页岩基质解吸-扩散-渗流耦合实验及数学模型

采用川南地区龙马溪组页岩样品,设计了页岩基质解吸-扩散-渗流耦合物理模拟实验,揭示了页岩基质气体流动特征以及压力传播规律.推导了页岩气解吸-扩散-渗流耦合数学模型并且利用有限差分法对数学模型进行数值求解,与实验结果相比较表明该数学模型能够很好地描述气体在页岩基质中的流动规律.同时对页岩基质气体流动的影响因素进行了分析,认为页岩基质的渗透率、扩散系数、解吸附常数等因素均能影响页岩基质气体的流量和压力传播规律,在页岩气藏的开发过程中需要考虑这些参数的影响,该数学模型为页岩气井产能计算提供了更准确的计算方法.      

页岩气藏渗流机理及压力动态分析

针对页岩气藏的特点,分析国内外对解吸、扩散等数学描述方法,建立三种机理作用下的渗流数学模型:①考虑有机基质表面解吸,解吸气和游离气共同窜流的数学模型;②考虑有机基质解吸和扩散的数学模型;③考虑有机基质中的气体解吸、扩散,以及无机基质中气体窜流综合作用的数学模型.运用点源函数方法,得到模型的基本点源解,对点源解作积分变换得到垂直压裂井、压裂水平井两种开采方式下的地层压力解,绘制出三种机理影响下的压力动态曲线,并从渗流机理上分析曲线特征以及不同曲线存在差异的原因.     

井筒气液两相流对致密气压裂水平井试井的影响

多段压裂水平井技术是目前开采致密气最常用的方法之一,在致密气压裂水平井试井测试中常常伴随着一定的产水量,井筒气液两相流会增加井筒流体的流动阻力,加大井筒流体流动对试井解释的影响.为了明确井筒气液两相流对致密气藏压裂水平井试井的影响,提高产水致密气压裂水平井的试井解释精度,建立了一种井筒气液两相流与地层渗流耦合的试井模型,采用数值方法对模型进行求解,获得了考虑井筒气液两相流的压裂水平井试井理论曲线、压力场分布及裂缝产量分布.研究结果表明:井筒气液两相流会增加试井理论曲线中压力和压力导数值,造成靠近入窗点的压力扩散要快于远离入窗点的压力扩散,引起靠近入窗点的裂缝产量要高于远离入窗点的裂缝产量.现场实例分析进一步说明,不考虑井筒两相流可能会对产水压裂水平井的试井解释结果产生很大误差,主要表现为水平井筒假设为无限大导流能力会使得拟合得到的表皮系数偏大,将测试点视为入窗点会使得拟合得到的原始地层压力偏小.所建立的考虑井筒两相流的压裂水平井试井模型为产水致密气井试井资料的正确解释提供了重要技术保障.      

径向积分边界元法确定非均质土石坝渗流自由面

浸润面位置的确定是无压渗流分析中非常重要的问题,本文将径向积分边界单元法应用到渗流问题中,通过直接将区域积分转化为边界积分的技术,克服了传统边界元解决该类问题的缺陷,编写了迭代计算程序,并用二、三维算例证明了算法的有效性。     

Capillary-gravity waves in the presence of infinite porous plates

Summary The wave motion generated by a porous plate immersed in a non-wetting liquid of infinite depth is investigated. The boundary value problem for the velocity potentials is solved using Taylor's assumption on the plate and a contact-line condition that accounts for the dynamic variation of the angle of contact and the vorticity there. The amplitude of the radiated waves and the energy dissipated are calculated both when the plate is oscillating horizontally and vertically with a prescribed velocity. Also the scattering of a harmonic wave incident normally to the plate is considered and the reflexion and transmission coefficients are obtained.     

Mechanisms of Enhanced Oil Recovery by Surfactant-Induced Wettability Alteration

Different measurements were conducted to study the mechanisms of enhanced oil recovery (EOR) by surfactant-induced wettability alteration. The adhesion work could be reduced by the surfactant-induced wettability alteration from oil-wet conditions to water-wet conditions. Surfactant-induced wettability alteration has a great effect on the relative permeabilities of oil and water. The relative permeability of the oil phase increases with the increase of the water-wetness of the solid surface. Seepage laws of oil and water are greatly affected by surfactant-induced wettability alteration. Water flows forward along the pore wall in the water-wet rocks and moves forward along the center of the pores in the oil-wet rocks during the surfactant flooding. For the intermediate-wet system, water uniformly moves forward and the contact angle between the oil–water interface and the pore surface is close to 90°. The direction of capillary force is consistent with the direction of water flooding for the water-wet surface. While for the oil-wet surface, the capillary force direction is opposite to the water-flooding direction. The highest oil recovery by water flooding is obtained at close to neutral wetting conditions and the minimal oil recovery occurs under oil-wet conditions.     

Transport of Reacting Solutes Through the Unsaturated Zone

Unsaturated flows within subsurface regions control many large-scale hydrological and environmental processes. This contribution presents and discusses the results of numerical calculations dealing with the flow of water, the chemical reaction at the water-mineral interface and the transport of chemical species caused by such flows. The source of the water flow through the soil is solely the rainfall. The water motion is calculated for two different soil classes and for a typical annual precipitation. The codes which were used are based on the following model: The transport of chemical species is described by a set of partial differential equations, and the homogeneous chemical processes, under the assumption of equilibrium, are described by a set of nonlinear algebraic equations. The source terms of these partial differential equations are given by rate laws of the chemical weathering. Rainfall and chemical weathering are, therefore, the sources of the transport of reactive multispecies in this model.     

The analysis of groundwater flows in unconfined aquifers with nonuniform hydraulic conductivity

Horizontal groundwater flows in unconfined aquifers with horizontal lower boundaries can be found exactly by the seepage analysis that allows the hydraulic conductivity to vary in the vertical direction. The exact analysis of flows when the lower boundary of the aquifer is not a horizontal plane, requires the soil-water pressure on this boundary to be known, and this is not generally the case except in the situation of a freshwater aquifer overlying saline water fed from the sea. For aquifers with spatial variations of hydraulic conductivity in both the vertical and horizontal directions, the seepage analysis can be modified to give groundwater flows in situations where the hydraulic conductivity can be represented by the product of independent functions of the three spatial coordinates. Different forms of three-dimensional variation are generated from suitably chosen functions. The use of such forms in calculations of equivalent uniform hydraulic conductivities of some groundwater flow regions demonstrates the dependence of equivalent hydraulic conductivity values on the flow boundary conditions. The exact groundwater flows calculated for particular groundwater situations by the seepage analysis provide results that are useful in validating numerical methods for solving groundwater problems in heterogeneous soils.     

等参元逆变换算法在渗流—位移耦合场分析中的应用

在渗流 -位移耦合场分析中应用等参元逆变换算法解决了两个场之间的数据传递问题 ,所提出的逆变换算法是基于解析性质的新算法 ,具有简便、高效和高精度的特点 ,便于在实际工程中应用。     

工程水文地质学及其在水电工程中的应用概述

工程水文地质问题产生于人类工程活动与地质环境中岩土体和地下水之间的相互制约和相互作用过程中,由于问题本身的复杂性,目前对这类问题的研究尚处于相对分散的单一研究状态,缺乏系统的从地质机制分析到地质模型抽象,进而由模拟再现到发展趋势预测以及治理措施论证的全过程研究。本文在系统分析、总结水电工程中水 -岩和水 -工程建筑的作用类型及特征基础上,认为可能出现的工程水文地质问题主要是;水库诱发地震、岩溶渗漏、库岸及高边坡的稳定、坝基、坝肩抗滑稳定、枢纽区深层承压水问题等。