Study on Reaction between Changxing Carbonate Rocks and Acids

The Changxing Formation in Jianxing Gas Field has two sedimentary types, bioclastic beach and biogenic reef, and different minerals in the reservoir formations react differently with acids. Lack of understanding of the reaction patterns of rocks and acids resulted in poor stimulation job quality. Laboratory study on rock samples showed that composition and maturity of crystal grain of the rocks greatly affected the reaction rate of rocks and acids, the reaction rate of bioclastic limestone and gelled acid was 1.3 times that of biolithite, 1.4 times that of limy-dolomite, and 1.9 times that of common limestone. The four rock samples, after reaction with acids, all produced non-uniform corrosion on their surfaces. Dolomite with erosion pores, after reaction with acids, will experience further permeability impairment because of compaction and particle migration. After reaction with acids, the calcite fillings of biolithite and bioclastic limestone reacted much easily with gelled acid, with erosion first formed in the inter-crystalline pores and inter-crystalline cracks, but acid wormholes were rarely seen.