Abstract: The semisubmersible drilling vessel has two spaced, parallel, horizontal, elongated submersible hulls which support a deck and a deck mounting structure. The deck has a central opening overhanging the space between the two hulls and is surmounted by a derrick. The mounting structure includes at least two vertical columns which connect the ends of the hulls to the deck and at least two hollow columns facing and spaced from one another substantially in the center of each hull. These central hollow columns form caissons on the interior of which is provided pipe manipulation apparatus which accommodates the handling and vertical storage of pipes associated with drilling a well.

Abstract: Well logging techniques and apparatus are disclosed for determining formation resistivity at different radial depths of investigation and with greater accuracy than prior techniques, for determining the existence, locations and properties of beds and caves, and for determining changes in the size of a borehole.

Abstract: A system for the quantitative analysis of one or more evolving gases exiting a borehole includes a Venturi ejector for substantially capturing liberated gases in the bell nipple and return line, a rotating disk extractor for substantially extracting gases entrained and dissolved in drilling mud, and a gas analyzer system for analyzing and quantifying the captured and extracted gases. The Venturi ejector preferably is operatively coupled to the return line, and a pipe wiper may be arranged to partially cover the bell nipple. The ejector sucks liberated gases out of the return line and causes a negative pressure to occur at the bell nipple such that air is sucked into the bell nipple rather than exiting the same. The rotating disk extractor has air flowing countercurrent to the mud flow. As the disks rotate, they pick up a thin liquid film of mud which is exposed to the air stream.

Abstract: The invention relates to the control of rotary type oil drilling operations. During a drilling test in which the drill string is held against vertical motion at the surface, known as the "drill-off test", an exponential decrease as a function of time, in the weight applied to the drill bit (WOB) is noted as is a threshold where the value of WOB remains constant. From this test the drillability of the formation drilled, the bit wear and the actual value of the weight applied to the bit may be determined.

Abstract: A measurement while drilling nuclear tool adapted to be coupled in the drill string to make formation evaluations and methods of using are described. A neutron source is positioned on the cylindrical axis of the tool while a connected gamma ray source is eccentered against an interior side of the cylindrical tool. Both sources can be axially removed from the tool along its interior. Novel source-detector configurations are provided in order to accommodate the constraints of the MWD environment. Gamma ray transparent windows are provided through both the drill collar and an external fluid excluder (stabilizer) at the positions of the gamma ray source and scintillator detectors. Neutron detectors may be of two different types at the same spacing from the source. Corrections are made for microphonic noise that arises while drilling and for natural gamma ray background. A drilling fluid density determination is made and is utilized to compensate for "borehole" or "standoff" effects.

Abstract: Samples of mud are taken periodically at the surface at one or several locations where the mud does not contain cuttings anymore. The mud samples are analyzed on the rig site to determine the successive values, as a function of time or depth, of a parameter representative of the weight of the fine solids present in the mud. In one aspect of the invention the weight of the fine solids present in the mud is determined by measuring the weight of the liquid phase of the mud and the weight of the electrolyte dissolved in a known weight of mud. Preferably the weight of the liquid phase is determined by drying to constant weight a given weight of mud and the weight of electrolyte is determined by chemical analysis of the mud filtrate using an ion chromatography system on the rig site.

Abstract: A drilling fluid to be circulated through a borehole as it is drilled is produced by mixing solid and liquid drilling fluid components in such proportions that the density of the fluid has a selected value which lies between upper and lower limits (c) calculated for all depths of the borehole to be drilled. The lower limits satisfy a shear failure criterion for the material forming the wall of the borehole and above which influx of pore fluid does not occur, and the upper limits satisfy either the same shear failure criterion or a tensile failure criterion, depending on which of the two criteria predicts the lower upper limit. Upper and lower shear failure values (b) are calculated as a function of depth and tensile failure values (a) are calculated as a function of depth. The calculations include determining the in-situ stress state at the site of the borehole, and calculating the stresses which will occur at the borehole wall as a function of depth and drilling fluid density.

Abstract: Downhole Torque and Rate of Penetration are utilized to develop indications of formations having high porosity or of the development of an undergauge bit. Downhole torque is normalized by dividing it by the product of downhole weight on bit and bit size to produce Dimensionless Torque while Rate of Penetration is normalized by dividing it by the product of downhole weight on bit and rotary speed. The values of Dimensionless Torque and Normalized Rate of Penetration are compared to "normally" expected values of these quantities. Deviations from the normal values are taken as an indication of the occurrence of bit penetration of a highly porous formation or of the development of an undergauge or damaged bit.

Abstract: A method and apparatus for testing and calibrating an electromagnetic logging tool are described. The tool includes a tansmitting antenna and a receiving antenna. A shielded receiving device is placed around the transmitting antenna and intercepts the transmitted signal. A shielded transmitting device is positioned around the tool's receiving antenna and transmits to the receiving antenna a signal which has a phase and/or an amplitude related to the signal transmitted by the tool's transmitting antenna in a known manner which simulates the effects that a geological formation would have on the signal if it were to travel from the tool's transmitting antenna to the tool's receiving antenna through the formation. Since the simulated effect is known, the output of the tool may be verified as being correct or corrected if erroneous.

Abstract: The invention relates to a method of real time control of fluid influxes into an oil well from an underground formation during drilling.The injection pressure p.sub.i and return pressure p.sub.r and the flow rate Q of the drilling mud circulating in the well are measured. From the pressure and flow rate values, the value of the mass of gas M.sub.g in the annulus is determined, and the changes in this value monitored in order to determine either a fresh gas entry into the annulus or a drilling mud loss into the formation being drilled.

Abstract: The invention relates to the braking, by means of a control lever, of the winch of a derrick equipped with a band brake and located away from the lever. The lever and the band brake are included in a servo-control circuit and connected by an electric transmission line. A force return is provided on the lever by means of a torque motor receiving the position error signal relative to the mobile end of the band in relation to the control value position given by the lever.

Abstract: A gradiomanometer 1 measures the difference in pressure between points 3 and 4 to indicate density and hence proportions of two phases (e.g. liquid and gas), each of known density flowing as indicated by arrow 6. A venturi meter 2 measures the difference in pressure between points 4 and 5 to indicate flow rate, initially assumed to be that of the heavier phase only. An iterative calculation makes it possible to obtain a density measurement corrected to allow for flow friction and individual flow rates of the two components, having regard to slippage therebetween. A step discontinuity 8 may be provided downstream to create turbulence and render the flow homogenous.

Abstract: Downhole torque and rate of penetration are utilized to develop indications of formations that are porous, argillaceous or tight. This information is useful as an aid in selecting drilling practices and drilling bits. The method separates bit effects from lithology effects when drilling with roller cone or PDC bits by utilizing surface and subsurface wellsite sensors to determine averaged values of real time penetration rate and downhole torque. Changes in bit torque are used to broadly classify the lithology into three categories: porous, argillaceous and tight formations while trends in bit torque and rate of penetration in shale are used to separate wear of the bit from changes in formation strength.

Abstract: The invention relates to the monitoring of the drilling operations of a well using a drill bit mounted at the end of a drill string, which can be taken up by the travelling block of a lifting gear installed in a derrick, in order to permit the addition or removal of members from the drill string. By measurement with the aid of sensors associated with the lifting gear and connected to a processing unit, the altitude and the hook load of the travelling block, it is possible to plot the curve, form which it is possible to deduce information concernig the structure and the behavior of the well being drilled.

Abstract: A pressure pulse generator which generates relatively sinusoidal pressure pulses in a fluid flowing in a borehole is disclosed. The pressure pulse generator for a MWD tool broadly comprises: a housing adapted to be connected in a tubing string so that fluid flowing in the string will at least partially flow through the housing; a stator mounted within the housing and having a plurality of lobes with intervening gaps; a rotor coaxial to the stator which rotates relative to the stator and which is mounted within the housing and has a plurality of lobes with intervening gaps between adjacent lobes, wherein the lobes of the rotor and stator are arranged such that as the rotor rotates relative to the stator, the area of the adjacent gaps between the lobes of the stator and rotor through which the fluid may flow in a direction parallel to the borehole varies approximately with the inverse of the square root of a linear function of a sine wave.

Abstract: A method for moving a radioactive source into and out of a well logging tool incorporated in the drill string is disclosed. Prior to moving the source, the logging tool is positioned sufficiently distant from and vertically under the drilling rig floor so as to avoid a hazardous radiation condition at the floor when the source is in its operative position in the tool. A tubular radiation shield containing the source is positioned at the end of the drill string hanging from the rotary table and a source manipulating device is engaged with the source. It is then lowered through the shield and the drill string into the tool. These steps are practiced in the reverse order when the source is being removed from the tool. An additional shield may be provided to envelop the first shield for added shielding during transportation or storage.

Abstract: The invention relates to a procedure for measuring the rate of penetration V.sub.F of a drill bit fixed to the lower end of a drill string lowered into a well. During an initial period, the well is drilled keeping, on average, the value of weight F of the drill string measured at the surface relatively constant, and the instantaneous values of the drill string rate of penetration V.sub.S and the weight F are measured at the surface at different successive moments. The value of the drill string average rate of penetration V.sub.SM at the surface is determined from the values of V.sub.S measured and the successive values of dF/dt of the first derivative with respect to time. The coefficient of apparent rigidity of the drill string during the initial period is then determined from the values of V.sub.SM, V.sub.S and dF/dt. Finally, the rate V.sub.F is calculated.

Abstract: This invention is intended for use in the process of drilling an oil well and has to do with a process for the detection of fluid influx which could lead to a blow-out. This process consists of measuring the inlet flow rate A of the drilling mud coming into the well and the outlet flow rate B of the drilling mud rising from the well in order to arrive at the quantity:C=a.B-Awhere a is a scale factor the value of which can be altered so as to bring about a recalibration of the outlet rate measurement. Such recalibration is made each time the average value of C, in relation to a given period of time, reveals a significant difference between the rates, and an alarm is set off in accordance with the frequency of the recalibrations corresponding to an excess in the outlet rate in relation to the inlet rate.

Abstract: Formation strength and other measurement while drilling parameters are combined in a formation volumetric analysis which produces not only the traditional volumetric components of clay volume, mineral volume, total porosity, and water filled porosity, but also, in shaley formations, an excess or overpressure porosity. The overpressure porosity is then utilized to generate an indication of pore pressure which in turn is used in the drilling process as an aid in determining the lowest optimal drilling mud weight for most efficient drilling without incurring excessive risks of a blowout arising from an overpressured formation.

Abstract: A floating drilling platform having dual work stations is disclosed for performing deep sea drilling and/or hydrocarbon production operations. The structure of the platform is designed to accommodate replaceable modules which facilitate the installation and removal of either a drilling derrick or production equipment. Thus, during the drilling phase of a reservoir's development, the platform may be outfitted with dual drilling derricks while at later times the platform may be outfitted with a drilling derrick and a full production facility. Various expedients are available to permit the equipment of one work station to be used in conjunction with the equipment of one other. Simultaneous management of dual conductors is enabled by a dual riser management system which models in real time riser behavior under varying environmental and other operational conditions. The dual riser management system includes a riser analysis subsystem, a mooring analysis subsystem and a vessel stability analysis subsystem.