超稠油注气次生泡沫油生成机理及渗流特征

为探索泡沫油在超稠油油藏中的形成机理、渗流特征及驱油效果，采用准噶尔盆地西北缘乌夏断裂带侏罗系齐古组原油及油藏参数，进行注气形成泡沫油介质筛选及原油泡点压力测定实验，并开展注气微观可视化和填砂管驱油实验，深入解析注气形成泡沫油过程中的渗流特征，评价了注气泡沫油驱油效果。研究结果表明：①准噶尔盆地西北缘乌夏断裂带侏罗系齐古组原油泡点压力为9.7 MPa，拟泡点压力随着注气量的增加而增加，随温度的上升而上升，50℃的拟泡点压力随着CO₂注入量的增加而增大，压力上升速度较缓，储层具有较好的注气特性。②研究区的泡沫油渗流可分为5个阶段：无气泡阶段、气泡析出阶段、气泡扩张阶段、气泡聚并阶段和气泡消亡阶段。③研究区蒸汽+CO₂方式驱油开采过程较纯蒸汽填砂管驱的采收率可提升13.3%，开采过程中随着压力的释放，气泡数目逐渐增多，产油量逐步缓慢上升；当压力降至泡点压力后，气泡数目趋于平稳，形成较稳定的泡沫油，产油量大幅提升，为主力产油期；当压力释放至拟泡点压力后，气泡数目迅速下降，泡沫油逐渐消亡，产油量缓慢下降。     

稠油溶解气驱泡沫油特征实验研究

压力衰竭速度是影响稠油溶解气驱泡沫油生产的一个关键因素。为定量描述压力衰竭速度对泡沫油现象的影响,实验选取了4组不同压力衰竭速度进行实验。研究不同压力衰竭速度下稠油衰竭开采中的采收率、产油量、生产气油比以及实验压力的变化。通过实验发现稠油溶解气驱过程中出现明显的泡沫油阶段,且压力衰竭速度越大,泡沫油拟泡点压力越小,泡沫油阶段越长。随着压力衰竭速度增加,采收率增加,生产气油比减小,油藏压力递减变慢。     

关于泡沫油黏度的若干问题

泡沫油现象被认为是加拿大和委内瑞拉一些稠油油藏在开采中出现异常高产和较高采收率的主要原因,对于泡沫油黏度的研究目前学术界尚无一致结论。针对泡沫油的黏度,主要从泡沫油黏度与异常高产之间的关系、泡沫油黏度模型以及泡沫油黏度的影响因素等3 个方面进行研究。压力衰竭速率、静置时间、测量装置、分散气体积分数、压力和流量、膨胀率和表面活性剂、分散气泡大小和剪切速率以及常规测试和非常规测试等对于泡沫油的黏度均有影响,目前学术界对于稠油泡沫油黏度的争议可能和这些影响因素有关,泡沫油黏度的测量问题可能是引起对泡沫油黏度争议的一个主要原因。泡沫油黏度的研究有利于澄清泡沫油的渗流机理,泡沫油的渗流机理对于稠油油藏数值模拟,尤其是稠油油藏注气开发过程中的优化设计均具有重要意义。     

CO2驱油实验研究

为研究CO2驱油机理，并为制定开发方案提供基础数据，严格按照规定取样，按拟合泡点压力的配样原则配样，通过室内高压相态实验、CO2减黏效果评价实验和细管驱油实验，测定CO2-原油多组分体系的相行为，评价压力-体积关系和CO2减黏效果，认识CO2驱的机理和规律。细管驱油实验结果表明，通过采收率随驱替压力曲线的变化规律来确定混相条件最为准确，本次实验油样(胜利油田油样)最小混相压力为26MPa。对比总结国内外大量相关资料，认为对于特定油田的不同油样，相对饱和压力、归一化体积系数、膨胀系数、CO2溶解度和相对黏度等参数与CO2注入浓度的关系曲线是一定的，可以用回归的曲线进行有关预测。图4表1参13     

委内瑞拉MPE-3区块超重油冷采过程中泡沫油开采机理

针对超重油沥青质含量高、原油重度高等特点,研究了水平井溶解气驱冷采的开采机理,包括冷采过程中泡沫油的形成机理、非常规PVT特性与驱替特征。实验结果表明,当油藏压力低于泡点压力时,原油中形成许多微小气泡,这些微小气泡能够长时间滞留在油相中,使得这种原油表现出与常规溶解气驱许多不同的特征;泡沫油的作用与油藏衰竭速度、油层压力下降水平及围压等因素有关。使用水平井冷采技术能够获得较高原油产量和采收率。     

稠油冷采泡沫油溶解气驱油藏开发动态数值模拟

稠油注蒸汽等热采开发方式面临着油层出砂、气窜和采油成本高等问题,而稠油冷采过程中形成的泡沫油,则使稠油油藏具有采油速度快、采收率高和生产气油比低等特点。在论述STARS模拟泡沫油机理及模型局限性的基础上,建立了稠油冷采泡沫油溶解气驱油藏模型。模拟结果表明,与常规溶解气驱油藏相比,泡沫油溶解气驱油藏具有生产气油比上升缓慢、累积产油量高等特点;在油相中气泡形成频率一致的情况下,气泡破裂速度越快,生产气油比越大,产油量越低;原油粘度越高,地层渗透率越低,开发效果越好,稳产时间越长。     

泡沫油油藏冷采后期注气吞吐开采实验

以脱气原油与活油为参照,利用非常规PVT实验方法开展了泡沫油溶气特性实验,揭示了泡沫油溶气特性,明确了天然气在泡沫油中的溶解能力以及地层压力对其溶解的影响规律,并通过岩心驱替实验研究了天然气吞吐提高采收率的可行性以及注气时机、注气轮次对泡沫油天然气吞吐开发效果的影响。泡沫油溶气特性实验表明,天然气溶解过程分为快速溶解、波动下降和稳定3个阶段。注气前期天然气溶解速度较大,累积溶气量增加迅速;天然气溶解能力随深度的增加逐渐减小,垂向上可形成一定的混相区域;增大地层压力有利于增加天然气溶解速度和累积溶气量;各压力下泡沫油溶气能力小于活油及脱气原油,但同一深度处其含气量最多,黏度最小。泡沫油天然气吞吐实验表明,天然气吞吐比冷采开发提高采收率7.8%,注气时机应在泡点压力与拟泡点压力之间,且焖井时间不宜过长,并应最大限度地提高地层压力。     

孔隙流体地震特性的计算

孔隙流体对岩石地震特性的影响为采油地震监测的物理基础,搞清地层条件下孔隙流体地震特性的变化规律对提高地震监测的精度具有重要的意义。在收集、分析前人研究结果的基础上,本文导出了当地层压力从高于饱和压力降低到低于饱和压力时,从原油中所脱出的游离气的体积百分含量计算式,并计算和分析了不同温度压力下原油、油气混合物以及地层水的地震特性,给出了一些新的认识。     

流压低于饱和压力油藏油井流入动态方程理论研究

水驱油藏油井生产过程中，当井底流动压力低于饱和压力时，天然气会从原油中析出，油井产量将受到很大影响，主要因素包括油藏的渗透率和油的相对渗透率的改变，以及原油地下粘度和地下体积系数的变化。通过原油流动系数与流动压力之间的二项式关系，建立了油藏在饱和和未饱和情形下的油井流入动态方程，并建立了新的油井流入动态方程的通式。     

泡沫油PVT性质实验

泡沫油在不同的压力条件下存在气泡不断产生与破灭的过程,因此,其压力-体积-温度（PVT）测试方法与常规原油的PVT测试方法不同,属于非稳态测试。在不同的压力衰竭速度条件下,测试得到的泡沫油PVT物性差别较大,为了准确表征泡沫油在不同操作参数条件下的PVT性质、准确表征在实际油藏生产过程中的PVT特征,需要对泡沫油的PVT关键参数进行实验分析。笔者开展了委内瑞拉超重泡沫油PVT特性系列实验,揭示了泡沫油开采“拟泡点”特性,总结出了一套泡沫油PVT参数的非常规测试方法,实现了泡沫油在非稳态条件下的PVT物性参数的精确测量,并描述了其影响因素。     

泡沫油油藏数值模拟研究

泡沫油是一种含有大量分散性小气泡的稠油,衰竭开发泡沫油具有产量高、气油比低、地层压力下降缓慢和采收率高等特点。提出了利用数值模拟技术模拟泡沫油的关键方法,并建立了泡沫油数值模型。通过与常规溶解气驱数值模拟结果的比较以及与室内实验结果的拟合,从定性和定量2个方面证明了所建立模型的可靠性,并利用该模型进一步研究了泡沫油的驱油机理。泡沫油油藏开发过程中产生的分散气,一方面增加了原油的流动能力,当平均地层压力降低到泡点压力以下后仍然能够以初始产量生产1a以上;另一方面增加了体系的膨胀能,减缓了地层压力下降速度,地层压力从6.0MPa降低到5.1MPa的时间接近于从10.0MPa降低到6.0MPa的时间。     

地层原油组成差异对高压物性参数的影响

地层油高压物性参数主要受温度、压力等因素的影响,而地层油自身的组成也对其有着重要影响。对S48井、G942井和F154井的地层油进行了一系列的高压物性实验研究。结果表明：相同气油比,原油含蜡量越高,地层油泡点压力越高,体积系数越大;当压力高于泡点压力时,原油含蜡量越低,溶解气量越多,地层油体积系数和密度受压力的影响越显著;含蜡量越高,体积系数和密度受压力的影响越小。含蜡量高的地层油溶解天然气后的降黏效果明显好于含蜡量低的地层油。     

Modeling of Compositional Grading and Plus Fraction Properties Changes with Depth in Petroleum Reservoirs

Abstract

In this work we use a nonisothermal model to predict compositional variation in a petroleum fluid column; at the same time, a nonisothermal model will be used to predict change of plus fraction molecular weight (and as a result all other its properties) with depth. We will investigate the effect of several factors as mode of characterization, binary interaction coefficients, volume shifts, and near-criticality on the change of physical properties, including bubble point pressure, solution gas–oil ratio, and oil formation volume factor. A computer program will be used to predict the location of the gas–oil contact and we will show how neglecting compositional grading (CG) can lead to serious errors in the calculated initial oil in place.     

凝析气藏注CO2提高采收率机理物理模拟

为深入研究凝析气藏注CO₂提高采收率机理,应用室内实验手段开展了CO₂对凝析气藏流体物性的影响实验。结果表明：注CO₂降低了凝析气的露点压力,降低幅度随注入量增加越来越大,注入0.4倍时的下降幅度达到了15.42%;CO₂注入倍数较小时,对凝析油以溶解、降黏、膨胀作用为主,凝析油膨胀体积的增量是萃取产出凝析油体积的9倍以上,溶解气油比和相对密度随注入倍数增加而增加;CO₂注入倍数较高时以萃取作用为主,生产气油比迅速增加,凝析油相对密度越来越大,采出程度达83%以上。在实际地层条件下,注CO₂开发,在远井区主要发挥降低露点压力的作用,并将露点线向产出井推移;在过渡带初期以溶解膨胀为主,压缩了该区带范围,后期主要为萃取作用,将液动线向产出井推进,缩小了近井带范围;在近井带初期主要为驱替作用形成气流通道,中后期主要为溶解、膨胀、携带和萃取作用。综合以上,凝析气藏注CO₂开发压缩了气液两相区,可大幅提高凝析气藏采收率。研究成果为凝析气藏的注CO₂开发和技术推广提供了重要的技术支撑。     

Experimental investigation on rheological property of foamy oil in Venezuela

Some heavy oil reservoirs present foamy oil flow behavior under primary production, and the foamy oil viscosity and rheological property are important factors that influence the efficiency of the process. The variation of the foamy oil viscosity during the depletion process is complicated due to the generation and migration of dispersed gas bubbles within the oil phase, and still remains as a controversial topic.

?This study aims to investigate this issue by measuring the foamy oil viscosity at different pressure, temperature and flow rate with a capillary viscometer system equipped with a specially designed foamy oil generator to guarantee the generation and stable flow of gas-in-oil dispersions. Meanwhile, the dead oil and live oil viscosities were also measured for comparison.

?Based on the results from all the tests the following conclusions can be drawn. Below the bubble point pressure, the dispersed gas-bubble volume fraction and foamy oil viscosity increase with pressure decline; the viscosity of foamy oil is higher than that of live oil, and the gap between them widens with pressure decline. Moreover, foamy oil behaves as shear-thinning power-law fluid, and the shear-thinning effect becomes stronger with the decrease of pressure. The foamy oil rheology is also affected by temperature, and the shear-thinning effect becomes milder with the increase of temperature. Based on the experimental data, a formula was established for estimating foamy oil apparent viscosity within porous media, which took flow rate, shear-thinning flow parameters, permeability, porosity and other factors into consideration.     

A Correlations Approach for Prediction of PVT Properties of Reservoir Oils

Reservoir oil properties are usually measured at reservoir temperature and are estimated at other temperature using empirical correlations. Fluid properties correlations cannot be used globally because of different characteristics of fluids in each area. Here, based on Iranian oil PVT data, new correlations have been developed to predict saturation pressure and oil formation volume factor at bubble point pressure. Validity and accuracy of these correlations were confirmed by comparing results of these correlations with experimental data. Checking the results shows that results for Iranian oil properties in this work are in good agreement with experimental data respect to other correlations.     

Prediction of Bubble Point Pressure From Composition of Black Oils Using Artificial Neural Network

In the present study, an artificial neural network (ANN) constitutive model was developed to predict bubble point pressure for the case of Canadian data. The accuracy of prediction of bubble point pressure was compared using two sets of inputs to the model. One was based on composition of the oil and the other based on easily available parameters such as solution gas-oil ratio, reservoir temperature, oil gravity, and gas relative density. The performance of bubble point pressure prediction with ANN was compared with that of equation of state (EOS) and other available empirical correlations. It was found that ANN models can produce a more accurate prediction of bubble point pressure than the existing empirical correlations and EOS calculations.     

高渗透砂岩油藏注水时机实验研究

设计了耐高温、高压的模型夹持器,并将该模型夹持器作为外接管线与模型的接口。在普通微观实验模型的基础上,研制了高温、高压微观实验系统,分析了降压过程中气泡动态变化现象、油气分布情况与油气运动规律、不同压力下水驱含气原油的流动现象以及自由气体对油水流动的影响。建立了高温高压宏观实验系统,研究了降压开采过程中油、气产量情况以及不同油藏压力下水驱油的开发效果。实验结果表明:在泡点压力附近,气泡数量少且体积小,析出的自由气体有利于油水流动,水驱波及面积大。在此之前注水,保持油层压力在泡点压力的87%以上,能够实现油田注入水少,综合含水率低,采出程度高。现场生产表明,研究成果是非常有效的。     

具有拐点的油井IPR方程建立及应用

油藏开采过程中,当流动压力低于饱和压力时,溶解于原油中的天然气析出,水驱油藏油井出现三相渗流,部分油井受其影响,产量出现随着流动压力降低而下降的现象,表现为IPR曲线发生倒转。利用新建立的油井流入动态关系方程,能够合理地拟合和描述这种倒转现象,并可以判断油井IPR曲线是否出现倒转现象或具有拐点,计算油井的最低合理流动压力。新建立的IPR方程通式囊括了大部分经典的IPR方程,包括经典的Vogel方程和Fetkovich方程及其推广式,具有较强的实用性。     

Visual Experimental Study of the Factors Affecting the Stability of Foamy Oil Flow

Abstract

Some of the heavy oil reservoirs in Canada, Venezuela, and China under solution gas drive illustrate important features: low gas–oil ratio, high production rates, and very high ultimate oil recovery. It is generally believed that the foamy oil flow is one of the important mechanisms contributing to these unusual performances. A series of two-dimensional etched glass micromodel experiments was carried out to gain an insight into the processes involved in foamy oil flow. In these experiments, the bubble nucleation, migration, coalescence, breakup, and ultimate generation of a continuous gas phase can be observed continuously. On the basis of the experimental analysis, there are two bubble-point pressures in the foamy oil: One is the true bubble-point pressure, and the other is the pseudo-bubble-point pressure. The greater the difference between these two bubble-point pressures, the more stable the foamy oil flow is and the greater the contribution to oil recovery from the foamy oil drive mechanism is. The visualization experimental results show that there are many factors affecting the stability of the foamy oil, including pressure depletion rate, crude oil viscosity, temperature, dissolved gas–oil ratio, etc.