Effective removal of small, sand-sized solids is critical for Successful drilling and completion operations in sand reservoirs. Recent experience in extended-reach drilling also indicates that inefficient transport of...
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Effective removal of small, sand-sized solids is critical for Successful drilling and completion operations in sand reservoirs. Recent experience in extended-reach drilling also indicates that inefficient transport of smaller cuttings is a main factor for excessive drag and torque. This Study was undertaken to determine two critical conditions for efficient transport of small solids. The two conditions are represented by the critical resuspension velocity (CRV), the minimum fluid velocity necessary to initiate solids-bed erosion and the critical deposition velocity (cdv), the minimum fluid velocity required to prevent bed formation. Experiments were conducted in a field-scale flow loop (8 x 4.5 in., 100 ft long) to determine CRV and cdv for 0.45-mm and 1.4-mm sands in different fluids over a range of bed heights and hole inclinations. The results show that, depending on sand size and fluid properties, cdv is approximately two to three times larger than CRV. Water is more effective than low-concentration polymer Solutions for bed erosion. However, polymer solutions are more helpful than water in preventing bed formation. This indicates the need for different drilling fluids for cleanout and drilling operations. A mechanistic model was developed to predict CRV for a solids bed. Both experimental and theoretical results indicate the importance of interparticle forces that are incorporated into the model. The model accounts for drillpipe eccentricity in any direction in an annulus, which is consistent with experimental observations. The model predictions are in good agreement with experimental results. Existing cdv correlations developed for larger cuttings were verified by experimental data for sands. The differences are approximately 25%. Results in this study will be useful not only in drilling and completion through sand reservoirs, but also in extended-reach drilling and sand control.
For VoD (Video on Demand) and the multimedia services in ATM (Asynchronous Transfer Mode) networks, guaranteeing QoS (Quality of Service) far rear-time traffic is emerging as an important issue. In this paper, we pres...
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For VoD (Video on Demand) and the multimedia services in ATM (Asynchronous Transfer Mode) networks, guaranteeing QoS (Quality of Service) far rear-time traffic is emerging as an important issue. In this paper, we present a novel multiplexing scheme to reduce the cdv (Cell Delay Variation) and jitter in ATM multimedia traffic. We propose a two-stage statistical multiplexing scheme using a FIRO (First In Random Out) window and a state queue. The simulation results show that the cdv is significantly reduced due to reduced clumping and dispersing among VCs (Virtual Channels) in VPs (Virtual Paths).
ATM switch performance largely depends on its cell scheduling scheme and buffering scheme. The cell scheduling scheme should guarantee the reserved bandwidth in any case, as well as providing maximally optimized perfo...
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ATM switch performance largely depends on its cell scheduling scheme and buffering scheme. The cell scheduling scheme should guarantee the reserved bandwidth in any case, as well as providing maximally optimized performance. In this paper, we propose an efficient cell scheduling algorithm to satisfy these requirements. With the proposed algorithm, the ATM switch can provide the stable link-utilization with high throughput.
The leaky bucket scheme has been widely treated as a traffic control mechanism. The corresponding multi-connection shaper, which intends to make the passing traffic comply with the declared parameters in the enforcer,...
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The leaky bucket scheme has been widely treated as a traffic control mechanism. The corresponding multi-connection shaper, which intends to make the passing traffic comply with the declared parameters in the enforcer, has also been implemented. However, we must point out that the regulated cells may be invalid at the corresponding enforcer, even if the cdv between the shaper and enforcer is neglected. In order to cope with this problem, two enforcing methods, say ALP LB and GCRA, are tried and evaluated. We modify the GCRA algorithm, which was suggested by recommendation 1.371 and even extended by ATM Forum '93, to be suitable for shaping. The shaper and enforcer architecture which is suitable for both ALP LB and GCRA methods is proposed. Simulation results verify the shaping and UPC functions of <(GC)over bar RA>. They also reveal that the GCRA shaper would not introduce long delay and queue length. The proposed shaper architecture does have some merits compared with others. Such a shaper is also suitable for regulating traffic for NPC (network parameter control) at the NNI (network node interface).
The cold tube drawing has been generally regarded as an effective technology because of its high productivity and low production costs. It has been used instead of the swaging process to form monobloc tube shafts (MTS...
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The cold tube drawing has been generally regarded as an effective technology because of its high productivity and low production costs. It has been used instead of the swaging process to form monobloc tube shafts (MTSs) with a constant outer diameter or hollow shafts without defects. MTSs are used nowadays to reduce the weight of shafts and to improve power transmission in the auto industry nowadays. The objective of this study was to design an optimal die that can prevent material fracture considering critical damage value in the tube drawing process. To achieve this objective, a finite element simulation and the flexible polyhedron search method are used. The drawing die shape is represented by the Bezier curve that is able to generate all the possible die shapes. The tube drawing experiments were carried out using the optimized tool. In the experiments, it was possible to produce sound products without fracture.
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