Analytical model for tracer transport in reservoirs having a conductive geological fault

Geological faults are frequently found in oil reservoirs and their presence dramatically impacts the underground fluid motion. Tracer tests provide a mean to dynamically characterize the conduit or barrier behavior of the fault. Although diverse analytical models have been developed to describe tracer transport in a geological conductive fault, only few of them capture the fact that injection and production wells are regularly located outside the fracture plane. In many cases, the tracer path length outside the fault structure is significant. In this work the system is represented by three coupled regions associated to the injector-to-fault, fault, and fault-to-production-well zones. The coupling is simplified by considering linear flow and aligned regions. This model includes hydrodynamic dispersion, an important phenomenon not considered in previous work. One-dimensional advective–dispersive tracer transport is assumed in each region. Border conditions require tracer mass conservation. The initial condition is a Dirac delta pulse at the injection site. The equations are analytically solved in Laplace space and the inverse transform is evaluated numerically by the Stehfest algorithm. Four specific cases have been studied; they comprehend a long and a short fault path length having low or high dispersivity respectively. The pulse behavior and the tracer breakthrough curve, as well as their sensitivity to fault dispersion, fault length and fault fluid velocity are analyzed. Clear differences in the pulse profile and breakthrough curve shape are found in relation to the case when no fault is present.     

Double-porosity model for tracer transport in reservoirs having open conductive geological faults: Determination of the fault orientation

Conductive geological faults in oil reservoirs have a major impact in the efficiency of fluid-flooding and enhanced oil recovery schemes. Inter-well tracer tests are a traditional mean to determine underground communication channel properties, and therefore have the potential to estimate fault features. In this work an analytical model is developed to describe inter-well tracer tests in reservoirs with open conductive faults. Specifically, a fault that intersects the flow path between the injection and production wells without reaching them is treated. In open faults fluid can be exchanged along the fault to external regions. In addition, the present model captures two new relevant aspects of the process: (i) the fault region is a fractured media, and (ii) a Danckwert's discharge condition is established at production well. To treat open faults a new source-coupling scheme is designed for linking the three independent path regions in which the system is discomposed. The first region comprehends the path from the injector to the fault, the second represents the zone along the fault, and the third one the path from the fault to the production well. The involved coupled advection-dispersion equations are analytically solved by the Laplace technique and numerically inverted. There are twelve parameters in the model; from them five concern the fault properties. By exploring their effect on the tracer breakthrough curve it is found that the curve is mainly sensitive to the tracer fault path length and the fault fluid velocity. The two factors describing the fracture-matrix coupling become important only when the fluid velocity in the fault is relatively low. No relevant sensitivity is found on the fault dispersivity. An outstanding attractive feature of the new model is its capacity to determine the fault orientation, which is not possible by the standard characterization means. The model has been successfully applied to data from a real reservoir tracer test performed in Loma Alta Sur Field. Here, the orientation of two faults have been determined.     

Averaging model for cuttings transport in horizontal wellbores

This paper presents a theoretical analysis of the problem of cuttings transport for a two-region system composed of a fluid bed (ω-region) and a stationary bed of drill cuttings, which is considered as a porous medium (η-region) in the two-phase system. The ω-region is made up of a solid phase (σ-phase) dispersed in a continuos fluid phase (β-phase), while the η-region consists of a stationary solid phase (σ-phase) and a fluid phase (β-phase). The volume averaging method was applied in this study. Volume-averaged transport equations were derived for both the fluid bed and the porous medium regions. These equations are based on the non-local form of the volume-averaged momentum transport equation that is valid within the bounded region. Outside this region, the non-local form reduces to the classic volume-averaged transport equation. From these equations, a one-equation model was obtained, and the constraints that the one-equation model must satisfy were applied. For estimating the averaged pressure drop and the averaged velocity, the one-equation model was solved numerically by using the finite-difference technique in the implicit scheme. Numerical results are in agreement with experimental data and theoretical results reported in the literature.     

用遗传算法求解广义S形增长模型

广义S形增长模型在用于预测油气田累积产量和含水率方面功能显著,但该模型是具有多个未知参数的非线性模型,常规求解方法存在的不足可能会造成计算精度变差,从而影响预测效果。以累积产油量广义S形增长模型的求解为例,说明了采用遗传算法求解的方法和效果。遗传算法可提高求解的精度,是求解广义S形增长模型的较好方法。     

埋地管道小泄漏模型及数值求解

随着全国范围的天然气管网逐渐形成,管道运行安全管理的重要性日益突出。在气体单相渗流理论的基础上,结合高速非达西渗流理论,建立了埋地管道发生穿孔小泄漏后在土壤中渗流的数学模型。利用有限体积法对控制方程做离散,以三对角阵（TDMA）和交替方向隐式线迭代法（ADI）对离散方程进行求解。结合实验研究,得到了适用于地表土壤的高速非达西渗流系数经验公式和土壤变形压力修正公式。采用该修正公式计算得到的压力分布与实验结果吻合较好,证明了数值模型的正确性。     

一种快速计算溶解油气比的工程实用方法

天然气在原油中的溶解度是评价油气溶解性的重要参数之一,在工程上需查取图版而得到,结果不够准确、使用不太方便,不适于现场快速应用。为了便于在实际工程中快速准确地计算该参数,在雷萨特的模型上将美国石油协会相对密度与脱气原油摩尔质量的图版进行取点拟合成函数关系,结合原雷萨特关系式将其数学模型归纳推理得到一个新模型,只需要代入绝对压力、温度、脱气原油对水的相对密度以及天然气对空气的相对密度4个已知参数,通过计算机便可快速计算出溶解油气比。研究结果表明:①较之于雷萨特相关式,新模型简化了繁琐的迭代,不仅可以一步到位计算溶解油气比,而且还可以从公式中反映出各个参数是如何影响溶解油气比的;②油气比随着绝对压力的增大而增大、随着温度的增大而减小、随着脱气原油对水相对密度的增大先增大后减小、随着天然气对空气相对密度的增大而减小。结论认为,新模型可以快速、准确地计算出溶解油气比,其计算结果与原雷萨特模型符合度高;新方法提高了工程上计算溶解油气比的效率及准确性,可以推广使用。     

裸眼系列完井方式下鱼骨井产量模型求解方法

为了向鱼骨井完井方案设计提供必要的理论参考依据,建立了鱼骨井产量稳态耦合模型,以裸眼系列完井方式为核心内容,以微元段法为求解手段,定量阐述完井筛管对耦合流动过程的影响,得到了鱼骨井流压分布剖面和流率分布剖面。经分析认识到,完井筛管管外环形空间储层砂堆积层产生的渗流附加压降影响了油藏渗流,井筒流压和流率分布剖面相对于裸眼完井整体下降,影响程度主要取决于储层砂粒度中值和筛管挡砂精度,同时也受到渗流干扰作用的局部控制;完井筛管尺寸、管壁质量交换效应以及基管孔眼参数影响了井筒管流,使得全生产井段井筒流压分布剖面相对于裸眼完井更加陡峭。通过与经典产量解析模型对比计算,证明了本文模型的合理性。     

莺歌海盆地砂质块体搬运沉积及其天然气聚集

通过莺歌海盆地XF13区三维地震、钻井资料分析,新识别出上中新统黄流组一段砂质块体搬运沉积体系,进而研究其沉积模式及优质天然气聚集机制。钻井岩心以砂质碎屑流沉积为主,发育块状层理、平行层理、突变接触面、泥岩撕裂和变形层等重力流沉积构造;地震资料上其与围岩差异显著,呈"削截"接触关系。砂质块体搬运沉积由多期构成,每期经历"早期侵蚀-充填迁移"和"晚期废弃"2个沉积阶段,相应发育近物源砂质碎屑流、块状厚层砂岩朵叶体和远物源泥质浊流、席状砂的沉积构型。构建了外陆架、海侵-高位体系域砂质块体搬运沉积新模式。以XF13大气田为例,从砂质块体搬运沉积、构造-岩性圈闭的形成到输导体系和天然气成藏过程分析,探讨了优质天然气聚集机制,认为莺歌海盆地中深部具备形成"优质储集体、高烃类气"天然气聚集的地质条件。     

封闭结构模型建立方法

在地震勘探中，模型正演技术广泛应用于地震资料的采集、处理和解释的各个环节，模型正演技术的基础是建立正演地质模型。本文提出封闭结构建模方法，以具有相同速度、密度属性的介质为单元，由包围它的界面组成封闭结构，彼此相连的封闭单元构建成具有封闭结构特性的地质模型。封闭结构模型同层状结构模型相比，最大优点是可以有效地描述任意复杂的地下地质结构。本文首先介绍了层结构模型的特点，然后描述了二维和三维封闭结构模型的拓扑关系，并给出了相关的数学处理方法。     

二维层状模型的快速三分量合成

对层状介质模型中的多分量波场传播进行简单分析及某些简化后,提出了三分量记录合成的快速近似算法。该算法使用射线追踪计算传播时间,应用波场界面方程计算反射振幅。由于采用了快速射线追踪算法及一些有效的简化,使该算法计算速度很快,一般模型在 AST 386微机上生成三分量记录仅需十几分钟至数十分钟。     

二维起伏层状模型的纵横波AVO模拟

本文采用快速射线追踪算法和平面波在反射界面上的反射和透射系数计算公式,模拟二维起伏界面层状模型的横波(包括P-P、P-SV、SV-SV、SV_P和SH_SH)的振幅随炮检距(AVO)的变化。该方法原理简单、计算速度快,可用于叠前振幅分析和反演,以及指导地震数据采集(特别是转换波采集)观测系统的设计。     

炮眼剪切对注入聚合物溶液粘度影响的数学模型

把聚合物溶液在炮眼处的流动过程看作是在一个变截面管道中先收缩后扩张的流动过程,在聚合物溶液经过等径圆管时的表观粘度模型的基础上,推导了炮眼剪切对聚合物溶液粘度影响的数学模型,分析了炮眼半径、炮眼密度和聚合物的注入量对聚合物溶液粘度在炮眼附近地层中分布的影响。计算结果表明:炮眼半径对聚合物溶液表观粘度的影响主要集中在聚合物进入炮眼的瞬间,炮眼半径既影响表观粘度大小的分布,又影响表观粘度的变化幅度,炮眼半径越小,聚合物溶液的表观粘度越小,表观粘度降幅越大;聚合物的注入量和炮眼密度对聚合物溶液表观粘度的影响都集中在注入井的中心位置,炮眼密度和聚合物的注入量只影响表观粘度大小的分布,炮眼密度越小或者注入量越大,聚合物溶液的表观粘度越小。     

二元混合表面活性剂在孔隙介质中流动时色谱分离的预测模型

为了增强表面活性剂的驱油效果,往往采用混合表面活性剂的复配体系进行驱油。但这种体系通过孔隙介质时,因其吸附能力的差异以及在油、水相中分配的不同而发生色谱分离。考虑到混合胶束行为、各种类型的吸附等温线以及在油、水中的分配等物理化学过程,给出了一个描述这一复杂过程的数学模型。该模型的预测结果与细管实验结果相吻合,较好地描述了色谱分离的实际过程。该模型可以用来预测三次采油中采用的二元混合表面活性剂在油藏中的色谱分离过程,因而可作为选择驱油体系的工具。     

A prediction model for a new deep-rod pumping system

The side-flow pump is presented for increasing the setting depth of sucker rod pumping system, which adopts a special structure of side-flow valve, ladder-type solid plunger and breathing hole. By transferring the load of liquid column to the tubing on the upstroke, the new pump achieves a smaller polished rod load. On the basis of in-depth study of the pump, this paper provides a brief formula of the static polished rod load. Assuming the tubing is anchored, a new one-dimensional vibration model of sucker rod pumping system is built, which takes into account the structure of the side-flow pump. Then a mathematical model is used to design the sucker rod pumping system of Well TKN-1, with a setting depth of 4716 m. The results of dynamometer analysis show that mathematical model of side-flow pumping system and its computer programs can successfully model deep rod string performance. The rod pumping system of Well TKN-1 has operated trouble-free for 8 months. The knowledge gained gives confidence for additional future applications.     

定向井中靶分析的圆弧模型及其解析解

建立了预测井眼轨迹为空间圆弧曲线的中靶分析几何模型,并得到了该模型的解析解,为中靶分析提供了一种新的计算方法。所建立的圆弧模型及求解方法可应用于定向井井眼轨迹控制和中靶质量评价等。     

Using foam in horizontal well drilling: A cuttings transport modeling approach

Foam is a frequently used compressible fluid in drilling applications. Cuttings transport with foam has been a focus of interest for years. Few studies have been conducted on vertical well configuration and successfully applied. However, less is known about the performance of foam in highly inclined and horizontal wells. In this study, a layered model is developed for describing cuttings transport in horizontal wells. Due to the presence of a cuttings bed, generalized rheological model parameters for foam are modified analytically as a function of fluid properties and complex conduit geometry. Using these parameters, friction between the fluid and the wellbore, between the layers and slip between the cuttings and the fluid are determined. Model performance is examined using experimental data established at The University of Tulsa's low pressure-ambient temperature flow loop. Results showed that, developed model can predict developed cuttings bed thickness and pressure loss in the wellbore with an error of less than 20%. It has been observed that very high foam flow velocities are required in order to prevent a thick bed development in the wellbore. Also, low-viscosity fluids show better performance on preventing bed development inside the wellbore than high-viscosity fluids at the same flow rates.     

复杂地质条件气藏储气库库容参数的预测方法

国内复杂地质条件气藏型地下储气库经过10余周期注采后工作气量仅为建库方案设计工作气量的一半,运行效率偏低。为此,利用气藏地质、动态及建库机理,建立了地下储气库注采运行剖面模型,根据气藏开发、气藏建库及稳定注采运行过程中纵向上流体的分布特征及其变化趋势,将地下储气库剖面分成4个区带(建库前纯气带、气驱水纯气带、气水过渡带及水淹带);按区带确定了影响建库有效孔隙体积的主控因素(储层物性及非均质性、水侵和应力敏感)及其量化评价方法,进一步考虑束缚水和岩石形变的影响,并引入注气驱动相,根据注采物质平衡原理建立了气藏型地下储气库库容参数预测数学模型。该模型涵盖了地质、动态及建库机理,从微观和宏观角度综合评价了影响建库空间的主控因素,大大提高了预测结果的准确度和精度,使建库技术指标设计更趋合理,目前已广泛应用于中国石油天然气集团公司气藏型地下储气库群的建设当中。     

页岩气纳米孔气体传输模型

页岩气纳米孔气体传输模型是准确进行页岩气数值模拟的基础,对页岩气经济开发具有重要的意义。页岩气纳米孔气体传输机理包括纳米孔体相气体传输和吸附气表面扩散,而纳米孔体相气体传输机理包括连续流动、滑脱流动和努森扩散。基于滑脱流动和努森扩散两种传输机理,分别以分子之间碰撞频率和分子与孔隙壁面碰撞频率占总碰撞频率的比值作为滑脱流动和努森扩散的权重因子,将这两种传输机理叠加,建立了纳米孔体相气体传输模型。基于Hwang模型,考虑高压条件下吸附气覆盖度的影响,建立了纳米孔吸附气表面扩散模型。结合纳米孔体相气体传输和吸附气表面扩散模型,建立了页岩气纳米孔气体传输模型,并采用分子模拟和实验数据进行了验证。结果表明:①滑脱流动、努森扩散和表面扩散对气体传输的贡献是此消彼长的,其主要受孔隙尺度和压力的支配。②滑脱流动在介、宏孔(半径> 2 nm)和高压条件下,对气体传输贡献大;在微孔(半径≤2 nm)和低压条件下,其贡献小,可忽略。③努森扩散在宏孔(半径> 50 nm)和低压条件下,对气体传输贡献不可忽略,在其他条件下均可忽略。④表面扩散在微孔(半径≤2 nm)和全压力范围内,总是主宰了气体传输;当孔隙半径> 25 nm和压力高于1 MPa时,表面扩散贡献可忽略;当孔隙半径在2~25 nm和压力低于5 MPa时,表面扩散贡献较高,不能忽略。     

一种改性淀粉溶液在多孔介质中的流动及对提高采收率的影响

为了提高聚合物驱用于非均质性较强油藏开发的采收率,对一种可溶性改性淀粉MS在岩心表面的吸附滞留能力及其对提高采收率的影响进行了实验研究。研究结果表明:MS在Berea岩心上有较强的吸附滞留能力,具有较高的残余阻力系数;MS能较多地进入并吸附在高渗透层,可有效改善注入流体的波及面积,增大流体在低渗透层的流动性;MS能够较大幅度地提高后续水驱采收率。     

水平井泡沫分流酸化数学模型及其数值解法

由于钻井过程中钻井液对储层的伤害,水平井的产能受到影响。酸化是一种常用的水平井增产措施,常规酸化存在地层进酸不均的问题;而泡沫酸化能有效地封堵高渗透储层,提高低渗透储层的渗透性,达到更有效的酸化增产效果。通过研究泡沫流体在水平井段流动和在油藏中的渗流特性,建立了水平井泡沫分流酸化数学模型,并对模型进行求解,得到了沿水平井段酸液的流量和压力的变化关系,以及沿水平井段流入地层泡沫酸量的变化规律。结果表明,沿水平井段流入地层的酸液量变化不大。因此,泡沫酸化能够解决地层进酸不均、解堵不均的问题,提高酸液利用效率,均匀改善受污染储层,提高受污染储层的渗透性,达到良好的均匀酸化的效果。