凝析油蒸发动态特征

凝析气藏开采到压力降到露点压力以后，会在储集层中产生液态凝析油，凝析油饱和度常小于临界凝析油饱和度，凝析油黏度大会产生流度差异效应，往往导致凝析油滞留在储集层中。由于相平衡效应，会产生3种不同的凝析油蒸发动态情形：①压力低于最大反凝析压力后的凝析油蒸发效应；②保持压力过程中的凝析油再蒸发效应；③注入流体使地层压力上升过程中的凝析油反蒸发效应。在降压开采过程中，液态凝析油体积逐渐减小，这主要是由于整个压力衰竭过程中平衡气相的中间组分和重组分含量越来越少，为了达到相态平衡，液相中的相应组分重新分配到气相中，从而出现凝析油的蒸发现象。富凝析气藏常常采用注气开发，注入气体与原始凝析气藏流体进行组分交换，使凝析油在地下蒸发现象明显，注入干气不仅能蒸发凝析油中的中间烃类，而且也能蒸发C20 以上的重烃。实际凝析气藏在高注采比条件下，产出凝析油中较重组分含量增加幅度较大，说明当凝析油析出后，通过注气提高地层压力，可以将反凝析的重组分部分反蒸发而采出。图2表1参10     

裂缝-孔洞型凝析气藏不同开发方式的长岩心实验

柴达木盆地塔中Ⅰ号气田裂缝-孔洞型碳酸盐岩储层表现出“双孔双渗”特征,凝析油反蒸发机理不同于砂岩凝析气藏,国内外对如何提高裂缝-孔洞型凝析气藏采收率的研究还比较少。为此,首先取得无裂缝的碳酸盐岩岩心进行孔隙度和渗透率测试（平均孔隙度6.5%,平均渗透率1 mD）,然后进行造缝（裂缝渗透率5~10 mD）,并将岩心组合成长岩心（105.8 cm）,最后采用塔中Ⅰ号气田凝析气（凝析油含量533 g/m³）进行了注气、吞吐和脉冲注气实验,优选出提高凝析油采收率的开发方式。实验结果表明：露点压力以上注气凝析油采收率最高,其次是最大凝析油饱和度下注气或脉冲注气;与低渗透砂岩凝析气藏不一样,注气吞吐提高凝析油采收率效果最差。该实验对裂缝-孔洞型储层高含凝析油型的凝析气藏的合理开发提供了技术支撑。     

凝析气藏开发中后期注气提高采收率

柯克亚凝析气田目前地层压力已经大幅下降,基本接近甚至低于最大反凝析压力,使得井筒周围析出的凝析油增多,渗流阻力增大致使多井无法正常生产。通过调研类比以及室内凝析油注干气抽提相态实验和长岩心驱替实验,结合现场试注结果,评价分析凝析气藏开发中后期注气提压、提高采收率的可行性。研究表明,随注气量增加,注入气对凝析油的抽提作用明显加强,同时凝析油注气膨胀后流动性能明显改善;在地层压力高于最大反凝析压力时注气,可提高凝析油采收率10%～25%,但地层压力若低于最大反凝析压力时注气,采收率增幅十分有限。柯克亚凝析气田部分砂体封闭性好,规模有限,地层压力接近最大反凝析压力,结合矿场情况优化注采参数,采用控制注采比,注气逐步增压,可以有效避免气窜,提高气藏开发效果。     

凝析气藏合理注气时机研究

凝析气藏的开发方式主要分为压力衰竭式和注气保压式,而目前对于后者合理注气时机的研究甚少,不清楚什么时候注气最有利于凝析气藏的开发:若过早注气,注气量较大,经济效益较低;而过晚注气,则有可能导致凝析油污染严重,产能及采收率均较低。为此,选取某凝析气井的真实岩心,利用长岩心驱替实验研究其合理的注气时机;并在此基础上,运用响应曲面法和数值模拟的方法来综合评价合理的注气时间。研究结果表明:①对于凝析油含量较高的凝析气藏,应在地层压力降低至露点压力附近时进行注气,即可避免析出大量凝析油而导致气井产能和采收率大幅降低;②对于凝析油含量较低的凝析气藏,合理的注气时机为地层压力低于露点压力且高于最大反凝析压力区域,这样既能获得相对较高的凝析油采收率,又具有较高的经济效益。结论认为:对于凝析气藏的开发,注气越早开发效果越好,但不一定都能获得较高的经济效益。     

牙哈凝析气藏注气开发过程反蒸发动态相态特征

针对牙哈凝析气藏出现的反凝析问题,利用油气相平衡理论,在对典型气井YH301井地层流体相态实验拟合的基础上,模拟研究了该凝析气藏的反凝析相态特征和组分变化特征,同时分析了注入气与地层剩余凝析油和剩余井流物的反蒸发相态变化特征。结果表明：①随着地层压力的降低,凝析气中C1含量逐渐增加,C₁₀⁺的含量逐渐降低,反之也成立;②加载不同比例注入气后,随着注入气比例从20%增加到80%,地层反凝析油的ｐ-T相图临界点从右向左偏移,当注入气摩尔含量超过40%后,整个体系在地层温度134 ℃下已经变成露点状态;③地下剩余流体注气后混合物体系反凝析液量降低,注入气所占摩尔含量越高,反凝析液量降低越多;④注入气摩尔含量大于40%有利于降低体系露点压力和反凝析液量,使凝析气不会再显著发生反凝析损失,反凝析饱和度明显降低,有利于牙哈凝析气藏开发中后期进一步提高凝析油的采收率。     

塔里木盆地大涝坝凝析气田循环注气开发设计

大涝坝凝析气田开发后期,地层压力降至露点压力以下,凝析油迅速析出,导致流体采出程度低,为了提高采出程度,进行了循环注气开发研究.分析了大涝坝凝析气田地质特征、流体相态特征,确定了凝析气藏注气地质条件,并根据在定容衰竭过程中介质作用对地层凝析油饱和度影响较大,对该凝析气藏采取注气保持压力方式开采.建立了气藏流体单井产出、注入方程,利用老井及新布井进行了注气方案优化.制定了凝析气藏循环注气布井方案,对循环注气开发指标进行了预测,形成了凝析气藏循环注气配套技术.通过气藏循环注气开发模拟,得出开发指标,并与衰竭方式开采指标对比,发现凝析油采收率大幅度提高,循环注气应用效果好.     

缝洞型碳酸盐岩凝析气藏不同开发方式全直径物理模拟研究

缝洞型碳酸盐岩凝析气藏储层结构、流体性质复杂,造成其流动机理及凝析油反蒸发机理不同于砂岩凝析气藏,需要进行开发机理研究来为缝洞型碳酸盐岩凝析气藏提高采收率提供理论基础。本文取得塔中Ⅰ号碳酸盐岩凝析气田露头岩心造缝造洞,采用现场取得的油气样进行配制,使用高温高压全直径岩心设备进行了垂直衰竭、水平衰竭、注干气保持压力、注水保持压力、注干气吞吐、注水替凝析油的全直径岩心物理实验研究。实验根据缝洞型储层不同结构特征分类对比了各种开发方式对凝析油采收率的影响,对缝洞型储层高含凝析油型凝析气藏的合理开发具有很好的指导意义。     

牙哈凝析气藏二次注气抑制反凝析机理及相态特征

为解决凝析气藏天然气回注率不足,地层压力低于露点压力而出现的反凝析损失等问题,以塔里木盆地牙哈凝析气藏反凝析损失监测井地层流体取样器(MDT)取样为基础,运用高温高压PVT相态实验测试和模拟技术,建立了牙哈凝析气藏二次循环注气抑制反凝析损失机理的相态特征研究方法,对提高牙哈凝析气藏凝析油采出程度的可行性和有效性做出了评价。通过目前地层压力下反凝析油和剩余凝析气体系的实验室再现,分别测定了其色谱组成、相态特征和p-丁相态图;分别针对反凝析油和地层剩余凝析气,开展了注气增溶膨胀实验、多次接触抽提实验和注气抽提实验,对地层剩余平衡凝析气还开展了加注干气传质扩散过程非平衡相态行为实验;分析了二次循环注气抑制反凝析损失、降低其反凝析油饱和度、使凝析油产生相态反转的相行为机理;给出了二次循环注气开发时应尽量使其注气压力高于露点压力的建议,当注入0.82 PV时,凝析油累积采出程度将提高13.55%。该研究成果为牙哈凝析气藏的增产提供了重要技术支撑。     

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凝析气藏循环注气开发注干气受气源及天然气价格因素影响较大；注氮气则可以节省宝贵的天然气资源，但会引起凝析气藏露点压力升高而造成一定量的凝析油损失。文章以实际凝析气藏为例，提出干气—氮气交替注入方法开发凝析气藏的方法，可发挥干气对析出凝析油的反蒸发作用，而将氮气作为一种单纯的驱替介质，减小因氮气与凝析气接触后导致露点压力升高而引起的凝析油损失。文章还利用数值模拟方法研究注气时机、储层非均质、段塞尺寸等因素对开发效果的影响，结果表明利用干气—氮气交替注入开发凝析气藏，其凝析油采收率分别比枯竭式和注氮气高31.8%和2.8%，同时可以减少50%的干气回注量，极大地提高了凝析气藏开发的经济效益。     

缝洞型凝析气藏注气吞吐提高凝析油采收率机理研究

基于凝析油采出的数学理论模型,以及凝析气典型PR状态方程,建立静态零维模型,并通过数模软件的相态软件包对缝洞型凝析气藏进行注气吞吐模拟,研究了注入气组成、注气时机以及注气量对凝析油采收率的影响规律。结果显示,在最大反凝析压力之前注气效果更佳,且越早注气越好;注气量越大效果越好,注气量过小反而将增大反凝析损失;注入气降低反凝析液量和露点压力有利于成功的注气吞吐。     

多孔介质中凝析气液相变实验新方法研究

现有多孔介质相变实验方法的实验压力、实验温度偏低,不能反映油藏条件下凝析气的相变特点。根据凝析气组分随压力变化的原理,设计出研究油藏条件下凝析气相变的高温高压实验流程：采用气相色谱分析仪分析凝析气在岩心中发生反凝析相变后的流体组成,同时与该凝忻气在PVT筒的相态特征进行对比．认识多孔介质对凝析气相变的影响。用该实验流程研究的结果表明：随着压力的降低,岩心中的烃类气体作等温衰竭,当压力降至上露点时．开始有凝析液析出,凝析油气体系进入两相区;反凝析过程中随着压力降低．液相中重烃组分含量增加、轻烃组分减少．气相中则是轻烃组分增加、重烃组分减少;当压力继续降低时,对应的衰竭压力低于多孔介质中凝析油气体系的露点,且已经进入油气两相区．流体组成发生明显变化,气相中轻烃组分增加,液相中重烃组分增加;但是在PVT筒中则还处于单相气区．采出气体的组成未发生燹化。与现有相变实验方法相比．新方法具有可靠性高、精度高的特点。图3表l参6     

Determination of Dew Point Pressure With and Without a Visual Cell

The dew point pressure of a gas condensate fluid is used for planning the production profile of gas condensate reservoirs and for determining their economic success. Usually the best method of the determination of the dew point pressure loci is by visual observation when a constant mass expansion (CME) test is performed on a sample in a high-pressure cell fitted with a glass window. In this test the cell pressure is reduced in steps and the pressure at which the first sign of a liquid droplet is observed and is recorded as the dew point pressure. The gas volume of the saturated fluid at dew point pressure is used as a reference volume and the total hydrocarbon volume measured for each pressure depletion step is reported relative to this volume. For lean gas condensate systems the amount of heavy components that can condense during pressure reduction is less than 4 mol% (<50 bbls/MMscf). Such experimental determination of dew point pressure for these gases require many small pressure reduction steps which make the observation method tedious, time consuming, and expensive. In this study the authors demonstrate that a graphical method of determining dew point pressure, which does not require a windowed cell for visual observation is possible. The authors have extended the Y-function, which is often used to smooth out CME data for black oils to gas condensate systems. They started from the initial measured pressure and volume and by plotting log of the extended Y-function, which they call the Y_RRR-function, with the corresponding pressure so that two straight lines were obtained: one above and one below the dew point. The point at which these two lines intersect is the dew point pressure. The Y_RRR-function method was applied to determine the dew point pressure for both a lean and a rich gas condensate system. The difference between the dew point pressures determined by the authors’ proposed Y_RRR-function method and the observation method was less than ±2.0% for both gas systems. This extension of the Y-function to determine dew point pressure was not found elsewhere in the open literature.     

轮南低凸起凝析气藏的蒸发分馏作用机制

在蒸发分馏作用控制下,凝析气藏的形成将不受烃源岩热演化程度的制约,这是对经典生油理论中凝析气藏成因机制的一种重要补充。轮南低凸起奥陶系及石炭系发育大规模的凝析气藏,地球化学的研究结果表明,这些凝析气藏中凝析油R_c在0.8%~1.0％（远低于热裂解成因R_o＝1.3％的门限）,凝析气为过成熟干气（回归R_o＞2.0％）;同时,区内原油与干气的充注期相异,表明轮南地区的凝析气藏并非热裂解成因的产物。通过分析该区各层系凝析气藏流体性质及相态特征发现,轮南地区凝析气藏具有典型的蒸发分馏特征：下部（奥陶系）层系中凝析气藏的地露压差较小,带有典型的油环;上部（石炭系）层系中凝析气藏的地露压差较大,以纯气相形式存在。石炭系的凝析油相对于下伏的奥陶系残余油具有密度较轻、饱和烃含量偏高的特征。结合该区烃源岩热演化、油气成藏时间、断裂活动史等成藏要素的四维耦合性剖析,结论认为：喜山期断裂泄压作用以及大量他源干气的侵入诱发了该区蒸发分馏作用的产生。     

凝析气露点压力的确定及影响因素

凝析气藏流体的露点压力受到许多因素的影响,如流体组分、气油比、多孔介质、非平衡效应等。不同组分对流体露点压力的影响程度不尽相同,其中C₃、C₄、H₂S等组分的影响很明显。气油比对露点压力具有双重效应,当气油比低于某一数值时,露点压力随气油比增大而增加;当高于此数值时,露点压力又随气油比增大而减小。关于多孔介质对流体露点压力的影响的认识还存在相互矛盾。流体的相态受到组分和组成的极大影响,在生产过程中,近井周围流体的组成在不断变化,从而导致近井周围出现复杂的相态变化。对凝析气露点压力的确定方法及其影响因素的深入研究,将有助于正确评价凝析气藏的生产动态特征。     

An investigation of different gas injection scenarios as enhanced condensate recovery method in a naturally fractured gas-condensate reservoir

In gas condensate reservoirs, when the bottom hole pressure falls below the dew point pressure condensates are formed. This causes hydrocarbon liquid saturation around the well bore region. This phenomenon is called condensate blockage or condensate banking. Condensate recovery reduction due to condensate banking near the well bore region is an important problem in gas condensate reservoirs. The common method to prevent the condensate banking is gas cycling (reinjection of produced dry gas) into the reservoir that can contribute to the condensate vaporization, thus increasing the condensate recovery factor. The objective of this study was to find a suitable replacement for gas cycling. For this purpose, an investigation on the effects of injection of different types of gases (CO₂, N₂, and C₁) on enhance condensate recovery factor and pressure maintenance were performed. This research was done on one of the Iranian gas condensate reservoirs through a compositional simulator. The two-parameter Peng-Robinson equation of state (EOS) and Lohrenz-Bray-Clark correlation were used to model reservoir fluid properties through regression on the pressure-volume-temperature (PVT) experimental data. A fracture network was distributed over the reservoir, so a dual porosity/dual permeability model was selected for better evaluation of the fracture system. Then, various scenarios of natural depletion and CO₂, N₂, C₁, and gas cycling injection were studied. The results showed that CO₂ injection scenario being associated with the highest efficiency compared to that of other gases.     

The Effect of Hydraulic Fracturing on the Performance of Gas Condensate Systems

Gas condensate reservoirs usually exhibit complex flow behaviors due to the buildup of condensate bank around the wellbore when the bottom-hole pressure falls below the dew point. Hydraulic fracturing improves well productivity by delaying the onset of dew point pressure and also reducing the condensate saturation near the wellbore area. The authors present the results of a study that compared the near wellbore behaviors and productivities of a vertical nonfractured well and a vertical hydraulically fractured well in a low permeability lean gas condensate reservoir. Results show that there is no indication of capillary number effects in this low permeability reservoir because of low production rates.     

注烃提高凝析气井产能方法研究

凝析气井在低于露点压力生产时，由于凝析油析出并在井筒附近发生聚集，导致气井产能下降，通过向井内注入烃类溶剂，利用反蒸发及混相机理，可以恢复气井产能，提高凝析气藏采收率。以实际凝析气藏为例，利用数值模拟方法研究注入介质、储层物性、流体性质等因素对提高气井产能的影响。结果表明，注入丁烷加戊烷可以完全解除近井地带凝析液堵塞，改善凝析气藏开发效果。     

利用气藏生产指示曲线计算凝析气藏水侵量

水驱凝析气藏在已开发的气田中占有一定比例,其在开发过程中会出现凝析油析出的特殊现象,导致该类气藏水侵量的计算更加复杂。 凝析气藏作为一类特殊气藏,当气藏压力低于露点压力时,流体中会出现反凝析液相物。 基于水驱凝析气藏的生产特征,推导出新型的水驱凝析气藏物质平衡线性方程, 该方程考虑了当凝析气藏压力低于露点压力时析出凝析油对水侵量计算的影响。 利用该方程绘制的生产指示曲线可方便、快速并准确地计算出水驱凝析气藏不同时期的水侵量。 实例应用表明,与其他水驱凝析气藏水侵量计算方法相比,该方法更简便、快捷,而且计算结果准确,实用性强。     

Experimental study into the effectiveness of the partial gas cycling process in the gas-condensate reservoir development

In this study a laboratory study was carried out with the purposes of estimating the effectiveness of the gas cycling process during gas-condensate reservoir development. Specific laboratory equipment was constructed to carry out an experimental investigation by modelling the gas injection and reservoir depletion process. Volumetric properties, fog up, liquid drop-out condition, and retrograde dew point pressures of gas-condensate fluids were investigated. The reservoir fluid was recombined based on samples from Azerbaijan natural gas-condensate reservoir. Results are describing gas injection effect on condensate/gas ratio and condensate recovery in each pressure step. These have provided an understanding on the influence of the retrograde dew point pressure on optimum gas injection stage. The analyses also assure that as condensate/gas ratio decreases continually during the gas injection process, which causes the reservoir fluid PVT characteristics to be changed accordingly furthermore the reservoir pressure can be depleted in order to vaporize the liquid phase and to maintain the reservoir fluid to be in a single phase state during the reservoir exploitation. It was seen to be closely related with retrograde dew point pressure and fog up pressures. Therefore, in terms of incorporating colloidal systems into the subject focusing more on the region between fogging up and retrograde condensation gave interesting results.     

LNG装置脱酸系统塔提前液泛的原因及改造

克拉美丽气田油气处理装置以控制外输天然气烃、水露点为目标,采用注乙二醇防冻、J-T阀节流制冷、低温分离脱水脱烃工艺对凝析气进行处理,凝析油处理采用二级闪蒸+一级稳定+提馏工艺。现有油气处理装置工艺流程存在醇烃分离困难、乙二醇再生塔再生损失严重、凝析油余热利用不合理、部分液烃进入排污管线排放等问题。通过提高醇烃分离温度、改进乙二醇再生工艺、改进凝析油换热流程、回收富气增压单元排出的液烃等措施,改进现有工艺流程,能够有效解决装置存在的问题。同时,每年使凝析油稳定装置节约燃料气10.9×104 m3,处理装置天然气产量增加13.2×104 m3,凝析油产量增加145.2t。