Application of Acoustic Wave Propagation Analysis Methods for Monitoring a Miscible Mixing Zone in Porous Media

Abstract

The Biot's acoustics theory, which describes acoustic wave propagation in a porous medium, and computer simulation techniques were utilized to model the behavior of acoustic waves entering and leaving a mixing zone in a miscible displacement in porous media. The results indicate that the angles of waves produced by a mixing zone are equal to angles of waves produced by an abrupt fluid-fluid interface. Therefore, acoustic methods and a relationship between the incident, reflection, and transmission angles can be used to determine the location and thickness of the mixing zone during a miscible displacement process in porous media.     

突变论在CO2混相驱油藏综合评价中的应用

应用突变理论和模糊数学相结合的方法产生突变模糊隶属度函数, 并由此建立CO2 混相驱油藏综合评价模型。该模型首先建立CO2 混相驱油藏指标体系结构, 并对油藏参数进行归一化处理; 然后应用突变模糊隶属度函数法, 对CO2 混相驱油藏进行综合评价和筛选。该模型避免了模糊评价、因子分析及层次分析等方法的弱点, 减少了主观性又不失科学性, 对注CO2 混相驱油藏的筛选具有指导意义。     

低渗油藏CO_2驱油混相条件的探讨

CO2与地层油能否达到混相状态对CO2驱油技术的应用效果有重要影响,界面张力法和细管实验法测量的最小混相压力(MMP)存在较大差异。岩心孔隙结构对原油相对体积及CO2密度的影响实验均说明,多孔介质的孔隙特征对流体物性参数产生较大影响,用细管实验MMP值作为油藏条件下CO2-原油体系MMP值的做法也需要理论完善。对影响CO2驱油混相条件的主要因素进行分析,认为岩石孔隙特征、地层压力以及注入流量对多孔介质中CO2-原油体系MMP有明显影响。渗透率下降,测量的MMP值也不同程度地降低;相对而言,平均地层压力较低的油藏,测量的MMP值也较低;对注入流量的研究认为优化流量可获得较低的MMP值。综合分析以上3个因素,初步建立计算多孔介质中CO2-原油体系MMP的方程。该研究将压力分布曲线进一步细化,补充了对不同压力间流体状态的描述。图7表1参11     

X区块低渗油藏注气可行性研究

为研究X区块低渗油藏注气混相驱油的可行性,通过室内实验探讨了原油相态特征和注入气与地层流体的相态特征,开展细管实验测试了注入气与地层流体的最小混相压力,为X区块低渗油藏注CO2和注伴生气可行性提供基础。实验主要得到以下结论:该区块原始地层压力为31.1 MPa,饱和压力为11.03 MPa;注CO2在保压、降黏膨胀和抽提方面的效果好于注伴生气;两种气体注入与地层流体不能实现一次接触混相驱,可以实现多级接触混相,压力分别为27.85 MPa和29.2 MPa。细管实验的驱替效率在94.2%,确定了CO2与原油的最小混相压力为23.56 MPa,由此可见X区块油藏适合注CO2混相驱油,为目标区块后续注CO2驱油提供了理论依据。     

Investigation of Low Frequency Elastic Wave Application for Fluid Flow Percolation Enhancement in Fractured Porous Media

In recent years, some numerical models have been proposed to investigate the effects of the elastic wave such as ultrasonic on fluid flow behavior in porous media. Nevertheless, none of these models are applicable to the fractured reservoirs, especially when the fluid is a Bingham plastic. In this work, the model proposed by P. P. Iassonov and I. A. Beresnev (2003) Iassonov, P. P. and Beresnev, I. A. 2003. A model for enhanced fluid percolation in porous media by application of low-frequency elastic waves. J. Geophys. Res., 108: 2138–2146. [Crossref], [Web of Science ®] , [Google Scholar] for flow under exposure of elastic wave in nonfractured porous media is considered and used for development of a new model of steady state flow of a Bingham plastic fluid in fractured reservoirs. The Kazemi's “block and fracture” model assuming negligible vertical permeability in blocks is considered for modeling. In addition, two-phase flow behavior under elastic wave in fractured system is investigated. The results showed that, at higher pressure gradients, vibration amplitude cannot highly influence the fluid percolation, in contrast at lower pressure gradients, the fluid flow through the fractured porous media can considerably be improved by increasing vibration amplitude. Also, it has been found that in two-phase flow systems, wave can increase the produced oil-water ratio in the fractured media. The results of this study can be applied to the fractured reservoir simulations and can be a path breaking to the future studies on the prediction of flow enhancement under elastic wave in the fractured reservoirs.     

多孔介质中凝析气相变实验的新方法

由于凝析气藏存在着复 杂的地下烃体系,凝析油气体系与储集层多孔介质间的相互作用,使得凝析气在多孔介质中相态变化规律十分复杂。而现有多孔介质相变实验方法中,压力、温度偏低,不能反映储集层中凝析气的相变特点。针对这一-问题,以凝析气相变理论为基础,利用气相色谱分析技术,创建了一种能真实反应凝析气在多孔介质中相变的实验新方法,在渗透率为0.011 μm2的介质与PVT简中的凝析气相变实验结果表明,低渗透介质对凝析气相态特征具有较大的影响。与目前相变实验方法相比,该方法的测试结果可靠性高、精度高。     

冰点以下多孔介质中CO2水合物生成特性的实验研究

多孔介质对CO2水合物的生成过程具有明显的影响。为了研究冰点以下多孔介质中CO2水合物的生成特性,利用1.8L的高压水合反应釜研究了粒径分别为380 μm、500 μm和700 μm的多孔介质中CO2水合物的生成过程。结果表明：多孔介质对冰点以下CO2水合物的生成过程产生重要的影响。与粒径分别为500 μm和700 μm的多孔介质体系相比,粒径为380 μm的多孔介质中CO2水合物的平均生成速率和储气量分别达到了0.01614 mol/h和65.094 L/L。研究结果还表明,当多孔介质粒径在380 μm到700 μm之间时,多孔介质粒径越小,多孔介质中水合物生成过程的平均生成速率和储气量就越大。     

彩9井区西山窑组特高含水油藏CO2混相驱先导试验

目前彩南油田彩9井区西山窑组已进入高含水低产低能阶段,开井率仅为23.0%,即将面临废弃停产。为了提高该井区特高含水油藏产能,降低含水率,利用类比法、油藏工程及数值模拟方法,对彩9井区西山窑组油藏开展CO₂混相驱可行性论证及油藏工程设计,并进行先导试验。结果表明:先导试验区应选择小井距反七点井网的C2576井组,注入层位选择剩余油富集的J₂x₁^2-2小层,合理注入量为0.3倍孔隙体积(地面CO₂注入量为10 500 t),注气速度为30～40 t/d,注采比为1.1~1.2。现场试验证实,该井组累计注入4 529.7 t CO₂后,累计增油达到1 269 t,CO₂换油率达到0.27 t/t,取得了较好的增产效果。该研究可为彩南油田CO₂混相驱扩大试验和全面调整开发提供技术支撑。     

低渗油藏CO2混相驱启动压力梯度实验研究

低渗透油藏开发过程中存在启动压力梯度,CO₂混相驱过程复杂,需要进行深入研究。将CO₂混相驱过程分为原始油相带、注气前缘带、混相油带和注气后缘带,主要采取短岩心驱替实验测定启动压力梯度。研究表明,低渗透岩心的压力梯度与流量关系图都呈凹型分布,存在非线性流动和线性流动。启动压力梯度的主要影响因素有流体粘度、有效渗透率、流体密度和气油比等。启动压力梯度与岩心渗透率成幂函数变化,指数为-0.482。     

两种新型驱油聚合物在多孔介质中的黏弹性

以HPAM ART525和MO-4000为对比，对疏水缔合聚合物HAP3和抗盐梳形聚合物CP4污水溶液的黏弹性进行了实验研究。实测参数为：HAP3、CP4与HPAM的表观黏度比Rη和储能模量比RG，HAP3、CP4的弹性黏度ηe（达西黏度与表观黏度之差）。讨论了ηe的测定原理。CP4的Rη和RG′小，溶液浓度Cp增大时增幅小，30℃、70℃的Rη～Cp曲线几乎重叠，CP4耐温性好。随Cp增大（在cac以上），HAP3的Rη大幅度上升而RG，大幅度下降，70℃的Rη～Cp曲线较30℃曲线大幅下移，HAP3黏度对温度敏感。1000mg／L聚合物溶液流经1．0μm^2岩心测得的ηe，ART525最小，CP4次之，HAP3最大；随γ增大，前二种聚合物ηe增大而HAP3的ηe却减小且随渗透率增大而明显减小，反映疏水缔合结构的易破坏性。认为HAP溶液通过多孔介质流动的压力降，除黏性和弹性分量外，还包含疏水缔合分量．后者应大于前二者之和，由此推断，HAP体系注入时起压快，注入压力高，易进入低渗区，造成的封堵易被破坏。将0．3PV浓度1000mg／L的聚合物溶液注入1．0／μm^2的岩心，ART525、HAP3、CP4提高采收率增幅分别为7．62％、11．28％、12．10％。用HAP溶液中形成类似“项链”结构的疏水缔合聚集体解释HAP3的黏弹性。图6参10。     

A Computational Scheme for Fluid Flow and Heat Transfer Analysis in Porous Media for Recovery of Oil and Gas

A finite-element scheme has been formulated, which is capable of solving transient analysis of both conductive and convective heat transfers due to fluid flow in porous media. The model also includes the latent heat effect to consider the phase change aspect of a frozen medium. To test the validity of the model, it was applied to six cases for which analytical solutions are available. The test cases cover (i) single-phase fluid flow through porous media, (ii) radial conduction with and without phase change, (iii) conductive and convective heat transfer in an aquifer, and (iv) two-phase immiscible flow in porous media. In all these cases, good agreement with analytical solutions are observed validating the computational scheme. This computational scheme should be useful in solving frozen ground problems, thermal stimulation technique for natural gas recovery from hydrates, and single-phase and two-phase convective heat transfer problems in enhanced oil recovery scheme in petroleum engineering.     

油气地下渗流发展评述

回顾地下渗流理论的诞生及其发展历程,对比地下渗流力学和粘性流体力学,指出影响油气渗流理论发展的主要因素,总结地下渗流力学的发展规律和发展路线。     

Prediction of time required for onset of convection in a porous medium saturated with oil and a layer of gas underlying the oil

The onset of convection for a viscous oil confined in a cylindrical porous medium and contacted with a gas to diffuse into it from below is investigated experimentally and theoretically. Two experiments are carried out, both at a specific reservoir temperature and pressure, starting with the medium saturated with the oil and bringing the gas into contact with it from the base. In the first experiment, the setup is arranged horizontally in order to determine the diffusion coefficient of gas in the absence of convection. In the second experiment, the setup is vertical to investigate the onset of convection. The pressure is maintained constant during both experiments and the volume of gas dissolving in oil is measured vs. time. The dissolved gas data obtained from the vertical experiment show a sharp slope change at the onset of convection. The observed onset time is in excellent agreement with the value obtained by means of an instability theory developed in this study.     

特低渗透油藏CO2驱油多相渗流理论模型研究及应用

根据一系列实验成果,对特低渗透油藏CO₂驱油渗流数学描述进行了理论研究,建立了特低渗透油藏CO₂驱油渗流数学模型。该模型能反映特低渗透储层CO₂混相和非混相驱油过程中油和CO₂的混相作用以及水、油、溶剂(CO₂)的相互作用与传输、质量的相互转换,包括对流扩散、质量转换和气、液间的转换,并能反映各相流体的非达西渗流、相对渗透率及有效黏度等特性。运用该模型在扶杨油层进行了注CO₂开发试验,取得了较好效果。     

CO2驱水气交替注采参数优化——以安塞油田王窑区块长6油藏为例

针对安塞油田王窑区块长6特低渗透油藏现阶段注水开发矛盾突出的问题,为进一步提高油藏采收率,评价CO2驱油效果,应用油藏数值模拟方法,优化了CO2驱水气交替注采参数。利用Eclipse的PVTi模块模拟了注气膨胀实验,研究了注CO2对原油相态的影响;采用正交试验设计方法,以提高采出程度和换油率为目标,对CO2驱水气交替过程中的气水比、注气速度、关井气油比和段塞注气量4个参数进行了优化研究,并用直观分析方法对试验结果进行分析。结果表明,当原油中溶解的CO2物质的量分数达到60%时,原油粘度降低幅度达80.51%,原油体积膨胀1.44倍;优化得到的最优气水比为1∶1,注气速度为13 000 m3/d,关井气油比为1 000 m3/m3,段塞注气量为0.005倍孔隙体积。     

二次采油与三次采油结合技术在埕东油田东区西北部Ng32层的应用

针对埕东油田东区西北部Ng32层的条件应用了二次采油和三次采油结合技术.在室内研究了各种工作液的优化配方,编写了实施方案并现场实施,取得了明显的效果,在试验期间,试验区累积增产原油1.775 0×104t,投入产出比达到1∶3.21,水驱开发效果改善.该技术在埕东特高含水油藏成功应用,为同类油藏提高采收率技术的推广提供了借鉴.