Successful Water Shutoff Chemical Treatment in Horizontal OpenholeCompletion in Carbonate Reservoir

摘要

The development of well completion strategy at the subject field has evolved from simple verticalcompletions to extended horizontal wells with selective openhole completions(Etuhoko et al.2014).Normally,well completions in this field involve large volume acidizing treatments.Matrix acidizing andacid fracturing stimulation are widely used in carbonate formations to improve oil recovery arising fromthe high solubility of the carbonate formation in hydrochloric acid.The ability to create wormholes in thenear-wellbore vicinity provides a stimulation effect by connecting to secondary porosity(natural fractures,voids,and vugs).The connection of the natural fracture network to the wellbore utilizing acid fracturingtreatments provides a stimulation effect because the hydraulically fractured reservoir increases the effectivewellbore radius and results in a negative skin factor.However,massive acid treatments raised certain issuesafter beginning to develop oil-bearing zones near water/oil contacts.Significant water production occurredin some flank wells after acid stimulation.High permeability channeling is suspected between the aquiferand the wellbore.There is a high probability of water flow through natural fracture networks because nobarrier exists to prevent drainage from the aquifer,which is connected to the wellbore with acid-stimulatedwormholes or via acid etched fracture faces.Because production facilities are not designed to handle a highwater volume,production wells with an unfortunate water cut are shut down.Obviously,field economicssuffer and an effective water shutoff solution is now a vital component of future field development.Although many advances have been made in both mechanical and chemical methods to reduce unwantedwater production,horizontal wellbores present challenges.If water breakthough is recorded,the fieldoperator conducts a multiphase production log(MPLT)survey to identify the influx depth.The first choicefor water shutoff is usually a mechanical isolation in which the water-producing interval is either shut in bya sliding sleeve(SS)or the entire wellbore is isolated by bridge plugs.Unfortunately,mechanical isolationdoes not help because the water flow easily bypasses the restriction by flowing through the carbonateformation and enters the wellbore in the upper interval(Fig.1).The most recent approach includes a totalshutoff of the water-producing interval by placing a polymer sealant in the targeted zone.Several chemicalwater shutoff jobs have already been performed by the field operator.Although some of treatments can beconsidered successful as a result of proven reduced water cut over an extended time period,some treatmentsdid not provide the expected results,despite a large chemical volume pumped into the formation.This document describes the materials used for chemical water shutoff purposes and the history of thetechnology application in the subject field.Avoiding known pitfalls and following best operational practicesmay help to increase the success rate of chemical water shutoff treatments.