Rapid loss of fracture conductivity after hydraulic fracture stimulation has often been attributed to the migration of formation fines into proppant pack or the generation of fines derived from proppant crushing. Findings presented in this paper suggest that diagenesis-type reactions that can occur between proppant and freshly fractured rock surfaces can lead to rapid loss of proppant-pack porosity and loss of conductivity. Generation of crystalline and amorphous porosity filling minerals can occur within the proppant pack because of chemical compositional differences between the proppant and the formation, and the compaction of the proppant bed due to proppant pressure solution reactions.
This damage mechanism is applicable to all propped, fracture-stimulated wells; however, it is more significant in high temperature and high stress wells. It provides a possible explanation for the difference often observed between reservoir simulation of production after fracturing and actual production.
Studies indicate as little as 25% of the initial proppant- pack porosity may remain after only 40 days at 300°F and 6,000-psi closure stress. The rate of porosity loss can be influenced by the surface treatment of the proppant, which indicates that some control of this process may be accomplished.
Significance of this discovery has great impact on the economic life of a fracture-stimulation treatment. It affects the choice of proppant composition and post-fracture cleanup procedures, and adds an additional dimension to the appropriate laboratory determination of fracture conductivity that might be expected with the use of a particular proppant.