BOPS surface

Fortunately, the judicious use of Cl yields a chemically reasonable DZ + P surface for F + H2 (Figure 1). In particular, the predicted classical barrier height of 1.66 kcal is in fortuitously close agreement with the experimental activation energy. Further, the exothermicity of the BOPS surface is -v3 kcal greater than the experimental value. Thus, the primary significance of the BOPS Cl surface was that it appeared to be the first qualitatively correct a initio surface for a chemical reaction more com-plicated than the prototype (1 ) H + H2 system. 

The earliest indication of the qualitative correctness of the BOPS surface came from the classical trajectory studies of Muckerman (1 1 ). Muckerman varied several features of the London-Eyring-Polanyi-Sato (LEPS) surface for F + H2 to get the best agreement between predicted and experimental (, 3) FH vibrational energy distributions. Although this work was done completely independent of the BOPS ab initio study, Muckerman s "best" semi-empirical surface (his surface V, summarized in Table I) has a saddle point position essentially indistinguishable from the BOPS surface. Since the saddle point position is probably the most critical surface feature not directly accessible to experimental determination, this concurrence was especially significant. 

Perhaps the next important development was the fitting of the BOPS surface to an LEPS form by Polanyi and Schreiber (12). 

It should be noted that this fitting was carried out against the present authors advice, our feeling being that the BOPS surface was not sufficiently accurate to be used without adjustment in dynamical studies. Nevertheless, Polanyi and Schreiber fit the 232 col linear points to the LEPS form with an ensuing rms deviation of less than 1 kcal per point. This exercise in itself is rather striking confirmation of the LEPS form, which has only seven adjustable parameters. The most obvious weakness of the BOPS-FIT surface was a spurious 0.4 kcal attractive well in the entrance valley. In addition, of course, the BOPS-FIT surface incorporated the known 3 kcal BOPS error in the predicted exothermicity. 

Col linear classical trajectory studies were then performed using the BOPS-FIT surface. By comparing with the experimental vibrational distribution, Polanyi and Schreiber (PS) concluded that although the BOPS surface was qualitatively reasonable, it does have a rather serious failing. That is, PS concluded that the BOPS surface drops too rapidly from the "shoulder" into the exit valley. It was noted, of course, that the known error of 3 kcal in the exothermicity is a major factor in this rapid drop. Our current feeling is that while this criticism of the BOPS surface may well prove to be at least partially valid, the use of classical (rather than quantum mechanical) dynamics and one (rather than three) dimension detracts from the strength of the PS conclusion. 

Polanyi and Schreiber also suggested a "best" adjusted LEPS surface, their SE-I, and this surface is also summarized in Table I. There it is seen that the SE-I surface has its saddle point position somewhat later than either BOPS or Muckerman V. Nevertheless, it seems clear that the primary features of all three surfaces are rather similar. Both Muckerman (11 ) and Polanyi and Schreiber (12 ) have argued that the agreement between their best surfaces and the ab initio BOPS surface supports their use of the generalized LEPS form. We concur. 

In an attempt to resolve some of the controversy arising from the BOPS surface, we decided in 1974 to attempt to determine an ab initio surface of sufficient reliability to be used directly or, with modest amounts of scaling, in dynamical studies. 

An important safety feature on every modern rig is the blowout preventer (BOP). As discussed earlier on, one of the purposes of the drilling mud is to provide a hydrostatic head of fluid to counterbalance the pore pressure of fluids in permeable formations. However, for a variety of reasons (see section 3.6 Drilling Problems ) the well may kick , i.e. formation fluids may enter the wellbore, upsetting the balance of the system, pushing mud out of the hole, and exposing the upper part of the hole and equipment to the higher pressures of the deep subsurface. If left uncontrolled, this can lead to a blowout, a situation where formation fluids flow to the surface in an uncontrolled manner. 

In the event of a sudden loss of mud In an Interval containing overpressures the mud column in the annulus will drop, thereby reducing the hydrostatic head acting on the formation to the point where formation pressure exceeds mud pressure. Formation fluids (oil, gas or water) can now enter the borehole and travel upwards. In the process the gas will expand considerably but will maintain its initial pressure. The last line of defence leff is the blowout preventer. However, although the BOP will prevent fluid or gas escape to the surface, closing in the well may lead to two potentially disastrous situations ... 

A formation fluid kick can be efficiently and safely controlled if the proper equipment is installed at the surface. One of several possible arrangements of pressure control equipment is shown in Figure 4-351. The blowout preventer (BOP) consists of a spherical preventer (Hydril), blind and pipe rams, and the drilling spool. 

This is set deeply enough to protect the borehole from caving-in in loose formations frequently encountered at shallow depths, and protects the freshwater sands from contamination while subsequently drilling a deeper hole. In case the conductor string has not been set, the surface casing is fitted with casing head and BOP. 

Blowout preventers (BOPs) function is to cut off the flow of potential blowout. In all wells being drilled there are normally three holes or pipes within pipes that are at the surface of the wellhead -conductor pipe, casing pipe, and drill pipe. The drill pipe is the actual hole while the outer two are annulus formed around the inner pipe. Any one of these under varying conditions can be a source of through which oil or gas can escape during drilling. The annular preventer is a valve that appears... 

The heat loss is 300 W for a surface temperature of 50 °C and an area of 1.5 m. The system offgas temperature was calculated by closing the energy balance. The offgas temperature is 121 °C for a cathode air flow rate of 1.2931 g/s (corresponding 60lN/min). The cathode air blower causes mainly the parasitic electrical demand of the BoP components. Overall, BoP power demand has to be less than 270 We to obtain the demanded electrical net system efficiency of 35 %. For that case, an electrical net power output of 390 W results. Thus, the initial performance goals seem feasible. 

Conditions at the deep ocean seabed are always just a few degrees above freezing. The oil reservoir itself - probably more than a billion barrels - was a further 4.5 km below the seabed, where the temperature would be about 100°C. Figure 14.3 gives a schematic representation of the layout, comprising Deepwater Horizon on the surface, the blowout preventer (BOP) on the seabed nearly 5000 feet - some 1500 m -below the surface, and the hydrocarbon reservoir 18,360 feet (nearly 6000 m) below the surface. 

A forensic examination of the BOP stack revealed that elastic buckling of the drill pipe had forced the drill pipe up against the side of the wellbore and outside the cutting surface of the Blind Shear Ram blades. As a result, the BSR did not completely shear the drill pipe and did not seal the well. 

In the opinion of one of the major manufacturers of BOP stacks, these very large seals normally fail as a result of mechanical damage. Thus the ability of special elastomers to resist more aggressive fluid environments is less important than high mechanical strength. The shear bulk of these seals limits chemical attack to the surface only. 

The melamine aggregates were been saturated surface dry. Therefore, melamine aggregates immerse in water at approximately 2 PC for 24 hr and removing surface moisture by warm air bopping. 

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