Proppant Fracture Conductivity With High Proppant Loading and High Closure Stress

Abstract

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 thisstudy, 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 manuallyplaced 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 higherconductivity values in some cases, while increasing the effective closure stress during an individualtest 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.

Experimental Investigation on the Fracture Conductivity Behavior of Quartz Sand and Ceramic Mixed Proppants

“…Since the conductivity of the proppant pack is a function of particle size distribution and arrangement, the proppant mixture and volume have an influence on fracture conductivity to some extent. For a single proppant pack, the proppant mass is usually calculated by proppant concentration (kg/m 2 or lb/ft 2 ). − However, due to the density difference of ceramic and quartz sand, the volume of the proppant pack at the same proppant mass is different. It is unreasonable to use proppant concentration to calculate the proppant mixture mass when two different densities of proppant are mixed.…”