WORLD OF OIL

[Music] separately in this film we'll discuss convection this heated iron ball provides a demonstration of convection the ball heats the air around it and the air expand and produces air currents a process called shear and photography makes these currents visible the warmed air actually moves carrying the heat energy with it this form of heat transference is called convection convection also occurs in liquids this tank is filled with water containing aluminium powder to make the currents visible the water near the flame becomes hot and less dense it rises and is replaced by cooler water from the side gradually a continuous convection current is set up and because convection requires the heated medium to move it cannot occur in solids convection currents are an important factor in the design of the domestic hot water system providing a constant supply of hot water in the storage tank the water is heated in the boiler and rises by convection to the top of a storage tank above cooler water from the bottom of the storage tank flows into the boiler to replace the hot a continuous circulation is set up and gradually the storage tank becomes filled with hot water the hot water taps are connected to the top of the tank where the water is hottest another application of convection is the design of certain ventilation systems this model will show you how they work normally the air in the channel is still and the smoke from the pipe travels straight upwards but a source of heat at one end of the channel creates convection currents that cause to flow through so ventilating it in the 18th century coal mines were ventilated in this way simply by lighting a fire at the bottom of one of the shafts but in the home the same effect can prove a nuisance an open fire creates convection currents and these are sometimes strong enough to produce an unpleasant draft what's more this draft chases most of the heat from the fire away up the chimney warming the air above the house rather than in the house this is clearly very wasteful especially world's energy resources are becoming scarce modern appliances are designed to minimize the draft effect so conserving heat and fuel they provide ventilation without dropped by causing air to circulate gently around the room distributing the heat evenly now only a little heat is wasted up the chimney convection has also been used in man's attempt to fly hot-air balloons were developed in France in the 1780s the hot air was provided by large fires on the launching platform and once filled the balloons were carried into the air recently there has been renewed interest in hot air ballooning the modern balloons use compressed gas as the fuel to provide the hot air but the principles on which they work are the same as in the 18th century balloons in effect they're getting caught up in a convection current hot-air balloons carry their own personal convection current around with them but gliders have to make use of naturally-occurring convection these natural convection currents are called thermals they occur because the Sun does not heat the ground evenly for instance the roofs of houses get hot more quickly than the green vegetation of fields and woods so warm air currents rise from towns and villages ripe corn fields or sunny wind protected slopes also produce thermals the glider pilot uses these currents to carry his aircraft higher into the air he then flies across country losing height as he goes until he finds another thermal to lift him again by sailing from one thermal to the next in this way he can cover hundreds of miles and the convection currents that carry the glider up to the clouds also play a part in their formation the air in a convection current contains water vapour as it rises the air expands and cools and the water vapor may condense into small water drops together these may form a cumulus cloud as the drops become bigger the cloud becomes darker and ultimately the drops may be heavy enough to fall as rain so convection currents are one of the causes of rain showers they also cause the well known sea breezes at the coast on sunny days these light winds blow onshore during the day and offshore at night this happens because during the day the Sun heats the land more quickly than the sea the land becomes hotter and convection currents occur these bring air into the land from the sea but at night the land cools quickly while the sea remains warm convection currents now rise from the sea and the wind direction is reversed heat is transmitted in gases and liquids by a process called convection this occurs because a heated gas or liquid expands becoming less dense it moves upwards carrying heat energy with it such movements are called convection currents convection currents have a number of practical applications in hot water systems in heating and ventilation and in unpowered flying naturally occurring convection currents are also partly responsible for some aspects of the weather crude oil is found below land or sea in layers of porous rock these hold the oil here shown in red just as a sponge holds water but the oil remains trapped only when the layers of rock above prevented escaping in practice the shape of these oil traps is not as simple movements of the Earth's crust have changed the shapes of the rock layers if the layers buckle like this then the oil and water shown in blue move up and collect vineeth the dome formed by the layer above trapped on top of the oil is usually some gas here shown in green this type of oil trap is called an anticline rock structures like this can vary in size from a few hundred yards across up to tens of miles this anticline is in Iran if the impermeable layer above the oil becomes worn or buckles again so that cracks appear in it then the oil may find its way up to the surface and form a pitch lake there are other types of oil trap which can be formed here the layers have tilted and slipped and they're not continuous anymore the oil and water remain separated but they're still trapped by impermeable Rock above again there may be gas present this type of rock formation is called a fault all these different traps have oil bearing potential and could make commercial oil or gas fuels such traps may occur singly or together how do we actually find them the early wells like this one drilled at Titusville in America in 1859 were sited where there was visible evidence of oil or gas on the land surface but even with clear signs like this many wells miss the target for the source of the oil can be a long way from the site where it seeps through onto the surface more systematic methods were needed to find the right type of rock formation aerial photography may be used to get a general picture of the countryside and of any rock structures that may exist in remote or jungle areas the photographs may have to be turned into maps before the survey teams can set off at ground level the most promising areas will be studied in more detail rock formations may be visited and samples taken tiny fossil remains may help scientists to tell the age of the rock layers and show whether they originated in shallow seas where sedimentary rocks might have been formed other methods measure small variations in the Earth's gravity and in its magnetic field or use a technique called seismograph II all these are called geophysical techniques the gravity meter measures the force of gravity at the Earth's surface small variations in this force can suggest the way rocks of different densities are distributed below the surface at sea a meter can be lowered to the seabed the results are studied using a computer and may indicate the presence of interesting rock formations below less dense rocks for instance are more likely to bear oil the strength and direction of the Earth's magnetic field can also be measured using an instrument called a magnetometer this tool shows how different types of rock are distributed below ground both magnetic and gravity surveys may be done over large areas size MOG Rafi is generally limited to smaller land areas a series of special microphones called geophones are laid out on the land surface then a shock wave is produced by dropping large weights or by firing small explosive charges at sea the microphones are towed by a small boat and the shock waves are created by a sparker or an airgun devices which don't harm any fish in the area when the air gun is fired or the weight dropped the shock waves are reflected back from the rock layers below the reflected waves are picked up by the microphones and fed to a recording device again computers are used and the results studied to try and build up a three-dimensional picture of what lies below a picture which can be interpreted by the geologists and other scientists even with all this information the whole thing is still very much a guess the rock structures may appear favorable but do they really contain oil there's only one way to be sure a test well someone must make the decision to drill a decision which could cost millions of pounds we shall see how an oil well is drilled in the next film [Music]