Oil Well

when your job is drilling for oil you lead a nomadic kind of existence you're rarely in one place for long and every time you move to a new location you take your drilling rig with you 800 tons of machinery and a few thousand horsepower to drive it setting it all up can take anything from a few days to a couple of weeks [Music] the choice of site for drilling an exploration well isn't ours it's made by the geologists and geophysicists from their knowledge of the rocks that lie below 10,000 feet or more a classic choice would be over a dome-shaped fold in the rock layers revealed by seismic survey but in this business choice is a gamble but chance you're counting on is that oil and gas formed somewhere in the vicinity millions of years ago could have migrated into the dome through layers of permeable Rock and have accumulated they're hemmed in by an impermeable layer above once there they would have separated the gas on top of the oil with groundwater round the flanks all of them at high pressure that's what we hope has happened but it could take 8 weeks or more to prove it we start with a relatively large bit to drill through the soft surface layers down to one thousand feet or so when your target is over ten thousand feet down you don't just sink a deep hole you build it carefully stage by stage [Music] the drill is driven from the surface turned by a rotary table on the platform the drill string suspended from the derrick [Music] down below the teeth of the trilling that break the rock into fragments they'd soon choke the hole unless we had a way of flushing them out what we use is a special drilling fluid pump down the drill pipe to cool the bit and carry the cuttings away back to the surface the mud as we call it is channeled out over fine mesh screens the shakers to remove the coarse cutting and then pass through separators and settling pits to get rid of the finer material before it's recycled back down the hole as long as the drill is turning the mud must be kept circulating but every 30 feet drilling has to stop to add another section of pipe [Music] it's a tough job and it calls for some slick coordination from the floor crew but they all get plenty of practice on an average well they'll add pipe over 300 times before they reach the bottom of the hole everything's done to a schedule supervised by the tool pusher nowadays he doesn't push anything but the drilling program he's responsible among other things for ordering supplies of materials as they're needed and making sure they arrive on time this steel casing for instance will be run into the hole and the drill has reached a thousand feet it's essential to stabilize the well at this stage to prevent the softer rocks found at shallow depths from caving in this will be the next job coming up in his program within the next few hours the casing flight drill pipe is assembled section by section and each of them weighs a ton or so these centralizers are fitted at regular intervals to keep the casing central in the hole as it goes down the casing is lowered in until it reaches a point just above the bottom of the hole the next job is to submit at home the cement is a wet slurry pump down the inside of the casing under pressure down hole it flows through the end of the casing and is circulated around the outside and back to the surface displacing the drilling mud ahead of it the cement is followed by drilling mud to the bottom of the casing the pumps are stopped and the cement is given time to set now we can cap the top of the casing with a set of safety valves known for obvious reasons as the blowout preventers if further drilling were to encounter extremely high pressure gas oil or water we could have a problem to contain it we need a means of sealing off the whole of the surface it's done by hydraulic rams that close off the gap between the drill string and the inside walls of the casing as we go deeper heavier well that equipment will be installed to control the higher pressures once the blowout preventers are fitted drilling can continue safely to greater depths but what if we were drilling not on land but way out at sea our rig might be on a floating platform anchored 500 feet or more above the drill hole but we'd still have to follow the same procedures on a marine well blowout preventers are every bit as vital but they have to be fitted by remote control sent down on guide wires and locked onto the casing under the watchful eye of the television camera on top goes a marine riser a conductor to to connect the rig directly to the blowout preventers and the drill hole down below this gives us the closed system we need for running pipe and circulating mud just as if we were working on land as drilling goes on the mud return shows the succession of different rock layers were passing through some of them could contaminate the mud and prevent it from functioning properly so we need to keep a constant check on its composition the mud must also be maintained at a given viscosity and density we don't want it altered too much by the rocks we're drilling through frequent checks are also made for any changes in the chemical composition if we were to hit a layer of salt for instance we could be in deep trouble the mud would cease to do its job causing the hole to collapse and prevent drilling [Music] we might have to replace the mud with a new supply of an entirely different composition to neutralize the salt up on the platform an equally close eye is kept on the performance of the drill bit cutting through hard rock its life is usually less than 12 hours loss of cutting power occurs when the bit becomes dull and it makes a distinctive noise now it's time to pull the whole string 90 feet at a time and stock it in the derrick [Music] [Music] [Music] we can easily have a hundred stands of pipe in the rack before we reach the bit maybe four hours to recover it another four to run the new one and again [Music] changing a bit is time-consuming but part of the normal program with drilling can sometimes encounter problems that are unpredictable conditions down hole might suddenly change and affect the consistency of the mud if it got too thick it could bind the drill pipe and stop further drilling if it happens you just pull out what you can then you go fishing and what luck you make contact but if the hole itself collapses you abandon the jammed in section and recover the rest by breaking the pipe you can't drill back down through the blockage you have to bypass it using special deviation equipment offsetting a new hole at a predetermined angle mechanical troubles don't happen all that often but on every well you have to be prepared for hazards of another kind that may lie buried in the rocks below a sudden increase in mud flow from the well stop drilling and close the blowout preventers everything shut down the pressures are measured and the pumps are restarted slowly while the cause of the flow increase is identified we've encountered high pressure gas trapped in a shallow sandstone it's flowing into the well and forcing out the mud before we can drill on we have to contain the formation pressure by pumping down a heavier mud this is usually kept in the storage tanks ready for just such an emergency [Music] at 3,500 feet below the gas is flowing into the hole but as the new heavier mud begins to circulate the pressure has gradually overcome and the flow stops as the pressure returns to normal the emergency is over with the mud weight increased we can now drill the rest of the Gaston then the hole can be lined with steel casing then with a smaller bit on towards the target still a long way to go as the drill bites through the Caprock and approaches the target zone its progress is monitored foot by foot inspection of the cuttings will give us the first indication of what really lies below the cap rocket whether or not the choice of drill site was correct it's sandstone all right and it could contain oil under the microscope a sample certainly looks promising coarse grain sand with a definite dark stain if it's oil it'll glow yellow under ultraviolet light [Applause] it's there alright but so far only a trace not until we've drilled all the way through the formation can we begin to assess its significance to find out more about what's down there we run a special instrument probe [Music] [Music] the probe contains devices which measure certain electrical acoustical and radioactive properties of the different rock layers and transmits them back to the surface square they are recorded as it passes back up through the formations the nature of the rocks penetrated by the drill and how much oil and gas they contain can be determined by the recorded measurements shale porous sandstone saturated with oil even more porous here limestone nothing much in this case then the gas layer and finally the impermeable shale of the cap rock [Music] we know there's other than gas down there but there's a lot to do yet before we've any idea of how much can be produced it certainly looks promising encouraging enough to justify a flow test the whole has been cased right down to the bottom and cemented in a flow tube is now run into the oil zone to get at the oil we have to perforate both the casing and the cement we do it by firing a string of specially designed charges the oil begins to flow as the pressure in the well is reduced the flare off of gas that comes up with the oil signals a successful test to get this far has cost anywhere from $600,000 on land to 4 million offshore get all we've managed to assess is the potential of the area immediately around a single drill hole what interests us now is the rest of the structure to find out the full extent of the oil reservoir we have to drill more Wells the first out step has found water bearing sands and we can now deduce the profile of the reservoir in this direction next we drill a third well in line with the other two this again finds water bearing sands and completes the profile the shape of the structure and the position of the oil gas and water contacts but the profile is still only a narrow band of information in one direction across the structure to round out the picture we now need to drill further out stepwells at right angles to the first three even with a classic dome shaped structure out stepping can have its disappointments nothing but water and much lower down than expected the rocks have slipped along a fault line blocking off the reservoir this is what's called a drive hole but it's information was vitally important we've now probed the limits of the structure and at last we have a three-dimensional impression of the reservoir we can now begin to plan its further development to bring the oil field into full production further wells will be needed these are drilled in the oil bearing zone beyond the edge of the gas so we get the maximum assistance from both gas and water pressures in driving the oil to the surface as more and more oil is withdrawn we can inject water back into the structure to maintain the pressure by drilling more wells outside the limits of the oil accumulation an oil field may extend over an area the size of a town with a network of pipelines for gathering the oil and maintaining pressures down hold if the oil field were offshore the whole installation complete with treating facilities and pumps would have to be concentrated into a very small area to be economic offshore drilling and producing facilities need to be located at a central point from a permanent platform the oil reservoir is then developed to the same pattern as on land by using the technique of deviation drilling new oil reserves are much harder to find nowadays but when they are it's most often in locations that are very difficult to develop but wherever they exist and however complex the development becomes it is our job to reach them using every human and environmental safeguard possible then to recover as much as we can for as long as we can [Music] you [Music]