CA2898932A1 - Methods and apparatus for wellbore annulus cementing - Google Patents

Abstract

A tubular installation in place in a wellbore includes a tubing string and cemented annular zones and annular zones free of cement between the tubing string and the wellbore wall. The annular zones are isolated from each other by annular packers on the tubing and the cemented annular zones are cemented through at least a pair of cementing ports axially spaced apart along the wall of the tubular string each providing communication between the inner bore and the annular zone to be cemented.
Cement in each cemented zone is introduced through a first of the cementing ports, with cement circulation permitted by evacuation from the zone through a second of the cementing ports. The cemented zones stabilize the wellbore and annular zones free of cement are open to receive fracing fluid through a frac port on the tubing string.

Description

Methods and Apparatus for Wellbore Annulus Cementing Field The present invention relates to wellbore methods and apparatus and, in particular, a methods and apparatus for assisting annulus cementing operations.
Background Wellbores are often completed by introduction of cement around the tubular in the annulus between the tubular and the borehole wall. The cement holds the tubular in place in the well and creates isolation by controlling against fluid passage through the wellbore annulus from one section of the well to another. Isolation serves the purpose of preventing flow of fluids or gas from one section of a well that may be undesirable such as water, to a section of the well that would otherwise produce hydrocarbon.
In addition, certain operations require that fluid be placed into the well at specific locations. These operations may include acidizing or hydraulic fracturing. The cement in these cases provides isolation by containing the fluid placement to the desired locations in the well to produce desired results. If ports are placed along a tubular string in the well, either cement or packers can be used to isolate one section of the well about one or more ports from one another section. If the ports are cemented in place, the cement circulated into the annulus section of the well may cause problems operating the WSLega1\045023\00454\12248506v1 ports. In addition, the ability to inject fluid into the formation through the ports may prove difficult because the cement will prevent contact and communication with the formation rock. If fracturing is planned, the cement in the annulus may require unreasonably high fracture initiation pressures.
When a ported tubular is positioned in a well, cement generally cannot be used in the usual way since the cement will block the outside of the port such that although the port is opened, fluid treatments are blocked from entering the wellbore because of the presence of the cement. If fluid is introduced at a pressure that would normally fracture the well, the force of the fluid injection is distributed over a wider area by the cement such that the force is dissipated and the treatment may be rendered less than effective.
Summary The invention relates to methods and apparatus for assisting annulus cementing operations by cementing some annular zones of the well while other are left uncemented and to provide the option to either perforate or to activate or open and close ports within these uncemented areas.
If ports are used and the annulus surrounding the ports is not cemented, but the adjoining areas on each side of the ports contain cement in the annulus, then the ports, when opened, will provide direct contact with the formation for production or fluid placement (formation stimulation), and at the same time cement is present in some zones to permit zonal isolation.
This invention provides a wellbore tubular, a method and a wellbore tubular installation to allow cementing of the annulus while leaving the area surrounding the ports uncemented.
WSLega1\045023 \00454 \12248506v1 2 In accordance with a broad aspect of the present invention, there is provided method for installing a tubular string in a wellbore, the method comprising: providing a tubular string including an inner bore and an outer surface, an upper annular packer encircling the tubular string, a middle annular packer encircling the tubular string below the upper annular packer and a lower annular packer encircling the tubular string below the middle annular packer, the upper annular packer and; running the tubular string into the wellbore to create an annulus between the tubular string and the wellbore wall; setting the packers to create (i) a first annular zone between the upper annular packer and the middle annular packer and (ii) a second annular zone between the middle annular packer and the lower annular packer, with the middle annular packer isolating the first annular zone from the second annular zone; cementing the second annular zone by pumping cement through a cementing inlet port from the tubular string into the second annular zone while fluids are circulated out of the second annular zone through a cementing outlet port, while the first annular zone is isolated from introduction of cement thereto; and allowing the cement to set.
In accordance with another broad aspect of the present invention, there is provided a wellbore tubing string comprising: an uphole end; an opposite downhole end; a wall defined between an inner bore extending from the uphole end to the opposite downhole end and an outer surface; a frac port through the wall providing communication between the inner bore and the outer surface, the frac port including an openable closure; a cementing inlet port through the wall providing communication between the inner bore and the outer surface; a cementing outlet port through the wall providing communication between the inner bore and the outer surface; an upper annular packer encircling the outer surface and positioned between the uphole end and the frac port; a middle annular packer encircling the outer surface and positioned between the frac port and a portion of the tubing string in which the cementing inlet and outlet ports are positioned;
and a lower annular packer encircling the outer surface and positioned between the portion of the tubing string and the opposite downhole end.
WSLega1\045023\00454\12248506v1 3 In accordance with another broad aspect of the present invention, there is provided a wellbore installation comprising: a borehole passing through a formation; a tubing string in the borehole creating an annular space between the tubing string and a formation wall exposed in the borehole, the tubing string including an uphole end; an opposite downhole end; a wall defined between an inner bore extending from the uphole end to the opposite downhole end and an outer surface; a frac port through the wall providing communication between the inner bore and the outer surface, the frac port including an openable closure; a cementing inlet port through the wall providing communication between the inner bore and the outer surface; a cementing outlet port through the wall providing communication between the inner bore and the outer surface; an upper annular packer encircling the outer surface and positioned between the uphole end and the frac port; a middle annular packer encircling the outer surface and positioned between the frac port and a portion of the tubing string in which the cementing inlet and outlet ports are positioned; and a lower annular packer encircling the outer surface and positioned between the portion of the tubing string and the opposite downhole end; the upper, middle and lower annular packers each being expanded to each create a seal in the annular space to isolate communication between the frac port and the portion of the tubing string, the middle annular packer and the lower annular packer creating an isolated annular zone accessed only through the cementing inlet arid outlet ports.
It is to be understood that other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein various embodiments of the invention are shown and described by way of illustration.
As will be realized, the invention is capable for other and different embodiments and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present invention. Accordingly the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.
WSLegal\045023\00454\12248506v1 4 Brief Description of the Drawings Referring to the drawings, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein:
Figure 1 is a schematic sectional view along a portion of a well bore with a tubing string therein, according to one aspect of the invention;
Figure 2 is a sectional view along the well bore of Figure 1 during a cementing operation; and Figure 3 is a sectional view along the well bore of Figure 2 following a cementing operation.
Description of Various Embodiments The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.
With reference to the Figure 1, a wellbore tubing string and an installation are shown according to various aspects of the present invention.
The invention provides a wellbore installation wherein some portions of the wellbore may be cemented and other portions of the wellbore may be left uncemented. The VVSLega1\045023\00454\12248506v1 5 uncemented portions may be present between cemented portions. The uncemented portions provide a zone of the wellbore that may be particularly suited to direct wellbore treatment fluid to the formation wall, which is left exposed in the wellbore by avoiding the placement of cement into that zone. The cemented portions, however, ensure wellbore stability and annular control. The use of cemented portions and their resultant wellbore stability and annular control may be particularly useful in unconsolidated formations, such as, for example, oil sand formations 8.
A wellbore tubing string 10 is installable in a wellbore 12 bored into formation 8.
VVellbore tubing string 10 includes a uphole end, an opposite downhole end and a wall defined between an inner bore 10a extending from the first end to the opposite end and an outer surface 10b; one or more frac ports 16 through the wall of the tubing string providing communication between the inner bore and the outer surface, each frac port including an openable closure 18. The frac ports and their openable closures may take various forms. For example, the frac ports may be open, have jetting or limited entry inserts, etc. and the openable closures may include burst discs, dissolvable materials, a shearable cap, a sliding sleeve valve (as shown), etc.
The tubing string further includes at least a pair of cementing ports 24a, 24b axially spaced apart along the wall of the tubing string each providing communication between the inner bore and the outer surface. In operation, one 24a of the cementing ports becomes the cementing inlet port and the other 24b of the cementing ports becomes the cementing outlet port. The cementing ports 24a, 24b allow cement to be pumped from within the string into the annular space. Ports 24a, 24b may be axially spaced apart along the string but are in communication the annular space 40 such that cement can be pumped into one port and the other port can permits evacuation of fluids as the annular space is filled with cement. After cement is introduced to the annular space, the cement is held in the annular space until it sets. As such, cementing ports 24a, 24b WSLega1\045023\00454\12248506v1 6 may take various forms. For example, the cementing ports may be open or have closures 26 that move to open and/or close the ports when actuated to do so.
For example, the cementing ports, if openable or closeable may include closures such as burst discs, shearable caps, sliding sleeve valves, check valves (to permit one way flow), closing mechanisms, such as a back up sleeve, etc. The two ports may be substantially the same in construction and the type of closure or one may be configured more for inlet functionality and the other may be configured to facilitate outlet functionality. In one embodiment, each cementing port includes an openable closure, such as a sliding sleeve valve. In one embodiment, the openable closure on one or both of the cementing ports operates as a check valve in response to pressure differentials established across the closure. For example, the check valve for a cementing inlet port may open when pressures inside the tubular string are greater than pressures in the annulus 40 and the check valve for a cementing outlet port may open when pressures inside the tubular string are less than pressures in the annulus 40, as may be the pressure situation during a cement pumping operation into an annular zone accessed by ports 24a, 24b.
The tubing string further includes packers 20a ¨ 20f including a liner hanger packer 20a, a first or upper annular packer 20b encircling the tubing string wall and positioned between the upper end and frac port 16, a second or middle annular packer 20c encircling the tubing string and positioned between frac port 15 and the portion of the string in which cementing ports 24a, 24b are located and a third or lower annular packer 20d encircling the tubing string and positioned between the portion of the string in which cementing ports 24a, 24b are located and the opposite downhole end of the string. The annular packers may also take various forms. The packers may be expandable, inflatable, etc. In one embodiment, the packers are solid body-type packers such as including one or more extrudable elements 21a, 21b that set to form a solid (not inflated) annular seal about the string, the solid material filling the space between the tubing string on which it is installed and the wellbore wall. The extrudable elements may be WSLegall045023\00454 112248506v1 7 ' driven to expand by hydraulic swelling or compression drivers that move compression rings against opposite sides of the element to axially squeeze it and cause the element to move radially outwardly. For example, one useful packer type may be a hydraulically driven compression set packer such as one available from the assignee of this application, under the trade name RocksealTM.
The wellbore tubing string may be used to form a tubular installation for placement in a wellbore. In such an installation an annular space 40 may be formed between the tubing string and a wall 12 of the borehole. Using a wellbore tubular such as that described above as an example, the tubular installation may include the wellbore tubular placed in the wellbore with the first, the second and the third annular packers each expanded. In such an installation, the packers divide the annular space into a plurality of annular zones which are each isolated along the annulus from the others.
For example, there is a first or upper annular zone 40a between the first and the second packers and a second annular zone 40b between the second packer and the lower packer. When set against wellbore wall 12, the second annular packer 20c isolates zone 40a from zone 40b. In other words, packer 20c seals against communication between the frac port 16 and cementing ports 24a, 24b through the annular space.
Third annular packer 20d seals against fluid communication along the annular space between the cementing ports and the annular space downhole of the lower packer, which in this embodiment includes an uncemented annular zone 40a between packers 20d and 20e and a cemented zone 40b between packers 20e and 20f.
The string is cemented in the wellbore using the cementing ports and the annular zones that are cemented are limited by packers. For example, packers 20c and 20d limited the axial length of the annular space that can be filled with cement. Since cementing ports permit flow into the annular space, to facilitate filling cement into the annular space, one cementing port 24a is positioned close to one packer 20d and the other WSLega1\045023 \00454 \ 12248506v1 5 cementing port is axially spaced away from the cementing port 24a and is positioned close to the other packer 20c.
The assembly may include a cementing apparatus 52 to facilitate zonal cementing. A
cementing apparatus may be employed to actuate the closures to be openable, to set a seal in the inner bore to divert cement and possibly also to conduct cement to the cementing inlet port. If a cementing string is employed it is run into the tubular string after the tubular string is set in the well.
In one embodiment, the cementing apparatus manipulates the closure for one or both of the cementing ports and then is manipulated to set a seal at least below the inlet cementing port and possibly as well above the inlet cementing port. The seals may straddle the inlet cementing port to ensure that cement enters the inlet cementing port.
The apparatus directs cement to the cementing inlet port 24a and permits cement to circulate through the string away from the cementing outlet port 24b. In one embodiment, the cementing apparatus includes a seal 54 to divert cement introduced from above within the string to the cementing inlet port. In another embodiment, the cementing apparatus includes a cementing string 56 that includes an inner bore through which cement can be conducted. String 56 can be run within the liner string and carries seal 54. String 56 may also include an upper seal 58.
Such an installation may be employed to cement a tubular string in a wellbore.

According to one embodiment, the method may include first using a tubular string including a frac port 16 extending from an inner bore of the string to open on the outer surface, at least a pair of cementing ports 24a, 24b axially spaced apart along the wall of the tubing string each providing communication between the inner bore and the outer surface, an upper annular packer 20b encircling the tubular string above the frac port and an intermediate annular packer 20c encircling the tubular string below the frac port and above both of the cementing ports and a lower annular packer 20d encircling the wsLegan45023\00454\122485060 9 tubular string below the cementing ports. The upper annular packer and the intermediate annular packer form a first zone 40a between them along the wellbore and the intermediate annular packer and the lower annular packer form a second zone 40b between them along the wellbore and the first zone is annularly isolated from the second zone.
Such a tubular string can be run into the wellbore, thereby creating an annulus between the tubular and a wall of the wellbore. Of course, running in the string may be by methods well known in the art. In such an embodiment, the inner bore 10a of the tubular may be in communication with the surface through an upper string extending above the tubular. Once in position in the wellbore, the packers may be set to form the zones and to annularly isolate the first zone 40a from the second zone 40b. To set, the packers may be expanded or allowed to expand to encircle the tubing string and fill the annular space between the tubular string and the wellbore wall. This isolates the zone on one side of a packer from the zone on the other side of a packer and prevents annular fluid communication between the zones.
Thereafter, cement may be pumped (arrows C) into second zone 40b by use of the cementing ports 24a, 24b, for example, into the zone through cementing inlet port 24a while cementing outlet port 24b allows circulation of fluid out of the zone to permit filling by cement. Cement is not introduced into the first zone.
Cement is introduced directly and specifically to the second zone while the first zone is maintained free of cement. First zone may be protected against infiltration of cement by at least closure 18 which remains closed over the frac port. Alternately or in addition, the cementing operation may be selected to only permit cement to flow in the tubing string adjacent ports 24a, 24b, as by use of straddle packing tools. In any event, while second zone 40b is cemented, the first zone remains uncemented and open to receive fracing fluid through the frac port.
WSLega1\045023\00454\12248506v1 10 If cementing ports 24a, 24b are not already open, in one embodiment, a cementing operating includes actuating the cementing ports to permit flow therethrough before introducing cement into the second zone via the cementing inlet port 24a.
Actuating may be electrically, mechanically or hydraulically.
Cement enters the second zone through the cementing inlet port and can be pumped to fill the second zone between the intermediate and lower annular packers by evacuating fluid through the second of the cementing ports: the outlet cementing port.
Cementing may include setting a seal, such as seal 54, in the inner bore of the tubular string below one of the cementing ports in the second zone such that cement introduced from surface can be diverted into the cementing port rather than passing down through the well beyond the cementing port of the zone being cemented.
Cementing may also or alternately include pumping cement after installing a seal in the inner bore between the first of the cementing ports and the second of the cementing ports such that a circulation path is establishable leading to the first of the cementing ports and on the opposite side of the seal leading away from the second of the cementing ports.
In one embodiment, a cementing string 52 may be employed. Cement may be conducted through or alongside the cementing string from above, for example, from surface, to pass through the cementing inlet port and enter the second zone.
The setting of seals may be through use of the cementing string, including running into the inner bore of the tubular string with cementing string 52 to set one or both seals.
The cementing string may possibly also actuate the closures of the cementing ports and/or act as the conduit to conduct cement to or away from the cementing ports. In WSLega1\045023\00454\12248506v1 11 one embodiment, the cementing string includes a tubing string and creates an annulus between the cementing string and the tubing string inner wall. Thus, two conduits are formed through the tubing string: a first conduit through the inner bore of the cementing string and a second conduit through the annulus between the cementing string and the tubing string inner wall. Cement can be pumped down one of the conduits and cement or fluids being pushed ahead of the cement, may move up through the other conduit.
Thus, a circulation path is established.
Generally annulus cement is often pumped down through the tubular string inner bore and up through the annular area. Thus, cement may be pumped from a lower of the two cementing ports in each zone to be cemented up through the annular area to the second cementing port in that zone. Pumping is continued until the zone is substantially filled with cement, such as when cement exits the uppermost (i.e. the one closest to surface) of the two cementing ports in that zone. However, it is to be understood that the method encompasses, and the wellbore tubular string is useful for, a reverse cementing procedure where cement is pumped down from the upper most cementing port towards the lowermost cementing port in that zone.
After the cement is pumped through the annular space to fill the zone, the cement is allowed to set as by holding the cement in the annular space by holding pressure against the weight of the cement or by use of closures for the cementing ports. The cementing string may actuate the cementing ports to close them to maintain the cement in the second zone and to allow the cement to set.
Cementing occurs through the cementing ports into the second zone and no cement is introduced into the first zone. As such the tubular can be annularly cemented into the wellbore, for example to stabilize the wellbore in an unconsolidated, such as oil sand formation, while leaving the annular area about the frac port of the tubular string open.
As such, the wellbore is supported in the second zone while fluids can pass from the WSLega1\045023 00454112248506v1 12 inner bore of the tubular out into contact with the wellbore (and vice versa) in the first zone without hindrance by avoiding the placement of cement about the frac port 16.
Thereafter, the frac port may be opened by, for example, moving or removing its closure. Wellbore operations can then begin, for example, production or wellbore treatments though the frac port such as for example by injection of fracturing fluid, stimulation fluids, etc. Treatment fluids can pass through the inner bore of the string and out through the frac port into contact with the wellbore without hindrance by cement in the annular region about the frac port. Fluids, for example, may effect a fracing operation such as that shown wherein fractures 62 are generated in the formation 8 about the wellbore.
The cement employed is selected to stabilize the formation and to inhibit axial annular migration of fluids. The cement may be selected in an oil sands formation to withstand the wellbore operations carried out in the well. In one embodiment, the cement is resistant to solvent-induced breakdown as when the formation is produced by solvent injection. In another embodiment, for example, the cement is thermally stable to withstand formation heating for example used in situ oil sand formations.
Heating may be by steam injection, combustion, etc. for example, using steam assisted gravity drainage (SAGD).
If the well includes further zones to be cemented, they may be each cemented one zone at a time. The plurality of zones may be all cemented in one operation. If a cementing apparatus is employed, the string may be moved through the tubular string 10 to cement one zone, then moved to cement the further zones (for example the zone uphole of packer 20b). The cementing apparatus may manipulate any closures for the cementing ports in those further zones and possibly conduct and/or divert cement into the further zones.
WSLega1\045023\00454\12248506v1 13 In a usual installation, there will be a number of cemented zones and a number of open, uncemented zones. The open uncemented zones are positioned in formations to be treated. Cemented zones may straddle the open, uncemented zones.
The frac port and the cementing ports may be opened by various means such as by tubing manipulation, bursting, shearing, check valves, etc. For example, the cementing ports may be opened by bursting or movement by physical engagement or hydraulics.
In one embodiment the closures 26 are each sliding sleeve type valves opened by physical engagement or hydraulics. Alternately or in addition, the cementing ports may be opened all at once, as by use of a hydraulically openable valve as disclosed in applicants corresponding PCT application PCT/CA2009/000599, filed April 29, 2009.
Likewise the frac ports may be opened by physical engagement or hydraulic movement of a sliding sleeve type valve, apart from the opening of the cementing ports.
In one embodiment, for example, the frac port is closed by a sliding sleeve valve 18 that is actuated by a device, such as a ball or plug, which can be conveyed by gravity or fluid flow through the tubing string. The device, in this case ball, engages against the sleeve and, when pressure is applied through the inner bore, as from surface through a string to the tool, the ball seats against and creates a pressure differential above and below the sleeve which drives the sleeve toward the lower pressure side.
In the illustrated embodiment, the inner surface of the sleeve which is open to the inner bore of the sub defines a seat onto which a suitably sized ball, when launched from surface, can land and seal thereagainst. When the ball seals against the sleeve seat and pressure is applied or increased from surface, a pressure differential is set up which causes the sliding sleeve on which the ball has landed to slide to a port-open position.
When the port is opened, fluid can flow therethrough to the annulus between the tubing string and the wellbore and thereafter into contact with formation.
WSLega1\045023\00454\12248506v1 14 The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope consistent with the claims, wherein reference to an element in the singular, such as by use of the article "a" or "an" is not intended to mean "one and only one" unless specifically so stated, but rather "one or more". All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are know or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 USC 112, sixth paragraph, unless the element is expressly recited using the phrase "means for" or "step for".
WSLega1\045023\00454\12248506v1 15

Claims (22)

l claim:

1. A method for installing a tubular string in a wellbore, the tubular string including a frac port extending from an inner bore of the string to open on the outer surface, at least a pair of cementing ports axially spaced apart along the wall of the tubing string each providing communication between the inner bore and the outer surface, an upper annular packer encircling the tubular string above the frac port and an intermediate annular packer encircling the tubular string below the frac port and above both of the cementing ports and a lower annular packer encircling the tubular string below the cementing ports, the upper annular packer and the intermediate annular packer forming a first zone between them along the wellbore and the intermediate annular packer and the lower annular packer forming a second zone between them along the wellbore and the first zone being annularly isolated from the second zone, such a tubular string defining an annulus between the tubular string and a wall of the wellbore, the method comprising: pumping cement into the second zone through a first of the cementing ports, with cement circulation permitted by evacuation from the second zone through a second of the cementing ports and leaving the first zone uncemented and open to receive fracing fluid through the frac port; and allowing the cement to set in the second zone.

2. The method of claim 1 further comprising: opening the frac port after allowing the cement to set.

3. The method of claim 1 further comprising: introducing wellbore treatment fluids to the first zone after pumping cement.

4. The method of claim 1 further comprising: heating the first zone to produce fluids from the first zone into the tubular string.

5. The method of claim 1 wherein the tubular string includes a further packer axially offset below the lower packer and forming a third zone below the second zone and the method includes; pumping cement into the annulus to fill the annular region below the third zone, while the third zone is left free of cement.

6. The method of claim 1 wherein pumping cement includes opening a closure over the first of the cementing ports and installing a seal in the inner bore below the first of the cementing ports to divert cement into the first of the cementing ports.

7. The method of claim 1 wherein pumping cement further comprises installing a seal in the inner bore between the first of the cementing ports and the second of the cementing ports such that a circulation path is establishable leading to the first of the cementing ports and leading away from the second of the cementing ports.

8. The method of claim 1 wherein pumping cement further comprises running a cementing apparatus into the inner bore to open a closure over the first of the cementing ports.

9. The method of claim 1 wherein pumping cement further comprises running a cementing apparatus into the inner bore to install a seal in the inner bore below the first of the cementing ports to divert cement into the first of the cementing ports.

10. The method of claim 1 wherein pumping cement further comprises running a cementing apparatus into the inner bore to conduct cement to the first of the cementing ports.

11. A tubular installation in place in a wellbore comprising: a tubular string in the wellbore and creating an annulus between the tubular string outer surface and a wall of the wellbore, the tubular string including a frac port extending from an inner bore of the tubular string to open on the outer surface of the tubular string, at least a pair of cementing ports axially spaced apart along the wall of the tubular string each providing communication between the inner bore and the outer surface; an upper annular packer encircling the tubular string above the frac port; an intermediate annular packer encircling the tubular string below the frac port and above both of the cementing ports;
and a lower annular packer encircling the tubular string below the cementing ports, the upper annular packer and the intermediate annular packer forming a first zone between them along the wellbore and the intermediate annular packer and the lower annular packer forming a second zone between them along the wellbore and the first zone being annularly isolated from the second zone by the intermediate annular packer;
cement in the second zone introduced through a first of the cementing ports, with cement circulation permitted by evacuation from the second zone through a second of the cementing ports; the first zone being uncemented and open to receive fracing fluid through the frac port.

12. The tubular installation of claim 11, further comprising an openable closure for the frac port.

13. The tubular installation of claim 11, further comprising an openable closure for each of the cementing ports.

14. The tubular installation of claim 11, wherein the first packer and the second packer are hydraulically settable.

15. The tubular installation of claim 11, further comprising a further packer below the lower packer, the further packer expanded to seal the annulus between the tubular string and the wall, creating a third zone and a second frac port providing access from the inner bore to the third zone and cement in the annulus below the third zone and introduced through a pair of cementing ports in the tubular string below the further packer.

16. The tubular installation of claim 11, further comprising a cementing apparatus sized to be run into the tubular string inner bore.

17. The tubular installation of claim 11, wherein the cement is thermally stable.

18. A tubular string for installation in a wellbore, the tubular string comprising: a frac port extending from an inner bore of the tubular string to open on an outer surface of the tubular string, at least a pair of cementing ports axially spaced apart along the wall of the tubular string each providing communication between the inner bore and the outer surface; an upper annular packer encircling the tubular string above the frac port; an intermediate annular packer encircling the tubular string below the frac port and above both of the cementing ports; and a lower annular packer encircling the tubular string below the cementing ports, the upper annular packer, the intermediate annular packer and the lower annular packer each being expandable and the frac port being isolated from communication along the outer surface from the at least a pair of cementing ports by the intermediate annular packer.

19. The tubular string of claim 18, further comprising an openable closure for the frac port.

20. The tubular string of claim 18, further comprising an openable closure for each of the cementing ports.
21. The tubular string of claim 18, wherein the first packer and the second packer are hydraulically settable.

21. The tubular string of claim 18, wherein a first cementing port of the at least a pair of cementing ports is positioned adjacent the lower annular packer and a second cementing port of the at least a pair of cementing ports is positioned adjacent the intermediate annular packer and the first cementing port is configured for passing cement outwardly from the inner bore to the outer surface and the second cementing port is configured for passing cement inwardly from the outer surface to the inner bore.

22. The tubular string of claim 18, further comprising a further packer below the lower packer, the further packer being expandable to create an annular seal about the tubular string and a second frac port providing access from the inner bore to the outer surface.