Hydro-slotted perforation
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| Hydro-slotted perforation - the effective and ecologically safe method for intensifying the operation in oil, gas and injection wells by opening the productive layers without destruction the casing and cement ring. Hydro-slotted perforation provides the use of special equipment: hydraulic engine (hydraulic brake) and the working fluid used abrasive sand and water. Hydro-slotted perforation also known like direct slotting fracturing (DSL), abrasive hydro jet, slit-cutting, hydro-slitting, hydro-slotting, hydro-slotter, slot-cutting, geo-slicing and terra-slicing (not to be confused with jet (blast) perforation without the use of special engine or hydro-mechanical slot perforation with cutter). |
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Contents
History
| The technology of opening the productive layers by hydro-slotted perforation for increase the productive flow of oil, gas and injection wells has been developed by two Russian research institutes in 1972 - "Institute of Oceanology" and "VNIMI" (St. Petersburg). The method and design of the hydraulic engine (hydraulic brakes) have been finalized in the special laboratory of the Institute of Oceanology Research Institute of PSU "Sevmorgeo". (“Oil and Gas Industry” № 1 January 2008). The first practical tests in the wells were made in 1975 on Archeda field (Volgograd, Russia). Hydro-slotted perforation is used like industrial basis since 1980. The method is widely used in Russia (especially in Western and Eastern Siberia), Uzbekistan, Kazakhstan, Udmurtia, Urals, North Caucasus, Ukraine, Komi Republic, China, Jordan, Yemen and Brazil. The first used of hydro-slotted perforation in America dates back to 1996, when together with "Shell E & P Technology Company", were discovered two wells (Abrasive Hydro jet Technology in Albert Load, Michigan). The method was highly appreciated by “Shell” company and Stanford University Department of Geophysics. Hydro-slotted perforation was used in California, Kansas, Michigan, Montana, New York, Texas states and in Canada (Saskatchewan).
Over the years this method has not undergone much change, but the used equipment with the development of technological progress continuously improved and refined. |
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Technology overview
After drilling in the well-bore zone the compressive stress strongly reduces the permeability in the zone. Hydro-slotted perforation is based on the following:
| Slot-perforation hydraulic engine makes precise dual bipolar (180º) slotting through the casing into the production layer using a high pressure abrasive mixture, excavating a cavern more than 6’ into formation. Effectiveness of the method depends on the formation type. The best improvements are observed in naturally fractured reservoirs and in clay-reach formations. Porous and fractured formations are subjected to compression, that deforms the rock mass and reduces its permeability. |
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| The greater the depth, the stronger the effect can be. When a well is drilled and put into production, the compressive stresses are concentrated around the borehole and further reduce the formation permeability in the near well-bore zone. In combination with drilling damage, the well flow potential is significantly reduced. Hydro-slotted perforation induces pressure discharge around the well-bore zone, which dramatically increases permeability and enhances the reservoir properties. Recycled high pressure abrasive mixture (3000-5000 psi) is used to cut slots in casing, cement and formation. The flow area increased by more than 5 times. Abrasive hydro-slotted perforation slots penetrate more 6 feet into the formation, in most cases sufficient to bypass the near well-bore damage and to significantly increase the well flow potential. |
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| Stress redistribution around the hydro-slotted perforation zone unlocks clay and formation particles. If desirable, the method allows for 100 % coverage of the production layers, as the abrasive hydro-slotted process can be designed and performed to complete communication between the well and productive layer. Unlike some other conventional stimulation methods, the hydro-slotted perforation achieves a long-lasting effect. Formations sustain two types of mechanical stress: vertical stress and horizontal stress. The act of drilling a bore-hole re-distributes mechanical stress. This is often made worse by drilling and completion damage particularly in older wells. Pay zone permeability can decrease by 5 to 10 times due to the effect of these stresses alone. (Permeability can be reduced to 10% of the natural state). Drilling and conventional completion technologies cause a high pressure low permeability area to form well-bore. Often conventional drilling and completion technologies also damage the near well-bore zone: mechanical stress, fluid, cement, and gun debris. |
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| Hydro-slotted perforation technology:
- Dislodges clay particles and fines - Hydro-slotted cuts through the compacted and low permeable near well-bore zone - Does not burn, scar, or “cook” the formation in carbonates - In sandstones reduces sand mobility problems - In deep gas sands, relieves overpressure damage from mud weight systems |
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Comparisons
Compare the hydro-slotted perforation with gun perforation, shock shooting, jet perforation, abrasive jetting makes no sense; it is the same like compare these methods with a hydraulic fracturing.
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Compare the hydro-slotted perforation can be with other hydro-jet methods only, but unlike hydro-mechanical, hydro-slotted perforation has more advantages:
- Open the casing and the productive layer in a single process (not separating a mechanical process of the casing opening and hydro-slit opening of the productive layer);
- The smooth forward movement of the perforator is performed automatically (without moving the tubing) with a constant set speed and controlled (automatic) with respect to temperature in the well. The incision is geometrically flat neat form. (Impossible to make the cut geometrically smooth sliding tubing);
- The excavated surface area for a single setup engine is 3500 square inches (more 24 square foot);
- Correlation log, tubing pressure test, forward and reverse flushing of well (not through a nozzles), chemical stimulation of the productive layer, mini-hydraulic fracturing run without lifting the equipment.
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Automatic hydraulic slot perforating engine
| Automatic slot-perforation hydraulic engine consists of the Adapter, Hydraulic block, Return block and Perforator. Automatic slot-perforation hydraulic engine makes precise dual bipolar (180º) slots through the casing into the production layer using a high pressure abrasive mixture, excavating a cavern more than 6’ into formation without any additional movement of the tubing. Effectiveness of the method depends on the formation type. The best improvements are observed in naturally fractured reservoirs and in clay-rich formations |
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| Accordingly, the present equipment to provide a slot-perforating system for oil, gas and hydro-geological wells that includes a working unit which generates and directs a working fluid to cut slot shaped passages in a productive formation, which is a further improvement of the existing systems. In keeping with these objects and with others which will become apparent hereinafter, one feature of the present equipment resides, briefly stated, in a slot-perforating system for an abrasive-hydro-slotting of a near well-bore zone for establishing an inflow path between a well-bore and a formation, comprising an adaptor connectable to a tubing; a hydraulic block connected to adaptor for regulating a speed of operation; a perforator providing a hydro-slotting, and a return block located between hydraulic block and said perforator and returning said perforator an initial upper position. In accordance with another feature of the present invention to adaptor can be formed so that during a downward movement said perforator is turn able around a vertical axis to provide a cut at an angle. The adaptor provided with formations engaging in helical grooves to generate a spiral movement of the perforator which produces the angular cut. The perforator have a streamline shape. For this purpose the perforator is formed as a body of rotation around a substantially vertical axis with a substantially elliptical vertical cross-section. The centering elements provided and include one set of springy elements which are spaced from one another in a circumferential direction about a vertical axis and each extending along the slot perforating hydraulic system to abut against an inner surface of a well-bore when the slot perforating system is located in said well-bore. Also, the system include another set of the spring elements which is offset from the first mentioned set, and wherein each of said spring elements has one end is connected to slot-perforating system and another end which is not connected to the latter. Another feature of the present equipment is the hydraulic block includes means for regulating a supply of a hydraulic liquid depending on a temperature in the borehole. The regulating means include a bimetal regulating means which change their orientation in dependence on the temperature in the borehole. The return block include spring elements providing the return of perforator and including a plurality of springs which are arranged one after the other in a vertical direction. The return block can also include a cylinder accommodating springs, connecting rods located inside springs, stop elements provided between springs, and ring elements surrounding each of stop elements and sliding over an inner surface of cylinder, wherein said ring elements are configured as elements having a low friction with the inner surface of cylinder. In the future we expect to put in equipment mechanical meters further control the stroke. |
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Technical characteristics
Diameter OD: 85 mm (3.35"), 90 mm (3.54"), 95 mm (3.74"), 102 mm (4.02")
Engine length: 4.2 m (13.78 ft), 4.5 m (14.76 ft), 4.8 m (15.75 ft), 5.1 m (16.73 ft)
Stroke length: 500 mm (1.64 ft, 19.69"), 1000 mm (3.28 ft, 39.37")
Weight: 114 lbs.(51.7 kg), 120 lbs.(54.4 kg), 135 lbs.(61.2 kg), 158 lbs.(71.7 kg)
Metallurgy: Case and components are made from hardened steel and mixture of alpha and beta titanium. Nozzles made from hard alloy mixture (tungsten carbide + cobalt).
Work conditions: The equipment can work in conditions of high pressures and different temperatures. Tightly on the influence of the environment.
Standard: Equipment of different diameters fits in casing 4" and larger, connect with standard and coiled tubing's via adapter.
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Benefits
Ability to work in diverse environments and conditions
- Different types of wells - oil, gas, hydro (operational and injection wells)
- All types of conditions - depth, pressure, temperature, fluid composition
- Any fracture including sand, clay and etc.
- The only technology that actually excavates rock
Ability to increase area of development
- Very deep penetration from 3 to 6 ft
- Vertical permeability
- Porosity >> 4-5 times
- Permeability >> 15 times
- Drainage volume >> 6 times
Ability to access reserves which are otherwise inaccessible
- In reservoirs located in close proximity to water, gas, and oil contacts
- In weakly permeable, tightly-cemented reservoirs
- In missed layers, or in layers covered by two or more columns
Gentle approach with the ability to repair well-bore damage
- In carbonates, dislodges clay particles and fines
- In sandstones, reduces sand mobility problems
- In deep gas sands, relieves overpressure damage from mud weight systems
- Does not crack casing or cement
- Maintains hydraulic integrity with no detonation impacts
- Redistributes stresses away from the near-well-bore zone
