One of the most important reports at the wellsite is the daily drilling fluid report, or “mud report”. In addition to containing basic well and rig information, chemical inventory and mud system costs, the mud report will contain a list of the fluid properties of the mud system. To maintain the required properties, certain tests are conducted on the drilling fluid. The most important are listed below.
Density
pounds/gallon (lb/gal)
The density of the drilling fluid is important to maintaining well control. As mentioned earlier, fresh water has a density of 8.34 lb/gal, with a corresponding gradient of 0.433 psi/ft. As long as the formations have the same gradient, fresh water will “balance” the formation pressures.
Since this is generally not the case, some weight material must be added to the fluid, the most common being barite and hematite. The drilling fluids density is measured using a “mud balance”. This balance contains a mud cup on one end of a beam with a fixed counter weight on the other end of the beam. The beam is inscribed with a graduated scale, contains a level bubble and a movable rider. When the cup is filled with fresh water, steel shot is added to the counter weight container until the beam is level, with the rider pointing at the 8.34 scribe line.
During wellsite operations, the mud’s density is checked by filling the cup with drilling fluid and moving the rider until the level bubble indicates the beam is balanced. The density is then read using the position of the rider.
