Overpressure

About: Overpressure is a research topic. Over the lifetime, 3236 publications have been published within this topic receiving 34648 citations.

Discovery of “Enveloping surface of oil and gas overpressure migration” in the Songliao Basin and its bearings on hydrocarbon migration and accumulation mechanisms

Abstract: The Fuyang oil layer of the Songliao Basin is a tight and low-permeability sandstone pay zone formed in the fluvial-shallow water delta environment. In the formation are mainly lithologic reservoir and tight reservoir. The lacustrine-mudstone of K2 qn 1 is a good source rock and also acts as a good regional cap rock. The Fuyang oil layer is a typical upper-source and lower-reservoir pattern distributed in a large area. Based on a large number of exploration and development data, a macroscopic enveloping surface is found developed in the Fuyang oil layer, which is below K2 qn 1. The effective reservoirs within the enveloping surface are commonly saturated with oil, and below the enveloping surface are mainly water layers. The distance from the enveloping surface to the bottom of the source rock is usually 100–350 m and at most 550 m. Through the research of the distribution patterns and the physical properties of the sandbodies above or beneath the source rock, it is concluded that: 1) the enveloping surface is the boundary of the overpressure hydrocarbon migration; 2) the spacial distribution of the pressure release beds controls the direction and the distance of the overpressure hydrocarbon migration; 3) tight oil reservoirs and lenticular oil reservoirs are mainly formed inside the envelope surface, whereas, conventional reservoirs are formed outside the envelope surface as a result of the buoyancy hydrocarbon migration. The discovery of the “overpressure hydrocarbon migration enveloping surface” and the concepts of overpressure hydrocarbon migration and buoyancy hydrocarbon migration not only challenge the old notion that “hydrocarbon migrates along the faults and is distributed along fault belts” in the Fuyang oil layer of the Songliao Basin, give a new explanation to the long-distance-oil-downwards migration (hundreds of meters) and expand the exploration potential of the Fuyang oil layer, and provide a rational guidance to the exploration of syncline plays, but also better categorize tight oil/gas and conventional reservoirs in all of the key elements related to hydrocarbon migration, accumulation, reservoir characteristics and oil and gas spatial distribution.

Influence of geometrical shapes on unconfined vapor cloud explosion

Abstract: The vapor cloud explosion (VCE) usually results in large financial and environmental damages. There are many methods to evaluate the consequences of VCE and one of them is the TNO Multi-Energy method (MEM). In the practical applications, the MEM has some weaknesses. For example, it is assumed that the explosion model is hemispherical, which is usually inconsistent with the actual situations. In order to examine the effect of the geometrical shapes on explosion characteristics, a constant volume of clouds with different height-width ratios and length-width ratios were studied. For the vapor cloud with a given volume (32 m3), the geometrical shapes have a great influence on the explosion overpressure, but little on the explosion temperature. When the height-width ratio is 0.5 (the corresponding geometrical shape is 4 m × 4 m × 2 m), the explosion peak overpressure reaches the maximum of 1.57 bar, which is 3.6 times of that (0.44 bar) for the 2 m × 2 m × 8 m vapor cloud. For a constant volume of clouds with the four different height-width ratios in this paper, the MEM predictions correspond to three different initial explosion strengths. As effect of the geometrical shapes on the vapor cloud explosion was not taken into account in the MEM, its predicted results have a greater deviation, especially in the far field. For the scenarios calculated in this study, the relative error for the explosion overpressure predicated in the MEM reaches 150%.

Stress wave propagation in confined soils

Abstract: : Phenomenon involved with the propagation of air-induced stress waves in soil were investigated in experiments on Edgar Plastic Kaolin (EPK) clay and Ottawa sand. The principal soil variables were moisture content and density in the case of clay, and density in the case of sand. The soil specimens were loaded with overpressures in the range of from approximately 50 to 300 psi. Two overpressure wave shapes were used, one where peak overpressure had a dwell time of approximately 1 msec and the other having essentially a zero dwell time of peak pressure. Stress-time and strain-time relationships were measured at various points along the length of the specimens. Peak stress attenuation, strain and strain-rate relationships, propagation velocity, changes in wave shape, and stress-strain relationships are discussed in the light of the data obtained. Experimental data are compared with theoretical predictions of a linear hysteretic model in the case of Ottawa sand, and a constant tan Omega viscoelastic model, in the case of the EPK clay. It was found that in both cases the theories could be used to predict the experimental results with proper evaluation of critical attenuation parameters to be input with the theories.