ABSTRACT
A new method of obtaining unproved zonal isolation using drilling fluid solidification technology has been developed. A water-base drilling fluid is converted into a cement using a hydraulic blast furnace slag. Hydraulic blast furnace slag is a unique material which has low impact on rheological and fluid loss properties of drilling fluids, can be activated to set in drilling fluids which are difficult to convert to cements with other solidification technologies, is a more uniform and consistent quality product than Portland well cements, and is available in large quantity from multiple sources.
Because of its low impact on drilling fluid properties, blast furnace slag may be added to a drilling fluid at low concentrations during drilling operations. The Alter cake and drilling fluid in washed out sections thereby contain a hydraulic material. After reaching casing point, a mixture of drilling fluid containing chemical activators and higher concentrations of slag may be used to cement the casing string. Chemical activators from this mixture cause the slag in the filter cake and any bypassed drilling fluid to set. The result is a more complete seal for the annulus.
Fluid and hardened solid properties of blast furnace slag and drilling fluid mixtures used for cementing operations are comparable to properties of conventional Portland cement compositions. The design, testing and field application for this technology are similar to conventional cementing methods. Fluids with densities between about 1198 kg/m3 (10 lb/gal) and 2397 kg/m3 (20 lb/gal) may be prepared. The mixtures have been applied in wells where temperatures range from about 4°C (40°F) to 315°C (600°F).
This new solidification method provides the proper combination of fluid and solid properties, simplicity of design and application, improved zonal isolation, and broad applicability to bring drilling fluid solidification technology into widespread use.