A downhole motor (107) which comprises a stator housing (108), a rotor assembly (106) rotatable relative to said stator housing, and an arrangement for enabling, in use, a drill bit connected to the rotor assembly of said downhole motor to be rotated by rotating a drill string connected to said stator housing, wherein said arrangement comprises a unidirectional clutch (117) disposed between said rotor assembly and said stator housing and having at least one pawl which can be displaced between an inoperative position adjacent said stator housing and an operative position in which rotation of said stator housing by said drill string in one sense is transmitted to said rotor assembly via said at least one pawl, means biasing said at least one pawl towards said operative position, means retaining said at least one pawl in its inoperative position, and means which, when sufficient pulling force is applied to said drill string, will cause said means retaining said at least one pawl to release said at least one pawl and enable said at least one pawl to move into its operative position.

A device for clamping an element includes a pressure chamber having a flexible wall section with an elastic jacket and a rigid wall section that acts as a counter-bearing. The jacket is provided with a contact surface to connect with the element.

A downhole oscillation tool and method for axially vibrating a drill bit. In some embodiments, modular actuation assemblies may be provided, which may be readily interchanged between a housing and a shaft to axially vibrate the shaft with respect to the housing. Modular actuation assemblies may be mechanical, hydraulic, electric, or piezoelectric, for example, and may be characterized by differing oscillation frequencies. In some embodiments, a piezo element may be provided between the housing and the shaft.

Overbalanced drilling (OBD) is known to be cheap and simple but formation damage and reduced rate of penetration (ROP) are some of its disadvantages. However, underbalanced drilling (UBD) minimizes formation damage and achieve high ROP, but it is expensive, complex and can't be applied in many cases.

This application introduces a new technique that incorporates the advantages and avoids the disadvantages of these drilling systems and is referred to as Dynamic Underbalanced Drilling (DUBD).

In DUBD a pressure drop at the environ of the bit, below and around, is created that is restored to normal pressure above the bit and such conditions requires some minor modifications to the design of drill bit. Thus at the zone located below and around the bit underbalance conditions are dominated while the rest of the hole is overbalanced.

The anticipated cost of this technique is nearly zero and it is expected to save much of drilling costs. DUBD is expected to provide higher ROP that may exceed ordinary UBD in some cases, so saves time, reduce formation damage, saves costs (cheaper than OBD) and enables gathering information about the reservoir while drilling. This can save some of logging and testing costs. In addition, DUBD may reduce drilling problems, particularly time sensitive problems, and overcome problems of UBD. Furthermore, it can be used safely in over pressurized shale and salt formations, where UBD is not recommended.

The invention relates to a drill drive device (10) for an earth drilling apparatus with a spindle arrangement which has an inner spindle unit (20) and an outer spindle unit (40) that is supported in an axially displaceable manner on the inner spindle unit (20) and floating between two spring means (50, 60). According to the invention provision is made in that a first front spring means (50) which is arranged on a drilling tool side comprises a combination of at least a compression coil spring and a first disk spring arrangement (54) and in that a second rear spring means (60) which faces away from the drilling tool side has a second disk spring arrangement (64).

The invention relates to a drill drive device (10) for an earth drilling apparatus with a spindle arrangement which has an inner spindle unit (20) and an outer spindle unit (40) that is supported in an axially displaceable manner on the inner spindle unit (20) and floating between two spring means (50, 60). According to the invention provision is made in that a first front spring means (50) which is arranged on a drilling tool side comprises a combination of at least a compression coil spring and a first disk spring arrangement (54) and in that a second rear spring means (60) which faces away from the drilling tool side has a second disk spring arrangement (64).

The invention relates to a drill drive device (10) for an earth drilling apparatus with a spindle arrangement which has an inner spindle unit (20) and an outer spindle unit (40) that is supported in an axially displaceable manner on the inner spindle unit (20) and floating between two spring means (50, 60). According to the invention provision is made in that a first front spring means (50) which is arranged on a drilling tool side comprises a combination of at least a compression coil spring and a first disk spring arrangement (54) and in that a second rear spring means (60) which faces away from the drilling tool side has a second disk spring arrangement (64).

The invention relates to a drill drive device (10) for an earth drilling apparatus with a spindle arrangement which has an inner spindle unit (20) and an outer spindle unit (40) that is supported in an axially displaceable manner on the inner spindle unit (20) and floating between two spring means (50, 60). According to the invention provision is made in that a first front spring means (50) which is arranged on a drilling tool side comprises a combination of at least a compression coil spring and a first disk spring arrangement (54) and in that a second rear spring means (60) which faces away from the drilling tool side has a second disk spring arrangement (64).

A horizontal drilling machine with an impact device, including a support frame, an armored cable, a cable-straightening mechanism, a cable-feeding mechanism, a power head, a drill pipe, a rotating chuck, a damper, a fishing device with the impact device, a core tube and a thrust cylinder. One end of the thrust cylinder is hinged with the support frame, and the other end of the thrust cylinder is connected to the power head. The power head is arranged on a slid rail of the support frame. An active drill pipe of the power head is connected to the drill pipe. An end of the armored cable is connected to a control system, and the other end is connected to the fishing device in the drill pipe. A fishing head of the fishing device is connected to a spearhead of the core tube.

A device for clamping an element includes a pressure chamber having a flexible wall section with an elastic jacket and a rigid wall section that acts as a counter-bearing. The jacket is provided with a contact surface to connect with the element.