页岩气井组分比例变化规律研究

页岩气开发过程中,生产井产出气的组分比例会随时间发生变化.本文基于组分模型数值模拟研究了生产井中甲烷组分比例变化的规律.研究表明,吸附气、渗透率与孔隙度影响页岩气组分比例的瞬态响应特征. 吸附气显著影响组分比例的变化规律,吸附量的大小决定组分比例的变化值及组分比例导数曲线的上下位置. 渗透率影响组分比例初期变化规律,但在后期,不同渗透率对瞬态组分比例规律的影响基本一致.孔隙度对组分比例变化及其导数曲线的影响与吸附气的影响类似,但在生产初期,孔隙度对组分比例的影响要小于吸附气对组分比例的影响. 本文的研究提供了一种进行页岩地层参数评价的新方法.      

裂缝性低渗透油藏流固耦合渗流分析

在低渗透油田的开发过程中，油藏流体渗流和储层岩土之间存在明显的耦合作用。本文首先研究给出了低渗裂缝性储层孔渗参数的等效方法，然后将渗流力学和岩土力学相结合，给出了低渗透裂缝性储层流固耦合渗流的数学模型，该模型不仅可以反映基质孔渗参数在开发中的变化，而且更能反映裂缝开度变化所引起的渗透率变化，而这对于低渗透裂缝性油田而言十分重要。最后对一实际井网进行了流固耦合油藏数值模拟，给出了开发过程中孔渗参数的变化及其耦合效应对油田开发的影响．     

利用三维网络模型研究滞留聚合物微观分布规律

再利用地下滞留聚合物是聚合物驱之后进一步提高原油采收率的新途径。基于油水两相流网络模拟模型,综合考虑聚合物渗流机理建立起聚合物驱微观模拟模型。用微观数值模拟手段研究了地下滞留聚合物分布规律及影响因素,为有效地开采聚合物驱后剩余油、合理利用滞留地下聚合物提供必要的依据。模拟结果表明,由于吸附和捕集作用将引起大量聚合物滞留在孔喉中,滞留聚合物占注入聚合物的61.7%。总体上看,大孔喉中聚合物滞留量较大,但滞留聚合物浓度较小。孔喉半径和形状因子为聚合物滞留的主要影响因素,孔喉滞留聚合物浓度与孔喉半径和形状因子平方根的乘积成反比。     

多孔介质非线性渗流问题的摄动解

考虑变形多孔介质渗透参数(渗透率和孔隙度)与孔隙压力呈负指数变化的特点，建立了多孔介质渗流问题的数学模型，采用积分变换方法求出了一维非线性渗流问题的摄动解，并对常数渗透参数和指数渗透参数的渗流问题进行对比分析，计算结果表明：两者之间的差别较大，且渗透参数的变化对于流体渗流中后期过程有着重要的影响，但对渗流早期影响不大，这对于定量研究工程中非线性渗流问题模型参数的相对重要性提供了可靠的理论依据。     

分子模拟在非常规油气开发中的应用

非常规油气资源储量丰富,具有广阔的开发前景.我国低渗/特低渗油藏以陆相沉积为主,储层特征差异性大,孔喉细小,孔隙度低,可动原油气大量储集于亚微米孔隙中,开采难度大,采收率低.岩油界面微观力学作用和限域传质力学机理是其中的关键科学问题.近年来,分子模拟技术在非常规油气开采的研究领域已经成为一种重要的研究手段.本文介绍了分子模拟的基本原理,然后给出了非常规油气藏储层流体和基质的组成及分子模型,并探讨了分子模拟在非常规油气开发中的应用及相关研究进展.     

无胶结材料的离散元微观参数交互作用研究

为研究无胶结材料离散元参数之间的交互影响,采用抗转动模型进行三轴排水试验模拟。首先,采用完全试验设计方法和析因试验设计方法,分别对宏微观参数相依规律以及参数之间的交互作用进行定性分析;然后,采用多元非线性回归分析方法对其进行定量分析,并提出了考虑交互作用的宏微观参数换算理论公式。着重探讨了无胶结材料微观参数中的刚度比α=k_s/k_n(0.3~0.9)、滚动刚度系数β(0.1~3)、颗粒内摩擦角θ(10~40)、法向接触刚度k_n(1×10~7~7×10~7)以及塑性弯矩系数η(0.1~3)与材料宏观力学性质峰值应力σ_p、残余强度σ_r、弹性模量E、泊松比ν以及内摩擦角φ之间的相关关系。研究结果表明,(1)颗粒材料的宏观强度参数主要受颗粒内摩擦角以及抗转动参数影响,而其变形参数主要由颗粒接触刚度及接触刚度比控制;(2)各个微观参数之间就存在不同程度的交互作用,且交互作用对试样宏观性质将产生一定影响;(3)对峰值强度、残余强度和宏观内摩擦角而言,两抗转动参数之间以及抗转动参数与颗粒内摩擦角之间存在较强交互作用。对于宏观弹性模量和泊松比而言,颗粒接触刚度和颗粒接触刚度比与其他微观参数产生较强的交互作用。研究成果对合理科学地确定离散元模型的微观参数具有一定的指导意义。     

基于孔与裂隙网络模型的平行微裂隙对驱油的影响规律研究

认识双重多孔介质中油水两相微观渗流机制是回答形成什么类型的裂隙网络可提高油藏采收率的关键. 微裂隙的分布可以提高多孔介质的绝对渗透率,但对于基质孔隙中的流体介质,微裂隙的存在会引起多孔介质中局部流体压力和流场的变化,导致局部流动以微裂隙流动为主,甚至出现窜流现象,降低驱油效率. 本文基于孔与裂隙双重网络模型,在网络进口设定两条平行等长且具有一定间隔的微裂隙,分析微裂隙的相对间隔(微裂隙之间距离/喉道长度)和微裂隙相对长度(微裂隙长度/喉道长度)对于微观渗流特征的影响. 结果表明:随微裂隙相对长度的增加,出现驱油效率逐渐降低,相对渗透率曲线中的油水共渗区水饱和度和等渗点增加,油水两相的共渗范围减小等现象;随着微裂隙之间相对间隔增大,周围越来越多的基质孔穴间的压力差减小,在毛管压力的限制下,驱替相绕过这些区域,而导致水窜现象.      

基于孔与裂隙网络模型的平行微裂隙对驱油的影响规律研究

认识双重多孔介质中油水两相微观渗流机制是回答形成什么类型的裂隙网络可提高油藏采收率的关键.微裂隙的分布可以提高多孔介质的绝对渗透率,但对于基质孔隙中的流体介质,微裂隙的存在会引起多孔介质中局部流体压力和流场的变化,导致局部流动以微裂隙流动为主,甚至出现窜流现象,降低驱油效率.本文基于孔与裂隙双重网络模型,在网络进口设定两条平行等长且具有一定间隔的微裂隙,分析微裂隙的相对间隔(微裂隙之间距离/喉道长度)和微裂隙相对长度(微裂隙长度/喉道长度)对于微观渗流特征的影响.结果表明:随微裂隙相对长度的增加,出现驱油效率逐渐降低,相对渗透率曲线中的油水共渗区水饱和度和等渗点增加,油水两相的共渗范围减小等现象;随着微裂隙之间相对间隔增大,周围越来越多的基质孔穴间的压力差减小,在毛管压力的限制下,驱替相绕过这些区域,而导致水窜现象.     

页岩有机质纳米孔隙气体吸附与流动规律研究

页岩储层孔隙结构复杂, 气体赋存方式多样. 有机质孔隙形状对受限空间气体吸附和流动规律的影响尚不明确, 导致难以准确认识页岩气藏气体渗流机理. 为解决该问题, 本文首先采用巨正则蒙特卡洛方法模拟气体在不同形状有机质孔隙(圆形孔隙、狭长孔隙、三角形孔隙、方形孔隙)内吸附过程, 发现不同形状孔隙内吸附规律符合朗格缪尔单层吸附规律, 分析了绝对吸附量、过剩吸附浓量、气体吸附参数随孔隙尺寸、压力的变化, 研究了孔隙形状对气体吸附的影响. 在明确不同形状有机质孔隙内气体热力学吸附规律基础上, 建立不同形状有机质孔隙内吸附气表面扩散数学模型和考虑滑脱效应的自由气流动数学模型, 结合分子吸附模拟结果研究了不同孔隙形状、孔隙尺寸有机质孔隙内吸附气流动与自由气流动对气体渗透率的贡献. 结果表明, 狭长孔隙内最大吸附浓度和朗格缪尔压力最高, 吸附气表面扩散能力最弱. 孔隙半径5 nm以上时, 吸附气表面扩散对气体渗透率影响可忽略. 本文研究揭示了页岩气藏实际生产过程中有机质孔隙形状对页岩气吸附和流动能力的影响机制.      

水对砂岩纵横波速及弹性参数影响的实验研究

水对含不同黏土矿物油气储层的纵横波速以及弹性参数有很大影响。为研究此影响,在相同条件下制作了三组(黏土成分分别为蒙脱石、伊利石和伊利石/蒙脱石混合)不同黏土含量(体积分数)的人造泥质砂岩岩样,并先后在常态、饱和及干燥三种状态下进行了纵横波速测量,在人工岩样黏土填隙分布模型下计算了孔隙度。首先,通过结合临界孔隙度模型和Gassmann模型,验证了人工岩样实验数据的合理性;然后,确定了影响岩样波速及弹性参数的主要因素,并在主要因素控制下对比分析了常态、干燥态岩样的纵横波速及剪切模量和体积模量。结果表明:对于含伊利石岩样,水对纵横波速及弹性参数影响较小,且孔隙度越大影响越小;对于含伊蒙混合岩样,水的影响较大,浸泡水后岩样纵横波速及弹性参数均明显变小,说明蒙脱石吸水膨胀后其内部微观孔隙不能被忽略。     

考虑材料设计变量的热-固耦合结构的优化设计

从材料-结构协同设计的角度研究了热-固耦合结构的优化设计问题,将决定结构材料性质的细观参数与结构宏观几何参数作为设计变量,利用均匀化方法推导了细观设计变量灵敏度显式计算式,并结合耦合场有限元方程构造了耦合场设计变量灵敏度计算式;提出了材料-结构协同设计的三种优化设计模型.利用结构响应最小优化模型对算例进行了计算,比较了宏观设计变量优化和材料-结构协同设计优化的效果.计算结果显示,材料-结构协同优化设计可以取得较单一宏观设计变量更好的优化效果.     

Pore-throat size correlation from capillary pressure curves

Void spaces in porous media can be considered as three-dimensional networks consisting of bulges (pores) connected by constrictions (throats). Computer simulations of drainage-imbibition processes show that the critical end points of wetting-phase and nonwetting-phase saturation, in drainage and imbibition respectively, and the form of simulated relative permeability curves all were significantly different for uncorrelated and correlated pore-throat models. Since these models were identical except for the arrangement of throats in relation to pores, the degree of pore-throat size correlation appears to be an important property influencing flow and fluid displacement. Examples of uncorrelated and correlated pore-throat structures in rocks are presented and it is shown that this property, although difficult to quantify by direct observation, can be evaluated from capillary pressure curves.     

Permeability of Porous Media from Simulated NMR Response

Nuclear Magnetic Resonance (NMR) is an increasingly popular well-logging tool in petroleum industry because it is the only tool that attempts to estimate formation permeability. In this paper, spatially correlated porous media are generated. Permeabilities of these media are computed by the lattice Boltzmann method. NMR relaxation responses are simulated by a random walk technique and formation factors are computed by solving a Laplacian equation. The testing of commonly used NMR permeability correlations shows that three conditions should be met for the validity of these correlations. The surface relaxivity should not vary significantly. The formation factor should depend only on porosity. And the characteristic pore body radius should be proportional to the characteristic throat radius. The correlations are improved by including surface relaxivity and formation factor.     

Prediction of Porosity and Permeability of Caved Zone in Longwall Gobs

The porosity and permeability of the caved zone (gob) in a longwall operation impact many ventilation and methane control related issues, such as air leakage into the gob, the onset of spontaneous combustion, methane and air flow patterns in the gob, and the interaction of gob gas ventholes with the mining environment. Despite its importance, the gob is typically inaccessible for performing direct measurements of porosity and permeability. Thus, there has always been debate on the likely values of porosity and permeability of the caved zone and how these values can be predicted. This study demonstrates a predictive approach that combines fractal scaling in porous medium with principles of fluid flow. The approach allows the calculation of porosity and permeability from the size distribution of broken rock material in the gob, which can be determined from image analyzes of gob material using the theories on a completely fragmented porous medium. The virtual fragmented fractal porous medium so generated is exposed to various uniaxial stresses to simulate gob compaction and porosity and permeability changes during this process. The results suggest that the gob porosity and permeability values can be predicted by this approach and the presented models are capable to produce values close to values documented by other researchers.     

The Sensitivity of Tracer Concentration to Nonuniform Permeability and Porosity

Concentration of tracer at a producing well is a function of time and of the flow field that transports the tracer from one well to another. Small localized changes in the permeability and porosity fields result in small changes in the observed concentration history. Calculation of the effect of changes in the petrophysical parameter fields on observed concentration is an integral part of most approaches to solving the inverse problem, i.e. calculation of permeability and porosity fields that are consistent with observed tracer concentrations. This paper does not address the inverse problem directly, only the forward problem, but the results are presented as semi-analytic formulas which are intended to provide physical insight into the limitations of the inverse procedure. In particular, for a simple example of dipole flow between two wells in a nearly homogeneous infinite 2D porous medium, the width of the region of significant influence is shown to scale as d where is the dispersivity and d is half the interwell distance. Also, for fixed injection and production rates the influence on concentration of variation in porosity and in log-permeability are shown to be similar in magnitude.     

Assessment of Stimulated Area Growth During High-Pressure Hydraulic Stimulation of Fractured Subsurface Reservoir

Hydraulic stimulation is performed by high-pressure fluid injection, which permanently increases the permeability of a volume of rock, typically transforming it from the microdarcy into the millidarcy range. After a period of stimulation, fluid injection and recovery boreholes are introduced into the stimulated rock volume, and heat is extracted by water circulation. In the present study a simplified mathematical model of non steady-state hydraulic stimulation is proposed and analyzed. Fluid flow is assumed to be radial, injected flow rate constant; and fluid density, rock porosity, and permeability depend on fluid pressure. The conventional boundary of the growing stimulated rock volume is introduced as a surface where the porosity and permeability of the stimulated rock exhibit a sharp decline and remain constant within the undisturbed area. The problem is solved analytically by a modified method of integral correlations. As a result, approximate close-form solutions for pressure distributions in the stimulated and nonstimulated (undisturbed) areas are obtained, and an equation for the moving boundary of the stimulated volume is derived. The correctness of the approximate solution is validated by comparison to an exact self-similar solution of the problem obtained for the particular case when the well’s radius is assumed to be equal to zero.     

Correlation of Water Vapor Permeability with Microstructure Characteristics of Building Materials Using Robust Chemometrics

This paper studies various microstructure parameters of natural and artificial building materials and aims to their correlation to the water vapor permeability. Three categories of building materials were investigated: stones, bricks, and plasters. Mercury intrusion porosimetry was applied in order to obtain the materials microstructure characteristics, a variety of pore size distributions and pore structure measurements, such as total porosity. The water vapor permeability of materials was determined experimentally according to ASTM standard E96-00. A robust principal component regression approach, coupled with multiple outlier detection, was applied in order to correlate water vapor permeability values to pore size distributions. A good quality correlation model was found by utilizing relative specific pore volume and relative specific pore surface distributions, whereas using pore structure measurements, such as total porosity, the correlation results were very poor. From the results, specific ranges of pore size distribution, corresponding to pores radius sizes greater than $10\,\upmu \text{ m }$ 10 μ m and between 1.778 and $0.421\,\upmu \text{ m }$ 0.421 μ m , contribute to the water vapor permeability of the materials.     

Possibility of determining the quality of well perforation by local acoustic probing

A theoretical problem of local acoustic probing of a perforated segment of the well is considered. The effect of porosity and permeability of the porous medium surrounding the well and the quality of perforation (porosity, length, and radius of perforation channels) on the velocity and the coefficient of decay of harmonic waves and on the evolution of finite-duration waves propagating in the perforated segment is studied. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 50, No. 1, pp. 52–57, January–February, 2009.     

气液非混相驱替过程中的卡断机理及模拟研究

研究气液非混相驱替过程中的相界面卡断机理及其影响因素在气驱, 气水交替及泡沫驱等提高油气采收率领域具有重要意义. 本文在原始伪势格子玻尔兹曼模型的基础上, 改进流体-流体作用力格式, 添加流-固作用力, 耦合RK状态方程, 并采用精确差分方法将外力添加到LBM框架中. 通过校准模型的热力学一致性以及模拟测试界面张力, 静态平衡接触角及液相在角隅的滞留等一系列两相体系验证模型的准确性. 基于改进的伪势格子玻尔兹曼模型, 在孔-喉-孔系统中开展气液非混相驱替模拟, 结果表明: 卡断现象与驱替压差, 孔喉长度比及孔喉宽度比有关, 只有当驱替压差处于一定范围内时, 气液两相驱替过程中才会发生卡断现象; 当驱替压差大于临界驱替压差上限时, 即使达到了经典静态准则所预测的卡断条件, 卡断也会被抑制; 当驱替压差小于临界驱替压差下限时, 无法克服毛管“钉扎”作用, 形成无效驱替. 对于固定孔喉宽度比的孔-喉-孔结构, 随着孔喉长度比的增大, 发生卡断现象的驱替压差范围增大; 对于固定孔喉长度比的孔-喉-孔结构, 随着孔喉宽度比的减小, 发生卡断现象的驱替压差范围增大.