Proppant fracture conductivity with high proppant loading and high closure stress
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Ultra-deepwater reservoirs are important unconventional reservoirs that have the potential to produce billions of barrels of hydrocarbons, and are usually high pressure and high temperature with relatively high permeability. One major challenge of an unconventional, ultra-deepwater reservoir is pumping an effective and robust fracture stimulation treatment. Hydraulic fracturing a high permeability reservoir (>100 md) can be different from hydraulic fracturing technology used in low permeability formations (<1 md) due to their difference in purpose. The main purpose of hydraulic fracturing a low permeability reservoir is to create a long, conductive path to enhance drainage area and ensure a commericially economic well. In a high permeability formation, hydraulic fracturing is predominantly used to bypass near wellbore formation damage, control sand production and reduce near wellbore pressure drop. Such a treatment is achieved by pumping a short fracture packed with high proppant concentrations and may also aim at achieving enough fracture length to increase productivity especially when reservoir fluid viscosity is high. To pump such a job and ensure long term productivity from the fracture, understanding the behavior of the proppant pack is critical. A series of laboratory experiments have been conducted to study conductivity and fracture width with high proppant loading, high temperature and high pressure using a Cooke conductivity cell. In this study, proppant was manually placed between two core samples and fracture fluid was initially pumped through the proppant pack. Conductivity was subsequently measured by pumping oil through the manually placed proppant pack to displace the fracture fluid and simulate reservoir conditions; resulting fracture fluid clean-up and proppant pack performance were studied. High strength proppant, ideal for fracture stimulations with high closure stress, was used to study the effects of proppant fracture conductivity with different proppant loadings and closure stresses. Proppant crushing and fracture width were also measured and compared to proppant pack conductivity in certain cases. Testing results while pumping oil through the proppant pack at reservoir conditions indicated almost immediate fracture fluid clean-up. Increasing proppant concentration in the fracture showed higher conductivity values in some cases, while increasing the effective closure stress during an individual test resulted in a significant loss in conductivity for all cases. Additionally, fracture width decreased with increased effective closure stress and time. Tests were also run to study the effect of cyclic loading and showed further degradation in conductivity and width. Copyright 2012, Society of Petroleum Engineers.
