Challenges with Securing Power Water Injectors Completed in the Reservoir Oil-Water Contact

Abstract

The paper outlines operational challenges during the well securement of a Power Water Injector (PWI) completed in the reservoir oil-water contact (transition zone). Surface integrity issue arose in Well-A necessitating the installation of adequate downhole barriers to carry-out surface remedial repairs safely. Well isolation shut-offs were not successful in eliminating surface pressure to meet the minimum stipulated operational requirements for this field. Well operator's barrier philosophy mandates the presence of two shut-offs; one of which is mechanical, to allow removing surface control equipment during rigless operations in power water injection wells with positive wellhead pressure. Water flooding strategy in Field-A calls for drilling water injectors at the flanks and maintaining a peripheral injection scheme. However, as more wells are placed towards the crust of the reservoir to sweep the remaining oil behind the flood front, this well placement strategy leaves behind a transitional zone where more than one fluid phase is present. Formation evaluation logs conducted on Well-A indicated that the completed reservoir interval lies within the oil-water-contact. Typical well completions for PWIs in Field-A use large casing sizes up to 9-5/8 in. of outer diameter. Bullheading pumping technique is conventionally sought as the primary securement method for water injectors. However, hydrocarbon displacement with kill fluid in such types of completions is challenging given that the hydrocarbon displacement velocity is often surpassed by its segregation velocity. Attempts to eliminate the persistent wellhead surface pressure build-up in Well-A were unsuccessful. Fluid circulation was then, applied to Well-A. Heavy fluid was forward-circulated against a blank mechanical plug installed below the wellbore oil-water interface which was detected by a wireline gradient survey. Accordingly, compromised wellbore fluid was displaced. This technique has set the pace for future well securement operations in PWIs completed in the reservoir transition zone.