Distribution and treatment of harmful gas from heavy oil production in the Liaohe Oilfield, Northeast China

The distribution and treatment of harmful gas （H2S） in the Liaohe Oilfield, Northeast China, were investigated in this study. It was found that abundant toxic gas （H2S） is generated in thermal recovery of heavy oil. The H2S gas is mainly formed during thermochemical sulfate reduction （TSR） occurring in oil reservoirs or the thermal decomposition of sulfocompounds （TDS） in crude oil. H2S generation is controlled by thermal recovery time, temperature and the injected chemical compounds. The quantity of SO4^2- in the injected compounds is the most influencing factor for the rate of TSR reaction. Therefore, for prevention of H2S formation, periodic and effective monitoring should be undertaken and adequate H2S absorbent should also be provided during thermal recovery of heavy oil. The result suggests that great efforts should be made to reduce the SO4^2- source in heavy oil recovery, so as to restrain H2S generation in reservoirs. In situ burning or desulfurizer adsorption are suggested to reduce H2S levels. Prediction and prevention of H2S are important in heavy oil production. This will minimize environmental and human health risks, as well as equipment corrosion.

An improved coupled flow-geomechanical model for cyclic steam stimulation

Considering the pore deformation and permeability changes during dilation-recompaction in cyclic steam stimulation(CSS),an existing geomechanical model is improved and thermo-mechanically coupled with the flow equations to form a coupled flow-geomechanical model.The impacts of dilation-recompaction parameters can be quantified through sensitivity analysis and uncertainty assessment utilizing the synergy between Latin hypercube designs and response surface methodology.The improved coupled flow-geomechanical model allows a more reasonable history-matching of steam injection pressure and volume and oil/water production volume.In both the linear and quadratic models,the rise in recompaction pressure has the most significant effect on the rise in the volumes of steam injection and water production,both rock compressibility and recompaction pressure are positively correlated with steam injectivity and oil/water production,and the dilation pressure is negatively correlated with steam injectivity and oil/water production.In the linear model,dilation pressure has the most significant negative impact on the cumulative oil production,and compressibility and recompaction pressure are positively correlated with oil production.In the quadratic model,the rise in recompaction pressure has the most significant effect on the rise in the cumulative volumes of oil/water production and steam injection.The interactions between the dilation/recompaction pressures and spongy-rock compressibility negatively affect the cumulative volumes of oil/water production and steam injection.