Ronald J. Crook

Deviated-Wellbore Cementing: Part 1 - Problems

Field experience suggests that in deviated wells, solids settling from the drilling fluid to the low side of the hole may adversely affect mud displacement during cementing. Large-scale laboratory cementing experiments confirm that in a deviated wellbore, solids settling from the drilling fluid can cause a continuous mud channel to remain along the low side of the cemented annulus. Tests also suggest that excess water in the cement slurry can result in a water channel along the high side of the cemented annulus in a highly deviated well.

Laboratory Investigation of Lightweight, Low-Viscosity Cementing Spacer Fluids

The use of lightweight, low-viscosity cementing spacer fluids was investigated with a large-scale apparatus that simulates actual field conditions. Results show that various fluids can be effective when used as cementing spacer fluids. Lightweight, low-viscosity cementing spacer fluids appear to improve the total mud-removal process by eroding the mud filter cake and increasing the mobility of the drilling fluid. To maximize total mud displacement, displacing fluids (both spacer fluids and cementing slurries) had to be pumped as fast as possible. Even when turbulent flow could not be achieved by the cementing slurry, displacing at a maximum flow rate was more effective than plug flow displacement. Laboratory results were independent of spacer volume. However, for long intervals of interest, such as those under field conditions, the volume of spacer fluid probably should be considered.

Deviated wellbore cementing: Part 2 - Solutions

Field experience suggests and full-scale laboratory test results confirm that mud displacement in high-angle wellbores can be complicated by a channel of hard-to-displace mud forming on the low side of the wellbore. This channel is caused by solids settling while the drilling fluid is circulating. Experimental test results obtained with full-scale, permeable and impermeable deviated wellbores indicate that this channel of solids can be prevented with proper rheological control of the drilling fluid. Results reported also demonstrate the effect of casing centralizers, pipe movement, and preflushes on the removal of this low-side channel of solids. Based on the laboratory results, displacement guidelines to improve deviated-wellbore cementing by eliminating the low-side solids-settling channel are presented.

Identifying water-flow problems

The most important element of conformance control in fields where water injection is used to enhance oil production is identifying the nature and source of the problem. Chemical analysis and water-flow logging can help operators isolate water-flow, invasion, and annular leaks that destroy casing integrity and decrease profitability. This article presents a case history that demonstrates use of analytical techniques to identify conformance-control problems and solutions.