Mechanism Research On Mineral Composition Controlling Acid-rock Reaction For Tight Sandstone

With the booming development of the complex and tight reservoirs,acidification has gradually became an important technical method for reservoir reconstruction.Due to the complexity of the acid-rock reaction mechanism in sandstone reservoirs,the sandstone acidification is not flawless,which seriously affects the success rate and efficiency of acidification.However,the core evaluation experiment can only evaluate the effect of acidification in a general manner,it cannot evaluate it in a microscopic way,such as rock mineral composition and the microstructure of the reservoir.Taking the tight sandstone reservoirs in west Sichuan basin as research subjects,in order to clarify the influence of different mineral components on the sandstone acid rocks reaction,in this thesis,we evaluate the stability and variation of individual mineral in the reaction with the help of HTHP Static Acid-rock Reaction Simulator.The results showed that at 70°C,the erosion sequence of four non-clay minerals with particle sizes between 150 and 200 mesh in 15% HCl+3% HF is calcite> dolomite> quartz> feldspar.Meanwhile,the erosion sequence of four clay minerals is kaolinite> chlorite> montmorillonite> illite.After obtaining the kinetic equations and activation energies of different minerals,we found that the reaction rate of different minerals depends on its own composition.In addition,the microscopic changes of the samples after the reaction show that Quartz,kaolinite,illite,montmorillonite,and chlorite will have siliceous precipitates after be in contact with 15% HCl+3% HF at 70°C.The concentration of silicon ions in residual acid reached the maximum 60 mins after the reaction.1 h after the reaction began,with the concentration of the reaction decreased,the silica precipitation occurred and the remaining element concentration generally increased.After the acid erosion,the crystallinity of minerals decreased which may produce transportable particles that finally damage the reservoir.After analyzing the mineral composition of west Sichuan basin Shaximiao FM,we conducted HTHP Static Acid-rock Reaction to obtain the acid-rock reaction kinetic equation and activation energy.The experiment results shows that the reaction rate is proportional to the calcite content and inversely proportional to the clay mineral content.Besides,experiments with different area volume ratios show that the larger area volume ratio,the smaller activation energy.The microscopic changes show that when the concentration of hydrochloric is higher,earth acid damage to the structure of sandstone mineral crystal is more obvious.Ion concentration changes in the acid solution after the reaction was similar to the individual mineral experiment,the precipitation occurred 1 hour after the reaction.