GB2031050A - A Well Cementing/Plug Drilling Apparatus and Cementing and Drilling Process - Google Patents

Abstract

The present invention provides a combined well pipe attachment and pump down wipe plug, in which interlocking means are provided at the interface between the plug and the attachment, which means comprise sharp protrusions operative to penetrate the surface of the plug and/or the attachment in order to inhibit or impede relative rotation between the plug and the attachment when a rotary drill bit is brought into contact with the plug, in order to drill out the plug. In one embodiment the interlocking means take the form of a flat plate (120) provided on both surfaces with teeth (117) which are strong enough and sharp enough to engage, dent and penetrate a cement surface (122) and a pump down wipe plug (121). Another embodiment comprises setting the teeth (117) in the cement surface (122), whilst a further embodiment comprises providing the teeth (117) on one, - or if the pump down wipe plug is a bottom plug as opposed to the illustrated top plug - both, ends of the pump down wipe plug (121). <IMAGE>

Description

SPECIFICATION A Well Cementing/plug Drilling Apparatus and Cementing and Drilling Process The cementing process is one of the most important processes in drilling and completing a well. It is an intimate part of the running of casing.

Cementing is performed at various points in the well and at various times while drilling both inside and outside of the casing.

The primary cementing can form a protective sheath around the casing, segregating producing formations to prevent migration of undesirable fluids. Secondary cementing takes place after the primary cementing and can be used to squeeze cement into the perforations in the casing or to seal off, isolate or repair parts of the well. Plug back cementing is used to place cement at desired points in the well or to shut off the bottom water or reduce the depth of the well.

Two of the apparatuses or pipe attachments routinely used in the cementing operations are the collar and the shoe. These are typically cement restrictions or shoulders which are attached to a pipe string as a part of the pipe string. The collar, for example a float coilar, is inserted between the top and bottom of a casing string usually one or two joints above a float shoe which is attached to the bottom of a pipe string.- Shoes and collars, among a number of things, help prevent the back flow of cement during the cementing operation. The collars and the shoes are usually equipped with a check valve (often a ball valve means) to aid in the prevention of back flow of cement.The shoes and collars are typically an outer cylindrical housing or pipe and an inner cement tube communicating with and fixed to the inner surface of the cylindrical housing, with a fluid passage running the length of the cement tube. When there is a check valve, it is usually part of an inner housing in concentric spaced relationship with the outer housing so that the cement tube fills the space between the two housings and the inner housing forms part of the fluid passage.

In addition to the collars and shoes typical cementing operations employ one or more pump down wipe plugs. Pump down wipe plugs can serve three purposes: 1) to separate or serve as the interface between the wet cement from the fluid it is displacing or the fluid which is being used to pump the wet cement to the desired level; 2) to wipe off the inner surface of the pipe string as it passes: and 3) to help prevent back flow while the cement is setting up.

In practice the well operator makes up his pipe string so that the collar or shoe is lowered into the well to the desired level. When he decides to cement he may place a bottom pump down wipe plug between the fluid already in the well and the wet cement. This bottom plug has a fluid passage through it which is sealed by a diaphragm or membrane. The cement is pumped into the well forcing the bottom plug down the well, displacing the fluid in front of it, until it reaches the top of the cement tube of the shoe or collar or shoulder. This restriction stops the plug and increased pumping pressure breaks the diaphragm or membrane and the cement passes through the plug and through the fluid passage of the collar or shoe.After the desired amount of cement is pumped into the well a top pump down wipe plug is inserted to act as the interface between the fluid used to force the cement to the desired level for the cement. Often the bottom plug is not used and only one plug as the interface between the cement and the fluid used to force the cement to the desired level is used. The top plug is usually pumped until it comes in contact with the bottom plug if one is used or the top of the cement tube part of the shoe or collar. The cement is allowed to set or harden and the well operator then carries out whatever other operations he intends to do.

The plugs used in the above operation are usually made of a pliable or rubbery material, such as plastic, wood or rubber, sometimes with hollow metal or plastic cores and they fit snugly in the pipe string. All of the plug is made of drillable material.

Once the cement has set and the well operator has carried out his desired operations he may decide to drill out the plug and/or plugs, collar or shoe and the cement. The plugs are typically made of drillable material, as are the cement tube and inner housing of the collar and shoe and of course, the cement which was pumped into the well. The well operator lowers the drill string into the well until the drill bit contacts the plug and he begins to drill by rotating the drill bit, usually clockwise. In many instances the rotation of the drill bit will cause the plug with which it is in contact to rotate, slipping over the surface on which it rests, i.e., cement, a bottom plug or the cement tube of the shoe or collar. This tendencey of the plug to rotate as the bit rotates, to slide across the surface below it, wastes both time and energy.Since ali of the components are made of readily drillable material, this wasting of time and energy in the drilling process is an unnecessary probiem.

According to a first aspect of the present invention there is provided a combined well pipe attachment and pump down wipe plug, in which interlocking means are provided at the interface between the plug and the attachment, which means comprise sharp protrusions operative to penetrate the surface of the plug and/or the attachment in order to inhibit or impede relative rotation between the plug and the attachment when a rotary drill bit is brought into contact with the plug to drill out the plug.

According to a second aspect of the present invention there is provided a well cementing/plug drilling apparatus comprising: a rigid drillable plate having a bottom face and a top face, said plate having a maximum diameter less than the inside diameter of the well in which it is to be used; and at least one drillable sharp protrusion protruding from each face of the plate.

According to a third aspect of the present invention there is provided a well cementing/plug drilling apparatus comprising a drillable rigid metal plate having a top face and a bottom face, with a maximum diameter lying in the range of 1.27 to 3.71 centimeters less than the inside diameter of the well in which it is to be used and having a number of drillable sharp metal protrusions on both the top and bottom faces, the protrusions extending beyond the respective face by a distance lying in the range from 2.54 to 5 centimeters and wherein the number of protrusions per face lies in the range from 4 to 6.

According to a fourth aspect of the present invention there is provided a well pipe configuration comprising, a well shoe or collar pipe attachment having a cement tube adapted to receive a pump down wipe plug; a cementing/plug drilling apparatus comprising a drillable rigid plate having a top face and a bottom face and having at least one drillable top protrusion extending upward from the top face and at least one drillable bottom protrusion extending downward from the bottom face, said bottom protrusion operably contacting the top of the cement tube, and a pump down wipe plug, said top protrusions operably contacting the bottom of the plug.

According to a fifth aspect of the present invention there is provided a process of cementing within a well and drilling through a pump down wipe plug comprising pumping a desired amount of wet cement into a cementing string, followed by a pump down wipe plug at the interface of the wet cement and the fluid used to force the cement to the desired level, forcing the cement and plug down the string until the plug contacts the cement tube of a well shoe or collar pipe attachment allowing the cement to harden, then drilling out the plug with a rotating drill bit, further comprising the steps of introducing a cementing/plug drilling apparatus between the cement tube and the pump down wipe plug said apparatus comprising a drillable rigid plate having a bottom face and a top face and at least one drillable protrusion extending beyond each face, contacting the top of the plug with a rotating drilling bit, forcing the protrusion on the top face to engage the bottom of the plug and the protrusion on the bottom face to engage the top of the cement tube thereby impeding the tendency of the plug to rotate with the rotating bit and enhancing the drilling action of the bit.

According to a sixth aspect of the present invention there is provided a process of cementing within a well and drilling out a pump down wipe plug, which comprises introducing into a well pipe string a bottom pump down wipe plug, followed by the desired amount of wet cement, followed by a top pump wipe plug, forcing the wet cement and plugs down the string until the bottom of the bottom plug contacts the top of the cement tube of a well shoe or collar pipe attachment and bottom of the top plug contacts the top of the bottom plug, allowing the cement to harden, then drilling out the plugs with a rotating drilling bit, further comprising the steps of introducing a first cementing/plug drilling apparatus between the top of the cement tube and the bottom of the bottom plug, and introducing a second cementing/plug drilling apparatus between the top of the bottom plug and the bottom of the top plug, said apparatus comprising a drillable rigid plate having a top face and a bottom face with at least one drillable protrusion extending from each face, the first apparatus having an opening on the top in fluid communication through a fluid passage with an opening on the bottom face, drilling out the top plug, the second apparatus and the bottom plug, the top plug's tendency to rotate being retarded by the protrusion of the second apparatus which engages the bottom of the top plug and the top of the bottom plug and the bottom plug's tendency to rotate being impeded by the protrusions of the first apparatus which engages the bottom of the bottom plug and the top of the cement tube thereby enhancing the drilling action of the rotating bit on the two plugs.

According to a seventh aspect of the present invention there is provided a well shoe or collar pipe attachment having a cement tube adapted to receive a pump down wipe plug comprising at least one drillable protrusion extending upward from the top surface of the cement tube, said protrusion having a sharp upper end capable of engaging a pump down wipe plug and strong enough to withstand the torque exerted by the tendency of a pump down wipe plug to rotate when in contact with a rotating drill bit.

According to an eighth aspect of the present invention there is provided a well shoe or collar pipe attachment having a cement tube adapted to receive a pump down wipe plug comprising a number of aluminium protrusions extending at least 1.27 centimetres above the top surface of cemenf tube, the number of protrusions being in the range 3 to 6, having a length in the range from 4 to 30 centimetres and which extend into the top surface and are fixed in the cement tube so that the protrusions are capable of engaging the pump down wipe plug, thereby impeding the tendency of the plug to rotate when engaged by a rotating drill bit.

According to a ninth aspect of the present invention there is provided a well cementing and drilling process comprising the steps of: pumping wet cement into the well pipe string, inserting a top pump down wipe plug between the wet cement and a forcing fluid used to pump the wet cement to the desired level, pumping the plug and the wet cement down the well with the forcing fluid until the bottom of the plug contacts the top of a cement tube of a well shoe or collar pipe attachement having at least one drillable toothlike means capable of engaging said plug, allowing the cement to harden, contacting the top of the plug with a rotating drill bit so that the bottom of the plug is forced on to the tooth-like means thereby impeding the tendency of the plug to rotate and enhancing the drilling action of the bit on the plug.

According to a tenth aspect of the present invention there is provided a well cementing and drilling process comprising the steps of: inserting a bottom pump down wipe plug into the pipe string, followed by pumping the desired amount of wet cement into the pipe string, pumping the plug/wet cement down the string until the bottom of the plug contacts the top of a cement tube of a well shoe or collar pipe attachment having at least one drillable tooth-like means capable of engaging said plug, forcing the wet cement through the bottom plug and through the pipe attachment and allowing it to harden, contacting the top of the plug with a rotating drill bit so that the bottom of the plug is forced on to the toothlike means, thereby impeding the tendency of the plug to rotate and enhancing the drilling action of the drill bit on the plug.

According to an eleventh aspect of the present invention there is provided a pump down wipe plug comprising at least one drillable protrusion extending below the bottom surface of the plug, said protrusion being capable of engaging a surface with which it is in contact during a drilling operation in order to impede or inhibit rotation of the pluq.

According to a twelfth aspect of the present invention there is provided a bottom pump down wipe plug comprising at least ohe drillable protrusion extending above the top surface of the plug.

According to a thirteenth aspect of the present invention there is provided a well cementing and drilling process comprising the steps of: introducing the desired amount of wet cement into a cementing pipe string, inserting a pump down wipe plug having at least one drillable protrusion extending below its bottom surface, pumping the wet cement and plug down the well until the protrusion engages the top of a well shoe or collar pipe attachment.

According to a fourteenth aspect of the present invention there is provided a well cementing and drilling process comprising the steps of: inserting 2 bottom pump down wipe plug having at least one drillable protrusion extending above its top surface and at least one drillable protrusion extending below its bottom surface into a cementing pipe string, intrdoducing the desired amount of wet cement into the string behind the bottom plug, inserting a top pump down wipe plug following the wet cement, pumping the plugs and cement down the pipe until the protrusion on the bottom plug contacts the top surface of a well shoe or collar pipe attachment, forcing the cement through the bottom plug and the pipe attachment such that the top plug contacts the protrusion extending from the top of the bottom plug, allowing the cement to set, drilling out the top plug, the tendency of the top plug to rotate being impeded by engagement with the protrusion extending above the top surface of the bottom plug and drilling out the bottom plug, the tendency of the bottom plug to rotate being impeded by engagement with the protrusion extending above the top surface of the bottom plug and drilling out the bottom plug, the tendency of the bottom plug to rotate being impeded by engagement between the protrusion extending below the bottom plug and the top surface of the pipe attachment.

According to a fifteenth aspect of the present invention there is provided a down hole well pipe configuration comprising: a well shoe or collar pipe attachment and a pump down wipe plug having at leat one protrusion of cast iron or aluminum protruding from its bottom surface, the protrusion operably contacting the top surface of the pipe attachment.

In one aspect the present invention provides an apparatus to be placed between a pump down wipe plug and a cement surface or between two plugs within a well in order to enhance the drillability of the plugs and an improved process for cementing with and drilling through a pump down wipe plug.

In one embodiment, the invention relates to a drillable plate having at least one drillabie protrusion or tooth-like means protruding or extending from each face of the plate where the end of the protrusion furtherest from the plate is sharp, the protrusions being strong enough and sharp enough to engage a pump down wipe plug and a cement surface, thereby retarding the tendency of the plug to rotate when contacted by the rotating drilling bit. In one embodiment, the invention further relates to a drillable plate having at least one drillable protrusion on each face and a fluid passage through the plate in fluid communication with an opening on each face, the positioning of the openings being such that they may communicate with the fluid passage and top and bottom openings on a collar or shoe with which the plate comes into contact.In a further aspect the invention relates to a process of cementing within a well using a pump down wipe plug and a collar or shoe and subsequently drilling through the plugs, wherein subsequent to positioning a collar or shoe in a well, one inserts a plate having at least one protrusuion on each face into the well pipe, followed by a pump down wipe plug at the interface of the wet cement and the fluid used to force the plug and the cement down the well, then forcing the plug and the plate down the well until the protrusions on the bottom face are in contact with and engaged in the top surface of a shoe or collar and the protrusion on the top face of the plate is in contact with and engaged in the bottom of the pump down wipe plug.

Subsequently, after the cement has set, a drill bit is lowered on a drill string until it presses on the top of the plug forcing the protrusion further into the cement and the plug so that the tendency of the plug to rotate with the rotating drill bit is retarded or stopped and the drilling action of the bit on the plug is enhanced.In a further embodiment, the invention relates to a process of cementing within a well pipe using 9 collar or shoe, a bottom pump down wipe plug and a top pump down wipe plug and subsequently drilling through the top plug and the bottom plug comprising the steps of: introducing a plate into the well pipe, the plate having at least one protrusion on both its top and its bottom face and having an opening on its top and on its bottom face with a passage in fluid communication with the top and bottom openings, introducing a bottom pump down wipe plug into the well pipe, said plate top opening being in fluid communication with the bottom opening of the fluid passage of the bottom plug and said bottom opening being in fluid communication with the top opening of the fluid passage of the shoe or collar, introducing the desired amount of cement into the well pipe, followed by a second plate having at least one protrusion on the top face and at least one protrusion on the bottom face, followed by a top pump down wipe plug at the interface of the wet cement and the fluid used to pump the wet cement and the top plug, forcing the first plate into the top of the shoe or collar, the bottom plug onto the top protrusion of the first plate, the bottom protrusion of the second plate onto the top of the bottom plug and the top plug onto the top protrusions of the second plate, allowing the cement to set or harden, then subsequently lowering a drill bit onto the plugs, the protrusions on the second plate serving to retard the tendency of the top plug to rotate over the top surface of the bottom plug and the protrusion of the first plate serving to retard the rotation of the bottom plug over the surface of the shoulder of the shoe or collar, thereby enhancing the drilling of the top and bottom plugs.

In one aspect, the invention relates to an apparatus for improving the process of drilling through the combination of plug and cement string restriction. The invention further relates to float or baffle collars and shoes. In one embodiment the invention particularly relates to a collar or shoe having one or more protrusions, teeth, projections or nodes on its top surface. In one embodiment, it relates to collars or shoes where the top cement surface has been molded so that there are cement protrusions, i.e. ridges or sharp mounds on the top surface. In another embodiment, it relates to a collar or shoe having one or more spikes fixed to or anchored into and protruding above the upper surface of the collar or shoe.In one aspect, the invention further relates to a method of drilling through a plug/well pipe attachment (collar or shoe) combination where the plug is in contact with the upper surface of the well attachment and the upper surface of the well attachment is equipped with protrusions, teeth or spikes that engage the plug, the bit engages the top of the plug pressing it on to the protrusions or spikes which retard the plug's tendency to slip or rotate over the top surface of the well attachment, thus allowing the bit to drill through the plug.

Preferably, in one aspect of the invention, there is provided a cement restriction apparatus in a well pipe adapted to recieve a pump down wipe plug wherein the top surface of the cement restriction has at least one drillable projection or tooth-like means protruding from its surface which may take the form of a cement collar or shoe wherein the top surface of the collar or shoe has been molded so that at least one cement projection or tooth-like means protrudes from its surface. The collar or shoe where the projections are drillable spikes or blades embedded in the cement and protruding upward and out of the top surface of the cement. This or these spikes, teeth or blades like means are made of material substantially stronger than the plug and capable of denting, penetrating and rending the material of the plug.These spikes, teeth or blades are made of drillable metals, woods or plastics.

Preferably, in another aspect of the invention, the process of drilling through a pump down wipe plug/collar or shoe combination is one in which the drill string is lowered until it contacts the top of a pump wipe plug, the bottom of said plug is in communication with the top of a collar or shoe, and the top of the collar or shoe is equipped with at least one protrusion or tooth-like means made of a drillable material strong enough to dent, penetrate and rend the plug, the interaction of the rotation of the drill bit on the top of the plug and the retarding effect of the protrusions or teeth on the bottom of the plug aids the drill bit to drill through the plug saving both time and energy.

In a further aspect, the invention relates to a pump down wipe plug having at least one drillable metal, plastic or wooden protrusion or tooth extending from the bottom surface. In one aspect, the invention also relates to a bottom pump down wipe plug having at least one metal, plastic or wooden protrusion or tooth-means extending from the top surface of the plug. In one embodiment, the invention further relates to a bottom pump down wipe plug having at least one protrusion extending from the top surface and at least one protrusion extending from the bottom surface.In another aspect, the invention relates to a process of drilling through a pump wipe down plug where the pump down wipe plug is held stationary or if tending to rotate retarded by at least one metal, wooden or plastic protrusion extending from the bottom surface cf the plug into solid cement or stationary second plug below the first plug. In one aspect, the invention also relates to the process of drilling through a top pump down wipe plug where the top pump down wipe plug is held stationary by at least one sharp protrusion extending from the top surface of the bottom plug. In a further aspect, the invention further relates to the process of drilling through the top and bottom pump down wipe plugs where the top plug is held stationary by at least one protrusion or tooth-like means extending from the surface of the bottom plug and the bottom plug is held stationary by at least one protrusion extending from the bottom of the plug into solid cement.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of the circular plate of Figure 2 showing four angle iron shaped protrusions or teeth on each face, Figure 2 is a view of one face of the plate of Figure 1, Figure 3 is a side view of the polygon shaped plate of Figure 4 with four bar like protrusions or barbs on each face and a fluid passage through the plates, Figure 4 is a view of the face of the plate of Figure 3, Figure 5 is a sectional view of the square plate of Figure 6 along line 5-5 where the plate has a hollow core, having four rod-like protrusions on each face and having a fluid passage through its centre, Figure 6 is a view of the face of the plate of Figure 5, Figure 7 shows a plate and its position between a collar and single plug following a cementing operation, Figure 8 shows the use of two plates when employing both a top and a bottom plug at the beginning of the plug drilling operation, Figure 9 is a sectional view of the apparatus of Figure 10 taken through line 9-9, Figure 10 is an example of the apparatus viewed from either face showing an irregular circumference, Figure 11 is a sectional view of the collar of Figure 12 along the line Il-Il showing molded cement projections shaped like pyramids, Figure 12 is a view of the top surface of the collar of Figure 11 from above, Figure 1 3 is a sectional view of the shoe of Figure 14 along line 13-13 showing molded cement projections shaped like blades, Figure 14 is a view of the top surface of the shoe of Figure 13 from above, Figure 1 5 is a sectional view of the shoe of Figure 16 along the line 1 5-1 5 showing projec.ions that were made of drillable material other than cement that have been molded into the shoe, Figure 16 is a view from above of the shoe top surface of Figure 15, Figure 1 7 is a sectional view of the collar of Figure 1 7-1 7, showing projections made of drillable material other than cement where the projections which are blades that fit into slots and where the portion extending above the surface of the collar is at an angle relative to the vertical which is counter clockwise, Figure 1 8 is a view from above of the collar of Figure 17, Figure 1 9 is an enlarged view of a projection which is moulded into the shoe as shown in Figure 15 and 16, Figure 20 is an enlarged view of a blade used in the shoe of Figures 17 and 18, Figure 21 is a sectional view of a pump down wipe plug along the line 21-21 of Figure 22, Figure 22 is a head on view of the bottom of the plug of Figure 21, Figure 23 is a sectional view of a bottom pump down pipe plug taken through the line 23-23, the plug being made with a hollow core, Figure 24 is a view of the plug of Figure 23 from the top, Figure 25 is a sectional view of a bottom plug, Figure 26 is a sectional view of the plug of Figure 27 along the line 24-24, and Figure 27 is a view of the top of the plug of Figure 26.

In the description of this invention a "cement pipe restriction" refers to a collar or shoe used in drilling operations having a cement shoulder.

These collars or shoes can be of the cement float type, cement baffle type cement guide type, or the like.

Figures 1 to 6, 9 and 10 show illustrative examples of a well cementing/plug drilling apparatus in which there is a drillable plate 110 having a top of first face 111 and a bottom or second face 112. The shape of the plate 110 when viewed perpendicular to either face 111 or 112 can be any shape, e.g. circular, square or a polygon, but the maximum distance between any two points on the outer circumference of the plate 110 must be less than the inside diameter of any well pipe through which the plate 110 must pass.

To ensure that the plate will not pass through any openings in the bottom plug or in the well collar or shoe. The circumference of the plate is such that the plate will not pass through any opening in the bottom plug or well collar or shoe with which the plate may come in contact. The preferred shape of the face of the plate is a circle and being between 1.27 and 3.71 centimeters less in diameter than the inside diameter of the well in which it will travel. The distance between the face 111 and 112 can be any distance, i.e. the thickness of the plate can be any thickness, but it is preferred that it be between about .6 and about 3 centimeters in thickness, preferably between about .7 and about 2 centimeters in thickness.It is possible to have the thickness vary across the face but the preferred embodiment of the invention is to have the faces of the plate 111 and 11 2 parallel to each other, i.e. a uniform distance apart: a flat plate.

The plate is made of drillable material. The preferred materials are rigid metals, plastics and woods which are strong enough to withstand the torque exerted on them by the tendency of the plugs with which they are in contact to rotate. The most preferred materials are metals and the preferred metals are cast iron and aluminum, while aluminum is the most preferred metal.

The plates can be solid or they can be made with hollow cores 113, as in Figure 5. The use of hollow cores 11 3 allows greater latitude in adjusting the density of the apparatus 110 so that the apparatus 110 can be made less dense than the fluid in which it is submerged, i.e, mud or cement, even when the density of the material the plate is made of is greater than the fluid in which it is floating.

In a preferred embodiment of the invention, there is a fluid opening 114 on the face 111 and a fluid opening 1 1 5 on face 112 with a fluid passage 11 6 in fluid communication with the openings 114 and 115.

Protruding from each of faces 111 and 112 is at least one protrusion or tooth-like means 11 7.

These protrusions or teeth 11 7 are rubber denting, penetrating and rending teeth. These protrusions or barbs 11 7 may be rods or bars or angle irons made of drillable material capable of withstanding the torque applied to the protrusions 11 7 by the tendency of the plugs to rotate caused by the rotating drill bit. The preferred materials are metal, plastic and wood. The most preferred materials are metals; aluminum and cast iron are the preferred metals, and aluminum is the most preferred metal.

The number of protrusions or teeth 11 7 per face may be between 1 and 10 inclusive, preferably between 2 and 8 inclusive and most preferably between 4 and 6 inclusive. The minimum length of a protrusion 1 7 is about 1.27 centimeters. The preferred length of the protrusion is between 1.27 and 7 centimeters, most preferably between 2.54 and 5 centimeters.

The ends of the protrusions or teeth furthest from the surface from which they protrude are sharp, either pointed (Figures 1, 2, 5, 9 and 10) or blade like (Figures 3 and 4). Preferably the protrusions or teeth 11 7 are pointed. The protrusions should be sharp enough to dent and penetrate the plugs and the cement when pressure is applied to the top of a plug by the drill bit.

The well cementing and plug drilling apparatus can be made by casting or manufacturing the protrusions 11 7 as part of the plate 110, fixing i.e.

welding, the protrusions 11 7 to the face of the plate or where a bar, rod or angle iron shaped member is used simultaneously as the protrusion 117 on both faces 111 and 112, the bar, rod or angle iron shaped member may pass through the plate and be welded to the plate.

A process of cementing and plug drilling well be described with reference to Figures 7 and 8.

The cementing and plug drilling process comprises introducing the cementing and plug drilling apparatus between the shoe or collar and a plug and between top and bottom plugs during the cementing operation; then after the cement has set, drilling away the plug or plugs with the aid of the cementing and plug drilling apparatus which retards or stops the tendency of the plug or plugs to rotating with the rotating motion of the drill bit.

In one embodiment (shown in Figure 7) the shoe or collar 118 is lowered to the desired level and wet cement introduced into the well. When the desired amount of cement has been pumped down the pipe 11 9, a cementing and plug drilling apparatus 120 is introduced, followed by a pump down wipe plug 121. The plug is forced down the well by a fluid such as mud or water until the protrusions or teeth 11 7 of one of the faces 111 or 112 of the cementing and plug drilling apparatus 120 have come to rest on the top surface 122 of the cement tube 123 of the shoe or collar 118 and the bottom surface 124 of the plug 121 comes to rest on the protrusions or teeth 11 7 on the opposite face of the same apparatus 120.

If the apparatus 120 does not have a fluid passage 116 so that the cement may feely pass through the cement tube top opening 125, passage 126, and bottom opening 127, or if the apparatus is not an irregular or star (Figure 10) shape such that cement may pass by the apparatus 120, then the apparatus 120 may interfere with the passage of cement, To overcome this, the apparatus 120 may be chosen so that its density is less than that of cement and the apparatus 120 is preferably introduced in to the well pipe immediately before the plug.

Alternatively, the apparatus can be attached to the bottom 124 of the plug 121 by embedding the teeth 11 7 of the apparatus 120 into the bottom 124 of the plug 121. Then the plug 121 and the apparatus 120 descend the pipe as the interface between the cement and the forcing fluid at the same time.

Once the plug comes to rest one has a well configuration comprising a shoe or collar, upon which rests an apparatus 120 its teeth 11 7 on face one 112, communicating with the surface 122 of the cement tube 123, upon the apparatus 120 rests a pump down wipe plug 121 its bottom surface 124 resting on the teeth 11 7 of the second surface 111 of the same apparatus.

In another embodiment of the invention (Figure 8) the pipe configuration comprises a shoe or collar 118 upon which rests the teeth 117 of a first apparatus 120, upon the teeth of the opposite face of the apparatus 120 rests the bottom 128 of a bottom plug 129, said bottom plug having a top opening 130, a bottom opening 131 and a fluid passage 132 in fluid communication with the openings 130 and 131, on top 133 of the bottom plug 129 is a second apparatus 120, its teeth resting on the top 133 of the bottom plug. On top of the second apparatus 120 is a top pump down wipe plug 121 its bottom 124 resting on the teeth 117 on the face 111 of the second apparatus 120. The process to obtain the above well pipe configuration comprises lowering the shoe or collar 11 8 to the desired level, introducing a first apparatus 120 followed by a bottom pump down wipe plug 129, this plug having a membrane strong enough to maintain the interface between the cement and a second fluid until the plug is held in place by a restriction, adding the desired amount of cement and a second apparatus 120 followed by a top pump down wipe plug 121 the bottom teeth 117 of the second apparatus 120 resting on the top surface 133 of the bottom plug 129 and the bottom surface 124 of the top plug 121 resting on the top teeth 11 7 of the second apparatus 120.In the preferred embodiment of the invention, the teeth 11 7 on the face 111 of apparatus 120 are essentially identical to the teeth 117 on face 112 so that the top teeth 11 7 and face 111 are merely those teeth that face upward relative to the earth.

In the case where there is both a top plug 121 and a bottom plug 129, it is necessary to ensure that fluid can easily flow past the first apparatus 120, between the bottom plug 129 and the collar or shoe 118. This may be done by choosing an apparatus 120 with a fluid passage (as in Figures 3-6) or by choosing an irregular shape apparatus 120 (like Figures 9 and 10).

To help ensure that the apparatus 1 20 reaches the surface on which it will rest so that the faces 111 and 112 are essentially perpendicular to the pipe 11 9, the apparatus 120 may be chosen so that the material from which it is made or a hollow core 11 3 ensure that its density is less than the fluid in which it will float and then the apparatus 120 is inserted into the well pipe immediately before the plug, bottom plug 129 or top plug 121 which serve to separate the different fluids. It is also possible to stick or attach the apparatus 120 on to the bottoms of each plug by having the teeth 11 7 penetrate the plug or even attaching one apparatus to the bottom 128 of the bottom plug 129 and another to the top 133 of the bottom plug 129.In this way the plugs and the apparatus travel together down the pipe.

If the fluid passage 1 32 of the bottom plug 129 has an irregular cross section so that the cement which hardens in the fluid passage 132 forms an irregularly shaped vertical bar that retards the tendencey of the bottom plug 129 to be rotated by the action of the bit, then it is possible to eliminate the use of the apparatus 120 between the bottom plug 129 and the collar or shoe 118.

Once the cement has hardened and the operator desires to drill through the plug or plugs, a drill bit is lowered on to the uppermost plug forcing the plug further down on to the teeth 11 7 on the face 111 of the apparatus 120, on which they rest and the bottom teeth 11 7 of the face 112 of the apparatus 120 further down into the surface (bottom plug 129 or cement) in which they rest. The rotating drill bit drills through the plug or plugs which are held stationary or their tendency to rotate is retarded by the apparatus 120, thereby making the drilling action of the bit more effective.

Referring to the Figures 11-18 a cement pipe restriction is made of a pipe or cylindrical housing member 210, having a top attachment means 211, usually female threads, and in the case of the collar, a bottom attachment means 212, usually male threads, to enable the collar or shoe to be attached to a pipe string. Inside the housing member 210 is a cement tube 213, the outer surface of the cement tube 21 3 communicating with and fixed to the inner surface of the pipe 210. This is usually done by having the inner surface of the pipe 210 equipped with both radial and longitudinal ribs 21 5. The cement tube 21 3 has a top opening 21 8 and a bottom opening 219 with a passage 220 which connects the top and bottom openings 218 and 219.Optionally the passage 220 is equipped with a valve 215 as in Figures 11, 15 and 17.

The top surface of the cement tube 21 6 which is below the top attachment means is adapted to receive a pump down wipe plug. The top surface 21 6 of the cement tube 213 can be flat, i.e.

perpendicular to a line running through the centre of the length of the pipe 210 and cement tube 213 as in Figure 5. The top surface 21 6 may also slope inwardly and downwardly as in Figures 11, 1 3 and 17, or even, inwardly and upwardly. The cement tube 213 and the valve 21 5 are made of drillable material.

Protruding from the top surface of the cement tube 216 is at least one protrusion or tooth-like element 21 7. The protrusion may be a drillable object of any shape, preferably extending at least 1.27 centimetres above the top surface 216 of the cement tube 213, capable of engaging and retarding the rotation of slipping of the plug over the top surface 216 of the cement tube 213 caused by the action of a drill bit on the plug. The protrusion or tooth-like means must be made of a material strong enough to dent, penetrate, hold and rend the plug. Pump down wipe plugs are usually made of drillable rubber, plastic or other friable or rubbery material. The preferred materials for the protrusion or tooth-like means 217 are cement, metal, wood or plastic.The most preferred materials are metals and of the metals, cast iron and aluminium are preferred, aluminium being the most preferred. The protrusion 21 7 must be high enough to engage dent, penetrate, hold and rend the plug, but it is preferred that the protrusions be between about 1.27 centimetres and 10 centimetres more preferably between about 1.27 centimetres and 7 centimetres most preferably between about 2.54 centimetres and 5 centimetres high above the top surface 21 6 of the cement tube 213. It is preferred that the protrusions 21 7 have tops 221 that are sharp, preferably pointed as in Figures 11, 12,15, 16 and 19, or forming a sharp edge or blade as in Figures 13, 14, 17, 18 and 20.The height of the protrusion 21 7 is dependent on the fit between the pump down wipe plug and the top surface of the cement tube 21 6 and on the case with which the protrusion 21 7 engages the material of the plug. The sharpness of the top of the protrusion 221 is also dependent on the ease with which it engages the plug material. In a preferred embodiment the top of the protrusion 221 is shaped as a series of teeth or barbs, i.e. like a saw.

The number of protrusions 217 is between 1 and about 10 inclusive, preferably between 2 and 8 inclusive, and most preferably between 3 and 6 inclusive. The number of protrusions 21 7 is dependent on the size of the top of the cement tube 213 and the height of the protrusions 217.

The greater the area of the top surface of the cement tube 21 6 and the smaller the protrusions 21 7 the larger is the number of protrusion 21 7 needed. The preferred spacing of the protrusions 217 on the top surface 216 of the cement tube 213 is one where the distance between protrusion 21 7 is maximized but if the protrusions 21 7 were placed on a single line from the centre of the top opening 21 8 to the pipe 210 without changing the radial distance from the centre of the opening 218 there would be a maximum and equal distance between each protrusion 217.

A preferred embodiment of the invention where the protrusions 21 7 are molded of cement is illustrated in Figures 11-14. This embodment may be made by using as part of the form for casting the cement tube 213, the female counterpart of the protrusions. This form would be in contact with the top of the cement tube while the cement sets. The protrusions 21 7 must have sharp tops 221 in order to engage the bottom of the plug and to prevent or impede its rotation or slips.

ing over the top surface 21 6 of the cement tube 213. The sharp tops can be either points as the protrusions of Figures 11 and 1 2 or blades or wedges as in Figures 1 3 and 14. The wedge shape protrusions 217 may have their sharp edge 221 running parallel to a line from the centre of the opening 218 to the pipe 210 or tangential to a circle about the centre of the opening 218 as in Figure 14, 217a and 221a.

The size of the cement protrusion 21 7 and the type of cement must be such that the torque exerted by the plug when engaged by the drilling bit wiil not break the protrusion 21 7. At the same time the top edge 221 must be sharp enough (or the plug material soft enough) to allow the protrusion to engage the bottom of the plug.

Another embodiment of the invention is illustrated in Figures 1 5-20. In this embodiment the protrusion 21 7 is made of drillable metal, wood, or plastic strong enough to engage, dent, penetrate, retard, hold and rend the plug as torque is applied by motion of the drill bit on the top of the plug.The protrusion 21 7 of the embodiment illustrated in Figures 1 5 and 1 6 is part of an element such as a drillable spike, rod, bar or angle from 223 that has been permanently fixed in the cement tube 21 3 by casting the bottom of the spike, bar, rod or angle iron 223 as part of or into the cement tube 21 3. The spikes, bars, rods or angle irons 223 typically have a pluraiity of holes through them or ribs on them to assist in anchoring them into the cement. The wet cement bridges through the holes or forms around the ribs and on during holds the protrusions 21 7 in place.

In another embodiment illustrated in Figures and 1 8 the protrusions are part of drillable rods, spikes, bars or angle irons 223 which may be readily slipped or fitted into pockets 222 when needed. The collar or shoe is made so that pockets 222 are formed in the cement tube 213 with openings on the top surface 21 6 of the cement tube 21 3. When needed the protrusions 21 7 may be formed by inserting spikes, rods, bars or angle irons 223, depending on the shape of the pocket 222 so that a portion protrudes above the surface 216.

These spikes, rod, bars or angle irons 223 can be between 4 and 30, preferably between 5 and 25 and most preferably between 6 and 24 centimetres in length.

The shape of the protrusions can be pointed as in Figure 19 or wedge or blade like as in Figure 20. In most drilling operations the drilling is done by rotating the bit in the clockwise direction. In one embodiment of the invention, to enhance the ability of the protrusions to retard the rotation of the plug, the point or edge is angled counter clockwise as in Figures 1 5-20.

The process of this invention comprises drilling through a plug/collar or shoe combination where a drill bit 224 is lowered into the well and brought in contact with the top of a drillable pump down wipe plug 225, forcing the bottom of the plug to be engaged by protrusions 217 which protrude from the top surface 216 of the cement tube 213 of a collar or shoe, the bit is rotated and the plug 225 is held stationary by the protrusions 217 and the bit drills through the plug 225, then the protrusions 21 7 and finally the cement tube portion of the collar or tube.

This drilling process is part of the cementing/drilling process. The improved collar or shoe is placed in the pipe or casing string, lowered to the desired depth and a pump down wipe plug 225 pumped down at the interface between a wet cement portion and another fluid portion, the plug 225 stops when it comes into contact with and is forced onto the protrusions 217. Once the cement has set and the well operator elects to drill out the plug 225 and the cement tube 213 of the shoe or collar, a drill bit 224 is lowered on a drill string until it contacts the plug 225 and forced the plug 225 down so that the protrusion 21 7 dents or penetrates the bottom of the plug even further.The rotating drill bit 214 can either drill away the upper portion of the plug 225 with the protrusions holding the plug stationary or force the plug to rotate thereby causing the protrusions 217 to rend the bottom of the plug thereby drilling the plug from the bottom.

The preferred embodiment of the process is to have the plug held stationary by the protrusions 217 and the drill bit 224 drill the plug away from the top. Since the plug 225 protrusions 217 and cement tube 213 are all made of drillable material the combination of plug 225, the cement tube 213 and protrusions 21 7 can be easily drilled out.

For two experimental situations in which the plug and the cement tube combinations were essentially the same except that one of the cement tubes was equipped with protrusions, it was observed that it took about twice as long to drill through the plug/cement tube combination as it did to drill through the plug/protrusion/cement tube combination.

Figure 21 is an illustration of a pump down plug 310 where the plug 310 is made with a core 311 which in this embodiment is hollow and can be made of drillable plastic, wood or metal. The core 311 is molded into the body of the plug 312 which is made of rubber or plastics. Typical plugs as shown in Figures 21-27 are shaped with a top section whose diameter is iarge enough so that the section exerts a positive wiping and sealing action on the pipe with which it communicates. It also has one or more fins 314 which serve to wipe and seal and a bottom section 31 5 where the top of the bottom section 316 is the same diameter as the fins and the bottom of the bottom section 31 7 has a diameter slightly less than the fins.The top of the plug 31 8 and the bottom of the plug 31 9 are normally flat or perpendicular to a line through the longitudinal centre of the plug or the pipe in which it travels.

Illustrated in the Figures 21-27 are protrusions 320 which protrude from the bottom surface of the plug 319 in Figure 21, the bottom and the top surfaces 318 and 319 of the plug 310 in Figures 23 and 24 and the top surface of the plug 318 in Figure 26. There is at least one protrusion 320 on each plug 310. These protrusions are part of a rod, bar or angle iron 321 which is embedded and fixed into the body 312 and sometimes the core 311 (Figure 21) of the plug 310. The rod, bar or angle iron 321 are made of a material strong enough to stop or retard the rotation of the plug 310 caused by the action of the rotating drill bit without breaking. Atypical materials are drillable metals, plastics and wood.

The preferred materials ate metals and the preferred metals are cast iron and aluminum, the most preferred metal is aluminum.

The length of the protrusion 32G is at least 1.27 centimeters, preferably between about 1.27 centimeters and about 8 centimeters, most preferably between about 2.5 and about 5 centimeters above the surface 318 or 319 of the plug 310. The total length of the rod, bar or angle iron 321 (the protrusion plus that part below the surface) is between about 4 centimeters and about 1 6 centimeters greater than the length of the plug 310. It should be recognised that the length of the protrusion or teeth-like means 320 and the bar, rod or angle iron 321 are dependent on how easily the protrusion 320 penetrates the surface in front of it and how solidly the rod, bar or angle iron 321 is held in the plug 310.

The tip or end of the protrusion furtherest from the surface from which it protrudes 322 is preferably sharp, either a point or an edge or blade (322a) capable of engaging or penetrating the surface with which it comes into contact.

Figures 23-27 illustrate plugs 310 which are known as bottom plugs because they have top fluid openings 323 and bottom fluid openings 324 with a fluid passage 325 potentially in open fluid communication with the openings 323 and 324. The bottom plugs 310 are introduced with a diaphragm or membrane blocking the fluid passage 325 as shown in Figures 23 and 26 which can be burst or broken by increased fluid pressure as shown in Figures 24, 25 and 27.

Figures 23 and 25 illustrate bottom plugs 310 where the protrusions or barbs 320 are on the top 318 and bottom 319 of the plug 310. The top protrusion 320 of Figure 23 has blade like ends 322a while the bottom protrusion 320 has pointed ends 322. Each protrusion 320 is part of a separate rod, bar or angle iron 321 in Figure 23 while in Figure 25 the top and bottom protrusion 320 is part of the same bar, rod or angle iron 321.

Also Figure 23 illustrates a plug 310 with a core 311 while Figures 25 and 26 illustrate solid plugs 310 made without a hollow core 311.

The preferred number of protrusions 320 per plug surface 318 or 319 is between 1 and 8 inclusive more preferably between 2 and 8 inclusive and most preferably between 4 and 6 inclusive.

The process of drilling through a pump down wipe plug 310 as illustrated in Figure 28 comprises lowering a rotating drill bit 326 into a well and on to the top surface 318 of a pump down wipe pump 310 having at least one protrusion or tooth-like means 320 of at least 1.27 centimeters in length protruding from the bottom surface 31 9 of the plug which engages the surface below the plug thereby holding the plug 310 stationary or retarding its tendency to rotating so that most of the effective drilling energy goes into drilling the plug 310, not rotating the plug 310.

The process of drilling through a top plug 310 and a bottom plug 310' as illustrated in Figure 29 where the tendency of the top plug 31 0 to rotate is retarded by at least one protrusion 320 of at least 1.27 centimeters protruding from the top surface of the bottom plug 310' which engages the bottom of the top plug 319 and where the tendency of the bottom plug 310' to rotate is retarded by at least one protrusion 320 protruding from the bottom surface 319' of the bottom plug which engages the cement below the bottom surface 31 9' of the bottom Dlug.

An embodiment of the process of drilling through the combination of a top plug 310 and a bottom plug 310' where a rotating drill bit 326 is lowered onto the top surface 31 8 of a top plug 310 whose tendency to rotate is retarded by at least one protrusion 320 protruding above the top surface of the bottom plug 318' and engaging and holding the top plug 310 while the tendency of the bottom plug 310' is retarded by cement core 327 that has set in the fluid passage 325 of the bottom plug 310' where that cement is part of the total cement which was pumped into the well. The effectiveness of the cement core 327 in retarding the rotation of the bottom plug 310' is enhanced when the cross section of the fluid passage 325 which forms the mold for the cement core 327 is asymmetrical or has longitudinal ribs as shown in Figures 26 and 27.

One embodiment of a cementing process comprises inserting a pump down wipe plug 310 into a pipe as the interface between the wet cement and the fluid used to pump the wet cement to the desired level, said plug 310 having at least one protrusion or tooth-like means 320 protruding from its bottom surface 319, the cement is pumped to the desired level by forcing the plug 310 down the pipe until the protrusion 320 comes into contact with the top surface of a cement shoulder or a collar or shoe 328.

Another embodiment of a cementing process comprises introducing a bottom plug 310' into a pipe as an interface between the wet cement and the fluid the cement is displacing, said bottom plug having at least one protrusion 320 extending from its bottom surface 319, and introducing a top plug 310 into the pipe as an interface between the wet cement and the fluid forcing the wet cement to the desired level, said top plug 310 having at least one protrusion 320 extending from its bottom surface 319 and pumping the plugs and cement down the pipe until the bottom plug 310' comes into contact with the top surface 328 of the cement.

Another embodiment of the cementing process comprises inserting a bottom pump down wipe plug 310' into the well pipe as in interface between the cement and the fluid it is displacing where the bottom plug 310' has at least one protrusion 320 extending from its bottom surface 31 9 and at least one protrusion extending from its top surface 318, pumping in the desired amount of cement then a top plug as an interface between the wet cement and the fluid used to pump the cement to the desired level and pumping the two plugs and cement until the protrusions 320 on the bottom 319 of the bottom plug 310' comes into contact with the top surface 328 of the shoulder of a collar or shoe and the top plug 310 comes into contact with the protrusions 320 on the top 318 of the bottom plug 310'.

Claims (46)

Claims

1. A combined well pipe attachment and pump down wipe plug, in which interlocking means are provided at the interface between the plug and the attachment, which means comprise sharp protrusions operative to penetrate the surface of the plug and/or the attachment in order to inhibit or impede relative rotation between the plug and the attachment when a rotary drill bit is brought into contact with the plug to drill out the plug.

2. A well cementing/plug drilling apparatus comprising: a rigid drillable plate having a bottom face and a top face, said plate having a maximum diameter less than the inside diameter of the well in which it is to be used, and 'at least one drillable sharp protrusion protruding from each face of the plate.

3. A well cementing/plug drilling apparatus as claimed in claim 2, wherein said protrusion is made of metal, plastics material or wood.

4. A well cementing/plug drilling apparatus as claimed in claim 2 or 3, wherein the height of the protrusion is in the range from 1.27 to 7 centi-, meters.

5. A well cementing/plug drilling apparatus as claimed in any of claims 2 to 4, wherein the number of protrusions per plate face lies in the range from 2 to 8 inclusive.

6. A well cementing/plug drilling apparatus as claimed in claim 5 wherein the plate and protrusions are made of cast iron or aluminum.

7. A well cementing/plug drilling apparatus as claimed in any of claims 2 to 6, having an opening on the top face in fluid communication through a fluid passage with an opening on the bottom face.

8. A well cementing/plug drilling apparatus as claimed in any of claims 2 to 7, wherein the shape of the plate when viewed perpendicular to a face is star shaped.

9. A well cementing/plug drilling apparatus comprising a drillable rigid metal plate having a top face and a bottom face, with a maximum diameter lying in the range of 1.27 to 3.71 centimeters less than the inside diameter of the well in which it is to be used and having a number of drillable sharp metal protrusions on both the top and bottom faces, the protrusions extending beyond the respective face by a distance, lying in the range from 2.54 to 5 centimeters and wherein the number of protrusions per face lies in the range from 4 to 6.

10. A well pipe configuration comprising, a well shoe or collar pipe attachment having a cement tube adapted to receive a pump down wipe plug; a cementing/plug drilling apparatus comprising a drillable rigid plate having a top face and a bottom face and having at least one drillable top protrusion extending upward from the top face and at least one drillable bottom protrusion extending downward from the bottom face, said bottom protrusion operably contacting the top of the cement tube, and a pump down wipe plug, said top protrusions operably contacting the bottom of the plug.

11. A configuration as claimed in claim 10, wherein the rigid plate has an opening on the top face in fluid communication through a fluid passage with an opening on the bottom face, the said pump down wipe plug being a bottom pump down wipe plug and wherein above the bottom pump down wipe plug is positioned; a second cementing/plug drilling apparatus comprising a drillable rigid plate having a top face and a bottom face and having at least one drillable top protrusion extending upward from the top face and at least one drillable bottom protrusion extending downward from the bottom face, the bottom protrusions of the second apparatus being operably in contact with the top of the bottom pump down wipe plug and a top pump down wipe plug, the bottom of the top pump down wipe plug being operably in contact with the top protrusions of the second cementing/plug drilling apparatus.

12. A configuration as claimed in claim 11, wherin the second cementing/plug drilling apparatus has an opening on the top face in fluid communication through a fluid passage with an opening on the bottom face.

13. A process of cementing within a well and drilling through a pump down wipe plug comprising pumping a desired amount of wet cement into a cementing string, followed by a pump down wipe plug at the interface of the wet cement and the fluid used to force the cement to the desired level, forcing the cement and plug down the string until the plug contacts the cement tube of a well shoe or collar pipe attachment, allowing the cement to harden, then drilling out the plug with a rotating drill bit, further comprising the steps of introducing a cementing/plug drilling apparatus between the cement tube and the pump down wipe plug, said apparatus comprising a drillable rigid plate having a bottom face and a top face and at least one drillable protrusion extending beyond each face, contacting the top of the plug with a rotating drilling bit, forcing the protrusion on the top face to engage the bottom of the plug and the protrusion on the bottom face to engage the top of the cement tube thereby impeding the tendency of the plug to rotate with the rotating bit and enhancing the drilling action of the bit.

14. A process of cementing within a well and drilling out a pump down wipe plug, which comprises introducing into a well pipe string a bottom pump down wipe plug, followed by the desired amount of wet cement, followed by a top pump down wipe plug, forcing the wet cement and plugs down the string until the bottom of the bottom plug contacts the top of the cement tube of 2 well shoe or collar pipe attachment and bottom of the top plug contacts the top of the bottom plug, allowing the cement to harden, then drilling out the plugs with a rotating drilling bit, further comprising the steps of introducing a first cementing/plug drilling apparatus between the top of the cement tube and the bottom of the bottom plug, and introducing a second cementing/plug drilling apparatus between the top of the bottom plug and the bottom of the top plug, said apparatus comprising a drillable rigid plate having a top face and a bottom face with at least one drillable protrusion extending from each face, the first apparatus having an opening on the top face in fluid communication through a fluid passage with an opening on the bottom face, drilling out the top plug, the second apparatus and the bottom plug, the top plug's tendency to rotate being retarded by the protrusion of the second apparatus which engages the bottom of the top plug and the top of the bottom plug and the bottom plug's tendency to rotate being impeded by the protrusions of the first apparatus which engages the bottom of the bottom plug and the top of the cement tube thereby enhancing the drilling action of the rotating bit on the two plugs.

15. A process as claimed in claim 13 or 14 wherein the apparatus is introduced by attaching the apparatus to the plug by forcing the protrusions to engage the plug and simultaneoulsy introducing the plug and the apparatus down the cementing pipe string.

16. A well shoe or,collar pipe attachment having a cement tube adapted to receive a pump down wipe plug, comprising at least one drillable protrusion extending upward from the top surface of the cement tube, said protrusion having a sharp upper end capable of engaging a pump down wipe plug and strong eneough to withstand the torque exerted by the tendency of a pump down wipe plug to rotate when in contact with a rotating drill bit.

17. A pipe attachment as claimed in claim 16, wherein the protrusion extends at least 1.27 centimeters above the top surface of the cement tube.

18. A pipe attachment as claimed in claim 17, wherein the protrusion is made of cement.

19. A pipe attachment as claimed in claim 17, wherein the protrusion is made of drillable metal, plastics material or wood.

20. A pipe attachment as claimed in claim 19, wherein the protrusion is part of a rod, bar or angle iron which has a length in the range from 4 to 30 centimeters and which extends below and into the surface of the cement tube.

21. A pipe attachment as claimed in claim 20, wherein the number of protrusions is between 3 and 6 inclusive.

22. A pipe attachment as claimed in claim 21, wherein the protrusion is made of aluminium.

23. A well shoe or collar pipe attachment having a cement tube adapted to receive a pump down wipe plug comprising a number of aluminium protrusions extending at least 1.27 centimeters above the top surface of cement tube, the number of protrusions being in the range 3 to 6, having a length in the range from 4 to 30 centimeters and which extend into the top surface and are fixed in the cement tube so that the protrusions are capable of engaging the pump down wipe plug, thereby impeding the tendency of the plug to rotate when engaged by a rotating drill bit.

24. A well cementing and drilling process comprising the steps of: pumping wet cement into the well string, inserting a top pump down wipe plug between the wet cement to the desired level, pumping the plug and the wet cement down the well with the forcing fluid until the bottom of the plug contacts the top of a cement tube of a well shoe or collar pipe attachment having at least one drillable tooth-like means capable of engaging said plug, allowing the cement to harden, contacting the top of the plug with a rotating drill bit so that the bottom of the plug is forced onto the tooth-like means thereby impeding the tendency of the plug to rotate and enhancing the drilling action of the bit of the plug.

25. A well cementing and drilling process comprising the steps of inserting a bottom pump down wipe plug into the pipe string, followed by pumping the desired amount of wet cement into the pipe string, pumping the plug/wet cement down the string until the bottom of the plug contacts the top of a cement tube of a well shoe or collar pipe attachment having at least one drillable tooth-like means capable of engaging said plug, forcing the wet cement through the bottom plug and through the pipe attachment and allowing it to harden, contacting the top of the plug with a rotating drill bit so that the bottom of the plug is forced onto the tooth-like means, thereby impeding the tendency of the plug to rotate and enhancing the drilling action of the drill bit on the plug.

26. A pump down wipe plug comprising at least one drillable protrusion extending below the bottom surface of the plug, said protrusion being capable of engaging a surface with which it is in contact during a drilling operation in order to impede or inhibit rotation of the plug.

27. A pump down wipe plug as claimed in claim 26, wherein the plug is a bottom pump down wipe plug and further comprises at least one drillable protrusion extending above the top surface of the plug and being capable of engaging so as to impede or inhibit the rotation of or to rend a second pump down wipe plug with which it is in contact during a drilling operation.

28. A bottom pump down wipe plug comprising at least one drillable protrusion extending above the top surface of the plug.

29. A pump down wipe plug as claimed in any of claims 26 to 28, wherein each protrusion is part of a rod, bar or angle iron having a length in the range from 4 to 1 6 centimeters, embedded and fixed in the body of the plug and made of metal, plastics material or wood.

30. A pump down wipe plug as claimed in any of claims 26 to 29, wherein each protrusion extends at least 1.27 centimeters beyond the respective plug surface.

31. A pump down wipe plug as claimed in claim 30, wherein each protrusion extends beyond the respective plug surface by a length in the range of 1.27 centimeters to 8 centimeters.

32. A pump down wipe plug as claimed in any of claims 26 to 31, wherein the number of protrusions per surface lies in the range from 4 to 6.

33. A pump down wipe plug as claimed in any of claims 26 to 32, wherein the protrusions are made of aluminium.

34. A well cementing and drilling process comprising the steps of: introducing the desired amount of wet cement into a cementing pipe string, inserting a pump down wipe plug having at least one drillable protrusion extending below its bottom surface, pumping the wet cement and plug down the well until the protrusion engages the top of a well shoe or collar pipe attachment.

35. A well cementing and drilling process comprising the steps of: inserting a bottom pump down wipe plug having at least one drillable protrusion extending above its top surface and at least one drillable protrusion extending below its bottom surface into a cementing pipe string, introducing the desired amount of wet cement into the string behind the bottom plug, inserting a top pump down wipe plug following the wet cement, pumping the plugs and cement down the pipe until the protrusion on the bottom plug contacts the top surface of a well shoe or collar pipe attachment, forcing the cement through the bottom plug and the pipe attachement such that the top plug contacts the protrusion extending from the top of the bottom plug, allowing the cement to set, drilling out the top plug, the tendency of the top plug to rotate being impeded by enegagement with the protrusion extending above the top surface of the bottom plug and drilling out the bottom plug, the tendency of the bottom plug to rotate being impeded by engagement between the protrusion extending below the bottom plug and the top surface of the pipe attachment.

36. A down hole well pipe configuration comprising; a well shoe or collar pipe attachment and a pump down wipe plug having at least one protrusion of cast iron or aluminum protruding from its bottom surface, the protrusion operabiy contacting the top surface of the pipe attachment.

37. A configuration as claimed in claim 36, wherein the plug is a bottom pump down wipe plug which is provided with at least one protrusion made of cast iron or aluminum extending beyond its top surface, the configuration further comprising a top pump down wipe plug which operably contacts the protrusion on the top surface of the bottom plug.

38. A configuration as claimed in claim 36, wherein the plug is a bottom pump down wipe plug; the configuration further comprising a top pump down wipe plug having at least one protrusion extending beyond its bottom surface which operably contacts the top surface of the pump down wipe plug.

39. A well cementing/drilling apparatus substantially as herein before described with reference to Figures 1 to 10 of the accompanying drawings.

40. A well pipe configuration substantially as herein before described with reference to Figures 1 to 10 of the accompanying drawings.

41. A process of cementing within a well and drilling through a pump down wipe plug substantially as herein before described with reference to Figures 1 to 10 of the accompanying drawings.

42. A well cementing and drilling process substantially as herein before described, with reference to Figures 11 to 20 of the accompanying drawings.

43. A well shoe or collar pipe attachment substantially as herein before described with reference to Figures 11 to 20 of the accompanying drawings.

44. A pump down wipe plug substantially as herein before described with reference to Figures 21 to 29 of the accompanying drawings.

45. A well cementing and drilling process substantially as herein before described with reference to Figures 21 to 29 of the accompanying drawings.

46. A down hole well pipe configuration substantially as herein before described with reference to Figures 21 to 29 of the accompanying drawings.