Following the same steps as above in #7 and #8, calculate what the pressure would have been at the bottom of the well after the driller replaced the mud with seawater. For this problem, vou will use the same height of the well column (3396 m) but now the density of the seawater 15 1023 kg/m\"3. =9 Pressure (in units of kg/m-sec\"2) Pressure (in units of P5I) How much did the pressure decline at the bottom of the well when the driller replaced the mud with seawater? #10 Pressure (in units of PSI) Explain how the reduced pressure within the wellbore combined with the failure of the blowout preventer are related to the catastrophic fire and release of o1l into the Gulf of Mexico. =11 Do vou think the need for oil is worth the potential environmental damage and economic and social costs associated with a deepwater accident? Do vou think the U5, should put more emphasis on replacing its energy needs with renewable sources? [s there some acceptable middle solution? Part Il Petroleum Geology Petroleum refers to the collection of naturally occurring organic molecules consisting mainly of hydrogen and carbon atoms, hence the name hydrocarbons. Crude oil is composed of hydrocarbon molecules that exist in the liquid state, whereas gaseous hydrocarbons make up what is collectively referred to as natural gas. As illustrated in Figure 11.4, oil and gas accumulate in places where the molecules can become trapped within porous and permeable rock formations. The key to trapping oil and gas is the presence of an overlying impermeable layer that prevents the hydrocarbons from rising to the surface. Once located, an economical deposit is extracted by drilling a well. During the refining process, crude oil is heated in order to separate the various hydrocarbon molecules based on their density (natural gas requires only minimal refining). Products refined from crude oil include gasoling, diesel fuel, kerosene, motor oils, and grease. Peatroleurn Oil wells following trend of droplets anticline trap and reservoir Figure 11.4 Oil and gas become trapped in the subsurface beneath an impermeabie rock formation, thereby allowing hydrocarbons to accumulate in some underlying porous and permeable rock. Well Blowouts On April 20, 2010, operators of the Deep Horizon drilling rig in the Guif of Mexico lost control of an oil and gas well when they were in the final stages of converting the borehole into a production well. This accident, and subsequent environmental disaster, highlights the inherent dangers of extracting oil and gas. As depicted in Figure 11.5, drilling operators keep the borehole filled with a mixture of mostly water and clay, commonly referred to as drilling mud. The dense mud is pumped down through the drill pipe where it eventually exits out the drill bit. The mud then circulates back up the borenole toward the surface, camying rock fragments that had been dislodged by the drilling bit. At the surface the mud is sent into a pit where the rock particles are allowed fo settle out. The mud is then re-circulated back down into the well. In addition to removing rock fragments from the well, the sheer weight of the drilling mud is crucial to keeping highly pressurized oil and gas from entering the wellbore (cement seals are later installed when the well is completed). If the drilling operator is unable to contain the pressure from within the rock formation, then oil and gas can quickly travel up the borehole and onto the drilling platform, resulting in what is called a blowout. Modern wells are equipped with a blowout preventer, which is a large safety device designed to quickly seal the well should the operator be unable to control the pressure within the hole. If the blowout preventer fails, as in the case of the Gulf of Mexico disaster (Figure 12.6), it can lead to an intense fire that is extremely dangerous. Moreover, it can be quite difficult for the operator to regain control of the well, thereby resulting in a major release of crude oil into the environment. Deep water A Drilling Rig Circulating mud open wellbore Pressure Blowout due to Weight of Sea floor drilling mud open borehole pressure drilling from bit oil & GAS oil 1 GAS Reservoir Figure 11.5- Illustration of a deepwater oil and gas well. The first inset shows drilling mud circulating through the drill pipe and well bore. The second inset shows how the weight of the mud produces pressure that keeps oil and gas from entering the open borehole. Figure 11.6 - The Deepwater Horizon drilling rig after the April 20, 2010, blowout in the Gulf of Mexico (courtesy of the U.S. Coast Guard). For more information on the 2010 Deepwater Horizon Oil Spill, you can check out the lengthy and detailed final report (PDF document) at the link below: Final Deepwater Report27 For questions #5-6, refer to Figure 11.4 in the Lab 11 - Conventional Fossil Fuel Resources exercise file. 28 29 Exploring for petroleum deposits is restricted almost exclusively to sedimentary basins. Describe the geologic reason why oil companies rarely bother to explore in igneous and metamorphic terrain. #5 30 31 32 Explain the meaning of the "oil and gas window" label located on the left side of Figure 11.4. #6 33 34 35 For questions #7-10, you may choose to refer to Figures 11.5 and 11.6 in the Lab 11 - Conventional Fossil Fuel Resources exercise file. 36 You may also find the following equation helpful: pressure = (density of mud) x (gravitational constant) x (height of fluid column) 37 Units: density = kg/meters*3 height = meters gravitational constant = 9.8 meters/seconds^2 38 The 2010 blowout in the Gulf of Mexico occurred after the drilling operator replaced the drilling mud in the well with seawater during the 39 final installation of the cement seals. Assuming that the drilling mud had a density of 2160 kg/m^3 and that the column of mud was 5596 #7 m high, calculate the pressure at the bottom of the well using the equation for pressure given above. 40 Pressure (in units of kg/m-sec 2) 41 42 Convert the pressure you calculated above in #7 into pounds per square inch (PSI) using the following relationship: 1 PSI = 6896.6 kg/m-sec^2 #8 43 Pressure (in units of PSI) 44