Effect of connate water vaporization on well injectivity during acid gas injection into an oil producing reservoir Paola Ceragioli. Ivan Maffeis, Alice Tegami Having H2S high EOR capabilities like those more widely known of CO2, acid gas reinjection in sour reservoirs, is an attractive option for sour oil fields developments, able to combine environmental preservation requirements with higher oil recoveries. Moreover, even though Sulphur market has been recently forecasted in growing trend, nevertheless overall sulphur production increase suggests to consider also sour reservoir scenarios alternative or even parallel to the production of high quantities of elemental solid sulphur. However, because of the high risk and the severe difficulties in H2S transportation, any environmentally friendly solution for acid gas injection has to be realized in place. However a careful design of such development scenarios involves the inclusion of additional complex phenomena. In fact, unlike what is usually accepted for non-acid fluids, full immiscibility between water and gas may not be valid anymore. In fact when a sour/acid gas stream contacts the connate brine, significant amounts of H2O gradually transfer to the acid phase, possibly leading to following halite precipitation from the more salty concentrated brine. At the same time, acid components dissolving into the connate brine from the contacted acid gas, may give rise to geochemical reactions, possibly able to alter rock properties. Here the dynamic study has been first focused around the variations on the injection/production throughout a sour reservoir sector, by taking into account injection gases with different acid components concentrations. In fact, at least as far as no water mobilization is expected within a carbonatic sour reservoir, porosity and permeability variations due to salts precipitation or calcite dissolution, in a previous work were estimated not too relevant, while connate water vaporization had been highlighted as the additional phenomenon presenting the major impact on the reservoir development description. The study will focus also on the needed preliminary modelling extensions, both with regards to thermodynamics and relative permeabilities, to be adequately set in order to make it possible the execution of these extended simulations.


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