采用脉冲注烃方式提高低渗透裂缝性灰岩油藏采收率实验研究

低渗透裂缝油藏直接注气容易产生气窜，采收率不高，使用实际岩心进行人工造缝，在长岩心中分别进行衰竭式开发、直接注烃气驱实验、注水实验和脉冲注气实验。细管试验表明，即使在破裂压力下注烃气也达不到混相，衰竭式开发可获得16．81％的采收率；直接注烃气比衰竭式提高采收率20．17％；脉冲注气比衰竭式提高采收率35．04％，脉冲注气驱油效果比直接驱油好得多，是值得选用的开发方式。     

注空气提高低渗透油藏采收率实验及低温氧化反应特征

空气驱是一种有效提高低渗透油藏采收率的方法。针对目前空气驱油生产特征不明确的问题,采用长岩心驱替实验,研究不同注入压力下的空气驱油效果和低温氧化反应特征。研究发现,空气驱油存在明显的“气窜拐点”。气窜发生前,采出程度随注气量的增加迅速增加,一旦发生气窜,采出程度的增加明显放缓。注气压力越高,“气窜拐点”出现越早,提高采收率效果越差。原油组分分析结果表明：在油藏温度下,随着注气量增加,产出原油中的轻质组分减少,重质组分增加,驱替过程中发生了低温氧化反应;注入压力越高,低温氧化反应越充分,采收率越高;对高含水油藏进行空气驱,低温氧化反应十分微弱,无法形成烟道气驱;水驱达到经济极限后转空气驱,采收率可提高近10百分点。研究成果为低渗透油藏开发后期注空气提高采收率提供了理论依据。     

KKY-X_5~2挥发性油藏注气驱机理及实验效果研究

KKY-X52挥发性油藏的储层物性为低孔低渗,平均孔隙度为12.08%,平均渗透率为13.52×10-3μm2。经过十多年的开采,目前该油藏存在地层压力低,原油脱气明显,采出程度低,剩余储量大等问题。为了研究该油藏注气、注水驱可行性,在室内进行了长岩心驱替实验,得到了不同方案下(原始地层压力下注烃类气、CO2驱,目前地层压力下注水、注烃类气、注CO2驱,压力恢复至20 MPa下注烃类气、CO2驱)提高原油采收率的效果。此外,利用细管实验确定了烃类气和CO2驱替的最小混相压力,这些关键参数对研究都有很大帮助。长岩心驱替实验研究结果表明:从目前地层压力11.4 MPa注CO2提压到20 MPa焖井12小时后,采收率提高了19.46%,注烃类气提高了10.69%。研究结果表明注CO2和注烃类气提压开发可以较大幅度地提高采收率,对现场提高采收率实施方案有一定的指导作用。     

低渗挥发性油藏CO2驱注入时机室内实验研究

低渗挥发性油藏流体性质特殊,弹性开采很容易变为衰竭开采,注气保压开采是低渗挥发性油藏的主要开采手段。针对低渗挥发性油藏CO_2驱开发技术难点,通过长岩心实验,研究了低渗挥发性油藏CO_2驱的注入时机。实验结果表明,地层压力衰竭至34.10 MPa时注CO_2后采出程度(96.44%)与在原始地层压力下注CO_2后采出程度(96.24%)相当;地层压力衰竭至28.58 MPa以下注CO_2后采出程度明显降低。确定了地层压力衰竭至34.10 MPa时为CO_2驱注入时机,为经济有效地实施CO_2驱提高低渗挥发性油藏原油采收率提供依据。     

特低渗透油藏CO_2驱油室内实验与矿场应用

延长石油特低渗透油藏储量丰富,注水开发中存在易水敏、注水困难等问题。CO_2驱能有效补充地层能量,改善地层原油性质,进而提高油藏采收率。利用CO_2-地层原油接触实验、岩心渗流和驱替室内实验,描述CO_2-地层原油两相渗流特征,分析CO_2驱油机理和驱油特征,并在靖边特低渗油藏进行了矿场实验。研究表明,特低渗储层CO_2-原油油气两相共渗范围大,CO_2具有降低原油黏度,使原油体积膨胀等作用,非混相驱和混相驱均可较好地开发特低渗透油藏,其中生产井见气前与低气液比阶段是油藏主要生产期。CO_2驱矿场试验表明,特低渗透油藏注气能力是注水能力的2倍,注气能快速有效补充地层能量,增加油田产量,目前试验区生产整体呈日产液、日产油上升态势。     

特低渗透油藏注氮气流体相态行为特征

特低渗透油藏储层孔道微细、渗透率低,油水流动时渗流阻力大,油藏注水开发存在注不进、采不出的问题.为了探索特低渗透油藏注气可行性,开展了注氮气室内实验.根据大庆油田特低渗目标油藏地层原油注N2气膨胀PVT试验、多次接触PVT实验、细管注氮气驱替最小混相压力测定实验结果,论述了特低渗透油藏注氮气气驱油藏流体相态行为特征.随着注入氮气量的增加,地层原油的膨胀能力增加,饱和压力升高.地层原油注氮气前接触地层原油气油比随接触次数的增加先增大再减小,再逐渐稳定,但变化幅度不大,地层原油密度随接触次数的增加基本保持不变.细管实验表明,氮气容易突破,气体突破后,采收率增幅变缓,综合采收率不高,表现为非混相驱特征.     

水驱后特低渗透油藏氮气驱驱油特性分析

特低渗透油藏水驱采收率低,注入压力高,而氮气在特低渗油藏具有良好的注入性。本文在特低渗透岩心水驱后分别进行了常规的注氮气、水驱后水气交替、水驱后脉冲注氮气驱替实验。实验结果表明:特低渗储层微观非均质性导致气体在大孔道易形成窜流,水驱后常规注氮气提高采收率的效果有限。水气交替通过多轮次的注入使油藏中不同相态流体的分散程度提高,在优势流动通道中形成毛管阻力,促使后续注入气体进入局部致密区,可有效提高采收率16.37%;脉冲注气通过周期性注气方式,在局部高渗区和局部低渗区间形成压力扰动与交互渗流,使流体在地层中不断地重新分布,从而启动油层低渗区原油,提高采收率15.94%。此外,脉冲注气的注气压力比较低,与水气交替开采方式比较注入性提高。图6表1参12     

低渗透油藏二氧化碳驱油防窜实验研究

低渗透油藏注 CO2驱油技术优势明显,一是注气阻力远小于注水;二是 CO2可有效提高驱油效率,但也存在一定的局限性,其中气窜是影响 CO2驱采收率的重要因素。针对低渗油藏 CO2驱油气窜问题,提出了将石灰水作为防窜剂注入储层,利用石灰水与 CO2的化学反应实现 CO2气体在储层纵向剖面的均匀推进,解决气窜问题。运用核磁共振技术和岩心驱替模拟实验,研究了 CO2气窜的主要机理,对比评价了 CO2驱油过程中石灰水的防窜效果。结果表明：石灰水可以有效防止或延缓气窜,改善 CO2驱油效果,对于低渗油藏注 CO2驱油高效开发具有重要指导意义。     

低渗透裂缝性油藏两级封窜扩大波及体积技术

为降低低渗透油藏CO_2驱油过程中窜逸现象的发生,选取低渗二维饼状岩心,用压裂设备逐渐加压对岩心造裂缝,采用反五点法模拟超前注水后低渗透油藏的开发,进行改性淀粉凝胶封堵裂缝后水驱、乙二胺封堵气窜通道后CO_2驱两级封窜实验。结果表明,改性淀粉凝胶可有效封堵地层中的裂缝,水驱及改性淀粉凝胶一级封窜裂缝后的采收率为23.4%;一次CO_2驱期间出现气窜,但气窜阶段仍是提高采收率的重要阶段,一次CO_2驱的采收率为21.3%;乙二胺可有效封堵低渗层气窜通道,扩大CO_2波及体积,乙二胺二级封窜后CO_2驱采收率为15.0%。在反五点法岩心物理模拟实验中,水驱及水驱后改性淀粉凝胶一级封窜地层中裂缝+CO_2非混相驱后乙二胺二级封窜气窜通道的采收率为59.6%,增油效果明显。图5表4参26     

裂缝性低渗油藏注气提高采收率实验研究

HH油田为典型的低孔特低渗油藏,部分地层伴有裂缝发育,现面临衰竭式开采后注水开采压力高的难题.通过基质单管岩心驱替实验,探究目标地层进行注气开发的可能性,明确何种注入气体及驱替方式具有较好提高采收率效果.通过基质+裂缝双管并联岩心驱替实验,确定目标地层中微裂缝对提高采收率效果影响.结果表明,CO2较减氧空气是更好的注入...     

鄂尔多斯盆地红河油田长8储层致密砂岩油藏注CO2提高采收率

鄂尔多斯盆地红河油田地层压力系数低,天然能量开发递减较快、采收率低,难以实现有效开发。而长8储层裂缝较发育,注水补充能量开发存在油井水窜严重、见效低等问题。为了解决补充能量的问题,进行红河油田长8储层注CO₂提高采收率的可行性实验研究,室内开展了PVT实验、最小混相压力实验和裂缝岩心CO₂驱油实验,并评价了CO₂吞吐的开发效果。实验结果表明：红河油田原油注入CO₂后体积增大,具有较强的膨胀能力。而且随着混合体系压力逐渐增大,原油与CO₂能产生明显的相互扩散传质作用。长细管混相仪法测得红河油田原油与CO₂的混相压力为17.34 MPa,低于红河油田原始地层压力,注CO₂驱油能达到混相条件。通过多轮次CO₂吞吐实验,在弹性开发采收率4.04%的基础上可提高采收率3.14%。综合室内可行性评价实验结果看,红河油田长8储层注CO₂补充能量开发具有可行性。     

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吉拉克凝析气田发育有两套含油气层系,上部为带油环、具正常压力、高凝析油含量的三叠系凝析气藏,下部为异常高压、低凝析油含量的石炭系凝析气藏。根据这两套油气层的特点,提出利用下部石炭系凝析气藏天然气对上部三叠系凝析气藏实施自流注气开发的设想,并围绕这一设想,进行了开采方式论证、室内实验、数值模拟等研究。研究结果认为：井下控制自流注气的开采方式对提高三叠系凝析气藏的凝析油和油环油采收率有显著效果,方案具有实施性。推荐的实施方案是：憋压１年,再自流注气开采２０年。其开发指标与衰竭式开采２０年的开发指标相对比,可提高三叠系凝析气藏凝析油采收率８５％、油环油采收率３２％、天然气采收率３９％。     

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水气交替注入（ＷＡＧ）是两种传统采油方法的综合,是二次采油和三次采油中颇具潜力的一种方法。由于高粘度的水趋向于在高渗层形成屏蔽,而使气体进入油气藏基岩层或低渗层,提高了气体的驱扫效率。通过层状二维剖面模型的模拟研究,证明了在层状凝析气藏中水气交替注入的采收率比循环注气的采收率高,根据全组分模拟器模拟结果可知：水气比、不同的注入采塞、渗透率和残余气饱和度对凝析渍打收率的影响非常明显;崦注入次序、注入     

Feasibility of Gas Drive in Fang-48 Fault Block Oil Reservoir

The Fang-48 fault block oil reservoir is an extremely low permeability reservoir, and it is difficult to produce such a reservoir by waterflooding. Laboratory analysis of reservoir oil shows that the minimum miscibility pressure for CO2 drive in Fang-48 fault block oil reservoir is 29 MPa, lower than the formation fracture pressure of 34 MPa, so the displacement mechanism is miscible drive. The threshold pressure gradient for gas injection is less than that for waterflooding, and the recovery by gas drive is higher than waterflooding. Furthermore, the threshold pressure gradient for carbon dioxide injection is smaller than that for hydrocarbon gas, and the oil recovery by carbon dioxide drive is higher than that by hydrocarbon gas displacement, so carbon dioxide drive is recommended for the development of the Fang-48 fault block oil reservoir.     

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使用中国大港板桥油气田板Ⅱ组废弃凝析气藏的真实岩心和配制的流体，首先在PVT、中进行了CVD试验，然后在长岩心中进行衰竭试验达到8MPa废弃压力，并在保持8MPa下进行了注水速度敏感的实验对比．还开展了注水增加压力到20MPa后再进行恒压注水方式开发试验。研究表明，长岩心中衰竭实验凝析油采收率比PVT筒中CVD测试凝析油采收率高1倍，与实际气田衰竭式开发凝析油采收率相近。在废弃压力下注水进行注采平衡开发凝析油可新增采收率3．39％，天然气新增采收率10．11％，效果较好；在废弃压力下注水速度快，获得的凝析油采收率相对较高；采用注水恢复地层压力到20MPa后再进行注采平衡开发油采收率可新增0．68％，天然气采收率新增5．39％。根据实验，现场采用强注污水开发凝析气藏试验，提高了采收率，同时解决了现场污水处理问题，取得了明显的经济效益和社会效益。     

The Simulation Study of Full Diameter Cores Depletion on Volcanic Condensate Gas Reservoirs

The depletion experiments about practical condensate gas samples were carried out with the three full diameter cores from X volcanic condensate gas reservoir in the laboratory. The depletion behavior of condensate gas in cores was studied under the circumstances of existing bottom water, and the results were compared with that of constant volume depletion in a pressure-volume-temperature (PVT) cell. The experimental results were simulated by the ECLIPSE software afterward. The results indicate that the condensate gas depletion performance is different from that of PVT test regardless of existing bottom water, and there is only a little difference for natural gas recovery in cores whether the bottom water is existing, but bottom water has significant effect on condensate oil recovery; the higher the permeability of cores is, the faster water influx rate is, the earlier water breakthrough in production outlet is; the variation laws of the recovery of gas and condensate oil and gas oil ratio obtained by numerical simulation fit well with the physical simulation results and the simulation effect is satisfactory.     

An Experimental Study on the Applicability of Water-alternating-CO2 Injection in the Secondary and Tertiary Recovery in One Iranian Reservoir

Abstract

The objective of this study was to experimentally investigate the performance of water-alternating gas (WAG) injection in one of Iran's oil reservoirs that encountered a severe pressure drop in recent years. Because one of the most appropriate studies to evaluate the reservoir occurs generally on rock cores taken from the reservoir, core samples drilled out of the reservoir's rock matrix were used for alternating injection of water and gas. In the experiments, the fluid system consisted of reservoir dead oil, live oil, CO₂, and synthetic brine; the porous media were a number of carbonate cores chosen from the oilfield from which the oil samples had been taken. All coreflood experiments were conducted using live (recombined) oil at 1,700 psi and reservoir temperature of 115°F. A total of four displacement experiments were performed in the core, including two experiments on secondary WAG injection and others on the tertiary water and gas invaded zones WAG injections. Prior to each test porosity and permeability of dried cores were calculated then 100% water-saturated cores were oil-flooded to obtain connate water saturation. Therefore, all coreflooding tests started with the samples at irreducible water saturation. Parameters such as oil recovery factor, water cut, and gas-oil ratio and production pressure of the core were recorded for each test. The most similar experimental work with the main reservoir condition, indicated that approximately 64% oil were recovered after 1 pore volume of WAG process at 136,000 ppm brine salinity. Although tests show ultimate recovery of 79% and 55% for secondary and tertiary injection in gas and water invaded zones, respectively, immiscible WAG injection efficiency in the gas and water invaded zones will not be proper. In the similar test to field properties, the average pressure difference about 70 Psig was observed, which shows stable front displacement. These experiments showed that there was significant improvement in the oil recovery for alternating injection of water and CO₂, especially in the secondary recovery process. Water breakthrough time in almost all of the tests shows frontal displacement of injected fluid in cores and produced gas-oil ratio changes a little whenever the injection is miscible and increases rapidly in immiscible processes.     

高含硫碳酸盐岩气藏衰竭实验研究

普光气田属于高含H2S和CO2海相碳酸盐岩气田,具有气藏埋藏深、地层压力高、有边底水存在等特点。边底水会对普光气田的衰竭开发产生怎样的影响,目前尚不清楚。同时,国内外对高含硫碳酸盐岩气藏物理模拟实验研究较少,国内还未见高含硫气藏衰竭实验的报道。为此,结合普光气田现场实际,进行了无水体和1倍水体(1倍水体指水体的体积等于长岩心的烃类孔隙体积)的衰竭实验研究。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(平均渗透率1mD),然后进行造缝(渗透率5~14mD),并将岩心组合成长岩心,最后采用高含硫气体(H2S含量为14.89%)进行了无水体和1倍水体衰竭实验。实验结果表明:无水体衰竭实验中,没有水产出。1倍水体衰竭实验中,一旦有水产出,产水量便迅速增加。1倍水体衰竭的天然气采出程度低于无水体衰竭的采出程度。无水体衰竭时,天然气中硫化氢含量变化不大;而1倍水体衰竭时,天然气中硫化氢含量逐渐增加。该实验结果对高含硫碳酸盐岩气藏的合理开发提供了技术支撑。     

牙哈5凝析气藏开发方式优化

凝析气藏作为一种特殊的油气藏类型,由于特殊的流体相态特征决定了其开发难度要比一般油气藏复杂得多,开发中不仅要考虑天然气的采出程度,而且还要兼顾凝析油的采出程度.牙哈5气藏为富含凝析油气藏,通过组分数值模拟对不同的开采方式进行对比,得出采用衰竭、注水和注气3种开采方式的开发效果.注水和注气是为了保持地层压力,防止凝析油在地层内大量析出,从而提高凝析油的采收率.对比研究表明,注水和注气开采牙哈5凝析气田要优于衰竭式开采.对注水和注气两种开采方式而言,由于牙哈5气田储层自身的特点,在提高凝析油采出程度方面注气开采方式又要优于注水开采方式.预测结果表明,采用大井距注气开发方式对于延缓气窜可以起到一定作用,从而有利于提高注气效率,增加凝析油采出程度.