Abrasive Water Jet
Abstract: with the improvements of industry techniques and the Application of proper material of proper material, abrasive waterjet is widely used in many industry areas. Several case histories will be presented in this paper to illustrated application and performance of abrasive jetting. And the development of abrasive jet drilling is also mainly described.
Keywords: Abrasive waterjet, Abrasive jet drilling, Perforating, Cutting, Fracturing aid
Use of sand-laden fluids for perforating well casing first came into commercial service in 1939. But the jetting was not practical because of the short lift of orifice when abrasive materials were added into the fluid. In 1958, the technique if abrasive jetting was revived and research was resumed to determine its present-day possibilities. It was found that orifice nozzles made of tungsten carbide had a working life of as much as nine hours, compared to only a few minutes for the earlier hardened steel nozzles. With the improvements of industry techniques and the applications of proper material, modern pumping units can provide high flow rates at much higher pressures than in the earlier days and orifice designed can produced less scattering jet stream.
A comparative evaluation of the old and new nozzle designs can be seen in Figs.1 and 2.The new more efficient jet cut a clean hole in the board,whereas the widely dispersed stream from the old jet had little effect.
Abrasive jetting has gained widespread acceptance in the petroleum industry.The abrasive-jetting technique is extremely versatile and lends itself to a wide variety of uses,ranging from perforating casing to enlarging open hole.Its use provides greater formation penetration and increased drainage area;it does not damage cement and casing,nor does it compact the formation.
2.1 Perforating Probably half of the jetting jobs have been for perforating casing.This technique has been used several times in the West Texas area to perforate two thicknesses of pipe and cement,and to penetrate into the formation where regular perforating methods failed.Abrasive jetting has been used to break down hard formations that would have been impossible to treat by regular fracturing or acidizing alone,without exceeding pressure limitations of well equipment.This type of application is illustrated in Table 1.
Location: Kern County,Calif.;North Tejon field.
Formation: Vedder sand;T.O.12,200 ft.
Purpose: Reduce pressure required to break down formation.
Previous Treatment: Producing zone was perforated with B shots/ft;during subsequent attempts to fracture the well,breakdown could not be attained at 10,000 psi.
Procedure: Formation was notched by abrasive jetting at seven different depths,and a fracturing treatment was performed at each depth.
Results: Formation broke down at pressure ranging from 6,000 to 7,400 psi,and production was increased from 80 BOPO at 50 psi to 480 BOPO at 540 psi.
2.2 Open-hole Jetting The next largest application for abrasive jetting has been for open-hole clean-up and well bore enlargement.This process provides an efficient and effective method of completely cleaning the face of the formation,removing residual mud cake,scale build-up or other plugging material,and restoring natural permeability.At the same time,it provides penetration into the formation rock.
2.3 Fracturing Aid The abrasive action of a sand-laden jet stream can produce a plane of weakness in the formation rock.And then a subsequent hydraulic fracturing treatment will extend the fracture pattern from that point.This type of application is illustrated in Table 2.
Location: Kern County,Calif.;North Tejon field
Formation: Vedder sand;T.D.12,808 ft.
Purpose: Provide single point-of-entry for fracturing treatment(partial monolayer technique).
Previous Treatment: New well.
Procedure: Formation was notched at four levels.Each notched zone was fractured separately using 3,500 lb of 8-12 mesh walnut shells in 30,000 gal of gelled brine
Results: Initial production rate of 430 BOPO.Productivity is estimated to be twice that which would have been obtained without the special fracture treatment.
2.4 Cutting Hydraulic jetting with abrasive compounds can be used for making either horizontal or vertical cuts in casing,and for cutting windows for whip stocking.Casing and tubing can be easily cut off by rotating the tool during operation.Abrasive jetting also can be used for other cutting jobs such as removing cement and bridge plugs.This type of application is illustrated in Table 3.
Location: Rio Arriba County,N.M.
Formation: lower Mesa Verde.
Purpose: Remove magnesium bridge plug which had set prematurely at 90-ft below the surface.
Previous Treatment: lower zone hod been treated and operator was try,ing to shut off this zone to fracture upper zone.Shut-in pressure on lower zone was 2,500 psi
Procedure: Special tool with two jets pointing down was run on drill pipe to jet sand laden fluid.Results:Bridge plug was cut out in six minutes of jetting.
2.5 Drilling Abrasive jetting can be used in decreasing drilling time.And we can see from the Table 4.
Formation: Hartshorne sandstone
Purpose:Reduce drilling time.
Previous Treatment: Usually takes 24 to 48 hours to drill rat and mouse holes in this very hard surface formation using conventional tools
Procedure:Jetting tool was used for complete a mouse hole and drill a rat hole.
Results: Conventional tools had made only 27ft on mouse hole in 20 hours;jet tool completed the hole in 34 minutes.A 30-ft rat hole was drilled with the jetting tool in one hour and 52 minutes
3 DEVELOPMENT OF ABRASIVE JET DRILLING
The first underground riling with waterjets was carried out in an operating lead mine in Missouri (Summers&Lehnhof1f,9 77). The rock was a relatively abrasive sandstone,expensive to drill using carbide bits.A simple,70 MPa pressure, waterjet drill was able to penetrate this rock faster than the mine’s pneumatic drills. The waterjets had a secondary advantage since the cutting occurred away from the nozzle. There was little wear on the equipment and the bits lasted longer than those of the mechanical drill.
Two commercial ways arose in part out of the development of that effort. One(Wolgamott,1985) maintained jet pressures of less than 70 MPa and concentrated on drilling relatively soft materials.The other(Anon,1985)led to a waterjet roof bolter. The problem with developing such a mine tool,however,is that it must be able to drill all the rock it encounters.And this includes very hard materials which is difficult for a waterjet to cut conventionally. The developers chose to increase jet pressure in order to effectively drill such rock.But this caused some others problems. As water pressures increase above 350 MPa,the equipment becomes more sensitive to water chemistry and high erosion problems can arise.The resulting equipment was initially more expensive and delicate than is acceptable.
Several solutions have been proposed to overcome this need for high pressure. One has been to combine waterjets with mechanical bits.The disadvantage of this lies in the relatively high thrust levels still required for the mechanical component. Any significant force along the drill string will,over long distances,result in too great a deflection of the hole.The lack of contact across the head of a waterjet drill significantly reduces such deviations,and eliminates the problems of drill accuracy which are controlled by geological changes.
A second alternative which has been suggested is to use cavitating waterjets (Johnston et al 1972). While extremely aggressive, cavitating jets are sensitive to environmental conditions and may be as aggressive to the drilling equipment as to the rock.No serious consideration can be given to this alternative,therefore,at present.
The third alternative is to add abrasive to the waterjets. In normal use,abrasive is added after the jet has reached final velocity,using a mixing chamber.This requires a dual feed of high pressure water and dry abrasive to the drill bit.With the drill rotating,this requires two concentric swivels-one of which must operate at 250 MPa. While not insurmountable,the solution is expensive.
A British alternative has, however, recently emerged (Fairhurst et al,1986). A method has been found to inject sand into the feed line between the high pressure pump and the nozzle.This not only overcomes the problem of the dual feed,but significantly lowers the required pressure for effective cutting. For example,such a jet,operating at a pressure of 10 MPa, can cut through a 13 mm thick steel plate.This approach appeared to have significant potential for drilling hard rock.
Abrasive jet get great improvements with the accumulation of a large amount of continuing research and experiments. And the technique need more optimization to apply with the more serious condition. Abrasive water jet have a promising prospect and will be widely used in more industry areas because of its special advantages,such as no thermal effects,more powerful,and economically.