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Measurement of Reduced Permeability at Fracture Face Due to Proppant Embedment and Depletion - Part II


 Fracture face permeability loss related to proppant embedment under depletion conditions is one of the factors that contribute to PI decline in hydraulically fractured reservoirs. The damage is a result of proppant embedment and proppant/core crushing that also generates fines and plugs the pores in the embedment zone. A recently developed test method was used to measure the effects of embedment on permeability reduction at the fracture face as a function of depletion, core porosity and permeability, core UCS and injected fluid types. A range of stresses was applied to the cores and the permeability values across the fracture face were tracked and compared.
 Standard proppant conductivity tests only measure permeability / conductivity losses within the proppant pack due to frac gel damage and compaction and do not measure the damage at the fracture face.
 Recently, we developed a new test method that can directly measure fracture-face permeability under depletion. The test flows fluid from the matrix into the fracture thus coupling permeability measurements within the proppant pack with those across the fracture face. Initial tests were conducted in intermediate permeability, intermediate strength rock. The resulting core permeabilities were compared to the values from conventional core permeability tests. The proppant conductivity values were compared to those measured using a modified API conductivity test set-up. During the second part of this study, a lower permeability, higher UCS rock system was tested and permeability decline was measured as a function of applied stress and flow rate. Cores saturated with different fluid systems were tested to mimic injected fluid imbibition into the fracture face and their effect on proppant embedment and permeability loss. A numerical model was built to calculate fracture face permeability reduction as a function of depletion and injected fluid systems in different types of fractured formations. By incorporating embedment induced permeability reduction into the detailed reservoir geomechanics model, we are able to evaluate the contribution of proppant embedment on overall PI decline. During post-test analysis, proppant embedment percentage and porosity reduction across the fracture face were measured, using Micro CT-scanning, and the damage was also studied using thin section analysis.