Viscous fingering and its effect on areal sweep efficiency during waterflooding: an experimental study

Viscous fingering is one of the main challenges that could reduce areal sweep efficiency during waterflooding in oil reservoirs. A series of waterflooding experiments were carried out in a Hele-Shaw cell at ambient temperature during which areal sweep efficiency was estimated and techniques to ease the fingering problem were examined. The onset and propagation of viscous fingers were monitored as a function of both injection rate and injection/production positions. Image processing techniques were utilized to quantitatively investigate the propagation of fingers. The experimental results show that, under specific conditions, increasing the number of finger branches could improve the areal sweep efficiency, whereas growth of a single narrow finger has a negative impact on oil displacement efficiency. According to the obtained results,increasing the injection rate improves the areal sweep efficiency up to a critical rate at which viscous fingers start to grow.The impact of heterogeneity of the medium on distributing the viscous fingers was also investigated by introducing two different arrangements of fractures in the model. The results show that fractures perpendicular to the direction of flow would distribute the displacing water more uniformly, while fractures in the direction of flow would amplify the unfavorable sweep efficiency.

Discussion on the sweep efficiency of hybrid steam-chemical process in heavy oil reservoirs: An experimental study

Non-condensable gas(NCG),foam and surfactant are the three commonly-used additives in hybrid steam-chemical processes for heavy oil reservoirs.Their application can effectively control the steam injection profile and increase the sweep efficiency.In this paper,the methods of microscale visualized experiment and macroscale 3D experiment are applied to systematically evaluate the areal and vertical sweep efficiencies of different hybrid steam-chemical processes.First,a series of static tests are performed to evaluate the effect of different additives on heavy oil properties.Then,by a series of tests on the microscale visualized model,the areal sweep efficiencies of a baseline steam flooding process and different follow-up hybrid EOR processes are obtained from the collected 2D images.Specifically,they include the hybrid steam-N_(2)process,hybrid steam-N2/foam process,hybrid steam-surfactant process and hybrid steam-N2/foam/surfactant process(N2/foam slug first and steam-surfactant co-injection then).From the results of static tests and visualized micromodels,the pore scale EOR mechanisms and the difference between them can be discussed.For the vertical sweep efficiencies,a macroscale 3D experiment of steam flooding process and a follow-up hybrid EOR process is conducted.Thereafter,combing the macroscale 3D experiment and laboratory-scaled numerical simulation,the vertical and overall sweep efficiencies of different hybrid steam-chemical processes are evaluated.Results indicate that compared with a steam flooding process,the areal sweep efficiency of a hybrid steam-N2process is lower.It is caused by the high mobility ratio in a steam-N2-heavy oil system.By contrast,the enhancement of sweep efficiency by a hybrid steam-N2/foam/surfactant process is the highest.It is because of the high resistance capacity of NCG foam system and the performance of surfactant.Specifically,a surfactant can interact with the oil film in chief zone and reduce the interfacial energy,and thus the oil droplets/films formed during steam injection stage are unlocked.For NCG foam,it can plug the chief steam flow zone and thus the subsequent injected steam is re-directed.Simultaneously,from the collected 2D images,it is also observed that the reservoir microscopic heterogeneity can have an important effect on their sweep efficiencies.From the 3D experiment and laboratory-scaled numerical simulation,it is found that a N2/foam slug can increase the thermal front angle by about 150 and increase the vertical sweep efficiency by about 26%.Among the four processes,a multiple hybrid EOR process(steam-N2/foam/surfactant process) is recommended than the other ones.This paper provides a novel method to systematically evaluate the sweep efficiency of hybrid steam-chemical process and some new insights on the mechanisms of sweep efficiency enhancement are also addressed.It can benefit the expansion of hybrid steam-chemical processes in the post steamed heavy oil reservoirs.

计算注水开发不同阶段体积波及系数的新方法

体积波及系数是油田评价开发效果、制定开发调整方案的重要依据。为了研究注水开发不同阶段体积波及系数的变化规律,从注入孔隙体积倍数角度出发,根据油水相对渗流理论与油藏工程原理,提出了驱油效率与注入孔隙体积倍数的计算模型,建立了体积波及系数计算方法,并以胜利油田3个试验区为例进行了计算与分析。结果表明:驱油效率与注入孔隙体积倍数之间满足指数方程,二者关系曲线呈上凸型;随着注入孔隙体积倍数的增大,驱油效率由最小驱油效率逐渐增大,并趋近于最大驱油效率;对驱油效率计算模型进行验证,预测值与实测值的平均相对误差仅为1.90%;水驱开发过程中体积波及系数与注入孔隙体积倍数关系曲线整体呈快升-缓升-近平台状演变趋势,计算结果能够指导开发调整措施的效果评价;3个试验区目前体积波及系数接近90%,波及区内存在大量剩余油,亟需开展波及区内主体剩余油的描述与启动方法研究。

纳米淀粉流体提高原油采收率

为了进一步促进纳米驱油技术在低渗透油藏中的高效应用,亟需开发新型的纳米驱油产品。纳米淀粉颗粒作为一种环境友好型的材料,分布广、价格相对低廉、性能优异,具备大幅度提高采收率的潜力。通过室内静态实验、岩心驱替实验、微观可视化实验、CT扫描实验等手段,从纳米淀粉流体的基本物性、提高驱油效果、扩大波及体积等方面研究了其提高采收率的过程和机理。研究结果表明,质量浓度为5000 mg/L的纳米淀粉流体因其亲水性和较小的粒径(30 nm)可改变水分子的赋存状态,使水相变温度从102℃升高至110℃,使得岩石表面的润湿接触角从78°降至34.2°,使油水界面张力从20 mN/m降至0.56 mN/m,注入压力下降39.6%。在微观可视化模型中,纳米淀粉流体可以明显降低多孔介质中的含油饱和度,特别是多孔介质固体表面的油膜量明显减少,提高驱油效果明显。在低渗透岩心中,纳米淀粉溶液的驱替前沿更加均匀,与水驱相比具有更大的波及体积。由于较大的波及体积、较高的驱油效率以及良好的润湿性等,注入0.4 PV质量浓度为5000 mg/L的纳米淀粉流体后,低渗透岩心的采收率增幅达21百分点。研究结果可为低渗透油藏的提高采收率提供一种新的技术参考。

A Research Progress of CO_(2)-Responsive Plugging Channeling Gels

In the heterogeneous reservoirs,CO_(2) flooding easily leads to CO_(2) gas channeling,which can seriously affect sweeping efficiency and reduce oil recovery.After thoroughly investigating the advantages and shortcomings of various CO_(2) plugging technologies,this paper focuses on the feasibility of improving conventional water-alternating gas(WAG)through CO_(2)-responsive gel materials.Based on the different chemical reaction mechanisms between the unique chemical structure and CO_(2),changes in the material’s physical and chemical properties can respond to CO_(2).The feasibility of utilizing these property changes for CO_(2)-responsive plugging is explored.Various CO_(2)-responsive gels and gel nanoparticles have been extensively researched in different fields,such as energy,medicine,and biology.This paper surveys the molecular structures,chemical compositions,response mechanisms,and changes of these CO_(2)-responsive gels,aiming to draw insights into the carbon dioxide-enhanced oil recovery(CO_(2)-EOR)field.Finally,the key issues and future development direction of CO_(2)-responsive plugging gels were analyzed.

可控震源动态扫描时距规则定量优化设计及应用

可控震源动态扫描地震数据采集过程中,相邻多组震源震动时产生的地震波会相互干涉,从而影响地震数据采集品质。合理设计采集时距规则可以降低可控震源高效采集时震源相互干涉的影响,同时平衡原始数据采集品质和可控震源高效采集施工效率。以往动态扫描时距规则设计时,对资料处理过程中高效采集噪声的压制效果考虑较少,并且时距规则的设计缺乏统一量化标准。首次将高效采集噪声压制效果引入动态扫描时距规则设计中,对现场不同地表类型采集的可控震源相关前记录采用互相关法获取高效采集噪声信息,以环境噪声能量、干涉时空位置和干涉区域能量比值为阈值建立量化统一的时距规则设计标准,形成了可控震源动态扫描时距规则定量优化设计方法。动态扫描时距规则定量优化设计方法优化了现场试验方案,降低了试验工作量,与地震数据处理信噪分离技术相适应优化滑动时间参数,定量与定性相结合设计时距规则避免了以频率扫描为主的常规定性分析方法带来的人为主观歧义。该方法不受勘探区地表特征约束,能够在保障地震数据品质条件下最大限度地提高可控震源采集施工效率,是对可控震源高效采集配套技术的补充和完善,有助于“两宽一高”地震采集技术的推广应用。

一种水驱油藏波及系数解析计算方法

水驱油藏波及系数是油藏开发过程中的重要参数,目前实验、数模等求取方法存在操作繁琐、精度低、实用性差等问题,基于水驱特征曲线建立的油藏工程计算方法虽简便但在理论推导过程中对驱油效率和含水饱和度概念认识不清楚,使得推导结果不严谨。因此,有必要建立一种简便准确的解析求解方法。基于分流量方程和威尔杰方程,通过理论推导建立了一种基于油水相对渗透率曲线的水驱波及系数解析计算方法,可根据生产数据计算不同开发阶段的水驱波及系数。X油田计算表明,对于边水能量充足的南海海相稀油砂岩油田,开发初期原油主要来自于水驱波及范围的扩大,开发中后期原油主要来自于水驱波及范围内驱油效率的提高,该类油田开发技术政策初期应以完善井网,扩大水驱波及范围为主,中后期以换大泵提液,提高水驱洗油效率为主。本文建立的方法具有数据基础简单、计算简便快捷等优点,可广泛应用于油田动态分析和开发效果评价。

Understanding aqueous foam with novel CO2-soluble surfactants for controlling CO2 vertical sweep in sandstone reservoirs

The ability of a novel nonionic CO2 -soluble surfactant to propagate foam in porous media was compared with that of a conventional anionic surfactant（aqueous soluble only）through core floods with Berea sandstone cores.Both simultaneous and alternating injections have been tested.The novel foam outperforms the conventional one with respect to faster foam propagation and higher desaturation rate.Furthermore,the novel injection strategy,CO2 continuous injection with dissolved CO2 -soluble surfactant,has been tested in the laboratory.Strong foam presented without delay.It is the first time the measured surfactant properties have been used to model foam transport on a field scale to extend our findings with the presence of gravity segregation.Different injection strategies have been tested under both constant rate and pressure constraints.It was showed that novel foam outperforms the conventional one in every scenario with much higher sweep efficiency and injectivity as well as more even pressure redistribution.Also,for this novel foam,it is not necessary that constant pressure injection is better,which has been concluded in previous literature for conventional foam.Furthermore,the novel injection strategy,CO2 continuous injection with dissolved CO2 -soluble surfactant,gave the best performance,which could lower the injection and water treatment cost.

Detection of Mechanical Deformation in Old Aged Power Transformer Using Cross Correlation Co-Efficient Analysis Method

Detection of minor faults in power transformer active part is essential because minor faults may develop and lead to major faults and finally irretrievable damages occur. Sweep Frequency Response Analysis (SFRA) is an effective low-voltage, off-line diagnostic tool used for finding out any possible winding displacement or mechanical deterioration inside the Transformer, due to large electromechanical forces occurring from the fault currents or due to Transformer transportation and relocation. In this method, the frequency response of a transformer is taken both at manufacturing industry and concern site. Then both the response is compared to predict the fault taken place in active part. But in old aged transformers, the primary reference response is unavailable. So Cross Correlation Co-Efficient (CCF) measurement technique can be a vital process for fault detection in these transformers. In this paper, theoretical background of SFRA technique has been elaborated and through several case studies, the effectiveness of CCF parameter for fault detection has been represented.

页岩油水平井体积压裂缝网波及体积评价新方法及应用

针对鄂尔多斯盆地庆城油田夹层型页岩油体积压裂缝网波及体积定量表征难度大的问题,应用物理模拟实验与矿场数据,耦合关键地质工程参数,建立缝网改造体积预测模型,基于岩石微观结构与润湿性,建立了考虑流体压力下的多尺度孔隙渗吸模型,对缝网渗吸体积进行定量表征,并提出新的缝网波及系数概念,定量评价缝网波及体积。研究表明:页岩油体积压裂裂缝总体呈现条带状缝网形态,形似“仙人掌”;影响缝网波及体积的主控因素依次为压裂液量、裂缝密度、脆性指数、施工排量、水平应力差、油层厚度、加砂量;缝网改造体积是水平井体积压裂缝网波及体积的主要贡献者,压裂液在缝网中的渗吸主要用于补充地层能量,典型平台缝网波及系数为33.2%~63.6%,需进一步提高缝网波及体积。研究成果可为页岩油水平井体积压裂效果评价提供参考。

弹性作用对驱油用聚合物扩大波及能力的影响

黏度是影响聚合物扩大波及能力最重要的因素。为了提高聚合物扩大波及能力,最常用的方式是提高聚合物的表观黏度。有关弹性作用对于提高聚合物微观驱油效率的研究比较多,但对于扩大波及能力的研究较少。为此,选择了相对分子质量不同但表观黏度相同的驱油用聚合物进行研究,首先表征了聚合物分子尺寸和微观聚集形态,然后对比了能够反映聚合物弹性大小和弹性占比的弹性模量及相位角,最后通过岩心及可视化驱油实验研究了2个聚合物的阻力系数和驱油效果。结果表明:在黏度相同的条件下,和相对分子质量为1000×104的聚合物相比,相对分子质量为3000×10^(4)的聚合物的弹性模量提升2.6倍,相位角由80°降低至65.5°,表现出更高的弹性和弹性占比,最终阻力系数提升2.5倍,采收率提高近1倍。因此,弹性对于提高聚合物扩大波及能力具有重要作用,新型聚合物的研发需要黏性和弹性并重。

油藏改建地下储气库库容量计算方法

库容量计算是地下储气库(以下简称储气库)建库地质方案设计的核心研究内容之一,油藏建库由于存在气油水三相渗流和复杂的气—油组分交换相行为,其库容形成机理与气藏建库具有显著差别。为此,基于多轮气驱、相平衡实验和数值模拟等研究,剖析了油藏建库库容形成机理及其影响因素,结合建库不同阶段储层流体分布及运移特征,提出了将建库油藏纵向划分为气驱纯油带、气驱水淹带/油水过渡带和纯水带3个不同区带,进行差异化计算库容量的新思路,并建立了以“有效储气孔隙体积”为核心,综合考虑不同流体区带注气微观驱替效率、宏观波及系数、剩余油二次饱和溶解及其性质变化等多相渗流和相行为的油藏建库库容量多因素预测数学模型和计算方法。研究结果表明:①油藏水驱后气驱改建储气库,微观气驱效率和宏观波及系数是影响油藏建库库容规模的主控因素;②剩余油二次饱和溶解及其体积收缩对库容规模具有一定的影响,原油挥发性越强、建库稳定剩余油越多,剩余油二次饱和溶解和原油性质变化对库容量影响越显著;③冀东油田堡古2挥发性油藏建库次生气顶自由气有效库容量为18.61×10^(8)m^(3),其中气—油组分交换相行为引起的建库稳定剩余油收缩增加库容量为2.81×10^(8)m^(3),贡献率为15.1%,自由气和剩余油二次饱和溶解总库容量为28.60×10^(8)m^(3)。结论认为,该方法在冀东油田堡古2号、南堡1号储气库进行了应用实践,所建立的油藏库容计算模型具有良好的应用效果,但由于油藏建库机理较气藏更为复杂,目前水淹区和纯油区的宏观波及系数和微观驱替效率以室内试验、数值模拟计算为主,高强度注采引发的气窜、气油水互锁等对库容的形成将产生较大影响,建库运行过程中需加强动态监测,实时修正数值模型,并建立合理的注气和排液技术界限,合理控制油气界面稳定扩展,提升达容达产效率。

支化预交联凝胶颗粒提高采收率机理实验

为解决华北油田河间东营某区块化学驱因聚合物老化导致的驱油体系黏度及驱油效果下降的问题,基于黏度和黏弹性测试、粒径分布测量、核磁共振测试、并联岩心驱替等多种实验手段,明确了支化预交联凝胶颗粒(B-PPG)的微观驱油机理以及并联岩心的驱油效果。结果显示:B-PPG分子的支链结构的水溶性较好,可提高溶液的表观黏度;B-PPG网状分子结构以破碎或变形的方式进入地层,从而改善流度比,提高非均质储层的波及效率;当主力油层的渗透率级差为7.4时,质量浓度为2000 mg/L的B-PPG体系提高采收率的幅度较水驱高20%。研究表明:B-PPG体系黏弹性好,变形能力强,具有理想的抗盐性,能在高渗层形成有效封堵,大幅度提高采收率。该研究为改善高温高盐油藏剖面、封堵高渗优势通道、大幅度提高油藏波及效率和采收率提供了借鉴。

无夹层底水稠油油藏水平井波及系数主控因素研究

在水平井开发底水稠油油藏过程中,受多种因素影响,底水呈现非活塞式推进、流线形态不断变化,导致波及系数难以预测。基于典型油藏实际生产动态分析,结合灰色系统关联分析法和数值模拟技术,确定了波及系数的主控因素及变化规律。研究表明,水平井开发的无夹层底水稠油油藏波及系数主要受产液能力、避水高度、水平段长度、井距和平均渗透率等因素的影响;可根据各主控因素对底水稠油油藏波及系数的影响,对水平井的设计进行优化。

Enhanced flushing of polychlorinated biphenyls contaminated sands using surfactant foam: Effect of partition coefficient and sweep efficiency

Foam flushing is an in situ soil remediation technology based on the traditional surfactant flushing method. The contribution of mobility control to contaminant removal by foam is helpful for improving this technology. Foam flushing of polychlorinated biphenyl （PCB）- contaminated unconsolidated media was performed to evaluate the effect of the partition coefficient （PC） and sweep efficiency （SE） on PCB removal. Column flushing with surfactant solution and foam with different types and concentrations of surfactant was carried out for PCB removal. Two types of quartz sand were investigated to evaluate the Jamin effect on the SE value of the washing agent. The results demonstrate that a small PC value and large SE value are necessary to achieve high PCB removal for foam flushing. Compared with solution flushing, the introduction of foam can effectively control the mobility of the washing agent. Similar to solution flushing, solubilization is a key factor which dominates the removal of PCBs in foam flushing, In addition, the SE value and PCB removal by foam flushing is less affected by particle size. Therefore, foam flushing was proved to be more effective in porous media with low hydraulic conductivity and high porosity. An integrated flushing with water, surfactant solution and foam was performed and the results prove that this technology successfully combines the advantages of solution solubilization and mobility control by foam, and thus further increases the remediation efficiency of PCBs to 94.7% for coarse sand.

采气速度对南海东部水驱气藏采收率的影响研究

由于海上气田都采用少井高产、高速高效的开发策略,因此海上气田采气速度普遍较高。为探讨高采气速度对南海东部水驱气藏开发效果的影响,针对此类储层较均质且物性好,水体能量较充足的海相砂岩气藏开展采收率影响因素分析。研究表明,废弃时地层压力、水侵体积波及系数及微观驱气效率是影响水驱气藏采收率的关键因素。通过微观可视化实验及数值模拟研究,明确了采气速度对气水渗流规律及气藏采收率的影响。气水两相微观可视化驱替实验结果表明,对于均质水驱气藏,驱气效率随驱替速度的增加而增大,适当加快开采速度可以提高气藏无水期采出程度。数值模拟研究表明,在其他条件相同时,提高开采速度可以增大水驱波及系数,降低气藏废弃压力,进而提高气藏采收率。气藏开发实例也证明了高采气速度有助于物性较好的均质水驱气藏取得较高的采收率。

浅层稠油油藏CO_(2)辅助蒸汽开发机理与效果研究

研究了CO_(2)辅助蒸汽开发浅层稠油的机理和效果。结果表明:CO_(2)溶于稠油后能增加原油体积系数、降低原油黏度和界面张力,增加油相相对渗透率以及降低残余油饱和度;蒸汽吞吐过程中增加CO_(2)辅助,能够有效弥补地层亏空,维持吞吐压力,可使吞吐采收率提高16.9个百分点。蒸汽驱后期采用CO_(2)与蒸汽交替注,能够产生水气交替作用,有效延缓注入压力快速下降,提高波及效率,可使原油采收率提高23.3个百分点,增油效果显著。

中低渗油藏极限井距及波及系数变化规律研究

注入水有效驱替是提高油田注水开发效果和最终采收率的核心。基于稳定渗流模型,建立了考虑启动压力梯度和储层应力敏感的极限半径公式,并结合油藏数值模拟方法,研究了多层合采油藏不同井距波及系数变化规律,首次明确了渗透率级差、注采井距和波及系数的关系。结果表明,启动压力梯度对极限半径影响较大,对部分中低渗储层的影响不能忽略。对于多层合采油藏,受渗透率级差影响,井距对注入水波及系数存在较大影响。缩小井距可以有效提高中低渗油藏波及系数,确保注水有效性,提高油田采收率。现场应用效果良好,可为油田加密调整提供借鉴与参考。

家用扫地机器人清扫效率提升方法研究

家用扫地机器人能够凭借一定的人工智能实现路径规划,自主地完成房间所有区域的地面清扫工作。清洁效率是家用扫地机器人性能的重要指标,尽量用最少的时间完成全屋地面的清洁工作。为了提高清洁效率,对路径规划有一定性能要求。文章实现了一种有效提升清洁效率的方法,其由三种方法共同组成,分别为虚拟分区递归弓字型方法、小区域困住检测及脱困方法、导航快速沿边绕障方法。