Blow-out prevention device for shutting off an annulus between a drill column and a well wall

Abstract: A blow-out prevention device (4) for shutting off a annulus (8) between a drill column (7) and a well wall by means of an expandable sealing device (3) when an unwanted blow-out of fluid and/or gas takes place from a geological unstable well formation when drilling for oil or gas. When a blow-out takes place, a compressive-pulse code is activated in the inlet of the drill column (7) and is transmitted through the drilling fluid to a pressure sensor (25) which transmits the compressive-pulse code on to the microprocessor (37) which is preprogrammed with the pressure code. If the pressure codes coincide, an electric motor (27) is activated, which, via a set of gears (30) and a nut-and-bolt device (32, 33), displaces a valve plate (22) axially towards the valve seat (26). The drilling fluid then flows out through the nozzles (24) and causes a big pressure drop which is used to expand a sealing device (3) so that the annulus (8) is shut.

Description: The present invention concerns a blow-out prevention device for shutting off an annulus between a drill column and a well wall when an unwanted blow-out of fluid and/or gas from an unstable geological well formation occurs when drilling for oil or gas. From US-A-4,367,794 and EP-A-0,116,443 and EP-A-0,205,297 devices are known which prevent an unwanted blow-out of fluid and/or gas from an unstable geological well formation when drilling for oil or gas. These known devices for shutting off a fluid and/or gas blow-out have considerable disadvantages. US-A-4,367,794 concerns an acoustically activated blow-out prevention device which, by means of a motor-activated, movable internal sleeve in the valve body and a flap valve, enables the drilling fluid to circulate out and the annulus to be shut off between the drill column and the well wall. Communication between the sealing device and the annulus is via doors and ducts in the valve body and chokes in the sleeve. The disadvantage is that the seals between the sleeve and the valve body are subject to too much erosive wear on account of the high differential pressure. EP-A-0,116,443 concerns a blow-out prevention device which is activated when a preset differential pressure arises between the annulus pressure and the internal pressure in the drill column. This differential pressure controls a slide valve which is mounted in the valve body. The disadvantage is that the slide valve can easily become stuck and that the seals are subjected to erosive wear. EP-A-0,205,297 concerns a blow-out prevention device in which a solenoid valve controls the pressure to a ball check valve which alters the circulation pattern of the drilling fluid. Activation is by pressure waves being sent through the drilling fluid in the drill column. The disadvantage of this invention is that there are at least three valves and that there is, therefore, a certain risk that one or more valves might become stuck or leak. US-A-3,908,769 discloses a blow-out prevention device to shut off an annulus between a drill column and a well wall by means of an expandable sealing device when an unwanted blow-out of fluid and/or gas takes place from a geologically unstable well formation for oil or gas. Drilling fluid flows through an internal flow duct in the well column to first and second valve systems and further to the drill bit at the end of the drill column or string. When a blow-out occurs, the pumps for the drilling fluid are shut down and a blow-out preventer at the surface is actuated to close off the annular space around the drill column. Then the upper end of the duct in the drill column is opened whereby, due to the blow-out pressure, the first valve system is moved upwards to open the second valve system so that, when the pumps for the drilling fluid are restarted, the pressure generated by the pumps expands the sealing device. This known device is very unsafe since it involves opening of the duct in the drill column when the blow-out occurs, and since it comprises a plurality of different valve components and procedural steps which easily might fail. Shallow, thin gas and/or fluid reservoirs under high pressure represent one of the most serious problems when drilling for gas or oil. Shallow gas is gas which is located in the upper part of the sedimentary geological formation and is usually 200 to 800 metres below the sea bed. These gas and/or fluid reservoirs are usually 2 to 6 metres thick and often consist of unconsolidated sand with high porosity and permeability. The extent of these reservoirs can be great and the probability of an uncontrolled blow-out can be high, with a correspondingly high risk of well damage. The formation pressure in the upper layer is usually low. To prevent reservoir fluid penetrating into the well, the weight of the hydrostatic drilling fluid column must be higher than the pressure in the reservoir, but not so high as to risk the well wall cracking. If this happens, the drilling fluid located in the drill hole might leak out in the formation and an uncontrolled blow-out might take place as a consequence of the reduced height and thus reduced weight of the hydrostatic drilling fluid column. To increase safety a blow-out prevention device down in the hole can be used to shut off the annulus between the drill column and the well wall above the unstable, critical reservoir layer. Thereafter, the fluid or gas located above the valve circulates out to the surface and the annulus is filled with fluid which has sufficient specific weight to withstand the reservoir pressure. The purpose of the present invention is to improve the operational safety of a blow-out prevention device located in a drill hole when drilling for oil or gas beyond that known from the above-mentioned solutions and which shuts off the annulus between the drill column and the well wall rapidly and efficiently and which, in its design, has a minimum of sealing and valve devices which can be subjected to destructive pressure and erosive wear. According to the present invention, this is achieved by means of a blow-out prevention device as mentioned in the introduction and which is, furthermore, characterized in that the valve is a two-way screw-down stop valve arrangement with a valve rod and a double-sided valve plate which is provided to be activated and directs the drilling fluid either, under normal drilling operation, to the drill bit or, when a blow-out occurs, through a number of exit nozzles subject to a large pressure drop in these nozzles, so that a pressure differential arises which is used to expand the sealing device. The particularly advantageous features of the present invention are defined in claims 2-7. The present invention will now be described in more detail by means of examples and with reference to the enclosed drawings, in which: Fig 1 shows a cross-section of a vertical well hole in which a blow-out prevention device is located in a normal operating situation. Fig. 2 shows a cross-section of the same device in the same position but in a blow-out situation. Fig. 3 shows a cross-section of a blow-out prevention device which shows its details. As stated above, fig. 1 is a cross-section of a well hole in a geological formation in which a drill column 7 is lowered and to the base of which is fastened a blow-out prevention device 4 with a drill bit 1 in accordance with the present invention. The situation shown in fig. 1 is a normal operating situation in which the drilling fluid is fed through the drill column 7, through the blow-out prevention device 4, to a nozzle 2 and further to a drill bit 1. The drilling fluid is fed to the surface in a annulus 8 between the well wall and the drill column 7 when a valve device 6, as shown in fig. 1, is open to allow the drilling fluid to flow to the drill bit 1 in an axial direction. Fig. 2 shows a blow-out situation in which the valve 6 is shut in the axial direction but open in the radial direction so that the drilling fluid cannot reach the drill bit. The drilling fluid flows through the nozzles 5 under high pressure. The pressure drop which occurs in the nozzles is used to expand a sealing device 3 which is designed to shut off the annulus 8 between the drill column 7 and the well wall. Fig. 3 shows the details of the blow-out prevention device 4. In a normal drilling situation the drilling fluid flows through a flow duct 20 to a nozzle 2 and the drill bit 1. A valve plate 22 is then in the position shown and any drilling fluid in the sealing device 3 (see fig. 2) will be evacuated to the annulus through a duct 23 and the exit nozzles 24. When a blow-out of gas or fluid takes place from a thin reservoir layer in an unstable geological formation a compressive-pulse code is activated in the drill column's inlet and is transmitted through the drilling fluid to a pressure sensor 25 in the blow-out prevention device 4. The compressive-pulse code is transmitted on to a microprocessor 37 which is preprogrammed to be able to recognise the activation code. If the codes coincide, an electric motor is activated which drives a set of gears 30 and a nut-and-bolt device 32, 33 which displaces the valve plate 22 in an axial direction until it meets a valve seat 26 in the valve body 21. The drilling fluid then flows in another direction and through the exit nozzles 24 with a considerable pressure drop which is used to expand the sealing device 3. To prevent the erosion of the well wall, the blow-out prevention device 4 is provided with a circular, externally located sleeve 29 which covers the exit nozzles 24, and a flexible sleeve 28 in connection with sleeve 29 to prevent drilling particles from penetrating into the exit nozzles 24 during normal drilling.

Claims: A blow-out prevention device (4) to shut off an annulus (8) between a drill column (7) and a well wall by means of an expandable sealing device (3) when an unwanted blow-out of fluid and/or gas takes place from a geological unstable well formation when drilling for oil or gas, where drilling fluid is circulated through an internal flow duct (20) in the drill column (7) to a driven valve (6) which in case of a blow-out is provided to utilize the pressure of the drilling fluid to expand the sealing device (3), characterised in that the valve is a two-way screw-down stop valve arrangement (6) with a valve rod (33) and a double-sided valve plate (22) which is provided to be activated and directs the drilling fluid either, under normal drilling operation, to the drill bit (1) or, when a blow-out occurs, through a number of exit nozzles (5, 24) subject to a large pressure drop in these nozzles, so that a pressure differential arises which is used to expand the sealing device (3). A blow-out prevention device in accordance with claim 1, characterised in that, in connection with the valve rod (33) for the two-way screw-down stop valve arrangement (6, 22), there is a spring (35) to ensure sufficient sealing pressure between the valve plate (22) and the valve seat (38). A blow-out prevention device in accordance with claim 1, characterised in that the valve rod (33) is driven by an electric motor (27) via a set of gears (30) and a nut-and-bolt device (32). A blow-out prevention device in accordance with claim 1, characterised in that it is provided with an external, circular, pressure-absorbing sleeve (29). A blow-out prevention device in accordance with claim 1, characterised in that a flexible sleeve (28). is fastened to the sleeve (29). A blow-out prevention device in accordance with claim 1, characterised in that the electric motor (27) is provided with a control unit which cuts off the power at a preset sealing pressure between the valve plate (22) and the valve seat (26). A blow-out prevention device in accordance with claim 3, characterised in that, in order to activate the motor (27) which drives the two-way valve-seat arrangement (6), a system is used which consists of a compressive-pulse code, a pressure sensor (25) and a microprocessor (37), which, when a blow-out takes place, is activated by a compressive-pulse code being generated in the inlet of the drill column (7) and being transmitted through the drilling fluid to a pressure sensor (25) which transmits the compressive-pulse code on to the microprocessor (37), preprogrammed with the pressure code, which activates the motor (27) when the pressure codes coincide.

Inventors: SANGESLAND SIGBJORN, SANGESLAND, SIGBJORN
Applicants: NORSK HYDRO AS, NORSK HYDRO ASA
Application year: 1993
Main classification: E21B21
IPC codes: E21B21, E21B33