The influence of litho-stratification on the infiltrating water front in a granite terrain

Abstract

Under a sustainable groundwater development and quality management project over a semi-arid granite terrain, several rainwater harvesting structures were proposed based on geophysical investigations in the study area. In order to validate the site suitability and check the efficacy of the recommended recharge structures in terms of source sustainability, certain hydrological tests, such as infiltration studies, were conducted within the recharge area of these structures. Infiltration rate estimation using a double-ring infiltrometer normally results in an exponential decay relationship with high initial infiltration rate followed by gradual reduction until, ultimately, a stabilized rate is attained. In this paper, we present the results of infiltration tests conducted using a double-ring infiltrometer (under constant head condition) within the tank bed area of a proposed percolation tank site. The results showed unique features in the infiltration rate at different time intervals within the total experimental period: a staircase-like evolution with intermittent stabilization for a short duration. Based on the integrated approach of geophysical investigations, hydrological tests, and supported by physical evidence, the infiltration behaviour observed over the study area was considered to be due to the lithological stratification with different permeability and textural conditions.

Citation Andrade, R. & Muralidharan, D. (2011) The influence of litho-stratification on the infiltrating water front in a granite terrain. Hydrol. Sci. J. 56(5), 907–915.     

Power law statistics of cliff failures,scaling and percolation

Large cliff failures have often been characterized by their size in terms of the horizontal eroded area at the cliff top, and the maximum local retreat of the coastline. Field studies suggest that the frequencies of these two quantities decrease as power laws of their respective magnitudes, defining two different decay exponents. Moreover, the horizontal area increases as a power law of the maximum local retreat, identifying a third exponent. This observation indicates that the geometry of cliff failures are similar for different magnitudes. It is shown that, under a ‘scaling hypothesis’, the exponents satisfy a precise mathematical relation that relates the exponent of the distributions of magnitudes of events and their geometry – a relation that could be useful to validate the analysis of field catalogs. In order to understand the observed scenario, a numerical model of rocky coast erosion is developed. Despite its minimal character, it reproduces the observed cliff failure statistics. Strikingly, the model precisely reproduces the geometric similarity of cliff failures observed in the field. These results suggest that the theory of percolation, which underlies the erosion model, can possibly be used as a guide to decipher the physics of rocky coast erosion and could provide precise predictions of the statistics of cliff collapses. Copyright © 2015 John Wiley & Sons, Ltd.     

致密气储层孔喉分形特征及其与渗流的关系--以鄂尔多斯盆地下石盒子组盒8段为例

选取鄂尔多斯盆地盒8段16块致密砂岩样品进行恒速压汞测试,结合同位样品核磁共振实验,分析了致密气储层孔喉分布特征;在此基础上,运用分形几何原理和方法,开展了致密气储层孔喉分形研究,并表征了分形与储层渗流特征和孔隙结构参数的关系。结果表明:致密气储层有效孔隙被亚微米-微米级孔喉所控制,其中孔隙主要为大孔和中孔,喉道由微喉道、微细喉道和细喉道所组成;致密气储层孔隙分布不具分形特征,而孔喉整体和喉道则符合分形结构,且分别对应分形维数D₁和D₂;基于储层孔喉分形结构与其渗流特征,将盒8段致密气储层孔喉分形结构划分为2种类型:Ⅰ型表现为阶段式分形特征,以进汞压力1 MPa为界,大于1 MPa孔喉具有分形特征,且储层阶段进汞饱和度主要由喉道贡献,反之,孔喉不符合分形特征,其进汞饱和度增量由孔隙贡献;Ⅱ型为整体式分形,进汞饱和度几乎全由喉道贡献。储层孔喉分形维数与渗透率、平均喉道半径和主流喉道半径存在较好的负相关性,与微观非均质系数呈现较明显的正相关性,而与孔隙度、平均孔隙半径和平均孔喉半径比之间没有明显的相关性。     

基于CT的数字岩心三维建模

为研究储层微观孔隙结构和建立微观渗流模型,本文通过对东营凹陷沙三中亚段H152井区的典型低渗透储层岩样进行CT（computed tomography）扫描及图像处理,建立了微观尺度的数字岩心模型;继而经过对该模型进行分析和计算,提取了储层孔喉网络模型,在三维空间上直观、清晰地显示了不同尺度的孔隙及喉道的形态、大小和分布;最后通过对孔隙结构特征、孔隙度、渗透率和压降等动静态参数的分析和计算,建立了储层岩样的微观渗流模型。根据算法对比和参数分析结果认为：与传统中值滤波相比,非局部均值滤波算法可在相似性比较的基础上进行滤波处理,从而提高模型的准确性;基于CT的数字岩心建模可为地质研究提供可靠的数字模型;根据近似等压面假设的微观渗流数值模拟分析了流体渗流特征,为揭示低渗透储层流体渗流规律提供了一种新的途径。     

鄂尔多斯盆地靖边－绥德地区古生界天然气运移和聚集的数值模拟

本文用二维盆地模拟方法研究鄂尔多斯盆地靖边－绥德地区古生界天然气的运移和聚集。在数值模型中，天然气的运移由渗流和扩散两种运移形式组成。模拟结果表明，研究区古生界天然气的运移以渗流运移为主、扩散运移为辅。以早白垩世末期燕山运动后幕为界，运移期大体上可分为两个阶段。由此，形成了研究区各井的三种不同的运移聚集史。     

遥感油气勘探对伊犁盆地的评价

遥感油气勘探技术是通过遥感影像的构造解译及烃类微渗漏信息的提取并结合其他地质资料，对目标区进行油气有利聚集区的预测及评价。利用这一勘探技术着重对伊犁盆地的构造特性、承压盆地、构造阶地、烃类微渗漏信息等进行了解译和提取，总结出伊犁盆地油气藏预测的九大要素，确定了３条油气聚集带和１４个油气远景区。     

水工建筑物岩溶渗漏问题综述

岩溶区水工建筑渗漏问题，与岩溶发育特征及其规律有密切关系，文拟从岩溶水动力循环条件，岩溶的立体空间配置，岩溶陷落等几个方面，对岩溶区的水库渗漏问题加以阐述。     

Effect of depression storage capacity on overland‐flow generation for rough horizontal surfaces: water transfer distance and scaling

Overland‐flow triggering on rough surfaces was investigated using an understanding‐oriented model. The model was based on conditioned‐walker technique and developed to simulate and analyse the evolution of puddle connection on numerically generated rough surfaces. The percolation theory gave a theoretical framework to formalize model outputs and to study overland‐flow scaling. Overland‐flow triggering appeared consistent with a percolation process. A scale‐change exponent was suggested. New insights based on the concept of transfer distance of water were emphasized. Transfer distance enabled us to analyse the water redistribution inside a field and helped to define rainfall efficiency when infiltration occurred. Copyright © 2002 John Wiley & Sons, Ltd.     

西北地区水库土石坝渗流隐患探地雷达图像特征分析

通过西北黄土地区水库土石坝渗流隐患探地雷达探测实践,从渗流部位的土体扰动、空隙比、含水量的变化入手,分析探地雷达波形特征变化、波形同相轴连续性的变化,总结了渗流隐患不同时期的探地雷达图像特征。