Showing papers on "Overpressure published in 1995"

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.

Overpressure Retardation of Organic-Matter Maturation and Petroleum Generation: A Case Study from the Yinggehai and Qiongdongnan Basins, South China Sea

Abstract: Three superimposed pressure systems developed in the Yinggehai Basin, South China Sea, as indicated by seismic data, well logs, and direct pressure measurements. The organic maturation profile is nonlinear, with three nonparallel segments that correspond to the shallow, normal-pressured system; the intermediate, overpressured system; and the deep, strongly overpressured system, respectively. The intermediate and deep overpressured systems have abnormally low R0 gradients. The organic maturity of these overpressured rocks is significantly lower than the maturity of normal-pressured source rocks in nearby wells with similar thermal histories and does not match the thermal histories of the rocks. Such an organic maturity anomaly is distinctly different from those aused by variation in activation energies, conductivity contrasts, and hydrologic effects, and is confirmed to be the result of overpressure retardation. The degree to which the organic-matter maturation is retarded, expressed as the difference between predicted and measured vitrinite reflectance, increases exponentially with increasing fluid pressure, confirming that pressure increases the activation energies of organic-matter maturation reactions. Overpressure retardation has been proven to be conditional and quite important for clearly understanding petroleum generation, migration, and accumulation in overpressured sedimentary basins.

Modelling of pore pressure evolution associated with sedimentation and uplift in sedimentary basins

Abstract: Unconformities, which represent either periods of interruption of sedimentation or, in most cases events characterized by deposition and subsequent erosion, are commonplace geological phenomena in sedimentary basins, and will affect the pore pressure evolution of the basin fill. The effect of unconformities on pore pressure, as well as on sediment compaction and on burial processes is studied using a numerical basin model. For coarse sediments, which are permeable so that their pore pressure always remains nearly hydrostatic, the effects of both pure deposition interruption (hiatus) and deposition-erosion events are negligible for pore pressure evolution. However, for fine-grained sediments, unconformities can modify the pore pressure and the stress state to varying degrees. The results show that the rate of removal of overlying sediments, the permeability of sediments and time play important roles in the pore pressure evolution. In the East Slope of the Ordos Basin (China), in which overpressure has not been detected in deep wells, the modelling results suggest that the large-scale erosion occurring in the Late Cretaceous and in the Tertiary may have removed high overpressure existing in the basin before the erosion.

Distribution and Generation of the Overpressure System, Eastern Delaware Basin, Western Texas and Southern New Mexico

Abstract: Three subsurface pressure systems have been identified in the Delaware basin: an upper normal pressure system, a middle overpressure system, and a lower normal pressure system. The overpressure system occurs in the eastern Delaware basin, covering six Texas and New Mexico counties. The depth of the overpressure system ranges from 3100 to 5400 m. The normal fluid pressure gradient is 0.0103 MPa/m in the eastern Delaware basin. The highest overpressure gradient, however, approaches 0.02 MPa/m, which is close to the lithostatic gradient of 0.0231 MPa/m. The overpressure system has a relatively flat top and a downwarped bottom. The maximum thickness of the overpressure system reaches about 2300 m at the depocenter and pinches out toward the edges. An area of excess pressure o curs within the system where the highest excess pressure reaches 60 MPa. Local underpressured areas due to production are found in the lower normal pressure system in the War-Wink field area. Overpressure in the eastern Delaware basin is mainly associated with Mississippian, Pennsylvanian, and Permian (Wolfcampian) shale sequences, which also are major source rocks in the basin. Initial sedimentation rates within the overpressure system range from 17 to 90 m/m.y. Corrected bottom-hole temperature measurements indicate that the geothermal gradient within the overpressure zone is 25.1°C/km, which is higher than the basin's average geothermal gradient of 21°C/km. Temperatures at the top and bottom of the overpressure system are about 80 and 115°C, respectively. This temperature range approximates the temperature of the average clay dehydration zone. The oil window in the War-Wink field is coincident with the overpressure system, which implies that hydrocarbon g neration and migration are active in the overpressure system. A two-stage overpressure model is proposed. Hydrocarbon maturation combined with mechanical compaction disequilibrium and clay dehydration are the initial causes for overpressure generation due to an abnormal increase of fluid volume and pore space. Subsequently, the increase in temperature due to a decrease of thermal conductivity and fluid migration within the preexisting overpressure system would reinforce further overpressuring due to the fluid thermal expansion.

The nature and diversity of pressure transition zones

Abstract: Pressure transition zones occur where the rate of pressure increase or decrease exceeds a fluid gradient. Transition zones are found between intervals of permeable rock and, in each case, fluid movement is impeded by a 9seal9, which acts as a temporary barrier over geological time. The composite profile of pressure vs. depth is a function of three phenomena: (1) the mechanism responsible for abnormal pressure, (2) redistribution of pressure due to fluid movement during and after the mechanism is occurring, and (3) the lithological profile of the rock succession. Pressure profiles in some overpressured systems can reveal which of the mechanisms is causing the overpressure. Once overpressure has been created, pressure decay and transference away from the interval of generation can strongly influence the nature of transition zones. Transition zones are controlled in a fundamental way by the permeability of the rocks in which the abnormal pressure is found.

Sonic boom propagation through a realistic turbulent atmosphere

Abstract: A model of the turbulent atmosphere based on the von Karman spectrum is used in conjunction with a scattering center‐based model to simulate sonic boom propagation. The distribution of rise times and peak overpressures predicted by the model are compared to those measured during a field test. Calculated rise times increase in the presence of turbulence, but the computed shift of the distribution toward higher values is less than measured. The predicted distribution of peak overpressure underpredicts the shift in overpressure to lower values displayed in the measured distribution. This underprediction is consistent with the rise time prediction. Future work will investigate the effect of anisotropic turbules on sonic boom propagation.

Neural network analyses of stress-induced overpressures in the Pannonian Basin

Abstract: SUMMARY Artificial neural networks can learn relationships between sediment characteristics (burial depth, composition, coordinates and thickness of overlying Quaternary deposits) and overpressures from well data, after which they can interpolate and extrapolate to areas and depths not covered by wells. We analyse data from the south-eastern part of the Pannonian Basin. We use a neural network for analysing fluid overpressures because of the complex interaction of the key variables, making it difficult to derive the functional relationships required for a statistical analysis. The optimal topology of the network (number of hidden layers and neurons) is found by minimizing the network’s training and testing errors. The optimal design of the network resembles the interactions scheme of the key variables. The Pannonian Basin, originally formed in an extensional regime, has been in a compressive state of stress since Late Pliocene, causing anomalous subsidence patterns. Numerical forward modelling of compaction-driven fluid overpressures shows that, due to an increase in the level of compressive interplate stress, the fluid overpressures in the deep subbasins have increased substantially since Late Pliocene, giving rise to a very high overpressure (up to 45MPa) at present. The neural network analyses provide an independent estimate of the current amount of overpressuring in this basin, complementing the numerical forward modelling results. The overpressure profiles obtained by the two modelling approaches are in excellent agreement, showing the same magnitude of overpressures, a reversal of the overpressure in the deepest parts of the subbasins and a general decrease of the overpressure from SW to NE.

Preliminary airborne measurements for the SR-71 sonic boom propagation experiment

Abstract: SR-71 sonic boom signatures were measured to validate sonic boom propagation prediction codes. An SR-71 aircraft generated sonic booms from Mach 1.25 to Mach 1.6, at altitudes of 31,000 to 48,000 ft, and at various gross weights. An F-16XL aircraft measured the SR-71 near-field shock waves from close to the aircraft to more than 8,000 ft below, gathering 105 signatures. A YO-3A aircraft measured the SR-71 sonic booms from 21,000 to 38,000 feet below, recording 17 passes. The sonic booms at ground level and atmospheric data were recorded for each flight. Data analysis is underway. Preliminary results show that shock wave patterns and coalescence vary with SR-71 gross weight, Mach number, and altitude. For example, noncoalesced shock wave signatures were measured by the YO-3A at 21,000 ft below the SR-71 aircraft while at a low gross weight, Mach 1.25, and 31,000-ft altitude. This paper describes the design and execution of the flight research experiment. Instrumentation and flight maneuvers of the SR-71, F-16XL, and YO-3A aircraft and sample sonic boom signatures are included.

Noise absorber with variable damping characteristic, for pulsed gas flow, especially exhaust silencers

Abstract: The chamber contains a housing (2), its gas supply pipe (2), pipes (3.1,3.2) integrated in the housing, a pipe coated valve, an actuating box (10) with a diaphragm (11), spring (12), piston rod (13), and pressure connecting union, and a pressure line (6). The actuating box is of overpressure type. The pressure line feeds a gas counter-pressure to the diaphragm overpressure side. The diaphragm low pressure side is engaged by ambient pressure and the spring. The piston rod has a tight seal (14) against the housing.

Pressure gauge overpressure safety release

Abstract: A pressure gauge in which the displacement tip of the Bourdon tube is sealed and secured to a bracket of an amplifier movement by a selected solder composition affording a failure response to an encountered overpressure at a pressure value lower than the burst pressure of the Bourdon tube. Overpressure causes a fracture in the solder to be incurred enabling release of the overpressure while a throttle plug situated in the inlet path to the Bourdon tube severely restricts continuing gas flow to the fracture site. As a consequence, released flow from the solder fracture will be at a pressure insufficient to potentially cause explosion of the gauge case/lens to occur.

Pressure Loads on a Plane Surface Submitted to an Explosion

Abstract: Research investigations of overpressure interactions with large surfaces were carried out with a series of small scale experiments. In this study, the overpressure is created by the detonation simulated by means of a soap bubble confining an explosible gaseous mixture.

Deep-well fluid-extraction pump

Abstract: This invention features a small-enveloped (with an outside diameter of at least approximately 38 mm), single-acting, hydraulically-operated, reciprocating, deep-well, fluid-extraction pump, operable in non-straight and angular wells, and its mode of operation. The hydraulically-operated, deep-well pump, in addition to having an above-ground installation of its motor-fluid generator and of its control valving, comprises a compound, stepped piston that is reciprocably mounted within a cylinder which in turn is divided into individual pressure chambers. Hydrostatic pressure created by a hydraulic pump is selectively directed to two outlet ports to produce an overpressure in one of the outlet ports at any given instant. The overpressure in each outlet port leads to creation of overpressure in one or more pressure chambers. Imbalances in pressure among the pressure chambers result in movement of the compound, stepped piston and extraction of hydraulic-well fluid by the compound, stepped piston. Reversals in flow pattern of the pressurized hydraulic-well fluid are realized by changing alignments of the outlet ports from parallel-flow porting to crossed-flow porting and vice versa. Individually adjustable pumping-cycle and suction-cycle time and independently adjustable up- and down-stroke velocity, as well as independently adjustable time delay for well recovery, may be allowed. An improved self-cleaning suction filter is used in screening any hydraulic-well fluid and an anti-gaslocking design is presented. Function of dynamic, preferably metallic, self-adjusting, fluid seals, used in the hydraulically-operated, deep-well pump is based upon a dynamic, pressure drop of turbulent axial flow through a plurality of closely-controlled, radial clearances and a plurality of closely-fitting seal rings.

Occurrence, origin and implications of overpressure in the Malay and Penyu Basins, offshore Malaysia

Abstract: There are four (4) common reasons why drilling of a well is terminated, namely reservoirs are not economical in the deeper section, reservoirs are poorly developed, operational problems and overpressure. Eighty percent of wells drilled in the Malay-Penyu Basin have been terminated either in anticipation or due to overpressure. This study uses pressure versus depth plots generated from RFT and DST readings taken in 94 exploratory well spread throughout the Malay-Penyu Basin. Overpressure in this area is found to be neither depth dependent nor age related. The margins of the Malay Basin and the entire Penyu Basin are fo~d to be normally pressured. The central portion of the Malay Basin is overpresswed. The onset of overpressure appears to be abrupt in the north and more gradual in the southern portion. Carigali drilled Resak 6F-18.4 in 1993 and successfully penetrated an overpressured zone finding hydrocarbon bearing reservoirs within and beneath this zone. An understanding of this phenomenon is crucial in the planning of safe and efficient drilling campaigns.

Quantitative models of very high fluid pressure: the possible role of lateral stresses

Abstract: Because of the occurrence of very large observed overpressure in a well located in SE Asia, numerical modelling has been undertaken to evaluate evolution of the sediments. The intensity of the excess pressure, close to lithostatic pressure, and the likely relation to induced, open-fracture anomalies, as well as evidence of large fluid transfers, all lead to the suggestion that the tectonic regime is related to the generation of high excess pressure. To verify this hypothesis, a 2D fluid-flow/compaction model (GEOPETTI) was used to test whether high excess pressure could be obtained without considering the effect of lateral stresses. While high excess pressures are possible, even if undercompaction is the only process considered, the distribution of fluid pressure with depth does not correspond to that observed, and the migration of fluids cannot be reproduced because of the extremely low permeability of the sediments. Accordingly, the model has been modified so that the effect of lateral stresses can be investigated through: (1) the value of the fracturing coefficient which controls the maximum overpressure that it is possible to generate; (2) the sensitivity of the system to a possible compressive event, which could squeeze the sediments laterally so that the rate of fluid expulsion would be greater than if the fluids were driven only by the mechanical load of sediments. Finally, the role of faulting or fracturing is discussed as a possible mechanism responsible for the upward transfer of fluid which can lead to an increase of excess pressure at depths shallower than the depth where excess pressure was first generated, a mechanism also leading to high excess pressure. Moreover, this mechanism allows for a good reproduction of observed excess pressure distributions.

Thermal expansion analysis for differential pressure transducers by the LIGA process

Abstract: Characteristics have been analyzed to understand the motion and the response of the microelectromechanical pressure transducers fabricated by the so-called LIGA process. The metal bridge for the overpressure protection of the diaphragm was built on the silicon substrate. The difference in thermal expansion coefficients between the metal and the silicon causes the crucial distortion of the differential transducers when temperature changes occur. A thermal expansion analysis has been made for temperature changes to provide the basis for credible designs. Thermal stresses, displacements and capacitance were calculated by the commercial finite-element code ANSYS. Interface shear stress between the substrate and the overpressure stop due to temperature changes increases with stop thickness, but eventually a small reduction in the peak occurs. The gap-bulging for the thin metal stop results from the bending at the interface.

ASME code safety valve rules -- A review and discussion

Abstract: Safety valve rules, i.e., rules for overpressure protection by the use of various pressure-relieving devices, vary somewhat among the five book sections of the ASME Boiler & Pressure Vessel Code which require such protection. This paper reviews those rules by discussing the following topics : Pressure relief device terminology and function. The problem of overpressure protection. Code rules for overpressure protection : rules for determining required relieving capacity ; for allowable overpressure ; for set pressure and set pressure tolerance ; for blowdown. The various pressure relief devices permitted by the Code. Design of pressure relief valves. How relieving capacities are established and certified. The qualification of pressure relief device manufacturers. Installation guidelines. Concluding remarks.

Overpressure in the Central North Sea

Abstract: The Central Graben of the North Sea is characterised by high levels of overpressure. This causes drilling problems and may control the migration and entrapment of hydrocarbons. Pressure measurements from repeat formation tests, mud weight and drilling gas levels have been compiled and interpreted, and integrated with the structural, lithostratigraphic and diagenetic framework of the basin. Interpretation of this data reveals that Jurassic sandstones in the region are divided into a boxwork of pressure cells. These are bodies of rock which are internally in hydraulic communication but externally isolated from adjacent cells by pressure seals. Pressure seals in the region are lithological and vary with depth, in contrast to previous hypotheses of diagenetic or temperature controls. The magnitude of overpressure in a pressure cell is controlled by the structural position of the cell, with high overpressures (close to the lithostatic pressure) occurring in structurally-elevated cells on an axial horst. Lateral hydraulic communication between deep regions and structurally-elevated positions increases the fluid pressure in the permeable sandstones in the elevated regions. This leads to focused vertical fluid flow through the thin aquitard at these elevated regions, which are termed "Leak Points". Here, the pressure seal occurs at the top of the permeable Jurassic sandstone, while in adjacent off-structure regions the pressure seal occurs in the Kimmeridge Clay Fm., the region's petroleum source rock. Analysis of density and sonic log data demonstrates excess mudstone porosity in the overpressured cells, suggesting that disequilibrium compaction is a cause of overpressure in the region. The location of pressure seals within gas-mature source rocks suggests hydrocarbon generation may also play an important role in causing overpressure. Quantitative computer modelling of the basin supports the data-driven model, emphasising lateral flow in Jurassic sandstones beneath the pressure seal and focused vertical flow across formations at structurally-elevated points. The model shows that rapid Cenozoic sedimentation, coupled to low permeability of the mudstone- dominated basin, has led to disequilibrium compaction due to restricted fluid flow. The model suggests that overpressuring began at 40 Ma in Jurassic sandstones of the Graben axis. A link between overpressure-controlled fluid flow and the K-Ar dates of authigenic illite in the Jurassic sandstones is delineated. Measured illite dates coincide with modelled periods of declining fluid flow. A link to the incursion of organic acids from adjacent mudstones into the sandstones is proposed, with the supply of organic acids controlled by the compaction and overpressure in the basin. The distribution of porosity within Jurassic sandstones is examined and is shown to be controlled by the complex distribution of overpressure. Overpressure supports the development of secondary porosity. Products of mineral dissolution are preferentially removed from Leak Points due to enhanced vertical fluid flow. This results in 10-12% excess porosity at 4.6 km depth. Overpressure is a dynamic system, with basin-scale structures such as pressure cells being caused by microscopic changes in pore size. The basin-scale overpressure systems in turn effect pore-scale alterations on the basin. Overpressure is an expression of the complex dynamic interaction of coupled hydrogeological and geochemical processes active throughout the evolution of the basin.

Atmospheric effects in spacecraft interiors following orbital debris penetration

Abstract: Orbital debris penetration of manned spacecraft is accompanied by a number of atmospheric effects that can pose a serious hazard to spacecraft and crew survival. These atmospheric effects can include overpressure, light flash, and temperature rise as hot particles from the penetration process impinge into the atmosphere of a manned spacecraft. This paper reports the results from a series of tests sponsored by the Marshall Space Flight Center and recently completed at the University of Alabama in Huntsville Aerophysics Research Center to study these effects. In these tests, a light gas gun was used to fire orbital debris particle simulants from 0.375 to 0.625 inches in diameter through target simulants into a large test chamber simulating the interior cabin of a spacecraft at 1 atmosphere. The test chamber was instrumented with pressure transducers, light sensors, and temparature gauges to measure the level of blast hazard associated with differing target and penetrator conditions at various distances from the target site. The mitigating effects of interior equipment racks and spall blankets were also measured. This report discusses the relationship between observed overpressure, light, and temperature effects and the hazard level that would be expected to cause crew injury.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Prediction of Overpressure from Finite Volume Explosions

Abstract: Tri-nitro toluene (TNT) equivalence is not a good criterion for evaluating the practically encounted nonideal blast waves during ignition and in explosion-safety problems. A theoretical model which shows the trends related to the effects of source volume and energy time release on blast wave strength is discussed. A slower energy release and a larger source volume are shown to be necessary to reduce the blast effects.

Rupturing element for use in overpressure rupturing protection devices for electrical capacitors

Abstract: A rupturing element (7) for use in overpressure rupturing protection devices for electrical capacitors has a weak point (8) which is produced by removing material on both sides, the removal of the material being arranged offset in the axial direction of the rupturing element (7).

Design and Testing of Low Sonic Boom Configurations and an Oblique All-Wing Supersonic Transport

Abstract: From December 1991 to June 1992, applied aerodynamic research support was given to the team working on Low Sonic Boom configurations in the RAC branch at NASA Ames Research Center. This team developed two different configurations: a conventional wing-tail and a canard wing, in an effort to reduce the overpressure of shock waves and the accompanying noise which are projected to the ground from supersonic civil transport aircraft. A generic description of this sensitive technology is given.

Method and apparatus for rapid pressure reduction in a plant, especially in a hydrogen-cooled generator

Abstract: A process and device are disclosed for quickly reducing pressure in an installation having at least one first and one second housing part (3, 4). The first housing part (3) contains in the normal state a hydrogen atmosphere under overpressure separated by a hydrogen seal (6) from the inside of the second housing part (4). When the hydrogen seal (6) breaks down, hydrogen overpressure is evacuated through a quick emptying pipe (8) in communication with the inside of the second housing part (4) through a venting pipe (9). The invention is preferably used in hydrogen-cooled generators.