Research and Application of a Novel Type of Efficient Acid System for Stimulation of Offshore Sandstone Oil Wells

Matrix acidizing is a well stimulation method that is applied to removal reservoir damage and enhance productivity.The presence of minerals like clays, feldspar, zeolites, and alumino-silicates makes acidizing a challenging task because they may form undesired precipitates when reacted with traditional .acid system. In this work, a novel acid system is mainly composed of clay lattice metal extractor and chelating agent.During the dissloution of minerals, minerals crystal structure, crystal composition and elemental valence and distribution are characterized.The results show that the dissolution rate of the novel acid system for four kinds of clay minerals (montmorillonite, kaolinite, mica, chlorite) is in the range of 20%-40%, and the dissolution rate for rock debris samples is in the range of 10%-30%. According to the XRD data, the relative content of the clay minerals decreased, which indicates that the clay minerals are involved in the dissolution reaction. It mainly destroys the microstructure of clay by extracting metal ion such as Al3+, Mg2+, K+, Fe3+, Ca2+ from the clay structure. Meanwhile, Moreover, the acidizing back-flow fluid has little impact on the offshore electro-dewatering process and a high back-flow efficiency. Since 2022, the novel acid system has applied more than 50 oil Wells of offshore sandstone. And the cumulative oil increase has exceeded 1.5 × 104 m3, verifying the engineering applicability and economic benefits of this technology.