DRILLING SYSTEM FOR ROCK DRILLING

Technical field

The present invention relates to a drilling system for rock drilling. Background

A usual solution for creating a hole in the earth's sub-surface is a drilling system for rock drilling. It can be used, for instance, when drilling water wells, oil wells, or natural gas extraction wells. A typical task performed during a drilling operation is pulling the drill string out of a wellbore and then running it back in. This task is commonly referred to as tripping or making a round trip. There are multiple reasons for performing such a task, for example to perform a casing operation or a cementing operation after a certain depth has been reached. Other reasons may be to replace a worn-out drill bit, a downhole tool that might have broken down or a damaged drill pipe.

The task of performing a round trip is known to be time consuming. The entire drill string needs to be removed from the wellbore and its drill pipes need to be disconnected and stored, usually in a rack, until they are connected together again to form the drill string to be run back in. A way to improve the efficiency of a round trip is disconnecting the drill string only in some of the joints when the drill string is pulled out of the wellbore, so as to form at least one segment with a length of at least two drill pipes. These

segments, usually referred to as stands, may be then stored until they are reconnected together for being run back in. As a consequence, a lower number of joints are disconnected, when the drill string is being pulled, and also a lower number of respective joints are connected, when the drill string is being run back in. Only the joints between the segments of a drill string need to be disconnected and connected, which reduces the time needed for disconnecting and connecting drill pipes. The ability to store a longer segment of a drill string when performing a round trip allows improving the efficiency of a round trip, which can, for example, represent a significant reduction in operation costs. However, it may be challenging to store longer segments of a drill string in a drilling system, in a cost efficient and stable manner. Nowadays, a drilling system adapted to store segments of the drill string, for the purpose of reducing the round trip duration, usually includes a hoisting structure such as a derrick. The segments are normally held in a vertical rack next to the hoisting structure. A well-known approach for storing longer segments in these drilling systems involves increasing the height of the hoisting structure in order to provide room for longer segments. For example, a drilling system with a 64-meter derrick is usually capable of holding segments with 40 meters in length, typically up to four drill pipes in length. However, several difficulties are observed due to the increased height. Since the segments of the drill string are longer and heavier, stronger equipment may be needed. Moreover, since the equipment supported by the hoisting structure is further elevated, security risks also increase and it also becomes more difficult to provide maintenance for the equipment due to the increased difficulty in reaching it. Also, a higher hoisting structure and the machinery required for handling longer segments becomes

significantly heavier. For example, a usual derrick capable of holding segments of a drill string with three drill pipes in length can weight, approximately, 30 metric tons, whereas a usual derrick capable of holding segments of a drill string with four drill pipes in length can weight, approximately, 100 metric tons. The difficulties resulting from the increased weight supported by the hoisting structure or its higher centre of mass, are normally solved by appropriately reinforcing the hoisting structure and altering it to have the required robustness. However, this change has a cost which may be significant.

In particular, in the case of a maritime vessel comprising a drilling system with a hoisting structure, for example a drillship, it is possible that the maritime vessel itself is prone to suffer disturbances due to the motion produced by the waves or due to the wind, such as disturbances in the roll axis of the maritime vessel, thus creating additional difficulties in the stability of the maritime vessel. Moreover, the increased height may also forbid the maritime vessel from entering certain important maritime passages such as the Panama canal, in which the maximum height allowed is 57 meters (190 feet), and the Turkish straits, in which the maximum height is 64 meters (210 feet).

Thus, although the well-known approach of reducing the usual duration of a round trip in a drilling system by increasing the height of a hoisting structure has proven to be an effective solution in the past, nowadays several technical and economical drawbacks are observed due to the increased height. And these drawbacks may make it unfeasible to keep on following this approach, which constraints the achievable reduction for the duration of a round trip.

Alternatively, instead of increasing the length of the segments of a drill string held temporarily while performing a round trip, the approach may be to provide the drilling system with equipment which would allow to manoeuvre the segments faster. This approach would not reduce the number of joints between drill pipes that have be disconnected and connected during a round trip. Also, this may add a significant cost, not only for the new equipment but also for any reinforcement required to withstand the additional forces in place, and the reduction in the duration of a round trip may be insufficient to compensate for this investment.

Disclosure of invention

The invention herein disclosed goes against the conventional approach of increasing the height of a hoisting system comprised in a drilling system in order to reduce the duration of a round trip.

Disclosed is a drilling system for rock drilling with a drill string, wherein the drill string comprises at least one bendable drill pipe, the drilling system comprising:

- at least two block and tackle systems for driving an end of the drill string in a first direction; and

- at least one conveyor device adapted to guide and bend the drill string between the first direction and a second direction, so as to convert a motion of the drill string between the first direction and the second direction.

The at least one conveyor device may be two conveyor devices for guiding the drill string in a curved path between the first direction and the second direction.

A conveyor device may comprise at least two rollers for guiding the drill string.

A conveyor device may comprise a groove for the drill string to run on. The second direction may be arranged vertically. The first direction may be arranged horizontally.

The first direction may be arranged with an inclination relative to a horizontal plane. The drilling system may comprise a topdrive for exerting a torque around the first direction on the end of the drill string.

The drilling system may comprise at least one rack for holding at least one segment of the drill string while performing a round trip, the rack being arranged parallel to the first direction.

Also disclosed is a maritime vessel comprising at least one drilling system as described above. The first direction of the at least one drilling system may be arranged longitudinally in relation to the maritime vessel.

The maritime vessel may comprise at least two drilling systems arranged vertically on top of each other. The at least two drilling systems may have a common second direction.

The maritime vessel may be a drillship. It may also be an oil and gas platform.

The invention may be advantageous in various ways as will be apparent from the description throughout. Particularly, the invention may reduce the duration of a round trip by allowing the manipulation of longer segments of a drill string, in a feasible manner, which in turn may represent a significant reducing in project costs. For example, drilling system which is capable of handling a segment of the drill string with at least 5 bendable drill pipes can be achieved without imposing a significant increase in cost, as it would occur for a drilling system with a hoisting structure such as a derrick. Brief description of drawings

Figure 1 is an illustration of a first embodiment of a drilling system observed from a side view, in which a drill string can be seen being guided and bent between a first direction and a second direction.

Figure 2 is an illustration of a second embodiment of the drilling system showing how a round trip can be performed while temporally storing longer segments of the drill string.

Figure 3 is an illustration of an embodiment of two conveyor devices for guiding the drill string in curved path between the first direction and the second direction.

Figure 4 is an illustration of a drill ship from including an embodiment of the drilling system in which the first direction of the drilling system is arranged longitudinally relative to the drill ship.

Figures 5, 6, and 7 illustrate three examples of arrangements of a drilling system on a drill ship.

Figures 8 and 9 are illustrations of a jack-up rig including a drilling system.

Figures 10 and 1 1 are illustrations of an oil and gas platform including a drilling system. Detailed description

Figure 1 illustrates a first embodiment of a drilling system 2 for rock drilling with a drill string 21 .

The drill string 21 is shown in its state during operation, being bent between a first direction 21 1 and a second direction 212. For the purposes of providing a simple example, the first direction 21 1 and the second direction 212 are arranged with an inclination of 90 degrees. The first direction 21 1 , horizontal, may be imagined as corresponding to the deck of a drill ship 1 1 and the second direction 212, vertical, may be imagined as corresponding to the direction on which a wellbore is to be drilled. An end of the drill string 21 is driven along the first direction 21 1 . There are several ways of accomplishing this actuation. One way is to use two block and tackle systems 23 for driving the drill string 21 back and forth in the first direction 21 1 , in which one of the systems exerts tension on the drill string 21 so as to pull it from the wellbore and another exerts tension on the drill string 21 so as to push it. In figure 1 , only the block and tackle system 23 for pulling the drill string 21 is shown. This block and tackle system 23 includes a traveling block 231 and a fixed block 232, each including at least one pulley, with a cable threaded between them. Also, a block and tackle system 23 may include a winch 233 for the purpose of driving the cable. Instead of two block and tackle systems 23, a winch and one long wire may be provided. In this case, the wire is connected to both ends of the travelling block 231 via sheaves and the winch acts in similar manner to a windlass. Furthermore, a further option is to use a rack and pinion system. The drill string 21 is guided and bent between the first direction 21 1 and the second direction 212 by two conveyor systems 22 which guide the drill string 21 in a curved path. As a result, a motion of the drill string 21 is converted between the first direction 21 1 and the second direction 212. In order to carry out the first embodiment when starting from a drilling system 2 without any drill string 21 , the following approach may be followed. A first bendable drill pipe 213 is firstly pushed along the first direction 21 1 into the space between the two conveyor devices 22. During this motion, the first bendable drill pipe 213 should be guided and bent towards the second direction 212. Secondly, after the first bendable drill pipe 213 reaches a position which allows for a subsequent bendable drill pipe 213 to be added in the first direction 21 1 , the first bendable drill pipe 213 is fastened in order to prevent its movement relative to the two conveyor devices 22, for example by using slips to hold the first bendable drill pipe 213 or any other known method for that effect. Then, an end of the subsequent bendable drill pipe 213 is joined with the end of the first bendable drill pipe 213 in the first direction 21 1 , as to form a drill string 21 which is now pushed into the two conveyor devices 22 until it is again possible for a second subsequent bendable drill pipe 213 to be added to the drill string. This cycle is repeated to further extend the drill string. Furthermore, this way of carrying out the first embodiment may start from a segment of a drill string 21 with more than one bendable drill pipe 213 in length, instead of starting with an individual bendable drill pipe 213.

With the drill string 21 in place, the extending and retracting the drill string 21 may be achieved in the following ways. On the one hand, the steps of pushing the drill string 21 through the two conveyor devices 22 and adding a subsequent bendable drill pipe 213 when possible, may be repeated for extending the drill string 21 until an intended depth is reached. On the other hand, the loop for extending the drill string 21 may be performed in reverse and each of the disconnected bendable drill pipes 21 or each of the disconnected segments of the drill string, can be stored one by one.

Figure 2 illustrates a second embodiment of the drilling system 2 in which the first embodiment includes a rack 24 for holding at least one segment of the drill string 21 and also, in which the rack 24 is arranged to hold the at least one segment of the drill string 21 parallel to the first direction 21 1 .

The rack 24 can be used, for example, in the same manner a setback is used in a drilling system 2 with a derrick, by storing segments of a drill string 21 temporally while making a round trip. In order to move the bendable drill pipes 213 or the segments of a drill string 21 to and from the rack 24, other external means may be used, such a crane or at least one robotic arm.

A drilling operation may be performed by applying a torque to the drill string 21 . In this second embodiment, the torque is exerted on the drill string 21 1 around the first direction 21 1 , which then transmits the torque, through the drill string 21 , to the second direction 212. In order to apply this torque around the first direction 21 1 , a topdrive 25 is provided at an end of the drill string 21 in the first direction 21 1.

Figure 3 illustrates an embodiment of two conveyor devices 22 for guiding and bendi the drill string 21 .

Each of the conveyor devices 22 include three rollers 221 supported by a curved frame. Each roller 221 is of the "bow tie" type, which provides a better contact with the drill string 21 . Particularly, these rollers 221 allow to bend the drill string 21 between the first direction 21 1 and the second direction 212 while it moves back and forth, or even if it turns, for example while drilling.

Figure 4 illustrates a drill ship 1 1 including an embodiment of the drilling system 2 in which the first direction 21 1 of the drilling system 2 is arranged longitudinally relative to the drill ship 1 1 . Also, the drilling system 2 is shown comprising a rack 24 which is arranged to hold at least one segment of the drill string 21 in parallel to the first direction 21 1 . Three examples of an arrangement of the drilling system 2 on a drill ship 1 1 are shown in figures 5, 6 and 7.

Figure 5 shows an embodiment of the drill ship 1 1 where the two conveyor devices 22 are positioned near the bow of the drill ship 1 1 .

Figure 6 shows an embodiment of the drill ship 1 1 in which the first direction 21 1 of the drilling system 2 is sloped in relation to the drill ship 1 1 . This embodiment can have the advantage of providing a simpler block and tackle system 23 which makes use of the gravity force to move the drill string 21 and, at the same time, still avoids the problems created by a drilling system 2 with hoisting structure.

Figure 7 shows an embodiment of the drill ship 1 1 in which the drill ship 1 1 has two drilling systems 2, in which one is on top of the other. The second direction 212 is common to both drilling systems 2. Also, the curved path achieved by the conveyor devices 22 used in each drilling system 2 have different radiuses. This has the advantage of allowing different bend radiuses for different tubular types, for example steel or composite tubular, and dimensions of the bendable drill pipes 213. For example, the drilling system 2 on the top can be set to handle bendable drill pipes 213 with a longer diameter, thus requiring a bigger bend radius, such as a 20-meter radius, as opposed to the drilling system 2 on the bottom which can be set to handle bendable drill pipes 213 with a shorter diameter, thus requiring a smaller bend radius, such as a 10-meter radius. In order to improve the efficiency of a round trip by increasing the length of the stored segments of a drill string 21 , a drill ship 1 1 may be occupied in a longitudinal manner. In this regard, a segment of a drill string 21 can have, for example, up to 500 feet, i.e. approximately 152,4 meters. As can be seen on, for example, figure 4, the drilling system 2 occupies almost the entire length of the drill ship 1 1 . Due to this longitudinal occupation of the drill ship 1 1 , rather than vertical, the amplification of disturbances on the drill ship 1 1 , due to waves or wind, is not felt. A higher structure can be prone to absorb disturbances from wind, acting as a sail, which can create difficulties in keeping the drill ship 1 1 stable. Also, a higher structure raises the centre of mass of the entire body comprising the drill ship 1 1 plus the drilling system 2, which can create difficulties in keeping the drill ship 1 1 stable due to the motion of the waves.

Figures 8, 9, 10, and 1 1 show two embodiments of different kinds of a maritime vessel 1 including drilling system 2 according to the present invention. Figures 8 and 9 show a jack-up rig and figures 10 and 1 1 show an oil and gas platform.

The embodiment shown in figures 10 and 1 1 for an oil and gas platform includes two drilling systems 2 positioned side-by-side. This particular arrangement allows achieving further improvements to the efficiency of a round trip. If a drill string is being pulled out of a wellbore using one drilling system 2, another drill string can be ready on the other drilling system 2 to be run in into the wellbore.

A further simplification can be achieved by providing a shared rack 24 when there is more than one drilling system 2 proximal to each other. For example, in figure 1 1 a single rack 24 could be positioned between the two drilling systems 2 shown, serving both of them. The same could happen in figure 7, where both drilling systems 2 could make use of a same rack 24 for holding at least one segment of a drill string 21 .

It should be noted that the above-mentioned ways of carrying out the invention illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. 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.