A system for exploration and production drilling for oil and gas or other fluids to be recovered from bedrock, including a non-rotatable drill string formed from several connectable drill-string sections, a bottom-hole assembly provided with a rotatable drill bit connected to a drill-bit drive, the drill string being provided with first and second line grooves arranged to receive, respectively, a fluid line and a power and signal line.

Drilling oil and gas wells has become constantly more challenging with respect to both directional control and communication between downhole equipment and a surface installation. The demand for efficiency and profitability is increasing as well. According to the prior art in the field, drilling operations are substantially carried out with equipment in which a drill string that consists of sections of pipe connections screwed together is rotating in its entire length. The rotation of the drill string is transmitted to a drill bit, and drilling fluid is supplied through a centric hole in the drill string and carries cuttings away from the drill bit and out of the borehole through an annulus formed between the drill string and the borehole, possibly between the drill string and a surrounding casing or riser. In some situations, the drill bit is rotated by a motor that sits between the drill string and the drill bit, for example by deviation drilling in horizontal well portions.

The rotation of drill strings up to several thousand metres long means that much power must be used for the operation. Hoisting a drill string weighing several hundred tonnes requires large and heavy hoisting machinery on the surface installation. In addition, the circulation of drilling mud must be interrupted when pipe sections are being joined together in the drill string. This gives discontinuous circulation and a risk of the drill string sticking in the borehole.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art. The object is achieved through features which are specified in the description below and in the claims that follow.

The invention provides a system for exploration and production drilling for oil and gas or other fluids which are to be recovered from bedrock. From a drilling rig an assembled, non-rotating drill string is fed in a conventional manner known per se. The drill string is extendable and is made up of several drill-string sections and provides several, longitudinal, continuous grooves which can accommodate fluid-, power- and signal- transferring lines extending between a surface installation and a bottom-hole assembly. The bottom-hole assembly includes a drill-bit drive, preferably an electric motor which, by a stator, is non-rotatably connected to the drill string, and a rotor is connected to the drill bit in order thereby to provide rotation of the drill bit relative to the drill string.

As the drill string is paid out from the surface installation, the lines are inserted into their recesses from respective line drums, the supplies of fluid, power or control signals, possibly a return of a borehole data signal, running through suitable swivels, slip rings, optical transmissions and so on between the static and rotating parts of a drum unit.

During drilling, drilling fluid is pumped continuously through a fluid line to the drill bit which is rotated by means of the drill-bit drive, preferably by the supply of electrical power to an electromotor.

On the surface installation, connection and feeding equipment is arranged, which makes it possible for drill-string sections to be connected and fed into the borehole in an approximately continuous process. The lines for drilling mud, power and signal transmission are inserted into the respective grooves in the drill string in a continuous process. Preferably, the drill string is lowered and lifted by means of a chain structure with two continuous, electrically or hydraulically operated chains. The chains are pressed against the drill string by hydraulic cylinders to achieve sufficient friction.

The drill-string sections are connected by means of drill-string connections which are locked in the connected position by means of one or more locking elements at each joint.

With the present invention, a drilling system that makes it possible to drill long boreholes with a non-rotating drill string with continuous communication between the drill bit and the surface installation is provided. This opens to the use of online communication for directional control and local seismology, and real-time data transmission con- cerning the conditions in the borehole.

The invention relates, more specifically, to a system for exploration and production drilling for oil and gas or other fluids to be recovered from bedrock, including a non- rotatable drill string formed from several connectable drill-string sections, a bottom- hole assembly provided with a rotatabie drill bit connected to a drill-bit drive, the drill string being provided with first and second line grooves arranged to receive, respectively, a fluid line and a power and signal line, characterized by the drill-string sections being provided with an asymmetric drill-string connection at their respective end portions.

The drill-string connection may be formed as a groove or an asymmetric tongue in order thereby to allow connection in only one direction.

The drill string connection may include a locking element.

The power and signal line may be formed of a separate power line and a separate signal line.

The power and signal line may be formed of a separate power line and a separate signal line, the power line being partially accommodated in a groove in the signal line.

In what follows, an example of a preferred embodiment is described, which is visualized in the accompanying drawings, in which :

Figure 1 shows in perspective a surface installation in accordance with the invention;

Figure 2 shows a side view of the surface installation;

Figure 3 shows a front view of a lower part of the surface installation, in which a feeder for lines is illustrated;

Figure 4 shows, on a larger scale, a section of the feeder;

Figure 5 shows, on a smaller scale, a longitudinal section through a feeding device for a drill string in accordance with the invention;

Figure 6a shows a side view of a portion of a drill string around a drill-string joint;

Figure 6b shows a cross section 6b-6b through the drill-string joint according to figure 6a; Figure 7 shows a side view of an early stage in the connection of a drill-string section and the drill string;

Figure 8a shows a side view of a drill string provided with lines;

Figure 8b shows a cross section 8b-8b through the drill string according to figure

8a;

Figure 8c shows a cross section 8c-8c through the drill string according to figure

8a;

Figure 8d shows a cross section 8c-8c through the drill string according to figure

8a with an alternative embodiment of the power and signal line, the two having being separated into a power line and a signal line; and

Figure 9 shows a longitudinal section 9-9 through the drill string according to figure 8a.

Reference is first made to figures 1 and 2, in which a surface installation 1, for example a drilling platform, is provided with a drilling rig 2 including a derrick 21 provided with a feeding device 22 for a drill string 3, among other things. A non-rotatabie drill string 3 is provided, in an end portion, with a bottom-hole assembly 37 including a drill bit 37a and a drill-bit drive 37b, typically in the form of an electric motor. The derrick 21 is provided with a hoisting apparatus 24 known per se.

Reference is now made to figures 6a, 6b and 7, in which the drill string 3 is shown in greater detail. Drill-string sections 31, shown here as first and second drill-string sections 31a, 31b, are connected by means of a drill-string connection 32 of the groove 321 and tongue 322 type which is locked, in a connected state, by means of a locking element 33. The drill-string sections 31a, 31b are provided with two diametrically opposite first and second line grooves 34a, 34b which are arranged to accommodate, respectively, a fluid line 36a and a power and signal line 36b (see figures 8a-8c and 9) extending from the surface installation 1 to the bottom-hole assembly 37.

Reference is now made to figure 3. The fluid line 36a and the power and signal line 36b are arranged on, respectively, first and second line drums 35a, 35b, on which they are connected via elements (not shown) relevant for the type of line, for example a swivel, slip rings and optical signal transmission, to fixed installations (not shown) outside the line drums 35a, 35b for the supply of fluid and power and for transmitting and receiving signals. The lines 36a, 36b are passed through sealing stuffing boxes 231, 132 in a feeder 23 into abutment in their respective line grooves 34a, 34b. The feeding device 22 for the drill string 3 works synchronously with the feeder 23 for the lines 36a, 36b.

Reference is now made to figure 5 which shows the feeding device 22 for the drill string 3 in greater detail. The feeding device 22 includes a stuffing box 221 which fits tightly against the drill string 3, and two feeding belts 222 bearing clampingly against the drill string 3. The clamping effect is provided by means of actuators, not shown, for example hydraulic cylinders, and ensures that the drill string 3 is held in a secure grip.

The stuffing boxes 221, 231 and 232 ensures that pressurized fluid in the riser 4 cannot escape into the surroundings through the feeding device 22 and the feeder 23.

Figure 8d shows an alternative exemplary embodiment of the power and signal line, it being formed of a separate power line 36ba and a separate signal line 36bb. In this embodiment, it is appropriate to provide the surface installation 1 with a further line drum (not shown) and the feeder 23 with a further stuffing box (not shown).