Abstract: A method is disclosed for determining rock compressive strength of a subterranean formation penetrated by a wellbore. A mathematical model of a drill bit and an estimate of rock ductility of a particular subterranean formation in conjunction with weight-on-bit (WOB), bit rotational speed RPM, and rate of penetration (ROP) are used as inputs. From the above inputs, the rock compressive strength can be determined while the wellbore is being drilled or afterwards. A depth correlated log can be generated of rock compressive strength that can be compared to other logs obtained from adjacent wellbores to obtain a refined estimate of the depth of a particular subterranean formation feature. Further, the above method can be utilized for obtaining an indication of bit wear or bit damage while the bit is drilling a wellbore by comparing a first rock compressive strength log of a wellbore to a rock compressive strength log being generated while the drill bit is actually drilling a second wellbore.

Abstract: Released film structures are employed in measuring the mechanical properties of the film material. By measuring the deformation of thin film structures held under intrinsic tensile stress and then released, these mechanical properties can be accurately measured.

Abstract: An endless metal carrier is bent and treated by a heat treatment process to provide residual stress. The product carrier is cut at a portion, and the radius of the cut carrier in the free state is compared with a standard radius of a standard carrier having a predetermined residual stress to determine whether the radius coincides with the standard radius.

Abstract: A complete, three-dimensional stress state of underground rock is determined by a method which includes the steps of: drilling a rock to form a borehole with a substantially spherical bottom; deforming the borehole either by releasing the rock from the stresses by overcoring or by applying an external static pressure to the rock; and measuring displacements of the spherical bottom in at least xx, yy, zz, xy, yz and zx radial directions during the deformation of the borehole.

Abstract: A caliper is mounted on two springs in a free-floating manner between interlockable upper and lower packers to be set in a well bore. The caliper has radially extendible arms which are extendible in response to independent forces exerted thereon as derived from the movement of a carriage driven by a single motor contained in the caliper tool. A clutch mechanism is used to lock the arms to precision measurement transducers only after the arms have been moved radially outwardly a sufficient distance. Other transducers for generating signals indicating the total movement of the arms and for indicating the forces exerted by the springs on the arms are included in the preferred embodiment.

Abstract: The present invention is directed to a method for determining the stress at the borehole boundary at a selected location within a borehole. The present invention comprises a method for determining the stress employing a plurality of mechanical properties of the formation, e.g., Poisson's Ratio, the rock strength properties and the elastic modulus, together with the measured deformation of the deformed borehole at the selected location. The method comprises measuring at the selected location a plurality of parameters indicative of the formation at that location and from which a plurality of mechanical properties of the formation, e.g., the rock strength properties, the elastic modulus and Poisson's Ratio are determinable, calipering the borehole at the selected location to determine the deformation of the deformed borehole and determining the stress at the borehole boundary at the selected location employing the information obtained by measuring and calipering.

Abstract: To measure the modulus of elasticity of the rock in the wall of a borehole, a plug is cut in the borehole wall. The plug, its base attached to the surrounding rock, acts as a short column in response to applied forces. A loading piston is applied to the top of the plug and compression of the plug is measured as load is increased. Measurement of piston load and plug longitudinal deformation are made to determine the elastic modulus of the plug material. Poisson's ratio can be determined by simultaneous measurements of longitudinal and lateral deformation of the plug in response to loading. To determine shear modulus, the top of the plug is twisted while measurements are taken of torsional deformation.

Abstract: The state of stress in a rock mass surrounding a borehole (21) can be estimated by measuring the initial dimensions of the borehole, cutting a cone-shaped opening extending outwardly from the borehole having a bottom wall (44), and cutting a conical slot (45) from the bottom wall (44) of the cone-shaped opening outwardly from the borehole at an angle to the axis of the borehole. The release of stress on the rock between the borehole and the conical slot results in a change in the dimensions of the borehole. An apparatus for carrying out the measurements includes one or more cutting arms (27) pivotally mounted to a main support housing (26) and capable of being rotated thereon while being pivoted outwardly to cut the cone-shaped opening.

Abstract: Measurements of the deformability of deep rock masses are made by positioning a borehole jack (20) having opposed bearing plates (22, 24) in a borehole at a position at which measurements are to be made, and driving the pressure plates (22, 24) apart to displace the walls of the borehole. A lateral displacement probe (30) is mounted between the pressure plate surfaces in position to detect and measure displacements of the wall of the borehole at points lying on a diameter perpendicular to the direction of the resultant of the equal and opposite forces applied by the pressure plates (22, 24) to the wall (21) of the borehole. The lateral displacement probe (30) includes probe tips (35) that are biased firmly against the wall (21) of the borehole to move inwardly or outwardly therewith. A displacement transducer provides an output signal transmitted to the surface which is indicative of the displacements of the probe tips (35).

Abstract: Residual stress measurements are made using a strain gage and stress relief achieved by local melting of a region of the object being tested by a laser beam or other finely directed heat source. Surface strain is measured dynamically before the heat of the molten region diffuses under the gage and results in thermal stress. The method is semi-nondestructive because the molten region recasts with little loss of material, is rapid, and can be utilized on difficult geometries such as the interior surface of reactor pipe.

Abstract: Residual stress measurements are made using a strain gage and stress relief achieved by local melting of a region of the object being tested by a laser beam or other focused heat source. Surface strain is measured after the molten region resolidifies, and the effect of thermal stress and recast stress is eliminated by subtracting a calibration measurement of an annealed specimen. The method is semi-nondestructive, less costly than existing techniques, and can be used to measure residual stress on the interior surface of pipes.

Abstract: Method for determining internal stresses in structural members in machine or apparatus manufacturing by machining, around a measuring location provided with strain gages, a circular slot into the surface of the structural member that is to be measured, measuring changes in strain of the core of the measuring location left standing, and calculating the internal stresses from the measured strains and a depth-dependent decay function determined on a calibrating material sample, the improvement therein affording the determination of internal stresses in the structural members at depths greater than about 5 mm, includes the steps of mechanically removing the measuring-location core down to a new surface at the base of the circular slot, securing a strain gage to a new measuring location at the new surface, machining another circular slot around the new measuring location, measuring changes in strain of the core of the new measuring location left standing while measuring changes in strain thereof and repeating the