CA2740457C

CA2740457C - Hydraulic set packer system and fracturing methods

Info

Publication number: CA2740457C
Application number: CA2740457A
Authority: CA
Inventors: Raymond Lockhurst; Christopher Bogue
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-05-13
Filing date: 2011-05-13
Publication date: 2018-10-02
Anticipated expiration: 2031-05-13
Also published as: CA2740457A1

Abstract

A hydraulic set packer system includes an upper assembly directly responsive to fracturing fluid pressure to provide an upper seal for the zone of interest; and a lower assembly directly responsive to fracturing fluid pressure to allow fracturing fluid to flow into the zone of interest and indirectly responsive to fracturing fluid pressure through a self- contained hydraulically sealed lower chamber to provide a lower seal for the zone of interest. By increasing and decreasing the fracturing fluid pressure, the hydraulic set packer system may be used alternately to seal and isolate the zone of interest, and to easily unseal and retrieve or move the packer system.

Description

HYDRAULIC SET PACKER SYSTEM AND FRACTURING METHODS
Field of the Invention [0001] The present invention relates to a hydraulic set packer system and methods for fracturing a zonc of interest in a subterranean formation with a hydraulic set packing system through a wellbore for the production of oil, gas or other formation fluids, Background of the Invention [00021 Packer systems are used to isolate zones of a wellbore casing for fracturing and stimulation processes in the production of oil and gas. A conventional packer includes a cylindrical expandable sealing element that engages the inner surface of a wellbore casing and thereby prevents the passage of fluids above or below the packer within the casing.
100031 In a fracturing method, two packers disposed at a distance from each other within the casing will isolate a zone of interest between them in the formation rock.
Fracturing fluid is then pumped into the isolated zone at a very high rate sufficient to increase the fluid pressure.
This increased pressure causes the surrounding formation rock to crack, and the fluid enters into and propagates the crack, Solid proppants, such as sand, may be added to the fracture fluid to maintain the crack in an open position and thereby form a high permeability conduit through which the formation fluids can flow into the wellbore.
[0004] Typically packers are set in the wellbore casing by inserting the packer into the easing using production tubing or wire line tools. When the packer reaches the desired depth, axial load is applied to the sealing element by mechanical force, hydraulic pressure or a

2 combination thereof to cause the sealing element to expand radially and engage the inner surface of the wellbore casing and thereby plug the wellbore.
[0005] Operational problems are well known in the use of packers. Wear of the sealing elements may impair the effectiveness of the packer. Packers may inadvertently become stuck during the setting process or be difficult to retrieve. Therefore, there is a continuing need to improve the state of the art in packer technology used in wellbore fracturing for production of formation fluids.
SUMMARY OF THE INVENTION
[0006] A hydraulic set packer system includes an upper assembly directly responsive to fracturing fluid pressure to provide an upper seal for the zone of interest;
and a lower assembly directly responsive to fracturing fluid pressure to allow fracturing fluid to flow into the zone of interest and indirectly responsive to fracturing fluid pressure through a self-contained hydraulically sealed lower chamber to provide a lower seal for the zone of interest.
By increasing and decreasing the fracturing fluid pressure, the hydraulic set packer system may be used alternately to seal and isolate the zone of interest, and to easily unseal and retrieve or move the packer system.
[0007] In one aspect, the invention comprises a hydraulic set packer system, having radial and axial directions, for use and connection with production tubing, comprising:
(a) an upper assembly defining an internal bore in fluid communication with the production tubing, an elastomeric annular upper seal, an upper piston, wherein

3 fluid pressure in the internal bore actuates the upper piston to compress the upper seal and expand the upper seal radially; and (b) a lower assembly defining a frac port in fluid communication with the upper assembly internal bore, a frac piston which reciprocates between a closed position which occludes the frac port, and an open position which does not occlude the frac port, an elastomeric annular lower seal, an internal hydraulic lower piston chamber, and a lower piston, wherein fluid pressure in the upper assembly internal bore acts on the frac piston to move it to its open position, and wherein movement of the frac piston to its open position compresses the internal hydraulic lower piston chamber to actuate the lower piston to compress the lower seal and expand the lower seal radially.
[0008] in another aspect, the invention comprises a method of fracturing a formation rock zone of interest with a hydraulic set packing system through a wellbore using a hydraulic set packer as described, BRIEF DESCRIPTION OF THE DRAWINGS
[0009] In the drawings, like elements are assigned like reference numerals.
The drawings are not necessarily to scale, with the emphasis instead placed upon the principles of the present invention. Additionally, each of the embodiments depicted are but one of a number of possible arrangements utilizing the fundamental concepts of the present invention. The drawings are briefly described as follows:

4 [0010] FIG. 1 is an elevation view of the upper assembly of the hydraulic set packer system connected to cross-over subs;
[0011] FIG. 2 is an elevation view of the lower assembly of the hydraulic set packer system connected to a cross-over sub;
[0012] FIG. 3 is a larger scale elevation view of the upper assembly of the hydraulic set packer system shown in FIG. 1 between line A and line 11;
[0013] FIG. 4 is a larger scale enlarged view of the lower assembly of the hydraulic set packer system of FIG. 2 between line C and line D.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0014] The present invention relates to a hydraulic set packer system and inethods for fracturing a zone of interest in formation rock with a hydraulic set packing system through a wellbore for the production of oil, gas or other formation fluids. When describing the present invention, all terms not defined heroin have their common art-recognized meanings. To the extent that the following description is of a specific embodiment or a particular use of the invention, it is intended to be illustrative only, and not limiting of the claimed invention. The following description is intended to cover all alternatives, modifications and equivalents that are included in the spirit and scope of the invention, as defined in the appended claims.
[0015] The terms "upper" and ''lower" as used herein denote the relative positions of various elements or components when the system is deployed in a substantially vertical orientation.

5 [00161 As shown in Figure 1 and 2, a hydraulic set packer system comprises an upper assembly (1) having an upper seal and a lower assembly (8) having a lower seal. The upper assembly and the lower assembly are connected by a pup joint, the length of which will define the fracturing zone between the upper and lower assemblies.
[00171 As shown in Figure 1, the upper assembly (1) comprises an upper mandrel (3), upper seal (4), upper piston (5) and upper housing (6). The upper seal (4) is typically constructed with rubber or other elastomer or other material having sealing and deformation properties suitable for use at high pressure and temperature. Suitable sealing material is well known in the art.
[00181 As shown in Figure 3, the upper mandrel (3) defines a through bore and has a widened upper cross-section defining an upper seal retaining lip (3a), a narrower lower-eross section defining an upper spindle (3b), and a lower spindle (3c). The lower spindle defines at least one port (3d). The annular upper seal (4) fits tightly around the upper spindle (3b) and is retained at its top end by the upper retainer (3a) and at its bottom end by the upper piston (5).
The annular upper piston (5) is retained at its top end by the upper seal (4) and its bottom end by the upper housing (6). A crossover sub (7) is connected to the upper housing (6) and provides a connection to a pup joint (not shown) which spans between the upper and lower assemblies.
[0019] The upper housing (6) is connected at its top end to the lower spindle (3c) of the upper mandrel (3) by a sealed threaded connection. The upper housing (6), upper spindle (3b), upper port (3d) and upper piston (5) collectively define an upper piston chamber (6a) in fluid

6 communication with the through bore of the upper mandrel (3) through ports (3d). The upper piston (5) is disposed within the piston chamber and fits around the upper spindle (3b), and reciprocates slidingly around the upper spindle (3b) and lower spindle (3c) within the upper housing (6), 0-ring seals (5a, 5b) seal the upper piston chamber. Upper chamber seal (6b) provides a seal below the upper chamber (6a).
[0020] The top of the upper piston (5) defines a seal retaining lip and bears on the seal. A
spring or other biasing means (not shown) may be provided in the space between the upper mandrel (3) and the upper piston (5) to bias the upper piston to a lower position.
[0021] As shown in Figure 2, in one embodiment, the lower assembly (8) comprises a crossover sub (9) which connects to the lower end of a pup joint (not shown), a frac sub (10) defining at least one frac port (10a), a frac piston (11), a frac housing (12), a lower mandrel (14), a lower seal (15), a lower piston (16) and a lower sub (17). The lower seal (15) is typically constructed with rubber, or other elastomer, or other material having sealing and deformation properties suitable for use at high pressure and temperature.
Suitable sealing materials are well known in the art.
[0022] As shown in Figure 4, the frac sub (10) has an inner bore and frac ports (10a) that are in fluid communication with the upper bore (3c) of the upper assembly (1). The frac housing (12) is connected at its top end to the bottom end of the frac sub (10) by sealed threaded connection. The lower mandrel (14) is connected at its top end to the bottom end of the frac housing (12) by a sealed threaded connection. The lower mandrel (14) defines a through bore and has a widened upper cross-section having a lower seal retaining lip (14a), a narrower

7 lower-cross section defining an upper spindle (14b), and a lower spindle (14c), The lower spindle extends into thc lower sub (17) and defines a port (14d) which provides fluid communication to the lower mandrel (14) throughbore.
[0023] The frac piston (11) is inserted into and sealingly reciprocates within frac housing (12) and the frac sub (10) between a closed position in which the upper end of the frac piston occludes the frac ports (10a) and an open position that does not occlude the frac ports (10a).
0-ring seals are provided which seal the frac piston within the frac housing (12) and frac piston seals (11a) are provided which seal the base portion of the frac piston within the frac housing (12). A biasing means (13) such as a spring disposed between and bearing on the base portion of the frac piston (11) and the top end of the lower mandrel (14) biases the frac piston (11) to its closed position.
[0024] The annular lower seal (15) fits tightly around the lower spindle (14b) and is retained at its top end by the retaining lip (14a), and at its bottom end by the lower piston (16). The annular lower piston (16) bears on the lower seal (4) and is retained within the bottom sub (17). The lower piston (16) fits tightly around the lower spindle (14b) but is capable of sliding along the lower spindle (14b) and within thc bottom sub (17). The cup-shaped bottom sub (17) is connected to the bottom end of the lower mandrel (14) by a sealed threaded connection. , [0025] The frac housing (12), frac piston (11), lower hydraulic bore (14c), lower port (14d), bottom sub (17) and lower piston (16) collectively define a sealed fluid-tight lower piston chamber (17a) filled with a hydraulic fluid such as mineral oil or other low compressibility

8 fluid. Lower piston inside seals (16a) and lower piston outside seals (16b) may be used to form a tight fit between the lower piston (16) and the lower spindle (14b) and the inner bore of the bottom sub (17), respectively.
[0026] In operation, the upper assembly and lower assembly (8) are connected by a pup joint (not shown) the length of which defines the zone of interest, between the upper seal and the lower seal.
[0027] The upper and lower assemblies are then lowered within the wellbore casing on coiled or jointed tubing as is well known in the art, until the lower seal (15) and the upper seal (4) reach the depth of the bottom and top, respectively, of the desired isolation zone in the subterranean formation.
[0028] Fracturing fluid is then pumped at a high rate into the production tubing. The fracturing fluid flows through the upper bore (3c) of the upper assembly (1), through the production tubing, and into the frac sub (10) of thc lower assembly (8). At the upper assembly (1), the fracturing fluid also flows through the upper bore (3c), through the upper port (3d) and into the upper chamber (6a). The attendant hydraulic pressure in the upper chamber (6a) is sufficient to displace the upper piston (5) upwards by axial compression of the upper seal (4) against the upper retaining lip (3a). As the upper seal (4) is upwardly compressed in the axial direction, it expands radially and tightly seals against the inner surface of the wellbore casing.
[0029] At the lower assembly (8), the fracturing fluid flows into the frac sub (10) and against the top end of the frac piston (11). The attendant hydraulic pressure exerted on the top end of

9 the frac piston (11) is sufficient to overcome the closing force exerted on the frac piston (11) by the spring (13). The frac piston (11) is thereby displaced in the downward axial direction to its open position allowing fracturing fluid to flow into the surrounding formation rock through the frac ports (10a). As the frac piston (11) displaces downward to its open position, it also pressurizes the hydraulic fluid in the lower piston chamber (17a). The attendant hydraulic pressure in the lower piston chamber (17a) displaces the lower piston (16) upwards by axial compression of the lower seal (15) against the lower retainer (14a). As the lower seal (15) is upwardly compressed in the axial direction, it expands radially and tightly seals against the inner surface of the wellbore casing.
[0030] Once the formation rock has been satisfactorily fractured, the fracturing fluid pumping pressure in the production tubing is decreased. Consequently, the hydraulic pressure within the upper chamber (6a) decreases and the upper piston (5) displaces downward as the upper seal (4) expands axially and contracts radially from the inner surface of the wellbore casing. If installed, a spring may also urge the upper piston downwards. The spring may be necessary if retraction of the seal does not provide sufficient force to move the upper piston (5) downward after pressure in the production tubing is reduced, [0031] Likewise, the hydraulic pressure on the frac piston (11) decreases and it is urged upwards by the spring (13) to its closed position. The hydraulic pressure within the lower piston chamber (17a) is thereby decreased, the lower piston (16) moves downwards, and the lower seal (15) expands axially and contracts radially from the inner surface of the wellbore casing. With the upper seal (4) and the lower seal (15) disengaged from the inner surface of

10 the wellbore casing, the upper assembly (1) and lower assembly (8) may be retrieved from the wellbore casing.
[00321 One skilled in the art will recognize that the geometric and mechanical properties of the constituent parts of the upper assembly (1) and the lower assembly (8) may be selected to allow for a differential between the onset of the upper seal (4) sealing against the inner surface of the wellbore casing, the onset of the lower seal (15) scaling against the inner surface of the wellbore casing and the onset of fracturing fluid flowing through the frac ports (10a) of the frac sub (10).

Claims

1. A hydraulic set packer system, having radial and axial directions, for use and connection with production tubing, comprising:
(a) an upper assembly defining an internal bore in fluid communication with the production tubing, an elastomeric annular upper seal, an upper piston, wherein fluid pressure in the internal bore actuates the upper piston to compress the upper seal and expand the upper seal radially; and (b) a lower assembly comprising a frac port in fluid communication with the upper assembly internal bore, a frac piston which reciprocates between a closed position which occludes the frac port, and an open position which does not occlude the frac port, an elastomeric annular lower seal, an internal hydraulic lower piston chamber, and a lower piston, wherein fluid pressure in the upper assembly internal bore acts on the frac piston to move it to its open position, and wherein movement of the frac piston to its open position compresses the internal hydraulic lower piston chamber to actuate the lower piston to compress the lower seal and expand the lower seal radially.

2. The hydraulic set packer system of claim 1 wherein the upper assembly comprises:
(a) an upper mandrel having an upper seal retaining lip and defining an inner bore and at least one fluid port;
(b) an upper housing rigidly connected to the upper mandrel and forming an upper piston chamber therebetween;

(c) wherein the upper seal is disposed radially around the upper mandrel and retained in the axial direction between the upper seal retaining lip and the upper piston which is disposed radially around the upper mandrel within the upper piston chamber;
(d) wherein the upper piston chamber is in fluid communication with the upper mandrel inner bore through the at least one fluid port; and (e) wherein the upper piston is responsive to increasing hydraulic pressure in the upper piston chamber by displacing along the upper mandrel in the axial direction and compressing the upper seal in the axial direction.

3. The hydraulic set packer system of claim 2 wherein the lower assembly comprises;
(a) a frac sub defining the frac port in fluid communication with the upper mandrel inner bore;
(b) a frac housing rigidly connected to the frac sub and a lower mandrel, wherein the frac housing is disposed between the frac sub and the lower mandrel in the axial direction, wherein the frac housing defines an internal hydraulic chamber;
(c) wherein the frac piston is disposed within the frac housing hydraulic chamber and moveable in the axial direction between the closed position and the open position;
(d) a biasing means disposed between the frac piston and the lower mandrel in the axial direction and biasing the frac piston to the closed position;

(e) wherein the lower mandrel comprises a lower seal retaining lip and defines an internal hydraulic bore;
(f) wherein the lower seal is disposed radially around the lower mandrel and retained in the axial direction between the lower seal retaining lip and the lower piston which is disposed radially around the lower mandrel and bears on the lower seal;
(g) a bottom sub which defines the lower piston chamber in sealed fluid communication with the lower mandrel hydraulic bore;
(h) wherein the frac piston is responsive to increasing hydraulic pressure in the upper assembly by displacing within the frac housing in the axial direction to the open position; and (i) wherein the movement of the frac piston increases hydraulic pressure in the frac housing internal chamber, the lower mandrel hydraulic bore, and the lower piston chamber, thereby actuating the lower piston to compress the lower seal in the axial direction.

4. A method of fracturing a subterranean formation zone of interest with a hydraulic set packing system through a wellbore comprising the steps of:
(a) lowering the system of Claim 1, 2 or 3 down hole into a wellbore to the zone of interest;
(b) increasing the pumping pressure of fracturing fluid in the system to:

(i) to seal the upper seal against the inner surface of the wellbore; and (ii) displace the frac piston to its open position so as to seal the lower seal against the inner surface of the wellbore and allow the fracturing fluid to egress through the frac openings into the zone of interest.