Downhole string for drilling through a low pressure zone |
|||||||
申请号 | EP14168872.1 | 申请日 | 2014-05-19 | 公开(公告)号 | EP2947259A1 | 公开(公告)日 | 2015-11-25 |
申请人 | Welltec A/S; | 发明人 | Hazel, Paul; | ||||
摘要 | The present invention relates to a downhole string (1) for drilling through a low pressure zone (Zlow) in a formation in a well (3), comprising a drawdown casing (2) having a first end (4) closest to a top (5) of the well and a second end (6), and an operational tool (8) connected to the second end of the drawdown casing, wherein the downhole string further comprises an annular barrier (10) having an expandable metal sleeve (11) surrounding the drawdown casing, each end of the expandable metal sleeve being connected with the drawdown casing, the expandable metal sleeve being adapted to contact a wall (16) of a borehole or another casing so that after expansion of the expandable sleeve, the drawdown casing can rotate and slide in relation to the annular barrier. Furthermore, the present invention relates to a downhole system and to a downhole method. | ||||||
权利要求 | |||||||
说明书全文 | The present invention relates to a downhole string for drilling through a low pressure zone in a formation in a well. Furthermore, the present invention relates to a downhole system and to a downhole method. When drilling a new borehole or a sidetrack in an existing well, the drilling head may drill into a low pressure zone, resulting in a loss of pressure. Thus, the mud entered into the hole while drilling to prevent blowout is lost in the low pressure zone, and there will be a substantial risk of a blowout if drilling is continued. Cementing and thus sealing part of the annulus above the low pressure zone is also impossible, since the injected cement is lost as it disappears into the low pressure zone, and then this partly drilled borehole is abandoned and plugged from above and a new well is drilled. It is an object of the present invention to wholly or partly overcome the above disadvantages and drawbacks of the prior art. More specifically, it is an object to provide an improved completion or drilling system, which renders it possible to continue drilling past the above-mentioned low pressure zone. The above objects, together with numerous other objects, advantages and features, which will become evident from the below description, are accomplished by a solution in accordance with the present invention by a downhole string for drilling through a low pressure zone in a formation in a well, comprising
casing so that after expansion of the expandable sleeve, the drawdown casing can rotate and slide in relation to the annular barrier. An annular space may be arranged between the expandable metal sleeve and the drawdown casing. Moreover, the annular space may comprise a compound adapted to expand the annular space. Also, the compound may comprise at least one thermally decomposable compound adapted to generate gas or super-critical fluid upon decomposition. Further, the compound may comprise nitrogen. In addition, the compound may be selected from a group consisting of: ammonium dichromate, ammonium nitrate, ammonium nitrite, barium azide, sodium nitrate, or a combination thereof. Furthermore, the compound may be present in the form of a powder, a powder dispersed in a liquid or a powder dissolved in a liquid. An opening may be arranged in the drawdown casing opposite the expandable metal sleeve for letting pressurised fluid into the annular space to expand the expandable metal sleeve. Moreover, a valve may be arranged in the opening. Said valve may be a check valve. Also, the valve may comprise an activatable closing element so that when an end of the expandable metal sleeve passes the activatable closing element, the valve is closed. One or both of the ends of the expandable metal sleeve may be connected with the drawdown casing by means of connection parts. Furthermore, sealing means may be arranged between the connection part or end of the expandable metal sleeve and the drawdown casing. Additionally, the operational tool may be a reamer, a drill head or a cement shoe. Further, the drawdown casing may be mounted from tubular casing sections by means of casing collars. Moreover, the drawdown casing may be capable of sliding between two adjacent casing collars. Also, a sliding sleeve or a frac port may be arranged in the drawdown casing closer to the first end in relation to the annular barrier. The present invention also relates to a downhole system for drilling through a low pressure zone in a formation in a well, comprising
Said operational unit may also be used for sliding and/or rotating the drawdown casing in relation to the expanded expandable metal sleeve. The downhole system as described above may further comprise a pressurising unit for pressurising a fluid in the drawdown casing for expanding the expandable metal sleeve. Furthermore, the downhole system as described above may further comprise a downhole tool, such as a cementing tool. Additionally, the downhole system may comprise a drilling head connected in an end of a drill pipe for drilling from within the drawdown casing out into the formation. The present invention furthermore relates to a downhole method for drilling past a low pressure zone in a formation in a well, comprising the steps of:
The step of drilling past the low pressure zone may be performed after a drilling head and a drill pipe have been inserted into the casing. Moreover, the step of providing cement may be performed after a cementing tool has been arranged opposite an opening in the casing above the annular barrier. In addition, the cementing tool may be removed from the casing before the drilling head is introduced. The invention and its many advantages will be described in more detail below with reference to the accompanying schematic drawings, which for the purpose of illustration show some non-limiting embodiments and in which
All the figures are highly schematic and not necessarily to scale, and they show only those parts which are necessary in order to elucidate the invention, other parts being omitted or merely suggested. When drilling a new borehole or a sidetrack in an existing well, the drilling head 8a, 8 may drill into a low pressure zone Zlow, and the mud entered into the hole while drilling to prevent blowout may consequently be lost in the low pressure zone, and thus there will be a substantial risk of a blowout if drilling is continued. In order to prevent loss of pressure, the downhole string 1 comprises an annular barrier 10 having an expandable metal sleeve 11 surrounding the drawdown casing 2. Each end 14, 15 of the expandable metal sleeve 11 is connected on the outside 12 of the drawdown casing. The annular barrier 10 has an unexpanded condition as shown in In order to cement the annulus 18 above the annular barrier 10, a downhole tool 21 in the form of a cementing tool is submerged into the drawdown casing. The cementing tool is arranged opposite the zone which is to be cemented, and a first packer 22 or bottom packer of the cementing tool 21 is set to close off the bottom part of the drawdown casing 2. Cement is then pumped down through the pipe string 23 and into the space 24 in the drawdown casing between the first packer and a second packer 25 and into the annulus 18 above the annular barrier 10. The second packer may be a cup seal movable towards the first packer to squeeze the cement out through openings 26 in the drawdown casing above the annular barrier 10. While cementing, the drawdown casing 2 oscillates up and down as illustrated by the double arrow, so that bubbles are not formed in the cement and a proper cementing job is executed. This oscillating movement of the drawdown casing 2 in relation to the annular barrier 10 is thus important to the subsequent cementing job. The annular barrier 10 comprises an expandable metal sleeve 11 which is connected with the drawdown casing 2 to form an annular space 28 as shown in In another solution shown in As shown in To prevent fluid from leaving the annular space 28 in the annular barrier 10, a valve 38 is arranged in the opening 20 as shown in In As shown in In The invention further relates to a downhole system 100, shown in The invention further relates to a downhole method for drilling past a low pressure zone in a formation in a well. First, a borehole is drilled and the presence of a low pressure zone is determined, then the expandable metal sleeve of the annular barrier is expanded above the low pressure zone in relation to a top of the borehole. Subsequently, cement is provided above the annular barrier in an annulus between the casing and a wall of the borehole through an opening of the drawdown casing, e.g. a frac port or a perforated opening. When performing the cementing job, the casing is oscillated in relation to the annular barrier, and then the drilling process is continued, drilling past the low pressure zone, e.g. while rotating the drawdown casing. In order to continue the drilling operation, a drilling head and a drill pipe may be inserted into the drawdown casing. By fluid or well fluid is meant any kind of fluid that may be present in oil or gas wells downhole, such as natural gas, oil, oil mud, crude oil, water, etc. By gas is meant any kind of gas composition present in a well, completion, or open hole, and by oil is meant any kind of oil composition, such as crude oil, an oil-containing fluid, etc. Gas, oil, and water fluids may thus all comprise other elements or substances than gas, oil, and/or water, respectively. By a casing is meant any kind of pipe, tubing, tubular, liner, string etc. used downhole in relation to oil or natural gas production. In the event that the tool is not submergible all the way into the casing, a downhole tractor can be used to push the tool all the way into position in the well. The downhole tractor may have projectable arms having wheels, wherein the wheels contact the inner surface of the casing for propelling the tractor and the tool forward in the casing. A downhole tractor is any kind of driving tool capable of pushing or pulling tools in a well downhole, such as a Well Tractor®. Although the invention has been described in the above in connection with preferred embodiments of the invention, it will be evident for a person skilled in the art that several modifications are conceivable without departing from the invention as defined by the following claims. |