This paper presents an investigation of several slurries using field and laboratory prepared drilling fluids solidified with Blast Furnace Slag. The data presented includes base mud properties, final slurry composition, and slurry properties. This investigation includes measurements of the common properties of thickening time, compressive strength, free water, etc. It also includes an evaluation of the bulk shrinkage ot the set material, shear bond, etc., as well as rheological compatibility studies of the finished slurries with the base muds. These additional tests are considered critical in the potential application of this process under field conditions. Results of large scale bond log tests are included.
One of the main benefits from any mud solidification process is the reduction in the environmental impact. The benefit is due solely to the reduction of the volume of mud disposal requirements. Due to the dilution requirements of the mud for the incorporation of the Blast Furnace Slag, the actual volume of mud that can be "saved" from disposal may be considerably less than that reported. This study evaluates the actual reductions in disposal volumes while accounting for the dilution volumes. Economic comparisons from field operations are included as well as a theoretical comparison for zero discharge areas like Mobile Bay. Operational considerations and the economics of required mud isolation and storage are reviewed.
From the laboratory data evaluated, environmental, and economic evaluations, it is apparent the use of Blast Furnace Slag slurries for oil field applications must be carefully evaluated on a per case basis. While the process may be a viable mud solidification process, the replacement of Portland cement by this material may compromise some properties considered essential in a cementing operation.
For this investigation, three typical field muds were chosen. The muds were taken from wells representing various parts of the drilling process. An 8.8 lb/gal lightweight spud mud typical of surface holes, a 12.6 lb/gal mud often seen at intermediate casing points and a 17.6 lb/gal mud representative of the final stages of a well were used as the base muds for this study. The mud properties for each mud are listed in Table 1.
Blast Furnace Slag (BFS) slurries were prepared for each of the muds. A temperature of l85°F BHST was chosen for the investigation as this is typical for a 10,000 ft well (with a 1.1 temperature gradient) in the Gulf of Mexico. The aim was to prepare a BFS slurry that would give three to five hours of thickening time at 150°F BHCT. The formulations used for preparing the BFS slurries are found in Table 2. Note that the BFS concentration is expressed in pounds of BFS per finished barrel of slurry. In earlier investigations1–3 it is not clear whether the BFS was added to a barrel of diluted mud or was expressed as pounds per finished barrel. If the concentration of BFS is expressed in pounds of BFS added to a barrel of mud, the apparent concentration is higher. This is due slmply to the additional volume taken up by the BFS. For example, in this study Mud 5 has 300 lb BFS per finished barrel or 428 lb added to a barrel of diluted mud.