Showing papers on "Overpressure published in 1994"

A physical explanation for the positioning of the depth to the top of overpressure in shale‐dominated sequences in the Gulf Coast basin, United States

Abstract: A one-dimensional model of fluid pressure and porosity evolution is used to investigate the physical processes that control the development and maintenance of overpressure in a compacting sedimentary basin. We show that for shale-dominated sequences the variation of the hydraulic diffusivity in both space and time is such that it produces a minimum between 2 and 4 km depth, consistent with observations from the Gulf Coast basin. This minimum inhibits the upward flow of fluid by acting as a “bottleneck” and thus determines the shallowest position of the depth to the top of overpressure. Above this region of bottleneck, overpressure does not develop because the porosity is sufficiently large to maintain high values of hydraulic diffusivity that are conducive to the rapid dissipation of excess fluid pressure. Within the overpressured shales, compaction propagates downward through the section, releasing fluids from the upper part of the section while continuing to restrain the upward flow of fluids from deeper within the section. As such, overpressures are predicted to be maintained within the deeper regions of a basin for tens to hundreds of millions of years. Further, fluid viscosity plays an important role in defining the depth behavior of hydraulic diffusivity as a function of time. Assuming a temperature-dependent fluid viscosity guarantees that the hydraulic diffusivity minimum will always exist during the development of the basin. On the basis of our results, we find that the depth at which the porosity equals 14±4% correlates with the depth to the local hydraulic diffusivity minimum and thus the depth to the top of overpressure. Moreover, we interpret that the 14±4% represents the threshold porosity for which a shale actually begins to act as a seal. Within the Gulf Coast basin, the gross sediment facies consists of lower massive shales across which deltaic systems have prograded allowing the deposition of an alternating series of sandstones and shales that grade vertically into massive sandstones. The massive sandstones are highly permeable and are connected hydrologically to the surface. We conclude that these sandstones play little role in the development of overpressure because of their high permeability except to the extent that the base of the massive sandstones marks the minimum depth possible for the top of overpressure. In contrast, overpressuring is observed to develop within either the shale-dominated sequence or the region of interspersed/interfingering sands and clays. The clay-encompassed sands play only a passive role in the development and maintenance of overpressure because it is the low-permeability clays that control the movement of fluids into and out of the sands.

Reservoir diagenesis and hydrocarbon migration under hydrostatic palaeopressure conditions

Abstract: Fluid inclusion studies from two contrasting fields in the Northern North Sea reveal hydrostatic pressure conditions during the formation of secondary quartz overgrowths which trapped both brine and petroleum inclusions. In these fields, dating of authigenic illite, part of the diagenetic sequence and broadly coeval with quartz cementation, permits comparison with modelled pressure conditions. Pressure modelling indicates the likelihood of several periods of overpressure in the past, interspersed with normal pressure. The timing of diagenesis coincides with one of these periods of hydrostatic pressure. Furthermore, as both fields are now highly overpressured, the cause and timing of overpressure generation post-date the diagenesis. A model is proposed to link the pressure history and diagenesis.

Method of producing overpressure valve for packaging containers

Abstract: A method of producing overpressure valves for packaging containers supplied in a roll, transported in this form to a packaging machine, separated at the machine and attached to packaging containers by means of an adhesive coated surface. For this purpose the overpressure valves have a layer of emulsion bonding on their underside. To prevent individual layers of the roll from sticking together, the overpressure valves have an adhesive-repelling layer on their top side. The overpressure valves are connected to one another in one piece and in a row, and are separated consecutively in a packaging machine.

A simple blast wave model for bursting spheres based on numerical simulation

Abstract: This paper deals with blast waves generated by a bursting spherical vessel filled with a pressurized gas. A large number of numerical simulations are performed. From the results of the simulations, a simple model comparable to the TNT-equivalent model is derived. The new blast wave model consists of a single relationship between the scaled peak overpressure and the scaled distance. Moreover, a closed-form expression for the explosion efficiency as function of the initial velocity only is provided.

Experimental Investigation on the Reduction of Railway Tunnel Sonic Boom.

Abstract: Sonic booms which were generated by the entrance of a high-speed train into a tunnel were experimentally reproduced using a scaled tunnel sonic boom simulator, whose test section was a tube with diameter 40 mm and length 25 m. An 18-mm-diam., 200-mm-long cylindrical piston was launched into the test section, so that a shock wave was emitted from the exit of the test section. An impulsive pressure wave, that is, the source of the sonic boom, was experimentally reproduced. A hood installed at the entrance of the test section effectively delayed the formation of the shock wave, thereby reducing the sonic boom. This method was effective in the range of relatively low piston speeds. By installing a 0.5-m-long porous wall at the exit of the test section, the pressure gradient of the shock wave became finite and the peak overpressure was decreased. Even in the case that the wall was only partially covered with the porous material, the poromeric effect was significant, in particular, for high piston speeds. When the hood at the entrance and the partially installed porous material on the exit wall were combined, the reduction of the peak overpressure became 50 to 80% in the range of the piston speeds from 60 m/s to 100 m/s.

Pore pressure estimation from velocity data: accounting for overpressure mechanisms besides undercompaction

Abstract: A new method for estimating pore pressure from formation sonic velocity data is presented. Unlike previous techniques, this method accounts for excess pressure generated by both undercompaction, and fluid expansion mechanisms such as aquathermal pressuring, hydrocarbon maturation, clay diagenesis, and charging from other zones. The method is an effective stress approach; the effective stress is computed from the velocity, and the result is subtracted from the overburden stress to obtain pore pressure. to include multiple sources of overpressure, a pair of velocity-vs.-effective-stress relations are introduced. One relation accounts for normal pressure and overpressure caused by undercompaction. The second is applied inside velocity reversal zones caused by fluid expansion mechanisms. Example applications of the method are presented from the U.S. gulf coast, the Gulf of Mexico, and the Central North Sea. some other pore pressure estimation approaches are also examined to demonstrate how these techniques have unknowingly accounted for overpressure mechanisms other than undercompaction. It is also explained how velocity-vs.-effective-stress data can be used to identify the general cause of overpressure in an area. For instance, the empirical correlation of Hottman and Johnson indicates that overpressure along the US gulf coast cannot be due only to undercompaction.

Safety device protecting against overpressure failure of a nuclear reactor pressure vessel

Abstract: A nuclear reactor has a core and a pressure vessel with a wall and an interior. A pressure relief responding as a function of temperature is provided in the case of insufficient core cooling (due to a highly improbable failure of the cooling devices and emergency cooling devices). A safety device protecting against overpressure failure of the pressure vessel upon insufficient cooling of the core includes a pressure pipe passing pressure-tightly through the wall and extending into the interior of the pressure vessel. The pressure pipe has at least one pressure compensation opening formed therein in the interior of the pressure vessel and has a fusible sealing body sealing the pressure compensation opening. The fusible sealing body is formed of a melting solder melting at a limit temperature, such as 600° to 700° C., and unblocking the pressure compensation opening, but keeping the pressure compensation opening sealed during normal operation. The pressure pipe in particular is a blow-off pipe with a pressure relief opening. However, the pressure pipe can also be a pressure control pipe, with which a blow-off valve provided outside the vessel can be triggered for reducing the system pressure.

Variability of measured sonic boom signatures

Abstract: The topics discussed include the following: atmospheric turbulence; BOOMFILE Database description; BOOMFILE flight conditions; XB-70 Database descriptions; analysis progression; extended database; prediction method; overpressure variability dependence on flight conditions; loudness variability on flight conditions; sonic boom variability in repeat flights; and statistical distributions.

Safety device against overpressure failure of a nuclear reactor pressure vessel

Abstract: A safety device against overpressure failure of a nuclear reactor pressure vessel in case of inadequate core cooling, includes a pressure relief system responding as a function of temperature. A differential-pressure-loaded pressure relief valve set in a wall or an immediately adjacent pipeline of the pressure vessel which is exposed to primary pressure, has a closure piece that is preferably a differential-pressure piston being mounted so as to be longitudinally displaceable and being sealingly retained in a closure position thereof by a fusible stop. When an upper threshold temperature is reached in the interior of the reactor, which causes the fusible stop to melt due to a threshold temperature heat flow reaching the stop, the differential-pressure piston is moved into an opened position thereof. With correspondingly lower cross-sectional dimensions of the pressure relief valve and lines connected thereto, the pressure relief line may alternatively be constructed as a control line for a separate relief valve.

Variability of measured sonic boom signatures. Volume 1: Technical report

Abstract: Sonic boom signatures from two databases, the BOOMFILE and the XB-70, were analyzed in terms of C-weighted sound exposure level (CSEL), A-weighted sound exposure level (ASEL), and Stevens Mark VII perceived level (PLdB), as well as the more traditional peak positive overpressure and rise time. The variability of these parameters due to propagation through atmosphere was analyzed for different aircraft Mach number and altitude groups. The low Mach number/low altitude group had significantly greater variation in rise time, overpressure, and loudness level than the high Mach number/high altitude group. The loudness of measured booms were found to have a variation of up to 25 dB relative to the loudness of boom predicted for a non-turbulent atmosphere. This is due primarily to the steeper ray paths of the high Mach number/high altitude group and the corresponding shorter distances traveled by these rays through the lower atmosphere resulting in reduced refraction effects. The general trend of decreased overpressure and loudness level with increasing lateral distance was also seen. Sonic boom signatures from early morning flights had less variation in rise time and overpressure than afternoon flights because of reduced turbulence. Measures of asymmetry (difference between compression and expansion portion of the signature) showed that the variability in Delta loudness level was greater than the variability in Delta overpressure due to the large influence of turbulence on rise time. Lastly, analysis of data within 50 percent of lateral cutoff showed that the mean value for overpressure and loudness level was independent of time of day but that the frequency with which it occurred was greater in the morning. This is a clear indicator of increased turbulence in the afternoon.

Thermal and pressure histories of the Malay Basin, offshore Malaysia

Abstract: The Malay Basin is a Neogene intracratonic basin characterized by high heat flow and rapid sedimentation; moderate to high overpressure is common in deeper reservoirs. Thermal conductivity and temperature data from 55 wells have been used to reassess the areal and vertical heat-flow distribution within the basin. Anomalously high temperatures have been observed in some sandstone intervals above the overpressured reservoir section. A narrow to rather abrupt pressure transition zone could be recognized. All hydrocarbon-filled reservoirs seemed to be associated with high heat flow (i.e., about 90 mW/m[sup 2]). Overpressure in some wells is approaching critical fracture pressure (i.e., 0.85 psi/ft. pressure gradient) in the region. In the central part of the basin, the overpressured sections are found within the shallower (<2000 m) hydrocarbon-bearing units. Selective studies of the temporal development of the pore pressure indicated that overpressure development is associated with episodes of rapid sedimentation. A preliminary fluid flow model supported by pressure modeling is proposed whereby hot fluids are currently being expelled from deeper overpressured sandstone and mudrocks through a fractured seal induced by overpressure. The latter is caused by relatively rapid burial since late Tertiary times. Hydrocarbon migration may have been aided by this fluid movement.

Barricade Influence on Blast Wave Propagation

Abstract: : As everyone knows, barricade is one of the most efficient means available to protect persons, goods and facilities against fragments. It is also an efficient solution to minimize blast hazards by reducing overpressure level just behind. Purpose of this study is to check that there is effectively an overpressure decrease behind barricade and to assess it. In order to improve our knowledge on this phenomenon, we analyzed scale model tests performed at Captieux (south of France). These tests consisted in overpressure measurements in free field and behind barricades to compare them. During these tests a double barricade efficiency was also assessed. Simultaneously, numerical simulations were carried out with a two dimensional finite volume code based on Euler equations. Following parameters were used in this study : NEQ (Net Explosive Quantity), Shape and sizes of barricade, Scaled distance between charge and barricade. Computed and experimental results are in a good agreement.

Contribution of thermal conduction effect to transition from self-explosion to detonation

Abstract: In this paper, we present a study concerning the special role of the thermal conduction effect on the transition from self-explosion to detonation occurring in the ignition by a pocket of hot reactive gas. At the initial moment, a uniform hot reactive pocket is assumed to be surrounded by cold reactive mixtures. The detailed evolution process from the initial conditions is simulated numerically taking into account chemical reactions, molecular transport effects and compressible effect for one dimensional geometry. It is found that thermal conduction may play a key role in the transition process for the case of intermediate initial temperature of hot pockets. When the initial temperature is just above the thermal extinction limit, a premixed flame is ignited after a diffusive explosion; and when the initial temperature is very high, it is also a premixed flame that is ignited after a constant density explosion. In these two cases, the produced overpressure is much smaller than that produced by the...

Variability of measured sonic boom signatures. Volume 2: Data report

Abstract: Sonic boom signatures from two databases, the BOOMFILE and the XB-70, were analyzed in terms of C-weighted sound exposure level (CSEL), A-weighted sound exposure level (ASEL), and Stevens Mark VII perceived level (PLdB), as well as the more traditional peak positive overpressure and rise time. The variability of these parameters due to propagation through atmosphere was analyzed for different aircraft Mach number and altitude groups. The low Mach number/low altitude group had significantly greater variation in rise time, overpressure, and loudness level than the high Mach number/high altitude group. The loudness of measured booms were found to have a variation of up to 25 dB relative to the loudness of boom predicted for a non-turbulent atmosphere. This is due primarily to the steeper ray paths of the high Mach number/high altitude group and the corresponding shorter distances traveled by these rays through the lower atmosphere resulting in reduced refraction effects. The general trend of decreased overpressure and loudness level with increasing lateral distance was also seen. Sonic boom signatures from early morning flights had less variation in rise time and overpressure than afternoon flights because of reduced turbulence. Measures of asymmetry (difference between compression and expansion portion of the signature) showed that the variability in Delta loudness level was greater than the variability in Delta overpressure due to the large influence of turbulence on rise time. Lastly, analysis of data within 50 percent of lateral cutoff showed that the mean value for overpressure and loudness level was independent of time of day but that the frequency with which it occurred was greater in the morning. This is a clear indicator of increased turbulence in the afternoon.

Twin shaft mangle useful esp. for avoiding hydrocarbon emissions

Abstract: The appts. gives pressure stages to give an overpressure and an underpressure.The stages operate independently of each other, simultaneously or separately. The entry and exit for each stage area accessible from outside the assembly.

Controllable pressure plasma torch for cutting and welding

Abstract: A controllable pressure plasma torch for both cutting and welding structurally features that it is mainly composed of cathode sleeve pipe, gas core tube, insulating body, anode sleeve pipe, nozzle, main exhaust channel, and overpressure exhaust valve. Gas goes to nozzle when overpressure valve is closed or is exhausted partially to outside of torch when the valve is opened as pressure exceeds a predetermined value. Thus pressure is constant.

Deep Pressure Seal in the Lower Tuscaloosa Formation, Louisiana Gulf Coast

Abstract: Repeat formation tester (RFT) pore pressure measurements spanning a depth range of 5500-6060 m in the lower Tuscaloosa Formation (Upper Cretaceous) document a pressure discontinuity of >20 MPa at ~5680 m forming a pressure seal in two natural gas fields in the Tuscaloosa trend, Louisiana. In the Morganza field the depth to the top of overpressure varies by less than 30 m across two adjacent fault blocks, though equivalent strata are downthrown by 100 to 120 m. In contrast, the depth to the top of overpressure in the nearby Moore-Sams field rises slightly across the same fault. Therefore, the nearly horizontal top of overpressure does not appear to coincide with time- or lithostratigraphic boundaries. The overpressures in all of the Moore-Sams and some of the Morganza fields wells follow a local hydrostatic gradient with increasing depth indicating that pore fluids below the pressure seal are in communication, and demonstrating that sandstone connectivity occurs below the pressure seal as well as above. In the remaining Morganza wells, overpressure increases with depth in a stair-step manner that may comprise offset local hydrostatic gradients, to magnitudes of 117 MPa at depths of 5.9 km. The occurrence of the pressure seal within interbedded sandstones and shales, where high sandstone connectivity is expected, suggests that the sandstones of the seal zone are unusually tight. The above observations coupled with a petrographic study of sandstones from the vicinity of the pressure seal suggest that extreme compaction of the sandstones after dissolution of carbonate cements may have contributed to the low permeability indicated by the pressure data, and that the seal formed a kilometer or more shallower than it is today.

An assessment of fluid flow and overpressure modelling in selected North Sea and Laramide basins

Abstract: The occurrence of overpressure observed in petroleum bearing basins must be understood in terms of generation and distribution in order to build up a fluid flow history. Overpressure influences expulsion and migration of hydrocarbons from source rocks. This thesis details and interprets observations and results of a case study into aspects of overpressure distribution, fluid flow patterns, causative mechanisms, palaeo- pressure and subsequent pressure history, the surface expression of overpressure and the mechanical strength relationships of sealing rocks. One of the principle study areas was the Alwyn field in the Northern North Sea. The overpressure distribution over the field area was seen not to be uniform. Organic geochemical data indicated that the source of reservoired hydrocarbons and associated fluids was the Viking Graben depocentre. Fluid inclusion data recorded in specific diagenetic mineral phases interpreted fluid flow conditions of hydrocarbons into the reservoir under normal pressures but elevated temperatures. When combined with computer generated pressure models, these diagenetic events were exclusive of modelled overpressure periods. The greatest contribution of overpressure was modelled as being a result of compaction disequilibrium but withalikely contribution from the thermal cracking of oil to gas which would also account for the present day distribution of overpressure across the Alwyn field area. The Uinta Basin with its relatively simple burial and thermal history allowed the production of a model . : involving a temporal history of overpressure generation, fracture development, regional tectonism, hydrocarbon maturation and expulsion and the process of Gilsonite emplacement. It is inferred that initial hydraulically induced fracturing of the Green River and overlying formations was a result of combined overpressure due to disequilibrium and regional extension with a possible contribution from the maturation of the source rock. This study recognised that the hydrocarbon was emplaced under a high pressure regime with evidence provide. by the existence of forcibly injected hydrocarbon sills. Hydrocarbons fractionated in the pre-existing vertical fractures to leave residual highly viscous and immobile hydrocarbons in veins seen at the present day. The third major component of this study detailed results from an assessment of the mechanical capacity of sealing rocks with respect to specific composition and mineralogy. It was found that increasing organic carbon decreased the compressive strength of the tested shale specimens. This relationship was interpreted as a possible result of the interaction of alkaline fluids to produce a dispersant which acts to reduce the cohesion of the organic rich shale.