question: If you have a small leak from a container full of sand (could be a few tons even) you can shut it by spraying a bit of water on the hole,how does this work? why is the huge mass of sand doesn't push out the wet sand on the hole?
comment: So first thing to mention is that sand isn't a liquid, it's a particulate solid. If it were water in that container, and you tried to plug it with sand, then it would absolutely be forced out. That's because water is far more fluid than sand. Sand will naturally compress down to form what almost resembles a solid, even when completely dry. Sand particles aren't perfectly smooth, and have friction, which means the particles don't easily move past each other when compressed. The particles need space around them to move. If you take some sand and "pour" it from one container to another, there's a lot of air in there that allows the particles to move around each other and "flow" as though it's a liquid. In your example, the tons of sand in the container are compressed under their own weight. The hole at the bottom is not under great pressure, because the sand has, for all intents and purposes, "solidified" and won't flow easily, so there's very little pressure at the hole.
passages: Sand box (civil engineering)
  
  A sand box or sand jack is a device used for removing the centering of an arch. Each prop is mounted on a sand box. After the plug is removed, the sand pours from the box, causing the centering to move downwards, diminishing the pressure from the arch, and enabling to ultimately remove it.
   When a kick (influx of formation fluid) occurs, rig operators or automatic systems close the blowout preventer units, sealing the annulus to stop the flow of fluids out of the wellbore. Denser mud is then circulated into the wellbore down the drill string, up the annulus and out through the choke line at the base of the BOP stack through chokes (flow restrictors) until downhole pressure is overcome. Once “kill weight” mud extends from the bottom of the well to the top, the well has been “killed”. If the integrity of the well is intact drilling may be resumed. Alternatively, if circulation is not feasible it may be possible to kill the well by "bullheading", forcibly pumping, in the heavier mud from the top through the kill line connection at the base of the stack. This is less desirable because of the higher surface pressures likely needed and the fact that much of the mud originally in the annulus must be forced into receptive formations in the open hole section beneath the deepest casing shoe.
   The following process is also illustrated from rightside figure. Depending on the number of barriers and number of confined states inside the well, the process described below could be repeated.
  
  Section::::Operation.:Positive resistance region.
  
  For low bias, as the bias increase, 1st confined state between the potential barriers is getting closer to the source Fermi level, so the current it carries increases.
  
  Section::::Operation.:Negative resistance region.
   In drilling a typical high-pressure well, drill strings are routed through a blowout preventer stack toward the reservoir of oil and gas. As the well is drilled, drilling fluid, "mud", is fed through the drill string down to the drill bit, "blade", and returns up the wellbore in the ring-shaped void, annulus, between the outside of the drill pipe and the casing (piping that lines the wellbore). The column of drilling mud exerts downward hydrostatic pressure to counter opposing pressure from the formation being drilled, allowing drilling to proceed.
   Cement is also used to form permanent barriers in the annulus outside the production liner, and temporary barriers inside the liner. The temporary barriers are used to "shut in" the well after drilling and before the start of production. Figure 4 shows a barrier being tested by replacing the heavy mud above it with lighter seawater. If the cement plug is able to contain the pressure from the mud below, there will be no upward flow of seawater, and it can be replaced with mud for the final shut in.
   The sand is treated with a hydrophobic compound to produce what is commonly known as magic sand or Moon Sand. When poured into water, it naturally clings to other grains, forming piles or lumps at the bottom of the bowl. The sand can be poured rapidly in a spray and will still re-form, adding to the illusion of it mixing into the water. The hand-stirring performed after pouring will leave these piles intact. The magician can then reach into the bowl and feel out the piles, grasping some of the sand and tossing it into the air. Water has been excluded from the piles, leaving the sand completely dry and free-flowing.
   Section::::Description.
   BULLET::::- Bailing sand and debris (removing formation sand/rock and other such debris left over from the drilling and completion of the well, using a specialized tool called a bailer. This tool uses either a Chinese water pump type stroke action or a hydrostatic vacuum action to suction up the downhole debris, allowing it to be conveyed back to surface via the wireline)
   Blind shear rams (also known as shear seal rams, or sealing shear rams) are intended to seal a wellbore, even when the bore is occupied by a drill string, by cutting through the drill string as the rams close off the well. The upper portion of the severed drill string is freed from the ram, while the lower portion may be crimped and the “fish tail” captured to hang the drill string off the BOP.
   The relatively small distance, around , between the Lusi mud volcano and the well being drilled by Lapindo (the Banjarpanji well) may not be a coincidence, as less than a day before the start of the mud flow the well suffered a kick. Their analysis suggests that the well has a low resistance to a kick. Similarly, a NE-SW crack in the surface in the drill site may be evidence of an underground blowout. The well may have suffered an underground blowout that resulted in a surface breach.
  
  Section::::Hypotheses on the possible causes.:Earthquake-induced fault reactivation, hence a natural event.
   The workover begins by killing the well then removing the wellhead and possibly the flow line, then installing a B.O.P commonly known as a blowout preventer, then lifting the tubing hanger from the casing head, thus beginning to pull the completion out of the well. The string will almost always be fixed in place by at least one production packer. If the packer is retrievable it can be released easily enough and pulled out with the completion string. If it is permanent, then it is common to cut the tubing just above it and pull out the upper portion of the string. If necessary, the packer and the tubing left in hole can be milled out, though more commonly, the new completion will make use of it by setting a new packer just above it and running new tubing down to the top of the old.
   The permit for the Macondo Prospect by the Minerals Management Service in 2009 did not require redundant acoustic control means. Insofar as the BOPs could not be closed successfully by underwater manipulation (ROV Intervention), pending results of a complete investigation, it is uncertain whether this omission was a factor in the blowout.
   Writing in "Nature", physicist Detlef Lohse and coworkers of University of Twente in Enschede, Netherlands allowed air to flow through very fine sand (typical grain diameter was about 40 micrometers) in a container with a perforated base. They then turned the air stream off before the start of the experiment and allowed the sand to settle: the packing fraction of this sand was only 41% (compared to 55–60% for untreated sand).
   As of October 30, 2008, the mud flow was still ongoing at a rate of 100,000 m per day. By mid August 2011, mud was being discharged at a rate of 10,000 m per day, with 15 bubbles around its gushing point.
   In order to clear a boulder choke the rocks obstructing the passage may need to be removed, often requiring breaking up first either mechanically or using a small explosive. The Three Counties System became the longest cave in the UK when cavers succeeded in clearing a route through a boulder choke for to connect two known cave systems, an exercise that took three years.
   The Sidojaro mud is rich in rock salt (Halite) and has provided a source of income for the local residents who have been harvesting the salt for sale at the local market.
  
  Section::::Current status.:2008.:Stakeholder exit.:2013.
   This is the most common open hole completion used today. It is basically the same described on the vertical open hole completion but on a horizontal well it enlarges significantly the contact with the reservoir, increasing the production or injection rates of your well. Sand control on a horizontal well is completely different from a vertical well. We can no longer rely on the gravity for the gravel placement. Most service companies uses an alpha and beta wave design to cover the total length of the horizontal well with gravel. It's known that very long wells (around 6000 ft) were successfully gravel packed in many occasions, including deepwater reservoirs in Brazil.
   The term probably originated from the concept that enough water is "squeezed" out of the slurry to render it unflowable, so the portion that has actually entered the zone will stay in place when the squeeze pressure is removed. After surface indications (e.g., pressure reaching a predetermined maximum) that a squeeze has been attained, any still-pumpable cement slurry remaining in the drill pipe or tubing ideally can be reverse circulated out before it sets.
   The natural arch is large enough for a sailboat to cross underneath it with ease. It is reachable by foot just off the beach joining the rock formation to the land at low tide. Visitors and tourists to the formation may find accommodation in the nearby village of the same name.
   One of the greatest drawbacks that inventors of squeeze casting have encountered is the configuration of reentrant cavities and internal passages that use the core. One of the possible solutions brought up was creating a core from conventional sand coring. Although this method seemed like a valid solution, the high temperatures from molten metal easily penetrated the core made from sand. Along the way, other inventors have also come up with different methods such as using traditional salt cores, but like sand coring, they are equally, if not more susceptible to stress and cracking.
   Separating the fill process from the lifting process is crucial in this system. After the void is filled with sand, the lift occurs. The concrete is lifted about ½ - ¾ inches and the filling process resumes. When the void is full the process starts again with the lift and repeating the iterations as many times as is necessary.
   When tripping out of the hole, the volume of the removed pipe results in a corresponding decrease in the wellbore fluid. Whenever the fluid level in the hole decreases, the hydrostatic pressure that it exerts also decreases and if the decrease in hydrostatic pressure falls below the formation pore pressure, the well may flow. Therefore, the hole must be filled to maintain sufficient hydrostatic pressure to control formation pressure. During tripping, the pipe could be dry or wet depending on the conditions. The API7G illustrates the methodology for calculating accurate pipe displacement and gives correct charts and tables. The volume to fill the well when tripping dry pipe out is:
   Expanding foam is used primarily with vertical shafts where the use of the shaft is no longer desired. It forms a plug 6 feet or more thick. A pipe through the plug allows for pressure equalization as well as for water drainage, or even as a bat entrance if necessary.
   It was later discovered that a second piece of tubing got into the BOP stack at some point during the Macondo incident, potentially explaining the failure of the BOP shearing mechanism. As of July 2010 it was unknown whether the tubing might have been casing that shot up through the well or perhaps broken drill pipe that dropped into the well. The DNV final report indicated that the second tube was the segment of the drill string that was ejected after being cut by the blow out preventer shears.
   In infrequently used floor drains where such a primer does not exist, evaporation can be mitigated a few different ways:
  
  BULLET::::- Routinely adding water to the floor drain
  
raw_presuppositions: Leaking sand behaves like leaking water.
raw_corrections: Sand is a particulate solid, so the sand that is leaking is not under great pressure.