Evaluation and Application of Efficient Gelled Acid for Carbonate Formation Fracturing

[Image: see text] In the middle and west of Sichuan Basin, the targeted carbonate formation exhibits features of deep burial and high temperatures at present. In order to obtain better acid fracturing results, the efficient gelled acid developed was investigated based on the carbonate formation characteristics. At the same time, the field application was conducted to prove its adaptability and effectiveness. The high-effective thickener is mainly polymerized by DMC and an allyl octadecyl trimethyl ammonium bromide monomer and a very small amount of diallyl polyethylene glycol. The efficient gelled acid has good compatibility with carbonate formation and formation water, and its thermal stability is great that the viscosity could obtain 25 mPa·s at a temperature of 180 °C after shearing at 30 min. Furthermore, compared with conventional gelled acid, the friction reduction rate of efficient gelled acid is higher of over 7–12%. Also, the induced fracture conductivity is more than 20 D·cm at a closure stress of 60 MPa, which is higher than that of conventional gelled acid with 16.81 D·cm. In addition, during the acidification fracturing of Well PS, the efficient gelled acid system exhibits a good friction reduction property. The flow rate could reach 6 m(3)·min(–1) and the obvious pressure drop could be observed, which indicated that the efficient gelling acid reacted with the carbonate formation, creating acidified fractures. The test production of Well PS is 23 × 10(4) m(3)·d(–1) and the acid fracturing adopted by the efficient gelled acid obtains a great break at a high-temperature carbonate formation.