Jetting tool for well cleaning

An apparatus for cleaning subterranean wellbores is described. The apparatus comprises a sleeve member which is fixed to a part of the drillstring and a rotatable jet head with nozzles through which an abrasive fluid is discharged. The nozzles are mounted such that the fluid jet is directed to an area of the wellbore immediately adjacent to a leading edge of the sleeve. The nozzle head is restricted in its protrusion out of the sleeve.

The present invention relates to an improved apparatus for cleaning a 
hydrocarbon well using a jet drilling apparatus. The invention 
particularly relates to a penetration control system or stabiliser system 
for such jet drilling apparatus and more particularly to removal of scale 
and other downhole deposits from the inside diameter of well tubulars. 
BACKGROUND OF THE INVENTION 
It has been common practice for many years to run a continuous reeled pipe 
(known extensively in the industry as "coil tubing") into a well to 
perform operations utilising the circulation of treating and cleanout 
fluids such as water, oil, acid, corrosion inhibitors, hot oil, nitrogen, 
foam, etc. Coil tubing, being continuous rather than jointed, is run into 
and out of a well with continuous movement of the tubing through a coil 
tubing injector. 
Coil tubing is frequently used to circulate cleanout fluids through a well 
for the purpose of eliminating sand bridges, scale, and similar downhole 
obstructions. Often such obstructions are very difficult and occasionally 
impossible to remove because of the inability to rotate the coil tubing 
and drill out such obstructions. These well tubulars vary from 
unperforated and perforated pipe, large diameter casing, production 
tubing, and slotted or wire-wrapped well liner. Well tubulars often become 
plugged or coated with corrosion products, sediments and hydrocarbon 
deposits. The deposits may consist of silicates, sulphates, sulphide, 
carbonates, calcium, and organic growth. 
It is desirable to perform drilling type operations in wells through use of 
coil tubing which can be run into and removed from a well quickly in 
addition to performing the usual operations which require only the 
circulation of fluids. The same types of well servicing can also be 
performed with various small diameter work strings. The present invention 
may be used with such work strings and is not limited to coil tubing. 
High pressure fluid jet systems have been used for many years to clean the 
inside diameter of well tubulars. Examples of such systems are disclosed 
in the following U.S. Pat. Nos.: 3,720,264, 3,811,499, 3,829,134, 
3,850,241, 4,088,191, 4,349,073, 4,441,557, 4,442,899, 4,518,041, 
4,919,204, 5,181,576 or 5,337,819. 
In U.S. Pat. No. 3,720,264, there is disclosed a jet tool for cleaning a 
liner. At its one end, the tool carries a bit to provide mechanical 
centralisation. The blades of the bit are selected to be only slightly 
less in diameter than the inside diameter of the liner which is to be 
cleaned. 
U.S. Pat. No. 5,337,819 discloses a washing tool for removing internal 
deposits in tubing parts and components in wells for oil. and gas 
production. The known tool comprises an actuation sleeve which has lateral 
dimensions related to the deposits to be removed. The sleeve actuates a 
valve to discharge a fluid jet through one or more discharge nozzles. 
In view of the above cited prior art it is an object of the invention is to 
provide a fluid jet cleaning tool to remove scale and other deposits from 
the inside diameter of a well tubular. It is a particular object of the 
invention to provide a novel stabilising and/or centralising means for 
such a fluid jet cleaning tool. 
SUMMARY OF THE INVENTION 
The objects of the invention are achieved by apparatus as set forth in the 
appended independent claims. 
In a first aspect of the invention, there is provided a gauge defining 
sleeve member. The sleeve member is mounted such that its lower 
weight-carrying edge is positioned in immediate vicinity of the trailing 
edge of a jet discharged through nozzles of a rotating head of a jet 
cleaning tool. Debris and deposits are hence removed preferably from an 
area immediately below the lower edge of the sleeve member. 
The sleeve member is rigidly fixed to the coiled tubing or drillstring. 
Sleeve member and coiled tubing are isolated from the rotation of the 
nozzle head. In this arrangement, the sleeve member does not rotate 
relatively to the coiled tubing or drillstring. 
The lower edge of the sleeve-member is shaped such that the supporting 
surface area, which, in operation, contacts the deposits, has an 
essentially annular outline. This essentially annular supporting surface 
may be interrupted by openings or cuts as described below. The width, or, 
in cases where the lower edge of the sleeve member is rounded, the radius 
of curvature of the area is preferably less than 10 mm, more preferably 
less that 5 mm. 
With respect to the prior art, it is another important feature of the 
present invention that the protrusion of nozzle head is limited so as to 
ease the introduction of the tool into a well and to prevent damages to 
the tool caused by obstacles in the well. 
In order to reduce the lateral dimensions of the tool, it is therefore an 
aspect of the invention, that the nozzles are located within a protruding 
distance of less that 0.5 times the outer diameter of the sleeve member. 
Preferably the protrusion is less than 0.3 times the outer diameter of the 
sleeve member. The protruding distance is measured as the vertical 
distance between the lower edge of the sleeve member and lowest nozzle. 
Even more preferably it is the protrusion of the nozzle head which is 
limited to the value given above, resulting in a very compact tool design. 
The lower part of the nozzle head is preferably formed in a tapered shape, 
e.g. rounded or conical. 
The main body of sleeve member has openings which form a passage for the 
cleaning fluids and cuttings. Preferably, the openings have a slit-like 
shape and are cut into the lower edge of the sleeve member. The preferred 
dimensions of the openings allow cuttings with less than 2 mm diameter to 
pass. 
In a preferred embodiment of the invention, the lower edge of the sleeve 
essentially forms an annular area which, in operation, i.e. when the 
downward motion of the tool is obstructed by deposits, carries the full 
weight of the tubular lowered into the well. Thus the jet cleaning tool 
will progress only when debris below the sleeve member has been completely 
removed. 
In a further preferred embodiment, the sleeve member comprises a 
frusto-conical shaped main body and a cylindrical part the outer surface 
of which engages against the wall of the tubular to be cleaned. 
In another aspect of the invention, an frustro-conical shaped protection 
member is mounted on the sleeve member such that the tapered end of the 
protection member points in direction of the bottom of the borehole. The 
protection member facilitates the process of lowering the tool into the 
wellbore. The base material of the protection member is chosen such that 
it can be readily dissolved or eroded by acids or abrasive fluid jets.

MODE(S) FOR CARRYING OUT THE INVENTION 
The invention is now described with reference to the attached drawings. 
The basic components of the invention are illustrated in FIG. 1. There is 
shown the lower part 10 of a hollow tube representing a drillstring or a 
coiled tubing. Attached to the tube is a sleeve member 12. The sleeve 
member in the described example is made of a solid cylinder of engineering 
steel having an outer diameter of 75 mm and a centre bore 121 of 45 mm. An 
alternative material may be tungsten carbide or other steels of sufficient 
hardness. 
Further components of the system are a nozzle head 14 which carries two 
nozzles 141, 142. The nozzle head is rotatably mounted in the drillstring 
10. 
In operation, the coiled tubing is reeled off to lower the tool arrangement 
including nozzle head 14 and sleeve member 12 into the wellbore 16. When 
the lower edge 111 of the sleeve member encounters an obstruction, e.g. 
deposits 161 to be removed, the downward progress of tool is stopped. At 
this point, the sleeve member 12 carries the weight of the coiled tubing. 
The operator activates the pumps to discharge jets of cleaning fluids 
through the nozzles 142, 142. The fluid and cuttings are pumped to the 
surface through openings 122. The rotating movement of the nozzle head 14 
is energised by the fluid flow by means of like turbines within the tool 
arrangement or by designing the nozzles such that rotation is effected by 
the discharge of the fluid. Though both methods are feasible, the latter 
is simpler and can be readily implemented by, for example placing nozzles 
such that a net rotating force is generated. It is important to note that 
the nozzle head 14 protrudes less than the outer diameter of the sleeve 
member 12. In the present example, the protrusion of the nozzle head, 
measured as the vertical distance between the lowest part of the nozzle 
head 14 and the lower edge 123 of the sleeve member is 2 cm. The limited 
protrusion of the nozzle ensures that the sleeve member 12 is the first 
part of the tool to contact any deposits. 
Depending on the nature of the deposits, the fluid jets are loaded with 
appropriate abrasives. The nozzles 142, 142 are oriented such that the 
jets remove the debris 161 immediately below the weight-carrying edge 123 
of the sleeve 12. The tool advances through the well tubing as the 
deposits are removed. The outer dimensions of the sleeve member determine 
the gauge of the cleaned wellbore. 
After removing the debris, the fluid flow through the tool is interrupted 
and the tool is either moved downwards to other locations within the same 
wellbore or it is lifted by reeling up the coiled tubing 10. 
Referring now to FIG. 2, mounted on the device of FIG. 1, there is shown a 
protection sleeve 20. The protection sleeve partially encapsulates the 
protruding part of nozzle head, thus facilitating the introduction of the 
tool through installation at the surface and within the wellbore. The 
protection sleeve is either pressed or glued onto the lower edge 123 of 
the sleeve member 12. The material of the protection sleeve is chosen such 
that it is readily dissolvable by acid treatment or eroded by the abrasive 
fluid, itself. Examples for suitable materials are plastics, such as 
phenolic resins, reinforced by glass fibres or a metal mesh, such as or 
aluminium. Aluminium is dissolved by pumping an acid (HCl) prior to the 
abrasive fluid while the reinforced resin can be removed by the jetting 
action of the fluid. 
FIGS. 3A and 3B illustrate variants of the sleeve member according to the 
invention. The sleeve member of FIG. 3A has openings formed as slanted 
slits 322 cut into the lower edge of the sleeve member. Together with an 
appropriate coning 324 of the inner surface of the member a volume is 
formed in which larger cuttings are trapped until they can pass through 
one of the openings 322. The slits 322 are 2 mm wide and 10 mm deep. The 
slant angle is 60 degrees. In FIG. 3B, a similar sleeve member is shown 
having a slant angle of 90 degrees. 
In FIG. 4, a more detailed view of an example in accordance with the 
invention is shown. The tool arrangement shown displays the bottom part of 
a swivel shaft 411 mounted in a swivel housing 410. Connected to the 
swivel shaft there is a nozzle shaft section 440 and a nozzle head 44 with 
the nozzles 441 and 442. An adapter section 413 with clamps 414, 415 is 
connected to the bottom part of the swivel housing. A sleeve member 42 is 
mounted on the adapter section and is held in place by the clamps. On the 
left of the figure, a hatched triangle indicates the position of a 
protection sleeve 420, whereas on the right the tool is shown in operation 
with area 46 denoting a part of wellbore and area 461 deposits to be 
removed. 
In operation, the abrasive fluids enter the nozzle head through a bore 412 
in the swivel shaft 411. The fluid is then discharged via nozzles 441, 
442. Rotational motion of the nozzle head can be generated by a turbine 
attached to the swivel shaft or be nozzle design and location. The fluid 
and cuttings are pumped through openings 422 to the surface. 
During the operation, an operator controls the weight set down on the lower 
edge of the bit in the same manner as the weight-on-bit (WOB) would be 
controlled during a drilling operation. As the tool removes the debris, it 
advances causing the monitored weight to fall and allowing the operator to 
reel off more tubing. As soon as the monitored weight exceeds a 
predetermined threshold, the operator initiates the pumping of the jetting 
fluids.