CA2527265A1 - A mud depression tool and process for drilling - Google Patents

Description

A MUD DEPRESSION TOOL AND PROCESS FOR DRILLING

A Canadian patent application meeting the minimum filing requirements under Patent Rule Section 93.

In an embodiment of the invention, a tool is provided which is located above the drill bit to isolate the bottom hole from the rest of the well to decrease the pressure of the mud around the bit. The tool consists two pieces forming a cylindrical body making the piston skirt system. These two pieces move axially relative to each other to activate an expandable centralizer located radial around them. This expandable centralizer when expanded closes the annulus between this tool and the walls of the well. A jet pump inserted in the body of the tool powered by the mud from surface, connected through its venturi with the annulus below the expandable centralizer, creates a low pressure area in the bottom of the well by sucking the mud leaving the bit and discharges it to the annulus above the expandable centralizer. An interior passage directs the mud from the annulus above the expandable centralizer to the bit, then through the nozzles for hole cleaning. A
locking mechanism on the piston skirt system engaged while drilling in depression effect keeps the jet pump in operation.

The expandable centralizer of this embodiment is made up of two groups of trapezoid bars inserted to each other, with the bases of the trapezoid of each group pointed in opposite directions forming a cylinder. Each bar is united by its lateral surfaces through sliding unions to the neighbouring bars of the other group and each group of bars is fixed to one of the pieces of the piston skirt system. When the piston skirt pieces move axially relative to each other, they slide both groups of bars relative to each other as well. This varies the outside diameter of the cylinder formed by these bars.

BACKGROUND
This invention for the interaction that takes place during well drilling between the drilling bit, the rocks of the underground strata, and the drilling fluid.
This is more advanced than the technology in Cuba Patent CU 22503 (20/95) where the importance of decreasing the pressure of the well bore fluid in the bottom hole for attaining high rates of penetration is outlined, as well as the different technical methods and devices used. These techniques cannot create high depressions because they use a large area, which tends to be inefficient. The mud depression tool illustrated in Cuban patent CU 22543 (24/96) includes the use of a metallic cylindrical packer formed by two groups of equal trapezoid wedges, located with the widest ends of the wedges of each group in opposite directions to each other.
The parts of the piston skirt system are fixed only while drilling and negate the extra load that is produced on the upper surface of the packer due to the difference of pressure created between the upper and lower surfaces of this packer. The patent CU

(24/96) succeeds in fixing solutions to problems confronted to the depression tools of the previous patent CU 22503 (20/95), however these solutions are still faulty and there are other deficiencies that are common to the patent CU 22503 (20/95).

2 Tools should not be over a certain external diameter to avoid the piston effect while tripping in or out of the well. The piston effect creates high depressions in the well while pulling the drill string out and can cause loss of well control, also well bore damage can be incurred as the formation pressure can push the sides of the well bore in. Sticking of the drill string due to accumulation of debris above a tool is a hazard, also this debris causes piston effect. If a tool has too large of a diameter while tripping in the well, the piston effect can cause the formation to be pressurized and be damaged.

Patent CU 22543 (24/96) and patent CU 22503 (20/95) uses bearings to mount both groups of trapezoid wedges of the packer to the piston skirt system.
The rubber element used to isolate the upper bearing is subjected to high friction, high rotation speed, and high pressure differential in a highly erosive environment.
This limits the useful life of this insulating element. When mud with solid particles and high pressure comes through the bearing, it shortens bearing life. As a result, the packer will not close which would force the tool to be pulled with an enlarged packer, creating a piston effect. Also, when the upper bearing jams, the upper part of the packer rotates with the tool with close contact between the packer and the well bore producing high friction causing high torque on the lateral sliding bars on the trapezoid wedges. Operation is not possible under these conditions.

Another deficiency of the patent CU 22543 (24/96) with the bearings and the pieces that mount the trapezoid wedges to the piston skirt system is the large cross sectional area used which takes away from the structural integrity of the surrounding parts making up the assembly.

3 In patent CU 22543 (24/96) the sliding unions between the group of upper trapezoid wedges and the upper piece of the tool use additional cross sectional area. This causes the diameter of the tool to be larger or the other parts of the tool to have their structural integrity compromised.

Another deficiency of the patent CU 22543 (24/96) is the hydraulic lock between the two pieces of the piston skirt system uses a large cross sectional area which is detrimental to the other pieces of the mud depression tool. Also, it does not have a reserve system to disable it in event it cannot be released by the way it was designed. In this case, it would not allow the packer to be closed.

Another deficiency of the patent CU 22543 (24/96) is the lock to keep the packer closed is weak and it uses considerable cross sectional area that is detrimental to the other components of the tool.

Another deficiency of the patent CU 22543 (24/96) and patent CU
22503 (20/95) is the pins for transmitting torque to the bit through the piston skirt system are not structurally sound and use considerable cross sectional area.
These pins also transmit the axial force to the bit, so any deformation of these pins would affect this function as well.

The deficiencies of the patents CU 22503 (20/95) and CU 22543 (24/96) mentioned above determine the main components of the tool must be stacked axially to provide enough cross sectional area. In these patents, the jet pump is located higher than the packer, thus taking away from the objective of having the depression effect as near as possible to the bottom hole. The higher the packer, the larger the distance between the jet pump and the drilling bit located in

4 the bottom of the well where the rock cuttings are taken to the annulus located above the packer by this jet pump. This situation shortens packer height limiting the effectiveness of the tool or distances the jet pump from the bit creating a higher chance of mud passage obstruction.

Another deficiency of patents CU 22503 and CU 22543 (20/95 and 24/96) is the axial displacement of the piston skirt system to open and close the packer is small. This is detrimental to the packer and deployment from the rig floor is difficult.

Another deficiency of the patent CU 22543 (24/96) with the small displacement to open or close the packer is a central relieve valve is required. This affects the mud circulation circuit that feeds the jet pump and it also has a relieve passage of bigger diameter using considerable cross sectional area, which again compromises associated parts.

Presently, while drilling, it is common to install a stabilizer directly above the drilling bit. This stabilizer is formed of a cylinder with a group of blades mounted to the surface of the cylinder that extend nearly to well bore diameter. The slot between the blades allows mud to pass to surface and eliminates piston effect.
The stabilizer must be structurally sound to withstand the high lateral loads of the bit allowing the bit to drill close to a perfect cylinder. This is important for running casing in the well as casing has a larger diameter and is more rigid than drill string.
Another deficiency of the patent CU 22543 (24/96) is when the packer is subjected to the variable lateral loads mentioned above, they are transferred to its

5 sliding unions. These loads can cause the unions to loose operation, thus not allowing the packer to close.

Another deficiency of the patent CU 22543 (24/96) is there is no means to keep the trapezoid wedges parallel to the axis of the tool. With this, the wedges will not act as a group, thus making the packer inoperable.

Another mud depression tool is shown in the Canadian Patent Application CA 2315969 dated August 15, 2000 titled: Under Balanced Drilling Tool and Method. This tool described in the application CA 2315969 uses a common jet pump to create the depression effect in the bottom hole and uses different packers sold by different manufacturers made of rubber or other elastic materials to isolate the annulus. These rubber packers are shaped as a cone or as a cylinder and are mounted on a metal base with bearings. This mud depression tool also proposes the use of a flow control valve above the drilling bit to regulate the quantity of fluid that is passed through the bit. In CA 2315969, to maintain the low pressure created by the jet pump below the packer when fluid is not circulating, it proposes to place a metal ball within the diffusion cone of the jet pump. This ball is a check valve to stop flow from above the packer. It is also proposed to mount a seal of elastic material around the nozzle of the jet pump closing the nozzle with a ball type valve.
In other embodiments of the tool it is proposed the use of packers with outside diameters larger than the diameter of the well with the same valves mentioned above.

Patent application CA 2315969 does not solve any of the difficulties that plague the current mud depression tools that use a device to hydraulically isolate the bit from the rest of the well and a jet pump to lower the pressure in the

6 annulus that surrounds the bit. Application CA 2315969 adds new problems that current mud depression tools do not have.

Packers currently used have little lateral displacement, so the well bore must have good structural integrity. The majority of these packers are not designed to seal and be moved along the well bore at the same time. Those that are capable of doing this can not do it under high pressures for a lingering time or considerable distances. Application CA 2315969 recommends the use of this type packers and refer to a specific model, the Guiberson AVA. At the same time, they recommend this packer should use small amounts of rotation, pressure, and axial displacement.

These actions are contrary to the main purpose of increasing rate of penetration.
Another deficiency of application CA 2315969 is while tripping in or pulling out of the well, this tool has a diameter close to the well bore. A
piston effect is created with this packer that does not permit the flow of mud around the outside and there is not good hydraulic communication on the inside.

Another deficiency of application CA 2315969 common to the proposal of I. P. Skvortsov and other authors in their work "Elevation of the Indexes of Work of Drilling Bits" on page 27 of the "Annual Summary of Scientific Works of the Oil Institute of Ufa City" dated 1990 titled "Oil and Gas Drilling Technology" is application CA 2315969 does not have a way to stop the depression effect when fluid is being circulated, but drilling is not taking place as in reaming or circulating off bottom. It is not advantageous to have a depression effect at these times.

Another mud depression tool in US Patent 4630691 dated December 23, 1986 titled: "Annulus bypass peripheral nozzle jet pump pressure differential

7 drilling tool and method for well drilling." This tool uses a plug centralizer mounted on bearings for isolating the bit from the rest of the well consisting of an elastic material that expands under hydrodynamic pressure created in the drill string while circulating. The amount of expansion is limited by metal elements keeping its maximum diameter close to the well bore. The depression effect is created using an annular jet pump.

The first defect of this tool described in the US Patent 4630691 is that a rubber plug centralizer mounted on bearings, as disclosed previously, is not resistant for ongoing drilling and it takes considerable cross sectional area.
Elastic material used as the main body of the packer is limited since the pressure down hole commonly reaches hundreds of atmospheres. For example, take a well of average depth of 3000 m where the mud has a specific weight of 1,2 g/cm3. In this well, the hydrostatic pressure will reach a value of 360 atmospheres. The rubber element suffers deformation, even before the pressure differential produced by the jet pump is considered. This is not an effective means to control the pressure down hole.

Another deficiency of US Patent 4630691 is the use of hydrodynamic pressure for expanding the plug centralizer creates a depression effect when circulating or reaming off bottom which stimulates the entrance of formation fluids, as discussed previously. This scenario worsens if the drill bit is moved up at same time there is circulation, which is common practice.

Another deficiency of US Patent 4630691 is the annular nozzle used in the jet pump requires its annular slot to be narrow. This allows the total area of the slot to be small enough so the mud can reach the necessary velocity to create the

8 required depression. This narrow slot is susceptible to easy blockage by the solids from the bit. This is a problem pointed out previously with some of the other patents.
Patent CU 22503 proposes the use of a venturi of oval cross section.

The jet stream from the nozzle divides the venturi into two equal parts. This offers some improvement for rock cutting transfer, but this double space reduces the high depression ability of this pump.

Patent CU 22543 (24/96) proposes the use of a jet pump with a venturi of variable dimensions to increases its internal diameter if a piece of rock becomes an obstruction. Operation of this jet pump is unpredictable since the low pressure created in the venturi causes the walls to collapse, thus making the rock cutting probiem worse. This variable venturi also uses considerable cross sectional area.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of this invention achieve high values of depression on the bottom hole while drilling while using low energy expenses to increase the productive parameters of the drilling bit. This tool has all the positive characteristics of former designs and offers a better solution to their shortcomings and also offers solutions to other problems that are not covered by other tools of its type.

An embodiment of this tool uses an all metal expandable centralizer for isolating the bottom from the rest of the well, so during all operations except drilling (i.e. tripping, reaming, circulating, etc), it has the configuration of a stabilizer with a small diameter. When at bottom hole, with drilling ready to start, this centralizer can

9 be opened where it takes the configuration of a complete cylinder that closes the annulus outside the mud depression tool. This double function of acting as a centralizer and a packer is better than doing each task separately. This centralizer does not use bearings to attach the pieces of the centralizer to the pieces of the piston skirt system. This centralizer uses a push pull mechanism to act on the upper group of trapezoid bars while using minimal cross sectional area. This expandable centralizer has more height than the common stabilizers used while having an equivalent structural integrity. This guarantees better centralization of the bit. Lateral loads on this centralizer while drilling are taken directly by the fixed lower part of the centralizer and also by the direct contact of both groups of trapezoid bars on the piston. The centralizer acting as a packer is higher than packers on other tools of this type and leaves a small gap of .5 to 1 mm to the well bore commonly used in the field when opened.

A form of jet pump used in this tool to lower the pressure of the drilling fluid in the bottom hole is located at the same level as the piston skirt system and the expandable centralizer. This eliminates the restrictions on the dimensions of each one of the components, which allows a better general efficiency of the tool.
The venturi exhausts to an area of clearance immediately above the packer, which permits better cleaning and avoids the possibility of obstruction of debris from the bottom hole, thus giving dependability to this tool.

Another positive characteristic of this tool is it requires quite a large axial displacement to open and close the centralizer. This eliminates problems in deploying and operating the tool, as it is easier to detect what is happening down hole from the rig floor. This axial movement can be used for a jar effect if the bit becomes stuck due to a drilling problem or a foreign object falls from above.
The centralizer bars are also capable of transmitting high torque values in the open or closed position, if it was desired to put torque to free the bit.

Another positive characteristic of this mud depression tool is the plug used for closing the port to direct the mud flow to the jet pump is of considerable length, so it will not have any erosion problems while using minimal cross sectional area.

Another positive characteristic of this tool is it uses a hydraulic lock to hold the piston and the piston skirt in the drilling position while pumping.
This guarantees the drilling configuration will not be lost when the bit is raised off bottom.

Another positive characteristic of this tool is it frees the function of torque transmission to the bit from the function of axial movement in the well bore unlike the other depression tools. Torque is transmitted through the trapezoid bars which provide a very robust means as they are further out in diameter and long, so there is a larger area for the torque transmission. The tool will take a large axial load compared to other components in the drill string, as the trapezoid bars are very robust and have a good mounting system.

Another positive characteristic of this tool is a means to keep the centralizer in the closed position until a certain axial force is encountered.
This will keep the centralized closed, not allowing it to open until the desired position is reached.

Another positive characteristic of this tool is the jet pump uses venturi and passages similar to the conventional configuration of jet pumps commonly used, but the axis of the nozzle is offset from the axis of the venturi. This increases the available area of the secondary circuit to allow rock cuttings twice as large as conventional jet pumps with little loss in efficiency.

Another positive characteristic of this tool is the upper trapezoid bars are always attached to the piston by a longitudinal bar that keeps their movement parallel to the axis of the tool. This constant engagement between this group of upper trapezoid bars and the piston negates any force that deflects the trapezoid bars permitting dependable opening and closing of the expandable centralizer.

Some novel and inventive characteristics of this tool include aspects of the expandable centralizer, handling of fluid dynamics in the tool, and mechanical robust construction.

An embodiment of the tool has a centralizer formed of a fixed part similar to common stabilizers used in drilling, with the expandable part that opens nearly to well bore diameter forming a full perimeter centralizer well while keeping the structural integrity common to normal stabilizers. This expandable centralizer acts as a packer which isolates the bottom area of the hole from the rest of the well bore. The length and full perimeter of the expandable centralizer has a hydraulic resistance, so the high pressure fluid above the expandable centralizer cannot migrate to the low pressure area below the packer.

Another novel characteristic of this tool is the expandable centralizer does not mount using bearings, but is mounted directly to the pieces of the piston skirt system, so it turns with them while drilling.

Another novel characteristic of this tool is the main components including the piston skirt system, the jet pump, and the expandable centralizer are at the same elevation, thus making the operating fluid dynamics and the manufacturing of the tool very efficient.

Another novel characteristic of this tool is the action of the piston on the upper trapezoid bars of the expandable centralizer when it moves axially into or away from the piston skirt is carried out by contact between different parts.
The piston pushes / pulls the group of upper trapezoid bars and the skirt makes the same action on the group of lower trapezoid bars. This changes the expandable centralizer from opened to closed position.

Another novel characteristic is the hydraulic lock between the piston and the piston skirt is equivalent to a thread of the same strength. It automatically disengages when the mud pumps stop. This hydraulic lock has an emergency forced deactivation if it does not automatically disengage.

Another novel characteristic of this tool is torque is transmitted through the tool using the different parts and pieces, simple and robust.

Another novel characteristic of this tool when the tool is closed it can transmit high torque values to the bit due to the special union of the trapezoid bars.
Another novel characteristic of this tool is it has comparable tension strength to the rest of the drill string when the centralizer is closed.

Another novel characteristic of this tool is it has a mechanical lock that keeps the centralizer closed until a certain axial force is encountered, so the centralizer does not open until drilling is ready to start.

Another novel characteristic of this tool is it has a permanent longitudinal union between the piston and each bar in the group of upper trapezoid bars that form the expandable centralizer. This longitudinal union absorbs any force on the bars that could cause them not to move in parallel direction to the axis of the tool during opening and closing of the expandable centralizer. This avoids the sticking of the sliding unions and permits sure operation of the expandable centralizer.

Another novel characteristic of this tool is that the nozzle axis of the jet pump is offset from the venturi axis of the jet pump allowing bigger rock cuttings to be transferred.

Embodiments of the invention are depicted in the drawings. The drawings which are intended to illustrate embodiments of the invention and which are not intended to limit the scope of the invention.

In Fig.1 are illustrated the two configurations of the tool during its use in the well: Fig.1-B shows its configuration while drilling and the Fig.1-A, rotated 900 related to the previous one, shows its configuration for other operations. To give a realistic image in Fig.1, the bit, mounted in the lower end of the tool and the drilling string, mounted on its upper end, as well as the bottom of the well bore are shown.

In Fig.2 the tool is shown in the configuration of Fig.1-B in lateral view cut to the axis by the left part and partial sectioned in the right part as well as auxiliary views A-A, B-B, C-C and D-D.

In Fig.3 the tool is shown in the configuration of Fig.1-A in lateral view cut to the axis by the left part as well as auxiliary views E-E, F-F, G-G and H-H.

Fig.4 is illustrates the hydraulic porting to the annulus during circulation of mud from the surface when it is off bottom: the Fig.4-A shows the tool full sectioned by a plane coincident with its central axis and with the central plane of the circulation circuit for feeding the jet pump and Fig. 4-B shows the tool cut by the same plane as the previous, but rotated 901 relative to it and is coincident with the central plane of the bit cleaning circuit. The arrows in the figure point out the fluid movement through the different passages of the tool. In this figure, the bit and the lower well bore are shown.

Fig.5 illustrates the hydraulic circuits of circulation while drilling: Fig.5-A
shows the tool full sectioned by a plane coincident with its central axis and the central plane of the circulation circuit for feeding the jet pump. Fig.5-B
shows the tool sectioned 90 from the previous, and coincident with the central plane of the bit cleaning circuit. The arrows in the figure point out the movement direction of the fluid through passages areas of the tool. This figure shows the bit and the lower well bore.

The tool, as illustrated in Fig.2 and 3, is formed by a steel body of cylindrical configuration with two main pieces: the piston 1 that attaches to the rest of the drilling string through the threaded connection 3, and the piston skirt 2 that attaches to the bit through the threaded connection 4.

The piston 1 is formed on the exterior by an upper neck 5, an upper conical surface 6 that finishes at the cylindrical surface 7 of larger diameter, another lower conical surface 8, and it finishes in a cylinder 9 of smaller diameter, where at its lower end fits inside the piston skirt 2. The piston 1 has on the lower part of the external surface of the upper neck 5 two filters 10 at 180 to each other and below on the cylinder 9 has a group of longitudinal bars 11 equally spaced located around the perimeter on its external surface. Longitudinal bar 12 is part of this group of longitudinal bars 11, but is shortened to allow for the entrance to the suction side of the jet pump. The radius of the ends of these longitudinal bars 11 is smaller than the radius of the cylindrical surface 7. Located on the external surface of the cylinder 9 of piston 1, there is another group of longitudinal bars of the piston 14 (see Fig. 3).
Longitudinal bars 14 are located between the group of bars 11, are shorter, and are equal in number. Near the lower end of piston 1 is the groove 15 of the hydraulic lock 16 and the piston stop groove 17 of piston 1 formed as two ring cuts. The sides of piston stop groove 17 are conical and have the same cone angle. The piston I
has inside from the threaded connection 3, a passage arranged so its plane of symmetry is coincident with the central axis of the piston 1 and includes:
cavity 18, a passage 19, a passage 20 of whose central axis turns close to 180 until the cylindrical passage 21 continues to a conical cavity that houses the nozzle base 22.
There is the suction area 23 and inside it is the nozzle 24 and the nozzle nut 25.
The nozzle base 22 extends to the interior of the suction area 23 with a threaded end on which the nozzle nut 25 is threaded, so that both are attached to the piston 1 and they hold the nozzle 24. The suction area 23 opens up to the external space of the piston 1 through the piston notch 13. Piston 1 has inserted in its body the jet pump 26 with its areas: the suction area 27, the mixing area 28 and the expansion area 29 that is channeled to the upper conical surface 6 of piston 1. The piston 1 has another group of passages whose plane of symmetry is coincident with the central axis of the piston 1, but rotated 90 to the plane of the jet pump circuit.
These second passages are mirrored on each side of the tool, beginning at the filters 10 (see Fig.3), onto the interior cavities 30, continue as passages 31 and the cylindrical passages 32 that open to the lower end of piston 1. Located in the lower end of piston 1 is the central cylindrical passage 33 concentric with piston 1 that intercepts the bottom of the passage 20. A group of galleries 34 equally spaced so that they port to the hydraulic lock groove 15. On the cylindrical surface 7 of piston 1, leading to the conical surface 8 are located cavities 35 that are equally spaced on the surface 7.

Piston skirt 2 forms neck 36 containing the threaded connection 4, continues with a conical external surface 37 that finishes in a external surface 38 of smaller diameter. On the conical external surface 37 is a group of centralizing blades 39 equally spaced, each one perpendicular to the conical external surface 37. These centralizing blades 39 have an upper portion aligned longitudinally with piston skirt 2 and a lower portion that forms an angle close to 45 related to the central axis of piston skirt 2. On the exterior faces, the centralizing blades 39 have a central area that reach their largest diameter forming cylindrical surfaces whose symmetry axis coincides with the central axis of symmetry of piston skirt 2.
For above and below these central cylindrical external surfaces forms conical surfaces that are tapered to the conical external surface 37. On the external conical upper part of centralizing blades 39 forms a triangular profile with different inclined planes, which has on both sides lengthened grooves 40 leading to the central external cylindrical surfaces of the centralizing blades 39. On this central external cylindrical surface, at the end of the lengthened grooves 40, are the lower trapezoid stops 41 that have rectangular form with all their faces flat except the external face whose form is cylindrical and has the same diameter as the central external cylindrical surfaces of centralizing blades 39. These lower trapezoid stops 41 are attached to centralizing blades 39 with screws 42 and are mounted so the upper and lower planes are perpendicular to the central axis of the tool. The central external cylindrical surfaces of the centralizing blades 39 have wear protection. On the upper end of the external cylindrical surface 38 of piston skirt 2 stands out the latches 44 distributed regularly on this surface. These latches 44 have an angled end 45 that stand out through the upper end of the cylindrical surface 38. The interior part of piston skirt 2 has a bore concentric with the axis formed by the threaded connection 4, located in the lower neck 36 of piston skirt 2. The threaded base 46 leads to bore 47 that extends to the upper end and has the same diameter as the cylinder 9 of piston 1 with which forms the piston and piston skirt system of the tool. On the surface 47, near its lower end, it is a set of grooves 48 (see fig 3 G-G) each of them with the same profile, that form an upper face perpendicular to the axis of piston skirt 2, a cylindrical surface for major diameter and a conical lower face forming a bevel that finishes on surface 47. The surface of the upper end of piston skirt 2 where the exterior surface 38 and interior surface 47 is beveled and its bevel angle is equal to the cone angle of the upper and lower conical surfaces of the piston stop groove 17.
The piston skirt 2 has a port 49 from its external surface below one of the centralizing blades 39 to the set of grooves 48 on the interior surface 47 of piston skirt 2 (see Fig.3 G-G).

In the piston stop groove 17 is the piston stop ring 50 that is sectioned and has two free ends with a determined space between them. The interior and exterior surfaces of the piston stop ring 50 are cylindrical and its upper and lower surfaces are conical with the same cone angle as the piston stop groove 17.
Height of the traverse section of piston stop ring 50 is equal to the height of its groove 17 and its width is less than the width of groove 17. Located freely within its groove 17 (see Fig. 3 F-F) piston stop ring 50 stands out from the cylindrical external surface 9 of piston 1 to a distance equal to the thickness of the piston skirt 2 on its upper end.

The corner of the lower surface of the piston stop ring 50 stands out from the external surface 9 of piston I and has a conical form with the same angle as the upper conical surface of piston skirt 2 in such way they contact evenly (see Fig. 3 F-F).

In the threaded base 46 of piston skirt 2 concentric with piston skirt 2, the round plug 51 with the same diameter as the central cylindrical passage 33 of piston 1. This plug 51 has two passages 52 leading to the base of the plug 51 and has the same diameter and angle of inclination as the cylindrical passages 32 of piston 1. The upper surface of plug 51 matches the bottom of the passage 20 of piston 1.

The hydraulic lock 16, a steel band sectioned axially so it can expand, is located inside its groove 15. Its external diameter is slightly smaller than the external diameter of the cylinder 9 and its interior diameter bigger than diameter of the hydraulic lock groove 15. The hydraulic lock 16 has the same quantity of angled rings with the same profile that match the set of grooves 48 in the piston skirt 2. On the inside of hydraulic lock 16 is the sleeve of the hydraulic lock 53 formed by a steel sleeve of the same height as hydraulic lock 16. This hydraulic lock sleeve 53 and is also cut axially, so that its free ends are 180 relative to the ends of the hydraulic lock 16.

Surrounding piston 1 and piston skirt 2 are two groups of metal trapezoid bars 54 and 55 inserted to each other so that form together a tubular body whose central axis coincides with the central axis of the tool. A group of lower trapezoid bars 54 have their bases or wider side of the trapeze directed down and the other group of upper trapezoid bars 55 have their bases or wider side of the trapeze directed up. Each one of the bars of both groups is dovetailed on both sides to the neighbouring bars of the other group to allow axial displacement between them but that maintain their connection to each other. The dovetails on each one of the contact planes with the neighbouring bars of the group of upper trapezoid bars 55 and the slots 57 on the upper trapezoid bars 55 have the same form. These slots 57 lead to the lower end of the upper trapezoid bars 55 and they have an upper cylindrical tip located at a certain distance from the upper end of the upper trapezoid bars 55. Correspondingly, the lengthened bands 56 extend from the lower end of each lower trapezoid bar 54 the same distance from its upper end that maintain the slots 57 of the upper trapezoid bars 55 relative to their upper end. The external surfaces of the trapezoid bars 54 and 55 are cylindrical and have the same radius as exterior cylindrical surfaces of the centralizing blades 39 and their upper surfaces coincide with a plane located perpendicular to the central axis of the tool.
The external surfaces of the trapezoid bars 54 and 55 have wear protection to combat the erosion from the walls of the well. The interior cylindrical surfaces of lower and upper trapezoid bars 54 and 55 are cylindrical and have the same diameter as the cylindrical surface 7 of piston 1. The bases of lower trapezoid bars 54 have an opening 58 (see Fig.3 H-H) that fits the triangular profile of conical upper surfaces of the centralizing blades 39 to form dovetail unions. The lower side of lengthened bands 59 form a plane perpendicular to the central axis of the tool. On the interior cylindrical surface of each one of the lower trapezoid bars 54 are two stop grooves:

upper 60 and lower 61. The upper groove 60 fits the form of the longitudinal bars 14 of piston 1. The lower groove 61 fits the form of the latches 44 of piston skirt 2. On the cylindrical interior surface of each one of upper trapezoid bars 55 stand out, at a certain distance from its wider upper end, a latch 62 (see Fig.2) located on center.
Under the latch 62 is a cavity 63 that fits the longitudinal bars 11 of piston 1 and whose central plane of symmetry coincides with the central plane of symmetry of the upper trapezoid bar 55. On both sides of the cavity 63 are edges 64 parallel to each other that extend along cavity 63. Both groups of lower trapezoid bars 54 and upper 55 have the same quantity of bars which is the same as the quantity of longitudinal bars 11 on the piston 1 and the centralizing blades 39 on piston skirt 2.

IN OPERATION

The operation of the tool for the two configurations are illustrated in Fig.1:

When tripping in or pulling out of the well, i.e. when the bit is not on bottom, the tool has the configuration of Fig.1-A. In Fig.3, piston 1 is almost outside of piston skirt 2 and the latches 44 of the piston skirt 2 contact the lower stop grooves 61 of lower trapezoid 54 prevent further separation. The longitudinal bars 14 of the piston 1 in the upper stop grooves 60 of the lower trapezoid bars 54 and they contact their upper surfaces limiting the travel of piston 1 to the extreme position illustrated in Fig.3. The two groups of trapezoid bars 54 and 55 are axially displaced relative to each other and are closer to the central axis of the tool, so they have a smaller external diameter similar to the rest of the bottom hole assembly.
The lateral profile 56 of lower trapezoid bars 54 are partially outside of slots 57 of upper trapezoid bars 55. The upper trapezoid bars 55 are below the conical surface 8 of piston 1 and their interior surfaces contact the cylindrical surface 9 of piston 1.
Longitudinal bars 11 of piston 1 (see Fig.4-A) are inside the central cavities 63 of upper trapezoid bars 55 and their lower planes contact the upper surfaces of longitudinal bars 13 of piston 1. The angled lengthened borders 64 contact both sides on the longitudinal bars 11 of piston 1.

The angled notches 59 of the bases of lower trapezoid bars 54 are up and in the notches 40 of centralizing blades 39 of piston skirt 2. The hydraulic lock 16 with the hydraulic lock sleeve 53 is inside the groove 15 of piston 1. The plug 51 attached to the threaded base 46 of piston skirt 2 is axially displaced down from the central cavity 33 of piston 1.

The piston stop ring 50 (see Fig. 3 F-F) is partially in groove 17 and protrudes outside of the external surface of the piston 1. The upper border of the piston skirt 2 contacts the angled border of the piston stop ring 50.

The tool maintains this configuration due to the forces that act on the piston skirt 2. These forces are: the weight of the drilling bit, the piston skirt 2 and the lower trapezoid bars 54. Also, the resistant force produced when the upper bevel surface of piston skirt 2 contacts the lower bevel surface of the piston stop ring 50. The resistant force is regulated by controlling the angle of the bevel surfaces or the thickness of the piston stop ring 50. When circulating, another force is created by the pressure differential between the inside of piston skirt 2 and the annulus around the piston skirt 2.

When tripping in and pulling out, the tool can be subjected to torsion and tension loads that are generally quite low. The torsion loads can occur when reaming the well bore and are received by piston 1 from the surface through the drilling string. In the configuration shown in Fig. 3, the tool transmits the torque to the drilling bit in the following way: the piston 1 transmits the rotational moment to upper trapezoid bars 55 through its longitudinal bars 11 that are united along the lengthened angled borders 64 of upper bars 55. These transmit it to lower trapezoid bars 54 that transmit it to piston skirt 2 through centralizing blades 39 of piston skirt 2 which transmits to the bit.

Tension loads to the bit through the tool is limited by the same means that limits the exit of piston skirt 2 from piston 1 previously described or from the drilling string the force is transmitted to the piston 1, from there to the longitudinal bars 14 of piston 1, from there to the lower trapezoid bars 54, from this last to the angled latches 44 of the upper end of piston skirt 2, then to the bit A common operation during tripping in and pulling out of the well is circulation through the drill string. Fig.4 illustrates fluid circulation inside the tool to the annulus with arrows. In Fig.4-A, the fluid flows to the threaded connection 3, then it passes to conical cavity 18, goes on into the passage 19 and to the setback cavity 20 where the circulation splits, part goes to the central cylindrical passage 33 and the other towards the cylindrical passage 21 that crosses the interior cavity of the base of nozzle 22, the nozzle 24, the suction area 23 and the different areas of jet pump 26 going to the annulus through the expansion area 29. The other part of the fluid that passed into the central cylindrical passage 33 also splits, part goes to the inside of piston skirt 2 from where it passes through the circular holes 52 of the plug 51 to the inside part of the bit and from there it leaves to the annulus through the bit nozzles and the other part comes out directly to the annulus through the bypass hole 49 (see Fig.4-B) of piston skirt 2. Lastly, part of the fluid that entered to the central cylindrical passage 33 passes through the passages 32 to passages (see Fig.4-B), from there it goes to interior cavities 30 of piston 1 and there it leaves to the annulus through the filters 10. This exit of fresh fluid through the filters 10 cleans them of any debris that may have obstructed the holes of the filters.

When tripping into the well the same process of circulation of fluid described previously takes place, but in reverse from the annulus to inside the string.
This high hydraulic communication diminishes the piston effect of the drilling string during movement and saves having to fill the drill string The tool goes to configuration in the Fig.1-B when it is on bottom in the following way:

When the bit is on bottom, part of it is subjected to the weight of the string through piston 1. The upper conical surface of piston skirt 2 contacts the beveled lower surface of the piston stop ring 50 and this ring pushes its upper beveled surface on the upper beveled surface of its groove 17 (see Fig.3 F-F).
This force causes the piston stop ring 50 to compress radial to the interior of its groove 17 until the piston 1 advances into the interior throat of the piston skirt 2.

When advancing piston 1 towards the inside part of piston skirt 2, its conical surface 8 contacts the upper plane surfaces of upper trapezoid bars 55 (see Fig.3) forcing these bars to move towards trapezoid bars 54 slipping on the sliding lateral unions that unite the neighbouring bars of both groups. With the advance of piston 1 inside the piston skirt 2 and the simultaneous advance of upper trapezoid bars 55 among lower trapezoid bars 54, both groups of bars move away from the centre of the tool to enlarge its external diameter. This movement continues until the inside surfaces of the group of upper trapezoid bars 60 is larger than conical surface 8 of piston 1. When this happens, the upper trapezoid bars 55 are completely within the group of lower trapezoid bars 54, upper surfaces of both groups of bars are on a plane perpendicular to the central axis of the tool, the lateral profile 56 of lower trapezoid bars 54 are fully contacted into the slots 57 of upper trapezoid bars 55 until they touch. The external diameter of the two groups of trapezoid bars is equal to the diameter of the centralizing blades 39 of piston skirt 2 with their external surfaces closing the annulus at this point. The cylindrical interior surfaces of upper trapezoid bars 55 and lower trapezoid bars 54 are concentric with the central axis of the tool and have a diameter of cylindrical surface 7. The longitudinal bars 11 of piston 1 are inside of the central cavities 63 of upper trapezoid bars 55 limited on both sides by the angled bars 64 of the upper trapezoid bars 55.

The lengthened bands 59 of the bases of lower trapezoid bars 54 have moved out and down relative to the lengthened grooves 40 of centralizing blades 39 until contacting the upper surfaces of lower trapezoid stop 41. When moving away from the centre of the tool the two groups of trapezoid bars 54 and 55 have formed a cavity 66 between their interior surfaces and the external surface 38 of piston skirt 2.
Piston 1 continues its advance inside of piston skirt 2, the cylindrical surface 7 of piston 1 begins to advance into the cylindrical surface of the upper and lower trapezoid bars 55 and 54. The plug 54 enters the central cylindrical passage 33 of piston 1.

This process continues until the lower end of piston I contacts the bottom of piston skirt 2. As this happens, the cylindrical surface 7 of piston 1 is completely inside of the cylindrical surface made by the interior surfaces of upper and lower trapezoid bars 55 and 54, and the plug 51 is completely inside the central cylindrical passage 33 of piston 1 and its upper surface is a certain distance "D" (see Fig.2 D-D) above the bottom of cavity 20 of piston 1. This distance "D" is the axial displacement of the plug 51 from passage 52 and passages 32 of piston 1, and the axial displacement from the set of grooves 48 of piston skirt 2 to the hydraulic lock groove 15.

Longitudinal bars 11 and 14 of piston 1 are close to the upper end of piston skirt 2 and each one of the longitudinal bars 14 contacts one of the angled ends 45 of the piston skirt 2. The latches 62 of upper trapezoid bars 55 will be inside and close to the bottom of one of the cavities 35 on the piston 1 on its cylindrical surface 7 (see Fig. 2 and 5 A).

The configuration of the tool at this moment is similar to the one in Fig.2 and 5, except the axial displacement of "D" pointed out above.

Next, the surface pumps are started and the drill string is rotated while holding it axially. The circuits of circulation when drilling starts (consider the small distance "D" pointed out previously) are illustrated in Fig.5. A circuit for feeding the jet pump in Fig.5-A begins with the mud from the drilling string to the threaded connection 3 of piston 1 through conical cavity 18, the passage 19, the setback cavity 20 and the cylindrical passage 21 of piston 1 and it is continued through the conical interior cavity of the nozzle base 22 and of the nozzle 24 until reaching the interior space of suction area 23. Inside the suction area 23, high speed fluid is forced out of the nozzle 24 contacting the fluid in the suction area 23 dragging it towards the suction area 27 of jet pump 26 creating a depression on the fluid in that area. This depression effect is transmitted to the bottom hole and to the area around the bit through the windows 13 of piston 1, as well as through the cavity 66 formed between interior surfaces of the groups of upper and lower trapezoid bars 55 and 54 and the external surface 38 of piston skirt 2. The fluid exiting nozzle 24 plus the fluid and rock cuttings that enter suction area 23 from the bottom hole pass to the different areas of the jet pump 26: the suction area 27, the mixing area 28 and the expansion area 29 that discharges into the annulus above the expandable centralizer. The fluid and rock cuttings are carried up the annulus to surface.

The other circuit created simultaneously to the one described previously is the cleaning circuit for the bit in Fig.5-B. This circuit is created by the pressure differential created by the jet pump between the annulus located above the expandable centralizer and the area of the bottom hole. This circuit forms starting with the high pressure fluid by the filters 10 and is pushed through the interior cavities 30, the cylindrical passages 31 and 32 of piston 1, into the bypass holes 52 of plug 51, and to the bit. From the bit, the fluid exits through the nozzles toward the bottom hole, takes the rock cuttings to the cavity 66 where it is taken to venturi 27 and is sucked by the fluid from nozzle 24 to the exit of expansion area 29 of the jet pump 26. The pressure loss of the secondary circuit is minimal, so the pressure at the filters 10 is the same as bit nozzle pressure.

Bypass holes 32 of piston 1(Fig. 5-B and 2-D) transmit high pressure to the interior part of the hydraulic lock cover 53 located in the groove of hydraulic lock 15.

The outside of hydraulic lock 16 is ported to the bypass hole of piston skirt 49 (Fig.3 G-G and 5-B) to equalize with the low pressure area around the bit.

The pressure difference between interior surface of the hydraulic lock cover 53 and external surface of the hydraulic lock 16 forces the hydraulic lock 16 to expand into the band of interior ring grooves 48 of piston skirt 2, but the lock will not expand completely into place due to the relative axial displacement "D" that exists.
When the weight on bit is allowed to drill off by holding the drill string axially while rotating the string, the weight of the bit, piston skirt 2, the lower trapezoid bars 54, and the upper trapezoid bars 55 will pull the piston skirt down, so the grooves of hydraulic lock 16 line up with the set of interior ring grooves 48 of piston skirt 2, thus ietting the hydraulic lock 16 expand into the set of interior ring grooves 48. When this happens, the distance "D" will be the distance between the lower end of piston 1 and the bottom of the bore of piston skirt 2 (Fig.2 D-D).

The hydraulic lock cover 53 covers the gap that opens between the ends of the hydraulic lock 16 when the pressure differential causes it to expand.

With the flow of the surface pumps set to drilling rate, there is a pressure differential from the top to the bottom of the expandable centralizer due to the workings of the jet pump. The differential adds to the weight on bit as the product of the area of the expandable centralizer and the pressure differential. This force is transferred through the piston skirt to the interior ring grooves 48 to the hydraulic lock 16 to the edge of the groove 15 to the drill string through the piston 1.

This extra force will stretch the drill string while it is anchored axially at the rig floor and rotating. Advancement of the bit stops once the forces equalize. The value on the weight indicator at this moment less the weight of the string in the non-pumping (static) mode determines the depression being developed below the expandable centralizer. This value is used to drill ahead.

While drilling, the mud depression tool is subjected to tension that is transmitted to the drilling string with the operation of the hydraulic lock 16. Tension results because the supplementary axial hydraulic weight is greater than the axial weight the bit needs while drilling.

Torque to turn the bit and the expandable centralizer comes from the drill string to the piston 1 to the piston skirt 2 (Fig.5 B-B) via the longitudinal bars 14 on the side of piston I to latches 44 with the angled tops 45 of the piston skirt 2.

The piston skirt transmits the torque directly to the drill bit. The torque is transmitted to the expandable centralizer from the side of the notches 35 of the area below cylindrical surface 7 to latches 62 of the upper trapezoid bars 55 (Fig.2 A-A). The lower trapezoid bars 54 are turned by the centralizing blades 39 of the piston skirt 2.
Torque to the upper trapezoid bars 55 and the lower trapezoid bars 55 equalize through the union of the 2 sets of bars.

Radial forces exposed to the expandable centralizer from the drill bit are mostly negated by the fixed part of the centralizer, the centralizer bars 39. The little force remaining is absorbed by the upper trapezoid bars 54 and lower trapezoid bars 55 which transfer the force to the piston 1 via cylindrical surface 7.
The natural tendency for fluid to migrate from the top of the expandable centralizer to below due to the pressure differential is negated as the small clearance between the expandable centralizer and the well bore is filled with rock cuttings from the bit.

The trapezoid bars 54 and 55 are hard surfaced to protect them from erosion due to contact from the well bore.

When drilling is stopped and it is desired to lift the bit to add a single or to pull out of hole, the tool is collapsed (Fig.1-A and 4) as follows:

When the circulation stops, the depression effect of jet pump 26 ceases and the pressure equalizes above and below the expandable centralizer.
The hydraulic lock 16 collapses because of the pressure equalization. The piston 1 is freed from piston skirt 2, so the piston skirt 2 moves axially from piston 1. The cylindrical surface 7 of piston 1 moves above the interior of trapezoid bars 54 and 55. The axial movement causes the trapezoid bars 54 and 55 to have a smaller diameter while getting longer (Fig.2). The expandable centralizer collapses until the longitudinal bars of piston 1 hit latches 62 of the upper trapezoid bars 55.
When the latches 44 of the upper end of the piston skirt 2 hit the stop grooves 61 of the corresponding lower trapezoid bars 54 and the longitudinal bars 14 of piston 1 contacts the upper stop grooves 60 of lower trapezoid bar 54 which stops the relative axial movement between piston 1 and piston skirt 2. The tool returns to the configuration in Fig.1-A, 3 and 4 The distance "D" (Fig.2 D-D) which is between the lower end of piston 1 and the bottom of piston skirt 2 while drilling (Fig.2 and 5) is designed to be an alternate means to disable hydraulic lock 16 in a mechanical way in case that it doesn't return to its normally closed position. In this situation, hydraulic lock 16 can be pushed into groove 15 by discharging part of the weight of the drilling string on piston 1 which will put piston 1 further inside of piston skirt 2 until contacting the bottom of the bore of piston skirt 2. This will put an inward radial force on the hydraulic lock 16 from the interior ring grooves 48 of piston skirt 2.

This tool modifies the operating conditions for the drill bit by using the expandable centralizer to hydraulically isolate the lower part of the well bore by the bit. The expandable centralizer uses the two groups of trapezoid bars 54 and that are controlled from the surface through the piston - piston skirt system.
With this hydraulic isolation in place, the conditions, the jet pump 26 requires to operate, are in place. The depression effect necessary for the operation of this tool is not possible without both the expandable centralizer and the jet pump.

Claims

CLAIMS.

1a. A mud depression tool positioned above a drill bit in a wellbore comprising a two piece cylindrical body forming a piston skirt system which move axially relative to each other to activate an expandable centralizer located radially thereabove which, when expanded, closes an annulus between the body and the wellbore; a jet pump in the body and powered by mud from surface and connected through its venturi with the annulus below the expandable centralizer for creating a low pressure area below the bit by discharging mud, leaving the bit, to the annulus above the expandable centralizer; an interior passage for directing the mud from the annulus above the expandable centralizer to the bit, then through the nozzles for hole cleaning; and a locking mechanism on the piston skirt system which is engaged while drilling in depression for maintaining the jet pump in operation.

1 - A Mud depression tool using expandable centralizer and jet pump, as well as process for well drilling of the type that includes a jet pump and a piston skirt system, characterized by a tool that consists of a piston 1 and of a piston skirt 2 introduced partially, for one of their ends, one inside the other one, forming a piston skirt system with a cylindrical surface of common contact; a cylinder of the piston 9 located inside the piston skirt 2 to form a piston skirt system; a metallic expandable centralizer formed by a group of components fixed with the piston skirt 2 and other group of mobile components, of a tubular form, located outwardly around and concentric with the piston skirt system that form piston 1 and piston skirt 2;
a hydraulic lock groove 15 of rectangular profile on the external surface of cylinder 9 of piston 1; a piston stop ring groove 17 of ring profile on the external surface of the cylinder 9 of piston 1; some longitudinal bars 11 of piston 1 located in a parametrical position of equal spacing to each other and angled on the external surface of the cylinder 9 of piston 1; some longitudinal bars 14 of piston 1 located parametrically and equally spaced to each other and angled on the external surface of the cylinder 9 of piston 1 between the group of longitudinal bars 11 of piston 1; a hydraulic lock 16 of sleeve form sectioned on its circumference and located inside the hydraulic lock groove 15; a hydraulic lock sleeve 53 sectioned on its circumference and located inside the hydraulic lock 16 ; a stop ring 50 sectioned on its circumference and located inside the stop ring groove 17; a cylindrical surface of piston 7 of greater diameter than the cylinder 9 and located above it; an upper neck 5 of piston 1 of a cylindrical form, of smaller diameter than the cylindrical surface of piston 7 and located above it; a conical superior surface of piston 6 that unites the upper neck 5 with the cylindrical surface of piston 7; a conical lower surface of piston 8 that unites the cylinder 9 of piston 1 with the cylindrical surface of piston 7; a group of cavities 35 opened on the lower corner of the cylindrical surface 7 of piston 1, passing to the lower conical surface 8 of piston 1; a suction area 23 that is opened up to the external surface of the cylinder 9 through the window of piston 13; a nozzle base 22 whose conical body lodges in a cavity opened up in the body of piston 1 and has a threaded end that stands out into the interior side of suction area 23; a nozzle 24 in the nozzle base 22 in its threaded end; a nozzle nut 25 located inside the suction area 23 threaded to the nozzle base 22 to attach the nozzle to the piston 1 and fixes the nozzle 24 in its base 22; a jet pump 26 with its suction area 27, mixing area 28 and expansion area 29, inserted inside the body of piston 1 in a such way that the exit of its expansion area 29 opens up on the conical upper surface of piston 6 and its suction area 27 opens up to the interior of the suction area 23; a group of cavities and passages connected to each other and opened inside the body of piston 1 in such way that their plane of symmetry which is common to the central axis of the tool and formed in successive order, starting from the threaded connection 3 opened on the upper neck of piston 5, by the conical cavity of piston 18, the cylindrical passage of piston 19, the passage of piston 20, the cylindrical passage of piston 21, a conical cavity that houses the nozzle base 22, the suction area 23 and the cavity that houses the jet pump 26; two similar groups of cavities and passages connected to each other in each group, opened inside the body of piston 1, located diametrically opposite to each other, and their plane of symmetry is common to the central axis of the tool, but rotated 90° relative to the plane of the precedent group and formed in successive order by the interior cavities 30 that open up passing on the conical upper surface 6 and the lower part of the external surface of upper neck 5, the cylindrical passages 31 and the passing cylindrical passages 32; two filters 10 fixed on the external surface of upper neck 5 on the entrance of the interior cavities 30; a central cylindrical passage 33 opened to the lower end of the cylinder 9, concentric with the central axis of piston 1 and leading to the cylindrical passages 32 and to the bottom of the cavity 20; a group of holes of piston 34 opened to the lower and interior part of the groove of hydraulic lock 15; a lower cylindrical neck of piston skirt 36; a conical external surface of piston skirt 37 located above the lower neck 36; a cylindrical external surface of piston skirt 38 of smaller diameter than the lower neck 36 and located above the conical external surface 37; some angled hooks located on the upper end of the external cylindrical surface 38 of piston skirt 2 with a tip 45 that stands out through the upper end of piston skirt 2; a threaded connection of piston skirt 4 opened to the end of the lower neck 36 and concentric with the axis of piston skirt 2; a threaded base of piston skirt 46 starting from the bottom of the threaded connection 4 and concentric with the axis of piston skirt 2; a bore of piston skirt 47 concentric with its central axis opened starting from the threaded base 46 connected to the upper end of piston skirt 2 and has the same diameter as the cylinder 9 with which forms a piston - piston skirt system; a set of interior ring grooves of piston skirt 48 opened on the interior surface of the bore 47 close to its bottom; a group of centralizing blades of piston skirt 39 that stand out on the conical surface 37; a equalization hole of piston skirt 49 that is opened on the conical surface 37, below one of the centralizing blades 39 connected to the set of interior ring grooves 48; a plug 51 in a cylindrical form, with an external diameter equal to the diameter of central passage of piston 33 fixed to the threaded base 46 in concentric form with the central axis of piston skirt 2; two circular bypass holes of the plug 52 starting from the base of the plug 51 to the external surface and the base of the plug 51, of same diameter and angle as the passages of piston 32 and diametrically opposed form one another.

2 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL AND
JET PUMP AS WELL AS PROCESS FOR WELL DRILLING of the type that is worked by a piston-piston skirt system, characterized by a centralizer that consists of a group of centralizing blades 39 fixed on the external conical surface of the piston skirt 37 with an upper part with its lateral planes parallel to the central axis of piston skirt 2 and a lower part with its lateral planes at an angle to the central axis of the piston skirt 2; a group of metal upper trapezoid bars 55 all equal and tapered whose external view looks like a trapeze, each one with two plane lateral surfaces and the widest side of the trapeze up; a group of metal lower trapezoid bars 54, of equal number with the same external form as the upper trapezoid bars 55 each one with two lateral plane surfaces, with the widest side of trapeze down, inserted within the upper trapezoid bars 55 and each one has a plane of lateral contact with each one of the adjacent bars of the group of upper trapezoid bars 55; two lateral profile 56 formed as a "T" on the lower trapezoid bars 54 with each one lengthwise protruding from the lateral plane surfaces of contact with upper trapezoid bars 55; two slots 57 on the upper trapezoid bars 55 of the same form as the lateral profile 56 cut out of lateral plane surfaces of contact with the lower trapezoid bars 54 to fit with the corresponding lateral profile 56 in such way that they can move in longitudinal sense to form sliding unions of dovetail type in each of the contact planes in the two groups of upper 55 and lower trapezoid bars 54.

3 - JET PUMP, MUD DEPRESSION TOOL, EXPANDABLE
CENTRALIZER AS WELL AS PROCESS FOR WELL DRILLING ...of the type that comprises a jet pump 26 with the following areas located in a successive order: a conical impulse area 22; a cylindrical nozzle 24; a conical suction area 27 that have three axis located on a plane of symmetry: an axis shared by the impulse area and nozzle 24, another axis of the mixing area 28 and a third axis of the expansion area 29.

4 - PROCESS FOR WELL DRILLING, MUD DEPRESSION TOOL, EXPANDABLE CENTRALIZER AND JET PUMP FOR IT... characterized by a process for drilling wells which uses a tool located above the drill bit when being tripped in or pulled out of the well assumes external dimensions similar to the rest of the bottom hole assembly with a group of fixed centralizing blades 39 whose outside diameter is equal to the diameter of centralizers commonly used; this tool also includes a piston 1 that on its upper end has a threaded connection 3 that attaches to the drilling string above it and on its other end forms a cylinder 9; a piston skirt 2 that has a threaded connection 4 on its lower end that attaches to the drill bit and on its upper end has a bore 47 of the same internal diameter as the outside diameter of the cylinder 9 which accepts the cylinder 9 to form a piston-piston skirt system in such a way that piston 1 can move in axial direction inside piston skirt 2; an expandable metallic centralizer located concentrically with the mud depression tool upon reaching the bottom hole and taking some of the weight of the drilling string, it opens and blocks nearly all of the annulus around the tool; a jet pump 26 located inside the body of piston 1 that uses the fluid pumped from surface whose suction area 27 is part of the annulus located below the expandable centralizer and whose expansion area 29 opens to the annulus located above the expandable centralizer in such way that the jet pump 26 sucks the fluid in the annulus below the expandable centralizer which creates lower pressure below the expandable centralizer lower than the pressure above the expandable centralizer; a hydraulic lock 16 that activates under the difference of pressure created by the jet pump 26 fixes the axial relative position of piston 1 and piston skirt 2 while drilling; a mechanism that fixes the relative position between the piston 1 and the piston skirt 2 in the opened configuration and a hydraulic circuit formed by two groups of passages located inside the piston 1 through which the fluid in the annulus above the expandable centralizer is directed to the drilling bit and is ejected through the bit nozzles into the bottom hole for cleaning and from there it is pushed to the suction area 27 where the fluid that leaving the nozzle 24 takes it through the jet pump 26 to the annulus above the expandable centralizer.

- MUD DEPRESSION TOOL ......... according to claim No.1 characterized because each one of longitudinal bars 11 of piston 1 has a central plane of symmetry common the central axis of piston 1 and its lateral surfaces are parallel to this central plane of symmetry.

6 - MUD DEPRESSION TOOL ......... according to claims No.1 and 5 characterized because the planes of all of the upper surfaces of each longitudinal bar 11 of piston 1 intersect the central axis of piston 1 under the same angle and plane of their lower surfaces are normal to the central axis of piston 1.

7- MUD DEPRESSION TOOL ......... according to claims No.1, 5 and 6 characterized because the angle of the upper surface of each one of longitudinal bars 11 to the central axis of piston 1 is equal to the taper angle of the lower conical surface of piston 8.

8 - MUD DEPRESSION TOOL ......... according to claims No.1, 5, 6 and 7 characterized because the outside radius of the longitudinal bars 11 of piston 1 is smaller than the radius of the cylindrical surface of piston 7.

9 - MUD DEPRESSION TOOL ......... according to claim No.1 characterized because the longitudinal bars 14 of piston 1 are equally spaced and each one has a central plane of symmetry common to the central axis of piston 1, its lateral surfaces are parallel to this central imaginary plane and the plane of their upper and lower surfaces are normal to the central axis of piston 1 - MUD DEPRESSION TOOL ......... according to claim No.1, 5, 6, 7, 8 and 9 characterized because longitudinal bars 14 of piston 1 are shorter than the longitudinal bars 11 of piston 1 and longitudinal bars 14 are located on the external cylindrical surface 9 of piston 1 in such way that the plane of their lower surfaces coincides with the plane of the lower surfaces of the lower ends of longitudinal bars 11 of piston 1.

11 - MUD DEPRESSION TOOL ......... according to claim No.1, 5, 6, 7, 8, 9 and 10 characterized because the outside diameter of longitudinal bars 14 of piston 1 is smaller than the outside diameter of longitudinal bars 11 of piston 1.

12 - MUD DEPRESSION TOOL ......... according to claim No.1 characterized because the hydraulic lock 16 has on its external surface a group of concentric ring grooves that have a harpoon shaped profile pointing down.

13 - MUD DEPRESSION TOOL ......... according to claims No.1 and 12 characterized because the internal diameter of the hydraulic lock 16 is larger than the internal diameter of its groove 15 and its outside diameter is smaller than the outside diameter of the cylinder 9 of piston 1.

14 - MUD DEPRESSION TOOL ......... according to claim No.1, 12, and 13 characterized because the hydraulic lock sleeve 53 is inside the hydraulic lock 16 with its two free ends located at 180° relative to the free ends of the hydraulic lock 16.

15 - MUD DEPRESSION TOOL ......... according to claims No.1, 12, 13, and 14 characterized because the height of the hydraulic lock 16 is equal to the height of the hydraulic lock sleeve 53 and both in turn are equal to the height of the hydraulic lock groove 15.

16 - MUD DEPRESSION TOOL ......... according to claim No.1, 12, 13, 14 and 15 characterized because the grooves that form the set of interior grooves 48 of piston skirt 2 have the same shape and quantity as the annular external grooves of the surface of the hydraulic lock 16 in such way that all surfaces of the external grooves of the hydraulic lock 16 will be accepted by the set of annular internal grooves 48 of piston skirt 2 when the hydraulic lock expands.

17 - MUD DEPRESSION TOOL ......... according to claims No.1 characterized because the groove 17 of the piston stop ring 50 is formed by two conical parallel surfaces, upper and lower and the vertexes of both cones are inclined to the upper end of piston 1 and an internal cylindrical surface which axis is coincident with the central axis of piston 1.

18 - MUD DEPRESSION TOOL ...... according to claims No.1 and 17 characterized because piston stop ring 50 has a profile common to the shape of its groove 17 by its upper and lower surfaces and possesses the same height as its groove 17 in such way that the piston stop ring 50 being located inside its groove 17 stays in full contact with the upper and lower conical surfaces of its groove 17.

19 - MUD DEPRESSION TOOL ......... according to claims No.1, 17 and 18 characterized because the external diameter of the piston stop ring 50 is larger than the outside diameter of the cylinder 9 of piston 1 and its thickness is less than the width of the groove of the piston stop ring 17.

20 - MUD DEPRESSION TOOL ......... according to claims No.1, 17, 18 and 19 characterized because piston stop ring 50 being inside its groove 17 stands out of the external surface of the cylinder of the piston 9 and the upper edge of the bore 47 of piston skirt 2 and the lower edge of the piston stop ring 50 are beveled.

21 - MUD DEPRESSION TOOL ......... according to claims No.1, 17, 18, 19 and 20 characterized because the angled beveled edge on the piston stop ring 50 has the vertex of its cone directed in the opposite direction as the vertexes of the cones of lower and upper conical surfaces of the groove 17 and its cone angle is smaller than the cone angle of these lower and upper surfaces.

22 - MUD DEPRESSION TOOL ......... according to claims No.1, 17, 18, 19, 20 and 21 characterized because the angled lower external conical surface on the piston stop ring 50 and protrudes out of the cylinder of the piston 9 has the vertex of its cone directed in an opposite direction to the vertexes of the cones of the lower and upper conical surfaces of the groove 17 and its cone angle is the same as the cone angle of the groove 17 lower and upper surfaces.

23 - MUD DEPRESSION TOOL ......... according to claim No.1 characterized because the suction area 23 of piston 1 has a flat bottom, an interior concave wall with its inside surface concentric with its central axis and rest of its inside surface formed by two flat surfaces the open to the external surface of the cylinder 9 to form the window of piston 13.

24 - MUD DEPRESSION TOOL ......... according to claim No.1 characterized because the central axis of the passage of piston 21 forms an arc that turns close to 180° between the start and finish of this axis.

25 - MUD DEPRESSION TOOL ......... according to claims No.1 characterized because the plane of symmetry of the upper part of each of the centralizing blades of piston skirt 39 is on the central axis of piston skirt 2, its lateral planes are parallel to this central plane of symmetry and the lateral planes of the lower part of each are parallel with each other and form an angle of inclination to the central axis of piston skirt 2.

26 - MUD DEPRESSION TOOL ...... according to claims No.1 and 25 characterized because each one of the centralizing blades of piston skirt 39 has on the exterior side a center cylindrical surface that extends to both upper and lower parts and is concentric with the axis of piston skirt 2.

27 - MUD DEPRESSION TOOL ......... according to claims No.1, 25 and 26 characterized because each one of the centralizing blades of piston skirt 39 has on their exterior, a smaller conical surface that meets the external surface of piston skirt 37.

28 - MUD DEPRESSION TOOL ......... according to claims No.1, 25, 26 and 27 characterized because each one of the centralizing blades of piston skirt 39 forms on their exterior, an upper surface that meets the exterior surface of piston skirt 37 and has on both sides, two inclined plane surfaces followed by two plane surfaces parallel to the central plane of symmetry of the upper part of the centralizing blades of piston skirt 39.

29 - MUD DEPRESSION TOOL ......... according to claims No.1, 25, 26, 27 and 28 characterized because each one of the two plane surfaces parallel to the central plane of symmetry of the upper part of the centralizing blades of piston skirt 39 has rectangular profile grooves 40 whose angle of inclination related to the central axis of piston skirt 2 is equal to the cone angle of the central conical surface.

30 - MUD DEPRESSION TOOL ......... according to claims No.1, 25, 26, 27, 28 and 29 characterized because each one of the centralizing blades of piston skirt 39 has a lower trapezoid stop 41 attached at the outside end of the rectangular profile grooves.

31 - MUD DEPRESSION TOOL ......... according to claims No.1, 25, 26, 27, 28, 29 and 30 characterized because each one of the grooves on the centralizing blades of piston skirt 39 forms two planes, one upper and one lower that are on perpendicular planes to the central axis of piston skirt 2.

32 - MUD DEPRESSION TOOL ......... according to claims No.1, 25, 26, 27, 28, 29, 30 and 31 characterized because each one of the centralizing blades of piston skirt 39 has wear protection 43.

33 - MUD DEPRESSION TOOL ......... according to claim No.1, 25, 26, 27, 28, 29, 30, 31 and 32 characterized because the lower trapezoid stops have the same profile as the grooves on the centralizing blades of piston skirt 39 and when mounted their external surfaces coincide with the external cylindrical surfaces of centralizing blades of piston skirt 39.

34 - MUD DEPRESSION TOOL ......... according to claim No.1, 25, 26, 27, 28, 29, 30, 31, 32 and 33 characterized because the width of the lower trapezoid stops 41 is smaller that the width of the centralizing blades 39 and each them are fixed that each of its lateral surfaces is equal distance to the upper lateral planes of the centralizing blades 39 35 - MUD DEPRESSION TOOL ......... according to claims No.1, 25, 26, 27, 28, 29, 30, 31, 32, 33 and 34 characterized because each one of the of lower trapezoid stops 41 is fixed inside its groove in a centralizing bar of piston skirt 39 by a screw 42 of the lower trapezoid stop 41 passing through the lower trapezoid stop 41, threaded into the groove of the lower trapezoid stop 41 and in perpendicular to the central axis of piston skirt 2.

36 - MUD DEPRESSION TOOL ... according to claim No.1 characterized because the upper surface of plug 51 is the same form as the bottom of the passage of piston 20.

37 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.1 and 2 characterized because the quantity of upper trapezoid bars 55, lower trapezoid bars 54, centralizing blades of piston skirt 39, longitudinal bars 11 and 14 of piston 1 are equal.

38 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.1, 2 and 37 characterized because the external surface of each one of upper trapezoid bars 55 and of lower trapezoid bars 54 are cylindrical and its radius is equal to the radius of the external surfaces of centralizing blades of piston skirt 39.

39 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.2, 37 and 38 characterized because the upper surface of each one of upper trapezoid bars 55 and of each one of lower trapezoid bars 54 is flat and are perpendicular to their central axis.

40 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.1, 2, 37, 38 and 39 characterized because the interior surface of each one of upper trapezoid bars 55, and interior surface of each one of lower trapezoid bars 54, are cylindrical and their radius are equal to the radius of the cylindrical surface of piston 7.

41 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.2, 37, 38, 39 and 40 characterized because the lower surface of each one of upper trapezoid bars 55 is flat and is perpendicular to its central axis.

42 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.2, 37, 38, 39, 40 and 41 characterized because each one of upper trapezoid bars 55 possesses a conical surface that forms a bevel between its interior and lower surfaces.

43 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.2, 37, 38, 39, 40, 41 and 42 characterized because each one of upper trapezoid bars 55 has a central longitudinal bar 62 angled on its interior cylindrical surface, located close to its upper end, that has a central plane of symmetry coincident with the central plane of symmetry of upper trapezoid bar and with a lower plane forms an angle with its central axis similar to the cone angle of lower conical surface 8 of piston 1.

44 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No. 2, 37, 38, 39, 40, 41, 42 and 43 characterized because each one of upper trapezoid bars 55 has a central cavity 63 on its interior directly below the longitudinal central bar 62, with a central plane of symmetry coincident with the central plane of symmetry of upper trapezoid bar 55 that has the same profile as the longitudinal bars of piston 11 and whose upper surface is flat and continues as the inclined lower plane of central longitudinal bar 62.

45 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.2, 37, 38, 39, 40, 41, 42, 43 and 44 characterized because each one of upper trapezoid bars 55 have two parallel edges 64 on its interior that angles to both sides of its central cavity 63 and continues to the lateral planes of central cavity 63, symmetrical to the central plane of symmetry of upper trapezoid bar 55 and extend along the central cavity 63.

46 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.2, 37, 38, 39, and 40 characterized because each one of lower trapezoid bars 54 is wider on its lower end with two inclined lateral planes symmetrical to central plane of symmetry of lower trapezoid bar 54.

47 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.2, 37, 38, 39, 40 and 46 characterized because each one of lower trapezoid bars 54 has on its lower end a notch 58 whose central plane of symmetry is on the general plane of symmetry of lower trapezoid bar 54 and has the same profile as the upper part of centralizing blades of piston skirt 39, but with added clearance.

48 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.1, 2, 37, 38, 39, 40, 46 and 47 characterized because each one of lower trapezoid bars 54 have on the notch 58 a profile 59 of same likeness, inclination angles and is the same as the grooves 40 of centralizing blades of piston skirt 39 in such way that the profile 59 when installed in grooves 40 form sliding unions of the dovetail type between lower trapezoid bars 54 and centralizing blades of piston skirt 39.

49 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.2, 37, 38, 39, 40, 46, 47 and 48 characterized because each one of the profile 59 on the lower trapezoid bars 54 forms a lower plane that meets the cylindrical lower surface of lower trapezoid bar 54 perpendicular to its central axis.

50 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.2, 37, 38, 39, 40, 46, 47, 48 and 49 characterized because each one of the edges 56 on the lower trapezoid bars 54 on each one of their lateral planes extends from its lower end to a certain distance from its upper end.

51 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.2, 37, 38, 39, 40, 46, 47, 48, 49 and 50 characterized because the surface of the upper end of each one of the edges 56 of lower trapezoid bars 54 is cylindrical.

52 - EXPANDABLE CENTRALIZER, MUD DEPRESSION TOOL
......... according to claims No.2, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 and 51 characterized because each one of the slots 57 on the upper trapezoid bars 55 on each of their lateral planes extends from its lower end a certain distance of its upper end similar to the upper ends of the edges 56 of the lower trapezoid bars 54.

53 - MUD DEPRESSION TOOL ......... according to claims No.1 and 2 characterized because when the lower end of the cylinder 9 is a certain distance "D"
from the bottom of the bore of piston skirt 47, the groove 15 of the hydraulic lock 16 is axially aligned with the set of interior ring grooves of piston skirt 48.
The profile of the external surface of the hydraulic lock 16 matches in height to the set of ring grooves 48. The plug 51 is fully inside the cylindrical passage of piston 33, each one of the longitudinal bars 11 of piston 1 has a lateral contact with the two parallel edges 64 of the corresponding upper trapezoid bar 55, the upper flat surfaces of the two groups of lower trapezoid bars 54 and upper trapezoid bars 55 coincide on the same perpendicular plane to the central axis of the tool, the upper end of each one of the slots 63 of upper trapezoid bars 55 contacts the upper end of the edge 56 of lower trapezoid bar 54 and it stops, the cylindrical surface of piston 7 is inside the upper end of the cylindrical surface formed by the cylindrical interior surfaces of the two groups of lower trapezoid bars 54 and upper trapezoid bars 55, the upper end of each one of central longitudinal bars 62 that have each one of upper trapezoid bars 55 inside one of the passing cavities 35 of piston 1 at a distance larger than "D" from the bottom of the cavity 35 and contacting laterally on the lateral faces of the cavity 35. The external surfaces of the two groups of lower trapezoid bars 54 and upper trapezoid bars 55 are on the same cylindrical surface as the central cylindrical surfaces of centralizing blades 39 of piston skirt 2. The longitudinal bars 14 of piston 1 are contacting the lateral side of the angled ends 45 of piston skirt 2 the distance from the upper end of piston skirt 2 is larger than "D". The lower plane surface of each of the edges 65 of lower trapezoid bars 54 contacts the corresponding upper plane surface of the lower trapezoid stop 41.

54 - MUD DEPRESSION TOOL ......... according to claims No.1 and 2 characterized because when the cylinder 9 of piston 1 is inside the bore 47 of piston skirt 2 in such way that the groove of the piston stop ring 17 is above the upper end of piston skirt 2, then the piston stop ring 50 is beveled to the surface of external surface of the cylinder 9 of piston 1 and has an outside diameter equal to the outside diameter of the piston skirt at its upper end. The lower beveled corner of the piston stop ring 50 is near to the upper end of the piston skirt 2, each one of the angled hooks 44 of piston skirt 2 is located within the lower cavity 45 of one of the lower trapezoid bars 54, each one of the longitudinal bars 14 of piston 1 is in the upper cavity 60 of one of the lower trapezoid bars 54, the plug 51 is outside of the central cylindrical passage of piston 33, each one of longitudinal bars 11 of piston 1 is in the central cavity 63 of one of the upper trapezoid bars 55 contacting its upper surface on the lower surface of the longitudinal central bar 62 of upper trapezoid bar 55.
The interior cylindrical surface of each of the upper trapezoid bars 55 contacts the cylindrical surface of piston 9, both groups of lower trapezoid bars 54 and upper 55 have axially moved relative to each other forming an external diameter similar to the external diameter of cylindrical surface of piston 7 and the lateral profile 56 of lower trapezoid bars 54 are partially outside of the slots 57 of upper trapezoid bars 55.

55 - JET PUMP, MUD DEPRESSION TOOL ........according to claim No.3 characterized because the axis shared by the impulse area 22 and nozzle 24, the axis of the mixing area 28, the axis of the expansion area 29 and the central axis of symmetry of the mud depression tool are located on the same plane.

56 - JET PUMP, MUD DEPRESSION TOOL ........according to claim No.3 and 55 characterized because the axis shared by the impulse area 22 and nozzle 24 and the axis of the mixing area 28 are parallel and are offset from each other at a distance equal to the difference of the radius of interior cylindrical surface of mixing area less the radius of the interior cylindrical surface of the nozzle 24.

57 - JET PUMP, MUD DEPRESSION TOOL ........according to claim No.3, 55 and 56 characterized because the axis shared by the impulse area 22 and the nozzle 24 is located closer to the center of the mud depression tool than the axis of the mixing area 28.

58 - JET PUMP, MUD DEPRESSION TOOL ........according to claim No.3, 55, 56 and 57 characterized because suction area 27 of jet pump 26 forms a flat surface perpendicular to the plane of the different axis of symmetry of the areas of the jet pump 26 and is tangent to interior cylindrical surfaces of nozzle 24 and mixing area 28.

59 - JET PUMP, MUD DEPRESSION TOOL ........according to claim No.3, 55, 56, 57 and 58 characterized because suction area 27 of jet pump 26 is completed with a conical surface whose plane of symmetry coincides with the plane of the axis of the other areas of the jet pump 26 and whose axis forms an angle to the axis of the mixing area 28 in such way that its exit opens in opposite direction to the central axis of the mud depression tool.