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 Fracture Treatment Design To Overcome Severe Near-Wellbore Damage, Mereenie Field, Australia
Anthony Papinczak, SPE, Santos Ltd., and
W.K. Miller II, SPE, NSI Technologies Inc.
Early fracturing attempts in the oil rim of this field were disappointing. Extensive well-testing, laboratory work and modeling were used to identify problems with formation fines migration and inadequate fracture conductivity. Photomicrographs show one of the primary damage mechanisms to be migration of formation fines and fibrous illite “hairs,” which plugged the pore throats, and resulted in severe production declines. To overcome this, hydraulic fracturing treatments were re-designed to provide a highly conductive flow path, resulting in significant improvements in both short- and long-term performance.
Although closure stresses were minimal in this 4500-ft depth reservoir, 20/40 CARBOLITE® was selected for the optimized designs, and tip screen out (TSO) fracture treatments were planned. Although the Young’s modulus of core samples ranged from 5 to 9 million psi, and Poisson’s ratio from 0.15 to 0.3, TSO fracturing was found to be feasible.
The re-designed, high conductivity fractures provided sufficient flow area to reduce the fluid velocity within the reservoir, thus reducing fines migration. (The higher conductivity fracture allows true bi-linear flow as opposed to substantial radial flow components present with lower conductivity fractures).
The decline rate of the optimized fractures has been quite low, indicating that fines migration has been mitigated. Fracture conductivity has been increased between 500% and 4000% compared to earlier designs. Well productivity was increased by 3 to 28 times greater than unstimulated rates, upgrading the field’s recoverable reserves, and encouraging additional development drilling.
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