Selection of Foam Flushes and Foamed Cement Proves Effective for Remedial Operations of Low-Pressured Formations—Case Histories

摘要

Remedial cementing operations and zone abandonment aredifficult to accomplish when low-pressure formations possesshigh feed rates at low, or even vacuum, surface pressures.Such is the case with several heavy-oil wells recentlyabandoned in Western Canada. These wells and theirrespective formations average an economic life ofapproximately ten years, during which a large amount offormation sand is produced. Traditionally, whenever exposedto hydrostatic pressure, these zones exhibit a vacuum at verylarge feedrates. Scorecard results of conventional cementsqueezes required an average of 2.6 attempts to obtain apositive squeeze pressure. Many conventional cementingabandonment attempts were unsuccessful, resulting in theplacement of a casing patch across the open perforations. Themechanical seal was effective in sealing the wellbore, whichallowed exploitation of deeper zones. However, this sealreduced the casing internal diameter and can limit furtherproduction operations. Also, this mechanical seal may notserve as a final abandonment under certain governmentregulations.The solution to this challenge was developed by tailoring atreatment pumping schedule that incorporates the use offoamed nonreactive, reactive spacers and foamed cementblends. This new treatment design was used on several wellsin early 2002. On most of the wells, positive squeeze pressurewas obtained on the first attempt and saved approximatelyCAD $15,000 per well. The improved process is now beingplanned for two adjacent fields. This paper details the wellchallenges and results found by a Canadian operator tosuccessfully abandon low-pressure, heavy-oil producingzones. The solution developed for the case history wells is alsopresented.