Correction of water column height variation on 2D grid high-resolution seismic data using dGPS based methodology

Variations in the physical properties of water column usually impede exact water column height correction on high-resolution seismic data, especially when the data are collected in shallow marine environments. Changes in water column properties can be attributed to variation in tides and currents, wind-generated swells, long and short amplitude wave-fronts, or variation in salinity and water temperature. Likewise, the proper motion of the vessel complicates the determinability of the water column height. This study provides a less time-consuming and precise differential Global Positioning System based methodology that can be applied to most types of high-resolution seismic data in order to significantly improve the tracking and quality of deduced geological interpretations on smaller depth scales. The methodology was tested on geophysical profiles obtained from the German sector of the North Sea. The focus here was to identify, distinguish and classify various sub-surface sedimentary structures in a stratigraphically highly complex shallow marine environment on decimeter small-scale. After applying the correction to the profiles, the sea floor, in general, occurs 1.1 to 3.4 m (mean of 2.2 m) deeper than the uncorrected profiles and is consistent with the sea floor from published tide corrected bathymetry data. The corrected seismic profiles were used in plotting the depth of the base of Holocene channel structures and to define their gradients. The applied correction methodology was also crucial in glacial and post-glacial valley features distinction, across profile correlation and establishing structural and stratigraphic framework of the study area.

Karst Water Pressure’s Varying Rule and Its Response to Overlying Strata Movement in Coal Mine

Karst water is widespread throughout China and is heavily influenced by complex geological conditions, and floor inrush of karst waters associated with coal seams is the second most common coal mine disaster in China. Due to the limitation of precision and cost of geophysical exploration technology, the volume and pressure of karst water are challenging to measure, especially during the mining process. Therefore, predicting karst pressure’s response to mining is critical for determining the mechanism of water inrush. Here, closed karst water pressure (CKWP) response to mining was studied in an innovative physical simulation experiment. In the simulation experiment, a capsule and a pipe were designed to reflect CKWP and the water level. In the experiment, the vertical stress and karst water level were monitored throughout the process of an advancing coal panel. Monitoring results show that the range of the abutment pressure was about 40 cm, and the peak coefficient value was about 2. When the working face is far away from the water capsule, the stress and water column near the water capsule have no obvious change. With the working face 10 cm from the water capsule, the stress and water column height increased significantly. When the working face was right above the water capsule, the stress and water column rose sharply and reached the maximum value. When the working face advanced beyond the water capsule, the stress and water column height declined. Through establishing a structural mechanics model, the karst water system underneath the working face is assumed to be a hydraulic press. Accordingly, the compressed area was assumed to be a piston. The karst water pressure increases sharply, while the piston is compressed, increasing water inrush risk. This discovery may help determine the water inrush mechanism from a novel point of view.

A novel numerical modelling of well-aquifer response induced by pressure disturbance

<p>Under hydrostatic conditions, the water level observed in a well is often supposed to be equivalent to the pressure head in the surrounding aquifer. When the aquifer is subject to disturbing processes and activities, fluctuations of water level can be observed. Generally, the measured water level in the well is often considered to be less than the pressure head in the aquifer due to wellbore storage and skin effects (Ramey et al., 1972). In fact, there is another factor that can suppress or enhance the oscillating water level, which is termed the amplification effect (Cooper et al., 1965). Related studies point out that this effect is affected by well geometry (e.g. well diameter, water column height and well screen length), aquifer properties (e.g. transmissivity and storativity) and the period of the disturbed pressure head (Kipp, 1985; Liu, 1989). However, previous studies have obvious divergences in quantifying the amplification effect.</p><p>In this work, we firstly established an idealized fluid model to simplify the complex solid-fluid coupling process, aiming to discuss the influence of different well geometry parameters on the amplification factor separately, such as the well diameter, water column height and well screen length. Subsequently, we built a well-aquifer coupling numerical model to study the well-aquifer response induced by disturbed pressure based on the finite element method. Simulations of 125 scenarios showed that the amplification factor gradually increased until it reached a peak, and then decreased to 1 as the period of disturbed pressure became larger. The corresponding period of an amplification factor peak was significantly influenced by the water column height, which controlled the position of an “optimal period”. Aquifer properties can also affect the amplification factor, especially its peak value. In further numerical studies, more complicated scenarios will be investigated, considering different types of wells and aquifers.</p>

Effects of surface loading on groundwater flow and skeletal deformation

This paper proposes a relationship for the physics and mechanics constants of porous media related to water storage rate and ground settlement under a surface load variation condition. This provides the basis for accurate calculation of ground subsidence. Traditional equations for vertical deformation, groundwater flow and land subsidence due to surface loading were developed using Jacob's assumptions. This paper derives a skeletal elastic specific storage rate. The new deformation and flow equations are similar to the traditional ones based on Jacob's assumptions except that the pore-water head in the traditional equations corresponds with the margin between the pore-water head and the water-column height given in the proposed equations representing the surface load. The analysis show that increasing the surface loading leads to land subsidence, rise in pore-water head and decrease in elastic water storage capacity. The maximum subsidence is equivalent to the subsidence triggered by lowering the water head to the equivalent water column height. The maximum rise of the water head is also equal to the equivalent water column height. The maximum water released to a specific volume of porous medium is close to that resulting from reduction in the water head by the equivalent column height.

Experimental Analysis of Solar Driven Multi-Stage Stepped Bubbler Humidifier for Humidification-Dehumidification (HDH) Water Desalination System

The fresh water is the essence of life and its scarcity is the most threatening concern for mankind. To alleviate the worries of the existing and approaching fresh water crisis, the answer for water sustainability may lie in developing the decentralized small-scale water desalination system. Solar humidification-dehumidification (HDH) is a carrier gas based thermal technique that is ideal for a small-scale decentralized water desalination system. An innovative design approach is to use the bubble column humidifier to enhance the performance of the HDH water desalination system. Therefore, a novel multi-stage stepped bubble column humidifier is proposed that is operated through solar thermal energy as the main source of energy input. The study addresses the relation between the pressure drop variations with varying water column height at different air superficial velocities. Findings revealed that the water column height and air superficial velocity should be optimized according to the geometric features of the perforated plate in order to achieve a higher humidifier performance with a lower pressure drop. The day round performance of the humidifier is investigated in single stage, two stage, and three stage configurations. Findings show that the average day round absolute humidity at the exit of the humidifier is increased by 9 % in two-stage and 23 % in three-stage configurations compared to the single stage humidifier. One major advantages of this proposed humidifier is its ability to have a direct solar thermal heating. Subsequently, it can be located in remote areas.

Analytical Method of Water Column Height in Liquid Loading Gas Well

The real-time and accurate analysis of water column height becomes the crucial step for measures of unloading flow is taken effectively to make sure gas well to work continuously and properly. Although the early researchers made a number of models used to calculate water column height, but they are the static calculation method and can not meet production requirements. This paper analyses the hydraulics of well-bore load-up for gas well, and present a computing method of transient water column height. This model based on node pressure analysis, and combined with pressure gradient formula of multiphase pipe flow and productivity equation of gas-water wells. Application of this technology allows real-time analysis to be used in production process, which is valuable in protection of gas reservoir and enhancement of ultimate recovery.