Curing Lost Circulation in Fractured Reservoirs Using a Level-Off CementPlugging Method-Case Studies in Drilling and Workover Applications

摘要

Controlling lost circulation during drilling operations in a reservoir prone to losses is typically remediedby cement squeezing or plug setting.The aim being to minimize or stop drilling fluid losses and to regainfull returns at surface,and to affect wellbore integrity.Different placement methods of cement plugs havebeen discussed in detail in the literature,except for the'level-off'method,which is particularly effective forcuring complete loss circulation cases.Following the mathematical modeling of this cement plug placementmethod,its design,procedure and execution are discussed,together with some successful field cases,bothdrilling and workover situations in highly-fractured carbonate reservoirs in the Middle East.Using drill pipe and an installed a Retrievable-Test-Treat-Squeeze(RTTS)packer,with some spacingfrom the loss zone,the method entails that the cement slurry is allowed to drop by gravity in order tocure lost circulation.As the column of fluid,mud and slurry in the well exceeds formation pore pressure,i.e.overbalanced conditions,a volume of acid-soluble cement slurry is allowed to slowly drop and freelypenetrate the formation,i.e.through its fractures or caverns.During the penetration of this viscous slurry intothe loss zone,the cement can set and the fracture or fissure openings are plugged.In addition,to minimizeor prevent further losses,this cementing technique may also mitigate formation damage of adjacent zones.Presented are detailed design calculations for the level-off placement technique:determination ofrequired cement slurry and displacement volumes,and recommended displacement and RTTS packer settingdepths.The expected depth of the top of cement is estimated.The design parameters are compared withfield cases and explanations are given for possible discrepancies.Detailed field procedures and executionare also presented.This is the first known,detailed description and modelling of the level-off cement placement techniquein the literature.