Study On Acidified Thickening Autogenous Acid System Of High Temperature Carbonate Reservoir

The Changxing group carbonate reservoir of Yuanba area in northeast Sichuan has the following geological characteristics:the depth of formation is about7000m, the temperature is up to150℃, the pressure is above60MPa, and the micro fracture growth. Acid fracturing is an important stimulation of Yuanba gas field, and the acidification effect by the acid properties. Aiming at the problem existing in the acid fracturing of conventional acid system, including the acidizing pipe was seriously corroded, the acid-rock reaction rate was too fast, and effective acid reaction had a very small range, the gelling self-generating acid which is low corrosivity and low acid rock reaction rate was studied in this paper.In this paper, based on the chemical reaction principle, through the acid concentration evaluation experiments of materials, salt brine and carbonyl compounds were screened out from the materials. And the acid producting process of the self-generating hydrochloric acid system was studied by the CO2weight loss method, with the reaction time increased, the acid concentration increased gradually and finally tends to a saturation value, and the saturation value increased with the increasing of temperature. Then according to industry standards, gelling agent and other additives were selected, and ultimately the gelling self-generating hydrochloric acid system which have good compatibility were developed:20%hydrochloric acid(salt brine and carbonyl compounds)+0.4%gelling agent+3.0%corrosion inhibitor+1.0%ferric ion stabilizer+0.5%cleanup additive.The paper systematically evaluate the indoor comprehensive performance of the acid system, including corrode property, friction property, thermo and shearing stability, retarding performance, filtrate reduction property, cleanup performance, core acidizing effect and flow capacity of acid-etched fractures. The evaluation results show that the gelling self-generating hydrochloric acid system has good performance:high temperature dynamic corrosion rate is55.37g/(m2·h), the friction reduction rate is about50%, under the condition of high temperature and shear, the acid viscosity remained at50mPa·s, the residual acid surface tension value is only28.52mN/m. Compared with gelling acid, the acid system has similar filtrate reduction property and improve effect of core matrix permeability. However, the acid system has better retarding performance and stronger flow capacity of acid-etched fractures.Based on the acid rock reaction mechanism, compare with acid rock reaction kinetics equation of gelling acid and self-generating acid, the gelling self-generating hydrochloric acid showed good retarding performance. Analysis of the micro characteristics of the core samples showed that compare with self-generating acid, the gelling self-generating hydrochloric acid have better retarding performance. And not as gelling acid which formed a layer of polymer on the rock surface, the gelling self-generating hydrochloric acid has lower damage to the formation.