| Acid gas reservoir contains hydrogen sulfide or carbon dioxide.Due to the existence of acid gases,the reservoir has more specific characters than conventional one.The study of sulfur deposition in sour gas reservoirs represented by high sulfur gas reservoirs has attracted more and more scholars’ attention in recent years.However,few researchers concerned about the effects of carbon dioxide,hydrogen sulfide and water on reservoir physical properties and fluid properties during the process of sulfate thermal reduction.In the process of production,formation water will enter the reservoir and react with acid gases,then the interaction between water and rock will happen,which has the effect for the reservoir physical properties.With the enhancement of the strength of acid gas-water-rock interaction,the minerals dissolve or precipitate and the porosity and permeability changes in different degrees,which affects the seepage capacity of the oil and gas in the porous media.The reaction equilibrium relationship is affected by multiple factors,such as pressure,temperature,and salinity of the formation water,mineral composition and acid gas partial pressure,etc al.Therefore,it is great significance that to study the interaction mechanism of water rock interaction in acid gas reservoir and to analyze the transformation degree of the reaction balance quantitatively to the physical property of the reservoir.The goal of this paper is realizing the effects of acid gas water rock reaction on the physical properties of reservoir.The main works and conclusions are as follows.(1)Study on physical properties of fluid involved in the acid gases-water-rock interaction,including in the phase state,density,viscosity and compression coefficient of the fluid,and the model which is suitable for the acid gas reservoir is optimized.(2)Study on the mechanism and the reaction kinetics of acid gas-water-rock interaction.Firstly,the adsorbent and desorption mechanism of acid gas in water is studied,and the solubility of two gases with different temperatures and pressures is calculated by Henry’s law.Secondly,the law of the diffusion mechanism of acid gas in water and the law of dissolution or precipitation of the minerals in the presence of acid are studied.Thirdly,the rate model of water-rock interaction is built,and an example is used to study the law of changes and its influencing factors.Finally,the relationship model of porosity and permeability is establishied.(3)Experimental study of the effects of acid gas-water-rock interaction on the physical properties.Taking a low porosity and medium low permeability carbonate reservoir as the object,and 10 samples from the field and an integrated reactor device for hydrogen sulfide have been selected to carry out the experiments.The results shows that all the cores except B7 are corroded,and there is increasement in porosity and irregular change in permeability.The smaller the particle is,the larger the effective reaction area is,and the faster the reaction rate is;the greater the partial pressure of acid gases is，the faster the reaction rate is,and the more obvious the transformation is;the greater salinity of formation water is,the smaller reaction rate is.(4)Numerical simulation of the effects of acid gas water rock reaction on the physical properties of reservoir.The commercial numerical simulation software CMG has been used to establish a model of saturated acid gases flooding in acid gas reservoir.By adding the reaction of acid gas in brine and the interaction between acid and minerals,numerical simulation of acid gas injection in carbonate reservoirs is carried out.The result shows that the pore volume of rock increases with a different degree due to acid gas-water-rock interaction.The rate of injected brine is the most effective factor,and the effective reaction area is the least affected.It is proved that the effect of water rock reaction on reservoir physical property should be considered when developing sour gas reservoirs. |
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