Dense Gas Dispersion On Complex Terrain

Firstly, start from why the dense gas diffusion occurs (specific choice of sour gas blowout accident), and then study the dense gas diffusion model, followed by risk analysis of the consequences of the dense gas diffusion, and finally for the dense gas diffusion accident, that is sour gas blowout accident, do a study of the emergency response.(1) accident analysis of sour gas blowout out of control in mountainFirst, the details of the specific process of drilling engineering and underground work, provides the basic conditions for analysis of the subsequent uncontrolled blowout accident cause. Meanwhile, in-depth study of the well control technology, well control are technology, in essence, means taking a certain method to control the formation pore pressure, and borehole pressure remained essentially balanced, to ensure the smooth progress of drilling. According to the different size and method of controlling well kick, well controlled operations are divided into one level of well control (ie primary well control), two level of well controls and three level of well controls. Kick phenomenon has not been brought under control when the two level of well controls failed, and the uncontrolled influx of formation fluids into well bore, spouting the ground, it will become a blowout.Informations showed blowout accident occurred after1993on Chuandong far less than that before1993, in order to compare those with time, so select and study the display characteristics of the blowout case in1996-2005, found that as technology advances, in all kinds of jobs, drilling blowout proportion has decreased, and tripping blowout proportion increased, and different of general awareness of the people, but also can be seen through the statistics, the occurrence of shallow gas and high pressure deep well blowout proportions are almost the same. We need to strengthen the safety of shallow gas drilling well control awareness. Signs display the overflow before the blowout, kick, lost circulation and gas emplacement of oil and water, are very obvious. Operational errors, equipment factors, drilling fluid factors have higher proportion of direct cause of uncontrolled blowout. Rules and regulations factor, and sense factor of well control occupies an important proportion of the indirect causes of uncontrolled blowout.Then, do causation analysis of uncontrolled blowout accident. The accident theories of causation are a lot. Blowout accident caused by a number of accident factors, and accident factors appear to have some causal hierarchy and relation between different factors, under certain environmental conditions, eventually leading to the blowout accident. So select system analysis method, the fishbone diagram, which is more applicable, this is the first time use the method to analyze uncontrolled blowout accident causation. Based of aterial factors, human factors, management factors and environmental factors, in-depth study of the factors causing uncontrolled blowout accident, provides a theoretical basis for safety management countermeasures of the uncontrolled blowout accident.Human factor in uncontrolled blowout is throughout the whole drilling activities, so human reliability analysis make use of Bayesian methods. Bayesian posterior distribution is based on the prior distribution and sample information. For the prior distribution, if there is no objective information on the reliability of data acquisition with less demanding, you can completely select subjective methods to determine. Bayesian network reliability causal level model and the specific ideas of the reliability analysis are given.(2) dense gas diffusion model on the complex terrainUsually because of their molecular weight than the average molecular weight of air, the gas temperature is low, the gas in the presence of a liquid spray or the ambient temperature is too low, and other reasons, so that the density of the gas is greater than the air, so the diffusion of the gases in the atmosphere, different from the Gaussian diffusion, has the slump phenomenon, known as a dense gas dispersion.H2S has toxicity, the relative density of1.189. According to of Kaixian gas blowout accident casualties distribution of personnel and animals, can be found that, when sour gas uncontrolled blowout accident occurred, H2S slumping phenomenon is very obvious. Consider H2S in the gas as the research object, considering its dense gas effect, solve the dense gas diffusion processes in complex terrain conditions.Dense gas dispersion models are composed as shown in the following figure. For instantaneous release, box model is improved, suitable for slope terrain, and the model needs to the input of the sloping wind feild. For continuous release and complex terrain conditions, Monte-Carlo model of passive diffusion model is improved. The density is slightly denser than the air (ie, the air density can not be ignored), or the density is much larger than the air (air density can be ignored) within dense gas diffusion. When the model takes into account of the entrainment effect, which gradually decreases the density, and finally the gas density may be less than air diffusion and the dispersion become into passive diffusion. Monte-Carlo model requires inputs of complex terrain wind field. And, respectively, use the different methods to simulate. Due to the presence of complex terrain, wind farm is no longer a homogeneous field, and because of the change of the wind farm, dense gas substances diffusion process was complicated and much different of dense gas diffusion on flat terrain. a) improved box model applys to the slopeWind overall transports and dilutes the dense gas, and then affects the distribution of the concentration of the gas. So, the movement process of dense gas cloud on the slopes is divided into two stages.The first stage, dense gas dilution model on the flat terrain based box model. Combined the wind clouds dilution and delivery role, dense gas clouds do negative buoyancy diffusion, and the distribution of characteristic parameters of the model introduced similar distribution. Top turbulent kinetic energy are from three aspects: shear turbulent caused by difference of the clouds and environmental fluid velocity, turbulence generated by the dense gas clouds moving on the ground and turbulence in the atmospheric boundary layer. Top entrainment rate that is improved Eidsvik method used in TWODEE model. Dense gas clouds dilution model can get the cloud mass, density, Dimensions, entrainment of air quality as well as the concentration of hazardous substances within the cloud changes over time.The second stage, the dense gas cloud as a whole, overall transport models of the clouds on the slopes by wind. By diluting simulation of the dense gas cloud, you can get a cloud of dense gas quality, shape, size, and other parameters, for the calculation of the overall delivery model. The change with time of speed and distance of movement of the cloud can be obtained through the overall delivery model of dense gas.b) dense gas dispersion models on complex terrainFor dense gas dispersion on complex terrain, select Monte-Carlo simulation. Monte-Carlo method must first establish a stochastic model, and then determine the probability distribution of the random variable, more than enough to do a randomized trial, the process modeling, make statistical analysis of the experimental results, according to the law of large numbers, the solution of the problem of approximate estimated value is the average of the observed values.Individual gas molecules, micelles, particles, or small enough air bag are transported in a wind field. On the one hand, micelle particles advected by the average wind speed of the wind, on the other hand, because the wind is random, natural wind is an combined wind of average wind speed and instantaneous turbulence that intensely changes. So the motion of particles in the process also has a random nature, and is a random process. So Monte-Carlo simulation method can be used to simulate this process.Model constructions consider three cases:①When gas density is less than the air, the micelle particle movement is a combination of average wind field and a random part.②For the case that the density of the gas is slightly larger than the air, the air density can not be ignored. So, in order to build a dense gas diffusion model, on the basis of the first case, the model also introduce the gravity effect into the motion of the particles. Dense gas diffusion model, considering the entrainment effect, can be assumed that the micelle is a small enough gas package, and expansion scales of the small gas package are much smaller than the wind eddy scale, then you can consider the gas packet entrainment effect. In the dense gas diffusion process, with the entrainment, the small gas package density gradually decreases, and finally is converted into non-dense gas diffusion.③For the case that the gas density is much larger than the air, then the density of the air can be ignored, the force of gravity during the movement of the particles introduced into the particle to create a dense gas diffusion model.Turbulence model parameters opt the empirical formula. Wind field opt the diagnostic mode of mass conservation, and need to gather the data of the observation points, and then are interpolated into the horizontal and vertical space. Vertical interpolation is in accordance with the formula of the wind profile, and horizontal interpolation has to consider the terrain factor weighting coefficient. Thereby obtain the initial wind field. Variational method adjust the initial wind field, and get diagnostic wind field of mass conservation.Finally, select the more mature software HYSPLIT, the dense gas dispersion modeling, and settling velocity is set to determine the effect of dense gas.(3) risk analysis sour gas uncontrolled blowout accident in the mountainThroughly study on the basic theory of risk analysis, risk definitions, characteristics, and risk analysis are introduced.Then the risk analysis model, MEVIP model, is applied to risk analyze uncontrolled blowout accident. Model elements include incident intensity, vulnerability,, the probability of accident occurrence, macro society management factor and the emergency response capacity factor. Analysze those various elements, and discuss those calculation method. Although the researchers used the model (MEVIP model) applied to the risk assessment of the industrial park, this is the first application of the model in the uncontrolled blowout accident risk analysis.Safety system reliability analysis of uncontrolled blowout accident process, mainly select bow-tie diagram. The middle key event is uncontrolled blowout accident, and the left side is Fault Tree, and the right is event tree. Establish the uncontrolled blowout accident bow-tie diagram, and select a danger evolution of a typical type accident that blowout and circulation loss concur, and cause the consequences of a poison gas cloud, in which safety barriers are given. And then provide the ideas and methods of control for well control work as well as the consequences of the accident. Although researchers also gave a bow-tie model of uncontrolled blowout, but he did not adopt the fault tree and event tree, and he simply gave the cause and effect, and safety barriers.Finally, study on the damage of toxic gas poisoning in the uncontrolled blowout accident. Study the relationship between toxic dose and response, and in-depth discuss on the toxic gas poisoning evaluation criteria, establish dose response curve model, and study on acute poisoning assessment methods.(4)sour gas blowout control emergency response on complex terrainFirst, analyze the existing problems of the emergency rescue in complex topographic features of Kaixian King sour gas blowout. Then, build emergency rescue system of sour gas uncontrolled blowout accident under complex terrain conditions, and carry out a detailed study of each part.Then, do research on emergency response mechanism in sour gas blowout out of control. Analyze the principle of the development of emergency response mechanisms, natural gas uncontrolled blowout emergency response program/mechanism, the key steps in accident alarm, hierarchy of emergency response, and emergency escaping. Determine the response level by a classification based on the risk of accidents, corresponding with the accident different levels with different emergency levels, and gave the response level table, considering the risk of accidents, after considering the situation trend, the trend of emergency of serious accidents elevates level to adopt a higher level of response.