Experimental and simulation study of improved oil recovery in shale formations

Date

2014-05

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Abstract

Shale has ultra low permeability and cannot produce without hydraulic fracturing to improve the contact between reservoir matrix with wellbore. In addition, shale production declines very fast due to many reasons including conductivity decline over time. The techniques for improving oil production may start at an early stage by optimizing drilling and completion technologies and at a later stage where secondary and tertiary recovery methods are applied.
In this dissertation, a number of improved oil recovery technologies potentially applicable in shale are examined. The primary oil recovery is improved by optimizing stimulation fluid additives. Matrix acidizing is proposed to be a part of the propped hydraulic fracturing by injecting slugs of weak HCl solutions (less than 2 wt%) near and away from wellbore. The matrix acidizing experiments using 1-3 wt% HCl on Eagle Ford, Barnett, Mancos, and Marcellus shale formations showed a great improvement in porosity and oil recovery factors at different acid contact time, while the compressive strength and hardness of the studied rocks were lowered after the treatment due to partial mineral dissolution up to 82%. The dissertation also examines a number of stimulation fluid surfactants to alter shale wettability while fracturing on reservoir samples from Bakken Shale. One of the tested surfactant was able to improve Bakken Shale primary oil recovery factors by about 20% more compared with using of brine neutral solutions alone. In addition, three enhanced oil recovery methods to improve waterflooding performance in shale were examined: Low Sal, alkaline, and surfactant pre-flood technologies. The three tested methods improved waterflooding oil recovery up to 30% more due to mineral dissolution and wettability alteration with shale damage effect for Mancos Shale samples when low saline solutions were used and Barnett Shale samples when higher alkaline solutions were used. Furthermore, the dissertation investigates the potential of waterflooding in Eagle Ford Shale by building a reservoir numerical model using Eagle Ford Shale average properties and hydraulic fracturing properties of the injector and the produced wells. The simulation study confirms the experimental potential of waterflooding in Eagle Ford Shale when modeled with closer and longer factures with a recovery factor of about 18% compared with 12% from the depletion case.

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Keywords

Improved oil recovery methods in shales, Matrix acidizing in shales, Waterflooding in shales, Surfactant pre-flood in shales, Wettability alteration in shales, Alkaline flooding in shales, Waterflooding simulation study on Eagle Ford Shale

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