HISTORY OF HYDRO-SLOTTING PERFORATION TECHNOLOGY
The idea of creating a lateral extension slots along the borehole, instead of traditional perforation holes, came from coal industry. In the coal mine created a special groove of different sizes, depending on the magnitude and direction of rock pressure. This procedure significantly unloaded the stress state of rock pressure in the near zone, and rock was getting with less effort.
Unloading effect in the near zone have decided to use for oil and gas wells.
The problem was that diameter of wells is not allowed to use available devices for cutting slots, and all attempts to make slots from the surface motion of tubing ended in failure. Was needed device able to cut slots within the wellbore, in the point of cutting.
First "classical" hydro-slotting perforation technology (HSP) was patented on July 24, 1972 (Inventors: E. Goncharov, A. Shabarov, V. Sidorov, N. Krotov, I. Petukhov), Patent # RU 1623290.
In 1975, with HSP has been developed the first oil well. Since 1980, hydro-slotting perforation technology has been recommended for use in Oil and Gas Industry.
Since 2008, on the basis of "classical" hydro-slotting perforation technology was written more then 50 full public books, and more than 500 patents (around 100 patents are "public"), therefore now only laziest intermediary or internet companies, absolutely have no relation to oil and gas industry, can discuss about hydro-slotting perforation (HSP) issues, as about "new", "advanced", "innovative" and "proprietary" technology.
1947 Cumulative perforation
1949 Hydraulic fracturing
1975 Hydro-slotting perforation
1980 HSP recommended for use in oil and gas Industry
1985 Jets-point (abrasive jetting) perforation
1987 Presentation HSP on oil and gas conference in Houston (Texas, United States)
1996 Use HSP in the United States
1999 Coiled Tubing
2011 Presentation HSP on oil and gas exhibition in Calgary (Alberta, Canada)
2011 Use HSP in Canada
2015 Created HSP equipment for horizontal wells
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Adding to the working fluid abrasive filler, due jets perforation, significantly increases the penetration depth in contradistinction to using only water cutting jets. For example, in in designs containing circular saws is impossible to use an abrasive filler, therefore the depth of penetration in such devices can only slightly exceed the diameter of saw blade.
Multiple tests show, that the maximum penetration depth due abrasive jets (point) perforation less than 1 foot, and regardless of the application time. It happens because reverse jets from holes prevents direct jets from nozzles. If cutting jets vibrates, it may form a cavity. But if the cutting jets give a straight and constant movement (not from the tubing), immediately formed penetration depth. It happens because reverse jets from a holes not prevents direct jets from nozzles, and are located always above the jets from nozzles, accordingly abrasive filler with waste rock can freely leave the slotted holes, and with reverse circulation fluid in casing flow to surface.
Multiple tests show, that opening casing, cement and productive formation by cutting extended deep slots along the borehole, gives a much greater and much lasting effect, than gun, cumulative or abrasive jets (spot) perforation. Large opening surface area provides a good and reliable hydrodynamic connection between productive layer with the well, occurs unloading of stress conditions in the near wellbore zone, and accordingly increases porosity, permeability, and ultimately increases the productive inflow to the well.
Multiple tests show, that maximum cutting depth due hydro-slotting perforation is 5 foot (1.5 m). Further increase in pressure does not affect to the depth. Unloading effect of stress conditions in the near wellbore zone (redistribution of stresses on the ends of circumcision extended slots) occurs at cutting depth 3 foot (0.9 m).
Multiple tests show, that all attempts to cut extended deep slots along the wellbore using a tubing motion from the surface lead to failure. This happens because each tubing (or coiled tubing) has different elongation parameters, and own resonant frequency (cutting jets jump in place the cut), and in this case, extended deep slots never happens. Conclusion: extended deep slots along the borehole can be obtained only by application of motion to cutting jets directly at the point of cutting (inside the wellbore).
Multiple tests show, that for cutting extended deep slots through the casing, cement, into the productive formation, the speed of movement the cutting jets along the wellbore should be sufficiently slow, rectilinear and constant.
Experimentally found, that for cutting extended deep slots through the casing, cement, into the productive formation along the wellbore, the optimal number of nozzles (cutting jets) in the perforator must not exceed four, and be located on one level. By arranging the nozzles (cutting jets) along the borehole (one after another) operate only front nozzles (cutting jets), the others do not work in the cutting process. Inordinate increase a number of nozzles (cutting jets) also not give a positive effect, and leads to almost complete loss of kinetic energy of the cutting jets.
As abrasive filler for cutting jets can be used abrasive quartz sand, or other abrasive components, with a weight of particles equal weight of abrasive quartz sand particles (particles with less weight will have a smaller kinetic energy for cutting), and with dimension, not greater the initial diameter of inner hole of nozzles (otherwise they will interfere with each other when passing through the nozzle’s hole, which will also reduce the flow kinetic energy). Abrasive gives to working fluid jets the great destructive power, and water (liquid) is required for the transport of abrasive particles.
MINING GEO-MECHANICS REQUIREMENTS
Cumulative perforation (shooting, gun-perforation). Does not meet any requirements (destroys the cement sheath, forms crust, the depth of penetration into the formation 1 foot maximum, diameter 1.9" maximum, drainage area 0.5 ft², volume 0.003 ft³), but very cheap method (does not require additional services), therefore most widespread. The duration of effect in average 7 years.
Hydraulic fracturing. The most effective, rather expensive method. Meets the requirements of A, B and C points. Opens a huge area, forms a crack network including microscopic cracks, which will eventually collapse. The duration of effect in average 5 years. Environmentally harmful, can not be used in the presence of water near of the wellbore.
Slotting perforation. Very efficient method, environmentally friendly. Meets all the requirements of A, B, C and D points. For cutting slots along the wellbore used water jet with abrasive filler, moving with a constant speed in a straight line along the wellbore. Movement created a special tool directly into the cutting zone. Due to movement the forward and reverse jets not interfere with each other, sludge free flow by working fluid and brought to the surface, jets cutting the formation deeper and deeper. The duration of effect in average more than 10 years.
Slotting perforation divided into two main categories:
Hydro-mechanical slotting perforation. Abrasive filler can not be used (mechanical milling), so the depth of cut is small enough: 2 foot maximum, drainage area per each linear foot 8.6 ft², volume 0.656 ft³ per each linear foot.
Hydro-slotting perforation. Uses water and abrasive filler. Is possible to use 4 nozzles in the perforator, respectively can be cut four deep slots simultaneously. The depth of cut 5 foot maximum, drainage area per each linear foot 21.4 ft² (with 2 nozzles) and 42.84 ft² (with 4 nozzles), volume 1.64 ft³ (with 2 nozzles) and 3.28 ft³ (with 4 nozzles) per each linear foot (this all elementaryis calculated by length, width and height).
Jets point (abrasive jetting) perforation. Meets the requirements of C and D points. The depth of penetration into the formation 1 foot maximum (diameter 1.9" maximum, drainage area 0.5 ft², volume 0.003 ft³), but simple cheap enough method (does not require additional services and special tool), therefore most widespread. Depth is limited because the reverse jet from the rocks prevents direct jet from the nozzle (no straight-line movement with constant velocity jet). The duration of effect in average 4 years.
A Large opening area of a casing, cement ring and productive formation (provides a good hydro-dynamic connection between productive layer and the well)
B The depth of penetration into the productive formation (provides the unloading the stress conditions in the near wellbore zone and accordingly increases the permeability)
C Preventing the formation of crusts on the border of opening zone (prevents the inflow of useful product and requires additional actions)
D Preventing cracked of cement ring (provokes the flows of water and increases the risk of well's flooding)