Land subsidence and uplift related to groundwater extraction in Wuxi, China

Wuxi City is located in the Yangtze River Delta region, China and is underlain by a multi-layered aquifer system in porous Quaternary deposits. Groundwater extraction, mainly from the second confined aquifer, has led to severe regional land subsidence. The ground surface started to recover after the restriction and, ultimately, the banning of groundwater pumping. This paper reports the results of long-term surveys, groundwater piezometric head (GPH) measurements and the monitoring of ground surface deformation by levelling and borehole extensometers. The subsidence is attributed to the compression of both the aquifer and aquitards in the porous strata. The spatial characteristics of subsidence are related not only to the distribution of the GPH, but also to the thickness and compressibility of different strata, the distance from the pumped aquifer and the distribution of pumping. There was a temporal lag in subsidence relative to groundwater drawdown. The uplift is related to a period of recovery following the peak pumping period and groundwater recovery subsequent to the restriction and/or banning of groundwater pumping. The uplift was <10 mm under these two conditions, although the GPH recovered to >40% of the previous maximum at the Qianzhou borehole extensometer station.

Entropy Analysis for MHD Generalised Couette Flow in a Composite Duct

This paper presents entropy analysis of electrically conducting Newtonian fluid flow inside a horizontal composite duct. The upper impermeable wall of the duct moves with a uniform velocity while the lower wall is porous strata of finite thickness with impermeable bottom. The upper wall and the impermeable bottom are at constant temperature but at different temperatures. The duct is divided into two regions: Region I of clear fluid and Region II of fluid saturated porous layer. Momentum and thermal regimes for clear and porous regions are matched at clear fluid-porous interface by employing suitable matching conditions. The governing equations are solved analytically. Analytical solutions obtained for velocity and temperature are utilized to compute entropy generation. The effects of pertinent parameter on temperature distribution, entropy generation, and Bejan number are portrayed graphically and discussed.

Nitrogen cycling on the livestock farm

The environmental or polluting aspects of nitrogen in relation to livestock farms are gaseous losses to the atmosphere, nitrate leaching into water supplies and the eutrophication of surface waters. Gaseous losses of ammonia by volatilisation from organic materials and denitrification losses from soil as nitrogen and nitrous oxide have been at various times implicated in acid rain, photochemical smogs and effects on the ozone layer although the latter is now largely discounted. Nitrate leached from soil may pass rapidly into surface waters where it can affect quality for drinking or encourage algal blooms. Over porous strata nitrate may take many years to percolate downwards so as to pollute groundwater supplies. Restrictions may face livestock farmers in the arable areas of eastern England to restrict nitrate leaching from their land.

Transient Response of Nonhomogeneous Aquifers

Many investigators have used the response of the "dimensionless aquifer" to a unit pressure drop or a unit fluid-withdrawal volume to calculate the performance of an aquifer in supplying water influx to an oil reservoir. In the past, these response functions have been calculated with the aid of the Laplace transform. With the advent of ultra high-speed digital computers, it becomes practical to solve for the response functions with finite-difference techniques. The computer method also permits extension of the dimensionless-aquifer concept to include the nonhomogeneous aquifer wherein the permeability and other properties vary as a function of the space co-ordinates. This paper gives results of calculating the response functions for a series of nonhomogeneous aquifers. Response functions are presented for both linear and radial aquifers whose thickness, permeability-viscosity ratio and porosity-compressibility vary. These functions are new and should prove useful to the petroleum engineer in analyzing the behavior of nonhomogeneous aquifers. Results are presented in the form of charts that can be easily used by the field engineer. Introduction Aquifers which surround many oil and gas reservoirs have the ability to supply water influx to such reservoirs as oil and gas are withdrawn. This water influx, called natural water drive, provides one of the most effective driving mechanisms for the production of oil and gas. In producing a reservoir, therefore, it behooves one to make the maximum use of natural water drive. To achieve the maximum use, the reservoir engineer must be able to predict the performance of an aquifer under a variety of production schemes that may be proposed for the reservoir. Unfortunately, the physical properties which dictate aquifer behavior often are known only within limits. Seldom do wells penetrate the porous strata of the aquifer.

CONSIDERATIONS ON THE VERTICAL MIGRATION OF GASES

The vertical migration of a perfect gas saturated with aqueous vapor is studied with a view toward determining what effect it may have on the porous strata through which it passes. It is found that evaporation of water and the consequent concentration of minerals may occur at certain depths. Further, it is pointed out that the cooling due to the evaporation of water and the expanding gas may be a contributing factor in the appearance of geothermal anomalies. Suggestions for further study are included.