High pressure well perforation cleaning

Improved method and apparatus for directionally applying high pressure jets to well casing or liners to clean openings in the casing, liner and the adjacent geologic formation which are plugged with foreign matter. High velocity jets of liquid having a velocity in excess of 700 feet per second are jetted from jet orifices having a 1/16th to 1/4th inch diameter and having a standoff distance between 5 and 100 diameters of the orifice from the openings to remove substantially all plugging material from the openings. Power swivels permit rotation and Kelly hoses allow reciprocation of the jet tool and tubing string while maintaining high pressure in the apparatus.

FIELD OF THE INVENTION 
This invention relates generally to well production. More specifically, the 
invention relates to cleaning openings in both the well casing or liners 
positioned adjacent fluid-producing formations, and the corresponding 
openings in the geologic formation itself, using high velocity liquid 
jets. 
BACKGROUND OF THE INVENTION 
The production of oil, gas, water, or any combination of these three are 
produced from wells penetrating the earth's subsurface strata. The wells 
are most often completed with casing (and liners) cemented through to the 
productive strata in the subsurface. Wells are also occasionally completed 
with uncemented liners. In either case, perforations or slots must be made 
through the casing and cement (if present) to provide a flow path for 
fluids from the productive strata into the casing. Fluids which have 
reached the inside of the casing via the perforations or slots may then be 
produced to the surface. However, the openings which, for example, may be 
slots in the liner preformed on the surface and/or perforations opened in 
the casing and formation, will often become plugged. 
If a perforation tunnel in the casing, cement sheath, or formation becomes 
obstructed, then fluid flow will cease or will be impaired. This problem 
is especially serious in areas where hard, insoluble scales plug 
perforations. In any event, removal and replacement of the casing or liner 
is costly and is only a temporary solution since the casing or liner, as 
well as the adjacent formation, will eventually again become plugged. 
Sections of recovered plugged casing and liner have been analyzed to 
determine the identity of the plugging material. Results have shown that 
the plugging material is mostly inorganic. Generally, it appears to be 
fine sand grains cemented together with oxides, sulfides and carbonates. 
Some asphaltenes and waxes are also present. Where water is produced, 
scale also seems to be present and presents a very tough plugging 
material. Examples of scale include barium sulfate, strontium sulfate, and 
silicates. 
Many methods for cleaning openings in well casing or liners have been 
heretofore suggested. There have been three general methods employed which 
may be classified as 1) mechanical, 2) chemical, and 3) hydraulic. 
Mechanical methods can be thought of as using physical force to scrape an 
obstruction from the perforation tunnel. There are no prior art mechanical 
means to effectively clean perforations. Mechanical methods at this time 
are limited to cleaning inside the casing, which does not address the 
perforation itself. The only mechanical alternative to deal with 
obstructed perforations is to drill and complete a new wellbore, which is 
usually economically unattractive. 
Mechanical methods of cleaning the openings in casing or liners include the 
use of scratchers and brushes to cut, scrape or gouge the plugging 
material from the perforations. There are many disadvantages of these 
approaches. For example, the knives or wires in the brushes must be very 
thin to enter the slotted perforations which generally measures only 0.040 
to 0.100 inches wide and, therefore, the knives and wires are structurally 
weak. Thus, an insufficient amount of energy is generally applied to 
really unclog the perforations. Furthermore, the cleaning tool must be 
indexed so that the knives or wires actually hit a perforation. Since only 
3% of the casing or liner surface area is generally perforated, the 
chances are not favorable for contacting a perforation. 
Chemical methods usually consist of using some chemical agent to dissolve 
or dislodge obstructions in the perforation tunnel. Common chemicals used 
to remove obstruction are acids, aromatic solvents, alcohols, and 
surfactants. These chemicals have been found to be very effective at 
removing a wide variety of obstructions in and around perforation tunnels. 
The chemical methods require that the obstruction be chemically reactive 
with the chemicals placed in the perforation tunnels. However, there are a 
number of substances which are essentially non-reactive and inert for all 
practical purposes. Some common examples of these relatively inert 
obstructions are barium sulfate, strontium sulfate, and silicates. These 
substances are frequently deposited as scales. The deposition of these 
scales in and around perforation tunnels can obstruct or impede fluid 
flow. 
Chemical solvents have been developed which purport to dissolve these 
non-reactive substances. These solvents have been evaluated in the 
laboratory and in field trials, and have been found to be very 
ineffective. The chemical solvents were found to dissolve such a small 
amount of these non-reactive substances that they are economically 
unattractive. 
The combinations of plugging materials often inhibits the reaction of the 
chemicals. For example, an oil film will prevent an acid from dissolving a 
scale deposit and a scale deposit will prevent a solvent from being 
effective in dissolving heavy hydrocarbons. The chemicals cannot always be 
selectively placed where they are needed due to varying permeabilities 
encountered in a well bore and/or they dissolve the material in a few 
perforations and then the chemicals are lost into the formation where they 
can no longer be effective in cleaning the perforations. 
Hydraulic methods include pumping a fluid between two or more opposed 
washer cups until the pressure builds up sufficiently to hydraulically 
dislodge the plugging material. Explosives such as primer cord (string 
shooting) have been used to form a high energy pressure shock wave to 
hydraulically or pneumatically blow the plugging material from the 
perforations. The disadvantages of these two methods are that the energy 
is applied non-directionally to the casing or liner and it always takes 
the path of least resistance. The use of these methods generally results 
in opening only one or two perforations out of a perforation row 
containing from 16 to 32 perforations. 
Jetted streams of liquid have also been heretofore used to clean openings. 
The use of jets was first introduced in 1938 to directionally deliver acid 
to dissolve carbonate deposits. Relatively low velocities were used to 
deliver the jets. However, this delivery method did improve the results of 
acidizing. In about 1958 the development of tungsten carbide jets 
permitted including abrasive material in a liquid which improved the 
ability of a fluid jet to do useful work. The major use of abrasive 
jetting has been to cut notches in formations and to cut and perforate 
casing to assist in the initiation of hydraulically fracturing a 
formation. The abrasive jetting method requires a large diameter jet 
orifice. This large opening required a large hydraulic power source in 
order to do effective work. The use of abrasives in the jet stream 
permitted effective work to be done with available hydraulic pumping 
equipment normally used for cementing oil wells. However, the inclusion of 
abrasive material in a jet stream was found to be an ineffective 
perforation cleaning method for use with liners in that it enlarged the 
perforation which destroyed the perforation's sand screening capability. A 
jet that uses abrasives also is likely to cause casing damage. 
Another method for directionally applying a high pressure jet to a well 
liner to clean openings in the liner which are plugged with foreign matter 
has been suggested. High pressure liquid jets having a velocity in excess 
of 700 feet per second are jetted at the liner from jet orifices having a 
standoff distance less than 10 times the diameter of the orifice to remove 
plugging material from the liner openings. An apparatus for concurrently 
circulating foam is provided in combination with the apparatus used to 
deliver the high pressure, high velocity jets, due to the relatively low 
circulation rate. 
Relatively small diameter, threadably attached orifices which produce jets 
of 1/16th of an inch or less were thought to be advantageous in this 
method. A preferred orifice diameter for use in accordance with the method 
was 1/32nd of an inch. The use of small diameter threadably attached jets 
was thought to be very advantageous in that liquid volume requirements are 
lowered, thus lowering horsepower requirements and reducing the 
possibility of formation damage in low pressure formations caused by 
liquid in the well overpowering the formation. For example, see U.S. Pat. 
Nos. 3,850,241; 4,088,191; 3,720,264; 3,811,499; and 3,829,134; each of 
which issued to S. O. Hutchison. Whereas Hutchison's invention was a 
substantial improvement over the prior art at the time regarding cleaning 
perforations in a casing or liner, his method did not provide a means to 
clean out the perforations in the geologic formation itself, adjacent to 
the perforations in the casing or liner, or to adequately remove insoluble 
scale. The cleaning radius of Hutchison's tool is limited by the small 
nozzles used (1/32nd of an inch). The retained energy of jets is a 
function of the number of nozzle diameters from the point of origin. Using 
water (without chemical additives) the effective cleaning range of a 
nozzle is typically taken as 10 nozzle diameters due to energy decay. This 
results in effective cleaning radius of up to 5/16ths of an inch for a 
1/32nd of an inch nozzle. 
The addition of high molecular weight polymers results in enhanced jet 
performance. The effective cleaning range of a nozzle can be extended out 
to 100 nozzle diameters. The Hutchison tool with the use of polymer would 
then have a cleaning radius of up to 31/8 inches. Typical perforations, 
usually extend from 3/16 of an inch out to 15 inches radially from the 
nozzle. Thus, the Hutchison tool can only clean a small fraction of the 
perforation tunnel, and fluid flow remains greatly impaired. 
Using larger nozzles, in the range of 1/16th to 1/4 inch, larger cleaning 
radii can be obtained. For the case of 1/8th inch nozzles, the effective 
cleaning radius can be increased four fold over Hutchison's tool to 121/2 
inches. This larger cleaning radius results in more of the perforation 
being cleaned, and hence improved fluid flow. 
Hutchison, as well as the other prior art, actually taught away from using 
larger nozzles in an effort to clean the perforations in casing. Hutchison 
maintained that the use of relatively smaller diameter jet orifices of 
less than 1/8 inch has the advantage of reducing to a minimum the amount 
of liquid being injected into the well, as well as reducing horsepower 
requirements. Also, Hutchison incorporated threadably attached, specially 
designed jet nozzles and made no mention of nozzles being attachable by 
0-rings. 
A further attempt to improve the existing methods was made by C W. Zublin. 
Zublin, a licensee of the Hutchison patents, received U.S. Pat. Nos. 
31,495; 4,441,557; 4,442,899; and 4,518,041. U.S. Pat. No. 31,495 added a 
centralizer to help center the jet nozzles and provide a means to pan out 
of tight places in the tubing. This device is rotated by a power swivel at 
the surface. Zublin, however, maintained that larger nozzles are 
disadvantageous in that they cause a pressure drop, and recommended that 
the jet orifices be only 0.03 (1/32) inch in diameter. Zublin also only 
taught the use of threadably mounted nozzles. 
U.S. Pat. No. 4,441,557 claims nozzles spaced so as to direct cleaning 
fluid onto the pipe in a certain pattern. The device is rotated at a 
constant speed by the power swivel at the surface. Again, 0.03 (1/32)-inch 
threadably mounted nozzles were used, as larger nozzles were said to cause 
a pressure drop. 
U.S. Pat. No. 4,442,899 claims a method and a system for a non-rotating 
device utilizing threadably mounted 0.0325 (1/32-inch) nozzles and 
alternating pressure to create an oscillating twisting force according to 
a certain formula, for use with coiled tubing. 
U.S. Pat. No. 4,518,041 claims a method and a system utilizing a device 
that is not rotated by the tubing at the surface. The device has 
threadably mounted 0.0325 (1/32-inch) nozzles which, like the device in 
U.S. Pat. No. 4,442,899 direct the flow of the cleaning fluid in such a 
manner as to tend to twist the tubing. 
A further attempt to improve the well cleaning process was made by Wm. H. 
McCormick, who received U.S. Pat. No. 4,625,799. U.S. Pat. No. 4,625,799 
claims an apparatus for pressurized cleaning of flow conductors. The 
device utilizes a control slot which assists in indexingly rotating the 
nozzle section. Neither nozzle size nor means of nozzle attached are 
discussed. 
The above methods and devices are all limited in the effective cleaning 
distance of the jets, to a distance of up to 10 times the diameter of the 
jet orifice. Also, none of the prior art teaches a method of how to remove 
insoluble scale, such as barium sulfate, strontium sulfate, or silicate. 
This limitation prevents actual cleaning of the perforation tunnels in the 
adjacent production geologic formation, which often become plugged and 
therefore inhibit oil or gas production. There is, therefore, still a need 
for a method of cleaning openings both in a well casing or liner and in 
the adjacent geologic formation which is a practical and relatively easy 
operation to perform. Further, there is need for a method of cleaning 
openings in such casings, liners, and geologic formations which does not 
destroy or alter the openings or damage the casing or liner. 
The above methods and devices are also limited in that the nozzles must be 
specially designed to be threadably attached to the cleaning tool. 
Constructing the individual nozzles is relatively expensive. There is 
therefore still a need for a method of attaching readily available, 
relatively inexpensive nozzles to the cleaning tool. 
SUMMARY OF THE INVENTION 
An apparatus for jet washing perforation tunnels in a well casing or liner 
positioned in a well and perforation tunnels in an adjacent geologic 
formation is described. A tubing means forms a well flow path from the 
earth's surface to a location adjacent to the well liner. A source of high 
pressure liquid provides a hydraulic horsepower of at least 1,000 HHP (or 
167 HHP per jet body of 1/8-inch nozzle diameter) to supply at least 0.77 
barrels per minute per jet body used at pressures in excess of 5,000 psi 
to jet the liquid at the liner. The effective standoff distance of 
cleaning is up to 100 times the diameter of the jet orifice, provided that 
a polymer additive is added to the high pressure liquid. The effective 
standoff distance of cleaning is up to 12 times the diameter if plain 
water is used. 
A conduit connects the liquid source to the tubing means. A jet tool means 
having at least one hole in the wall jets the high pressure liquid at the 
perforation tunnels in the casing or liner. The jet tool comprises a 
tubular member connected to the lower end of the tubing means. 
A jet seat is fixedly connected to the tubular member, and has a central 
opening aligned with the hole in the jet tool wall. A jet body, having a 
central opening of 1/16th to 1/4th inch in diameter is hydraulically 
sealed in the jet seat member, so that the jet body can be rotated to 
provide axial movement with respect to the jet seat member. 
In another embodiment, a jet tool means has a hole in the sidewall for 
jetting the high pressure liquid at the perforation tunnels. A jet seat 
member is fixedly connected to the tubular member, and has a central 
opening positioned over the hole. The tubular member is connected to the 
jet seat member and a jet body, having a central opening of approximately 
1/16th to 1/4th inch in diameter is detachably engaged and hydraulically 
sealed in the jet seat member so that the jet body may be rotated to cause 
axial movement of the jet body with respect to the jet seat member. 
The use of the jet bodies (or nozzles) having relatively large central 
opening is very advantageous and novel. If a 1/8 inch nozzle diameter is 
used, the effective cleaning radius of the apparatus is increased to 
approximately 12.5 inches or 100 nozzle diameters if a polymer additive is 
used, or 1.5 inches or 12 nozzle diameters if plain water is used. The 
effective cleaning radius of 100 diameters corresponds to an 80% energy 
loss. The same is true for the effective cleaning radius of 12 diameters, 
if plain water is used. This larger sized jet body opening permits actual 
cleaning of the perforation tunnels in the adjacent geologic formation as 
well, whereas the prior art was limited to a far shorter cleaning radius. 
Also, the larger sized jet body openings permit the removal of insoluble 
scale, such as barium sulfate, strontium sulfate, or silicate. Current 
technology now provides an economic source of high pressure liquid that is 
able to provide a hydraulic horsepower of at least 1,000 HHP (167 HHP per 
nozzle) for supplying liquid at a flow rate of at least 4.6 barrels per 
minute, if 6 nozzles are incorporated (or 0.77 barrels per minute per 
nozzle) at pressures in excess of 5,000 psi. For example, pump trucks are 
widely used in routine downhole fracturing of a potentially productive 
geologic formation, and are able to generate the needed hydraulic 
horsepower described above.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is an elevation view, partially in section, and illustrates the 
preferred embodiment of apparatus assembled in accordance with the present 
invention positioned in a well. FIGS. 1 and IA thus illustrate the overall 
view of the preferred apparatus of the present invention. FIGS. 2 through 
4 illustrate portions of the preferred apparatus in greater detail. 
In FIG. 1 a production or injection well is shown drilled into a fluid 
producing formation 19 from the earth's surface 15. The well is cased with 
a suitable string of casing 13 through the productive or injective 
interval 19. FIG. 1(A) is an elevation view, partially in section, 
illustrating the preferred embodiment of apparatus assembled in accordance 
with the present invention positioned in a well liner. Note that the tool 
can be utilized equally well for a well liner. A liner 20 having suitable 
openings 21 is hung from the casing 13 and extends along the producing 
formation 19. 
The openings which may be slots or perforations permit flow of formation 
fluids from formation 19 into the interior of the well. As the formation 
fluids are produced, the openings in both the slotted liner 21 (or a 
casing 18) and the adjacent formation 19 tend to become plugged by 
depositions of scale, asphalt, clay and sand. The plugging material in the 
various slots or perforations at different elevations in the liner 20 (or 
casing 18), cement sheath 14, or formation 19 will vary in composition 
and, depending on the composition, will be more or less difficult to 
remove in order to reopen the slots. As the slots or perforations become 
plugged production from the well will tend to decline. Once it has been 
determined that the openings in the well casing 18, cement sheath 14 or 
liner 21 or formation 19 have become plugged to the extent that cleaning 
is required for best operation of the well, the apparatus shown in FIG. 1 
is assembled to accomplish such cleaning. 
The present invention utilizes high velocity jets 23 of liquid 2 to clean 
plugged openings (or perforation tunnels) both in well casings and liners, 
liners and in the adjacent geologic formation. The high kinetic energy of 
the jet is directionally applied to the openings by means of a rotatable 
and reciprocal jetting apparatus. Thus, the apparatus of the present 
invention can be rotated while jetting high pressure liquid jets 23 at the 
casing or liner. Additionally, the present apparatus may be concurrently 
raised or lowered in the well to provide for overall coverage of the liner 
by the jetted liquid. 
The use of high velocity jets 23, i.e., having pressures in excess of 5,000 
psi, permits maximum energy release to clean the openings of a liner or in 
a formation. Only three to nine jets are incorporated, so there is no 
pressure drop or extra volume of liquid required. To increase the jet 
nozzle (or jet body) size from 1/32nd inch diameter, (taught by the prior 
art) to the novel recommended size of 1/16th to 1/4th inch diameter, the 
number of nozzles has to be reduced from about 14 to no more than 9 to 
avoid an excessive loss of pressure. The cleaning radius of the tool 
increases from 3.1 inches using a polymer or 0.38 inches if plain water 
was used for a 1/32-inch nozzle, to approximately 12.5 inches or 100 
nozzle diameters for a 1/8-inch nozzle if a polymer additive is used, or 
1.5 inches or 12 nozzle diameters if plain water is used. The effective 
cleaning radius of 100 diameters corresponds to an 80% energy loss. The 
same is true for the effective cleaning radius of 12 diameters, if plain 
water is used. The hydraulic horsepower must also be increased about 
eight-fold from 125 HHP (9 HHP per nozzle) with a 1/32-inch nozzle to 
1,000 HHP (167 HHP per nozzle) with a 1/8-inch nozzle. Typical service 
company pump trucks generally have this much hydraulic horsepower 
available. As a flow rate in excess of 4.6 barrels per minute if 6 nozzles 
are incorporated (or 0.77 barrels per minute per nozzle) is utilized, the 
flow rate is sufficient to clean the dislodged material from the well. 
In accordance with the invention, a method of jet cleaning a well casing or 
liner is provided by flowing high pressure liquid down a flow path from 
the earth's surface to a point adjacent the plugged openings in the casing 
or liner. A jet of liquid is formed by passing the liquid through a small 
diameter jet orifice from 1/16th to 1/4th inch in diameter at a velocity 
of at least 700 feet per second and directing the jet of liquid at the 
casing or liner to clean the slots or perforations thereof from a distance 
of between 5 and 100 diameters of the orifice. The jet is rotated and 
reciprocated in the liner to ensure substantially complete coverage of the 
surface of the liner (or casing). It is also necessary to prevent damage 
to the liner or casing from occurring, due to the high pressure of the 
jetted liquid. This rotating and reciprocating is accomplished while the 
jet is simultaneously jetted against the liner to thereby clean the 
perforations of the casing or liner. 
In order to facilitate the understanding of the present invention, the 
preferred embodiment of apparatus will be generally discussed from top to 
bottom in relation to FIG. 1. The apparatus of the present invention is 
hung above and in the well by means of traveling blocks 6 which are 
connected to a draw works (hoisting equipment; not shown). Suitable long 
links (holes) 7A and 7B connect the traveling blocks to the elevators 8. 
The links (bales) 7A, 7B are connected to a traveling block on the 
conventional hoist which is utilized to move the elevators up and down 
thereby raising or lowering the apparatus of the present invention. A high 
pressure pump 4 capable of maintaining a hydraulic horsepower in excess of 
1,000 HHP (167 HHP per nozzle) is connected through a suitable conduit 5 
to the high pressure rotating swivel 9 to provide a flow path for high 
pressure liquid 2 (which is stored in reservoir tank 1) into the tubing 
string 10 which forms a first flow path down the well. 
In accordance with the invention then, a flow path for high pressure liquid 
is provided from the surface of the earth to a position in a well adjacent 
to a casing or liner having openings which are to be jet cleaned. High 
pressure liquid is jetted against such a casing or liner and the formation 
from a distance of up to approximately 12.5 inches for 1/8-inch nozzles or 
100 nozzle diameters if a polymer additive is used, or 1.5 inches for 
1/8-inch nozzles or 12 nozzle diameters if plain water is used. The 
effective cleaning radius of 100 diameters corresponds to an 80% energy 
loss. The same is true for the effective cleaning radius of 12 diameters, 
if plain water is used. When the standoff distance is reduced to less than 
5 diameters the jet bodies are subject to undesirable erosion by 
splashback. A high pressure rotating swivel utilized on the tubing which 
forms the flow path for high pressure jet liquid permits rotation of the 
jetting string during jetting operations. This rotation is important to 
insure substantially complete coverage of the area to be cleared and to 
prevent damage to the liner or casing from occurring, due to the high 
pressure of the jetted liquid. The jetting string may also be reciprocated 
in the well during such operations and by combining a preplanned program 
of rotation and reciprocation substantially complete coverage of the 
casing or liner with the high pressure jet can be obtained. 
The apparatus of the present invention will be discussed in greater detail 
with reference to FIGS. 2-4 and the various sections thereof. Briefly, 
FIGS. 2 and 3 show the jet tool; and FIG. 4 shows cleaning radius in 
accordance with the invention. 
FIGS. 2 and 3 illustrate jet washing tool 17 in more detail. The jet tool 
17 is positioned adjacent well casing 13 or liner 20 which has 
perforations 18 or slots 21, respectively, which need cleaning or adjacent 
geologic formation 19 which has perforations 18 which need cleaning. A 
tubular member 22 having its upper end connected to tubing string 10 
extends the length of the jet tool 17. Three to nine jets 23 are connected 
to tubular member 22 and placed at 90.degree. 120.degree. phasing on the 
jet tool 17. The tubular member 22 has its upper end connected to tubing 
string 10 and continues to form annulus 25 with tubular member 22. The 
jets communicate with the interior of tubing member 26 and the annular 
space 25. The jets comprise a jet body 30 (or nozzle) having a central 
opening 27 of from 1/16th to 1/4th inch diameter formed therein. The jet 
body 30 thus forms the orifice through which the jet is formed. A jet 
member 24 is matable with the jet body 30 by suitable means such as 
O-rings 28 and retaining rings 29. The jet seat member 24 may be 
constructed of carbide to resist erosion, and can consist of the same 
nozzles that are used in rotary bits. This permits a quick, economical 
access to various jet body sizes, as needed. The tubular members have 
axially aligned openings to receive the jet seat member 24. The jet seat 
members 24, serve the function of seating the jet bodies 30. The jet seat 
members 24, are also novel in the respect that this type of jet seat is 
readily available in the industry, as they are used in drill bits. 
Therefore, no new jet seat members need to be designed or manufactured. A 
jet body 30 has an exterior portion adapted to be mated with the jet seat 
members 24. The diameter of the jet as it leaves the tip of jet body 30 
determines the standoff spacing of the jet. This is clearly shown in FIG. 
4. Note that the standoff spacing B-B must be at least 5 times the 
distance A-A (central opening). 
The preferred use of relatively large diameter jet orifices of 1/8th inch 
in the present invention is novel and is advantageous in that the 
effective cleaning radius of the apparatus is increased to approximately 
12.5 inches for 1/8-inch nozzles or 100 nozzle diameters if a polymer 
additive is used, or 1.5 inches for 1/8-inch nozzles or 12 nozzle 
diameters if plain water is used (from 3.1 inches using a 1/32nd inch 
central opening with use of a polymer additive). Also, the larger sized 
jet orifices permit the removal of insoluble scale such as barium sulfate, 
strontium sulfate, or silicate. This larger sized jet body opening permits 
actual cleaning of the perforation tunnels in the adjacent geologic 
formation as well, whereas the prior art was limited to a far shorter 
cleaning radius. Current technology now provides an economic source of 
high pressure liquid that is able to provide a hydraulic horsepower of at 
least 1,000 HHP (167 HHP per nozzle) for supplying liquid at a flow rate 
of at least 4.6 barrels per minute if 6 nozzles as used (or 0.77 barrels 
per minute per nozzle) at pressures in excess of 5,000 psi. For example, 
pump trucks are widely used in routine downhole fracturing of a 
potentially productive geologic formation, and are able to generate the 
needed hydraulic horsepower, described above. Table I below indicates the 
effect of jet size on flow volume and standoff distance on power. It also 
illustrates the difference in fluid requirements to obtain the necessary 
jet velocities with different sized jets. 
TABLE 1 
______________________________________ 
EFFECT OF JET SIZE ON FLOW VOLUME 
AND JET STAND-OFF ON POWER LOSSES 
WITH A POLYMER ADDITIVE 
SIZE GPM @ FULL POWER 1/2 POWER 
1/5 POWER 
JET 7000 psi (60 D) (75 D) (100 D) 
______________________________________ 
1/32" 2.0 1.875" 2.344" 3.125" 
1/8" 34.0 7.500" 9.375" 12.5" 
______________________________________ 
Table 2 below gives the performance of nozzles (or jet bodies) for various 
diameters. It can be seen that as the nozzle diameter is doubled that the 
hydraulic horsepower and flow rate must be increased by four-fold to 
maintain the same jet velocity and pressure drop. The nozzle discharge 
coefficient has an important effect on nozzle performance. The discharge 
coefficients observed under field conditions can range from 0.65 to 0.99 
depending upon the nozzle design. 
Table 3 below gives the performance characteristics of a well cleaning 
assembly over a practical operating range for six 1/8-inch nozzles. For 
this specific case the required hydraulic horsepower varies from 518 to 
1126. The flow rate and jet velocity varies from 168 GPM (4.0 BPM) and 732 
FPS to 218.4 GPM (5.2 BPM) and 952 FPS. Tables of this sort can be 
developed for 1/8-inch through 1/4-inch nozzles. For 1/8-inch nozzles, 3 
to 12 nozzles would cover the optimum operating range to keep the 
horsepower and friction to practical levels For 1/4-inch nozzles, 2 to 3 
nozzles would cover the optimum operating range. The number of 1/4-inch 
nozzles used, is limited by symmetry about the tool axis. Therefore, a 
minimum of two 1/4-inch nozzles must be used. Failure to maintain symmetry 
and a force balance about the tool axis would result in excessive tool 
drag during reciprocation and excessive torque during rotation. For 
1/16-inch nozzles, 12 to 48 nozzles would cover the optimum operating 
range. The required hydraulic horsepower for 1/16-inch through 1/4-inch 
nozzles range from 400 to 2000 hydraulic horsepower when variations in the 
number of nozzles and nozzle discharge coefficients are considered. A 
typical value for hydraulic horsepower requirements for most practical 
application is 1000 HHP. 
TABLE 2 
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Pressure and Rate Requirements 
for Nozzles of Various Diameters* 
Nozzle Nozzle Hydraulic 
Diameter 
Pressure Flow Rate Jet Velocity 
Horsepower 
(inches) 
Drop (psi) 
(GPM) (FPS) per Nozzle 
______________________________________ 
1/32 7244 2.1 878 9 
1/16 7244 8.4 878 36 
1/8 7244 33.6 878 142 
1/4 7244 134.4 878 568 
______________________________________ 
*Fluid specific gravity is 1.0, nozzle discharge coefficient 0.85. 
TABLE 3 
______________________________________ 
Performance of Six 1/8 inch Nozzles with Polymer 
at a Depth of 5000 feet with Tubing Having an 
Inside Diameter of 2.441 inches** 
Nozzles Tubing 
Flow Tubing Pressure Surface 
Surface Jet 
Rate Friction Drop Pressure 
Hydraulic 
Velocity 
(GPM) (psi) (psi) (psi) Horsepower 
(fps) 
______________________________________ 
168 253 5030 5283 518 732 
176.4 266 5546 5812 598 769 
184.8 280 6087 6366 687 805 
193.2 293 6653 6946 783 842 
201.6 306 7244 7550 888 878 
210 320 7860 8180 1002 915 
218.4 333 7860 8835 1126 952 
______________________________________ 
**Fluid specific gravity is 1.0, nozzle discharge coefficient 0.85