Experimental study of fracture conductivity in dolomite reservoirs treated with different acid fracturing technologies

Abstract

The acid fracturing stimulation mechanism of dolomite reservoirs is entirely different from that of limestone. Most existing research on dolomite acid fracturing still uses the research method of limestone. There is no unified understanding of dolomite reservoirs' acid rock reaction mechanism and stimulation mechanism. The rock outcrops of the Dengying Formation of the Sinian system in the Sichuan Basin, China, with the size of about 17.8 cm × 3.8 cm × 2.5 cm, were used to test the acid-etching morphology, corrosion volume, reaction kinetic parameters, and conductivity under different acid types, injection modes, displacements, and alternating stages with the acid corrosion experiment. The materials used in the experiment are gelling acid, crosslinking acid, and diverting acid, the dolomite content of the rock sample is about 93.79%. The experimental results show that the diverting acid had a lower viscosity and higher mass transfer rate than gelling acid, so it could form a more effective etching, the dissolution volumes in the two acids were 22.15 and 23.38 cm3, respectively. Compared with the injection mode of a single acid fluid, the alternative injection of two fluids with different viscosities can improve the nonuniform etching effect and conductivity, under the “fracturing fluid + acid fluid” alternate injection mode, the dissolution volume of rock was approximately 17.16 cm3, under the “crosslinking acid + diverting acid” alternate injection mode, the dissolution volume of rock was approximately 20.83 cm3. The reaction rate of dolomite is low, and it may be dissolved along the joint and natural fractures. The research results can provide a reference for optimizing the dolomite reservoir's stimulation technology and injection parameter design.