Experimental analysis of matrix moveable oil saturation in tight sandstone reservoirs of the south Ordos Basin,China

Tight oil reservoirs in the south Ordos Basin are characterized by fractured,heterogeneous oil-bearing strata(an oil saturation of less than 55%on average),normal pressure(0.8±)and extra-low permeability(less than 0.3 mD).In the Chang 8 tight sandstone reservoir in Honghe oilfield,micro-and nanopores,especially those with a pore-throat radius of less than 1 mm,account for more than 90%.Fluid flow in the matrix is non-linear and crude oil flow rates are very low under normal pressure gradients.An improved understanding of oil mobility in a tight matrix is key to further development of normalpressure tight-oil resources in the continental basin.In this study,constant-velocity and high-pressure mercury injection experiments were conducted using samples of typical tight sandstone cores obtained from the south of Ordos Basin.A new method for reconstructing the full-scale pore-throat distribution characteristics of tight sandstone reservoirs was established successfully,based on which multistage centrifugal tests,tests of low-pressure differential displacement of oil by water,and nuclear magnetic resonance tests were conducted in order to obtain the distribution characteristics of moveable fluid in different pores.The moveable oil saturation(MOS)and degree of oil recovery(i.e.ratio of accumulative oil production to producing geologic reserves)of the core samples under different differential pressures for displacement were determined.As for the tight oil reservoirs in the south Ordos Basin,the moveable fluids are mainly stored in sub-micron(0.10-0.5 mm)pores.For Type I reservoirs(k>0.1 mD),the volume percentage of moveable fluid in pores with a radius larger than 0.5 mm is relatively high(greater than 40%).The degree of oil recovery of water flooding serves as the basis for forecasting recoverable reserves for tight oil reservoirs.Recoverable reserves under water flooding,mainly occur in pores with a radius greater than 0.5 mm.The contribution of Type I reserves to oil production is observed to be greater than 60%,and the degree of oil recovery reaches up to 17.1%.These results help improve our understanding on the evaluation and classification of Chang 8 tight sandstone reservoirs in Honghe oilfield and serve as theoretical basis for pilot tests to explore effective injection media and development methods to improve the matrix-driven pressure differences and displacement efficiency for oil.

Theoretical eduction and numerical simulation researches on the relationship between resistivity and water saturation of waterflood oil zone

In the process of water displacing oil,the relationship between resistivity and water saturation is the fundament of the quantitative research on the waterflooded grade and the remaining oil saturation with well logging data. A large number of core analysis data and production data are cumulated in the process of oil field exploitation,which offers the basis for the above research. This paper educed two methods from the Archie equation and material balance theory to calculate the quantitative relationships between Rz and Sw,and between Rt and Sw. The relationships set up by the two methods are similar to those set up by the real core measurements. The results can be used to analyze influencing factors and determine saturation quantitatively.

Compositional modeling and simulation of dimethyl ether (DME)-enhanced waterflood to investigate oil mobility improvement

Dimethyl ether （DME） is a widely used industrial compound, and Shell developed a chemical EOR technique called DME- enhanced waterflood （DEW）. DME is applied as a miscible solvent for EOR application to enhance the performance of conventional waterflood. When DME is injected into the reservoir and contacts the oil, the first-contact miscibility process occurs, which leads to oil swelling and viscosity reduction. The reduction in oil density and viscosity improves oil mobility and reduces residual oil saturation, enhancing oil production. A numerical study based on compositional simulation has been developed to describe the phase behavior in the DEW model. An accurate compositional model is imperative because DME has a unique advantage of solubility in both oil and water. For DEW, oil recovery increased by 34% and 12% compared to conventional waterflood and CO2 flood, respectively. Compositional modeling and simulation of the DEW process indicated the unique solubility effect of DME on EOR performance.

Fuzzy Comprehensive Evaluation of Oil Field Waterflooding Effect

Oil field waterflooding is a complex man-controlled systematic behavior, and the related evaluation methods vary greatly. This paper put forward a fuzzy comprehensive method of evaluating controlled development level by analysis of the macroscopic evaluation to oil field waterflooding effect with combination of original reservoir geological state. This fuzzy evaluation technique bears unique advantages because there is little difference among evaluation indexes which represent the dynamic and static state of regional neighborhood of development units (blocks, Production Company, etc.). Not only the mathematical method for evaluating oil field waterflooding effect is set up, but also the method is applied in three blocks of D oil field. The calculated results show the effectiveness and practicability of the method.

Mechanisms and experimental research of ion-matched waterflooding to enhance oil recovery in carbonate reservoirs: A case of Cretaceous limestone reservoirs in Halfaya Oilfield, Middle East

Based on systematically summarizing the achievements of previous ion-matched waterflooding researches,the diversity and synergy of oil recovery enhancement mechanisms and the interaction between mechanisms are examined according to two classification standards,and the influence of behaviors of different ions on different mechanisms and oil displacement efficiency are investigated.Ionic strength is proposed to characterize the behavior differences of univalent and divalent ions,the relationships between ionic strength,effective concentration,and mechanisms are established to characterize the ion behavior behind various mechanisms,and evaluate the performance of ion-matched injection water.The mechanisms of enhancing oil recovery by ion-matched waterflooding include:(1)The ion-matched water can reduce the ion strength and match the ion composition of formation water,thereby reducing the difference between the effective concentration of univalent ions and divalent ions on the surface of carbonate rocks,and improving the effective concentration of potential determining ions(especially SO42-).(2)It can improve wettability,oil-water interface properties,pore structure and physical properties of the reservoir,and finally enable the establishment of a new ionic equilibrium conducive to waterflooding while breaking the original equilibrium.In this study,experiments such as relative permeability curve,interfacial tension,and core-flooding were carried out on carbonate core samples from the Cretaceous Mishrif Formation reservoirs in Halfaya Oilfield,Middle East,a method for injection water evaluation was established and the injection water suitable for these reservoirs was selected:6 times diluted seawater.Compared with ordinary seawater,oil displacement efficiency can be increased by more than 4.60%and compared with the optimum dilution of formation water,oil displacement efficiency can be increased by 3.14%.

高倍数水驱砂岩中原油黏度、岩心润湿性时变规律核磁共振实验

根据模拟原油黏度与横向弛豫时间谱几何平均值的变化关系,建立了模拟原油黏度预测模型,并结合高倍数水驱核磁共振(NMR)实验实现了孔隙介质中模拟原油黏度的时变规律定量表征;基于核磁共振弛豫理论推导出新的NMR润湿性指数计算公式,结合砂岩岩心高倍数水驱实验,定量表征了水驱过程岩石润湿性的时变规律。研究表明:岩心中剩余油黏度与过水倍数正相关,过水倍数较低时剩余油黏度升高速度较快,过水倍数较高时剩余油黏度升高速度趋缓。剩余油黏度的变化与储层非均质性相关,储层均质性越强,剩余油中重质组分含量越高,黏度越高。注水后储层润湿性将发生改变,亲油储层向亲水储层转变,亲水储层则亲水性更强,且改变程度随过水倍数增加而增强。原油黏度的时变性与润湿性的时变性具有很高的关联性,原油的黏度变化不可忽略,考虑模拟原油黏度变化时计算得到NMR润湿性指数与测试Amott(自吸法)润湿性指数更具有一致性,更加符合储层润湿性时变规律。

窄条带状背斜油藏边部注水开发产能影响因素

JY油田Y油藏为典型窄条带状背斜油藏,其储集层注入水极易沿河道中心方向突进,导致油井快速水淹,产量递减快;由于对水体大小、构造幅度、储集层物性等产能影响因素认识不清,此类油藏开发难度较大。针对上述问题,建立了窄条带状背斜油藏精细数值模型,通过对比论证提出了“边部注水+逐步转注”开发,并在此基础上开展了水体大小、构造幅度、储集层物性等参数对产能的影响研究。结果表明:“边部注水+逐步转注”开发不仅可以增大边水能量,使得井网双向受效,还可以有效延缓构造高部位油井的见水时间,大幅度降低油井含水率。另一方面,在考虑油藏构造特征的前提下,量化了不同影响因素下的产能特征,明确了水体大小、构造幅度、垂向渗透率与水平渗透率之比等参数的合理界限,论证了不同储集层物性下油藏面积的适应性。可为同类型油藏改善注水开发效果提供借鉴。

石油地质工程中改善高含水期油田注水开发的措施

随着油田开发程度不断加剧,许多油田进入高含水期,对注水开发的效果提出了新的挑战。基于此,本文首先介绍了高含水期的概念及注水开发作为维持和提高油田产量的重要手段,随后详细分析了高含水期油田注水开发面临的主要挑战,最后提出了改善高含水期油田注水开发的具体措施,包括优化注水策略以减少水窜、加强水质管理与设备保护、提高能量效率与经济效益等方面的方法,希望为高含水期油田注水开发提供相关参考。

致密油藏开发特征及开发技术研究

致密油藏作为近年主力产建及开发层系,是后期稳产增产的主战场,目前,X区长8油藏面临着渗透率低,裂缝发育,注水开发主向井见水、侧向井不见效,地层能量下降快,递减大等问题,通过对开发区块的特征及矛盾进行研究,总结出一些关键治理及调整技术,为后期相类似油藏高效稳定开发提供一定借鉴。

低盐水驱对中低渗砂岩采收率及润湿性影响

低盐水驱是一项前沿的改善水驱技术,具有成本低、环境友好等优点。大庆油田中、低渗储层物性较差,化学驱效果不理想,而低盐水驱在中、低渗储层应用前景良好。分别选大庆油田中、低渗透率岩心各5块,采用矿化度为1 000~10 000 mg·L^(-1)盐水开展岩心驱替实验和接触角测试。结果表明:当注入水矿化度由10 000 mg·L^(-1)降为5 000 mg·L^(-1)时,采收率增加,等渗点右移,含油饱和度下降,储层变为水湿;当注入水矿化度从5 000 mg·L^(-1)降为1 000 mg·L^(-1)时,采收率下降,等渗点左移,驱替压力上升,引发黏土膨胀,含油饱和度上升,储层为中性润湿。因此,利用低盐水驱开发大庆油田中、低渗油藏可行,能够提高原油采收率,并改善注入能力,并且矿化度阈值为5 000 mg·L^(-1)。

基于控制水驱前缘速度的注采井组参数优化方法研究与应用

低渗致密油藏注水开发与中高渗油藏不同,井组见效极其不均衡导致无效注水是造成水驱采收率低的主要原因,有必要形成1套以油井同步见水为目标的注采参数调整方法来指导现场注水调整。结合延长油田低渗致密且油水混储的实际情况,建立了考虑毛细管力作用的平面分区径向流水驱前缘推进数学模型;通过优化注水强度与注采压差,形成了两端注采结构调整方法;定量研究了影响井组均衡水驱的3个关键因素。结果表明:通过调整注采井距和注采压差可有效解决渗透率级差导致的平面水驱不均衡的问题;当f w<60%时注采井距比对井组采出程度的影响较大,渗透率级差为20时对应的最佳注采井距比为1.5~2.0。对于注采井网固定的开发老区,主要通过控制各油井方向的生产压差来控制水驱前缘速度。基于两端注采参数调整方法,将D4430-8井组内注水井注水强度从1.87 m^(3)/(d·m)提高到2.50 m^(3)/(d·m),并通过调整3口油井的泵挂来改变注采压差。调整之后D4430-8井组综合含水由37.80%下降至25.29%,单井平均日产油量增加0.53 t,水驱开发效果明显改善。研究结果对低渗致密油藏注水开发老区改善平面波及效率具有重要指导意义。

Effects of microscopic pore structure heterogeneity on the distribution and morphology of remaining oil

Waterflooding experiments were performed using Micro-CT on four cores of different pore structures from Donghe sandstone reservoirs in the Tarim Basin. The water, oil and grains were accurately separated by the advanced image processing technology, the pore network model was established, and parameters such as the number of throats and the throat size distribution were calculated to characterize the microscopic heterogeneity of pore structure, the flow of oil phase during displacement, and the morphology and distribution of remaining oil after displacement. The cores with the same macroscopic porosity-permeability have great differences in microscopic heterogeneity of pore structure. Both macro porosity-permeability and micro heterogeneity of pore structure have an influence on the migration of oil phase and the morphology and distribution of remaining oil. When the heterogeneity is strong, the water phase will preferentially flow through the dominant paths and the remaining oil clusters will be formed in the small pores. The more the number of oil clusters(droplets) formed during displacement process, the smaller the average volume of cluster is, and the remaining oil is dominated by the cluster continuous phase with high saturation. The weaker the heterogeneity, the higher the pore sweep efficiency is, and the remaining oil clusters are mainly trapped in the form of non-continuous phase. The distribution and morphology of micro remaining oil are related to the absolute permeability, capillary number and micro-heterogeneity. So, the identification plate of microscopic residual oil continuity distribution established on this basis can describe the relationship between these three factors and distribution of remaining oil and identify the continuity of the remaining oil distribution accurately.

智能水驱基于界面离子调控机制的提高采收率机理研究

通过调节关键离子的浓度,智能水驱技术能够有效提高原油采收率已经得到学术界及工业界的广泛认可,但其微观机理仍存在争议。重点研究了硫酸根离子在砂岩及碳酸盐油藏中的提高采收率效果及机理。通过长岩心驱替实验探究硫酸根离子浓度对原油采收率的影响;通过开展油水界面张力、油水界面扩张模量、接触角及液桥收缩-断裂动力学行为分析,分析硫酸根离子浓度对油-水界面及固-液界面的影响规律及机制。结果表明,在低温条件下,将海水中硫酸根离子的浓度提高3倍能有效提高Berea砂岩及Indiana石灰岩中的原油相对渗透率及采收率;其微观机理包括两个方面:①硫酸根离子提高了两种岩石表面的亲水性;②硫酸根离子不仅降低油水界面张力,而且提高了油水界面扩张模量及油水界面稳定性,从而抑制地层中“颈缩-分离”(Snap-off)行为的发生,提高原油的连续性。

延安北S井区长21储层潜力及剩余油精细表征新探索

文章紧密结合研究区开发生产实际,并应用最新空间三维建模方法表征长21储层剩余油的分布,兼顾储层构型对油藏剩余油的控制作用和油藏渗流特性,为油田后期注水开发方案的调整提供了新的思路。

南海东部A油田带夹层底水油藏水淹模式及剩余油分析

底水油藏内部发育隔夹层,对油藏早期开发井起到延缓底水的作用,但开发后期,准确寻找剩余油富集区是一大难题,水平井呈现底水和边水双重驱动的特征,剩余油分散,实施调整井难度大。在结合动态资料和静态资料分析后,研究不同部位水平井的水淹模式、剩余油分布,打破原有思路,在底水油藏开发后期精准寻找剩余油,实施调整井。为油田后续高效开发提供了依据。

水驱优势通道对水驱开发效果的影响研究

提出了水驱优势通道的概念。采用流线数值模拟技术研究了优势通道属性对水驱开发效果的影响。研究结果表明优势通道是通过影响油藏中生产井和注水井控制的油藏体积来影响水驱开发效果的。对于存在优势通道的油藏 ,水驱开发中存在两种流线 :一种是从井筒出发平行优势通道的流线 ,另一种是从优势通道出发垂直于优势通道的流线。

油田注水开发系统能耗整体优化方法

为了解决注水开发系统能耗整体优化的问题,应用能量守恒定律及流体能量表征方法,建立了油藏系统能耗表征方法,阐述了表征方法分项物理意义。在此基础上,以阶段时间内吨油能耗最低为目标函数,以注水、油藏和举升3个系统能耗表征方法及油藏开发方案为约束条件,以注水系统单井采油量和注水量为决策变量,建立油田注水开发系统能耗整体优化模型。应用整体优化方法,借助数值模拟手段获取油藏相关参数,对某一注一采实际井组方案进行优化,得到最佳注采方案以及地层压力保持水平,验证了该方法的合理性。

水驱微观渗流特征及剩余油启动机理

通过微观驱油实验、岩心驱油实验及渗流理论分析,明确了水驱微观渗流规律,量化了水驱后微观剩余油分布特征,提出了改善水驱效果及提高采收率方法机理。水驱后剩余油启动需要克服启动压力,按照驱油机理划分,水驱后剩余油可划分为受黏附力控制的剩余油和受毛管力、黏滞力控制的剩余油2种类型,其中受毛管力和黏滞力控制的剩余油占90%以上。通过增加驱替压力梯度、降低界面张力启动和增加驱替体系黏度可以提高油层采收率。

油藏天然能量指标在注水动态分析中的应用

传统的油藏天然能量指标分析方法仅用来分析注水前的油藏天然能量大小。经理论研究发现:Δ(平均地层压力降)与Np(r无因次弹性产量比值)呈幂指数关系,双对数曲线呈线性规律;双对数图上等时间间隔点越密集,边底水补充地层能量越及时,水侵速度越快;驱动能力指标同样适用于注水后的分析与评价,且变化规律不变,注水后等时间间隔点越密集,注水效果越好;运用Δ与Npr关系式可以准确地预测原油采出程度,同时结合油藏水驱特征曲线还可以确定合理累积注采比和阶段注采比。最后,用于实例分析取得了良好的预测效果。

胜坨油田注水开发过程中的润湿性变化

以胜利油区胜坨油田二区沙二段油层为例 ,研究了油层原始润湿性及其在注水开发过程中的变化 ,探讨了含油饱和度、韵律非均质性对润湿性的影响。研究证明 ,原始亲油油层 ,含油饱和度下降 10 %时 ,开始转向亲水 ;原始亲水油层 ,含油饱和度下降 8%时 ,亲水性开始加强。