Research And Development Of Autogenous Acid System And Its Mechanism Of Retarded Acidification

Acidizing is the key technology for the efficient development of conventional and unconventional oil and gas resources,and the deep acidizing of carbonate reservoir is a recognized acidizing problem in the world.Conventional acid system construction has the problems of too fast acid reaction speed and short acidizing distance,which will not only lead to excessive dissolution near the well and damage of reservoir structure,but also make it difficult to form effective wormhole and realize deep acidizing.With the development of dense and deep layer,the existing acid system gradually exposed some problems,such as poor high temperature stability,high pump injection friction,limited acid corrosion or inhibition effect,easy to cause secondary damage and so on.In this paper,through the screening and optimization of autogenous acid components,a neutral autogenous acid system with stable and continuous acid generation in the ground and deep formation is developed,and its acid generation ability,corrosion inhibition ability,formation water compatibility and speed inhibition performance are evaluated;the dynamic acid rock reaction experiments of limestone and dolomite were carried out to study the difference between autogenous acid rock reaction kinetics and conventional acid and thickened acid;the limestone slab was used to conduct the acid fracture conductivity experiment,and the three-dimensional laser scanning and digital analysis method were used to describe the etching morphology of the limestone slab.The optimum formula of autogenous acid system is 12.0%formaldehyde+12.0%ammonium chloride+15.0%ethyl lactate+1.0%corrosion inhibitor hsj-1+1.0%drainage aid byh-09+2.0%iron ion stabilizer yty-03.At 150℃,the concentration of autogenous acid can reach 19.8%,and the corrosion rate is only 0.984 g·m^-2·h^-1,which is lower than the first-class industry standard.The reaction rate is one order of magnitude different from that of hydrochloric acid,and the dissolution rate of carbonate rock is slightly different from that of hydrochloric acid.Therefore,it has excellent inhibition,corrosion inhibition and dissolution performance.By analyzing the point cloud data of authigenic acid etched rock plate morphology and the variation of rock plate falling height,it is found that the conductivity,etching height and non-uniformity of authigenic acid etched rock plate increase with the increase of acid generation time.Comparing the etching height curves of autogenous acid and hydrochloric acid with the length of rock plate,it can be seen that the similar acidizing effect can be achieved by autogenous acid and hydrochloric acid with approximate concentration,but the effective action time of autogenous acid is longer and the diversion channel formed is longer than that of hydrochloric acid.