Numerical Modelling of Salt Precipitation During Gas Production

Abstract

The decline in productivity in mature gas fields is often attributed to liquid loading but in reality it may be a result of salt deposition which can have similar consequences. The phenomenon of salt precipitation is gradually increasing and is becoming a serious issue in the North Sea. The North Sea operators are aware of the serious consequences of the issue of salt precipitation in the gas wells. During gas production the reservoir brine will evaporate leading to an increase in dissolved salt concentration. Salt precipitation results in a decrease of porosity and permeability and consequently a decrease in gas production and eventually in the killing and the abandonment of the well. Currently water washes are used to remove and dissolve the salts but a good understanding is still lacking as the problem is complex. In this study we model radial flow near the well bore and further enhance it to a layered inhomogeneity structure. Numerical simulations using TOUGH2 with the EWASG module are done to determine the rate and location of salt deposition. Various parameters are investigated in order to observe the sensitivity of the model as a basis for further studies. This study shows that the location of salt precipitation is influenced by parameters such as a change in differential pressure and salinity content while the introduction of heterogeneity does not influence the location of salt deposition for this particular model.