Experimental Study on the Acid-Etched Fracture Conductivity of Novel Nano Retarded Acid System

Abstract The novel nano retarded acid system has merits of low viscosity and strong retardation, which overcomes the challenges of high friction pressure of emulsified acid and polymer residue damage of gelled acid and has been widely used in carbonate acidizing in China offshore Oilfield. However, the acid-etched fracture conductivity is not clear. The paper researches the acid-etched fracture conductivity of nano retarded acid in low-permeability carbonate reservoirs to guide acid fracturing onsite application effectively. The smooth rock plate and rough rock plate are taken as experimental objects. The gelled acid and emulsified acid are used as comparative acid systems. Acid-etched fracture conductivity, surface morphology scanning, and continuous strength testing equipment are used to study the effects of acid type, alternating injection stage, injection rate, viscosity ratio, reaction time, and rock plate type on fracture conductivity. Through experimental study, construct characteristic parameters of high acid-etched fracture conductivity, establish the relationship between acid fracturing technical and acid-etched fracture conductivity, and clarify the mechanism of nano retarded acid differential acid etching and alleviating rock plate strength damage. Results from the lab study indicated that the nano retarded acid system is a new type of acid system with nanostructure, low viscosity, low damage, low friction, and strong retardation performance. Compared with gelled acid and emulsified acid, nano retarded acid can form a strong channel etching morphology, which has a high differential dissolution and low rock plate damage strength and can maintain high conductivity under high closing pressure. Increasing the number of alternating injection stages, injection rate, viscosity ratio, and initial surface roughness of the rock plate for nano retarded acid system can help to form a dominant acid flow channel through differential acid etching. This research on nano retarded acid fracture conductivity can provide effective guidance for field application.