness proportional damping for the dynamics of rigid multi-block systems

The distinct element method(DEM)has been used successfully for the dynamic analysis of rigid block sys- tems.One of many difficulties associated with DEM is modeling of damping.In this paper,new procedures are proposed for the damping modeling and its numerical implementation in distinct element analysis of rigid muhi-block systems.The stiff- ness proportional damping is constructed for the prescribed damping ratio,based on the non-zero fundamental frequency ef- fective during the time interval while the boundary conditions remain essentially constant.At this time interval,the funda- mental frequency can be estimated without complete eigenvalue analysis.The damping coefficients will vary while the damp- ing ratio remains the same throughout the entire analysis.A new numerical procedure is developed to prevent unnecessary energy loss that can occur during the separation phases.These procedures were implemented in the development of the dis- tinet element method for the dynamic analyses of piled multi-block systems.The analysis results |or the single-block and two-block systems were in a good agreement with the analytic predictions.Applications to the seismic analyses of piled four- block systems revealed that the new procedures can make a significant difference and may lead to much-improved results.

Iterative coupling reservoir simulation on high performance computers

In this paper, the iterative coupling approach is proposed for applications to solving multiphase flow equation systems in reservoir simulation, as it provides a more flexible time-stepping strategy than existing approaches. The iterative method decouples the whole equation systems into pressure and saturation/concentration equations, and then solves them in sequence, implicitly and semi-implicitly. At each time step, a series of iterations are computed, which involve solving linearized equations using specific tolerances that are iteration dependent. Following convergence of subproblems, material balance is checked. Convergence of time steps is based on material balance errors. Key components of the iterative method include phase scaling for deriving a pressure equation and use of several advanced numerical techniques. The iterative model is implemented for parallel computing platforms and shows high parallel efficiency and scalability.

A systematic rheological study of alkyl amine surfactants for fluid mobility control in hydrocarbon reservoirs

The basis of this study is to identify the versatility of N,N,N＇-trimethyl-N＇-tallow-1,3-diaminopropane（DTTM） surfactant in high saline environments. The surfactant was examined with sodium chloride, NaCl, to understand how triggers such as salt, p H, temperature, and surfactant concentration influences the viscoelastic response of the surfactant solution. The DTTM surfactant and salt（NaCl） concentrations used in steady-state shear viscosity analysis range from 0.2 wt% to 2 wt%and 5 wt% to 25 wt%, respectively. Along with DTTM results, three similar chemical structures are investigated to understand how viscosity changes with alterations in tail and head group composition. It was found that DTTM surfactant has the capability of transitioning from a foam-bearing to viscoelastic state at low surfactant concentrations under moderate to high saline conditions. A longer tail length promotes viscoelasticity and shear-thinning behavior. Terminals consisting of hydroxides or ethoxylates have a lower viscosity than that of methyl terminals. A head group consisting of two nitrogen atoms has a higher viscosity than those containing one nitrogen atom. The rheological characterization of DTTM presented in this paper is part of a larger study in determining the capability of this surfactant to foam CO2 for improving mobility control in CO2 enhanced oil recovery in high saline oil formations.

Carbon Dioxide Storage and Sequestration in Unconventional Shale Reservoirs

Carbon Dioxide (CO2) storage and sequestration in unconventional shale resources has been attracting interest since last couple of years due to the very unique characteristics of such formations have made them a feasible option for this object. Shale formations are found all around the world and the conventional assets are easily accessible, and also the huge move of operators toward developing unconventional reservoirs during past years leaves many of such formations ready for sequestering CO2. Today, the use of long horizontal wells that are drilled on a pad has the lowest amount of environmental footprint in which for storage and sequestration purpose also provides much more underground pore spaces available for CO2. In this paper we study the state of the art of the technology of CO2 storage and sequestration and provide different and fresh look for its complex phenomena from a mathematical modeling point of view. Moreover, we hope this study provides valuable insights into the use of depleted shale gas reservoirs for carbon sequestration, which as a result, a cleaner atmosphere will be achieved for the life of our next generations. Also, we present that the depleted shale gas reservoirs are very adequate for this purpose as they already have much of the infrastructure required to perform CO2 injection available in sites.

Sorting Techniques for Plastics Recycling

This paper presents the basic principles of three different types of separating methods and a general guideline for choosing the most effective method for sorting plastic mixtures. It also presents the results of the tests carried out for separation of PVC, ABS and PET from different kinds of plastic mixtures in order to improve the grade of the raw input used in mechanical or feedstock recycling.

Nuclear magnetic resonance(NMR) microscopic simulation based on random-walk: Theory and parameters analysis

The microscopic response characteristics of nuclear magnetic resonance(NMR) are widely used for characterizing complex pore structures of rocks. Due to the prohibitive NMR experiment cost, numerical simulation was employed as an alternative approach to verify some theoretical aspects of NMR responses. Firstly, the basic principles of pore-scale NMR simulation based on random-walk method(RWM) were introduced. The RWM-simulated results were benchmarked with the analytical results for an ideal spherical pore model. Then, the effects of two numerical parameters, namely diffusion radius and walk numbers, were studied on the simulation accuracy. The simulation method is then applied to various pore models with different pore sizes and pore shapes filled with different fluids to study the microscopic NMR response characteristics. The numerical experiments are useful for understanding and interpreting NMR measurements and the simulation code provides a numerical tool to perform pixel-based digital rock analysis.

Numerical investigation of fluid phase momentum transfer in carbonate acidizing

This work mainly studies the effect of fluid phase momentum transfer mechanisms on the acidizing results,including the retardation effect of the porous structure and the interaction between the fluid phase,such as viscous dissipation and inertial effect.The results show that the acid fluid momentum transfer is influenced by the complex porous structure and fluid viscous dissipation.Eventually,the Stokes-Darcy equation is recommended to be adopted to describe the fluid phase momentum transfer in the following numerical simulation studies of the carbonate acidizing process.Based on this model,a parametric research is carried out to investigate the impact of acid on rock physical characteristics in the stimulation process.Increasing the acid concentration appears to minimize the quantity of acid consumed for the breakthrough.The acid surface reaction rate has a considerable impact on the pore volume to breakthrough and the optimum acid injection rate.The influence of permeability on the acidizing results basically shows a negative correlation with the injection rate.The difference between the acidizing curves of different permeability gradually becomes insignificant with the decrease in injection rate.The existence of isolated fracture and vug significantly reduces acid consumption for the breakthrough.

Characterization of complex hydraulic fractures in Eagle Ford shale oil development through embedded discrete fracture modeling

This study extends an integrated field characterization in Eagle Ford by optimizing the numerical reservoir simulation of highly representative complex fractured systems through embedded discrete fracture modeling(EDFM). The bottom-hole flowing pressure was history-matched and the field production was forecasted after screening complex fracture scenarios with more than 100 000 fracture planes based on their propped-type. This work provided a greater understanding of the impact of complex-fractures proppant efficiency on the production. After compaction tables were included for each propped-type fracture group, the estimated pressure depletion showed that the effective drainage area can be smaller than the complex fracture network if modeled and screened by the EDFM method rather than unstructured gridding technique. The essential novel value of this work is the capability to couple EDFM with third-party fracture propagation simulation automatically, considering proppant intensity variation along the complex fractured systems. Thus, this work is pioneer to model complex fracture propagation and well interference accurately from fracture diagnostics and pseudo 3 D fracture propagation outcomes for multiple full wellbores to capture well completion effectiveness after myriads of sharper field simulation cases with EDFM.

Numerical simulation of the impact of polymer rheology on polymer injectivity using a multilevel local grid refinement method

Polymer injectivity is an important factor for evaluating the project economics of chemical flood,which is highly related to the polymer viscosity.Because the flow rate varies rapidly near injectors and significantly changes the polymer viscosity due to the non-Newtonian rheological behavior,the polymer viscosity near the wellbore is difficult to estimate accurately with the practical gridblock size in reservoir simulation.To reduce the impact of polymer rheology upon chemical EOR simulations,we used an efficient multilevel local grid refinement（LGR）method that provides a higher resolution of the flows in the near-wellbore region.An efficient numerical scheme was proposed to accurately solve the pressure equation and concentration equations on the multilevel grid for both homogeneous and heterogeneous reservoir cases.The block list and connections of the multilevel grid are generated via an efficient and extensible algorithm.Field case simulation results indicate that the proposed LGR is consistent with the analytical injectivity model and achieves the closest results to the full grid refinement,which considerably improves the accuracy of solutions compared with the original grid.In addition,the method was validated by comparing it with the LGR module of CMG_STARS.Besides polymer injectivity calculations,the LGR method is applicable for other problems in need of near-wellbore treatment,such as fractures near wells.

用粒度分布参数计算单相渗透率

渗透性介质的单相渗透率取决于基体内部相互连通的孔隙系统的物理性质(如孔隙度和曲折度)和它的粒度分布(psd)统计参数。一个描述渗透率与孔隙级别性质之间关系的表达式是卡尔曼一科泽尼(Carman—Kozeny)方程(简称CK方程)。这个方程在过去曾被用来描述渗透性形成的机理,因为它提供了一个介质属性和流动阻力之间的连接关系。因为CK方程未曾被应用于具有混合粒度的介质,因此我们修改了CK方程,用粒度分布统计参数与基体物理性质来描述未固结介质的单相渗透率。我们发现,能够把未固结介质的渗透率与粒度分布参数联系起来,这个关系与已经发表的资料相匹配。它通常不适用于渗透率小于1μm^2(约1达西)的介质,可能是因为在这个渗率范围内的介质中,并非所有孔隙空间中的流体都能流动。在这个模型被实验数据部分验证后,我们用它来研究渗透性介质的渗-孔关系及渗透率变化的原因。这将有可能解释很多在野外露头研究中所观察到的渗透性差异。

Low-tension gas process in high-salinity and low-permeability reservoirs

Polymer-based EOR methods in low-permeability reservoirs face injectivity issues and increased fracturing due to near wellbore plugging,as well as high-pressure gradients in these reservoirs.Polymer may cause pore blockage and undergo shear degradation and even oxidative degradation at high temperatures in the presence of very hard brine.Low-tension gas(LTG) flooding has the potential to be applied successfully for low-permeability carbonate reservoirs even in the presence of high formation brine salinity.In LTG flooding,the interfacial tension between oil and water is reduced to ultra-low values(10^-3 dyne/cm) by injecting an optimized surfactant formulation to maximize mobilization of residual oil post-waterflood.Gas(nitrogen,hydrocarbon gases or C02) is co-injected along with the surfactant slug to generate in situ foam which reduces the mobility ratio between the displaced(oil) and displacing phases,thus improving the displacement efficiency of the oil.In this work,the mechanism governing LTG flooding in low-permeability,high-salinity reservoirs was studied at a microscopic level using microemulsion properties and on a macroscopic scale by laboratory-scale coreflooding experiments.The main injection parameters studied were injected slug salinity and the interrelation between surfactant concentration and injected foam quality,and how they influence oil mobilization and displacement efficiency.Qualitative assessment of the results was performed by studying oil recovery,oil fractional flow,oil bank breakthrough and effluent salinity and pressure drop characteristics.