Because of the converging-diverging con guration of the valve passage, venturi valves have been widely used in large turbines to regulate inlet ow as turbine governing valves for about half a century. From the 1960s, a number of valve failure incidents have been reported. Improvement to current designs was strongly demanded but, owing to the complicated nature of the uid-structure interaction mechanisms, the basic mechanism causing valve failure is still far from being fully understood. Experimental investigations on a half-scale valve were performed here. The study con rmed that asymmetric unstable ow is the root cause of valve problems, such as noise, vibration and failure.
The use of relative density as a method of control for compaction of cohesionless soils is hampered by lack of an adequate method for determining the maximum soil density. Previous investigations have shown that higher densities are obtained for most cohesionless soils by vibratory methods than by the standard impact compaction methods. This paper presents the results of an investigation of vibratory methods to determine the combination of variables which would give the highest density. Four electromagnetic table-type vibrators, an immersion-type concrete vibrator, and a pneumatic table-type vibrator were used in this investigation. The effect on the soil density of magnitude of surcharge, time of vibration, amplitude of vibration, and water content were studied for seven cohesionless soils representing a wide range in gradations. A summary of the Bureau of Reclamation's test procedure for determining the relative density of cohesionless soils using a vibratory table is included. For the range of amplitudes investigated, maximum densities were generally obtained at the higher amplitudes. Additional research is needed to determine the optimum deadweight surcharge. The increase in density was insignificant for times of vibration greater than 6 min, and 8 min seems to be a reasonable and sufficient time for the equipment and soils tested. The initial density of the soil prior to vibration did not have a significant effect on the final density. The difference between the densities obtained using oven-dried soil and initially saturated soil was not significant for most of the soils tested.
L.G. Jones (Lloyd Jones & Associates), SPE, R.J. Tibbles (Schlumberger Dowell), SPE, L. Myers (Mobil Equatorial Guinea Inc.), David Bryant (Mobil E&P U.S. Inc.), SPE, Jim Hardin (U.S. Filter/Johnson Screen), & Gary Hurst, SPE, (STIMLAB) Abstract Because of the abnormal length of most horizontal wellbores, they present an exceptional challenge for gravel packing. Previously, the only way to gravel pack a long horizontal wellbore in a permeable formation was to seal off the wellbore from the formation to such an extent that substantial circulation could be maintained during the entire packing operation. While this approach has shown limited success, it necessitates the removal of the filter cake after the job is completed, which can be both difficult and expensive. In this paper, equipment and procedures are described which allow gravel packing of long cased or open hole horizontal wellbores using alternate path shunts, without requiring circulation. The design methodology, procedures and evaluation have been developed with information obtained from studies using a series of physical wellbore simulators ranging from 150 to 500 feet in length. The simulators are described and results from the simulator studies are presented. Two case histories are included. The advantages of the new methodology are that it permits removal of the filter cake before or during the gravel packing operation and allows modest fracturing while packing, if desired. Summary The pumping techniques and apparatus used in alternate path gravel packing have been extended here to allow gravel packing of long, open hole horizontal wellbores with or without substantial leak-off. Modest fracturing is possible, if desired. The major pumping change is the use of gels that suspend the proppant during the entire job. The major apparatus changes are the use of larger exit ports from the shunts and use of a shroud over the screen and shunts to act as both a protector and centralizer. The pumping and apparatus design changes are based on results of experiments performed with wellbore simulators ranging from 150 to 500 feet in length. Description of the experiments and results are provided below. Two case history of the first field applications are presented. Total solids placement was 150% of the calculated annular volume of the 500-foot horizontal wellbore, suggesting that some modest fracturing took place. Productivity index for the well was 21, resulting in a production rate of 12,000 bbl/day from a formation with modest permeability thickness. Introduction Gravel packing of horizontal wellbores in unconsolidated formations is appealing because a tight gravel pack stabilizes the formation face. This will prevent movement of formation sand to the sand screen and permit use of a normal screen, which won't be plugged by the few fines that move through the gravel pack. While gravel packing in cased horizontal wellbores has been used in places like the North Sea since 1991, Open hole horizontal well gravel packing has been difficult to accomplish because fluid leak-off along the horizontal interval dehydrates the slurry, leading to early annulus bridging and sand-out with long unpacked intervals. Numerous studies have explained and documented the weaknesses and strengths of using either gels with good carrying capabilities or low viscosity fluids, such as water, for high angle and horizontal well gravel packing. Horizontal water packing requires enough fluid velocity to maintain turbulent flow along the top of the wellbore to move the sand downstream. P. 739^
The paper reviews the development of a second-generation rotary steerable drilling tool. The principle of operation is a bendable shaft that points the bit in the opposite direction to the shaft bending direction. This tilting action is a departure from other rotary steerable device concepts that push the bit sideways to change the wellbore trajectory. Combining this tilting action with extended gage bit technology provides maximum effectiveness in torque and drag reduction while reducing vibration and further improving hole cleaning. Important to the tool development was basing the design on lessons learned by others thereby improving both performance and reliability. The paper also discusses the application of proven technology from outside the drilling industry. Core elements such as strain wave gearing transmissions and electrically operated clutches were developed initially for use in industrial robots. Other significant elements are examined such as the shaft design, rotary seal systems and anti-rotation devices to limit housing roll rate. The "steering system" was integrated with an existing MWD system to allow automated or manual control from surface using a bi-directional communication system. This is also discussed. Introduction Back in the 70's and 80's we started hearing the term "I've been replaced by a computer". Mostly these were comical comments made at social gatherings but in reality it was true for many people involved in the manufacturing industry. Today we couldn't imagine a machine shop operating without computerized or robotic controlled machinery such as the common CNC system. It took a while but the task automation revolution of the manufacturing industry has started to make it's way below the rotary table to the point now that some (not all) functions traditionally handled by Directional Drillers are being handled by a computer, changing the nature of what a Directional Driller does at a drilling rig. It is likened to the revenge of the nerds, oil field style. The oil and gas operators continue to challenge the drilling service companies to reduce drilling time and costs while increasing technical limits of the equipment. For rotary steerable tools in particular, this effect is amplified primarily by the offshore market where costs run substantially higher than land based operations and where small incremental savings in drilling time result in impressive money savings to the drilling operation. The other obvious challenge is to pack as much production volume and life from each slot on a platform as possible. That need has never changed and has no apparent limit. This voracious requirement drives the need for multiple target well paths to maximize the capital investment returns in the asset. Attempts to slide a PDM over such tortuous well path geometries often are difficult or impossible as weight transfer to the bit is quickly lost to high drag on the drillstring. With the introduction of rotary steerable tools we are now seeing some operators pushing the limits of well bore geometries, drilling wells that are impossible to drill with a positive displacement motor (PDM) and requires a complete dependence on rotary steerable technology to drill the well. On the flip side of the equation is tool reliability. The cost of tripping failed tools is now a significant factor for wells depending on rotary steerable tools. The technology is new and prone to higher failure rates than more mature products and the industry has had to weigh this against their drilling objectives. More often than not, the current markets in Norway and the U. K. continue to use rotary steerable technology because the benefits still out weight the drawbacks in reliability. This has been a significant issue as it has allowed for this type of technology to gain a foothold in our industry.
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