考虑压裂影响的低渗气藏高压平面供气机理探讨

采用高低渗区"串联"方法开展了考虑压裂影响的高压(最高为45 MPa)平面非均质供气机理渗流实验,研究了配产、物性、压裂改造等对供气能力的影响,通过建立单井平面非均质渗流数值模型对实验结果进行了论证。结果表明,配产越高,稳产期越短,总采收率越低;生产初期高渗区贡献率从60%左右逐渐降低,高低渗区最终贡献率受各区储量控制;渗透率级差越小,基质渗透率越高,相同配产下采收率越高,低渗区动用程度越高;压裂后近井高渗区压差变小,更有利于提高低渗区压差,高低渗分区采收率和总采收率均提高,储层平均渗透率越低,压裂后采收率提高幅度越大;当渗透率级差大于50倍时,近井高渗"甜点"并不能有效激活远井低渗储层,储层总体采出程度低。本文研究成果对高效开发低渗非均质气藏有重要的生产指导意义。     

大庆五站低渗气藏数值模拟研究

目前变形介质气藏数值模型方面已有大量研究，但这些模型中只考虑了渗透率对压力的敏感性，而忽略了孔隙度对压力的敏感性。大庆油田五站低渗透气藏通过岩心应力测试表明，孔隙度和渗透率均具有应力敏感性，因此在得到大庆五站气藏岩心孔隙度、渗透率随净围压的变化规律基础上，建立了同时考虑孔、渗介质变形的低渗气藏数值模拟型，并采用IMDES方法进行求解。通过大庆五站气藏5口气井的产量历史拟合分析表明，综合考虑渗透率和孔隙度应力敏感时历史拟合更符合开采实际，说明模拟方法可在类拟气藏中应用。与此同时，通过气藏模拟表明目前气藏井控动态储量较低，要提高气藏开发效果应在有潜力和储层有效厚度增大的地区部署新开发井。     

准噶尔盆地二叠系芦草沟组致密油岩心覆压孔渗变化规律研究

油层条件下岩石的孔隙度和渗透率与净上覆压力的关系是储量计算和油气田开发研究的重要内容。 利用 CMS-300 覆压测试系统,根据岩心压汞、铸体薄片、扫描电镜及场发射等多项实验分析资料,研究了致密油在地层条件下的孔隙度和渗透率与净上覆压力的关系,同时为分析致密油与低孔、低渗储层的差异,还对低孔、低渗储层岩心进行了实验。 研究结果表明： ① 随着净上覆压力的增加,覆压孔隙度和覆压渗透率均与净上覆压力呈幂函数递减关系; ② 与低孔、低渗储层相比,压实作用对致密油造成的孔隙度和渗透率的损失率均较小; ③ 恢复压力后,致密油的孔隙度和渗透率基本能恢复到初始值,岩样具有较好的弹性。     

异常高压油气藏储层物性随有效压力变化的研究

选取中原油田文13西块和渤中25-1油田共50块岩心样品进行岩心覆压孔渗实验,对异常高压油气藏储层孔隙度和渗透率随有效压力的变化进行了研究。孔隙度和渗透率随有效压力的增加呈非线性减小,在有效压力小于20MPa时减小幅度最大。建立了以不同有效压力为基准的异常高压油气藏储层孔隙度和渗透率随有效压力变化的通用数学模型,即幂函数模型,并在渤中25-1油田某油井射孔段进行了实际应用。     

考虑应力敏感性的低渗透气藏气井产能分析

低渗透气藏储层在开发过程中,由于受到的净覆压差增大,储层孔隙度、渗透率等物性会随之降低。结合国内某低渗气藏的室内岩心实验,用实验数据拟合回归出了孔隙度与净覆压的二次多项式,建立了覆压渗透率与净覆压、常压渗透率的经验公式。根据Forchheimier非达西渗流公式,建立了气藏在考虑应力敏感性时的二项式产能方程,对比分析了常压渗透率与覆压渗透率下的单井产能。结果表明,考虑应力敏感的气井,无阻流量降低了12.3%,累积产气量减少20.5%。     

提高缝洞型气藏采出程度的物理实验——以高磨地区震旦系灯影组气藏为例

高磨地区震旦系缝洞型气藏孔隙、溶洞、裂缝搭配关系复杂,储层渗流能力的较大差异导致难以准确预测气藏的采出程度。为认识并量化储层非均质性对储量可采性的影响,开展地层条件下各类储层岩心的串、并联衰竭式开发实验。通过改变实验压差和岩心的组合方式,明确流量与压力随时间的变化关系,评价现有工艺技术条件下储层类型、生产制度对气藏采出程度的影响。串联实验中,气体流动路径为孔隙→孔洞→裂缝-孔洞时,岩心采出程度最大;气体流动路径为孔洞→裂缝-孔洞→孔隙时,采出程度减少14%。并联实验中,实验压差5 MPa时最终累计产气量最大,但由于高渗岩心孔隙压力下降过快,后期累产气量增加幅度减小;实验压差3 MPa时,各类岩心同时供气的时间延长,实现了"动态供给平衡",累产气量增加幅度保持稳定。该实验研究从微观上认识了不同类型储层组合下的产量贡献特征,量化了低渗储层对高渗储层的制约性,对缝洞型气藏早期开发对策的制定具有指导意义。     

致密油储层渗透率界定指标探讨

近年来,由于美国致密油产量快速增长,引起了全球范围内的广泛关注,但是对于致密油的渗透率评价指标国内外尚不统一。基于油藏产能评价、实验室岩心相对渗透率、岩心排驱压力以及岩心孔隙度—渗透率关系等多个方面分析,结合现行标准及覆压渗透率—地面渗透率关系,提出了主要以地面渗透率1m D作为致密油储层与常规储层的分界点;并分析了致密油储层与常规特低渗透储层3个方面的差异,包括孔隙空间构成、孔隙度—渗透率关系以及束缚水饱和度等;最后提出了致密油储层两种辅助表征方法即渗流速率法和孔喉半径法等供参考使用。     

低孔隙度低渗透率复杂断块油气田储层有效性评价方法

某区块为典型中生界低孔隙度低渗透率复杂断块油气田,不同断块储层埋深差异较大。不同埋深储层常规岩心分析孔隙度渗透率关系复杂,为储层参数准确计算及储层有效性评价带来很大困难。通过实验室岩心分析对比发现,储层渗透性受孔隙度、孔隙结构、储层埋深等多种因素共同制约,覆压孔隙度渗透率关系明显优于常压孔隙度渗透率关系。在岩心分析认识与试油相结合的基础上,建立了综合考虑储层埋深、孔隙度、孔隙结构的常压、覆压渗透率计算模型,提出了利用覆压孔隙度渗透率综合指数评价储层有效性的方法,在实际应用中取得了良好的应用效果。     

低渗气藏储层应力敏感性实验研究

低渗透气藏的开采会导致地层压力发生变化,从而引起储层孔隙度和渗透率发生相应的变化。实验表明,孔隙度随有效应力变化很小,而渗透率随有效应力变化较大。利用第二次增减压应力敏感实验的数据进行分析,避免了因为地层压实对渗透率伤害的过高估计,更符合生产实际。使用应力敏感指数对低渗气藏岩心进行评价,得到渗透率较高的岩心应力敏感指数要高于渗透率较低的岩心,这是由于其内部在覆压增加时小孔道闭合比后者要严重;地层压缩所引起的渗透率伤害是可以恢复的。     

基于岩石物理相的酸性火山岩储层渗透率计算方法

火山岩储层非均质强,应用单一孔隙度-渗透率关系模型计算渗透率难以满足气藏精细评价需求。针对火山岩储层特征,首次将岩石物理相引入火山岩储层孔渗关系研究中,应用层流指数对孔渗关系分类并建立相应渗透率计算模型;应用岩心分类结果对储层缝洞指示参数进行刻度后,通过单井孔隙度频谱分析得到的储层缝洞指示参数选取相应渗透率计算模型,对储层渗透率进行计算。对45口井的数据进行处理,计算渗透率与223块岩心分析渗透率对比验证,具有较好一致性,满足气藏精细评价与开发需求。     

涡流排水采气技术数值模拟研究

为了促进涡流排水采气工艺在我国的推广应用,开展了涡流工具特性的模拟研究。建立了涡流工具排液过程的数理模型,对涡流工具引发的旋流场进行了模拟研究,获得了不同雷诺数及持液率下的气液螺旋涡流的流场结构及特点,气速对液膜螺旋流的影响规律,螺旋流动强度的变化规律。研究结果表明,涡流工具使气液两相流体调整为类环状流动,井筒中心以连续气柱的形式向上运动,壁面附近的液膜螺旋上升运动,这种流动结构降低了管柱摩阻,提高了气体携液能力。     

The Effect of Water Vaporization on the Well Productivity of Gas Condensate Reservoirs

Well productivity is a crucial concern in predicting the performance of many gas condensate reservoirs. Accurate forecasting of gas-condensate well productivity usually requires fine-grid simulation to model the formation of the liquid bank and to account for high-velocity phenomena and changes in relative permeability at high capillary numbers. At early stages of production, the pressure drop in the near-wellbore region builds up the molar content of water in gas. This, in turn, results in water vaporization, and hence a drop in the connate water saturation. When water vaporization occurs, pores that were formerly filled by connate water now becomes occupied by gas and condensate only. This causes a change in gas and condensate saturations near the wellbore that can affect the well productivity. No lucid numerical simulation approach considering this effect is suggested in the literature. The authors investigated the effects of water vaporization on the near-wellbore region by compositional simulator of GEM. Enhancement of gas well productivity is observed.     

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目前在研究凝析气的渗流和相态问题时，当地层压力降低到露点压力之后，采用的都是等温瞬时平衡的概念，而在凝析气井生产过程中，当近井带压力降至体系露点压力以下后，采用的都是等温瞬时平衡的概念，而在凝析气井生产过程中，当近井带压力降至体系露点以下，由于气相的高速流动，气液相并不充分接触，液相析出后运动滞后而逐渐沉积，部分液相组分会因高速气流夹带而呈气相运动一段距离后才变成液相析出，也就是说液相析出量的多少要受到平衡时间的影响。章从体系的强度性质出发，引往平衡时间因素建立非瞬时平衡相态描述方法。利用LHSS方程研究了凝析气井近井地带高速流动区在非瞬时相平衡条件下凝析液的析出和温降。结果表明，由于非瞬时平衡作用导致高速流动区液相析出量减少，近井带的凝析油动态饱和度比用瞬时平衡预测的低。     

异常高压对储层物性的影响

异常高压作为一个封闭系统,它的主要作用在于影响烃源岩的成熟和储层的性能。探讨异常高压对储层物性的影响作用可以为油气勘探评价提供重要的决策依据。通过实验模拟和对典型超压盆地孔渗性与超压关系的研究,认为超压不仅有利于储层孔、渗性的保存,而且通过物理和生物化学两种作用机理改善了储层物性。     

Simulation of unconventional well tests with the finite volume method

The finite volume method has been successfully applied in several engineering fields and has shown outstanding performance in fluid dynamics simulation. In this paper, the general framework for the simulation of near-wellbore systems using the finite volume method is described. The mathematical model and the numerical model developed by the authors are presented and discussed. A radial geometry in the vertical plane was implemented so as to thoroughly describe near-wellbore phenomena. The model was then used to simulate injection tests in an oil reservoir through a horizontal well and proved very powerful to correctly reproduce the transient pressure behavior. The reason for this is the robustness of the method, which is independent of the gridding options because the discretization is performed in the physical space. The model is able to describe the phenomena taking place in the reservoir even in complex situations, i.e. in the presence of heterogeneities and permeability barriers, demonstrating the flexibility of the finite volume method when simulating non-conventional tests. The results are presented in comparison with those obtained with the finite difference numerical approach and with analytical methods, if possible.     

Gas-Condensate Reservoir Pseudo-relative Permeability Derived by Pressure-Transient Analysis. Incorporation of Near-Wellbore Effects

Abstract

Gas-condensate reservoirs exhibit a near-wellbore complex behavior due to the existence of a two-phase system when pressure drops below dew point. In analyzing well-testing data, a single-phase approach is only valid for well condition above dew point, whereas a multi-phase pseudo-pressure approach is widely adopted for a gas reservoir operating below dew-point. This article utilizes the pseudo-pressure approach, for analyzing well-test data in gas-condensate reservoirs producing below the dew-point pressure, to generate Corey exponents for relative permeability in order to determine near-wellbore representative relative permeability that history matches the actual well-testing data.     

含水凝析气相态特征及非平衡压降过程产液特征

气态水的存在对凝析气藏相态特征的影响不容忽视,常规的相态测试过程无法模拟含水凝析气田开发过程中近井带的非平衡压降过程的实际产液特征。利用PVT筒开展了含气态水凝析油气体系相态特征实验,研究了气态水对凝析气相态特征的影响,并通过缩短凝析气体系定容衰竭过程的平衡时间,模拟含水凝析气田开发过程近井带的非平衡压降衰竭过程,对比分析了非平衡压降过程含水凝析气体系中凝析油、水的抽提蒸发效应。结果表明,气态水的存在引起了凝析油气体系中重质含量的增加,导致露点压力升高,反凝析提前,最大反凝析压力提高,反凝析液量增加。含水凝析油气体系在非平衡压降衰竭过程中,由于气液相体系未达平衡,导致液相滞后析出并随气相运动一起被采出,造成凝析油采出程度和产水量提高,且非平衡压降速度越大,凝析油采出程度越高。因此,凝析气田近井带的非平衡压降有利于凝析油的开采并缓解液锁的发生。     

利津洼陷北部砂砾岩储层异常高孔渗带形成机制

济阳坳陷利津洼陷北部利563块沙四上段发育厚层砂砾岩储层。基于岩心、测录井数据和储层微观观察等,明确了储层异常高孔渗带的存在及其形成机制。研究表明:2500~2900 m深度范围内异常高孔渗带特征显著;异常高孔渗带成因机制有石油早期侵入、异常高压作用、溶蚀孔隙和压裂缝的发育等。储层粒间及压裂缝中沥青质的残余说明石油早期侵入;泥岩声波时差曲线的异常高值说明异常高压的存在。岩心和薄片观察揭示研究区砾石中压裂缝广泛存在,并显著提升了储层渗透率。储层溶蚀面孔率整体为2%左右,压裂缝发育基础上的溶蚀扩缝作用可有效提高储层孔隙度。     

Gas-Condensate Reservoir Pseudo-relative Permeability Derived by Pressure-Transient Analysis. Incorporation of Near-Wellbore Effects

Gas-condensate reservoirs exhibit a near-wellbore complex behavior due to the existence of a two-phase system when pressure drops below dew point. In analyzing well-testing data, a single-phase approach is only valid for well condition above dew point, whereas a multi-phase pseudo-pressure approach is widely adopted for a gas reservoir operating below dew-point. This article utilizes the pseudo-pressure approach, for analyzing well-test data in gas-condensate reservoirs producing below the dew-point pressure, to generate Corey exponents for relative permeability in order to determine near-wellbore representative relative permeability that history matches the actual well-testing data.     

Effect of surfactants on wettability of near-wellbore regions of gas reservoirs

The flow of gas in tight, low-pressure gas wells can be partially blocked by the water saturation build-up near the hydraulic fracture face if the drawdown pressure does not exceed the capillary pressure. To increase the productivity, the water saturation may be reduced by alteration of the near-wellbore wettability from water-wet conditions to intermediate-wet conditions. Many surfactants have been identified which change the wettability of carbonate and sandstone rocks from water-wet to intermediate-wet in water–air–rock systems. Among fluorosilanes, as the number of fluoro groups increases, rocks become less water-wet. One day of aging period and 1 wt.% concentration appear to be sufficient for altering wettability. Interaction with field brine plays a crucial role in selection of appropriate surfactants. The increase in gas relative permeability due to the change in wettability is a function of the pressure gradient.