凝析油气渗流理论研究进展

本文综述了凝析油气渗流研究的现状。简要介绍了凝析油气藏特征。开采方案及其试井分析方法,着重讨论了凝析油气渗流的基本方程、解析解法和数值模拟。在此基础上,提出了该理论研究的发展前景。      

分子模拟在非常规油气开发中的应用

非常规油气资源储量丰富,具有广阔的开发前景.我国低渗/特低渗油藏以陆相沉积为主,储层特征差异性大,孔喉细小,孔隙度低,可动原油气大量储集于亚微米孔隙中,开采难度大,采收率低.岩油界面微观力学作用和限域传质力学机理是其中的关键科学问题.近年来,分子模拟技术在非常规油气开采的研究领域已经成为一种重要的研究手段.本文介绍了分...     

页岩油气高效开发中的基础理论与关键力学问题

我国页岩油气开发刚刚起步,许多基础理论和关键科学（力学）问题亟需明确和解决．本文按页岩油气开发的全过程自然地将其分为四个相互关联的科学问题展开介绍和讨论,包括：页岩工程地质力学特征与预测理论,地质力学找到气;多重耦合下的页岩油气安全钻井完井理论,钻井完井够到气;页岩地层动态随机裂缝控制机理与新概念压裂理论,体积压裂释放气;页岩油气多尺度渗流特征与开采理论,解吸运移产出气．本文提出用水力压裂创造页岩传气能力,用气体二次压裂页岩基质来解决气源问题,实现水力压裂创造的页岩传气能力与页岩基质气体供应能力相匹配,避免“断气”现象发生,最终达到页岩气可持续性开采．解决这些关键科学（力学）问题可以为页岩油气高效开发奠定可靠的基础,具有重要的理论意义和应用前景．     

页岩基质解吸-扩散-渗流耦合实验及数学模型

采用川南地区龙马溪组页岩样品,设计了页岩基质解吸-扩散-渗流耦合物理模拟实验,揭示了页岩基质气体流动特征以及压力传播规律.推导了页岩气解吸-扩散-渗流耦合数学模型并且利用有限差分法对数学模型进行数值求解,与实验结果相比较表明该数学模型能够很好地描述气体在页岩基质中的流动规律.同时对页岩基质气体流动的影响因素进行了分析,认为页岩基质的渗透率、扩散系数、解吸附常数等因素均能影响页岩基质气体的流量和压力传播规律,在页岩气藏的开发过程中需要考虑这些参数的影响,该数学模型为页岩气井产能计算提供了更准确的计算方法.      

海陆过渡相页岩气藏不稳定渗流数学模型

海陆过渡相页岩常与煤层和砂岩呈互层状产出, 储层连续性较差、横向变化快、非均质性强, 水力压裂技术是其获得经济产量的关键手段. 然而, 目前缺乏有效的海陆过渡相页岩气藏不稳定渗流数学模型, 对其渗流特征分析及储层参数评价不利. 针对这一问题, 首先建立海陆过渡相页岩气藏压裂直井渗流数学模型, 其次采用径向复合模型来反映强非均质性, 采用Langmuir等温吸附方程来描述气体的解吸和吸附, 分别采用双重孔隙模型和边界元模型模拟天然裂缝和水力裂缝, 建立并求解径向非均质的页岩气藏压裂直井不稳定渗流数学模型, 分析海陆过渡相页岩气藏不稳定渗流特征, 并进行数值模拟验证和模型分析应用. 分析结果表明, 海陆过渡相页岩气藏不稳定渗流特征包括流动早期阶段、双线性流、线性流、内区径向流、页岩气解吸、内外过渡段、外区径向流及边界控制阶段. 将本模型应用在海陆过渡相页岩气试井过程中, 实际资料拟合效果较好, 其研究成果可为同类页岩气藏的压裂评价提供一些理论支撑, 具有较好应用前景.      

致密砂岩气藏纳微观结构及渗流特征

随着常规油气资源的减少,致密砂岩气藏逐渐成为勘探开发的热点.然而致密砂岩气高效产出机理研究还相对滞后,已经成为目前制约致密砂岩气大规模经济有效开发的瓶颈.致密砂岩由于其特殊的地质特征, 基质微观结构复杂,天然裂缝一定程度发育, 投产一般需要水力压裂等增产措施,气体在其中渗流存在跨尺度效应.研究揭示出致密砂岩气在多孔介质中的流动分为解吸、扩散、渗流等几个方式,包括浓度场下的扩散、压力场中的渗流等.综述了致密砂岩存在的非常规地质特征及其研究描述方法,并依据克努森数大小, 对致密砂岩气的渗流状态进行流态区域划分,为更好的理解和模拟致密砂岩气的流动状态提供了理论依据,并指出建立一种高效、简洁的微观结构精细描述方法,以及解决致密砂岩气在多尺度条件下的传质优化等是今后研究的重点方向.      

CCS工程中盖层渗透率对CO_2逃逸的影响

针对CO_2埋存后可能存在的逃逸问题进行了分析.在对ABAQUS商用软件进行二次开发的基础上,针对各个因素进行了计算;并对简单情况进行了理论推导,验证了数值模型的正确性.考虑到CO_2逃逸过程中可能发生相态变化,数值模拟时分别采用理想气体状态方程和范德华方程以对结果进行比较.结果表明,在盖层均匀和通常的气藏条件下,CO_2完全渗漏需要15×10~4年以上;盖层含井或有裂缝时会导致CO_2快速逃逸,完全逃逸在1×10~4年左右,在选址时应该尽量避免.     

矩形页岩气藏压裂直井解析解产能评价

为了准确评价矩形渗流区域内页岩气藏压裂直井的产能,加强气井生产过程中的科学性管理。通过运用Fick扩散定律和达西渗流规律,建立页岩气藏压裂直井基质扩散方程和裂缝渗流方程。结合时间叠加原理,通过Green函数给出矩形封闭边界和矩形定压边界下无限导流垂直裂缝井不稳定渗流的解析解。研究结果明确了页岩气藏矩形边界压裂直井的渗流特征及不同扩散特征下的压力响应,提出了矩形页岩气藏压裂直井产能评价方法,达到了快速评价及准确预测气井产能的目的。矩形页岩气藏的流动能分为7个阶段。通过将本文提出的矩形封闭边界模型与实际生产数据拟合,得到单井产量平均拟合误差为11.6%,压力平均拟合误差为8.3%,累计产气量平均拟合误差为7.12%。     

TRANSIENT WELL TEST MODEL FOR THE WELL WITH GAS AND WATER DISTRIBUTED IN COALBED

煤层气是一种高效清洁的非常规天然气资源,其开采过程是一个排水降压采气的过程. 由于煤层气主要是以吸附态的形式存在于煤层中,当煤层压力降低到临界解吸压力以下时煤层气从煤层中解吸出来并与水一起采出,因此煤层中流体是气水两相分布的. 本文根据煤层气藏排采过程中的解吸特征,通过考虑气水两相分布的渗透率关系,提出了一种与解吸区域大小相关的煤层气井不稳定试井模型. 该模型较好地描述了煤层气排采过程中煤层内气水的流动状态,采用分区模式对气水两相进行描述. 通过有限体积方法求解了所建立的试井模型,计算得到了煤层气井气水两相分布不稳定试井理论曲线,分析了煤层气解吸系数、解吸复合半径、气水饱和度分布等对试井理论曲线的影响.     

具有振动边界自激系统的混沌行为

鉴于初轧机轧制过程中振动的非线性和边界可动,本文建立了轧机轧制过程中主传动系统的扭转自激振动模型,通过对所建模的研究表明,该系统具有多种非线性振动模式,且在近共振区出现了混沌行为,这为分析,诊断及控制这一具有混沌行为为系统的振动提供了理论依据。     

Microvisual Study of Multiphase Gas Condensate Flow in Porous Media

Gas condensate reservoirs constitute a significant portion of hydrocarbon reserves worldwide. The liquid drop-out in these reservoirs may lead to recovery problems such as near wellbore permeability impairment and uncertainty in the actual location of the target condensate. Such technical issues can be addressed through improved understanding of the formation of condensate and the multiphase flow of gas/condensate/water in the reservoir as characterized by relative permeability curves. The appropriate relative permeability curves in turn can be used in reservoir simulators to assist in optimization of field development. This paper reports results of experiments conducted in micromodels, in support of possible core flow tests, using reservoir fluids under reservoir conditions. In particular, visualizations of condensate formation with and without connate water are presented and the differences between the two cases as well as the possible implications for the relative permeability measurements are discussed. Furthermore, the flow of gas and condensate at different force ratios (capillary and Bond numbers) are presented. It is postulated that a single dimensionless number may not be sufficient to characterize the multiphase flow in gas condensate reservoirs. The physical mechanisms occurring under various field conditions are examined in the light of these observations.     

3D pore network modeling and simulation for dynamic displacement of gas and condensate in wellbore region

Condensate dropout in near a wellbore region in gas condensate reservoir is the main reason of low well deliverability. Many researchers have studied gas and condensate relative permeabilities (RPs) in this region to find the condition for better deliverability. It is known that RP is a function of capillary number in low interfacial tension (IFT) systems such as gas-condensate. The positive dependency of RPs to velocity which is referred to as "positive coupling effect" is related to the simultaneous flow of gas and condensate associated with intermittent opening and closure of channels in porous media. The negative dependency of RPs to velocity named "negative inertia" is due to non-Darcy high-velocity flow. In this study, a 3D pore network modeling is developed to investigate fluids distribution in a gas-condense system at a pore scale to find out the effects of IFT and velocity on RPs. A new method is developed that applies a flash calculation in all throats in the network to estimate the amount of accumulated condensate in throats' corners at different time steps. A modified form of Poiseuille's law for polygonal cross-sectional throats is used to find and update pressure field and fluids distribution in the network and to determine the quantity of pushed out condensate from closed throats to neighboring throats. The displacement mechanism is considered to be determined by the volume of displaced phases in throats without applying any correlation. Simulation results indicate that gas and condensate RPs are increased by an increase in velocity. However, RPs sensitivity to velocity is reduced by increasing IFT which is in agreement with previous studies.     

Injection of carbon dioxide into a reservoir saturated with methane and water

This paper presents a mathematical model for the injection of carbon dioxide into a natural gas reservoir saturated with methane and water accompanied by the formation of carbon dioxide hydrate in an extended region. The dependence of the coordinates of the boundaries of the region of phase transitions on the pressure of the injected gas and the initial parameters of the reservoir are investigated. It is established that the velocity of the near boundary of the region of hydrate formation decreases with increasing water saturation and initial temperature of the reservoir and the velocity of the far boundary of the region of phase transitions increases with increasing pressure of the injected gas and reservoir permeability. It is shown that at high initial temperatures of the reservoir, a regime is possible in which replacement of methane by carbon dioxide without hydrate formation occurs at the far interface, and at the near interface, water is completely incorporated into gas hydrate.     

Phase Behaviour,Fluid Properties and Recovery Efficiency of Immiscible and Miscible Condensate Displacements by SCCO<Subscript>2</Subscript> Injection: Experimental Investigation

This paper presents a quantitative investigation of the interfacial tension dependent relative permeability (IFT-DRP) and displacement efficiency of supercritical CO₂ injection into gas-condensate reservoirs. A high-pressure high-temperature experimental laboratory was established to simulate reservoir conditions and to perform relative permeability measurements on sandstone cores at a constant reservoir temperature of 95°C and displacement velocity of 10 cm/h. This investigation covers immiscible displacements (1100 and 2100 psi), near-miscible displacement (3000 psi) and miscible displacements (4500 and 5900 psi). The coreflooding results demonstrated that displacement pressure is a key factor governing the attainment of optimum sweep efficiency. The ultimate condensate recovery increased by almost threefold when CO₂ was injected at near-miscible conditions (i.e., 23.40% ultimate recovery at 1100 psi compared to 69.70% at 3000 psi). Miscible flooding was found to give the optimum condensate recovery (9% extra ultimate recovery compared to near-miscible injection). Besides improving the ultimate recovery, miscible floods provided better mobility ratios and delayed gas breakthrough (0.62 PV BT at 5900 psi compared to 0.21 PV BT at 1100 psi). In addition to the elimination of IFT forces in miscible displacements, favourable ratios of fluid properties and phase behaviour relationships between the SCCO₂ and condensate were believed to be the driving force for the improved recovery as they provided a stabilising effect on the displacement front and stimulated swelling of the condensate volume. This paper incorporates the theoretical aspects of phase behaviour and fluid properties that largely affect the microscopic displacement efficiency and serves as a practical guideline for operators to aid their project designs and enhance their recovery capabilities.     

井筒气液两相流对致密气压裂水平井试井的影响

多段压裂水平井技术是目前开采致密气最常用的方法之一,在致密气压裂水平井试井测试中常常伴随着一定的产水量,井筒气液两相流会增加井筒流体的流动阻力,加大井筒流体流动对试井解释的影响.为了明确井筒气液两相流对致密气藏压裂水平井试井的影响,提高产水致密气压裂水平井的试井解释精度,建立了一种井筒气液两相流与地层渗流耦合的试井模型,采用数值方法对模型进行求解,获得了考虑井筒气液两相流的压裂水平井试井理论曲线、压力场分布及裂缝产量分布.研究结果表明:井筒气液两相流会增加试井理论曲线中压力和压力导数值,造成靠近入窗点的压力扩散要快于远离入窗点的压力扩散,引起靠近入窗点的裂缝产量要高于远离入窗点的裂缝产量.现场实例分析进一步说明,不考虑井筒两相流可能会对产水压裂水平井的试井解释结果产生很大误差,主要表现为水平井筒假设为无限大导流能力会使得拟合得到的表皮系数偏大,将测试点视为入窗点会使得拟合得到的原始地层压力偏小.所建立的考虑井筒两相流的压裂水平井试井模型为产水致密气井试井资料的正确解释提供了重要技术保障.      

Effect of Hydrogen Sulfide on Condensation and Flow of Gas Condensate Fluids in Porous Media

Condensation and flow experiments were conducted at subsurface conditions in a glass micromodel using reservoir fluids with and without the hydrogen sulfide component. It has been noted that the formation of the condensing phase as well as modes of condensate flow are similar for both fluids. Furthermore, an additional condensate transport mechanism, termed lamella flow, was observed with the sour fluid. It has been concluded that core flow experiments conducted with sweet reservoir fluid should reproduce the flow of sour fluid to a large extent.     

页岩气在超低渗介质中的渗流行为

基于页岩气藏复杂孔隙结构和页岩气在纳米孔隙表面的滑脱和吸附-解吸附等现象,通过引入表观渗透率,修正Darcy渗流模型,得到了页岩气渗流本构方程. 将计算结果与Darcy模型计算结果进行了比照,结果表明,在产量定常情形下,基于非Darcy渗流模型得到的井底压力高于Darcy流结果; Darcy流模型得到的压力衰减速度较快,改进后的渗流模型更能准确描述与表征页岩气渗流过程;研究结果可为页岩气藏的经营与管理提供基础参数.      

Near-Critical Gas–Liquid Flow in Porous Media: Monovariant Model, Analytical Solutions and Convective Mass Exchange Effects

We examine a class of hydrocarbon reservoirs whose thermodynamic state remains close to the critical point during the all period of reservoir exploitation. Such a situation is typical for the so-called gas–condensate systems, in which the liquid phase is formed from gas when pressure decreases. Due to proximity to critical point, the mixture contains many components which are neutral with respect to the phase state. This determines a low thermodynamic degree of freedom of the system. As the results, the mathematical flow model allows a significant reduction in the number of conservation equations, whatever the number of chemical components. In the vicinity of a well, the system may be reduced to one transport equation for saturation. This nonlinear model yields exact analytical solutions when the flow is self-similar. In more general case of flow, we develop partially linearized solutions which are shown to be sufficiently exact. The spectrum of examined cases covers the flow in a medium with a sharp heterogeneity and a sharp variation in the flow rate. A significant relative gas flow past liquid gives rise to a convective mass exchange phenomenon which appears highly different from that observed in static. In the case of a medium discontinuity, the convective mass exchange gives rise to a phenomenon of condensate saturation billow formation. A sharp variation in the flow rate leads to a hysteretic behavior of the saturation field.     

页岩有机质纳米孔隙气体吸附与流动规律研究

页岩储层孔隙结构复杂, 气体赋存方式多样. 有机质孔隙形状对受限空间气体吸附和流动规律的影响尚不明确, 导致难以准确认识页岩气藏气体渗流机理. 为解决该问题, 本文首先采用巨正则蒙特卡洛方法模拟气体在不同形状有机质孔隙(圆形孔隙、狭长孔隙、三角形孔隙、方形孔隙)内吸附过程, 发现不同形状孔隙内吸附规律符合朗格缪尔单层吸附规律, 分析了绝对吸附量、过剩吸附浓量、气体吸附参数随孔隙尺寸、压力的变化, 研究了孔隙形状对气体吸附的影响. 在明确不同形状有机质孔隙内气体热力学吸附规律基础上, 建立不同形状有机质孔隙内吸附气表面扩散数学模型和考虑滑脱效应的自由气流动数学模型, 结合分子吸附模拟结果研究了不同孔隙形状、孔隙尺寸有机质孔隙内吸附气流动与自由气流动对气体渗透率的贡献. 结果表明, 狭长孔隙内最大吸附浓度和朗格缪尔压力最高, 吸附气表面扩散能力最弱. 孔隙半径5 nm以上时, 吸附气表面扩散对气体渗透率影响可忽略. 本文研究揭示了页岩气藏实际生产过程中有机质孔隙形状对页岩气吸附和流动能力的影响机制.