Method and apparatus for perforating and slotting well flow conductors

Apparatus and a method for cutting round perforations and elongated slots in well flow conductors used in solution mining. The apparatus comprises a jet nozzle head for discharging a fluid to cut the perforations and slots, a string of continuous tubing for handling the jet nozzle head in a well bore, a tubing injector or tubing guide, a tubing storage reel having a flow conducting central hub connected with the tubing on the reel for forcing the abrasive fluid into the tubing at the reel, fluid pump and storage means connected with the reel hub, means for mounting the tubing injector above a well, and a wellhead having annular stripper rubber for sealing around the tubing and a side outlet for fluid returns. The method includes the steps of supporting the nozzle head on a first end of the tubing, lowering the nozzle head in a well bore with the tubing injector until the nozzle head is at the desired depth, pumping a fluid through the hub of the storage reel into the tubing and outwardly through the nozzle head until the perforations are cut. For slotting the tubing and nozzle head are reciprocated the distance equal to the length of slots desired. The returns from the nozzle head flow upwardly in the annulus to the wellhead and outwardly through the side outlet.

This invention relates to perforating and slotting well flow conductors and 
more particularly relates to slotting and perforating well flow conductors 
used in solution mining. 
In essentially all types of wells including oil and gas wells, water wells, 
and wells which are drilled for the purpose of solution mining, it is a 
well known practice to case the wells by inserting a pipe or flow 
conductor to the desired depth and cementing the conductor in place by 
pumping cement downwardly, out of the lower end of the flow conductor, and 
upwardly around the flow conductor within the wellbore where the cement is 
allowed to set and securely fix the flow conductor in the wellbore. 
Various types of materials are used for the flow conductors. For example, 
in oil and gas wells and water wells in most instances the casing is made 
up of steel or iron pipe joints. In some wells, however, such as those 
used in solution mining where minerals such as uranium, sulphur, copper, 
and nickel are washed or bleached from an earth formation, the well casing 
may be of a non-metallic type such as formed of a polyvinyl chloride 
material or glass reinforced thermosetting epoxy resin material. In all 
these various types of wells in order to carry out the particular process 
for which the well has been drilled, it is necessary to provide 
perforations which are generally round or elongated slots through the well 
casing to permit communication between the well bore and the earth 
formation around the cemented well casing so that flow may occur either 
from the formation into the wellbore through the casing or from the 
wellbore outwardly through the casing into the formation. In the case of 
solution mining, usually one or more central production wells are located 
within a ring of injection wells, thus both the injection and producing 
wells must be perforated or slotted in order to flow the solutions between 
the wells for removal of the desired minerals. One type of available 
apparatus and method which has been used to perforate and slot well casing 
and other well flow conductors has usually involved running and pulling of 
an operating string made up of a plurality of pipe sections connected 
together end to end and run into the well and pulled by a means of a rig 
or derrick mounted over the well adapted to manipulate the string by 
sequentially adding or removing the pipe sections one at a time. This is a 
time-consuming and expensive process which involves individually 
connecting together adjacent pipe section ends during both running and 
pulling each time a pipe section is handled. 
Other types of apparatus and methods which have been used to perforate well 
casing and other well flow conductors have involved using explosive 
charges. However, while the use of explosive charges to perforate well 
casing and other flow conductors is a convenient well completion means, 
the jets of hot gaseous material emanating from the explosive charges upon 
detonation tend to damage the surrounding wellbore formation. In this 
connection, if the well casing is of non-metallic type, such as a 
polyvinyl chloride material or a glass fiber reinforced thermosetting 
epoxy resin material, the jets of hot gaseous material emanating from the 
explosive charges, while temporarily perforating the well casing, cause 
the material surrounding the perforations to be heated sufficiently to 
flow into the perforations subsequent to their formation thereby causing 
the well casing to become impervious to the flow of formation fluids into 
the wellbore. Also in the case of a glass fiber reinforced thermosetting 
epoxy resin material type well casing, when an explosive charge is used to 
perforate the well casing, the well casing is usually shattered and is 
subject to delamination from the effects of the jet of hot gaseous 
materials emanating from the explosive charge. 
In accordance with the present invention there are provided apparatus and a 
method for perforating and slotting well flow conductors. The preferred 
apparatus includes a string of continuous tubing of a length sufficient to 
reach a depth in the well at which the perforations or slots are desired, 
a jet nozzle head connected with a first free end of the continuous 
tubing, a storage reel for the continuous tubing having a fluid conducting 
central hub connected with the second end of the continuous tubing on the 
storage reel, pump and fluid storage apparatus connected with the hub of 
the storage reel for pumping fluid through the storage reel hub into the 
continuous tubing, a tubing injector mounted above the well in which the 
method is to be carried out for running and pulling the continuous tubing 
and jet nozzle head, and a well head on the well flow conductor provided 
with an annular stripper rubber member for sealing around the continuous 
tubing as it is run and pulled, and a side outlet into the wellhead below 
the stripper rubber for fluid returns from the wellhead. The method is 
carried out by connecting the jet nozzle supported on the continuous 
tubing from the reel through the tubing injector and the wellhead into the 
well flow conductor. The tubing is lowered by means of the injector until 
the jet nozzle is at the depth in the well at which the perforations or 
slots are to be formed. A fluid is then pumped through the storage reel 
hub into the continuous tubing and outwardly into the wellbore through the 
jet nozzle head. The discharging jets cut the desired perforations in the 
flow conductor in the wellbore with the fluid returns passing upwardly in 
the annulus of the wellbore around the continuous tubing and outwardly 
through the side outlet of the wellhead below the stripper rubber. If 
slots ar desired in the flow conductor, the tubing injector is operated to 
reciprocate the tubing and the jet nozzle head a distance equal to the 
length of the slots desired until the slots are cut. The continuous tubing 
and jet nozzle head are then removed from the wellbore by means of the 
tubing injector.

Referring to FIG. 1, the invention is shown in its preferred embodiment. A 
continuous tubing type jet perforating and slotting system 10 is shown 
supported over a well 11 which is provided with a well casing 12 which has 
been cemented in the wellbore at 13. The apparatus of the invention is 
employed to form perforations 14 in the well casing 12 to communicate from 
the wellbore with the earth formations 15 around the wellbore. 
The perforating and slotting system 10 includes a string of continuous 
tubing 20 supporting a jet nozzle head 21, a continuous tubing injector 22 
mounted on a platform 23, a continuous tubing guide assembly 24 operable 
with the injector 22, a continuous tubing storage reel 25, a pump 30 
connected with the storage reel, and a fluid storage tank 31 connected 
with the pump. 
The continuous tubing used in the invention is preferably a form of 
flexible tubing which may be made of a material such as steel and which is 
constructed to be stored on a reel and is adapted to be wound onto and 
from the reel without exceeding the acceptable stress standards for the 
tubing. Such tubing is available in sizes ranging from one-half inch to 1 
inch outside diameter. The size selected must be large enough to permit 
the fluid to be injected without a pressure drop sufficient to affect the 
cutting ability of the jet streams emitted from the jet nozzle head. 
The conditions tubing is operated through a wellhead 32 mounted on the wall 
casing 12 for sealing around the continuous tubing and directing the flow 
of the fluid returns as discussed in detail hereinafter. 
The wellhead 32 includes a pipe section 33 connectable by a coupling 34 
with the upper end of the conductor 12. An outlet 35 is secured with the 
pipe section 33 for the discharge of fluid returns passing up the flow 
conductor in the annulus around the continuous tubing string. Above the 
outlet 35 a seat flange 40 is formed in the pipe section to support an 
annular stripper rubber member 41 which is held in place and forced 
radially inwardly around the continuous tubing by a plurality of 
circumferentially spaced set screws or bolts 42 which typically may 
comprise six or more such set screws. The outlet 35 may simply discharge 
to the ground around the wellhead or may be connected back into the tank 
31 for recirculation of the fluid used to form the perforations and slots 
in the well casing. 
The jet nozzle head 21 includes a tubular body 43 closed at a lower end by 
a plate 44 and secured at the upper end with a coupling section 45 used to 
connect the nozzle head with the free end of the continuous tubing 20. The 
upper and lower ends of the body 43 are each provided with radially 
outwardly extending centralizer ribs 50 circumferentially spaced at 
90.degree. intervals around the upper and lower ends of the nozzle head to 
function as centralizers for keeping the nozzle head centrally located 
within the well casing as it is lowered and retrieved and operated within 
the casing. A set of upper jet nozzles 51 are secured around the body 43 
at 90.degree. intervals opening into the body below the upper centralizer 
set. Similarly a set of identical lower jet nozzles 52 are secured through 
the nozzle head body on 90.degree. circumferential spacing, each of the 
lower nozzles being located equidistant between the adjacent pair of upper 
nozzles 51 as evident in both FIG. 2 and FIG. 3. The particular 
configuration of jet nozzle head illustrated will provide a total of eight 
round perforations in the well casing comprising an upper set of four at 
90.degree. intervals and a lower set of four at 90.degree. intervals 
spaced at 45.degree. intervals between the upper perforations. If slots 
are desired, the nozzle head will provide eight longitudinal slots of any 
desired length spaced at 45.degree. intervals around the well casing. The 
jet nozzles 51 and 52 are made of a suitable abrasive resistant material 
which will permit the use of either a non-abrasive fluid or an abrasive 
fluid to be pumped through the nozzles to form the perforations or slots 
in the well casing and preferably have diameters ranging from 0.03125 
inches to 0.093 inches to form a perforation or slot which is sufficiently 
large enough to allow the ingress of formation fluids but small enough to 
resist the ingress of formation materials. 
The continuous tubing injector 22 is one of a number of available apparatus 
which straightens and drives the continuous tubing downwardly through the 
wellhead into the wellbore and pulls the tubing from the wellbore. One 
such available unit is known as the OTIS CONREEL CONTINUOUS TUBING UNIT 
illustrated and described in Otis Engineering Corporation Catalog Sheet 
5117A published October 1976 which also illustrates the tubing guide 
assembly 24. Another unit which may be used to insert and pull the 
continuous tubing is illustrated in U.S. Pat. No. 3,182,877 issued May 11, 
1965 to D. T. Slator, et al. 
The guide assembly 24 has a curved member 53 secured with the injector 22 
supporting a plurality of guide rollers 54 aligned along a suitable arc 
which will permit the required change of direction in the continuous 
tubing as it moves between the reel 25 and the injector 20. An outer guide 
rail 55 is secured with the member 53 formed along an arc parallel with 
the member 53 and the rollers 54 to hold the continuous tubing against the 
rollers as it moves between the reel and the injector. The guide rail 
assembly is a part of the OTIS CONREEL UNIT previously referred to. 
The storage reel 25 for the continuous tubing is a suitable available reel 
which also is a part of the OTIS CONREEL UNIT as previously identified 
having a central hub connected with the second end of the continuous 
tubing 20 and providing a fluid connection with the second end of the 
tubing leading to a conduit 60 running from the reel hub to the pump 30. 
The pump is connected by conduit 61 with the storage tank 31 so that fluid 
in the storage tank may be discharged from the tank into the second end of 
the continuous tubing string 20 through the reel hub as the tubing is 
unwound from the reel. 
For the operation of the system 10 to provide perforations or slots in the 
well casing 12, the tubing injector 22 is supported on the platform 23 
over the wellbore 11. The continuous tubing 20 on the storage reel 25 is 
manipulated from the storage reel through the guide assembly 24 and the 
injector 22 until the free end of the tubing extends downwardly below the 
platform from the ejector. The free end of the continuous tubing is 
inserted through the stripper rubber 41 within the wellhead 32, with the 
wellhead off of the upper end of the well casing 12. The jet nozzle head 
21 is then connected with the free end of the continuous tubing and the 
rjet nozzle head 21 is placed downwardly into the upper end of the well 
casing 12. The well head 32 is then mounted on the upper end of the well 
casing by means of the coupling 34. The sew screws 42 are adjusted to 
tighten the stripper rubber 41 around the continuous tubing to prevent any 
leakage of the cutting fluids through the wellhead along the tubing. 
The injector 22 is then operated to pull the continuous tubing 20 from the 
reel 25 through the guide assembly 24 and push the tubing through the 
wellhead into the wellbore until the jet nozzle head 21 is at the depth in 
the wellbore at which the perforations 14 are desired in the well casing 
12. As the jet nozzle head 21 is lowered in the well casing and when the 
jet nozzle head reaches the desired depth in the casing, the guide fins 50 
moving along the inner wall surface of the well casing 12 keeps the jet 
nozzle head at a central location along the axis of the well casing. 
A suitable fluid is prepared and placed in the storage tank 31. The fluid 
may comprise either water or sandmixed with water in a concentration range 
of about one-eighth to 1 pound of sand per gallon of water. Depending upon 
the diameter of the nozzles 51 and 52 and the type of material to be 
perforated, the sand may range in size from 40-60 mesh size to 200 mesh 
size with 100 mesh size sand generally being the most satisfactory. A gel 
comprising a thixotropic solution such as water, bentonite, and sand may 
be used so the sand will remain suspended when flow ceases, and will flow 
when pumping resumes. 
The fluid is pumped from the tank 31 into the hub of the reel 25 through 
the conduit 60. The fluid flows through the reel hub into the second end 
of the continuous tubing 20 which is secured with the hub on the reel. The 
fluid is pumped through the continuous tubing downwardly into the wellbore 
to the jet nozzle head 21. The fluid is forced outwardly through the 
nozzles 51 and 52 impinging upon the inner wall surface of the well casing 
12. The fluid within the annulus in the well casing around the head 21 and 
the continuous tubing 20 flows upwardly along the wellbore to the wellhead 
32 from which the returning fluids flow outwardly through the outlet 35 
below the stripper rubber 41 which prevents any leakage from the wellhead 
along the continuous tubing. The fluids either are discharged to some 
disposal facilities, onto the ground, or back to the storage tank 31. The 
circulation of the fluid through the jet nozzle head 21 is continued until 
the abrasive action of the fluid cuts through the well casing 12 and the 
surrounding sheath of cement 13 into the earth formation 15. 
The jetting action is continued until the desired number of perforations 
are cut through the well casing 12 and the cement sheath 13. The length of 
time required to cut the perforations will vary depending upon the 
operating conditions and the materials of which the well casing is made 
and the materials included in the abrasive fluid. Previously conducted 
surface tests on a casing section provide a guide as to the maximum time 
required to accomplish the necessary cutting. Under some conditions an 
indication of the cutting of the perforations may be obtained by a change 
in the volume of the returns through the outlet 35. Another method of 
determining when the casing is properly cut is the lowering of a camera, 
though this does require pulling the tubing 20 and jet nozzle head 21. 
Longitudinal slots may be cut in the well casing 12 and the cement sheath 
13 by reciprocating the jet nozzle head 21 using the tubing injector 22 to 
move the continuous tubing and the jet nozzle head upwardly and downwardly 
until slots of the desired length are cut. During reciprocation of the jet 
nozzle head 21, each of the jet nozzles 51 and 52 will cut a longitudinal 
slot in the well casing. 
When the desired perforations or slots have been cut in the well casing the 
continuous tubing 20 and jet nozzle head 21 may be removed from the well. 
The tubing injector 22 is used to pull the tubing 20 and jet nozzle head 
21 upwardly until the jet nozzle head 21 is pulled into the wellhead 32. 
The coupling 34 is then manipulated to release the pipe section 33 from 
the upper end of the well casing. The wellhead 32 along with the jet 
nozzle head 21 are lifted from the upper end of the well casing 12 and the 
jet nozzle head 21 is then disengaged from the end of the continuous 
tubing 20. The tubing injector 22 and the reel 25 are then operated to 
fully withdraw the continuous tubing 20 from the well. The well may then 
be equipped with such other wellhead facilities as are required for the 
particular procedure to be carried out in the well. 
When perforating polyvinyl chloride material well casing, it is preferable 
that the fluid used be only water which is ejected at a pressure of 5,000 
psi to 15,000 psi, preferably 8,000 psi to 10,000 psi, to yield 
satisfactory results. Furthermore, the nozzle jet head 21 should be within 
one to 20 jet nozzle diameters of the well casing to produce holes 
sufficiently small in diameter in the casing to exclude formation 
materials from flowing into the well casing during formation production. 
In the case where glass fiber reinforced thermosetting epoxy resin material 
well casing is to be perforated, it is desirable to use an abrasive fluid 
supplied at a pressure less than 4,000 psi to yield satisfactory results. 
In this instance, it is desirable to maintain the nozzle jet head 21 
within two to twenty, preferably two or three, jet nozzle diameters of the 
well casing to produce holes sufficiently small in diameter in the casing 
to exclude formation materials from flowing into the well casing during 
formation production. If the jet nozzle head 21 is within a distance of 
less than two jet nozzle diameters of the well casing, excessive nozzle 
jet wear occurs on the exterior surface of the nozzle jets due to the 
abrasive fluid splashing on the nozzle jet exterior surfaces. If the 
nozzle jet head 21 is more than twenty nozzle jet diameters from the well 
casing, the perforations made by the nozzle jet head 21 are large enough 
to allow formation materials to flow into the wellbore. In this 
connection, if glass fiber reinforced thermosetting epoxy resin material 
well casing is perforated using water only as the fluid, the well casing 
will delaminate and break rather than be cleanly perforated. 
It will now be seen that a new and improved method and apparatus for using 
continuous tubing to provide perforations or longitudinal slots in a well 
casing has been described and illustrated. The use of the continuous 
tubing allows the procedure to be carried out in one continuous sequence 
of steps without the necessity for the more expensive and time consuming 
procedure of using pipe sections which are connected and disconnected with 
each other during the running and pulling of the tubing string and jet 
nozzle head 21. However, if desired, conventional pipe sections are a 
continuous string of reinforced rubber hose may be used as the tubing 
string. If pipe sections or a continuous string of reinforced rubber hose 
is used rather than the continuous steel tubing, the OTIS CONREEL 
CONTINUOUS TUBING UNIT must be replaced with conventional manifolding 
equipment including a tubing guide for insertion of the tubing into the 
wellhead and, in the case of a continuous string of reinforced rubber 
hose, the use of a storage reel is optional. 
It would be understood that these and other modifications can be made 
within the scope of the invention and the following claims will be 
understood to include such modifications as do not depart from the broad 
scope of the invention.