Once the drilling of an oil or gas well is finished the bore must be cased and cemented. It is important that the cement lining be complete, and to ensure this it is necessary to sweep out the mud in the annulus ahead of the rising cement. Unfortunately, this often proves difficult, and various procedures and mechanisms have been devised in the past to improve the chances of achieving efficient mud-removal. It has now been discovered that a considerably increased amount of lateral motion, and thus a very significantly enhanced degree of mud removal capability, is provided if the liquid be a multiphase liquid in which one of the phases is a gas - in other words, if the liquid be full of bubbles - and the invention provides a cleaning method particularly suitable for the cleaning of gelled mud deposits off the casing and bore walls of an oil/gas well prior to cementing the casing in place, in which there is caused to flow over and in contact with the dirty surface a "burbulent" liquid.

A high pressure foam slurry generator (10), including a source of slurry, a source of gas, and a means for combining the slurry and the gas, which is usually nitrogen. A housing (36) receiving the slurry and the gas has a connector (40) with multiple channels. One channel (42) for the nitrogen gas acts as an inlet and has a bushing with a series of multiple holes through which the nitrogen gas is broken into a plurality of high velocity streams. The slurry with a foamer agent added combines at right angles with the nitrogen gas and is foamed before being pumped through a tubing string into a gas or oil well (14). Also included herein is a process for making foamed slurry by pumping a slurry capable of being foamed to a housing, pumping nitrogen to the same housing, separating the nitrogen into a plurality of high velocity streams, and combin­ing the streams and the slurry in a foaming action. Either the slurry or the nitrogen may have two sepa­rate streams entering the housing as right angles to each other. All of the streams are normally combined at right angles to obtain the proper amount of foaming action.

a method of removing at least a substantial proportion of fluid left in a generally horizontal section of a pipeline, by injecting into the pipeline a pressurized, high expansion foam and advancing the foam through the pipeline section in contact with a layer of the fluid left therein to displace the layer towards a remote end of the pipeline by frictional pick-up of the layer by the foam and to effect mass transfer of a foaming agent from the foam to the fluid, followed by passing into the pipeline a pressurized gas to create turbulence in fluid left in the pipeline causing foaming of the fluid and to displace a substantial proportion of the foam left within the pipeline. At least some of the bulk of the fluid in the pipeline may be displaced by injecting the foam so as to establish a transverse foam/fluid interface which is advanced through the pipeline at or above a minimum velocity required to maintain said interface leaving a residual amount of fluid which is treated as aforesaid. The method may include the further subsequent step of injecting into the pipeline a pressurized foam containing a treatment agent to displace residual foam left in the pipeline, and then allowing the foam to decompose in the pipeline to deposit the treatment agent within the pipeline either on the pipewall or in solution with any liquids remaining therein.

A down-the-hole drill is hydraulically powered with air flushing. The rotation motor (16) is on the drill string (10) and rotates a percussion hammer (20) to which the drill bit is chucked. Hydraulic fluid flows in umbilicals (11) clipped into grooves on the sides of the drill rods. The shuttle valve (26) for the hammer is in line with the piston (25).

A method of stimulating a subterranean well permits each desired location within a portion of a well to be isolated from other portions of the well during stimulation operations therein, but does not require lining a portion of the well with casing and cement, and does not require the use of sealing devices, such as inflatable packers, in the well portion. In an embodiment, a stimulation method includes the steps of depositing a barrier fluid (32) in a portion of a well, forming a radially extending opening (56) through the fluid, and flowing stimulation fluids through the opening and into a formation surrounding the portion of the well.