Abstract: A rock breaking seismic source and active source three-dimensional seismic combined detection system uses a tunnel boring machine for three-dimensional seismic combined detection by active seismic source and rock breaking seismic source methods. Long-distance advanced prediction and position recognition of a geological anomalous body are realized using the active source seismic method. Machine construction is adjusted and optimized according to the detection result; real-time short-distance accurate prediction of the body is realized using the cutter head rock breaking vibration having weak energy but containing a high proportion of transverse wave components as seismic sources and adopting an unconventional rock breaking seismic source seism recording and handling method. An area surrounding rock quality to be excavated is represented and assessed.

Abstract: Apparatus include a downhole tool comprising an outer member; and a probe body positioned inside the outer member; an electronics carrier positioned inside the probe body; and a lateral support system, including members cooperating to maintain a relative position of the electronics carrier with respect to the probe body, and a biasing member. The plurality of members may include an outer support ring having an axial passage therethrough for receiving the electronics carrier, the outer support ring having an inner surface; and an inner support ring within the probe body having an axial passage therethrough for receiving the electronics carrier, the inner support ring having an outer surface. The biasing member may be configured to urge a member of the plurality of members against an inner surface of the probe body by urging the outer surface of the inner support ring against the inner surface of the outer support ring.

Abstract: Methods and apparatus are disclosed for generating fluid pulses in a fluid column, such as within a well. A described example fluid pulse generator has a valve member comprising a piston that is linearly movable within a piston chamber to control flow by selectively obstructing a fluid passage. The fluid passage may extend around at least a portion of the piston chamber and intersect at an angle relative to the axis of movement of the valve member. The piston is linearly movable, such as from a closed or minimal-flow position to a maximal-flow position, and optionally to any of a number or range of positions therebetween. The position of the valve member may be varied to generate fluid pulses of a selected pattern of duration, amplitude, and so forth, to generate a signal within the fluid column detectable at a location remote from the fluid pulse generator.

Abstract: A cutting element includes a table coupled to a substrate at an interface. The table includes a working surface opposite the interface and defined by a perimeter, a table thickness measured between the interface and the working surface, and a torque transmittable depression formed in the working surface of the table a distance away from the perimeter. The torque transmittable depression extends a depth into the table and has a cross-sectional profile with a torque transmittable shape. The depth of the depression may be greater than the thickness of the table, or an optional sensor may be placed in the depression.

Abstract: Various embodiments include systems and methods of operation with respect to well logging. The systems and methods can include a number of transmitter sensors and a number of receiving sensors arranged to operate as a system including one or more multi-pole sensors. Such systems may be controlled to generate deep high-order azimuthal sensitivity. Additional apparatus, systems, and methods are disclosed.

Abstract: In a fracking context the object that will ultimately block a passage in an isolation device is introduced into the zone with the bottom hole assembly. The object is not released until the guns fire to create a pressure spike in the borehole that triggers the object retaining device to release the object. The retaining device is placed in close proximity to the isolation device and its setting tool to allow a larger object and passage in the isolation device to be used. If the guns misfire, the object is not released and comes out with the guns. The replacement guns can be pumped in because the passage in the isolation device has stayed open during the misfire. Direct and indirect object release in response to pressure created from the firing of the guns is contemplated.

Abstract: A system for tracking an object in oil and gas wellbore operations wherein a releasable object carrying a first signal system is released into tube system associated with a wellbore. The first signal system communicates with one or more second signal systems positioned along the travel path of the object; along the surface of the formation; and/or throughout the wellbore. First signal system and the second signal system may communicate by RF signals. First signal system and any second signal systems positioned on the surface communicate by through-the-earth or very low frequency signals. A global positioning system may be utilized in conjunction with any second signal systems on the surface to identify the absolute location of the object in the underground wellbore. The first signal system carried by the object may be a piezoelectric system disposed to transmit a signal when the object experiences a predetermined pressure.

Abstract: The invention relates to a method for estimating pore pressure in subterranean shale formations such as gas- or organic-rich shale where pore pressure predictions based on either a resistivity log or a porosity-indicative log such as sonic tend to be inaccurate. The method involves combining the resistivity log with the porosity-indicative log using a Eaton formula to give an estimate of pore pressure which is accurate both for conventional water wet shale and for organic-rich shale.

Abstract: A system and method for testing of electrical connections, conductors, and loads prior to energizing those connections is disclosed. For example, an interlocking socket can comprise a receptacle designed to be coupled to a connector of a load. The interlocking socket can comprise a microprocessor coupled to the receptacle, the microcontroller operable for testing one or more faults in the connector, a conductor, or the load coupled to the connector. In another example, a microprocessor can be coupled to a switch comprising a conductor, where the microprocessor is operable for testing one or more faults in the conductor or a load coupled to the conductor.

Abstract: An assembly for use in subsurface drilling includes a downhole probe supported in a drill string section by centralizing features of a centralizer that is slidably removable from the drill string section. The centralizer may comprise a tubular body having a bore defined through it. A bore wall of the centralizer is fluted to provide inward contact points that support the downhole probe. The downhole probe may be supported for substantially its entire length. The centralizer may optionally comprise and/or be coated with a vibration damping and/or electrically insulating material.

Abstract: A method including selecting a forward model based on a modeled well structure and including a single modeled acoustic source located in a modeled wellbore and a plurality of modeled acoustic sensors located in a modeled source area, simulating an acoustic signal generated by the single modeled acoustic source and received by each modeled acoustic sensor, calculating phases of the simulated acoustic signals received at each modeled acoustic sensor, obtaining with a principle of reciprocity a plurality of modeled acoustic sources in the modeled source area and a single modeled acoustic sensor in the modeled wellbore, calculating phase delays of the simulated acoustic signals between each modeled acoustic source and the single modeled acoustic sensor, detecting acoustic signals generated by a flow of fluid using acoustic sensors in a wellbore, and processing the acoustic signals using the phase delays to generate a flow likelihood map.

Abstract: According to certain embodiments, formation fluid properties, such as gas-oil ratio (GOR), formation volume factor (FVF), and density, may be measured at multiple times during sampling. In one embodiment, data representing the measured properties is analyzed and a characteristic of interest is determined through extrapolation from the analyzed data. Various other methods and systems are also disclosed.

Abstract: A method for determining the bend of a tubular structure, including determining the inclination of first and second rigid objects fixed in distinct locations along the tubular structure. The method includes supplying accelerometers (A1, . . . AN) rigidly linked by the object to measure an acceleration in at least one direction of measurement (vj), the respective directions of measurement of at least two of said accelerometers being non-collinear. The measurement, by the accelerometers, of the components of the Earth's gravitational field along said directions of measurement, the measurement providing, for each of said directions, a measurement value, denoted mj for a measurement direction of index i. The method includes solving a defined matrix equation to determine the inclination ? of the object relative to the reference frame of reference.

Abstract: The disclosure relates to an electrocrushing drilling fluid with an electrocrushing drilling base fluid including a non-polar oil, water, and glycerin. The base fluid may further include a polar oil and an alkylene carbonate. The electrocrushing drilling fluid may further contain at least one additive. The electrocrushing drilling fluid may have a dielectric constant or dielectric strength of at least a set amount, an electric conductivity less than a set amount, or a combination of these properties. The disclosure further relates to an electrocrushing drilling system containing the electrocrushing drilling fluid and an electrocrushing drill bit.

Abstract: A discrete fracture network model is upscaled to a simulation grid having effective permeabilities for each grid cell. Prior to computing the effective permeabilities, the grid cells are grouped in distinct grid cell clusters, such that flow via fractures is only possible between grid cells that mutually belong to the same grid cell cluster. This is achieved by grouping fractures into distinctive fracture clusters, whereby all fractures that are physically connected with each other by intersection, either directly or indirectly via a number of other physically connected fractures, exclusively belong to one fracture cluster. Each grid cell is assigned to exclusively one fracture cluster. After defining the grid cell clusters, effective permeabilities are calculated for each grid cell using only the fractures of the fracture cluster to which the grid cell is assigned while fractures from other fracture clusters are ignored. Inter-cluster flow impediment data is assigned to selected grid cells.

Abstract: A downhole system provides a data interface to a first downhole tool such as a steerable rotary tool. The data interface uses a close proximity data connection such as a connection between inductive loops or coils or a direct wired or optical connection. The interface provides data to a second downhole tool in a drill string section adjacent to the first downhole tool. In some embodiments data is passed to a third downhole tool that includes a telemetry transmitter. The third downhole tool may comprise a MWD (measurement while drilling) tool.

Abstract: The present invention relates to a process for treating a sandstone formation comprising introducing a fluid containing glutamic acid N,N-diacetic acid or a salt thereof (GLDA) and/or methylglycine N,N-diacetic acid or a salt thereof (MGDA) and having a pH of between 1 and 14 into the formation. The invention in addition relates to a fluid suitable for use in the above process containing 5-30 wt % of glutamic acid N,N-diacetic acid or a salt thereof (GLDA) and/or methylglycine N,N-diacetic acid or a salt thereof (MGDA), a corrosion inhibitor, a surfactant, and a mutual solvent.

Abstract: Example computer-implemented method, computer-readable media, and computer system are described for generating subterranean imaging data based on initial isotropic and/or anisotropic velocity models for the vertical seismic profile (VSP) data and stored ocean bottom sensor (OBS) data. In some aspects, VSP data and OBS data of a subterranean region are received. Angle attributes for each image point are computed to image primary reflection and free surface multiples of the received VSP data and OBS data, respectively. Angle-domain common-image gathers (ADCIG) are generated according to a ray-equation method based on the angle attributes computed based on the received VSP data and OBS data, respectively. The ADCIG are further post-processed.

Abstract: A hollow body composed of an electrically conducting material and extending longitudinally along an axis is connected at one axial end to a connection element composed of an electrically conducting material and extending along the axis. A first thread is provided on the hollow body at the one axial end running about the axis, while a second thread is provided on the connection element running about the axis, so that the second thread is mechanically supported by the first thread. An insulation-material extent between the first thread and the second thread electrically isolates the hollow body from the connection element.

Abstract: A probe for a trenchless guide instrument includes an antenna, a control circuit board and at least one battery supplies power to the control circuit board; one battery is disposed inside the battery region; the control circuit board is disposed inside the electronic region; a first insulating pipe is disposed inside the antenna and outside the battery, the antenna further includes a magnetic core, and a coil winds around the magnetic cores and one end of the coil is connected to the control circuit board; the magnetic core further includes magnetic core units, each magnetic core unit is made from magnetic material, the magnetic core units are positioned on a peripheral surface of the first insulating pipe, and are insulated from each other.

Abstract: In-phase and quadrature components have different relationships with some important petrophyscial parameters, such as water saturation and mineral cation exchange capacity (CEC). In clay-containing subterranean rock formation such as shaly sand formations, these parameters can be estimated using different components of array induction tool data combined with other knowledge about the clay-containing formation. Some parameters, such as mobility and fraction of counterions are valid in cases where the pore water solution is an electrolyte of NaCl.

Abstract: An electromagnetic telemetry system can be used for determining a resistivity of a portion of a wellbore drilled through a subterranean formation. For example, the electromagnetic telemetry system can include a computing device and a downhole transceiver positioned on a well tool in the wellbore. The computing device can receive, from the downhole transceiver, a signal indicating a load impedance across an electrically insulating segment of the downhole transceiver. The computing device can determine a resistivity associated with a portion of the wellbore based on the load impedance. The computing device can determine a corrected resistivity by modifying the resistivity associated with the portion of the wellbore using a correction factor.

Abstract: A system of formation sampling while drilling, comprising: a suction pup joint provided to pump out and clean the formation fluid; a sampling pup joint provided to sample and store the formation fluid; a setting pup joint provided between the suction pup joint and the sampling pup joint and provided to establish a fluid channel between the formation fluid and the suction pup joint, the sampling pup joint; and an electrohydraulic high voltage connection device provided between the setting pup joint and the sampling pup joint. The embodiments of the present invention can be applied in the field of formation exploration technology, the function of storing the formation sample in the process of logging while drilling can be accomplished and the current logging instrument can be effectively optimized, the universality and precision of the current logging function can be effectively improved according to the embodiments of the present invention.

Abstract: The systems, devices, and methods described herein describe a control system that automatically determines a trip speed for a surge operation or a swab operation. The control system is used to automatically adjust the trip speed during the respective surge or swab operation in order to optimize the trip speed according to the changing environment of the wellbore that the bottom hole assembly traverses without exceeding the fracture gradient in the wellbore location. A well plan identifies formations along the wellbore route, dynamic real-time tracking of the tubulars added to the drill string and removed therefrom identifies the current location of the BHA in the wellbore, and pressure and fractional gradient at the location of the BHA, and in some embodiments a real-time pressure measurement from the BHA, together are used to automatically determine the maximum tripping speed possible for the formation that the BHA is traversing.

Abstract: A system for ranging between two wellbores. The target wellbore includes a conductive body (e.g., casing) disposed within a portion of the target wellbore. A second wellbore includes an electromagnetic field sensing instrument positioned within the wellbore. A current delivered to the conductive body in the target wellbore results in a magnetic field emanating from the target wellbore. The electromagnetic field sensing instrument is utilized to measure an electromagnetic gradient based on the magnetic field, which electromagnetic gradient can be utilized to determine the range between the wellbores.

Abstract: A microresistivity logging tool and method for making microresistivity measurements, of which the tool includes a logging tool body having a longitudinal axis, a transmitter coil deployed in the tool body, the transmitter coil including an electrical conductor wound about a magnetically permeable core, the electrical conductor being connected to a high frequency alternating current generator deployed in the tool body, a receiver coil deployed in the tool body and including an electrical conductor wound about a magnetically permeable core, the electrical conductor being connected to a high frequency alternating voltage sensor deployed in the tool body. The transmitter and receiver coils each define a coil axis that is substantially perpendicular to the longitudinal axis of the tool body. The receiver coil and the transmitter coil are coaxial and deployed in the same plane.

Abstract: A method includes performing pulse echo measurements using a pulse echo tool. The method also includes detecting a casing collar using the pulse echo measurements performed by the pulse echo tool. The method further includes estimating a tool response of the pulse echo tool response at the casing collar using one or more processors based on the pulse echo measurement at the casing collar. The method also includes and removing the pulse echo tool response estimation from at least some of the pulse echo measurements not at the casing collar.

Abstract: A hand-held electric circuit tester includes a probe. The probe includes a hollow body, a control circuit, a probe member, and a speaker. The probe member is operatively mounted in the hollow body, and is configured to contact a probe location of an electric circuit to be measured and electrically connect the probe location with the control circuit to produce a measurement. The control circuit is configured to generate a voice signal with reference to the measurement of the probe and output the voice signal to the speaker, which is configured to generate a voice output with reference to the voice signal indicative of the measurement. The probe can include a first switch for operating the probe member, a microphone for voice activation, or a second switch for selecting between different voices for the voice output, with the different voices stored in computer-readable memory.

Abstract: Various implementations described herein are directed to a method for assessing risks of compartmentalization. In one implementation, the method may include receiving seismic data for a formation of interest; identifying areas in the formation having a dip angle greater than about 30 degrees; performing a plurality of downhole fluid analysis (DFA) within a wellbore around the formation having the dip angle greater than about 30 degrees to identify areas experiencing mass density inversion; and determining the areas experiencing mass density inversion by DFA as having one or more risks of compartmentalization.

Abstract: Measurements made by a near-bit magnetic sensor on a bottomhole assembly are used to determine the azimuth of the BHA. The sensor may be uncalibrated. The measurement may include a cross-axial component of the magnetic field. The method may include estimating the axial component of the near-bit magnetic field using the measurement. The method may include using the estimated azimuth of the BHA for controlling a direction of drilling. The method may include estimating the component Hxy. The method may include correcting the estimated axial component using an offset between a gravitational toolface and a magnetic toolface.

Abstract: A drill pipe (1), particularly for a drill string, has at least one electrical conductor (4, 7, 8, 9) and an inner pipe (2) which is arranged inside the drill pipe (1). The drill pipe (1) and the inner pipe (2) are spaced at a distance to one another in sections, wherein the drill pipe (1) and inner pipe (2) bound a hollow space (3). At least one electrical conductor (4, 7, 8, 9) is arranged on one outer side of the inner pipe.

Abstract: Provided in some embodiments are systems and methods for developing a hydrocarbon reservoir. A method may include, for each of a plurality of prosed hydrocarbon wells, determining a reservoir entry point corresponding to a location at a top limiting surface of the hydrocarbon reservoir, determining a reservoir exit point corresponding to a location at a bottom limiting surface of the hydrocarbon reservoir, and determining a well trajectory that includes a path that extends downward gradually from the reservoir entry point at the top limiting surface to reservoir exit point at the bottom limiting surface. The method also including generating a field development plan (FDP) for the hydrocarbon reservoir, the FDP including development information for each well of the plurality of wells, including the determined well trajectory for the well.

Abstract: A system for use in a wellbore can include a first transceiver that is operable to transmit a wireless signal. The first transceiver can be positioned in an electrically isolated chamber between a tubular and a casing string for confining a transmission of the wireless signal to within the electrically isolated chamber. The system can also include a second transceiver that is positionable in the electrically isolated chamber for receiving the wireless signal from the first transceiver.

Abstract: A wellbore E-field wireless communication system, the communication system comprising a first E-field antenna, and a second E-field antenna, wherein the first antenna, and the second antenna are both arranged in a common compartment, such as an annulus of a wellbore and further arranged for transferring a signal between a first connector of the first E-field antenna and a second connector of the second E-field antenna by radio waves.

Abstract: A method for magnetic ranging includes rotating a downhole tool in a drilling well in sensory range of magnetic flux emanating from a target well having an AC magnetic source deployed therein. The downhole tool includes a magnetic field sensor deployed therein. The magnetic field sensor measures a magnetic field vector while rotating. The measured magnetic field vector is processed to compute at least one of a distance and a direction from a drilling well to a target well.

Abstract: System and methods for performing look-ahead and look-around (LALA) inversion are provided. Measurements of formation properties accumulated by a downhole LALA tool are obtained during different stages of drilling a wellbore through layers of an underground formation. A distribution of formation properties measured for the layers behind a current layer is determined. A formation model for look-ahead inversion is defined based on the determined distribution of formation properties behind the current layer. Measurements of the current layer's formation properties collected by the downhole LALA tool are obtained. A distribution of formation properties for one or more layers ahead of the current layer is estimated based on the formation model and the measurements of formation properties obtained for the current layer. The estimated distribution includes a gradient transition of formation properties between the current layer and the one or more layers ahead of the current layer.

Abstract: A collar-mountable antenna for transmitting and receiving signals in a downhole environment, in at least some embodiments, comprises a bobbin having an inner surface and an outer surface, each of the inner and outer surfaces defining multiple slots, conductive wire disposed within the multiple slots on the outer surface of the bobbin, and ferrite disposed within the multiple slots on the inner surface of the bobbin.

Abstract: Devices and methods for well logging using a wear-resistant electrode are provided. A downhole device may include a drill collar and a first electrode mounted on the drill collar. Further, the first electrode may include a wear-resistant face. The first electrode may be movably coupled within the drill collar, and the first electrode may be configured to extend and retract into a wellbore to maintain contact with a wall of the wellbore. Furthermore, the first electrode may be configured to measure impedance of a geological formation.

Abstract: A method for determining a future rotational speed of a rotating drive shaft of an internal combustion engine is described, in particular while the internal combustion engine coasts after being turned off, the future rotational speed being calculated from a course of measured rotational speeds. To predict a future rotational speed of the drive shaft of the internal combustion engine as accurately as possible, instantaneous rotational speeds measured at different rotational positions of drive shaft are evaluated.

Abstract: System and methods of generating calibrated downhole images of a subterranean formation (110) surrounding a wellbore (105). The method involves placing a pad at a distance from a highly conductive surface and measuring a current between return electrodes of the pad and the highly conductive surface. The current may be used to determine a theoretic impedance of the current path, and impedance amplitude and impedance phase may be calibrated using theoretical impedance phase and theoretical impedance amplitude. Multiple standoff calibrations and temperature variation calibrations may also be used.

Abstract: An actuator for a mud pulse telemetry tool. The actuator includes a solenoid-based servo valve with a coil shaft responsive to data transmitted by a data processor. The coil shaft is movable between an extended position and a retracted position. Movement of the coil shaft to the extended position moves a poppet to close a servo orifice thereby preventing mud flow to a main mud pulse valve of the mud pulse telemetry tool. Movement of the coil shaft to the retracted position moves the poppet to open the servo orifice thereby allowing mud flow to actuate the main mud pulse valve. The poppet is connected to a poppet shaft and the poppet shaft cooperates with the coil shaft in a slide hammer mechanism to amplify force provided by the coil shaft against the poppet shaft with linear movement of the coil shaft to the extended position and to the retracted position.

Abstract: In one aspect, an apparatus for use in a wellbore is disclosed that may include a transmitter placed on an electrically-conductive member at a first location in the wellbore configured to induce electromagnetic waves that travel along an outside of the conduit and a receiver placed on the electrically-conductive member at a second distal location in the wellbore configured to detect the electromagnetic waves induced by the transmitter.

Abstract: A method and apparatus for downhole data transmission. The method comprising monitoring electrical impedance properties of a downhole formation by applying an electrical signal between a first portion and a second portion of a drill string that are electrically insulated from each other by an insulating portion, selecting a frequency for transmitting data by electromagnetic telemetry based at least in part on the monitored electrical impedance and transmitting the data by encoding the data in a waveform having the selected frequency and applying the waveform between the first portion and the second portion of the drill string.

Abstract: Methodology for detecting and monitoring the propagation of a volume of liquefied material underground without measuring the resistivity of the ground. Liquefied material is charged by injecting current through electrically-conducting member in contact with the material to form a spatial distribution of electric potential underground. Measuring time-dependent change of such spatial distribution caused by movement of liquefied material and associated with propagation of a Gaussian surface of electrical charge associated with the outer surface and/or the front of the volume is detected with a system of electrodes to determine a time of arrival of liquefied material to target location.

Abstract: This invention relates to an apparatus and method for controlling a part of a downhole assembly, and to the downhole assembly. The downhole assembly may include a steering mechanism adapted to steer a drill bit in a chosen direction, and the steering mechanism may be the part of the downhole assembly which is controlled by the apparatus. The downhole assembly includes a drill bit and a motor, the motor having a stator and a rotor, the rotor being driven to rotate relative to the stator by the passage of a drilling fluid along a drilling fluid path between the rotor and the stator. The motor has a conduit through which the drilling fluid can pass, the conduit being separate from the drilling fluid path, and the apparatus has a valve to control the flow of drilling fluid through the conduit. The invention provides a robust and reliable means of delivering high pressure drilling fluid downstream of the motor.

Abstract: Systems and methods for cement evaluation by determining a shear velocity of a shear wave (26) propagating within a medium (20) located between a formation (12) and a casing (13) in a borehole (11) are presented. The method can include positioning an ultrasonic transducer array (21) in the borehole inside the casing. The method can also include in a pushing mode, generating a shear wave in the medium with the ultrasonic transducer array inside the casing. The method can also include in an interrogation mode, measuring a shear velocity of the shear wave in the medium with the ultrasonic transducer array. The shear velocity may be used to determine whether the medium is solid or liquid.

Abstract: A method and apparatus for generating a borehole image by firing a signal in the direction of a borehole formation using at least one transmitter in a horizontal array, firing a signal in the direction of the borehole formation using at least one transmitter in a vertical array, where the fired signals engage the downhole formation, receiving signals associated with the transmitted signals after the fired signals have engaged the formation, and using the received signals to determine one or more vertical and horizontal formation parameters for generating an omni-directional image using the formation parameters.

Abstract: Downhole nuclear magnetic resonance (NMR) methods that utilize oleophilic nanoparticle may allow for differentiation of light oil and oil-based filtrates. For example, a method may involve drilling a wellbore penetrating a subterranean formation using an oil-based drilling fluid that comprises an oil base fluid and a plurality of oleophilic nanoparticles; performing a plurality of NMR measurements at a plurality of depths of investigation (DOI) of a near-wellbore portion of the subterranean formation; and producing an invasion profile of an oil-based drilling fluid filtrate into the near-wellbore portion of the subterranean formation based on the plurality of NMR measurements.

Abstract: Systems, methods, and apparatuses related to automatically and simultaneously charging a plurality of autonomous seismic nodes on a marine vessel before and/or after deployment to the seabed are disclosed. A plurality of autonomous seismic nodes are simultaneously charged in a CSC approved ISO container. Each autonomous seismic node may comprise a plurality of power connectors, a plurality of rechargeable batteries, and a battery management system. Each of the nodes may be configured to couple with a charging system on the marine vessel, which may include a power source, one or more power/charging stations, one or more power connectors, and a network. The node may have a plurality of power connectors disposed within a plurality of grooves that are configured to couple with a plurality of charging rails for simultaneous charging.

Abstract: A system comprises a wellbore having a plurality of casings disposed therein and one or more electromagnetic coils disposed within the wellbore. The one or more electromagnetic coils are configured to generate and direct one or more excitation signals toward the plurality of casings and receive one or more response signals based on interactions of the one or more excitation signals with the plurality of casings. The system further comprises a casing evaluation module comprising a processor and memory and communicably coupled to the one or more electromagnetic coils. The casing evaluation module is operable to determine whether defect exists in at least one of the plurality of casings using a first response signal received from the one or more electromagnetic coils and elemental defect information, the elemental defect information comprising a plurality of combinations of small defect information.