Screw-driven wellhead isolation tool

BACKGROUND OF THE INVENTION

The present invention relates to wellhead equipment, and more particularly to a wellhead isolation tool for isolating a wellhead from the high pressures and the abrasive and/or caustic substances used in well treatment procedures.

It is not unusual for oil and gas wells to require stimulation to restart, or to improve, a flow of hydrocarbons from a hydrocarbon bearing formation. Such stimulation typically involves pumping fluid mixtures into the formation at high pressures. Such fluid mixtures often comprise acidic solutions and/or proppants that can be caustic and/or abrasive. Hydraulic fracturing, one common form of stimulating a hydrocarbon bearing formation, forces liquids and/or gasses which may include proppants or other abrasives therein into the formation. Extremely high pressures and high flow rates must be employed in the hydraulic fracturing process so that the proppants will be forced into the hydrocarbon bearing formation.

Conventional wellheads, commonly called well trees, are not generally designed to withstand the pressures and/or the abrasive or caustic nature of the substances required to stimulate a formation. Generally, the wellhead is designed to withstand pressures of less than about 5,000 psi. The substances utilized to stimulate the formation will be pumped into the well at pressures greatly exceeding 5,000 psi and may be as much as 20,000 psi.

There are a number of existing wellhead isolation tools that provide for the reciprocation of a mandrel through the wellhead into the well so that the substance utilized to stimulate the well passes through the mandrel and into the well without damaging the wellhead. However, because of the potentially dangerous nature of the well stimulation operation, there is a continuing need to provide a wellhead isolation tool which can be easily connected to the wellhead and disconnected therefrom, which provides easy access for connection of lines to supply the treatment fluid, and which provides an efficient and safe method to stimulate the hydrocarbon bearing formation.

SUMMARY OF THE INVENTION

The present invention is directed to a wellhead isolation tool for injecting substances through a wellhead into a tubular element, such as a production tubing, in a well. The wellhead isolation tool includes a tubular mandrel adapted to be received through a longitudinal passage defined by the wellhead. The tubular mandrel defines a mandrel flow passage and has a nonthreaded outer surface.

The wellhead isolation tool further includes at least one high pressure valve connected to an upper end of the tubular mandrel. Treatment substances such as fracturing fluids containing proppants and other treatment fluids may be communicated through the high pressure valve into the mandrel flow passage when the at least one high pressure valve is in an open position. The tubular mandrel has an upper position in which the mandrel does not extend through the wellhead into the well and a lower position in which a lower end of the mandrel is sealingly received in the production tubing in the well. A threaded drive rod for reciprocating the tubular mandrel is vertically aligned with the tubular mandrel and is connected to the at least one valve.

The wellhead isolation tool further includes a drive mechanism for vertically displacing the threaded rod to urge the tubular mandrel downward through the wellhead and into the tubular element in the well. Once the tubular mandrel is sealingly engaged in the well, treatment fluids can be flowed into the well at extremely high pressures through the tubular mandrel without damaging the wellhead. The wellhead isolation tool further includes a support structure which provides for the easy location and connection of the wellhead isolation tool to the wellhead.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is perspective view of the wellhead isolation tool of the present invention.

FIGS. 2A-2C

show a front elevational view of the wellhead isolation tool of the present invention.

FIGS. 3A-3B

show a cross section of the wellhead taken from line

3

—

3

of

FIGS. 2A-2C

.

FIGS. 4A-4B

are cross sections of the wellhead isolation tool of

FIGS. 2A-2C

showing the mandrel in a down position. The section is taken through the front legs and the mandrel.

FIG. 5

shows a prior art connection between a wellhead isolation tool and the wellhead.

FIG. 6

is a top view of a wellhead adapter sub of the present invention.

FIG. 7

is a side view of the wellhead adapter sub of the present invention.

FIG. 8

shows the lower end of the mandrel of the present invention sealingly engaged in production tubing in the well.

FIG. 9

shows a perspective view of the roller assembly of the present invention.

FIG. 10

is a view from line

10

—

10

of FIG.

3

A.

FIG. 11

shows a view from line

11

—

11

of FIG.

10

.

FIG. 12

is a detail showing a roller plate of the present invention.

FIG. 13

is a detail showing a support plate of the present invention.

FIG. 14

is a front view of an alternative embodiment of a support structure of the present invention.

FIG. 15

is a left-side elevation view of the support structure of FIG.

14

.

FIG. 16

is a right-side elevation view of the support structure of FIG.

14

.

FIG. 17

is a view from line

17

—

17

of

FIG. 14

, rotated 180°.

FIG. 18

is a view from line

18

—

18

of FIG.

14

.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to the drawings and more particularly to

FIGS. 1-3

, a wellhead isolation tool designated by the number

10

is shown. Wellhead isolation tool

10

has a front

12

and a rear

14

.

FIG. 2C

shows wellhead isolation tool

10

connected to a wellhead

15

defining a longitudinal passage

17

, positioned over a well

20

. Well

20

may comprise a wellbore

25

having a casing

30

cemented therein. Well

20

has a tubular element, which may be a production tubing

32

disposed therein.

Wellhead isolation tool

10

comprises a drive rod

34

which is preferably an externally threaded drive rod. Drive rod

34

preferably has a regular screw thread on the exterior thereof. Drive rod

34

has a longitudinal central axis

35

, an upper end

36

and a lower end

38

. As will be explained in more detail herein, drive rod

34

may be moved vertically by a type of screw drive mechanism. For example, a machine screwjack

39

driven by a motor

40

of a type known in the art may be utilized. The details of each are not depicted, but are shown schematically in the figures. Motor

40

is not shown in

FIG. 1

, but is schematically represented in FIG.

2

. Screwjack

39

may be, for example, a machine screwjack model 50 MSJ, available from Nook Industries, Inc. An outer protective tube

41

may be disposed about drive rod

34

above screwjack

39

. Drive rod

34

has internal threads

42

at the lower end

38

thereof. A coupling

44

is threadedly connected at its upper end

46

to drive rod

34

at internal threads

42

. Coupling

44

has a lower end

48

with a wing nut assembly

50

a

disposed thereabout. Wing nut assembly

50

a

is connected at a threaded connection

52

to a valve

54

which may be referred to as an upper valve

54

. Wing nut assembly

50

a

is connected to upper valve

54

at the upper end

56

thereof. Drive rod

34

is thus connected to upper valve

54

with coupling

44

and wing nut assembly

50

a.

As will be explained in more detail hereinbelow, wing nut assembly

50

a

may be easily disconnected from upper valve

54

so that a fluid line may be connected thereto. Upper valve

54

is depicted as a remote control valve which is movable between open and closed positions. In the open position, fluid may be displaced through a passage

58

, and in the closed position no fluid is allowed to pass therethrough.

Upper valve

54

has a lower end

60

. A wing nut assembly

50

b

is disposed about the lower end

60

of upper valve

54

, and connects upper valve

54

with a lower valve

62

. There are a plurality of wing nuts

50

utilized with the wellhead isolation tool

10

. Wing nuts

50

are referred to as wing nuts, or wing nut assemblies

50

a

-

50

e

for ease of identification. Wing nuts

50

a

-

50

e

may be identical to one another.

Lower valve

62

is depicted as a manually operated valve which defines a passage

64

. Lower valve

62

is movable between an open position wherein fluid may be displaced through passage

64

and a closed position wherein fluid flow therethrough is prevented. Although the wellhead isolation tool

10

of the present invention shows two valves, namely upper and lower valves

54

and

62

, respectively, it is understood that wellhead isolation tool

10

will have at least one valve and preferably a plurality of valves. In the embodiment shown, a remote control valve is shown as upper valve

54

and a manually operated valve is shown for lower valve

62

. The positions of the valves may be switched or both may be manual or remote control.

Lower valve

62

is connected at its upper end

66

to upper valve

54

with wing nut

50

b,

and is connected at its lower end

68

with a wing nut

50

c

to a mandrel assembly

70

. Mandrel assembly

70

has a longitudinal central axis

71

and comprises an upper mandrel

72

and a lower mandrel

74

. Longitudinal central axis

71

and longitudinal central axis

35

are collinear, such that drive rod

34

and mandrel assembly

70

have a common longitudinal axis and are thus coaxial. Upper mandrel

72

is connected at its upper end

76

to wing nut

50

c

at the lower end

68

of lower valve

62

. A wing nut

50

d

is disposed about lower end

78

of upper mandrel

72

. Mandrel assembly

70

may be reciprocated between an upper position

80

as shown in

FIGS. 2A-2C

, to a lower position

82

as shown in

FIGS. 4A-4B

. In upper position

80

, wing nut

50

d

disposed about the lower end of

78

of upper mandrel

72

is not connected to any other part. In lower position

82

, however, wing nut

50

d

is connected to a lower central support, as will be explained in more detail hereinbelow.

Lower mandrel

74

has an upper end

84

connected to upper mandrel

72

at threaded connection

86

. An O-ring seal

88

may be disposed above threaded connection

86

to provide a sealed connection between the upper and lower mandrels

72

and

74

. Lower mandrel

74

has a lower end

90

. Lower end

90

is connected to a sealing device

91

as shown in FIG.

8

. Sealing device

91

may comprise a cup mandrel

92

with a cup seal

93

connected thereto. A shoe

94

is disposed about cup mandrel

92

. A diffuser, like that shown in U.S. Pat. No. 4,262,743, the details of which are incorporated herein by reference, may also be used. Mandrel assembly

70

defines a passageway

96

for the flow of substances such as treating fluids or other fluids therethrough. Passages

58

,

64

and passageway

96

thus define a longitudinal central flow passage

98

which provides for flow therethrough into production tubing

32

. Lower mandrel

74

has an outer surface

100

.

Wellhead isolation tool

10

further includes upper and lower central supports

110

and

112

respectively, which may also be referred to as upper and lower hubs

110

and

112

. Upper central support

110

comprises a body portion

114

and upper and lower flanges

116

and

118

, respectively, extending outwardly from body portion

114

. Upper and lower flanges

116

and

118

define a space

120

therebetween. Upper and lower flanges

116

and

118

are preferably circular flanges. Screwjack

39

and motor

40

, or other means for vertically displacing drive rod

34

, may be mounted by any means known in the art to upper flange

116

. Upper and lower flanges

116

and

118

define pin receiving holes

122

and

124

, respectively. Pin receiving holes

122

and

124

are aligned with one another. Upper central support

110

defines an opening

126

therethrough which allows drive rod

34

to reciprocate between its upper and lower positions

80

and

82

, respectively.

Wellhead isolation tool

10

also comprises lower central support

112

. Lower central support

112

has an upper end

132

and a lower end

134

. Upper end

132

preferably has a threaded outer surface so that in the lower position

82

of mandrel assembly

70

, wing nut

50

d

may be threadedly connected thereto to connect upper mandrel

72

to lower central support

112

, and fix mandrel assembly

70

in lower position

82

. Lower central support

112

includes a body portion

136

and has upper and lower flanges

138

and

140

extending radially outwardly therefrom. Upper and lower flanges

138

and

140

define a space

142

therebetween. Upper flange

138

has a plurality of pin receiving holes

144

defined therethrough and lower flange

140

has a plurality of pin receiving holes

146

defined therethrough. Pin receiving holes

144

and

146

are aligned with one another. Lower central support

112

includes a sleeve

148

. Lower central support

112

defines a central opening

150

to allow lower mandrel

74

to pass therethrough and be moved vertically in and out of wellhead

15

. A wellhead adapter

152

is connected to lower central support

112

at its lower end

134

. Wellhead adapter

152

is connected to lower central support

112

with a clamp

154

which may comprise two clamp portions

155

bolted together, or which may comprise any type of clamp known in the art.

Sleeve

148

extends downwardly into a central opening

156

defined by wellhead adapter

152

. Sleeve

148

has a flange

158

positioned between lower central support

112

and wellhead adapter

152

. A gap

159

thus exists between wellhead adapter

152

and lower central support

112

. Sleeve

148

is held in place in lower central support

112

by wellhead adapter

152

which is connected to lower central support

112

with clamp

154

. Sleeve

148

is a removable sleeve such that sleeves having any desired inner diameter may be utilized to accommodate mandrels of different outer diameters. Wellhead adapter

152

comprises a wellhead adapter housing

160

having a wing nut

50

e

connected to a lower end

162

thereof.

Wellhead isolation tool

10

may further comprise a wellhead adapter sub

164

as shown in

FIGS. 6 and 7

. Wellhead adapter sub

164

, which may be also referred to as mounting sub

164

, comprises a mounting plate

166

having a plurality of bolt or pin holes

168

therethrough. A threaded neck

170

extends upwardly from mounting plate

166

. A prior art wellhead

15

is depicted in

FIG. 5 and

, as shown therein has a plurality of bolts

172

extending upwardly therefrom in a defined bolt pattern. Bolt holes

168

in wellhead adapter sub

164

are adapted to match the pattern of bolts

172

so that wellhead adapter sub

164

may be mounted to wellhead

15

simply by placing wellhead adapter sub

164

thereon and threading nuts onto the bolts

172

extending upwardly on wellhead

15

. As shown in

FIG. 2C

, wing nut

50

e

may be connected to wellhead adapter sub

164

simply by threading wing nut

50

e

thereon, thus connecting wellhead adapter

152

to wellhead

15

. Prior art wellhead isolation tools included a wellhead adapter

174

that had mating holes to connect directly to the bolts

172

as shown in FIG.

5

.

The wellhead isolation tool

10

of the present invention provides for easier connection and disconnection of the wellhead isolation tool

10

on any wellhead

15

, including those with differing bolt patterns, since a plurality of wellhead adapter subs

164

may be designed having different bolt patterns to match the bolt patterns on different wellheads. The wellhead adapter sub

164

can be placed on the wellhead

15

prior to the time the wellhead isolation tool

10

is to be connected thereto which will provide for easier connections that can be made in less time, since the wellhead adapter

152

can simply be threaded to wellhead adapter sub

164

.

Sleeve

148

has openings

176

therethrough. An annulus

178

is defined between outer surface

100

of lower mandrel

74

and wellhead adapter

152

. Likewise, an annulus

180

exists between the outer surface

100

of lower mandrel

74

and an inner diameter

182

defined by sleeve

148

. Inner diameter

182

defines a portion of central opening

150

in lower central support

112

. Annulus

178

and annulus

180

define a fluid path

183

that is communicated with an annulus

184

through openings

176

. Annulus

184

is defined between an outer diameter

186

of sleeve

148

and inner diameter

188

of body portion

136

of lower central support

112

. When lower mandrel

74

is inserted through wellhead

15

into well

20

, fluid can pass from a relief valve

190

, through openings

176

, annulus

178

and annulus

180

to urge cup seal

93

inwardly so that it will not engage production tubing

32

as it is lowered therethrough. Once the wellhead isolation tool

10

reaches its desired location, fluid flow through relief valve

190

ceases, and in operation, the cup seal

93

will expand to engage production tubing

32

as shown in FIG.

8

. Although in the embodiment shown, the sealing device

91

engages production tubing

32

, the mandrel assembly

70

and sealing device

91

can be used to seal other tubular elements, such as casing

30

in the well

20

.

Wellhead isolation tool

10

includes a support structure

200

. Support structure

200

includes an upper support plate

202

, a lower support plate

204

and a plurality of vertical support members, such as support legs

206

. In the embodiment shown, support structure

200

includes four support legs

206

.

Upper support plate

202

has forward and rear edges

208

and

210

respectively and side edges

212

. Upper support plate

202

has a cutout

214

which may be referred to as a semicircular or generally U-shaped cutout

214

on the forward edge

208

thereof. The U-shaped cutout

214

is adapted to be received in space

120

about body portion

114

of upper central support

110

. Upper support plate

202

has a plurality of openings

216

defined therethrough. Openings

216

are positioned to align with pin receiving holes

122

and

124

so that connectors, such as pins

218

, may be inserted therethrough to mount upper central support

110

to upper support plate

202

. One or more pins

218

may be utilized. Support legs

206

are connected to upper support strips

220

, preferably by welding or other means known in the art, at upper end

222

thereof. Support legs

206

likewise have a lower end

224

. Support legs

206

are connected by welding or other means known in the art at lower end

224

to lower support strips

226

, which may be identical to upper support strips

220

. Support legs

206

have tension rods

228

disposed therein. In the embodiment shown, each of four support legs

206

has a tension rod

228

therein. If desired, tension rods

228

may be included only in the two support legs

206

at the front

12

of wellhead isolation tool

10

. Tension rods

228

have an upper end

230

and a lower end

232

. Upper end

230

is threadedly connected to a tension rod connecter

234

which extends upwardly in support legs

206

through upper support strips

220

and openings

235

defined in upper support plate

202

. Tension rod connectors

234

have an upper end

236

which is threaded so that nuts

238

may be threaded thereon thus connecting support legs

206

and tension rods

228

to upper support plate

202

. A nut and bolt arrangement

239

may be utilized to further connect upper support strips

220

to upper support plate

202

.

Lower end

232

of tension rod

228

is threaded. Tension rods

228

extend through openings defined in lower support strips

226

and through openings

242

defined in lower support plate

204

. Nuts

243

are threaded on lower ends

232

of tension rods

228

to connect tension rods

228

and thus support legs

206

to lower support plate

204

.

Lower support plate

204

has a forward edge

244

, a rear edge

246

and side edges

248

. Forward edge

244

has a semicircular or generally U-shaped cutout

250

so that lower support plate

204

may be received in space

142

between the upper and lower flanges

138

and

140

of lower central support

112

. Upper and lower support plates

202

and

204

may be identical and thus interchangeable. Lower support plate

204

has a plurality of openings

251

positioned to align with pin receiving holes

144

in upper flange

138

and pin receiving holes

146

in lower flange

140

so that pins

252

may be inserted therethrough to mount lower support plate

204

to lower central support

112

. One or more pins

252

may be utilized and may be held in place with a cotter pin or by other means known in the art.

Support structure

200

has a forward, or front

253

, and a back or rear

254

, corresponding to the front and rear

12

and

14

of wellhead isolation tool

10

, and has sides

256

. Support structure

200

further includes a plurality of rear cross braces

260

. The embodiment shown includes three rear cross braces

260

that extend between two support legs

206

at the rear

254

of support structure

200

. Rear cross braces

260

may be connected by welding or by other means known in the art.

Wellhead isolation tool

10

may also include side cross braces

262

at the sides

256

of the well isolation tool

10

. Side cross braces

262

may be connected by welding or otherwise and extend from the support legs

206

at the front

253

of support structure

200

to the support legs

206

at the rear

254

of support structure

200

. Support structure

200

may also include rear angle braces and side angle braces

264

and

266

, respectively, at locations where rear and side cross braces

260

and

262

are mounted. Rear and side angle braces

264

and

266

may be welded or otherwise connected to support legs

206

and to the rear and side cross braces

260

and

262

respectively.

Support structure

200

likewise includes a guide beam

268

. Guide beam

268

essentially comprises an I-beam having a center section

270

, rear flanges

272

and forward flanges

274

extending from center section

270

. Guide beam

268

is mounted to rear cross braces

260

by welding or other means known in the art. Guide beam

268

has an upper end

276

and a lower end

278

. Guide beam

268

has a pair of forward flanges

274

which may be referred to as first and second forward flanges

280

and

282

respectively.

Wellhead isolation tool

10

further includes a roller assembly

284

. A perspective view of roller assembly

284

is shown in FIG.

9

. Roller assembly

284

includes a base

286

which is preferably a circular base, having a cap

288

rigidly connected thereto by welding or other means known in the art as shown in FIG.

10

. Roller assembly

284

also includes a mounting plate

290

, which is rotatably mounted to cap

288

, with a nut and bolt arrangement

292

, and can be rotatably mounted thereto by any means known in the art. For example a hexagon socket head shouldered screw may be utilized to provide the necessary rotation.

FIG. 11

shows a bolt

293

with a shoulder

294

extending through cap

288

. Threads

295

, which are smaller than shoulder

294

, extend through mounting plate

290

, and a nut

296

is threaded thereon. Such an arrangement will allow rotation of cap

288

and base

286

, relative to mounting plate

290

. Roller assembly

284

includes a pair of roller plates

298

, a detail of which is shown in FIG.

12

. Roller plates

298

have first and second sides

300

and