With its introduction of SentinelCem™ cement, Halliburton has achieved major success incuring lost circulation issues in Iraq. Using this innovative system cured severe losses inthe challenging karstified dolomite of the Dammam Formation, saving operators millions ofdollars annually.
OPERATORS IN SOUTHERN IRAQ EXPERIENCE SEVERE CIRCULATION LOSSES
For years, operators drilling in the Rumaila, Zubair, and West Qurna fields in southern Iraqhave routinely experienced severe and even total circulation losses at depths of 450–750meters (1,476–2,461 feet). Underlying these fields is the karstified dolomite of the DammamFormation, which has geological characteristics that include caverns, vugs, and largefractures.Encountering these voids compromises the wellbore and results in lost circulation,complicating operations and driving up rig time and costs. To address the problem, operatorshave historically used conventional lost circulation materials (LCMs) and treatment pills, and,in many cases, have simultaneously pumped multiple conventional cement plugs – all withlittle or no success.
UNIQUE LOW-DENSITY CEMENT SOLVESCIRCULATION ISSUES
In early 2017, Halliburton found a solution – theapplication of SentinelCem™ cement.Designed specifically to treat severe circulationloss, SentinelCem cement is a low-densitycement that rapidly develops gel strength toprevent the fluid from being consumed by theloss zone. When first mixed, SentinelCem is arelatively thin fluid, which allows it to be easilypumped through the bottomhole assembly (BHA)and to achieve deep penetration into the targetedzones. As it enters lost circulation zones, thepumping rate (shear rate or velocity of its flow)is slowed, causing it to thicken into a gel thatplugs the problematic voids. For a few cycles,shear can be reapplied to return the slurry to its liquid state, a robust property that enables optimal placement. Upon being static, the cement in theslurry hydrates and develops compressive strength that prevents future losses from occurring in theproblematic zone.Unlike conventional LCMs, SentinelCem cement’s effectiveness comes from its unique chemicalproperties rather than mechanical bridging from particle additives. This makes it ideal in places likethe Dammam Formation, where the voids are simply too big for the particles in conventional LCMs.It is also operationally easier to apply than standard cement plugs because it can be pumped throughthe BHA, meaning its application does not require pulling the drillstring out of the hole and runningopen-ended drillpipe – a major benefit that saves considerable time and money.Technology teams with the Cementing and Sperry Drilling product service lines (PSLs) collaboratedto conduct a risk assessment in order to overcome a widely held belief that the innovative cementposed a risk when pumped through the BHA. The two PSLs then worked together to applySentinelCem cement to three wells in the Zubair Field, two wells in the South Rumaila field, and onewell in the North Rumaila field.
INNOVATIVE CEMENT SAVES OPERATORS SIGNIFICANT RIG TIME
The treatment proved effective. After application, no further losses were observed in any of the sixwells. In each well, the operators were then able to move ahead with drilling and cementing the nextcasing strings, and observed cement returns to surface according to design.Following its success, SentinelCem cement has quickly become the first choice to cure lossesamong operators in the area. In addition to its effectiveness in stopping circulation losses, operatorshave cited SentinelCem cement’s ability to be pumped through the BHA, along with its minimalwaiting-on-cement time, as factors that make it the go-to solution.The first six treatments in Iraq saved an estimated 250 hours of rig time valued at USD 1.5 million.