Evaluating the Impact of Rock Hardness and Roughness on Acid Fracturing Conductivity

Different techniques are used to increase the hydrocarbon production from carbonate reservoirs; the common approach is applying acid fracturing. Channels and rough fracture surfaces can be created due to the acid injection at high pressure. The rock properties and mineralogy will have a significant impact on the treatment performance. This paper presents the impact of rock hardness and roughness on the fracture conductivity during HCl and GLDA chelating agent as acid fracturing fluids. Silurian dolomite, Indiana limestone, and Austin chalk were used in this work. Smooth initial fracture surfaces were created by cutting the rock samples into two parts. Six coreflooding experiments were conducted by injecting the acid fluids into the carbonate samples. The rock strength and the surface roughness were measured using Brinell hardness tester and Kruss high-resolution surface analyzer respectively. The results showed that the fracture conductivity was controlled by the type of injected fluids and the rock hardness and roughness. Strong acids such as HCl can produce higher conductivity compared to chelating agent solutions, due to the higher created surface roughness. Significant increases were observed in the fracture conductivity for chalk and limestone rocks when treated with GLDA, while a slight increase was achieved for the dolomite conductivity. Overall, this work can help in improving the performance of acid fracturing treatments by providing a better section for the acid type based on the rock hardness and roughness.