Field Success in Carbonate Acid Diversion, Utilizing Laboratory Data Generated byParallel Flow Testing

摘要

In order to treat the total interval in an anisotropic,heterogeneous carbonate formation, acid diversion isnecessary. Many diverting agents are commercially availablewhich will plug higher permeability portions of the formationand divert the acid treatment to lower permeability zones.For an oil-productive reservoir solid diverting agents such aswax beads, benzoic acid flakes, or polymers are used. Severalproblems may be associated with the use of these divertingagents: 1) too much additive may be used which may result ina severe reduction in acid injectivity and diverter may be verydifficult to remove after the treatment; 2) flow may not bediverted from one zone to the other, but, rather, flow isequalized between the high permeability zone and the lowpermeability zone.Recently, viscoelastic surfactants have been used in acidtreatments for diversion.1-3 The viscoelastic surfactant containsneither solids nor polymer so clean up is of no concern. Theappropriate concentration of surfactant is determined bylaboratory flow testing of formation cores under reservoirtemperature conditions.2A parallel flow set up has been constructed which allowsindependent monitoring of flow parameters for a higherpermeability and lower permeability formation core pair. Datademonstrate, through pressure analysis and effluent volumes,that flow is diverted from the higher permeability core to thelower permeability core, until acid break through occurs.Pressure data are confirmed by acid effluent volumes whichare collected at regular time intervals throughout testing. Inall cases, the effluent volume through the lower permeabilitycore is greater than through the higher permeability core.Core plugs are photographed and imaged by the CT-scantechnique before and after testing. Parallel flow testing hasalso been applied to stage treatments in which a stage of stablefoam of viscoelastic surfactant in 2 wt% KCl is injected priorto the main acid stage. Appropriate surfactant concentrationsin the foamed stage are determined by flow testing withformation cores.The results of core diversion testing and fluid rheologytesting of both the foamed and non-foamed viscoelasticsurfactant diverting fluids are discussed. Field case historiesof the application of acid treatments, which are designed onthe basis of laboratory generated data, are reviewed.