Overpressure detection

The -sonic log can also be used to detect overpressured zones. The sonic measurements until recently were available only on wireline. Now, MWD sonic tools have been developed adding one more parameter for overpressure detection while drilling. Two equations relating the formation porosity to the transit time are used ... 

Example 24 Overpressure Detection with Rate of Penetration... 

Example 26 Overpressure Detection with Shale Resistivity... 

Design to contain overpressure where practical Maintain ignition source control Maintain use of inert atmosphere Provide automatic isolation via quick closing valves of manifold duct system on detection of fire/flammable atmosphere or overpressure in duct system... 

Figure 8.19 illustrates another example of the versatility of multidimensional OPLC, namely the use of different stationary phases and multiple development ("D) modes in combination with circular and anticircular development and both off-line and on-line detection (37). Two different stationary phases are used in this configuration. The lower plate is square (e.g. 20 cm X 20 cm), while the upper plate (grey in Figure 8.19) is circular with a diameter of, e.g. 10 cm. The sample must be applied on-line to the middle of the upper plate. In the OPLC chamber the plates are covered with a Teflon sheet and pressed together under an overpressure of 5 MPa. As the mobile phase transporting a particular compound reaches the edge of the first plate it must-because of the forced-flow technique-flow over to the second (lower) stationary phase, which is of lower polarity. 

Abnormal Formation Pressure Detection from Kicks. The kicks, or flow of formation fluids into the borehole, are the ultimate indication that the well has encountered an overpressured zone. Kick detection during drilling usually is achieved by use of a pit-volume indicator and/or a flow indicator. The usual pit-volume alert is 10 barrels drilling fluid volume increase. A differential mud flow indicator can also be used to detect kicks more quickly. 

Another important feature of mud logging and MWD/LWD, is the capability of overpressure zone detection. As was discussed previously in this section, overpressure estimates can be done during drilling with many techniques and accuracy increases with the number of parameters available. 

Figure 7.19 Chronpes 25 overpressure development chamber for forced-flow TLC. The configuration shown is for on-line detection. 

Pressure detection shall be used for closed enclosure applications. Threshold detectors provide an electric signal when a preset overpressure is exceeded. Dynamic detectors provide an electric signal to the control and indicating equipment (CIE). Typically they have both rate-of-rise and pressure threshold triggering points that can be configured specifically to the application conditions. Although this type of detector minimizes spurious activation of the isolation system (due to pressure fluctuations other than explosion pressure rise), care shall be taken to set up such detectors to meet appropriate detection response criteria for the particular application and protected enclosure geometry. 

Gas detection is provided in the petroleum industry to warn of and possibly prevent the formation of a combustible gas or vapor mixture that could cause an explosive overpressure blast of damaging proportions. There are two types of gas detectors used in the oil and gas industry. The most common and widely used is the catalytic detector. More recently, infared (IR) beam detectors have been employed for special "line of sight" applications, such as perimeter, boundary or offsite monitoring, pump alleys, etc. 

The technique was then changed to entrap a small mass of water under a molten aluminum surface and simultaneously to overpressure the system. In this manner it was hoped to collapse steam films around the water. The actual procedure employed a small glass sphere containing water. The sphere was moved beneath the aluminum surface and broken by impulsively loading the system from a falling steel cylinder which impacted on a graphite toroid immediately above the molten aluminum. About 0.7 g of water was released into I kg of aluminum at 1170 K and pressurized to about 8 MPa. No explosions were detected. 

Spatial coverage (At-Risk Volume Approach)—based on the correlation between flammable gas accumulation and the resultant overpressure upon ignition. The detection spacing is determined by estimating the size of the cloud that can present a credible escalation hazard. 

The equipment required to develop this type of sensor is very simple and resembles closely that used to implement ordinary liquid-solid separations in FI manifolds. The only difference lies in the replacement of the packed reactor located in the transport-reaction zone with a packed (usually photometric or fluorimetric) flow-cell accommodated in the detector. Whether the packing material is inert or active, it should meet the following requirements (a) its particle diameter should be large enough (< 80-100 fim) to avoid overpressure (b) it should be made of a material compatible with the nature of the integrated detection system e.g. almost transparent for absorbance measurements) and, (c) the retention/elution process should be fast enough to avoid kinetic problems. 

One of the main reasons why POSRVs are used in the process industry is because they can resist much higher backpressures than any other valves. This is without the use of vulnerable bellows, which can easily rupture. Worse, it is difficult to detect whether a bellow inside a valve has failed if the bellows have failed, the system is no longer protected against overpressure. 

Fig. 9.10. Enantiomer separation on a 29.5 cm (overall length, 38 cm) capillary packed with (3R, -/S)-Whelk-0-stationary phase by CEC under slight overpressure (10 bar). Conditions MES (25 mM, pH 6.0)-acetonitrile (1 3.5, v/v) 25 kV UV detection, 230 nm. Reproduced from [48], with permission.

Fig. 9.11. Enantiomer separation of thalidomide on a vancomycin chiral stationary phase by CEC under a slight overpressure (10 bar). Conditions 75 pm x 35.5 cm capillary mobile phase, methanol-acetonitrile-glacial acetic acid-triethylamine (80 20 2 0.2, v/v/v/v) 20 kV, UV detection, 220 nm. Reproduced from [52], with permission.

With a newly installed precautionary blind in the overflow line, the hidden blind in the vent line, and no additional overpressure devices, the tank was destined to fail. As liquid was pumped into the vessel the inerts had no place to go and the tank was pressurized to destruction. To the best of everyone s knowledge and the evidence, this hard-to-detect blind may have been inserted over a year prior to the incident for a previous internal inspection of the acid tank. Obviously the mechanic(s) who removed the other blinds a year or so before and on this occasion did not notice this one. 

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