Modelling atmospheric dispersion during oil and gas extraction activities

摘要

There exists a great interest to evaluate the environmental impact every time that a accident occurs. This phenomenon are transient in their behaviour and in general very dangerous to nature. Field observations show that emergency planning may not be reliable if only if a single wind observation is made, and can often be completely unreliable if the wind observation site is located 10 Km or more from the hazardous gas release point. As an alternative to a full three-dimensional model, many engineers and researchers are using puff models based on wind fields derived from interpolated wind observations. The concentration downwind of the source or sources is estimated using agaussian puff trajectory model for non-dense emmissions. The model can also handle multiple receptors. It is not expected to be valid for very dense gases close to the source, but is useful for many types of hazardous gas release with nearly neutral or slight positive bouyancy. The mass of pollutant is given by Q_i. Dispersion coefficients (Pasquill, Irwing) derived for plumes are used because they are based on extensive experimental evidence. The rate of dispersion can change with time as atmospheric stability changes. The model is used to evaluate a sudden break of a pipe that carried H_2S. The results allows the prediction of the dilution, the height of the cloud above the ground and the concentration of the gas downwind of the emission. Concentrations values for a region cover by ten receptors are presented for three diferents dispersion algorithms. Maximum concentratios are evaluated as a function of position and time.