A Green and Environmentally Friendly Chelated Retarding Acid for Acidification of Sandstone Reservoirs

Abstract

Matrix acidizing is the main method to relieve formation damage in sandstone reservoirs. However, many problems in conventional mud acid acidification need to be carefully considered, such as fast acid-rock reaction, short effective action time, excessive dissolution near the well zone, and the secondary sedimentations from fluorosilicic acid, aluminosilicate, calcium fluoride and other pollution of the reservoir. In this paper, a green and degradable amino acid chelating agent is investigated. This new type of sandstone chelating retarded acid system have features of chelating metal ions and slow proton release. The chelating ability of new retarder acid to calcium and iron metal ions was determined by complexometric titration. The retarding performance of chelating retarder acid were studied by core flow instrument and microscopic scanning electron microscopy. The results show that the new acid system is manifested by strong chelating ability to iron and calcium ions, low corrosion rate, good retarding performance. The permeability is increased by 225% after acidification. The results of electron microscopy scanning of the core surface before and after acidification show that the new acid solution acidification can effectively enlarge the pore-throat without generating secondary precipitations, which is a good choice for sandstone acidification practice.