Granulated quick-quenched blast furnace slag (BFS or slag) in water-based drilling mud systems has been studied before, mainly from the perspective of mud-to-cement (MTC) conversion. However, the concept of using slag in a drilling mud for an effective low permeability filter cake, which minimizes formation damage, has not been explored.

This work explores the potential of using slag to consolidate filter cakes, thereby achieving reduced filter cake permeability. Also investigated is the overall impact on the reduction in formation damage by selective activation of BFS in dynamically deposited filter cakes. Studies were conducted on lignosulfonate, partially hydrolysed polyacrylamide (PHPA) and CaCO3 Drill-In fluids with BFS as a mud additive. Various mud properties, such as rheology (ambient as well as high pressure/high temperature), pH, filtrate loss and initial spurt loss are reported for muds containing variable loadings of BFS, and a control containing no BFS.

This study demonstrates the possibility of reducing invasion of mud into permeable formations through addition of small quantities of BFS to drilling mud. BFS appears to produce a more consolidated filter cake, which can be very useful for reducing wellbore stabilization problems in formation intervals that exhibit lost circulation and poor zonal isolation. In some cases BFS-containing drilling fluid appear to reduce formation damage in the near -wellbore environment.

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