The application of a water-base spacer ahead of cement during oil or gas well cementing operations improves cementing results. Better bond logs are achieved, better zone isolation is accomplished and stimulation treatments are more effectively applied. With more effective stimulation treatments, production results are improved. Bond logs production results are improved. Bond logs and field results including production data are presented.
Wells in the Illinois Basin drilled through the St. Genevieve limestone and all formations through the Trenton formation have had production which was far below the expectations of formation log and drill-stem tests. These fractured limestone formations occur between 2000 and 4000 feet and are drilled with a simple, light-weight, waterbase drilling mud. The poor production is attributed to a lack of zone isolation by the cementing treatment. Poor zone isolation occurs when mud is left in the annulus and forms a channel behind the cement.
To ensure a good cement job, the best cementing techniques must be employed. Of course the first element of a good cement job is the cement itself. The cement system must be properly designed for the well conditions If well conditions permit, casing hardware such as centralizers and scratchers should be employed, especially across any zones of interest or future zones of interest. After the casing or liner, has been run into the hole, mud should be circulated at least "bottoms up", or until it is in good shape. Following mud conditioning, cement must be mixed and placed using proper techniques. For cement to make intimate contact with the formation and pipe, which is necessary to achieve good bonding and good zone isolation, all the mud must be displaced by the cement. Pipe movement, such as rotation or reciprocation Pipe movement, such as rotation or reciprocation during placement of cement will greatly aid mud removal. Spacers are also available which will improve mud removal and its replacement by cement.
Removal of mud may be a very difficult task, even with proper mud conditioning, pipe movement, and use of casing hardware. Most muds are incompatible with cement, whether they are high density muds or simple, lightweight muds.