Abstract: A spontaneous potential (SP) sub is interconnected between two metallic housings of a wellbore apparatus and is lowered into a wellbore. A spontaneous potential (SP) of an earth formation trasversed by the wellbore is measured by the SP sub, and a log is generated from the sub which is representative of the spontaneous potential of the formation, the log being substantially free of a special type of distortion which typified the prior art SP measurements taken by prior art SP measurement apparatus. The SP sub includes a measurement electrode, monitoring electrodes placed on both sides of the measurement electrode, a bucking electrode placed on both sides of the monitoring electrodes, current driving circuitry connected to the bucking electrodes, and receiving circuitry connected to the monitoring electrodes. The current driving circuitry delivers a current of sufficient magnitude to each bucking electrode such that the voltage potential between the monitoring electrodes is approximately equal to zero.

Abstract: An apparatus for measuring transient earth current includes a detection electrode and a second electrode disposed beneath the surface of the earth in vertical alignment with one another at depths greater than those to which electromagnetic waves generated above the surface of the earth having commercial power line frequencies penetrate, such that the electrical resistance between the detection electrode and the second electrode is on the order of several tens of thousands of ohms, and a charge detector for detecting only high frequency components of a current flowing between the detection electrode and the second electrode. On the basis of these detected high frequency components, the likelihood of an occurance of an earthquake may be determined.

Abstract: The present system is directed to an improved dipmeter system including plural sensors on isolated pads around a sonde. An independent output is formed from each of the sensor pads, and each output is provided to its own adjustable high pass filter. The several high pass filters delete low frequency constituents in the sensor signals. Then, the signals are provided to a dipmeter computer to determine depth with greater accuracy. As a variation, the high pass filters can be selectively adjusted to provide an adjustable frequency for the filters, and one version utilizes the derivative of the dipmeter signal as a function of velocity or time.

Abstract: An adaptive transversal filter is incorporated with an SP conductor extending through a logging cable to the surface from an SP electrode supported on a sonde. This logging cable is operated in a noisy environment and there is the risk of noise on the logging cable obscuring the SP signal. The SP signal is obtained at the surface and is passed through a filter system. One input to the filter system utilizes an AC ammeter connected to the AC power source for the logging cable and that signal is input to a multi-stage adaptive transversal filter. The filter output is a recreation of the noise imposed on the SP conductor and when summed with the SP output signal, provides a signal which is substantially noise free.

Abstract: A method for time lapse electric logging in a cased hole in which electrodes are implanted in the casing or the hole is completed with a gravel packed non conductive, perforated liner that allows an open hole logging tool to be used for time-lapse logging. Thereafter, the implemented electrodes or a self-potential (SP) logging tool are used to monitor a steam-flooding EOR method by detecting two-phase flow with time lapse logging. A potential drop between the surface and zones of interest is measured with electrodes installed in a non-conductive casing or the SP logging tool.

Abstract: A method and apparatus for determining the location in space of a formation sample is set forth. This involves a tool which is typically run on a wireline in a well, the tool supporting orthogonal positioned magnetometers and similar orthogonal accelerometers for measuring movement of the tool along the well borehole whereby components of the magnetic field and gravity field are measured to enable determination of the well in space. The tool supports an axially positioned centrally located core cutting apparatus and a laterally projecting plug cutting apparatus; scribe marks formed on the formation samples orient the samples relative to the tool and the tool is located in space from the above mentioned measurements so that the position of formation samples can be determined.

Abstract: An apparatus and method for obtaining a spontaneous potential curve, which pparatus is comprised of: (a) an elongated body: (b) a series of vertically spaced electrodes for measuring electrical potential, wherein one of the electrodes is a reference electrode; and (c) a means for recording or transmitting the various electrical potentials to the surface. Preferably the apparatus is part of drillstring for taking measurements while drilling.

Abstract: Method and apparatus for obtaining fine detail of spontaneous potential (SP) along a bore-hole wall in the earth, in connection with exploration for petrochemical deposits. A laterally-extending array of SP-sensing electrodes is mounted on an insulating pad, each slightly below the pad surface, and the pad is moved along and against the bore-hole wall while the SP's at the electronics are sampled and sent to up-hole electrodes for processing. The processed electrode samples are used to form a two-dimensional visually-observable image of the segment of the bore-hole wall swept over by the electrodes on the pad.

Abstract: A borehole telemetry system has a transmitter located in the borehole, a surface receiver, and surface signal sensors for receiving the transmitted signal. There are usually plural sources of electromagnetic noise at a well site which degrade the usefulness of the telemetry system. The method places noise sensors where the reception of noise is maximized. Simultaneous measurements are taken of the ambient noise with the noise sensors and the signal sensors. The relationship between the measurements of the noise and signal sensors is determined. The transmitted signal is then received by the signal sensors and simultaneous measurements of the ambient noise are made by the noise sensors. The noise portion of the transmitted signal as received by the signal sensors is determined from the simultaneous noise measurements and the determined relationship. A received signal having reduced noise is then produced by removing the noise portion.

Abstract: Responses of subsurface formations adjacent a well borehole are obtained from a number of types of well logs. The well logs typically include a resistivity log, a gamma ray log, a density log, a neutron log and an induction or electromagnetic wave log. Parameters of interest are determined in evaluating whether the subsurface formations are of interest for petroleum contents by a non-linear programming technique based on the log responses obtained. The parameters of interest are maintained self-consistent, i.e. their contribution to log measurements is based on the same value for the parameter in its effect on each log in which they produce a response.

Abstract: An electrode insulated from and mounted to the outside of a drill collar in a drill string positioned in a borehole is used for measuring formation spontaneous potential. A current measuring device, such as an ammeter, is connected through a varible ammeter resistor and a switch between the electrode and the drill collar. The ammeter measures current flow from the formation along the walls of the borehole to the drill string to determine the spontaneous potential of the formation at various points along the borehole while it is being drilled. The switch in the ammeter circuit is interrupted at a pre-selected rate and the ammeter current signal is connected through a lock-in amplifier to cancel random noise in the signal and produce an accurate measurement of the very small currents flowing between the electrode and the drill collar. The currents are indicative of spontaneous potentials in the formation.

Abstract: A signal amplifier system for use in a downhole logging system wherein a signal transmitter is mounted in a sonde suspended on a logging cable thousands of feet into a borehole. Variable slew rate amplifiers connected to a differential amplifier are set forth. Preferably, programmable amplifiers having a gain determined by a driving current are used. Two such amplifiers are connected to the input signal, and they are driven by different current sources. The output signals are summed at a differential amplifier. Through the use of different slew rates, the incoming signal is amplified by the two programmable amplifiers and the outputs of the two amplifiers are then subtracted from one another. Signals which pass equally through both programmable amplifiers (due to slew rates which do not cause limiting) thus are subtracted from each other.

Abstract: A method and apparatus for measuring the differential or gradient of an earth variable within a well bore (e.g., the spontaneous earth potential) and producing improved logs of this gradient or differential and its integral variable essentially free of any accumulated instrument and base line drift or error. The differential spontaneous potential of an earth formation traversed by a well bore is measured at repeated multiple depths by moving a pair of closely spaced electrodes through the well bore wherein each electrode is electrically insulated externally from the other and from a third downhole local ground (such as the well tool cable) to which each is internally resistively referenced.

Abstract: In accordance with illustrative embodiments of the present invention, methods for processing well logging data comprises deriving measurements of a plurality of earth formations parameters and combining these measurements in a new manner to enable interpretation of shales and shaly sand type formations. More particularly, measurements of a plurality of the hydrogen index, bulk density, radially deep and shallow resistivity, spontaneous potential, acoustic travel time and natural formation radioactivity content are made and combined in a manner to produce data useful in evaluating shales and shaly sand type formations.

Abstract: In the disclosed and illustrated embodiment, an improved method and apparatus for obtaining an improved spontaneous potential log is set forth. On a single sonde, multiple spontaneous potential electrodes, aligned vertically along the length of the sonde at spaced location, are positioned to transverse a well bore as the sonde is pulled from the well to obtain a measure of spontaneous potential from each electrode. The apparatus and method further discloses means multiplexing the signals from the several spontaneous potential electrodes whereupon the signals are converted by an analog to digital converter into digital words. By synchronizing with the multiplexing, a digital word is obtained for each electrode at a time such that such electrode is read at a common elevation. The several digital words are then input to delay lines, there being one delay line for each electrode, wherein the delay occurs in multiples of T where T equals the time delay between electrodes.

Abstract: The present invention relates to the completion of wells and, more particularly, it relates to a method of drilling a productive bed.The herein disclosed method of drilling a productive bed comprises the tapping of the bed roof using a starting flushing fluid and the determination of the redox potential value at the moment of tapping the bed roof, and subsequent replacement of the starting flushing fluid with a fluid having redox potential value and sign equal to those of the productive bed rock.

Abstract: In accordance with illustrative embodiments of the present invention, techniques are shown for processing well logging data to provide improved results. More particularly, a technique is disclosed for determining the reliability of well logging computations. Another technique is disclosed for making a preliminary pass of the well logging data to automatically select certain input parameters. Still another technique is disclosed for automatically determining the minimum possible hydrocarbon density for each formation level. This last technique is contrasted with the prior art technique which set one minimum value for the entire length of a borehole.

Abstract: In accordance with illustrative embodiments of the present invention, methods for processing well logging data comprise deriving measurements of a plurality of earth formation parameters and combining these measurements in a new manner to enable interpretation of shales and shaly sand type formations. More particularly, measurements of a plurality of the hydrogen index, bulk density, radially deep and shallow resistivity, spontaneous potential, acoustic travel time and natural formation radioactivity content are made and combined in a manner to produce data useful in evaluating shales and shaly sand type formations.

Abstract: A method of computer generating a subsurface characteristic model which is substantially consistent with readings taken in a well with a well logging device. A set of actual measurement values which represent readings taken over a given depth interval of a well is derived. An initial trial model of the subsurface characteristic under investigation is then selected. Next, a set of simulated measurement values is generated by applying the approximate response characteristic of the logging device to the discrete trial model. The simulated measurement values are compared with the actual measurement values and the initial trial model is then modified in accordance with the comparision. The modified trial model is utilized to form a new set of simulated measurements which are, in turn, compared with the true measurement values. The model can then be remodified and the procedure continued in iterative fashion until there is obtained a model which yields acceptable simulated measurement values; i.e.

Abstract: A method which determines output parameters (such as porosity .phi. or water saturation S.sub.w of formations) from a set of logging measurements taken at each level of a borehole is proposed.Measurement and response equation uncertainties of each logging apparatus are determined at each measurement level. Assumed values of the output parameters are chosen and, applying the response equations, calculated values of the measurements are determined. The calculated values of the measurements and the actual measurements are then compared to determine deviations which are weighted by factors calculated from the previously determined uncertainties. An incoherence function is determined from the weighted deviations and a number of "a-priori" constraints. Minimization of the incoherence function gives the most probable output parameters whose uncertainty is in turn calculated.

Abstract: Disclosed are a process and a system which relate to well logging, to converting logs to dips of subsurface formations and to producing a new type of a map record of dips. The map record conforms to a plane which is transverse to the borehole and contains a number of map line representations the position of each of which conforms to a range of dips consistent with the displacement between two similar reflections on respective well logging signals. The displacements relate to reflections on logging signals at borehole depths within an interval which is small as compared to the depth of the entire borehole, and the predominant locus of intersections of such line representations on the map record determines a likely dip of a subsurface feature which is in the borehole depth interval of interest.

Abstract: A method of computer generating a subsurface characteristic model which is substantially consistent with readings taken in a well with the well logging device. A set of actual measurement values which represent readings taken over a given depth interval of the well is derived. An initial trial model of the subsurface characteristic under investigation is then selected. The model includes discretely-boundaried beds, the location of boundaries being based on subsurface characteristic data. A simulated measurement value at a particular depth level is generated by applying the approximate response characteristic of the logging device to the model. The simulated measurement value at the particular depth level is compared to the actual measurement value at that depth level and the model is then modified in accordance with the comparison.

Abstract: A method of computer generating a subsurface characteristic model which is substantially consistent with readings taken in a well with a well logging device. A set of actual measurement values which represent readings taken over a given depth interval of a well is derived. An initial trial model of the subsurface characteristic under investigation is then selected. Next, a simulated measurement value at a particular depth level is generated by applying the approximate response characteristic of the logging device to the model. The simulated measurement value at the particular depth level is compared to the actual measurement value at that depth level and an error value is generated as a function of the comparison. The model is then modified in accordance with the error value, the modification being performed over a depth interval which includes the model beds within a preselected span from the particular depth level.