Slot In Screen Research Articles

Field, laboratory, and modeling investigation of the skin effect at wells with slotted casing, Boise Hydrogeophysical Research Site

Understanding and quantification of wellbore skin improves our ability to accurately measure or estimate hydrologic parameters with tests at wells such as pumping tests, flowmeter tests, and slug tests. This paper presents observations and results from a series of field, laboratory, and modeling tests which, together, explain the source of wellbore skin at wells at a research wellfield and which support estimation of skin thickness ( d s) and skin hydraulic conductivity ( K s). Positive wellbore skin effects were recognized at wells in the shallow, unconfined, coarse-grained fluvial aquifer at the Boise Hydrogeophysical Research Site (BHRS). Well development efforts at the BHRS removed residual drilling fines but only marginally reduced the skin effect. Likely causes for the remaining wellbore skin effect were examined; partial clogging of screen slots with sand is consistent with field observations and can account for the magnitude of wellbore skin effect observed. We then use the WTAQ code ( Barlow and Moench, 1999) with a redefinition of the term for delayed observation well response to include skin effects at observation wells (in addition to pumping wells) in order to analyze aquifer tests at the BHRS for average K s values at individual wells. Systematic differences in K s values are recognized in results at pumping ( K s_Q) and observation ( K s_obs) wells: larger values are seen at observation wells (average K s_obs=0.0023 cm/s) than pumping wells. Two possible causes are recognized for the occurrence of higher K s values at observation wells than pumping wells: (1) flow diversion between aquifer layers on approach to a pumping well with positive skin; and (2) larger portion of flow passing through lower-K zones in the heterogeneous aquifer near the pumping well than the observation wells due to strongly radially convergent flow near the pumping well. For the well-aquifer system at the BHRS, modeling analyses of drawdown vs time at observation wells provide better K s estimates than those from pumping wells.

Influence of Pump Intake Location on Well Efficiency

We tested the influence of pump intake location on well efficiency using three intake locations—one above the screen, as recommended by current well design guidelines, and two in the screen. Testing was done in a semicircular physical model of a well with a screen, casing, and gravel pack. The experiments used three screen slot sizes, two sand sizes, and average screen entrance velocities from 0.18 to 0.55 m/s. For the finer sand, experimental results indicated that placing the pump intake at both positions in the screen increased well efficiency; the lowest intake position was generally the most efficient. For the coarser sand, the lowest intake position was also the most efficient; the intake position above the screen and the higher intake position in the screen produced similar, and lower, well efficiencies. These results indicate that the common practice of placing the pump intake above the screen may lead to less efficient well designs. The physical model also showed that the hydraulic head distribut...

Slot antenna in a resistive screen

The loss resistance and efficiency are calculated for a slot in a resistive screen and for the complementary dipole. Double numerical integration of the magnetic near field is used. The strip dipole loss resistance is three to five times that of the complementary slot for short elements.

Efficiency of solid particle screening as a function of screen slot size, particle size, and duration of screening The theoretical approach

The theoretical dependence of the separation efficiency on the physical data of the screen and the duration of the screening operation as well as on the relationship between particle size and slot dimensions is discussed on the basis of a phenomenological approach, the problem being solved with a deterministic and probability model. The statistical exponents of the particle distribution according to size and the statistical precision of the manufacture of screen holes (“slots”) was taken into account. Difficulties in particle separation and screening, despite small differences in size, are defined. The application of the results obtained to the selection of the appropriate screen and to the construction of the screening network of the separation machine is discussed.

流体生産に伴う出砂と抑制に関する基礎的研究

When producing fluid from an unconsolidated sandstone reservoir or producing fluid with high viscosity such as an oil sand, sand production may cause well damage and reduce production rate. Therefore sand control is a very important factor for an efficient and economical fluid production in the above situation.This paper discussed experimental results on mechanical sand control methods with a screen (wire gauge) or gravel (glass beads) obtained through one dimensional flow model that visualized sand grain movement. Following conclusions were obtained.(1) Sand production could be controlled by a screen having a larger slot width than sand grain size. This was because the sand bridge was formed on screen slot surface.(2) The maximum screen slot width was four or five times larger than the 50 percentile sand grain size.(3) It was observed that there existed an optimum screen width which could control sand and keep minimum pressure loss in laminar or turbulent flow respectively.(4) It could be noted that screen (wire gauge) could control sand better than gravel (glass beads) from our experimental results.

A Simple Theory For Estimating Well Losses: With Application To Test Wells In Bangladesh

A set of formulae are presented that can be used to estimate total well losses when flow into the well is uniformly distributed along its screen. The components of well loss included are: aquifer loss due to partial penetration and non-Darcian flow, loss in the gravel pack, loss through the screen slots, frictional loss in the well casing, and (in particular) loss inside the well screen due to both momentum and frictional loss. The formulae are used to estimate the coefficients of nonlinear well loss for experimental wells constructed in Bangladesh: the values obtained are in good agreement with values determined from step tests on those wells.

Laboratory Testing of Filters and Slot Sizes for Relief Wells

Results of a laboratory experimental program conducted to evaluate three different criteria for the selection of the required screen slot width for gravel pack relief wells are presented. A widely graded filter is used in conjunction with continuous slot screen sections based on the D20 size and the D50 size of the filter. A third test involves a uniform filter with a continuous slot screen section based on the D10 size of the filter. The two filters are compared in terms of (1) Entrance head losses; (2) amount of material entering the screen; and (3) effective radius of the well. The investigation indicates that all three systems result in minimal entrance head losses at the screen. The largest loss of filter material occurs in the well designed with the D50 size of the filter. A larger effective well radius is obtained using the widely graded filter. The conclusion applies to conditions shortly after the well is installed and does not consider changes in entrance losses after clogging of well screens an...

Effect of Pod Maturity and Plant Age on Pod and Seed Size Distributions of Florunner Peanuts

Abstract Florunner peanut pods (Arachis hypogaea L.) were sampled at nine weekly intervals from 92 to 148 days after planting (DAP) in crop year 1979. The fresh pods were divided into six maturity categories according to the color and structure of the mesocarp. After drying, individual pods and seed for each maturity class and date were sized over a series of screen slots conforming to official grade standards. The cumulative distribution function (CDF) for the logistic distribution was used to quantify the cumulative percentage by weight of pods and seed which rode a designated screen. The parameters of the logistic CDF were regressed separately by maturity class as functions of plant age. These relationships provide a mathematical approach for a better understanding of the influence of pod maturity and plant age on pod and seed sizes.

Types and Usages of Drilling Fluids Utilized to Install Monitoring Wells Associated with Metals and Radionuclide Ground Water Studies

AbstractEvaluation for metal and radionuclide contamination associated with selected inactive uranium mill tailings repositories required the installation of monitoring wells in both shallow unconfined and deep artesian aquifer systems. To prevent ionic exchange between the dissolved cationic metals and the cations in bentonitic drilling fluids, organic‐based fluids were used during the drilling and installation of monitoring wells. Experience gained at three western U.S. sites involving inactive uranium mill tailings indicates organic drilling fluids can be used to advance drill holes in soil materials ranging from saturated silts and fine sands to unsaturated gravels. However, it has been determined that certain types of these organic fluids can clog very narrow screen slots and remain present in well discharge, even after several hours of well cleaning. Certain types of organic drilling fluids appear to be preferable for these types of water chemistry studies.

Experiments to Assess the Hydraulic Efficiency of Well Screens

ABSTRACTThe hydraulic properties of commercial well screens were investigated to determine which screen design features affected head loss. The test program began with laboratory experiments and continued as a field‐scale experiment with the installation of a well field in the Thames Valley Gravel Aquifer.The laboratory experiments indicated that, for all practical purposes, the head loss attributable to all of the screens tested was negligible. The experimental head loss, however, did vary from screen to screen, particularly at high intake velocities, and the screens could be ranked on the basis of their hydraulic efficiencies. This efficiency hierarchy is explained tentatively in terms of the screen construction methods and slot geometry. The field experiments showed that the hydraulic performance of all well screens is independent of screen design provided that the open area of the screen is above about 10%. The field experiments also indicated that the development capacity of a screen in a gravel aquifer is not wholly dependent on screen design, but that progressive development does increase the hydraulic efficiency of a well.

Electromagnetic diffraction by a slot in a ground screen covered by a dielectric slab

An integral equation is formulated for the problem of transverse electric (TE) illumination of an infinite slot in a conducting screen situated between two dielectric slabs having different electromagnetic properties. Numerical results are given for the slot magnetic current for selected cases where a slab exists only on the shadow side of the screen. Far-zone magnetic fields are presented.

Fundamental Concepts of Well Design

ABSTRACTWell performance and production life can be enhanced greatly by proper design and operation. Using screen entrance velocity as the only design criteria is not sufficient for describing flow around the well, and in many cases leads to an overly optimistic design. Approach velocity and turbulence (Reynolds Number) are more direct concepts in regard to the factors influencing long‐term well efficiency, and their use as design criteria is strongly encouraged. In addition, sizing of screen slots and filter materials is haphazardly practiced by too many in the ground‐water industry, and requires a renewed awareness.Distribution of flow along the screen, as well as the vast number of aquifer conditions, are also factors to be considered during design. It is here that the judgement and practical experience of the hydrogeologist are most important.The fundamental design criteria are relatively simple to apply, and for the practicing hydrogeologist, the design process is aided by composite graphs. Several such design graphs are given for convenient reference.

General analysis of narrow strips and slots

The general problems of TE- and TM-excited slots in screens and conducting strips whose widths are narrow relative to the wavelength are investigated. The narrow width approximation is imposed upon the slotted-screen and strip equations from which result approximate equations that are solved exactly. For general excitation, solutions are presented for both polarizations as products of series of Chebyshev polynomials and appropriate singular functions exhibiting the known edge condition. Special attention is afforded the problem of the slot/strip excited by illumination which can be represented by two terms of a Taylor series due to the practical importance of this situation.

Static Screening of Feedlot Dipping Vat Solution

ABSTRACT USE of a Hydrasieve screen for suspended solids removal doubles the useful life of coumaphos feedlot cattle dip solution and reduces pesticide disposal requirements by 50 percent. The system produced a 13.5 cent/head savings to feedlot management and paid for itself in 7 months. The op-timum screening duration was 1 h per 1,000 head dip-ped, and the optimum screen slot size was 0.51 mm. Dry solids removal from the pesticide solution was 0.036 kg per head dipped.

Leaky modes in slotted semielliptical or semicircular waveguides

The characteristics of propagation of leaky modes in a semielliptical or semicircular waveguides with a slot radiating into half-space are investigated. The method of analysis is exact in that no infinite expansions in eigenfunctions are used. It is based on single mode representation of the field in the half-space and the waveguide with subsequent exact matching. Such modes can be used for the determination of radiation patterns of slots in infinite screens excited by semicircular guides.

Predicting Well Yields —

ABSTRACTTwo case histories are presented which illustrate that by analyzing drill cuttings or bailed samples, by knowing total depth of a test hole and position of the static water level, and by studying the driller's log, not only can a well's yield be predicted—but also drawdown may be predicted for any well in advance of a pumping test.The estimation of specific capacity (gpm/ft of drawdown) is invaluable in well design, particularly in the United States, where drilling contractors work rapidly and efficiently. Knowledge of probable specific capacity can aid in recommending proper screen length, diameter, slot width, and setting. It will enable cost estimates for proper pump size to be made, for casing requirements to be determined, and also for ultimate well diameter and depth to be determined. Test‐pump setting can also be anticipated.Case History No. 1 illustrates the above techniques, and how a new well was drilled, developed, designed, and completed adjacent to a poorly designed and equipped water well. The new well proved to be nine times more efficient (i. e., “better”) than the old well. Reasons for this improvement are shown, and the two wells are compared and contrasted.Case History No. 2 shows data from a constant‐rate pumping test following calculation of a well's specific capacity using estimates of aquifer permeability. Analysis of dynamic water‐level recovery measurements resulted in a transmissibility of 16,150 gpd/ft compared to an estimated 16,000 gpd/ft from a visual inspection of sand analysis grading curves. The well's specific capacity was estimated to be between 8.4 and 8.9 gpm/ft of drawdown. The measured specific capacity was 8.35 gpm/ft with an efficiency of 85 percent. Actual permeability was 230 gpd/ft compared to the estimated 228 gpd/ft2!Six figures are included showing well construction details, sieve analysis curves, a semi‐log plot of recovery measurements obtained during an aquifer pumping test, and graphic representations of approximate permeabilities for granular materials ranging from clay/silt to fine gravel. Six tables give characteristics of samples recovered from two test wells, permeability estimates of the disturbed samples, approximate permeabilities of various granular materials, and specific capacities for 100 percent effective water wells with varying diameters, coefficients of storage, and pumping periods. Three photographs further illustrate the principles enumerated.The methods described can give acceptable results (although they may not be as spectacular as the two detailed case histories) if sound judgement is used; if local conditions are somewhat known; if sampling methods are described; and if the procedures are not abused by expecting extreme accuracy. A reasonable estimate, or perhaps, just a close scientific “guesstimate” is all that should be hoped for by the hydrogeologist and his client in predicting well yields. But these techniques are a great advance over the“forked peach stick” philosophy still used for similar purposes by pseudo‐scientists in the United States and foreign countries (although no cases where a dowser or “water witch” has successfully predicted drawdown in addition to yield have come to the attention of the writer).The data in this report are derived from approximately 500 wells or more designed by the author in 26 States and in many locations abroad. Rather good success has been obtained regarding close correlation between estimated and measured specific capacities from a variety of geologic environments and aquifer parameters.