Abstract: A method of creating a wellbore in an underground formation is provided. A borehole is drilled in the underground formation, whereafter a casing of a ductile material is lowered into the borehole. The casing is selected to have a smaller elastic radial deformation than the surrounding formation when the casing is radially expanded against the borehole wall by application of a radial force to the casing. Said radial force is applied to the casing so as to radially expand the casing against the borehole wall thereby inducing a plastic radial deformation of the casing and an elastic radial deformation of the surrounding underground formation, whereafter the radial force is removed from the casing.

Abstract: A hydrogen-oxygen acoustic logging device is provided for generating acoustic waves for logging a subsurface formation when arranged in a borehole through the formation. The device is electrically driven for electrolyzing water to a gaseous hydrogen-oxygen mixture and for firing the gaseous mixture for generating the waves. The device comprises an inflatable compartment to be inflated by the gaseous hydrogen-oxygen mixture. The device further comprises a housing having an outer wall facing and closely fitting to a borehole wall portion, and provided with a recess. The recess contains the inflatable compartment and, when arranged in logging position against said borehole wall portion, defines a substantially closed wave generating chamber.

Abstract: A method is provided for detecting outflow of fluid from an offshore wellbore to a surrounding earth formation or inflow of fluid from the formation of the wellbore. The wellbore is in fluid communication with a conduit extending between the wellbore and an offshore structure floating above the wellbore, which wellbore and conduit are at least partly filled with a body of fluid. Liquid is injected into the body of fluid at a first predetermined flowrate, and liquid is discharged from the body of fluid at a second predetermined flowrate. A variation of the content of the body of fluid is then determined.

Abstract: Vibrations in borehole equipment are controlled by defining the energy flow through the equipment as the product of an "across" variable and a "through" variable, wherein fluctuations in one variable are measured and the energy flow is controlled by adjusting the other variable in response to the measured fluctuations in said one variable. Suitable variables for defining the energy flow are voltage times current of an electrical drive, pressure times flow rate of a hydraulic drive, or torque times angular velocity of any rotary drive.

Abstract: A jarring apparatus is provided for vibrating a pipe string in a borehole. The apparatus thereto generates at a downhole location longitudinal vibrations in the pipe string in response to flow of fluid through the interior of said string.

Abstract: A directional drilling assembly comprises a downhole drilling motor and stabilizer assembly which stabilizes the drilling assembly in such a manner in the borehole that the drilling bit driven by the output shaft of the downhole motor has a tilted orientation in the borehole. The stabilizer assembly comprises a lowermost stabilizer which is connected to the output shaft of the motor so as to suppress any sticking tendency of said lowermost stabilizer to the borehole wall.

Abstract: A method of directionally drilling a borehole makes use of a drilling assembly including an apparatus having an upper section with a longitudinal axis I, and a lower section having a central axis II and including at least part of a rotary drill bit, said sections being interconnected by a universal pivot mechanism. The method comprises rotating the assembly in such a manner that the upper section rotates about said longitudinal axis I and the lower section rotates about said central axis II. During at least part of the drilling operations said central axis II is tilted and rotated in an orbital mode relative to said longitudinal axis I such that a plane containing said two axes is maintained in a predetermined orientation relative to a reference direction.

Abstract: An impermeable and continuous coating is formed on the wall of a borehole in which a drill string is present by injecting coating forming components and a carrier fluid through the drill string. Subsequently the coating forming components are separated, e.g. in a decanting centrifuge, from the carrier fluid and plastered to the wellbore as a continuous layer.