NO342251B1

NO342251B1 - A controlled borehole wall collapsing method for sealing a ductile rock formation in a borehole

Info

Publication number: NO342251B1
Application number: NO20161177A
Authority: NO
Inventors: Sverre Bakken; Silje Harestad
Original assignee: Archer Oiltools As
Priority date: 2016-07-14
Filing date: 2016-07-14
Publication date: 2018-04-30
Also published as: NO20161177A1

Abstract

A controlled borehole wall (60) collapsing method for sealing a ductile rock formation in a borehole (6) about a casing (4) having at least one casing port (43), the borehole wall (60) being pressure balanced by mud in the casing (4) annulus (61), comprising the steps of step (A) - run a casing port (43) operating tool (1) on a drill pipe string (0) into the casing (4), the tool (1) having athrough bore pipe stem (10) with a dog (11) for engaging the casing port (43), and a lateral liquid outlet (19), said tool (1) further having - inward-facing swab cups (13, 14) and outward-facing swab cups (15, 16) fluid bypassed via upper and lower bypass ports (17, 18); and - a lower valve (2) in said pipe stem (10) with outlet below said lower bypass port (18) and said lower swab cup (16); step (B) - circulate in a volume of Iow density fluid (FL) to fill all or part of the drill pipe string (0) down to the tool (1) and simultaneously circulate out ordinary density mud (M), and close the valve (2); step (C) - use the dog (11) to open the casing port (43); step (D) - allow fluid to flow in from the annulus (61) via the casing port (43) and into the lateral liquid outlet (19) to displace said low density fluid in said drill pipe string (0), and allow the ductile rock formation to start expanding to collapse the annulus (61) in the vicinity of the casing port (43); step (E) - close the casing port (43). The geological formation will quickly collapse about the casing.A controlled borehole wall (60) collapsing method for sealing a ductile rock formation in a borehole (6) about a casing (4) having at least one casing port (43), the borehole wall (60) being pressure balanced by mud in the casing (4) annulus (61), comprising the steps of step (A) - run a casing port (43) operating tool (1) on a drill pipe string (0) into the casing (4), the tool (1) having athrough bore pipe stem (10) with a dog (11) for engaging the casing port (43), and a lateral liquid outlet (19), said tool (1) further having - inward-facing swab cups (13, 14) and outward-facing swab cups (15, 16) fluid bypassed via upper and lower bypass ports (17, 18); and - a lower valve (2) in said pipe stem (10) with outlet below said lower bypass port (18) and said lower swab cup (16); step (B) - circulate in a volume of Iow density fluid (FL) to fill all or part of the drill pipe string (0) down to the tool (1) and simultaneously circulate out ordinary density mud (M), and close the valve (2); step (C) - use the dog (11) to open the casing port (43); step (D) - allow fluid to flow in from the annulus (61) via the casing port (43) and into the lateral liquid outlet (19) to displace said low density fluid in said drill pipe string (0), and allow the ductile rock formation to start expanding to collapse the annulus (61) in the vicinity of the casing port (43); step (E) - close the casing port (43). The geological formation will quickly collapse about the casing.

Description

Field of the invention

The present invention is a method of establishing a mechanical contact between a casing or liner and its surrounding borehole wall. More specifically, it is a method of establishing contact between the casing and a mechanically plastic or ductile geological formation which has a pore fluid pressure.

Background art

A casing or liner is usually cemented to the borehole wall. Usually this is done using a casing port or a casing cementing valve and a corresponding valve operation tool similar to what is illustrated in Fig 9. The casing port or cementing port is opened by moving the gate sleeve and injecting cement similar to the flow in Fig. 2, via the drill pipe string. This will fill the annulus with cement to a desired degree, the port is closed, the excess cement is circulated out, and the annulus allowed to set and harden. This is an ordinary cementing operation which proves sufficient for most rock with good mechanical integrity.

The cementing injection part of the above process is itself a costly operation and requires setting and hardening time to complete the operation. It also generates waste fluids which must be handled, also a costly part of petroleum exploitation.

Weak formations with excess pore pressure represent a problem to drill and case-support. Geological formations about a borehole always have a pore pressure. A ductile geological formation also has low mechanical integrity, i. e. high plasticity, and easily collapse when subject to borehole pressure support, and are notoriously difficult both to drill through and to insert liners into while maintaining the integrity of the borehole wall. A sufficiently high mud pressure against the borehole wall is required to balance the pore pressure in the porous formation may incur collapse of the formation into the borehole during drilling or during arrangement of a casing or liner; there is a risk of obstructing the string in the well. Such weak formations are usually cemented, too, using cementing valves in the casing as mentioned above.

Utilizing naturally occurring formation collapse to seal a casing has been described in US8336620 Williams, Carlsen, Constable, Statoil ASA. In col. 4, lines 39 -44, we cite: "In this case, the shale formation has crept laterally due to natural causes over time and is shown in abutment with the casing sections in the regions of the casing annuli where there is no cement. The following steps are carried out to verify that the shale formation forms a seal that functions as an effective annular barrier." Williams et al thus describes not how to initiate and conduct such a creep seal, but how to verify the naturally occurring sealing properties.

In an SPE publication "Identification and Qualification of Shale Anular Barriers Using Wireline Logs During Plug and Abandonment Operations, published before the above patent, Williams, Carlsen, Constable and Guldahl describes logging and pressure testing in sealed off zones in order to verify naturally formed annular barriers. However, the method employs perforation in order to conduct pressure tests, which may be undesirable.

Kristiansen, T.G., Why Shale Could be used as a Permanent Well Barrier Element, P&A Forum 29 October 2015, Stavanger (https://www.norskoljeoggass.no/Global/PAF%20seminar%202015/10%20-%20Shale%20as%20well%20barrier%20material_BP_TGK%20final.pdf?epslanguage=no ) shows a shale collapse method using two packers and a downhole pump to form a well barrier element.

US4334582 depicts a method for cementing an annular cavity between a subsea well casing and a borehole from a floating vessel.

US2838119 describes a well treating tool adapted to be connected to a string of pipe or tubing and lowered into a casing, the tool being provided with suitable upper and lower packer cup assemblies adapted to isolate a space within the casing, a permanent unobstructed fluid conduit communicating the interior of the pipe string with such space, a by-pass passageway communication the interior of the casing below the tool with space above the tool and exteriorly of the pipe string, and a simple, selectively operable means whereby the space between the packing cup assemblies can be placed in communication with the interior of the casing above and below the tool.

Short summary of the invention

A main object of the present invention is to disclose a method of collapsing a porous ductile geological formation of a borehole into contact with a casing pipe, said geological formation having a pore pressure. The invention is defined in claim 1 and other independent claims.

The current invention comprises of a controlled borehole wall (60) collapsing method for sealing a ductile rock formation in a borehole (6) about a casing (4) having at least one casing port (43), the borehole wall (60) being pressure balanced by mud in the casing (4) annulus (61), characterized by the steps of:

step (A) - run a casing port (43) operating tool (1) on a drill pipe string (0) into the casing (4), the tool (1) having a through bore pipe stem (10) with a dog (11) for engaging the casing port (43), and having a lateral liquid outlet (19), said tool (1) further having

- inward-facing swab cups (13, 14) and outward-facing swab cups (15, 16) fluid bypassed via upper and lower bypass ports (17, 18); and

- a lower valve (2) in said pipe stem (10) with outlet below said lower bypass port (18) and said lower swab cup (16);

step (B) - circulate in a volume of low density fluid (FL) to fill all or part of the drill pipe string (0) down to the tool (1) and simultaneously circulate out ordinary density mud (M), and close the lower valve (2);

step (C) - use the dog (11) to open the casing port (43);

step (D) - open a topsides valve on the drill pipe string (0) to allow fluid to flow in from the annulus (61) via the casing port (43, 143);

step (E) - close the casing port (43).

The current invention also discloses a tool (1) for inducing shale collapse, said tool (1) mounted on a drill pipe string (0), the tool (1) having

- a through bore pipe stem (10) with

- a dog (11) for engaging a sliding sleeve (42) of a casing port (43, 143), and - a lateral liquid outlet (19),

the tool (1) further having

- inward-facing swab cups (13, 14) straddling said lateral liquid outlet (19) and said dog (11), and

characterized by outward-facing swab cups (15, 16) straddling said inward-facing swab cups (13, 14) and fluid bypassed via upper and lower bypass ports (17, 18); and

- a lower valve (2) in the pipe stem (10) with outlet below the lower bypass port (18) and the lower swab cup (16).

An advantage of the present invention is that one may do away with the cementing step by utilizing the weakness and pore pressure of the rock formation to solve the problem posed by the same weakness. The pore pressure may be high or not excessive, as long as the rock formation has a ductility sufficient to be utilized to deform through creeping. The invention presented saves both casing installation time and the costs otherwise used on the cementing part of the casing installation operation.

Figure captions

The attached figures illustrate some embodiments of the claimed invention.

Fig. 0 illustrates a drill-pipe string borne tool (1) for cementing and operating a valve sleeve for a casing port (43, 143).

Fig. 1 illustrates the same tool (1) inserted in a petroleum well in a casing, with its drag blocks engaged against the casing wall below a cementing valve housing. For continuity in the illustrations we have illustrated the top of a cementing valve (41) adjacent to a little kink in the (un-expanded) borehole wall, please see Figs. 1 - Fig. 8. In an embodiment of the invention, for optional injection pressure testing, the drill pipe string is rotated to close a ball valve (21) below the lower bypass port (18) and the lower swab cup (16). Please see step (A) below.

Fig. 2 illustrates an embodiment of the invention comprising opening of the casing port (43, 143) and conducting the optional injection pressure test, see step (A2) below.

Fig. 3 illustrates closing the casing port (43, 143) by pulling upwardly on the drill pipe string to move the sleeve gate to close the casing port (43, 143) if not already closed, please see step (A3) in the description of embodiments below.

Fig. 4 shows the tool unlatched from the valve and opening the lower valve (2, 21), please see step (A4) below. Now there is opened a path for circulating fluid down through the drill pipe string, through the tool (1) and the lower valve (2, 21), back up within the casing and into the lower bypass port (18), through the bypass to the upper bypass port (17), and up within the casing, for circulating fluid down through the drill pipe string and up through the casing bore annular space about the drill pipe string.

Fig. 5 illustrates the step (B) of the method according to claim 1, utilizing the fluid path established above, of circulating in a low density liquid (FL) into the drill pipe string, and simultaneously circulating out a corresponding volume of ordinary density liquid (M) through the casing bore. This creates a potential U-tubing pressure difference which is held back by closing the lower valve (2, 21). Since this lower density liquid (FL) must be pumped down, one must maintain the topsides pressure in the drill pipe string when closing the lower valve (2, 21).

Fig. 6 illustrates step (C) of the method according to claim 1, of opening of the casing port (43, 143). Now the hydrostatic pressure of the lower density liquid (FL) and the topsides pressure in the drill pipe string balances the formation pressure via the open casing port (43, 143).

Fig. 7 shows step (D) of the method according to claim 1, the response from the surrounding formation when opening the topsides valve on the drill pipe string. The ductile rock will expand. Fluid will flow in from the porous formation and the annulus, into the casing and into the tool (1) and upwardly within the drill pipe string to displace the low density fluid standing in the drill pipe string. The ductile rock will start collapsing the casing annulus slowly to envelope the casing.

Fig. 8 illustrates the formation having collapsed completely in a brief range about the casing port or cementing port (43, 143) and its adjacent casing or liner pipes. (We have illustrated the fully expanded rock surface sealing against the casing valve and casing in a slightly exaggerated bold line for illustration clarity.) Please see step (E). Now the formation above is pressure isolated from the formation below, and the casing and the local valve housing is mechanically fixed in the borehole. The cementing valve is closed, the ball valve is opened, and one may circulate out the low density fluid and move on to the next cementing valve to be formation-collapse fixed.

Fig. 9 illustrates a drill pipe string borne cementing and valve operating tool for a so-called Cflex cementing valve of Archer Oiltools. It has inward facing swab cups (102, 106) and a dog (105) for engaging a sliding sleeve gate to open and close the casing port, and a cementing outlet (104) on a stem (103) between the swab cups (102, 106), all bypassed by upper and lower bypass ports (101, 107).

Fig. 10 is a general well context showing three ductile rock zones and a petroleum bearing zone, and four cementing valves, all before conducting the present invention method. Note that the upper cementing valve illustrated should be operated for an ordinary cementing operation if at all necessary.

Embodiments of the invention

The invention will in the following be described and embodiments of the invention will be explained with reference to the accompanying drawings.

The invention is a borehole wall controlled collapsing method for a ductile geological formation, a ductile rock, to seal about a casing. The formation will always have a fluid pressure, regardless of whether it is considered as an ordinary pore pressure or a high pore pressure. The pressure must under most circumstances be balanced by the borehole mud at least up to the well is cased, preferably also up until the casing is cemented in the desired stages. The present invention's method comprises the use of a drill pipe string -borne tool (1), see Fig. 0, for being run in a casing string (4) with one or more casing ports (43), preferably cementing ports (143) of cementing valves (41), please see Figs. 1 to 8.

The method comprises providing the tool and the casing arrangement in the borehole, if not already established, and the steps of using the tool in the casing string. We consider the tool (1) as new, and the casing string (4) with the casing ports (43) or cementing valves (41) as prior art. The method comprises the steps of:

The casing string

- step (0): Provide a borehole with a casing string (4) in a borehole (6) in the ductile geological rock formation, if not already provided. The casing string (4) has at least one casing port (43); preferably the casing ports (43) are embodied as cementing ports (143) closed and opened by a sliding sleeve (42). A geological formation has a pore pressure within the rock, and the rocks near its borehole wall (60) are usually pressure balanced by mud in the annulus (61) about the casing string (4); please see Fig. 1, otherwise mud may undesirably enter into the formation or the formation may expand in an uncontrolled manner, or one may have a kick in the well.

The valve operating tool

- For running the present method in the casing string (4), one must provide a drill pipe string (0) operating tool (1) for operating the casing port (43), the tool (1) comprising the general mechanical features as follows:

- a through bore pipe stem (10) with a dog (11) for engaging and actuating the casing port (43), and having a liquid outlet (19) to the local casing bore,

- with at least the liquid outlet (19) arranged between a set of inward-facing swab cups (13, 14),

- the inward-facing swab cups (13, 14) further arranged between a set of outward-facing swab cups (15, 16),

- the outward-facing swab cups further encompassed by bypass line connected upper and lower bypass ports (17, 18), and

- a lower valve (2) with outlet below the lower bypass port (18) and the lower swab cup (16);

The usual reason for having the bypass line in similar cementing tools, see Fig. 9, is for enabling running such tools into the well or out of the well through blank casing. Any fluid in the casing bore will then pass through the bypass line; otherwise the tool would get stuck due to pressure buildup. The tool (1) of the present invention may be made from modifying an ordinary cementing tool such as the one shown in Fig. 9, while adding an outward-facing set of swab cups (15, 16) and a valve (2) such as a ball valve (21) with a set of drag blocks at the lower end.

Conducting the controlled formation collapse operation

When having run the tool (1) on the drill pipe string (0) down to a target ductile rock formation is, where a casing port (43) is arranged within the ductile rock zone, one conducts the following basic steps:

A) - run the tool (1) into the casing string (4) near the casing port (43). The tool is run through the well with passage across the bypass ports (17, 18) and preferably with the lower valve (2) open. When in place, close the valve (2) if an injection pressure test shall be conducted.

Further steps (A2), (A3), (A4) on injection pressure testing, please see Figs. 2, 3, and 4, are not essential to make the invention work, but may be required by the field operator for ascertaining the well conditions before the present operation, e.g. such as checking whether there actually is a fluid communication through the casing port (43) or not (i.e. whether there is an annulus or the annulus already has collapsed), and are optional. Field operators usually require an injection pressure test when opening a casing port (43) before cementing. Those further injection pressure testing steps (A2), (A3), (A4) are given below.

B) - Circulate in low density fluid in the drill pipe string (0).

Using pressure on the drill pipe string, pump and circulate in a volume of low density fluid such as base oil to fill preferably the entire drill pipe string (0) and circulate out ordinary density mud to fill the casing bore (4) above the tool (1), and close the valve (2). Now having closed the valve (2), the potential pressure difference between the light fluid in the drill pipe string (0) and the heavy fluid in the casing bore, prevents socalled U-tubing between the casing bore and the drill pipe string. Maintain the topsides pressure on the light fluid (FL) in the drill pipe string by using a topsides valve on the drill pipe string, please see the illustrated pressure meter indicated as high in Fig 5.

Open the casing port (43).

Any subsea geological formation has a pore pressure, and this pore pressure is utilized in the present invention. We have formed a blocked differential pressure between the casing bore mud pressure, which is much similar to the borehole mud pressure. This port (43, 143) - blocked differential pressure is thus the difference between, in the annulus, the borehole mud pressure which must balance the formation pore pressure, and, in the drill pipe string, the low density liquid column exerting a lower hydrostatic pressure. We utilize this differential pressure to more or less abruptly expand the rock formation in the next step, but so far the pressures are in balance.

D) - Release the pressure in the drill pipe string.

In more detail, release the topsides pressure on the low density fluid in the drill pipe string (0), such as by opening the topsides valve on the drill pipe string to allow fluid to flow in from the annulus (61) via the casing port (43, 143). Please see the illustrated pressure meter indicated as low in Fig. 7. The inflowing annulus fluid (most probably a mixture of drilling fluid initially and a pore fluid from the geological formation) will displace the low density fluid in the drill pipe string (0). The ductile geological formation will thus start collapsing the borehole wall towards the casing port and the casing, and thus collapse the annulus (61) in the vicinity of the casing port (43). The volume and pressure of the low density fluid received at the surface may indicate the degree of collapse.

Close the casing port (43).

The formation will, depending on the pore pressure and the rock mechanical ductility properties, collapse within minutes, hours or days. When considering the formation collapsing or enveloping process sufficiently complete, to halt the process, close the casing port (43). For further details, see embodiments of the invention described below. In an embodiment of the invention, pull upwardly on the drill pipe string (0) to move the sleeve gate (42) to close the cementing port (143). For balancing the fluids within the casing bore, open the ball valve (21), and, if desired, circulate out the light fluid within the drill pipe string (0). However, it may not be necessary to circulate out the light fluid before all such operations according to the invention are finished. The tool (1) may now be moved to the next casing port (43), such as another cementing valve (41) with a cementing port (143) in order to repeat the process (A) - (F) to collapse another part of the borehole wall about the subsequent cementing valve.

The amount of light fluid returned via the drill pipe string on the surface may indicate the volume of annulus being filled by the ductile expansion process, but an acoustic log of rock to casing contact may be required to verify the collapse of the annulus.

An advantage of the present invention is, given the right local ductility and pore pressure conditions in the rock, one may dispose of a stage cementing step making the borehole wall in contact with the casing outer wall in order to achieve mechanical borehole support for the casing or for pressure isolating between a zone above and below the cementing valve. Disposing of the stage cementing step will significantly reduce the time and costs and achieve the same operational result: a mechanically supported and zone isolated casing in the well.

Further on the casing port (43) - a cementing valve embodiments

In an embodiment of the invention, the casing string (4) comprises at least one cementing valve (41) having an axially operated sleeve gate (42) for closing and opening a cementing port (143) to the annulus (61), the cementing port (143) being the casing port (43). There may be one, two or more such cementing valves (41) arranged down along the casing string (4), please see the overview illustration in Fig. 10. The applicant Archer Oiltools, Norway, manufactures such cementing valves under the brand name Cflex, and they are full-bore to allow access for valve operating and cementing tools such as the one shown in Fig. 9 and also the tool (1) described below, but also for allowing the passage of other tools for operation below the casing valves (41).

Further on the tool (1) - cementing tool embodiments

The tool (1) of the invention is a casing port (43, 143) operating tool (1) for being run on a drill pipe string (0). The tool (1) has a through bore pipe stem (10) with a dog (11) for engaging the casing port (43, 143), and a lateral liquid outlet (19). The tool (1) further has the following components:

The dog (11) is for engaging and moving the sleeve gate (42) of the cementing valve (41) to open and close the casing port (43, 143). The fluid outlet (19) from the hollow stem (10) is usually used for letting out cement from the drill pipe string to the space between the swab cups and which shall be pumped further out through the casing / cementing port (43, 143) when open, but in the present invention the flow is the opposite direction; fluid shall be allowed in. Notice, however, that the present tool (1) may be designed to be used for conducting an ordinary stage cementing in a Cflex cementing valve.

Both the dog (11) and the cementing outlet (19) of the shown embodiment are arranged between inward-facing swab cups (13, 14); to block flow from the drill pipe string (0) to the casing (4) bore. Those first, inward-facing swab cups (13, 14) are further arranged between a second set of outward-facing swab cups (15, 16), to block fluid from the casing bore to enter into the drill pipe string.

The outer swab cups (15, 16) are encompassed by a bypass-line connected upper and lower bypass ports (17, 18), usually for allowing such a tool to be moved through blank casing without stopping due to a piston effect, but now also for allowing circulating fluid down through the tool (1), through the lower valve (2) and back up via the bypass line to the casing bore.

The ball valve assembly (2) comprises in an embodiment of the invention a ball valve (21) and drag blocks (22) arranged at the lower end of the valve operating tool (1). In an embodiment of the invention the valve (21) is opened and closed through rotation of the drill pipe string. This is advantageous because the ball valve (21) may be opened and closed by rotation of the drill pipe string to the left or right. The opening or closing may be done in other ways with darts or balls, but such an approach is increasingly difficult if one shall open and close multiple times, as one would then have to have a large set of different balls and ball seat mechanisms.

The present method is for utilizing ductile formations to seal about the casing where one has casing ports (43) available. However, if, during the operation of the present invention, one has a rock formation about one casing port (43) wherein the rock formation is not ductile, thus not suitable for sealing using the present formation collapse method, but instead must be cemented, one may use the present tool (1) for conducting the cementing job, too. It is not necessary to remove the tool (1) in order to shift from the present invention operation to an ordinary cementing operation. This is a further advantage of the invention.

Further on closing the casing port (43)

When considering the formation collapsing or enveloping process sufficiently complete, to halt the process, close the casing port (43). For further details, see embodiments of the invention described below. More specifically, pull upwardly on the drill pipe string (0) to move the sleeve gate (42) to close the cementing port (143). For balancing the fluids within the casing bore, open the ball valve (21), and circulate out the light fluid within the drill pipe string (0) if necessary. After step (D) the cementing tool (1) may be moved to the next casing port (43) or cementing port (143) in order to repeat the process (A) - (D) to collapse another part of the borehole wall about the subsequent cementing valve.

Further on optional steps of formation pressure test

A so-called formation pressure test may be required by the field operator ascertaining the well conditions, among others the formation pressure and the annulus pressure before the present operation, or simply such as for checking whether there is fluid communication through the casing port (43) before this entire operation is conducted. One might risk that the formation accidently has already collapsed about the casing near the casing port, and then a "formation pressure test" will reveal whether there is fluid communication to the annulus at all.

A2) - Open the casing port (43, 143). More specifically, in an embodiment of the invention, latch the dog (11) into the sleeve gate (42) and move it to open the cementing port (143), the inward facing swab cups (13, 14) will direct the pressure through the cementing port, and conduct an injection pressure test via the drill pipe string (0); Now we will get to know the pore pressure in the ductile rock formation more precisely. When moving the tool (1) vertically the drag blocks will also be dragged along the blank casing; this is no problem as both the drag blocks and the casing (and the valve sleeve (42) are designed for this.

A3) - Close the casing port (43), or more specifically, pull upwardly on the drill pipe string (0) to move said sleeve gate (42) to close the cementing port (43).

A4) - Unlatch the tool (1) from the casing port (43) and open the lower valve (2). More specifically, unlatch the tool (1) from the sleeve gate (42) and open the ball valve (21). Preferably both those are done by using right hand rotation of the drill pipe string.

Further on step C: opening casing port (43)

In an embodiment of the invention, the cementing port (143) is the casing port (43). In an embodiment of the invention, to open casing port (43), latch the dog (11) into the sleeve gate (42) and move the sleeve gate (42) to open the cementing port (143). The topsides pressure on the drill pipe string is maintained and closed.

As an alternative to the sets of inward-facing swab cups (13, 14) and outwardfacing swab cups (15, 16) fluid bypassed via upper and lower bypass ports (17, 18), one may use other sealing elements such as a first packer (13', 15') above the outlet (19) and a second packer (14', 16') below the outlet (19), and fluid bypassed via the upper and lower bypass ports (17, 18). Such first and second packer would make the tool (1) and the method work, in principle, in an equivalent way, but would require expansion mechanisms such as inflation or mechanical compression. Swab cups are easier to use.

Claims

1. A controlled borehole wall (60) collapsing method for sealing a ductile rock formation in a borehole (6) about a casing (4) having at least one casing port (43), the borehole wall (60) being pressure balanced by mud in the casing (4) annulus (61), characterized by the steps of:

step (C) - use the dog (11) to open the casing port (43);

step (E) - close the casing port (43).

2. The method of claim 1, in step (B), after circulating in the low density fluid (FL) in the drill pipe string (0), maintaining the topsides pressure in the drill pipe string, preferably by closing a topsides valve on the drill pipe string.

3. The method of claim 1 or 2, in step (D), while having opened the casing port (43, 143), releasing a topsides valve on the drill pipe string to allow back flow of the lower density fluid (FL).

4. The method of any of the preceding claims, the lower valve (2) comprising a ball valve (21) with a set of drag blocks (22).

5. The method of any of the preceding claims, in step (C) - the casing port (43) part of a cementing valve (21) with a sleeve gate (42) with a cementing port (143); conduct the action of latching the dog (11) into the sleeve gate (42) and move it to open the cementing port (143).

6. The method of claim 5, in step (E) - pull upwardly on the drill pipe string (0) to move the sleeve gate (42) to close the cementing port (143).

7. The method of any of the preceding claims, in step (E) - open the lower valve (2) and circulate out the light fluid from the drill pipe string (0).

8. The method of claim 1, wherein in step (A), said lower valve (2) comprising a tool axial bore ball valve (21), one further conducts the steps of using a set of drag blocks (22) of the tool axial bore ball valve (21) below the lower bypass port (18), the drag blocks (22) arranged below the casing port's (43) sleeve gate (42); and close the ball valve (21), preferably by left hand rotation.

9. The method of claim 1, wherein after step (A), conduct a step (A2): open the casing port (43) and conduct an injection pressure test via the drill pipe string (0).

10. The method of claim 9, wherein the step (A2), the casing port (43) being part of a cementing valve (41) with a sleeve gate (42) for a cementing port (143); the action of opening the casing port (43) comprising

- using a latch dog (11) into the sleeve gate (42) and move it to open the cementing port (143).

11. The method of claim 10, conduct a step (A3) of pulling upwardly on the drill pipe string (0) to move the sleeve gate (42) to close the cementing port (143).

12. The method of claim 11, conduct a step (A4) of unlatching the tool (1) from the sleeve gate (42) and open the ball valve (21), preferably by using right hand rotation.

13. A tool (1) for inducing shale collapse, said tool (1) mounted on a drill pipe string (0), the tool (1) having

- a through bore pipe stem (10) with

the tool (1) further having

14. The tool (1) of claim 13, the lower valve (2) comprising a ball valve (21) and drag blocks (22).

15. The tool (1) of claims 13 or 14, wherein said sleeve gate (42) is arranged for being axially operated by said dog (11) on the drill pipe string (0) for closing and opening the casing port (43) to the annulus (61).

16. The tool of claims 13 or 14, said tool (1) arranged for operating a sleeve gate (42) of a cementing port (143) of the casing port (43) forming part of a cementing valve (21).