Primary Cementing | What is primary cementing?

Cementing Horizontal Intervals

Cementing casing strings in extended reach or horizontal intervals presents special challenges. These include:

• Efficient cleaning of the low side of the borehole of both cuttings and mud
• Formation of free-water phase in cement slurry on high side of annulus
• Maintaining borehole stability during cementing
• Effective centralization of the casing
• Impact of increased drag within the horizontal interval on hole conditions

Typically, complex cement jobs are designed using sophisticated software to model the process. The software takes into account factors such as density, friction, setting time, geometry, and chemistry.

In addition to normal good cementing practices, follow these additional recommendations for cementing horizontal laterals (Matson and Bennet 1990):

• Pay special attention to the development of good annular velocity (180 to 300 feet per minute) for the angle build and horizontal sections of the wellbore during mud conditioning and circulating.
• Maintain a standoff of 67% or greater by using software to optimize centralizer spacing.
• When the casing is in place, circulate the hole two to three times with a target of 95% of an accurately calipered annular volume being circulated.
• Use fluid marker materials (such as oats, nut shells, dyes, or beads) while drilling the horizontal hole section (at about every 100 ft), on clean-up trips, and when the casing is in place to provide a comparison of how much of the calculated (calipered) hole is circulating.
• Plan the total cement job fluid-density sequence to reduce gravity effects by displacing the top wiper plug with the lightest fluid possible without causing safety problems. Lighter displacement fluid inside the casing will improve pipe buoyancy and allow the centralizers to be more effective.
• Employ some form of pipe movement to enhance mud removal – rotation and, if possible, reciprocation-depending on rig and tool considerations. Normally, rotation speeds from 10 to 22 rpm are adequate.
• Use a spacer with a density about 0.5  greater than the mud density, but less than the cement density, and a volume designed to allow 10 minutes or more of uncontaminated contact time under turbulent conditions.
• Design cement slurry to control free water at bottom hole conditions, maintain fluid-loss within a range of 30-50 ml/30 min, and control gel strength development so the slurry remains fluid with little gelation up to the limit of its pumpability.