Slot In Screen Research Articles

Evaluating the screen performance in sand control design by laboratory sand retention test

To produce oil and gas from unconsolidated sandstone reservoirs, sand screens are necessary to control sand flowing from the formation into the wells, causing well pluggings. In open hole completion, stand-alone sand screen is an essential component to prevent sand production, thus, selection of suitable sand screens is critical to minimize sand production and optimize the well’s production life. 
 Nowadays, premium screens with steel meshes make the openings of the screen slots complex in shape, resulting in a very different effect of sand retention compared to the traditional screens. The sand retention test is considered a standard and must be conducted to select screen opening and size, which decides the sand prevention capacity of the screen. 
 The paper presents the factors affecting the results of laboratory sand retention tests and proposes solution in the direction of considering the data trend rather than relying completely on the output results. The paper also brings about the evaluation method through the change the screen’s permeability to have better qualitative results compared to the traditional methods.

Physical Experimentation and 2D-CFD Parametric Study of Flow through Transverse Bottom Racks

In the present study, the hydraulic operation of flow through transverse bottom racks screens with conventional triangular wedge wire and alternative circular section wire is experimentally and numerically analyzed. A laboratory prototype is built for experimentation with clean water and sediment. The numerical experiment is developed with the Ansys Fluent software, and a 2D CFD parametric study is designed to evaluate the influence on the captured flow of geometric variables, such as the screen incline, position of the screen along the channel (top, middle, bottom), and shape, wire width, or slot width. The physical model results make it possible to determine the efficiency of the screens in terms of collection capacity and sediment removal. In contrast, numerical experimentation determines the influence of geometric variables on the collection flow. The flows captured by each screen slot are determined numerically. The trends of the total flows captured are determined, and the performance of each studied screen type is assessed using the relevant non-dimensional parameters.

Laboratory testing of real-time flux measurements in fractured media

The In-Well Point Velocity Probe (IWPVP) was originally developed for use in screened porous media wells. The tool can characterize small-scale aquifer heterogeneity from wells that have been carefully developed to ensure an open screen and good hydraulic connection with the surrounding aquifer. This capability led to the hypothesis that the IWPVP could be adapted to characterize flow in fractured media, which features small-scale openings (i.e. fractures) that resemble screen slots. To test this hypothesis, a lab-scale fracture flow apparatus (FFA) was fabricated. The FFA consisted of two parallel acrylic plates that could be separated by a fixed distance, simulating a fracture with a known aperture. Two lengths of PVC well casing served as a cylindrical access port and were centrally placed in the plates. This mock-well left the interface with the fracture open – analogous to a fracture intersecting an uncased borehole. The probe was calibrated experimentally by relating known fluxes through the FFA with those measured inside the IWPVP. The ratio of these fluxes was found to be predictable for two aperture sizes (500 μm and 1290 μm), based on a flux balance and the Cubic Law. Additionally, the ability of the probe to discern flow direction in a fracture was tested and found to be accurate within ±20° under the conditions of the laboratory testing. The results suggest that an IWPVP could be reliably used in fractured media to directly measure horizontal flux and flow direction in a single fracture without reference to Darcy’s Law.

One-Dimensional Convolutional Neural Network with Adaptive Moment Estimation for Modelling of the Sand Retention Test

Stand-alone screens (SASs) are active sand control methods where compatible screens and slot sizes are selected through the sand retention test (SRT) to filter an unacceptable amount of sand produced from oil and gas wells. SRTs have been modelled in the laboratory using computer simulation to replicate experimental conditions and ensure that the selected screens are suitable for selected reservoirs. However, the SRT experimental setups and result analyses are not standardized. A few changes made to the experimental setup can cause a huge variation in results, leading to different plugging performance and sand retention analysis. Besides, conducting many laboratory experiments is expensive and time-consuming. Since the application of CNN in the petroleum industry attained promising results for both classification and regression problems, this method is proposed on SRT to reduce the time, cost, and effort to run the laboratory test by predicting the plugging performance and sand production. The application of deep learning has yet to be imposed in SRT. Therefore, in this study, a deep learning model using a one-dimensional convolutional neural network (1D-CNN) with adaptive moment estimation is developed to model the SRT with the aim of classifying plugging sign (screen plug, the screen does not plug) as well as to predict sand production and retained permeability using a varying sand distribution, SAS, screen slot size, and sand concentration as inputs. The performance of the proposed 1D-CNN model for the slurry test shows that the prediction of retained permeability and the classification of plugging sign achieved robust accuracy with more than a 90% value of R2, while the prediction of sand production achieved 77% accuracy. In addition, the model for the sand pack test achieved 84% accuracy in predicting sand production. For comparative model performance, gradient boosting (GB), K-nearest neighbor (KNN), random forest (RF), and support vector machine (SVM) were also modelled on the same datasets. The results showed that the proposed 1D-CNN model outperforms the other four machine learning models for both SRT tests in terms of prediction accuracy.

The influence of screening process parameters on paper properties produced from wastepaper

The influence of screening process parameters on paper properties produced from wastepaper. Wastepaper processing is of pivotal importance for environmental protection; it is also crucial for the economy and the management of raw materials. Not only does recycling save space at landfills, it also saves an extremely valuable raw material used for paper production, i.e. wood. Unlike primary pulps, however, wastepaper contains much more than just cellulose fibres and fillers. The fact that recycled paper contains many contaminants, such as metal staples, paper clips, plastic film, glass fragments, and others, makes it necessary to develop a much more complex pulp preparation systems compared to the ones used for primary pulps. Contaminants affect not only the usable quality of paper made of wastepaper, but also cause the wear and tear of paper processing equipment. Thus, the purifying and screening of secondary pulps for further processing is very important. Considering the above, the authors’ objective was to study the impact of the width of screen slots on paper properties if produced from screened wastepaper pulp. Paper strength and paper surface properties were used as the main evaluation criteria. White and mixed wastepaper was used as research material. Based on the tests, the screen slot width was found not to have any significant impact on either paper mechanical strength or paper surface properties.

New Concepts for Water Well Screen Opening and Gravel Pack Size

The purpose of the study to obtained well screens opening size and gravel packs size, and to access within the groundwater inter through the aquifer to the well screen and prevent running sand from entering the well. The use of properly designed screen and gravels are important and this paper is an important reference for the design of groundwater wells. In this study, the purpose of the circle method is to design water well and the benefits of sand control. The determination of screen slot size and its variation in the opening is often a major aim of hydrogeological studies. However, measurement of hydraulic conductivity (K) at a high spatial resolution in sedimentary aquifers is a challenge. One commonly used approach is to estimate slot size from grain size analysis. The objectives of this study are to compare between curve of grain size analysis, bar graph and circle method used applied different formulas for the determination of slot size from grain-size data and to evaluate how well this method predicts slot size and gravel pack. Correlation between the mechanical analysis curve, bar graph and the circle methods were found for the used applied different formulas. Based on circle results, the applied circle formulas appear to be suitable for an initial assessment of aquifer properties. However, considering the difference in calculated aquifer parameter values, results are smaller significantly and reliable for the high analysis of aquifer materials.

Hydrodynamic analysis of radial collector well ageing at Belgrade well field

The origin and effect of hydraulic resistances on the rate of ageing of radial collector wells are identified through numerical hydrodynamic analysis. The research includes hydrodynamic modeling of one such well with new laterals at Belgrade well field. The performance of the laterals is aggravated by rapid ageing. The change in the hydraulic parameters of the laterals during the first decade of operation is analyzed through simulations of the groundwater regime with realistically specified geometries and hydraulics of the laterals. Contrary to previous investigations, two genetically different types of clogging were identified. The initial hydraulic resistances are a result of colmation due to the gravel pack grain-sizes and screen slot sizes being mismatched with the sand and gravel sediments of the aquifer deposited at the depth of the laterals. Colmation affects the hydraulic performance of the laterals. Well ageing is aggravated by incrustation, caused by high iron concentrations in the captured groundwater. The research highlights a strong correlation between increasing resistances at the laterals, on account of iron precipitation, and groundwater entrance velocities at the laterals. It is possible to differentiate between colmation and incrustation and accurately define the increase in resistances at the laterals by specifying known thicknesses of the near-lateral screen zones and quantifying hydraulic conductivities of those zones. MODFLOW–USG code and Connected Linear Network Process package are recommended for simulating laterals and defining real rather than hydraulically equivalent characteristics of the laterals, as an approach to hydrodynamic investigations relating to radial collector wells.

Scattering by an Electrically Large Slot in a Rectangular Cavity

This paper presents a new approach to describe the scattering of an electrically large slot aperture between half-space and a rectangular cavity. The developed method generalizes known theories for the scattering of electrically small apertures and presents a general and understandable formalism for correctly calculating the induced scattering moments. The theory is first developed and validated for the electrically long thin wire in free space. Then, it is applied to describe the scattering of an electrically large thin slot in an infinite screen and backed by a rectangular cavity. The results can be used to determine the effects of external excitation, e.g., a high-power and wideband electromagnetic pulse, on the internal and external fields caused by the scattering slot. The external fields can also be analyzed for the internal resonances of the cavity.

Well-screen and well-head clogging by hydrous ferric oxides

In the production of drinking water from groundwater by aeration and rapid sand filtration (RSF), iron(II) may be removed in two ways: at pH > ~8 by homogeneous oxidation and precipitation, and at ~6.0 ~7) by development of HFO flakes resulting in minimal clogging of the screen slots, and at “low” pH (pH < ~7) by massive HFO precipitates and biomass resulting in extensive clogging of the screen slots. As HFO precipitation continues, both processes result in extensive well-head clogging, i.e. fouling of submersible pumps, collector lines, etc. While well-screen clogging may be monitored conveniently, no general method is available for monitoring well-head clogging. Recognition of both chemical clogging types is important for effective well construction, operation and maintenance. During rest, HFO precipitation processes continue, further blocking pumps and water lines. If a vertical hydraulic gradient is present over the height of the well screen, HFO precipitates may accumulate on the well screen and enter the aquifer. Consequently, the behavior of the well is important not only during operation, but also during rest. These findings are illustrated by numerous observations on well fields exploited by the drinking water utilities in the Netherlands.

Effects of ageing on the hydraulics of water wells and the influence of non-Darcy flow

Well ageing is mostly caused by mechanical and biogeochemical clogging processes, which affect the gravel pack, screen slots and casing. Clogging deposits increase head losses due to a constriction of the hydraulically effective area. For this study, clogging is mimicked by systematically reducing the gravel pack porosity, the screen open area and the nominal inner casing diameter. Groundwater flow velocity strongly increases close to the well, inducing inertial and turbulent flow components. Therefore, gravel pack head losses were calculated using the Forchheimer-Engelund equation, in conjunction with the Kozeny-Carman equation, which relates gravel pack porosity and hydraulic conductivity. Screen losses were assessed using the Orifice equation and turbulent casing losses with the Darcy-Weisbach equation. For the settings chosen here, a dramatic increase of head losses occurs when the clogging has reduced the effective porosity in the gravel pack by ~65%, the open area of the screen by ≥98%, and the casing diameter by ~50%. Since the latter two conditions are rarely reached in actual wells, the clogging of the gravel pack is the decisive parameter that controls well ageing. Regular monitoring of the well yield is therefore needed, since processes in the gravel pack are difficult to track directly. Unlike the deposits on the casing and in the screen slots, obstructions in the gravel pack are much more difficult to remove.

Chemical and mechanical clogging of groundwater abstraction wells at well field Heel, the Netherlands

Well field Heel, in the south east of the Netherlands, consists of a row of wells drilled in an anoxic pyrite-containing aquifer alongside a former gravel pit, which now serves as a recharge basin, where water is actively aerated. All wells are seriously affected by chemical (screen slot) and/or mechanical (well bore) clogging. The objective of this study is to explain this combined occurrence. A combination of chemical, hydraulic and well-maintenance data indicate three groundwater quality types: (1) oxic basin water, (2) anoxic iron-containing basin water after oxidation of the traversed aquifer, and (3) deeply anoxic native groundwater. Wells abstracting a mixture of oxic basin water and anoxic basin water and/or native groundwater experience chemical well clogging, whereas wells abstracting (only or partly) native groundwater are vulnerable to mechanical well clogging. In the end, after oxic basin water has completely oxidized the traversed the aquifer, only two groundwater quality types will be present. Wells abstracting only oxic basin water will show no clogging, and wells abstracting a mixture of native groundwater and oxic basin water will experience chemical and possibly also mechanical well clogging. In this reasoning, the sequence in abstracted groundwater quality types coincides with a sequence in well clogging: from mechanical to chemical to no clogging. As well field Heel is situated in sloping terrain, the interplay between regional hydraulic gradient and different water qualities results in one-sided chemical clogging in the upper part of the well screen during abstraction, and in the lower part during the resting phase.

Computationally efficient analysis of extraordinary optical transmission through infinite and truncated subwavelength hole arrays.

The authors present a computationally efficient technique for the analysis of extraordinary transmission through both infinite and truncated periodic arrays of slots in perfect conductor screens of negligible thickness. An integral equation is obtained for the tangential electric field in the slots both in the infinite case and in the truncated case. The unknown functions are expressed as linear combinations of known basis functions, and the unknown weight coefficients are determined by means of Galerkin's method. The coefficients of Galerkin's matrix are obtained in the spatial domain in terms of double finite integrals containing the Green's functions (which, in the infinite case, is efficiently computed by means of Ewald's method) times cross-correlations between both the basis functions and their divergences. The computation in the spatial domain is an efficient alternative to the direct computation in the spectral domain since this latter approach involves the determination of either slowly convergent double infinite summations (infinite case) or slowly convergent double infinite integrals (truncated case). The results obtained are validated by means of commercial software, and it is found that the integral equation technique presented in this paper is at least two orders of magnitude faster than commercial software for a similar accuracy. It is also shown that the phenomena related to periodicity such as extraordinary transmission and Wood's anomaly start to appear in the truncated case for arrays with more than 100 (10×10) slots.

Review: Hydraulics of water wells—head losses of individual components

Knowledge about the hydraulics of water wells is important to optimize their energy efficiency. By minimizing head losses around the well, energy consumption and ageing processes can be limited, thereby prolonging the well’s service life. The contribution of the individual components to total head loss (drawdown) in the well is analyzed in detail. The single most important contributor to drawdown is commonly the aquifer. Its hydraulic conductivity can only be improved slightly through development. The second most important contributor is the formation of a wellbore skin layer. This occurs if no proper well development was performed after drilling; the layer contains remnants of drilling-fluid additives or mobilized fine aquifer particles. The head loss caused by groundwater flow in the gravel pack, through the screen slots and inside the well, was found to be small. Thus, well development is the most important measure to influence well performance and energy efficiency. For longer operation times and pumped volumes, the energy gains outperform the cost for the development.

Experimental study of some factors affecting pulp screen capacity

Abstract The effect of screen cylinder geometry, pulp type, and rotor speed on screen capacity was investigated. Five screen cylinders with different slot geometries were tested using different ratios of softwood/hardwood kraft pulp mixtures and different reject ratios. The relationship between the rotor speed and screen slot velocity at the verge of plugging, taken here as a measure of "capacity", was found to be remarkably linear. Feed consistency and fibre length were found to have significant influences on capacity

Effect of injection screen slot geometry on hydraulic conductivity tests

Summary Hydraulic conductivity and its spatial variability are important hydrogeological parameters and are typically determined through injection tests at different scales. For injection test interpretation, shape factors are required to account for injection screen geometry. Shape factors act as proportionality constants between hydraulic conductivity and observed ratios of injection flow rate and injection head at steady-state. Existing results for such shape factors assume either an ideal screen (i.e., ignoring effects of screen slot geometry) or infinite screen length (i.e., ignoring effects of screen extremes). In the present work, we investigate the combined effects of circumferential screen slot geometry and finite screen length on injection shape factors. This is done in terms of a screen entrance resistance by solving a steady-state potential flow mixed type boundary value problem in a homogeneous axi-symmetric flow domain using a semi-analytical solution approach. Results are compared to existing analytical solutions for circumferential and longitudinal slots on infinite screens, which are found to be identical. Based on an existing approximation, an expression is developed for a dimensionless screen entrance resistance of infinite screens, which is a function of the relative slot area only. For anisotropic conditions, e.g., when conductivity is smaller in the vertical direction than in the horizontal, screen entrance losses for circumferential slots increase, while they remain unaffected for longitudinal slots. This work is not concerned with investigating the effects of (possibly turbulent) head losses inside the injection device including the passage through the injection slots prior to entering the porous aquifer.

Sand pumping and well design in consolidated and semi-consolidated sandstone aquifers

Ingress of sand usually occurs in wells abstracting from sandstone aquifers that are poorly cemented. Impacts can be serious and may add significantly to production costs. They include loss of yield and continuity of supply, a reduction in the efficiency and operational life of wells and pumps, more frequent maintenance of wells and ultimately well replacement. The design of high-capacity sand-free wells in sandstone aquifers is often problematical. This is partly because a substantial proportion of the flow is through fractures, which means that well design criteria of screen slot size and artificial pack grain size and grading that have been developed for unconsolidated granular aquifers are not generally applicable. Also, many sandstone aquifers are multi-layered. Interbedded fine-grained and friable sandstone layers or loose sands are often responsible for sand entering a well. Excluding them is often difficult in practice without blocking productive fracture zones, and, therefore, risking a reduction of well yield. Well design alone is not always capable of controlling sand pumping. Pumping at a lower discharge rate, regulating flow at start-up, and the use of sand traps at the ground surface or inside wells are other measures that can assist in alleviating the problem.

Numerical Model Assessment of Radial-Well Aging

There are 99 radial wells at Belgrade's groundwater source which lies along the banks of the Sava River. The capacity of this source has been declining over time due to two dominant processes: riverbed colmation and well aging. Both have resulted in substantial additional well-maintenance costs. Aging of radial-well laterals is a result of physical, chemical, and biochemical processes which depend on a number of parameters. The objective of the study presented in this paper was to assess changes in hydraulic losses at the entrance to the laterals due to colmation (clogging) of screen slots of the laterals in order to define the well-aging process and take timely action. Groundwater flow to a single well was numerically simulated using a three-dimensional model. Special software was developed for this purpose; in addition to standard groundwater flow calculations, it allows for geometry and spatial positions of well laterals to be specified in a user-friendly manner. This paper highlights reasons for developing the software and its special features. Model application and results are illustrated using a case study of a well which taps the alluvial aquifer of the Sava River and is part of Belgrade's water supply system.

The application of sedimentology in the characterization of borehole gravel packs and screen slot sizes for the Nanka and Ajali formation aquifers, Anambra Basin, southeastern Nigeria

The drilling of a borehole into a poorly cemented and unstable reservoir/aquifer system like the Ajali and the Nanka Sands and the withdrawal of its fluids trigger movement, because unconsolidated grains and matrix materials are dislodged and entrained in the produced fluid (water, gas or oil). The undesirability of pumping any fluid togetherwith sand and matrix material is reflected in the dangers posed to the equipment by way of ; abrasion of downhole pumps and accessories, casing pipes and surface equipment on one hand; and the loss of production, compaction of reservoir and handling/disposal problems on the other hand. Produced sand thus must be stopped, while allowing formation fluid to pass into the borehole. Two measures of sand control for the Ajali and Nanka fluid production are discussed herewith; a screen placed at the reservoir interval and a gravel pack in the screen-hole annulus. Gravel pack character and screen slots design are directly dependent on the size of formation/aquifer sand size. Relevant equations were used to compute the sizes of gravel pack material and screen slot sizes for twenty boreholes; eleven (11) that penetrated the Ajali and nine (9) that penetrated the Nanka Sands, (the two most prolific and most exploited aquifers within the Anambra basin). Results show that gravel pack sizes for the Ajali Sands range from 1.42mm, through 2.13, 3.37 to 5.06mm, indicating an average gravel diameter size range of 2.13 to 5.06mm. For the Nanka Sands, the gravel pack values range from 0.57mm, through 0.75, 3.17 to 4.73mm indicating an average range of 0.57 to 4.75mm. Uniformity coefficients (Uc) for the Ajali and Nanka Sands are 0.6 and 0.32 respectively, indicating perfect or nearly so, but it is broad for most individual boreholes. Under broad uniformity conditions, recomputed screen slot widths are 0.33 and 0.18mm for the Ajali and Nanka Sands respectively. In commercial terms, these figures generally translate into ‘24inches gage’ and ‘7inches gage’ screen slot sizes for the Ajali Sands and ’13 inches gage’ for the Nanka Sands.KEY WORDS: Ajali and Nanka Sands, Sand Control, Gravel Pack and Screen Slot Sizes

Preventing two types of well clogging

Wells abstracting groundwater are often susceptible to screen slot (chemical) clogging and well bore (mechanical) clogging. Well clogging can cause a decrease of a well—s specific capacity over time and may threaten its reliability. Both types of clogging can be easily diagnosed during operation with the help of entrance resistance—the difference in head between the abstraction well and the observation well in its gravel pack. An increase in entrance resistance over time indicates screen slot clogging. The increasing resistance is caused by accumulation of chemical precipitates in the screen slots and adjacent gravel pack. Well bore clogging, however, does not show an increase in entrance resistance. Both types of clogging can be easily prevented, or at least mitigated, by two opposing methods of well operation: continuous abstraction for wells susceptible to screen slot clogging, and discontinuous abstraction (alternating operation with idle periods) for wells susceptible to well bore clogging.

Installation of Horizontal Wells in Landfilled Waste Using Directional Drilling

Leachate levels within a landfill must often be controlled for environmental and/or regulatory reasons by means of pumping from wells. Conventional vertical wells are usually used for this purpose, but there is a perception that they are inefficient. In this paper, the feasibility of using directional drilling to install horizontal wells for leachate control in landfills is investigated with reference to pilot and full scale field trials at Rainham, U.K. The difficulties of well-screen design and installation in a landfilled waste are discussed; the insights gained during trial installation are described; and the effectiveness of three trial wells is assessed with reference to the leachate flow rates and drawdowns achieved, in comparison with conventional vertical wells. It is concluded that the drilling rig used must be sufficiently powerful to cope with the likelihood of at least partial borehole collapse around the well-screen during installation; that the screen slot size can be based on at least the D30 particle size of the waste and a natural filter allowed to develop around the well (provided that the resulting well screen is strong enough); and that as experience with the technology grows, directionally drilled horizontal wells could represent a viable, cost effective alternative to conventional vertical wells for leachate control in landfills.