The invention concerns a method for establishment of a new well path from an < ing well. More specifically, the invention concerns a method which provides mec stability in the form of a well plug formed around the entrance of the new well f being formed through an opening in an existing casing.

It is known to form new well paths, sidetracks, from an existing well by drilling well path out through the wall of a casing. This is carried out by anchoring a wh at a desired location in the well, whereby a drilling body, which is brought into c gagement with the whipstock, changes direction and drills from the inside and t the sidewall of the casing. Oftentimes, such a drilling operation leaves an oblom opening, a window, in the wall of the casing. It is customary to form such a side at a relatively shallow level in a well, and far away from the reservoir, so as to < that the casing, which is to be drilled through, is cemented to the surrounding f mation. By so doing, the window becomes sufficiently stable, thereby ensuring i there is no danger of the portion having the window being allowed to rotate dur subsequent operations, for example when the drill string is pulled back through window. Given that the sidetrack is formed at a relatively shallow level in the w< new well path oftentimes becomes very long, which incurs large costs to an ope

The object of the invention is to remedy or to reduce at least one of the disadve of the prior art, or at least to provide a useful alternative to the prior art.

The object is achieved by virtue of features disclosed in the following descriptioi in the subsequent claims.

More specifically, the invention concerns a method for establishment of new we from an existing well, wherein the existing well, at least in a portion where the ι well path is to be established, is delineated radially by a casing, and wherein th< method is characterized in that it comprises the following steps:

(A) disposing and anchoring a plug base in the well; (B) providing a plug above the plug base in the well along a longitudinal seel wherein the plug, at least in a portion, covers substantially the entire cross-sect the well;

(C) removing a portion of the plug in such a manner that at least a cross-sec section of the plug remains on the outside of the casing;

(D) disposing and anchoring a direction-guiding element in the well at least | ly within the longitudinal section; and

(E) by means of the direction-guiding element, guiding a drilling tool against inside of the casing in the well in order to form a hole through the casing and t maining cross-sectional section of the plug within the longitudinal section, whicl up to formation of a new well path, characterized in that step (B) also comprise following sub-steps:

(Bl) conducting a perforation tool down into the casing and to the longitudina tion where the plug is to be set;

(B2) forming holes in the casing and along the longitudinal section by means perforation tool; and

(B5) pumping a fluidized plugging material down through the string and out ir casing, thus also into the annulus via the holes in the casing.

For example, the plug may be established by means of a method and devices a: closed in Norwegian patent application 20111641 bearing the title "Method for c bined cleaning and plugging in a well, a washing tool for directional washing, ar of the washing tool", and in Norwegian patent application 20110450 bearing the- "Apparatus for positive drive of liquid, permanent plugging material through a p rated casing in oil or gas wells", both of which have been filed by the present ap cant.

The remaining cross-sectional section of the plug may contribute to provide a gi base around the hole in the casing, and at the entrance of the new well path.

In one embodiment, step (C) may include removing a portion of the plug in sue manner that also a longitudinal section of the plug remains centrally in the well within the casing. This will have the advantage of allowing the remaining longiti section of the plug to be used as a base for various tools and equipment desirec placed permanently or temporarily in the well. It may be a direction-guiding ele for example a whipstock or similar.

In a further embodiment, the longitudinal section remaining centrally in the wel constitute less than half of the longitudinal section along which the plug was set Step (C) may include removing the portion of the plug by means of drilling.

In one embodiment, the plug may be formed from a fluidized plugging material prising cement slurry.

In another embodiment, the plug may be formed from a fluidized plugging mat< comprising a particulate mass.

In yet another embodiment, step (B), and between sub-steps (B2) and (B5), m include the following sub-steps:

(B3) by means of a washing tool, which is attached to a flow-through string a conducted down to the longitudinal section, pumping a washing fluid down throi string and out into the casing via the washing tool; and

(B4) by means of a directional means connected to the washing tool, conducti washing fluid out into an annulus between the outside of the casing and the sur ing formation.

It may be of advantage to use a displacement body in the form of a pressing ap ratus, as described in said Norwegian patent application 20110450, to further d and distribute the fluidized plugging material in the casing and further out into t annulus.

In one embodiment, the steps of perforating and washing may be carried out in rate trips down into the well.

In another embodiment, the steps of perforating and washing may be carried oi one and the same trip down into the well. This, for example, may be carried oul manner described in the above-mentioned Norwegian patent publication 201111 and by virtue of the perforation tool and the washing tool being connected to th string. The perforation tool may also be releasably connected to the washing toi

In one embodiment, the method may further comprise a step of leaving the per tion tool in the well. This may prove particularly appropriate if the perforation tc drillable and/or may be left in a suitable place in the well.

In another embodiment, the method may also comprise a step of leaving the wi tool in the well. This may prove particularly appropriate if the washing tool is dr and/or may be left in a suitable place in the well.

After step (E), the method may also comprise a step of drilling out a new well p said hole formed through the casing. A use of a cement plug as a base for a whipstock in a subterranean well is also scribed.

Hereinafter, an example of an embodiment is described and is depicted in the a panying drawings, where:

Fig. 1 shows, as viewed from the side, a simplified and schematic section of a w

Fig. 2 shows, as viewed from the side, the well after having set a plug base in t and a string with a perforation tool has been conducted down into t well;

Fig. 3 shows, as viewed from the side, the well after the perforation tool has for holes in a casing;

Fig. 4 shows, as viewed from the side, the well after having conducted a washir down into the well;

Fig.5 shows, as viewed from the side, the well after having set a plug in the wel

Fig. 6 shows, as viewed from the side, the well after having drilled away a porti the plug;

Fig. 7 shows, as viewed from the side, the well after having inserted a direction guiding element in the well; and

Fig. 8 shows, as viewed from the side, the well after having drilled a hole throuc casing so as to open up to a new well path.

In the following, reference numeral 1 denotes a well as used in context of the rr of the present invention. The well 1 is depicted in a simplified and schematic mi and elements not being central to the invention may be left out from the Figure

Figure 1 shows the well 1 having an existing well path 2 lined with a casing 21 i upper portion of the well 1, and having a production liner 211 extending from a portion of the casing 21 and further down into the well 1 along the well path 2. annulus 7 filled with a fluid and/or a deposited solid (not shown) is located betv\ the casing 21 and a surrounding formation 9.

Figure 2 shows the well 1 after having conducted a perforation tool 33 down int well 1 within the casing 21 and on a string 3, and after having set a plug base 2 the well 1. The perforation tool 33 is positioned above the plug base 23 and alo longitudinal section LI of the well 1 within which plugging is desired .

Figure 3 shows the well 1 after having formed, by means of the perforation tool several holes 213 in the casing 21 along the longitudinal section LI .

A combined washing and plugging tool 35 is then conducted down into the well within the casing 21, as shown in Figure 4. Perforating and washing and pluggir be carried out in the sa me trip or in separate trips down into the well 1. A wash fluid (not shown) is conducted through the string 3, out into the casing 21, and out into the annulus 7 via the holes 213. The washing fluid is directed radially o the annulus 7 by means of a directional means 351, as described in Norwegian application 20111641. A washing fluid at high velocity will be able to remove va particles, deposits and remnants from previous downhole operations, whereby t plugging material, which is to be conducted into the annulus 7 at a later stage, flow freely and be adhered in a better way. Then a fluidized plugging material is pumped through the string 3 and out into the casing 21, and thus also into the lus 7 via the holes 213 in the casing 21, whereby a plug 25 is formed along the tudinal section LI, as shown in Figure 5. The plug 25 extends, at least in a porti thereof, across the entire cross-section Tl of the well 1. It may be of advantage an apparatus of the type described in Norwegian patent application 20110450 ti ther displace and distribute the fluidized plugging material in the casing 21 and into the annulus 7. The apparatus is not shown in the Figures associated with tl" sent document.

In Figure 6, the well 1 is shown after having drilled away a portion of the plug 2 means of a drilling tool 31. After the drilling, a cross-sectional section T3 of the 25 remains along the entire length of the plug 25, whereas a longitudinal sectio the plug 25 remains at the bottom thereof, and against the plug base 23. The r< ing longitudinal section L3 constitutes ca . 1/3 of the original length of the plug .

A direction-guiding element 27, here in the form of a whipstock, is placed on to the remaining longitudinal section L3 of the plug 25, as shown in Figure 7. The i tool 31 is then used to drill through the casing 21, and through the remaining c sectional section T3 of the plug 25, in a direction given by the geometric shape direction-guiding element 27. The drilling tool drills further into the formation 9 to form a new well path 5, as shown in Figure 8.