Sunday, January 06, 2013

Overview of my job

The division that I work for provides directional services and formation evaluation services. Directional services means that as the well is drilled we measure the azimuth of the hole, which is like the compass bearing and measure the inclination, which is the angle from vertical to horizontal. The measurement are taken every 90 feet or 30 meters and from these measurements, the path of the hole can be determined and plotted. In addition we have tools, behind the bit that we can communicate with and can steer the hole in any direction or inclination we want. Before the hole is drilled the oil company provides us with a plan for the hole path, based on where the oil or gas is located, and we then steer the well on this path, something like steering a car down a road. Formation evaluation means that we measure properties of the rock we are drilling to determine the type of rock and whether it has oil or gas. To accomplish this we have sensors in the pipe behind the bit that measures the rock properties and sent that information to our computer systems on the surface. Presently there are many different types of drill pipe tools containing many different sensors and  more being developed all the time. The most common ones are as follows. A gamma tool measures the natural gamma radiation in the rock and from this it can be determined if we are drilling in sandstone or shale. Oil or gas is found in sandstone. A  resistivity tool measures the natural resistivity of the rock which is really measuring the resistivity of the fluid in the pores of the rock. Low resistivity is water and high resistivity means oil or gas. So now we can see if we are drilling in sandstone or not and if the sandstone contains oil. The third most common type are the nuclear tools. Radioactive sources are put in the pipe which bombard the formation with gamma radiation and neutron radiation. Without going into detail, from this measurement the density of the rock can be determined from which can be determined the porosity of the rock. Porosity means how big the pores of the rock. The higher the porosity the bigger the pore are and the more fluid that is in the pores. Hopefully this fluid is oil or gas. In summary from these first three formation evaluation measurements we can determine if we are drilling in sandstone or not, containing oil or not and form the porosity how much oil is there.

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