Abstract: A system has been invented for producing a final earth model of part of an earth formation having N (one or more) layers, the method including, in one aspect, generating an initial earth model based on raw data produced by a wellbore logging tool at a location in a borehole through the earth, performing 2-D forward modeling on the initial earth model to produce an interim earth model that includes a set of synthetic tool responses data for the wellbore logging tool, comparing the synthetic tool response data to the raw data to determine whether there is misfit between them; if misfit between the synthetic tool response data and the raw data is acceptable, saving and storing the interim earth model as the final earth model; if misfit between the synthetic tool response data and the raw data is unacceptable, performing 1-D forward modeling N times on the interim earth model, producing a secondary earth model; performing 1-D inversion on the secondary earth model; and either saving the secondary earth model as t

Abstract: Long-term changes in the distribution of a mineral in a subsurface deposit, due to commercial production of the mineral, are monitored by suitable instrumentation. The monitoring instrumentation is installed in combination with commercial mineral production equipment but the monitoring instrumentation is transparent to production. The monitoring instrumentation measures long-term changes in selected petrophysical attributes that are due to re-distribution of the mineral within the deposit in response to production.

Abstract: A method of adjusting induction receiver signals for skin effect in an induction logging instrument including a plurality of spaced apart receivers and a transmitter generating alternating magnetic fields at a plurality of frequencies. The method includes the steps of extrapolating magnitudes of the receiver signals at the plurality of frequencies, detected in response to alternating magnetic fields induced in media surrounding the instrument, to a response which would obtain at zero frequency. A model of conductivity distribution of the media surrounding the instrument is generated by inversion processing the extrapolated magnitudes. Magnitudes of the receiver responses at the plurality of frequencies are synthesized based on the model of conductivity distribution.

Abstract: A method of determining selected parameters of an earth formation surrounding a borehole by first, obtaining at least one induction logging measurement of the selected parameters in a first predetermined volume of the formation surrounding the borehole having known first radial and vertical dimensions, then obtaining at least one galvanic logging measurement of the identical selected parameters in a second predetermined volume of the formation surrounding the borehole having known second radial and vertical dimensions that overlap the first radial and vertical dimensions of the first predetermined volume, whereby the overlapping volumes form a representative common volume of the formation, and then combining the induction and galvanic logging measurements using an inversion technique to obtain a measurement of the selected parameters of the earth formation surrounding the borehole in the representative common volume of the formation.

Abstract: A method of determining a plurality of formation models each of which will simulate the response of a well logging instrument. A measured response of the well logging instrument is used to generate an initial model using inversion processing. A response of the instrument to the initial model is synthesized. A singular value decomposition is performed on the synthetic response to generate eigenparameters of the initial model. Eigenparameters having the least significant overall contribution to the synthetic response are sequentially substituted with linear equations representing prior constraints on the initial earth model. A linear system, including the remaining ones of the eigenparameters and the linear equations is solved so that the eigenparameters are preserved exactly and the linear equations satisfy a least squares fit. An additional synthetic instrument response is generated for each solution to the linear system which falls below a predetermined error threshold.

Abstract: A method of joint inversion processing acoustic velocity and electrical resistivity well log data. The method includes generating an initial model of earth formations over an interval of interest. The initial model corresponds to earth formations for which the acoustic velocity and resistivity well log data have been measured. The initial model includes layers each having a geometry, a value of resistivity and a value of acoustic velocity. Acoustic velocity and resistivity data are synthesized based on the initial model. Differences are determined between the synthesized data and the measured data. The initial model is adjusted and the steps of synthesizing the log data and determining the differences are repeated until the differences reach a minimum, thereby generating a final model of the earth formations.

Abstract: A physical signal is represented by a linear system. The linear system is transformed from the time and space domain to the frequency domain, generating a transformed system. The least significant portions in the transformed system are determined. The least significant portions are deleted from the transformed system, generating a smaller pruned system. The pruned system is solved in the frequency domain, generating a solution. The solution is inverse transformed from the frequency domain to the time and space domain, generating an approximation to the physical signal.

Abstract: A method for producing synthetic tool responses for a well logging tool for an earth formation, the method including, in one aspect, generating wellbore logging data for a particular part of an earth formation with a wellbore logging system with a wellbore logging tool, the earth formation having at least one layer, producing an input earth model of the particular part of the earth formation based on the wellbore logging data, inputting the input earth model to a trained artificial neural network, e.g. resident in a computer, the computer with the trained artificial neural network processing the input earth model and producing synthetic tool responses for the wellbore logging tool for one point or for a plurality of points in the earth formation.

Abstract: A method for determining the 2-dimensional distribution of horizontal and vertical electrical conductivities of earth formations surrounding a wellbore using measurements made by a transverse electromagnetic induction well logging instrument. A model is generated of the axial distribution of the horizontal and vertical conductivities, from induction signals acquired by the instrument using two-frequency alternating current. The model is generated by calculating an initial estimate of the conductivity distribution and axially inverting the estimate with respect to the measurements made using the two-frequency alternating current. Shoulder correction is applied to measurements made by the instrument using single-frequency alternating current. An estimate of the radial distribution of the conductivities is generated from the shoulder corrected induction signals acquired using the single-frequency alternating current.

Abstract: A method for determining a profile of a wall of a wellbore drilled through earth formations. The earth formations are irradiated by a source of gamma rays. Scattered gamma rays are detected at axially spaced apart locations from the source. At least one of the axially spaced apart locations is positioned on an opposite side of the source from the other ones of the spaced apart locations. A function, related to a rate of detecting the scattered gamma rays at a first one of the spaced apart locations with respect the rate of detecting scattered gamma rays at the at least one spaced apart location positioned on the opposite side of the source is calculated. Density of the earth formations, density of the fluid in the wellbore, and a difference between the densities is determined. An area bounded by the function is determined. The area is scaled with respect to the difference between the densities, and the profile is calculated from the scaled area bounded by the function.

Abstract: A method of determining the conductivity of earth formations penetrated by a wellbore. The method includes inserting an induction well logging instrument into the wellbore. The instrument includes a transmitter, a source of alternating current connected to the transmitter, and a receiver. The transmitter is energized with the alternating current, voltages induced in the receiver are recorded, and area enclosed with respect to a baseline, by voltage peaks present in the recorded voltages is determined. The enclosed area corresponds to the conductivity.

Abstract: A method for estimating porosity of an earth formation from measurements of acoustic energy traversing the earth formation and from measurements of seismoelectric voltages generated in the formation in response to the acoustic energy. The method includes the steps of measuring the acoustic energy traversing the earth formation and measuring said seismoelectric voltages generated in response to the acoustic energy traversing the formation. A seismoelectric signal is synthesized from the measurements of the acoustic energy using an initial value of the porosity. A difference is determined between the synthesized seismoelectric voltages and the measured seismoelectric voltages. The initial value of porosity is adjusted, and the steps of synthesizing the seismoelectric voltages from the acoustic signal, determining the difference, and adjusting the value of porosity are repeated until the difference drops below a predetermined threshold or the difference reaches a minimum value.

Abstract: An apparatus and method for retaining shaped charges. A foam core having charge carrying recesses can be constructed from a single piece or from multiple sections. Shaped charges are insertable within the foam core recesses so that the shaped charges are proximate to a detonator cord positioned inside or outside of the foam core. The foam core assembly holding the detonator cord and shaped charges is inserted into a housing such as a cylindrical tubing to construct the perforating gun. A seal isolates the shaped charges from pressurized well fluids. The housing can be attached to a firing head and lowered to the desired depth in a well casing. Additional foam sections can be added to modify the number and orientation of the shaped charges. The invention is particulaly useful with thin housing material and substantially reduces the manufacturing cost of perforating guns.

Abstract: A nuclear magnetic resonance sensing apparatus, comprising a magnet for inducing a static magnetic field in a region containing materials to be analyzed. The magnet has a longitudinal axis and substantially uniform magnetization along the axis. The apparatus includes a system for generating a radio frequency magnetic field to excite nuclei of the materials to be analyzed, which includes a first antenna having an axial length shorter than a length along the axis over which the magnet has said substantially uniform magnetization. The axial length of the first antenna is shorter in a direction of motion of the apparatus so that the radio frequency magnetic field excites the nuclei where they are substantially prepolarized by the static magnetic field to an equilibrium state along the direction of motion. The apparatus includes a system for receiving nuclear magnetic resonance signals from the excited nuclei.

Abstract: An apparatus for measuring conductivity of earth formations penetrated by a wellbore including a magnet for inducing a static magnetic field in the earth formations penetrated by the wellbore. The apparatus includes means for generating a radio frequency magnetic field in the wellbore and the earth formations, means for selectively varying a frequency of the radio frequency magnetic field, and means for receiving a nuclear magnetic resonance signal from excited nuclei in the earth formations. The means for receiving includes means for measuring a difference in phase between the magnetic resonance signal and the radio frequency magnetic field. The phase difference measured is related to the conductivity of the earth formations.

Abstract: An unconstrained transformation filter operator that is efficient in terms of computer resources and that improves circularly symmetric migrated impulse response for steep dips. The filter operator combines selected desirable attributes of the more efficient McClellan transformation filter with selected desirable attributes of the more accurate Laplacian transformation filter. The novel filter operator is not constrained along the k.sub.x and k.sub.y spatial axes by the requirement that it equal cos (k). The transformation filter is averaged over all azimuths to improve its accuracy of response.

Abstract: An apparatus for measuring induction resistivity and nuclear magnetic resonance properties of earth formations penetrated by a wellbore. The apparatus includes a magnet for inducing a static magnetic field in the formations, a transmitter antenna positioned proximal to the magnet and having a principal magnetic axis substantially perpendicular to the principal magnetic field direction of the magnet. The apparatus includes receiver antennas positioned at spaced apart locations from the transmitter antenna, a circuit for generating radio frequency power pulses which is selectively connected to the transmitter antenna, and circuits for measuring the voltages induced in both the transmitter antenna and induced in the receiver antennas. The measuring circuit is adapted to measure voltages in the receiver antennas during the radio frequency power pulses, when the voltages are induced in the receiver antennas by electromagnetic induction.

Abstract: A method of simulating response of a through casing electrical resistivity well logging instrument to a set of simulated earth formations, cement and casing. A model of the earth formations, casing, cement and a configuration of electrodes on the instrument is initialized. Space surrounding the instrument is divided into segments. Conductance of each of the segments is calculated. A system of linear equations describing the electrical potential at each junction of segments is set up. The system expresses the balance of electrical current at each junction disposed outside the instrument and satifies the conditions that the potential on an outer surface of the space is zero, that the current normal to an insulating part of the instrument is zero, and that the potential is substantially equal at all junctions contained within one of the electrodes. The system of linear equations is solved by the conjugate gradient method with Incomplete Cholesky preconditioning.

Abstract: A method for determining oil saturation in an earth formation penetrated by a wellbore. Measurements of relative amounts of carbon and oxygen are made by spectral analysis of neutron-induced inelastic gamma rays detected from the earth formation at spaced apart locations. The method includes calculating an apparent oil holdup in the wellbore at each of the spaced apart locations from the relative amounts of carbon and oxygen. A corrected oil holdup is calculated in the wellbore from differences between the apparent holdups determined at each of the spaced apart locations. An apparent oil saturation in the formation is determined at each of the spaced apart locations from the relative amounts of carbon and oxygen and the corrected oil holdup. A corrected formation oil saturation is determined from differences between the apparent oil saturations at each of the spaced apart locations.

Abstract: A well logging instrument string including a first section adapted to be operated substantially in contact with a wall of a wellbore, a coupling connected at one end to one end of the first section. The coupling includes first and second flexible joints for enabling relative angular deflection between the first section and a second section. The coupling includes a biasing mechanism for urging at least one of either the first or the second flexible joints, or both, to assume their positions of maximum angular deflection. The instrument string includes a second section connected to the other end of the coupling. The second section is adapted to be operated spaced apart from the wellbore wall.