| Acid-fracturing technology is considered as the main stimulation of Carbonate formation, which can greatly improve the permeability of the reservoir and increase the production of oil and gas wells. Acid fluids play a very important role in the fracturing acid fracturing, which controls the success possibility of acid-fracturing. Confronting with the problem of high filter loss, fast acid-rock reaction,, incomplete gel broken of reacted acid which cause secondary damage in carbonate reservoir acid-fracturing, this article synthesized a kind of betaine amphoteric surfactant as viscosifier and developed surfactant variable viscosity acid which own the property of low filter loss, retardance, low damage.We choose carboxyl, no branching structure of the carbon chain Containing eighteen carbon atoms and Amide as beanie’s hydrophilic groups, hydrophobic groups and the linking group respectively. Furthermore, we designed out the molecular structure of betaine amphoteric surfactant. The octadecyl amide propyl betaine (BET-18) was synthesized by oleic acid and N, N-Dimethyl-1,3-diaminopropane through condensation reaction and quaternization reaction. Synthetic product was characterized by infrared spectroscopy. Moreover, through single-factor investigated the ratio of reactant reaction time, reaction temperature for Synthesis of the octadecyl amide propyl betaine to determine the conditions for a better response. the optimum parameters of condensation reaction are:n(oleic acid): n(N,N-Dimethyl-1,3- diaminopropane) is 1.0:1.08 by mole ratio, reaction temperature is 160℃, reaction time is 8h. the optimum parameters of quaternization reaction are:n(alkyl amine):n(sodium chloroacetate) is 1.0:1.1 by mole ratio, reaction temperature is 70℃,reaction time is 7h.On the base of study the basic property of betaine, we determine the amount of surfactant in the acid. Additive agents that prepare variable viscosity acid were optimized. The formula of surfactant variable viscosity acid is as follows: 5%BET-18+2.0%JCI-1+2.0%SD1-11+1.0%SD 1-5+1.0%KCl+1.0%TDC-15The performance of variable viscosity acid is evaluated in the experiment. The experiment results showed that in the condition of that temperature is 80℃, Shear rate is 170s-1, pH vary from 1 to 3.5, the viscosity of BET-18 reacted acid could increase to 280mPa.s sharply.The surfactant variable viscosity acid has low filter loss, the reacted variable viscosity acid with high viscosity only loss the 7.5% of total volume after 36 minutes in static filtration experiments; this kind of variable viscosity acid own slow-rated ability, At 90℃and after 90min the acid-rock reaction, the Concentration of hydrochloric acid in surfactant variable viscosity acid is 5-6 times Higher than the Concentration of hydrochloric acid in Blank hydrochloride; The variable viscosity acid has a low damage to the Permeability of Reservoir, the reacted variable viscosity acid has a property of automatic gel broken with oil and gas or other hydrocarbons, then viscosity of reacted acid can decrease to 3 mPa.s.Then we found the reacted acid which has gel broken made 13.37% damage to the core, and it didn’t have acid residues;Furthermore, the surfactant variable viscosity acid has good shearing resistance and good thermal stability, when the temperature is 90℃, variable viscosity acid on the corrosion rate of steel was 3.62 g·m-2·h-1, the corrosion performance has reached the national standard one. |
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