Kinetics Exploration And Mechanism Analysis Of Reservoir Mineral Dissolution Process

Carbonatite?calcite,dolomite?and silicalite?feldspar?as typical minerals of Bohai Bay Reservoir can react with formation fluid under burial condition,which is the main way to form high-quality reservoirs.Water-rock interaction is a complex dynamic coupling process of dissolution and precipitation.Therefore,it is extremly important for us to define its dissolution and precipitation process and control factors,quantitatively determine its rate and the mechanism of reaction process,so as to evaluate and predict the development of reservoir pore.A large number of dynamic simulation experiments were conducted to mainly discuss the following contents:?1?the main influence factors?temperature,salinity,ion type,pH?in the process of dissolution,kinetics analysis,relationship between kinetics and thermodynamics and dissolution characteristics and corresponding mechanism under acetic acid system for calcite;?2?the main influence factors?temperature,pH?in the process of dissolution,kinetics analysis,relationship between kinetics and thermodynamics and dissolution characteristics and corresponding mechanism for dolomite in acetic acid;?3?the process of dissolution-precipitation,kinetics and dissolution precipitation mechanism in K-feldspar-acetic acid-water system?pH=3,7?and alkali feldspar-acetic acid-sodium chloride system.The results showed that:?1?dissolution rate of the calcite increased first and then decreased with the increase of temperature?50-150??and salinity(0-1mol.L^-1),decreased with the increase of pH?3-7?and increased with the increase of valence for ionic type.The kinetic relations show that the process of calcite dissolution is mainly affected by the diffusion.At the same time,dissolution occurs on the surface of high Gibbs free energy first,and the whole dissolution process is from dissolution pore to dissolution pits,then to the dissolution zone,followed by the formation of the corrosion cone.Finally,new crystal surface is exposed;?2?the dissolution rate of dolomite increases with the increased temperature,and decreases with the increase of pH.The results of linear dynamics fitting show that the increase of temperature will weaken the concentration effect.The whole process of dissolution shows obvious dedolomitization,and many kinds of dissolution phenomenon were took place such as dissolution joints,corrosion holes and rhombic seams.The process of dissolution is that the seams formed first,then the orifice,and eventually the honeycomb dolomite is formed.?3?The process of dissolution-precipetation is mainly divided into three stages?boehmite,kaolinite,moscovite?and the contribution to the reservoir pore was 4.58%by calculating the dissolution process under the condition of pH=3 in K-feldspar-acetic acid-water system.While on the condition of pH=7,the process can be divided into two stages?muscovite,boehmite?,the corresponding reservoir was only 0.74%.In alkali feldspar-acetic acid-sodium chloride system under the condition of pH=7,and will reach to equilibrium between alkali feldspar and boehmite,then to k-feldspar and muscovite.At the same time,the transformation between k-feldspar and albite were taken place during the process.Finally,It is estimated that the improvement to porosity is 0.3%.Dissolution of feldspar can be divided into three intervals:?a?in high concentration of H⁺ions,the reaction order for H⁺ions is 0.5,?b?at low concentration of H⁺ions,the reaction order for H⁺ions is 0.25?c?in the alkaline range,the reaction order for OH^-ion is 0.5.