| To clarify the dissolution-precipitation process of K-feldspar has always been one of the more active areas in geochemistry,and the researching results benefit us to understand the inter-mineral transformation process under reservoir conditions,subsequently providing positive guidance for studying oil and gas gathering of sandstone reservoirs.In this paper,K-feldspar worked as research object,was corroded by organic acid(acetic acid,oxalic acid)and water under static conditions respectively.In combination with Gaussian simulation software used to calculate the binding energy of the complex reaction from the perspective of quantum chemistry,ICP-MS,SEM and other characterization methods,specific transformation reactions among minerals were identified and the corresponding reaction rates were calculated.The results showed that:(1)The process of K-feldspar dissolved in water could be divided into two stages:firstly,potassium feldspar was mainly dissolved,and its rate was 1.57×10-9mol·kg-1·s-1;secondly,the precipitation reaction of muscovite was dominant whose rate was 1.13×10-11mol·kg-1·s-1.The functional relationship between RA-?G was highly nonlinear and could be divided into three different regions:(a)?G<-75k J·mol-1 was far equilibrium region,and the dissolution rate decreased slowly with the growth of?G;(b)-75k J·mol-1??G?-55k J·mol-1was transition equilibrium zone where the dissolution rate decreased sharply;(c)-55k J·mol-1<?G<0k J·mol-1was near equilibrium region where the RA tended to be stable and the dependence of rate on free energy was weaker than that of previous stage.(2)The process of acetic acid corroding K-feldspar was roughly divided into two stages:first,K-feldspar was mainly dissolved,and the rate was 3.27×10-9mol·kg-1·s-1;second,the precipitation reaction of kaolinite predominated at a rate of 4.55×10-11mol·kg-1·s-1.The functional relationship between RA-?G was highly nonlinear and was divided into three distinct regions:(a)?G<-105k J·mol-1was far equilibrium region where the dissolution rate was constant;(b)-105k J·mol-1??G?-45k J·mol-1 was transition equilibrium zone in which there was a strong negative correlation between rate and?G;(c)-45k J·mol-1<?G<0k J·mol-1was near equilibrium area where the reaction rate tended to be constant as the free energy increased and the dependence of rate on free energy was weaker than in the previous stage.(3)The process of oxalic acid dissolving K-feldspar was divided into two stages:at first,potassium feldspar was mainly dissolved and its rate was 5.94×10-9mol·kg-1·s-1;next,the precipitation reaction of kaolinite prevailed at a rate of 7.36×10-11mol·kg-1·s-1.The relationship of RA-?G was highly nonlinear and was divided into three different regions:(a)?G<-116k J·mol-1was far equilibrium region and the dissolution rate was approximately constant;(b)-116k J·mol-1??G?-58k J·mol-1was transition equilibrium zone where the dissolution rate decreased sharply with the increase of?G;(c)-58k J·mol-1<?G<0k J·mol-1was near equilibrium zone in which the average dissolution rate RA were almost same.In this paper,by comparing the dissolution of K-feldspar corroded by three common fluids in strata,the intrinsic reason of the difference of dissolution was analyzed from the chemical view.The reaction rate of K-feldspar under far equilibrium and near equilibrium was calculated for the first time respectively and the corresponding reaction was inferred.The chemical reaction clearly defined the range of far and near equilibrium,and the reasons for the difference in reaction rates in the indoor and outdoor were obtained,which provided a strong theoretical support for on-site oil and gas exploration. |
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