Development And Performance Evaluation Of Cross-linked Acid System For High Temperature Dolomite Formation

Acid fracturing is an important means to increase production of carbonate reservoirs,and the performance of acid solution directly affects the effect of acid fracturing.In the acid system currently used,the cross-linked acid has the strongest temperature resistance,and most of the cross-linked acid systems do not withstand temperatures above 150 degrees Celsius.In view of the problem that the temperature of crosslinking acid system is insufficient,the reaction speed of acid rock is too fast and the penetration distance is short.This article has carried out research on the cross-linking acid with a temperature resistance of 160°C.In this paper,four monomers of acrylamide（AM）,2-acrylamide-2 methyl propane sulfonic acid（AMPS）,vinylpyrrolidone and acrylic acid were selected to synthesize thickener.The synthetic conditions were preliminarily selected by orthogonal test.The optimum synthesis conditions of thickener were obtained by single factor analysis,and thickener LHZ-1 was synthesized.Through the analysis of crosslinking type,ionic bond crosslinking was chosen.Zirconium isopropanol was chosen as organic intermediates.Glycerol and sodium lactate were chosen as intermediate.The optimum reaction pH is 7.And the crosslinker LJL is synthesized.Other additives were selected according to the industry standard,and finally forming a set of crosslinked acid system with good compatibility:20%hydrochloric acid+1%thickener LHZ-1+1%crosslinking agent LJL+1%crosslinking assistant agent LJL-1+2%corrosion inhibitor BSF-5+2%iron ion stabilizer FRK-TW6+1.2%assisting agent FRK-ZP2+2%clay stabilizer HL-4+0.2%gel breaker（0.1%ethylenediamine tetra acetic acid EDTA+0.1%Capsule gel breaking agent）.In this paper,the comprehensive properties of crosslinked acid are evaluated,and the experiments of resistance to shear,gel breaking performance,compatibility of crosslinked acid and formation water,core damage experiment,diversion experiment and acid rock reaction kinetics experiment have been completed.The experimental results show that the crosslinking time of crosslinking acid is 2³min,the viscosity is120 mPa·s after shearing at temperature of 160℃and at shear rate of 170s^-1.The breaking time of crosslinking acid is one hour,the viscosity of the gel breaking solution is less than 5 mPa·s.The compatibility of the crosslinked acid and the formation water is good.The rate of damage to the dolomite core is between 18%²5%.The fracture conductivity of dolomite increases with the increase of contact time of acid rock or the temperature and decreases with the increase of closure pressure.At temperature of160℃,the diffusion coefficient of hydrogen ion is 7.11709 cm²/s.At the rotational speed of 200r/min,the surface reaction kinetics equation of the crosslinked acid and dolomite is （?）.The crosslinking acid prepared in this paper can resist temperature up to 160℃,and its comprehensive performance is good.It can be used in acid fracturing of high temperature dolomite reservoir to improve acid fracturing effect.