MULTI-STAGE WELL ISOLATION AND FRACTURING

Abstract

In a first aspect, a frac valve tool is taught, said tool comprising one or more ports a sleeve movable between a closed position in which the sleeve prevents fluid flow through said one or more ports and an open position in which the sleeve allows fluid flow through said one or more ports and a ball receiving seat removably connected to the sleeve wherein receipt of a ball on the ball receiving seat moves said seat and said sleeve from closed to open positions. In a second aspect, a frac valve tool is taught, said tool comprising a ball receiving seat removably received within said tool, said seat comprising a seating profile for receiving a ball; wherein said seating profile matches a radius of said ball to nondeformably grip said ball.

Description

FIELD OF INVENTION

The present invention relates to devices for multi-stage, horizontal well isolation and fracturing.

BACKGROUND OF THE INVENTION

An important challenge in oil and gas well production is accessing hydrocarbons that are locked in formation and not readily flowing. In such cases, treatment or stimulation of the formation is necessary to fracture the formation and provide passage of hydrocarbons to the wellbore, from where they can be brought to the surface and produced.

Fracturing of formations via horizontal wellbores traditionally involves pumping a stimulant fluid through either a cased or open hole section of the wellbore and into the formation to fracture the formation and produce hydrocarbons therefrom.

In many cases, multiple sections of the formation are desirably fractured either simultaneously or in stages. Tubular strings for the fracing of multiple stages of a formation typically include one or more fracing tools separated by one or more packers.

In some circumstances frac systems are deployed in cased wellbores, in which case perforations are provided in the cemented in system to allow stimulation fluids to travel through the fracing tool and the perforated cemented casing to stimulate the formation beyond. In other cases, fracing is conducted in uncased, open holes.

In the case of multistage fracing, multiple frac valve tools are used in a sequential order to frac sections of the formation, typically starting at a toe end of the wellbore and moving progressively towards a heel end of the wellbore. It is crucial that the frac valves be triggered in the desired order and that they do not open earlier than desired. Once open, it is also important that the frac valves do not become closed until it is desirable to close them.

Many configurations have been developed in the field to frac multiple stages of a formation. For example fracing tools are known in which a ball is pumped into the tool and sits in a seat to block fluid flow through the central bore, thereby causing fluid pressure to build up and forcing fluid to flow through multiple jet nozzles located circumferentially around the liner.

Other frac valve tools are known for use with coiled tubing, in which a ball is dropped to block flow down the liner and redirect flow through pressure firing heads in a fracking sleeve. Some downhole tools teach including a packer with a ball seat and a ball, in which fluid can be redirected to fracking ports on a fracing tool. Others teach the use of balls of different sizes to control downhole surge pressure.

A need still however exists for frac valve tools that are simple in construction, small in size and effective at fracing formations in multiple stages

SUMMARY OF THE INVENTION

In a first aspect, a frac valve tool is taught, said tool comprising one or more ports a sleeve movable between a closed position in which the sleeve prevents fluid flow through said one or more ports and an open position in which the sleeve allows fluid flow through said one or more ports and a ball receiving seat removably connected to the sleeve wherein receipt of a ball on the ball receiving seat moves said seat and said sleeve from closed to open positions.

In a second aspect, a frac valve tool is taught, said tool comprising a ball receiving seat removably received within said tool, said seat comprising a seating profile for receiving a ball; wherein said seating profile matches a radius of said ball to nondeformably grip said ball.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a horizontal well fitted with the tools of the present invention;

FIG. 2 is a cross sectional view of one example of the frac valve of the present invention in a closed position;

FIG. 3 is a cross sectional view of one example of the frac valve of the present invention in an opened position;

FIG. 4 is a cross sectional view of one example of the frac valve of the present invention in an open position with the seat drilled out;

FIG. 5 is a cross sectional view of one example of the frac valve of the present invention in a closed position with the seat drilled out; and

FIG. 6 is a cross sectional elevation view of a quality control inspection fixture for use with the frac valve of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A frac valve tool is provided that improve on existing ball drop, multi-stage, horizontal fracturing tools, by providing increased safety during installation, reduced rig time and greater dependability in fracing multiple stages in a horizontal section of the wellbore.

By combining both a slim outside diameter and short length, the present frac valve tool eliminates the need for handling pup joints, thereby reducing the rigidity of the liner. These features permit the more flexible, reduced outside diameter tool string to be deployed into the wellbore with greater ease.

The present frac valve tools can be lifted by hand and hand threaded onto the liner, which is typically gripped at the rig floor, and then a section of upper liner, typically gripped in an elevator or similar device, can lowered onto the frac valve tool and the one piece body of the frac valve tool allows torque to be applied from the upper liner section, through the frac valve tool and into the liner to make up the liner string.

The present frac valve tool can be deployed with associated tools along a liner and deployed into the open hole section of the wellbore. The present frac valve tools provide a means of stimulating a section of the formation to induce fracturing of the formation and flow of formation fluids. The short length of the frac valve tool 400 eliminates the need for pup joints on either end. The small outside diameter and short length increases liner flexibility, further aiding deployment into the wellbore. In a preferred embodiment, the present frac valve tool 400 eliminates the typical threaded connection between the top of the tool and the mandrel. Instead, a box end connection and the mandrel are integral and an installation tool is utilized to insert the frac valve tool 400 inside the mandrel. The use of the special installation tool permits the elimination of a threaded connection thereby shortening the frac valve tool length.

With reference to FIG. 1, in a preferred method of deployment, the present frac valve tools can be deployed on a tubing string further comprising a float shoe or guide 50 at the toe of the liner, an activation tool 100 at a pre-determined distance from the guide shoe 50, a first stage frac valve tool 200, and then an series comprising an open hole packer 300 alternated with the present frac valve tools 400 to a final cased hole packer 500. It would be well understood by a person of skill in the art that FIG. 1 merely represents one example of a tubular fracing string of tools and that additions, omissions and alterations to the illustrated string and its components can be made without departing from the scope of the present invention.

The present frac valve 400 is located in the liner between two open hole packers 300 and is depicted in FIGS. 2, 3, 4, 5 and 6. The frac valve 400 comprises a mandrel 420 that is preferably full bore and has an inside diameter matching the inside diameter of the liner. One or more ports 410 are formed around the circumference of the mandrel, said ports 410 providing fluid communication between the inside of the liner and the open hole wellbore. The mandrel 420 contains within it a sleeve 408 connected to the mandrel by one or more shear screws 406. In a closed position, the sleeve 408 blocks fluid passage through the one or more ports 410. Within the sleeve 408 is a seat 404 that can receive a ball 402 that is deployed into the liner from the rig floor and pumped onto the seat 404 by fluid pressure.

The present frac valve 400 is preferably pressure balanced due to sealing by o-rings that straddle the ports, such that the sleeve 408 is not shifted to the open position until the ball 402 lands on the seat 404. After the ball 402 is pumped onto the seat 404, liner pressure generates a force which shears shear screws 406 allowing the seat 404 and sleeve 408 to shift, opening communication through the one or more ports 410.

The seat 404 of the present frac valve 400 is preferably surface hardened to prevent erosion that can be caused by proppants pumped through them. The seats 404 are manufactured from a material and in a geometry that can withstand the stress generated by the ball 402 landing and seating under high differential pressure, while providing adequate support for the ball 402. Suitable materials for the present seat 404 may be most cast irons, including Class 40 Gray Iron or Class 50 Gray Iron, although other suitable materials would be known to a person of skill in the art and are encompassed by the scope of the present invention. The seats are more preferably treated with liquid nitrogen to achieve a Rockwell hardness rating of HRC 50 to 55.

The present seat preferably comprises a seating profile 416 that receives and in part grips the ball 402 in the seat to ensure the ball 402 is not inadvertently unseated until desired. The seat radius 416 is advantageously designed to allow gripping of the ball 402 without sheering the ball 402 or causing plastic deformation. The present seating profiles requires only low pump off pressure to lift the ball 402 off of the seat 404 by pressure from the formation, after fracturing is complete. This is due to the seating profile 416 being preferably matched to a corresponding ball 402 radius to prevent the ball 402 from deforming and becoming wedged into the seat 404.

The relationship between the geometry of the seating profile 416 and the matching ball 402 is preferably designed to permit a variety of ball 402 to seat 404 size ratios for a number of liner applications. The matching geometry of the seating profile 416 and the ball 402 permits a seat 404 of the present design to be adapted for use with many ball and seat sizes, thereby reducing the size increments of seats 404 that need to be manufactured. In a preferred embodiment, the size and geometry of the seating profile 416 can be adjusted relation to the size of ball 402 to be used, this reduces potential hoop stresses that can build up in the ball 402, and ensure that an optimal relationship between proper seating and low pump off pressure.

The ball 402 used with the present invention can be any ball well known and used in ball drop tools found in the state of the art. More preferably, the ball 402 is composed of a non-elastomeric material that shows strength, corrosion resistance against stimulant fluids and wellbore fluids and a degree of flexibility. Such materials can include but are not limited to phenolics, composites or aluminum.

The seat 404 is preferably manufactured with a minimum amount of material to allow the seat 404 to be drilled out after use, thereby minimizing drill out times. In particular, the seat material is designed to be friable and crumble upon drilling, thereby reducing the chance of large drilled out fragments from blocking the liner.

With reference to FIG. 4, the seat 404 of the present frac valve 400 is drilled out after fracturing is complete. The geometry of the seat 404 and the method used to fasten it to the sleeve 408 ensures the seat 404 will drill up into fine particles, eliminating the possibility of large pieces of debris falling onto the next seat 404 to be drilled out. Such debris adds to the time required for the subsequent seat 404 to be drilled out and tends to rotate and grind against the next seat 404.

Preferably one or more anti-rotation tabs 414 located inside the frac valve 400 assists seat drill out by holding the seat 404 stationary. More preferably the seat 404 is threaded into the sleeve 408 in such an orientation that drilling out the seat 404 urges the threads into tightening, thereby additionally serving to hold the seat 404 in place in the sleeve 408. The threads 418 on the seat 404 and on the sleeve 408 are most preferably left hand threads that tend towards tightening when the seat 404 is drilled. These threads 418 also allow the seats 404 of any frac valve tool 400 to be changed as needed, for example should damage be detected in a seat 404, or should on-site adjustments need to be made for different ball and seat sizes for one or more frac valve tools 400.

In a further preferred embodiment, a quality control inspection fixture 700, illustrated in FIG. 6 is used to check five dimensional characteristics of each frac valve 400, to ensure correct placement of each valve in the liner. The quality control fixture 700 checks the bore hole size through the seat 404, and the bore in which the ball 402 lands. It checks the concentricity of both bores to ensure proper sealing whenever the ball 402 lands on the seat 404. The quality control inspection fixture 700 checks the geometry of the seat profile 416 and also the distance from the seat 404 to the top of the frac valve 400, to ensure proper assembly of the frac valve tool 400. The quality control inspection fixture 700 is preferably attached to a seat installation tool (not shown) to assist in ensuring the correct seat 404 is being installed into the frac valve tool 400.

In some cases, the frac valve seat 404 can be drilled out to the drift inside diameter of the liner Drift diameters are specified by the American Petroleum Institute (API) for each weight of casing. An object of a given drift diameter and given length as specified by API must fit through the inside diameter of the pipe.

Although it is common to run one frac valve 400 per isolated section of the formation, it is also possible to place multiple frac valves 400 in any given isolated section. In a preferred embodiment, the frac valve 400 can be configured to have a closable feature. The closable frac valve 400 can be closed by a number of means. One embodiment permits the frac valve 400 to be closed before drilling out the seats, in this case a shifting tool run on tubing is used to close the frac valve 400. A second embodiment, illustrated in FIG. 5, allows the frac valve 400 to be closed after the seat 404 is drilled out. Multiple frac valves 400 or a single frac valve 400 may be shifted from an open to a closed position with a further second style of shifting tool 412.

The total flow area through all of the fracture ports 410 of the frac valve 400 is preferably greater than the flow area through the liner.

Sometimes a sand off occurs during the fracing operation when no more sand can be pumped into the formation and the sand remains indie the liner preventing the ability to pump the next ball down the well. In such cases, an opening tool (not shown) can be run through the tubing and landed on the seat 404. In such cases, applied pressure in the annular area between the inside wall of the liner and the outside diameter of the tubing is used to pump the frac valve 400 into the open position.

In one example of operation of the present frac valve tool 400, a liner may be assembled with a float shoe 50, an activation tool 100, a liner, a first stage frac valve tool 200, and then a series comprising a liner, an open hole packer 300, a liner and the present frac valve tools 400. Optionally, an open hole anchor may be used between the activation tool 100 and the first stage frac valve tool 200 to anchor the liner to the wellbore. Alternative to an open hole anchor centralizers, stabilizers or other suitable means known in the art may also be used for this purpose.

Preferably up to 40 frac valves 400, on a 4½″ liner for example, separated with open hole packer 300s can be used in a string. In operation, the seats 404 of the frac valve tools 400 sequentially increase in the size of ball 402 they can receive; with the smallest seat 404 being closest the toe end of the wellbore and the largest seat 404 being at the heel end. A cased hole packer 500 is attached to the upper end of the liner. A latch seal assembly or other known means can be used to attach the cased hole packer 500 to the work string.

The liner is run into the conditioned bore hole by a work string or on a frac string. At a predetermined depth the activation tool 100 is activated to stop fluid flow. Pressure in the liner now increases from a triggering pressure at which both the cased hole packer 500 and the open hole packers 300 begin to set, to a final pack off pressure at which the cased hole packer 500 and open hole packers 300 are fully set. A pressure test may optionally be performed inside the casing to determine if the cased hole packer 500 has set properly. If the liner was run on a work string, the latch seal assembly or other connection means can next be removed from the cased hole packer 500 and the work string and latch seal assembly are removed from the well and a frac string and latch seal assembly are deployed. Otherwise, if the liner was run downhole on a frac string, no replacement has to be made.

Further pressure is applied to the fracture string. At a pre-determined opening pressure that is higher than the pack off pressure, the first stage frac valve tool 200 shifts to the open position and stimulation fluid is pumped into the formation and causes it to fracture. Proppant is then pumped into the fracture. Next, a first ball 402 is pumped into the liner corresponding to the seat sizes of the frac valve tool 400 closest the toe of the wellbore. By this process the frac valve tool 400 is activated to thereby open ports 410 to allow communication between the inside of the liner and the isolated section of the formation between the two open hole packer 300 straddling the particular frac valve 400. Subsequent frac valve tools 400 are similarly activated by pumping subsequent balls 402 into the liner in sequential size order.

The stimulation fluid pumped through the ports of the frac valve 400 fractures the exposed formation between the open hole packers 300 used to isolate that stage. Whenever this stage has been fractured, a next frac valve 400 is activated and the process is repeated. The process can be repeated up to 40 times in total in a 4½″ liner, for example. Other sizes of liners have a different number of frac valve tools 400 and open hole packers 300. When all the desired stages have been fractured, the well is allowed to flow and formation pressure from formation fluid flow acts to deactivate the frac valves 400 by pumping balls 402 off of the seats 404, and allows formation fluid flow into the liner. Afterwards the frac string and connecting means can be removed from the well.

If desired, the seats of the frac valves 400 can be drilled out at a later date.

In the foregoing specification, the invention has been described with specific embodiments thereof; however, it will be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention.

Claims

1. A frac valve tool, said tool comprising: wherein receipt of a ball on the ball receiving seat moves said seat and said sleeve from closed to open positions.

a. one or more ports;

b. a sleeve movable between a closed position in which the sleeve prevents fluid flow through said one or more ports and an open position in which the sleeve allows fluid flow through said one or more ports; and

c. a ball receiving seat removably connected to the sleeve;

2. A frac valve tool, said tool comprising a ball receiving seat removably received within said tool, said seat comprising a seating profile for receiving a ball; wherein said seating profile matches a radius of said ball to nondeformably grip said ball.

3. The frac valve tool of claim 1, wherein the seat further comprises a seating profile to receive and grip the ball.

4. The frac valve tool of claim 3, wherein the seating profile has a geometry that non-deformably grips the ball.

5. The frac valve tool of claim 4; wherein the removable seat is changeable to accommodate more than one size of seat and more than one size of ball in the tool.

6. The frac valve of claim 1, further comprising one or more shear screws affixing the sleeve to the tool, said shear screws being shearable at a predetermined liner pressure accumulated in the tool when the ball lands on the seat, wherein shearing of said one or more shear screws allows the seat and sleeve to shift to the open position.

7. The frac valve tool of claim 6, further comprising a mandrel within which the sleeve is movably affixed via the shear screws and through the circumference of which the one or more ports are formed.

8. The frac valve tool of claim 1, wherein the total flow area through all of the one or more ports is greater than the flow area through the liner.

9. The frac valve tool of claim 1, wherein the seat is a drillable seat.

10. The frac valve tool of claim 9, wherein the drillable seat is made of a friable material that crumbles upon drilling.

11. The frac valve tool of claim 10, wherein then seat is composed of a cast iron.

12. The frac valve tool of claim 11, the seat is surface hardened

13. The frac valve tool of claim 12, wherein the seat has a Rockwell hardness rating of HRC 50 to HRC 55.

14. The frac valve tool of claim 1, further comprising a closable feature.

15. The frac valve tool of claim 14, wherein the frac valve tool is closable before the seat is drilled out.

16. The frac valve tool of claim 14, wherein the frac valve tool is closable after the seat is drilled out.

17. The frac valve tool of claim 1, further comprising one or more anti-rotation tabs inside the frac valve tool to stabilize the seat against rotation during drill out.

18. The frac valve tool of claim 17, wherein the seat is threadably affixed into the sleeve in a direction that serves to tighten against rotation during drill out.

19. The frac valve tool of claim 18, wherein the seat is left hand threaded into the sleeve and tend towards tightening when the seat is drilled.

20. The frac valve tool of claim 1, further comprising a quality control inspection fixture to inspect dimensional one or more characteristics of the frac valve tool.

21. The frac valve tool of claim 20, wherein the quality control inspection fixture inspects bore hole size through the seat, the bore hole of seating profile, concentricity of both bore hole through seat with bore hole through seating profile, geometry of the seat profile and distance from the seat to a top surface of the frac valve tool.

22. The frac valve tool of claim 21, wherein the quality control inspection fixture is attached to a seat installation tool to install a predetermined seat into the frac valve tool.