Patent Application
20220003057
Not Applicable.
The present disclosure relates to a drilling system for drilling a well, the drilling system having a well centre through which a drill string may be run into and out of the well, said drilling system comprising a coilable drill string; a first reel for storing said coilable drill string; a deflection means for directing said coilable drill string from said first reel and into said well centre; and a drive means for rotating said first reel. The disclosure also relates to a method for operating the drilling system.
Drilling of a well is not a continuous process. During drilling, the drill string usually needs to be pulled out of and run back into the well numerous times before completion of the well. The retrieval and insertion of the drill string is e.g. done for replacing a drill bit because of wear or for changing the type of drill bit. The drill bit also needs to be removed from the well in order to allow for casing and cementing of the well. During a three months' drilling operation, it is not uncommon having to make 20 or more trips into and out of the well. The retrieval and insertion of drill pipe is commonly called tripping, and it is known to account for as much as up to of 40% of the total drilling time. The main reason for the great amount of time that it takes to make a trip out of and into the well, is that the drill string is made up of a great number of individual pipes that are connected by means of threaded connections. This is often referred to as sectional tubing. The pipes are typically removed from or added to the drill string in stands including 3 or 4 individual pipes with a total length of approximately 30 to 45 metres. Taking into account that an average well is in the order of 4000-6000 metres deep, that some wells are more than 10,000 metres deep, and that the wellhead of some subsea wells are located thousands of metres below sea level, this implies that a great number of stands need to been broken out from or added to the drill string for each tripping operation.
A top drive is used for lifting the string into and out of the well and for rotating the drill string from top-side in order to provide torque to the drill bit. The top drive, which is placed inside the drilling tower, commonly called a derrick, allows for powerful drilling with good torque control from topside. The torque that is transferred to the drill bit is also substantially independent of circulation of drilling mud down into the well through the drill string and back up through the annulus around the drill string. The circulation of mud is important for removing drill cuttings from the well, for cooling the drill bit, and for controlling the pressure conditions in the well. The main drawback of the top drive-based drilling is the long tripping times, which typically only allows for an average tripping speed of in the order of 0.3 m/s. Rotation of the drill string from top-side also reduces the friction for axial movements of the drill string.
Coiled tubing consists of one long string that is stored on a rotatable reel, and driven into and out of the well by rotation of the reel. Coiled tubing allows for retrieval and insertion of the drill bit at an average speed which is significantly faster than that of a drill string made up of sectional tubing. For drilling purposes, the coiled tubing commonly relies on a downhole motor driven by the circulation of mud. The torque on the drill bit then becomes directly proportional to the mud circulation rate and to the pressure difference across the motor, and it is not possible to optimize drilling performance independently of the flow and pressure conditions of the mud. Since only the drill bit rotates, whereas the rest of the drill string has to be slid into and out the hole, the risk increases for various drilling equipment to get stuck in the well due to increase friction. Also, downhole motors commonly have a significantly lower torque output than top drives.
Finally, providing the drill string as a long, heavy single piece of equipment also entails logistic challenges in terms of handling and transporting. Indeed, the reel with the coiled tubing needs to be lifted and moved together as one piece of equipment with a weight that may exceed 50 tons or more.
Hybrid drilling rigs are known that include both a top drive-based sectional tubing drilling system and coiled tubing drilling system and that allows switching between the two. One such system is described in U.S. Pat. No. 6,408,955 B2. However, with the hybrid drilling rigs according to the prior art, including in the one disclosed in U.S. Pat. No. 6,408,955 B2, one needs to choose between the sectional tubing drilling system and coiled tubing drilling system for each run into the well, and tripping and drilling operation will as such always include the drawbacks of one of the two drilling schemes; sectional tubing or coiled tubing.
The disclosure is directed to remedying or reducing at least one of the drawbacks of the prior art, or at least provide a useful alternative to prior art.
The drilling system and method according to present disclosure solve at least some of the above-mentioned problems by using a drill string that may be coiled on a reel while at the same time having sufficient torsional stiffness for allowing rotation from topside. This is solved practically by feeding the drill string into the well by rotation of the reel, similarly to normal coiled tubing. When the drill bit and bottom-hole-assembly reach the targeted depth, the coilable drill string is disconnected from the reel, leaving a stick-up that may be engaged by the top drive, typically via a stand. When pulling the drill string out of the well the operation is substantially reversed; the top drive is disconnected from the drill string, which is once again connected to the reel that may then spool in the drill string at a significantly higher speed than in normal tripping. The drilling system and method according to the present disclosure may as such be described as combining the advantages of sectional tubing top drive-based drilling with the advantages of coiled tubing, while at the same time, at least to a large extent, avoiding the drawbacks of the two schemes.
In a first aspect the disclosure relates to a drilling system for drilling a well, the drilling system having a well centre through which a drill string may be run into and pulled out of the well, said drilling system comprising:
The first and second connections will normally be threaded connections, but other connections, such as clamped or wedged connections, may also be used.
The drive means, which may be a plurality of hydraulic, pneumatic or electric drive units/motors, may be adapted to rotate the reel so as to run said coilable drill string from said first reel, via the deflection means and into the well through the well centre and to pull said coilable drill string out of the well through the well centre, via said deflection means and onto said first reel. It should also be noted that the drive means do not necessarily need to be directly connected to and rotating the reel. The drive means may be any device adapted to pull the coilable drill string into or out of the well so as to indirectly rotate the reel. In one embodiment such an indirect rotation of the reel may be realized by means of a well tractor.
The first connection is adapted to connect the coilable drill string to a bottom-hole-assembly or to any other tool or pipe string that may need to be lowered into the well.
The second connection of said coilable drill string may be directly or indirectly connectable to the top drive. The well centre may be provided with means, so-called slips, for securely holding the drill string in the well centre before the reel is disconnected from the drill string. Disconnection is typically done by rotating the drill string from the well side, as opposed to the reel side, of the drill string as will be explained in more detail below. Once the reel is disconnected, a pipe handler/column racker may present a stand to the stick-up in the well centre. A connection between the stand and the stick-up may typically be made by a power tong/roughneck as will be understood by a person skilled in the art. The stand may be of equal diameter as the stick-up and the drill string in general or the stand may be of a different diameter. In the latter case an adapter/cross-over may be needed in order to connect the two parts. Finally, the top drive may connect to the stand, the slips may be released and drilling may commence.
In one embodiment said coilable drill string may comprise a composite material, such as carbon fibre or glass fibre or preferably a mix between the two. Such composite drill pipes have recently been shown to be very promising for drilling applications. The composite pipes have relatively small minimum bending radii, such as in the order of 6-7 meters, while at the same time having sufficiently high tensile and torsional capacity for common drilling applications, similar to that normally obtainable with some steel pipes. The composite pipes are light-weight compared to steel pipes, and they have shown high fatigue, wear and corrosion resistance, pressure performance and robustness to impact in general. One type of composite drill pipe that may be used for this application is the so-called Magma m-pipe® available from Magma Global Ltd. However, a variety of different composite pipes are available on the market. The m-pipe has so far been used for marine subsea risers, but has recently also been proven to be suitable for use in drill pipes. Advantageously, the amount of (S-2) glass fibre may be increased compared to the standard m-pipe, in order to increase the axial load carrying capability without impairing the minimum bending radius. In case the drill pipe is to be provided as sectional, composite tubing, also the end fitting, i.e. the threaded ends that make up the tool joints, may be provided in the same composite material. Another type of composite drill pipes that could be used for this application is available from the company Advanced Composite Products and Technology Ltd (ACPT). Composite drill collars and casings are also commercially available.
In another embodiment, the drill string may comprise or essentially consist of steel. When using steel pipes, as opposed to composited pipes, the drilling torque and load may have to be limited in order to let the pipe be able to coil with a minimum bending radius that is practical to handle. As an example, if using a 2⅜″ (OD) Grant
Priedco™ drill pipe, which is commercially available from National Oilwell Varco, the minimum bending radius is 15 metres, implying that the reel needs to have a diameter in the order of 30 meters, which may be unpractical in many applications. On the other hand, if using a conventional steel coiled tubing, such as QT-1300 with an OD of 2⅞″, the coil would only have to be in order of 4 meters in diameter, though this would limit the available torque, In general, the design criteria for such a drilling system when using steel pipes will be a trade-off between the required torque and the size of the reel.
In one embodiment, the drill string may comprise a plurality of connected drill pipes, similarly to conventional sectional tubing. Composite drill pipes and smaller diameter steel pipes may be provided with threaded ends as in a normal sectional drill string. On the other hand, if using pipes commonly used for coiled tubing, the coiled tubing may be cut into sections connected by tool joints that allow transfer of substantially the full torque and yield ratings of the coiled tubing material. A person skilled in the art will be aware that joining of coiled tubing sections e.g. may be done by means of weld-on connectors or by means of slip type connectors that engages the outer diameter of the coil tubing section. In either case, the joint will normally represent a section with a larger outer diameter (OD) than the rest of the pipe. Preferably the reel may therefore be formed with recesses for accommodating the joints so as to avoid local stresses in the sectional drill string and allow for smooth spooling of the sectional drill string. It should also be noted that the joints of the sectional pipe string do not necessarily need to exceed the diameter of the pipe string itself.
In contrast to having a sectional drill string, the drill string may also be provided as a long, continuous unit with connections only at its end, alternatively as a few long sections with connections only at the ends. This embodiment will not give the same flexibility for connecting and disconnecting the reel from the drill string at basically any desired length, but may instead be used for a fixed tripping length for each run into and out of the well. On the other hand, a continuous, long coilable drill string may be easier to and less costly to implement, compared to a sectional, coiled tubing.
In one embodiment said deflection means may be skiable to and from said well centre. This may be beneficial for freeing space around the well centre when the deflection means is not in use, typically when top drive is engaged or is about to be engaged. Said deflection means may typically be a sheave or a part of the sheave that leads the drill string in the direction between the reel and the well centre. In an alternative embodiment, the deflection means may be a curved guide beam, similarly to that commonly used in so-called “goosenecks” in conventional coiled tubing injections. The deflection will be able to guide the drill string in various drilling system configurations, whereas in a preferred embodiment, the deflection means will change the direction of the drill string in the order of 90°. The deflection means may simply be slidable on a pair of rails/skid by means of an electric, pneumatic or hydraulic drive unit/motor. The motors may be push/pull units moving the deflection means step-wise along the rails.
In a drilling system according to the first aspect of the present disclosure, the top drive may connect to the coilable drill string via drill stand. The drill stand will typically be latched to the well centre by means of a pipe handler/racker. The drill stand may then be connected to the second end, the stick-up, of the coilable drill string. The drill stand may be of the same material and/or diameter and minimum bending radius as the coilable drill string or said drill stand may be provided with/from a different diameter and/or material and minimum bending radius. In case of different diameters and/or thread pitch the drill stand may connect to the coilable drill pipe via an adapter/cross-over.
In one embodiment, the drilling system according to the first aspect of the disclosure may further comprise a second reel for storing a coilable string, wherein said coilable string may be a drill string or a wire rope. This may be beneficial for being able to switch between a coilable drill string with a first configuration to a coilable drill string of a second configuration or to be able to switch between a coilable drill string and another coilable string, such as a lifting string. A lifting string, such as a steel wire rope, may be used for lifting particularly heavy equipment, such casing and BOPs. In another embodiment the lifting string could be a thick-walled pipe allowing for circulation of mud therethrough, which may be needed in some lifting operations to maintain control of the well. Each of the first reel and the second reel may be slidable on skids to and from an operational position and an idle position. The drilling system may also comprise further reels than the mentioned first and second.
The first reel in the drilling system may be provided with a diameter in the range of 10-15 metres, preferably around 13 metres, which may be particularly useful in combination with coiled composite pipes. However, as mentioned above, the first reel may be significantly larger than 15 meters should this be practical, and it may also be made smaller than 10 meters, in particular in applications that do not require high drilling torques. The second reel may be of a similar diameter or a different diameter than the first reel. In an embodiment where the second reel stores landing strings for heavy lifting operations, the diameter of the second reel may be larger than that of the first reel. In particularly deep wells, often also provided in deep water, it may be necessary to use two or more reels in order to provide a drill string that is sufficiently long.
The drilling system may further comprise cooling and/or lubrication means. The deflection means, where the coiled drill pipe is bent into the well centre, is an area where a lot of friction may occur, both between the coilable drill pipe and the deflection means but also internally in the coilable drill pipe. It may therefore be advantageous if coilable drill pipe and/or deflection means is cooled and/or lubricated in order to cool and reduce friction, respectively. This cooling and/or lubrication may be implemented by providing an enclosure over or around the deflection means, where a coolant or lubricant is pumped onto the coilable drill string and/or deflection means. A drilling system including such cooling and/or lubrication means may preferably also be provided with a drain for the coolant and/or lubricant. Preferably the drain will be provided with or connected to a pump enabling circulation and re-use of the coolant and/or lubricant. Cooling may be done by means of water- or electrolyte-based liquids, air jets or other cooling fluids. In an alternative embodiment, cooling of the coilable drill pipe may be realized by pre-cooling the mud circulated down into the coilable drill pipe.
There is also described herein a drilling rig comprising a drilling system according to the present disclosure. The drilling system may be provided both on offshore rigs and land-based rigs. Offshore rigs may include bottom founded drilling rigs (jack-up barges and swamp barges), combined drilling and production facilities either bottom founded or floating platforms, and deepwater mobile offshore drilling units (MODU) including semi-submersibles and drill ships.
There is also described herein a drilling system according to the first aspect of the invention, wherein the top drive is providable at any angle relative to the well centre. The top drive is normally provided vertically above the well centre. In European patent application EP17178322.8 is disclosed a drilling system wherein the top drive (“torque exerting means”) is adapted to provide torque to bendable drill pipes while being oriented in any direction, including horizontally, i.e. with the length axis of the pipe oriented substantially perpendicularly, relative to the well centre. The top drive will then be provided between the reel and the deflection means. EP17178322.8 is hereby incorporated by reference.
In a second aspect, the disclosure relates to a method for operating a drilling system according to the first aspect of the disclosure, said method including the steps of:
It should also be noted that the method may equally well be exploited with any tool or pipe string that may need to be lowered into the well, instead of the bottom hole assembly.
A person skilled in the art will know that before drilling a well, the seabed (or ground if land-based), and wellhead need to be prepared. The preparation steps will not be described in detail herein, but it should be noted that the system and method according to the first and second aspects of the disclosure may also be used during the preparation phase. The method according to the disclosure may commence when the well is ready to be drilled. When the well is ready to be drilled, the deflection means and reel are slid/skidded into their operating positions. The first end of the coilable drill string is connected to the bottom hole assembly with the drill bit that is to be lowered into the well. The drill string is spooled out by rotation of the reel so as to lower coilable drill string and the bottom hole assembly and drill bit into the well. When the bottom hole assembly has reached a desired depth, the slips in the well centre are set, and the coilable drill string may be disconnected from the reel, leaving a stick-up in the well centre. A drill stand is brought into the well centre by means of a pipe handler/column racker, and connected to the stick-up, potentially via a cross-over in case the stick-up and drill stand are of different diameters. The connection is made with a roughneck. The top drive is then finally latched to the drill stand and drilling may commence by rotation of the coilable drill string from topside. After an initial drilling phase, normally after a few hundred metres of drilling (but it could be anything from a few meters to a few kilometres), the drilling tools will typically have to be removed (trip out) from the well in order to lower cementing and casing tools into (trip in), whereby the process discussed above is reversed.
In one embodiment of the method, the step of disconnecting said reel from said second end of the coilable drill string may include the step of rotating the coilable drill string on the well-side of the drill string, as opposed to the on the reel side, while keeping said coilable drill string substantially fixed on the reel side of the drill string.
Details about how the coilable drill string may be connected to the stick-up in the well centre in the first place, and how the connections of the coilable drill pipe may be made up and broken out will be discussed in the following with reference to the drawings.
In the following are described examples of preferred embodiments illustrated in the accompanying drawings, wherein:
In the following the reference numeral 1 will indicate a drilling system according to the present disclosure, whereas the reference numeral 10 indicates a drilling rig comprising such a drilling system. Identical reference numerals will indicate identical or similar features in the drawings. The figures are drawn simplified and schematically and various features therein are not necessarily drawn to scale.
Once the target depth has been reached in the well, the coilable drill string 2, if any remains on the first reel 4, needs to be disconnected from the part of the coilable drill string 2 that has been run into the well as will been shown in the following figures. In one embodiment the full length of the coilable drill string 2 is run into the well, while in another embodiment a joint of the coilable drill string 2 is broken up in order to separate the part of the coilable drill string 2 run into the well from the coilable drill string 2 on the first reel 4, as will be explained in the following. In both embodiments a stick-up 36 remains at the well centre 8, as shown in
In addition or as an alternative, cooling of the coilable drill string 2 may also be effectuated indirectly by cooling the drilling mud circulating therethrough during operation.
It should be noted that the above-mentioned exemplary embodiments illustrate rather than limit the claimed invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the invention as defined by the claims that are set out below. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.
The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17178425.9 | Jun 2017 | EP | regional |
This application is a 35 U.S.C. § 371 national stage application of PCT/NO2018/050165 filed Jun. 18, 2018 and entitled “Drilling System and Method”, which claims priority to European Patent Application No. 17178425.9 filed Jun. 28, 2017, each of which is incorporated herein by reference in their entirety for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/NO2018/050165 | 6/18/2018 | WO | 00 |
