QUANTITATIVE ESTIMATES OF OIL LOSSES DURING MIGRATION, PART II: MEASUREMENT OF THE RESIDUAL OIL SATURATION IN MIGRATION PATHWAYS

Recent experimental observations have demonstrated that losses of oil in a secondary migration pathway depend largely on the characteristics of the pathway itself. Accurate assessments of the residual saturation are required to quantify losses during migration. In the present paper, the authors report on experimental procedures designed to evaluate the oil saturation at various stages of the migration/invasion process. The experiments made use of both apparatuses filled with an artificial medium composed of glass beads, and cores composed of reservoir sandstones from oilfields in NE China. The saturation of residual oil in the pathways was measured by nuclear magnetic resonance imaging.
Experiment results show that mobile oil continues to migrate in a porous medium when the supply of oil has been stopped, but that the migration pathway shrinks and may become disconnected into isolated segments. Once active migration ceases, the residual oil saturation varies significantly from location to location within a pathway, and the average residual oil saturation falls to 30∼60%, depending on grain size and composition. A porous medium composed of large grains commonly contains large pores and pore throats and thus may correlate with low residual oil saturations.     

QUANTITATIVE ESTIMATES OF OIL LOSSES DURING MIGRATION, PART I: THE SATURATION OF PATHWAYS IN CARRIER BEDS

Estimates of hydrocarbon losses during migration are critical to petroleum resource assessments based on mass balance calculations. Using knowledge acquired from physical experiments, we conducted numerical experiments to qualitatively simulate migration processes on a basin scale, and we have estimated the proportions of oil lost along different parts of the migration pathway. Between the point where oil is expelled from a source rock and its arrival in a trap, migration pathways were divided into three sections, namely vertical and lateral pathways within the area of the effective source rock (W₁), and lateral pathways outside this area (W₂).
With reference to the concept of an independent migration unit (IMU), a prism-shaped domain with square top and bottom faces, the proportion of vertical pathways (Q₁) and lateral pathways (Q₂) in carrier beds in W₁ may be estimated, using parameters obtained in migration experiments. The proportion of oil lost in W₂ was obtained by statistical analysis of modelled results. It is found that the loss of oil within W₂ decreases rapidly with increasing distance from the contact between W₁ and W₂.
Relative oil losses in migration pathways were estimated by considering two typical migration models: a sloping rectangular plate model, and a circular synclinal model. Simulation results show that, for sandstone carrier beds at a basin scale, Q₂ is one order of magnitude less than Q₁, and losses (Q₃) in W₂ are two orders of magnitude less than those (Q₁+ Q₂) in W₁.     

核磁共振成像技术分析油运移过程中含油饱和度

利用核磁共振成像技术，观察玻璃珠填装管状模型与河砂填装管状模型内油的运移过程，测量并分析油运移路径形态特征和内部含油饱和度。原始油柱内油饱和度可达83％；路径形成油沿路径运移时，油在路径内的饱和度为40％～50％；运移完成后，在没有油继续供给的条件下，原有路径收缩，宽度减小，路径内的油呈不连续状态，残余油饱和度降为20％～35％。实验装置中孔隙介质的颗粒成分对路径内的油饱和度有一定影响。图2表1参16     

石油二次运移不同模式条件下含油饱和度测量

石油二次运移具有活塞式、指进式、优势式3种不同模式。利用湿填模型,在仅有浮力作为运移动力、以泵压和浮力综合作用作为运移动力的实验条件下,用不同粒度、不同充填介质填装的玻璃管模型系统,观测在3种运移模式条件下路径含油饱和度、残余油饱和度及残余油在通道中所占比例等变化规律。结果表明,路径含油饱和度和残余油量占通道的比例因运移模式不同而明显不同,残余油饱和度则基本不受运移模式的影响。     

核磁共振成像技术在油气运移路径观察与分析中的应用

利用核磁共振成像技术观察圆管填玻璃珠物理模型内油的运移过程,对成像处理方法进行改进后,可以定量地观察和分析运移路径的形态特征及其内部的油饱和度.实验结果表明,被油占据的运移路径在整个通道内的比例取决于路径的形态,而路径内的油饱和度并非100%.在实验模型的尺度上,运移路径上的油饱和度在运移过程中可达80%以上;在运移结束后,因运移路径收缩、分离,油饱和度只占20%～0%,甚至更低.     

Migration and occurrence of high wax oils in the Damintun Depression, Northeast, China: Implication for primary controls of petroleum migration pathways in heterogeneous carrier beds

This paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in the Damintun Depression, Bohai Bay Basin. There are two types of crude oils in the Damintun Depression: a high wax oil (wax hydrocarbon content between 8 and 60%) and a normal oil (wax hydrocarbon content lower than 8%). The high wax oil and normal oil are distinctly different both in biomarker compositions and in distribution patterns of carbon isotopic ratios for individual alkanes, and were confirmed to have been generated from different source rocks. Modeling of secondary migration pathways of both the high wax oil and the normal oil was conducted using a simple three-dimensional model, which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces without taking into consideration the influence of permeability heterogeneity (the morphology-controlled migration model). The modeling results have reasonably well predicted the occurrences of both the high wax oil and the normal oil. All commercial petroleum accumulations are along the predicted preferential petroleum migration pathways (PPMP) formed by focusing of numerous “small petroleum streams” close to the kitchens. The focusing of oils originating from a large area of the generative kitchens is essential for the formation of large oilfields. The strong porosity and permeability heterogeneities of the carrier beds, and the relatively high prediction accuracy of the modeling, suggest that the preferential petroleum migration pathways, although influenced by permeability contrast at local scales, can be effectively predicted at a basin or depression scale under certain circumstances using a model that does not take into consideration the effect of heterogeneity. Most dry holes are not on the predicted petroleum migration pathways, suggesting that the three-dimensional migration pathway modeling may provide a useful tool to reduce exploration risk.     

An interative procedure to determine depth and time of primary oil migration and expulsion efficiency of source rocks

This study seeks to propose an iterative procedure for estimating time and depth of primary oil migration and expulsion efficiency of a source rock. The procedure is based on two assumptions: (a) oil moves out of the source rock as a separate phase; and (b) oil migration does not start until residual oil saturation is reached. Oil saturation increases with oil generation and porosity reduction during burial. Changes in total volume, pore and oil volumes by oil generation and compaction are calculated at discrete time steps. Oil expulsion begins when oil saturation reaches residual oil saturation and relative permeability of oil rises above zero. The volume of oil expulsion can also be calculated iteratively after oil migration starts. The difference between oil generation and residual oil gives the volume of oil expulsion at each time step. The mass ratio of oil expelled to total oil that is generated provides the expulsion efficiency of the source rock.     

单井化学示踪剂法测残余油饱和度——回顾与展望

经过第一次和第二次采油后 ,还有大量的石油滞留地下深处不能被有效采出。而每年新发现的石油地质储量在不断减少 ,勘探开发的难度越来越大 ,这就要求必须采用先进的方法和技术将残余在地下的原油采出 ,也就有了确定SOR的需要。在进行三次采油的潜力评价中 ,SOR是一个至关重要的参数。测残余油饱和度的方法较多 ,但各有优缺点。单井化学示踪剂是其中一种较为有潜力的方法 ,它始于2 0世纪 60年代后期 ,由Cooke首先提出 ,它利用地层的色谱效应 ,用示踪剂法测残余油饱和度。Deans于 1 967年用此法在室内成功地测定了模型内的残余油饱和度 ,1 968年应用于现场获得成功 ,1 971年取得了美国专利权。该法首次现场测试获得成功以来已广泛应用。单井示踪法成本低 ,测定简便 ,测定体积大并且可调 ,应用范围广 ,灵敏准确 ,是测定残余油饱和度的理想方法。作者调研了大量国内外资料 ,对单井化学示踪剂测残余油饱和度的产生背景、应用及其发展作了回顾 ,并在与其它测残余油饱和度进行对比的基础上 ,对其应用发展前景作了展望。     

碎屑岩输导层非均质性与油气运聚成藏

碎屑岩地层普遍具有非均质性。然而,在勘探尺度的油气运聚和成藏研究中,输导层内部成分、结构和物性等方面的非均质性被忽略,致使输导层的非均质性特征及其对地层流体和油气运聚的作用没有得到应有的重视。碎屑岩输导层的非均质性受沉积构造控制,在浅层埋藏过程中即已发生明显的差异性成岩作用,其中渗透性岩石被低渗透性隔夹层所分隔,具有一定的空间结构特征。在结构非均质性输导层中,油气运移路径的分布极不均匀,与传统上物性表现为宏观均质性的输导层模型相差甚远。结构非均质性输导层中的油气总体向上倾方向运移,在原先认为应发生垂直运移的层段运移的油气受隔夹层阻碍,运移路径变得十分复杂,侧向运移则可发生在输导层的上、中、下任意部位,但处于上倾方向的圈闭仍然是油气运移的最终指向和有利目标。在运移途中,油气可在任何地方聚集,其单个油气量较小,但数量众多,分布范围很广,总量可能远大于处于高点圈闭中的油气藏。结构非均质性输导层中,油气的运移路径和聚集方式与传统认识不同,为油气运聚和成藏过程的认识带来许多启示,勘探应该具有更为广泛的目标选择,洼陷区和斜坡区都可能成为有利勘探区域。     

An optimization methodology of alkaline–surfactant–polymer flooding processes using field scale numerical simulation and multiple surrogates

After conventional waterflood processes the residual oil in the reservoir remains as a discontinuous phase in the form of oil drops trapped by capillary forces and is likely to be around 70% of the original oil in place (OOIP). The EOR method so-called alkaline–surfactant–polymer (ASP) flooding has proved to be effective in reducing the oil residual saturation in laboratory experiments and field projects through the reduction of interfacial tension and mobility ratio between oil and water phases.A critical step to make ASP floodings more effective is to find the optimal values of design variables that will maximize a given performance measure (e.g., net present value, cumulative oil recovery) considering a heterogeneous and multiphase petroleum reservoir. Previously reported works using reservoir numerical simulation have been limited to sensitivity analyses at core and field scale levels because the formal optimization problem includes computationally expensive objective function evaluations (field scale numerical simulations). This work presents a surrogate-based optimization methodology to overcome this shortcoming.The proposed approach estimates the optimal values for a set of design variables (e.g., slug size and concentration of the chemical agents) to maximize the cumulative oil recovery from a heterogeneous and multiphase petroleum reservoir subject to an ASP flooding. The surrogate-based optimization approach has been shown to be useful in the optimization of computationally expensive simulation-based models in the aerospace, automotive, and oil industries. In this work, we improve upon this approach along two directions: (i) using multiple surrogates for optimization, and (ii) incorporating an adaptive weighted average model of the individual surrogates.The cited approach involves the coupled execution of a global optimization algorithm and fast surrogates (i.e., based on Polynomial Regression, Kriging, Radial Basis Functions and a Weighted Average Model) constructed from field scale numerical simulation data. The global optimization program implements the DIRECT algorithm and the reservoir numerical simulations are conducted using the UTCHEM program from the University of Texas at Austin.The effectiveness and efficiency of the proposed methodology is demonstrated using a field scale case study.     

原油二次运移过程中的逾渗主脊实验研究

利用Hele-Shaw模型开展二维空间原油持续二次运移过程实验研究。在初始运移路径形成后改变注入煤油的颜色,验证二次运移过程中的逾渗主脊现象,初步从机理上指出初始运移路径形成后毛管力的变化是逾渗主脊形成的主要原因。逾渗主脊的尺寸和分形维数都要小于对应的初始运移路径的尺寸和分形维数。油气以这样的方式发生二次运移,加速了运移速率,二次运移过程中的烃损失量只限于初始路径。      

基于成藏体系理论的碳酸盐岩含油气区带评价方法——以塔里木盆地寒武系为例

以成藏体系理论为基础,参考前人区带评价参数标准,针对塔里木盆地碳酸盐岩层系,分别从烃源体、圈闭体、输导体和体系的有效保存性出发,建立了碳酸盐岩地质评价参数标准体系。该区纵向上以一套具有类似地质背景的圈闭体为核心,和其相关联的烃源体和输导体共同组成一个完整的成藏体系。在参数体系中,提出了输导体的3个评价参数:输导层类型、供烃方式和运移距离的评价标准。利用统计学方法,考虑运移距离和成藏几率的关系,指出油气运移距离评价参数分为小于10 km、10~50 km、50~100 km和大于100 km。针对塔里木盆地寒武系膏盐岩下碳酸盐岩地层,采用同时考虑油气聚集单元和盆地构造单元的双要素子体系划分方法,以及考虑地质参数的不确定性开展评价。塔北隆起东侧盖层覆盖区和塔中隆起北侧为1类地区;顺托果勒低隆区、塔西南地区、塔中隆起南侧、巴楚隆起北侧、塔北隆起西侧为2类地区。      

石油幕式运移实验研究

在饱含水的填装玻璃微珠的玻璃板模型中注入染色煤油进行油运移模拟实验,观察孔隙介质中油形成优势运移路径的过程及在幕式油充注过程中路径的变化,取得了如下认识:第一,油运移优势路径一旦形成后,油再次运移基本是沿着原先形成的运移路径进行运移,而油运移路径的模式及其形态基本保持不变;第二,相同注入速率下油再次运移的前缘平均速率远大于第一次油运移的前缘平均速率,运移速率与注入速率基本呈正相关关系;第三,运移结束后路径收缩、油饱和度降低,但残余油仍能清晰地勾画出原运移路径时的形态。     

剩余油分布研究现状及展望

剩余油分布的研究始终是一项重要且具有挑战性的工作，准确地评价剩余油饱和度对油田开发中后期调整挖潜及三次采油方案的实施至关重要。在有关文献的基础上将目前剩余油分布的研究方法按专业划分为四大类：地质、地震方法；油藏工程、试井及数值模拟方法；室内实验技术和工艺技术。阐述了各类研究方法的国内外发展现状，并指出了剩余油分布研究的主要方向。     

An Experimental Investigation of Optimum Capillary Number on Vertical Immiscible Gas Injection in Iranian Carbonate and Sandstone Rocks

Abstract

The authors' purpose was twofold: (a) to study optimum capillary number for acquiring maximum oil recovery in vertical gas-oil displacement using carbonate and sandstone cores, and (b) to investigate the influence of capillary end effect on optimum capillary number extracted from experimental data. Two sets of forced gravity drainage experiments were performed on carbonate and sandstone cores. The first set of experiments comprised seven vertical nitrogen injection tests using carbonate core, which had been saturated by kerosene in ambient laboratory condition. The second set consisted of six vertical nitrogen injection tests using sandstone core that had been saturated by live oil under reservoir temperature and pressure conditions. In each set of experiments, in constant bond number, one optimum capillary number (optimum flow rate) was recorded in which the maximum oil recovery was achieved. When capillary end effect was negligible, optimum capillary number was compatible with critical capillary number, which was calculated in critical gravity drainage velocity while in considerable end effect, optimum capillary number was higher than the calculated critical capillary number. In addition, the residual oil saturation in carbonate rock showed a declining trend when capillary number increased, whereas the minimum of residual oil saturation in sandstone core has been observed in optimum capillary number.     

鄂尔多斯盆地中生界石油运移特征分析

鄂尔多斯盆地中生界构造简单平缓,储层主要为低孔、低渗,油气运移独具特色。侏罗系和延长组上部储集层孔隙度、渗透率条件较好,油气运移聚集驱动力以浮力为主,三叠系顶部不整合面和侏罗系古河道砂体共同构成了侏罗系油藏的油气主要运移通道,其油气主要分布在侏罗系古河道内及不整合面附近。延长组中下部储集层在石油大量生成时期,储集层已非常致密,地层基本丧失水交替能力,异常压力为石油二次运移的主要动力,石油沿渗透性砂体主要向东北和西南两大方向运聚成藏,多分布在生烃中心及周边地区。      

准中1区块古构造恢复及其演化对油气成藏的作用

准噶尔盆地中部1区块油气的成藏受车莫古隆起演化的影响较大,晚白垩世及古近纪时期是主要成藏期及调整期。文中通过目的层选取、计算地层残余厚度、去压实校正、建立压实参数平面分布模型等步骤,求得油气成藏调整期车莫古隆起的真实地层沉积厚度,以此来反映古构造特征及演化,据此分析目的层古油藏的规模及油气运聚规律,指出下一步有利勘探方向。研究表明:区内晚白垩世存在2个古背斜,是油气有利运聚方向,并通过含油包裹体、测录井、试油资料综合确定了古油水界面及古油藏的规模。工区古近纪初北部开始隆升,古背斜逐渐消失,到现今古背斜调整成为低幅构造梁。古构造破坏后,部分圈闭仍存在,能保留大量原生油气,为原生保留型油藏,部分油气经微幅构造梁调整后,在现今有利构造位置处的圈闭聚集,形成调整再聚集型油藏。建议围绕古背斜及与古背斜形成优势运移路径进行勘探。     

利用地层原油物性和油层压裂梯度研究陕甘宁盆地侏罗系油气二次运移

甲烷含量与油气比关系曲线可用来区分两种不同的运移方式;此曲线结合其它资科为查明中生界垂向运移提供了一些重要依据;菱形图和P.C.卡西莫夫运移系数可初步确定侏罗系油藏油气侧向运移的方向和距离;压裂梯度结合岩芯资科,可以判断裂缝类型,区分运移方式,进行油(气)藏预测.本文所提供的成果和认识有助于研究侏罗系古地貌油田的形成和分布,并指导侏罗系的勘探.      

断层物性和倾角变化对济阳坳陷斜坡带油气运聚影响的实验模拟

通过二维模拟实验探讨了断层物性和倾角变化对济阳坳陷斜坡带油气运聚的影响, 结果表明: ①断层物性的差异影响着油向各砂层运移的动力。由于物性的变化, 使各砂层与断层之间的毛细管力差发生变化。断层物性较差时, 毛细管压力差对油的运移起动力作用, 有利于油运移; 断层物性较好时, 毛细管压力差对油的运移起阻碍作用, 不利于油运移。②断层倾角的差异影响着油向各砂层运移的动力。由于倾角的变化, 使浮力在各砂层的分力发生变化。断层倾角较小时, 浮力在各砂层分力大, 有利于油向各砂层充注; 断层倾角较大时, 浮力在各砂层分力小, 有利于油沿断层向上运移。③断层物性和断层倾角对油气运聚具有互补性。物性愈好、倾角愈大, 愈有利于油气向上部砂层中运聚; 物性愈差、倾角愈小, 上下砂层均有利于运聚。     

高邮凹陷北斜坡韦码地区阜宁组油气富集差异分析

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