Oil, gas, and other fluids moving into a well bring both dissolved andparticulate material into the well bore. As well, injection fluids may alsoadversely affect the formation. Back flow may cause movement of formationsolids into the well bore.
In all these cases, plugging of the vertical well bore by deposits of inflowedmaterial can result. These deposits are often tenacious and hard. Their removalcan be costly and, most important, such deposits reduce either inflow ofinjected fluid or production of the desired hydrocarbon.
This paper addresses a clean out method for injection wells plugged with claybearing materials in the well bore. Many clays are very sensitive to waterchemistry. When fresh water is used for injection, these clay bearing materialsexpand and can backflow into the well bore upward through any packers to causevery tight plugging of the injection tubing. Some of these plugs extended for300 m (1000 ft) in the vertical well bore and tubing in the wells describedherein. To remove these plugs a conventional high pressure pump (69 MPa (10,000psi)) was coupled to a conventional 32 mm (1–1/4 inch) coil tubing unit towhich a special jet drill head was welded. That drill head then pushed down thecased well bore to jet it clean.
The jet drill head used in this work is called a Conical Jet drill head. It iswelded to the outer of the coil tubing string. The drill head creates a conicalshell of high velocity water particles that sweeps the entire casing or wellbore without any rotation of the drill head or coil tubing string. The resultis a rapid cleaning of both cased and open hole well completions. The samecleanout technology is applicable to many types of vertical injection andproduction wells.
The theory of the well bore cleaning mechanism evolves from the design of the Conical Jet. That jet is shown schematically in Figures 1 and 2. It consists ofa conventional Leach and Walker nozzle shown in Figure 1. The Leach and Walkernozzle design is used in many drill bits and other high velocity jet drillheads to provide a highly collimated jet stream of about 2 degrees angulardivergence, as show in Figure 2. A Conical Jet is created by placing a set offixed vanes upstream of the inlet converging section of a Leach and Walkernozzle. These vanes are formed into a logarithmic spiral. The result is thatthe water stream is caused to spin rapidly in the converging section of thenozzle by the twist in the vanes. The water stream continues to spin while inthe straight exit section of the nozzle.
When the fluid stream exits the nozzle, the water breaks up into small waterparticles. At the exit of the nozzle, the water particle stream trajectoriescombine to form a diverging conical shell.