Abstract: In electrical resistivity tomography and electrical impedance tomography, interference effects of the metal well casing can be reduced by disposing measurement electrodes in the form of conductive bands around a region of primary insulation on the well casing. Secondary insulation can be provided longitudinally adjacent the primary insulation to further reduce the interference effects. Parameters of the primary and secondary insulation may be determined using finite element methods. The conductive band electrode can connect to a wire of a multi-strand cable using a novel takeout arrangement. Novel measurement methods are also described.

Abstract: A technique for determining conditions downhole in a well, particularly load conditions acting on a well tool, e.g. a bottom hole assembly. The loads acting on a bottom hole assembly or other well tool during a well related operation are measured. Load data is collected and may be transmitted uphole in real time for evaluation at a surface control unit. Based on the load data and other possible data related to the downhole operation, corrective actions can be taken to improve the operation.

Abstract: Methods and apparatus for reducing the impact of guided (or “tube”) waves in permanently installed seismic systems. By utilizing passive acoustic absorbers, the impact of tube waves may be reduced, leading to improved performance of permanently installed seismic systems that are installed onto production tubing when the well is completed.

Abstract: A method of connecting a first threaded tubular to a second threaded tubular includes: engaging threads of the tubulars; and rotating the first tubular relative to the second tubular, thereby making up the threaded connection. The method further includes, during makeup of the threaded connection: measuring torque applied to the connection; measuring turns of the first tubular; and detecting a shoulder position. The method further includes: displaying the measured torque and turns; overlaying a reference curve onto the display; evaluating the threaded connection by comparing the measured torque and turns to the reference curve; and graphically displaying the evaluation.

Abstract: A wellbore monitoring system comprising a length of tubing defining an axial flowbore, two or more data conduits extending within the axial flowbore of the coiled tubing, two or more sensors, each of the two or more sensors configured to measure a wellbore parameter and to communicate data indicative of the measured wellbore parameter via one of the two or more data conduits, and two or more deployable tubular packers, each of the deployable tubular packers disposed within the axial flowbore of the tubing, wherein each of the deployable tubular packers is selectively secured within the axial flowbore of the tubing, and wherein the two deployable tubular packers provide fluid isolation between a first region of the axial flowbore, a second region of the axial flowbore, and a third region of the axial flowbore.

Abstract: A device for processing hydrocarbon resources in a subterranean formation having a laterally extending wellbore therein may include a radio frequency (RF) antenna configured to be positioned within the laterally extending wellbore, and at least one feedback conductor configured to be positioned along the laterally extending wellbore. The device may also include an RF circuit configured to supply RF power to the hydrocarbon resources via the RF antenna. The RF circuit may be configured to supply the RF power at a frequency tracking a resonant frequency of the RF antenna and the RF circuit and based upon the at least one feedback conductor.

Abstract: An alert system for a downhole operation including a tubular string in a borehole. The tubular string having at least one sensor positioned in the borehole for measuring at least one parameter during operation of the tubular string. A unit in data communication with the tubular string and operatively arranged to enable an operator to obtain information regarding operation of the tubular string. A work area positioned proximate to the unit and operatively arranged to receive the operator when the operator is interfacing with the unit. A vibration module operatively arranged to vibrate the work area or a structure therein, wherein the vibration module is triggered in response to a first parameter being outside of a predetermined range set by a first threshold value. Also included is a method of alerting an operator during a drilling operation.

Abstract: A system and method for controlling an advancing water front in a reservoir toward a wellbore is provided. The system has a production control unit. The production control unit has a reservoir unit for producing a reservoir model and a production path unit for producing a production path model that determines at least one pressure parameter about the wellbore during a life of the wellbore. The production control unit has a production optimizer unit for producing a well plan that optimizes a function of the wellsite. The production control unit may be for controlling an advancing fluid front in the reservoir with at least one control device, and wherein a production path is constructed based on the well plan.

Abstract: The present invention relates to a device for transfer of heat energy in a well logging tool, where a variable heat flow from a chamber for electronics via a thermovalve is transmitted into a heat sink consisting of cooled metal, thereby establishing an approximately constant temperature in the chamber for electronics. The device comprises an electronics modular unit and a heat sink modular unit, which modular units are connected via an intermediate section, where a heat-regulating thermovalve provides heat conduction between a conical piston and a conical piston seat, for transferring heat energy.

Abstract: A well logging instrument deployment device according to this aspect of the invention includes a housing configured to be coupled to a pipe string. A latch disposed in the housing and is configured to retain a well logging instrument in a first longitudinal position inside the pipe string. An actuator is configured to release the latch to enable longitudinal movement of the well logging instrument inside the pipe string. A signal detector is operatively coupled to the actuator and is the configured to detect a command signal for operating the actuator.

Abstract: Apparatus and methods for controlling and communicating with one or more tools in a downhole tool string including a tractor, an auxiliary tractor tool, a logging tool, a safety sub, a release mechanism, a unit containing sensors for monitoring downhole conditions, a setting tool, and a perforating gun. Control and communication are accomplished by sending signals from the surface to control switches in the control units on the tool, with redundant switches for safety, to state machines in the respective control units, each state machine returning a signal verifying switch status to the surface. The state machine need not return a signal including a unique identifier.

Abstract: A system for attaining and maintaining a pre-determined fluid level in a petroleum-producing well having a pump, such as a progressive-cavity pump, and a pump motor having a variable-frequency drive control using two sensors: a pump pressure sensor located at the pump depth and a casing pressure sensor located at the casinghead of the well. A programmable computer is connected to the first and second pressure sensors and the motor speed control so that the programmable computer controls the operation of the pump motor to attain and maintain a target fluid level in the well over a predetermined time interval for reaching the target fluid level in the well. The programmable computer computes an error signal to control a variable frequency drive motor, where the error signal is computed periodically from the difference between in the actual fluid level in the well and the target fluid level in the well according to a rate reference curve.

Abstract: A wellbore servicing tool comprising a housing comprising ports, a triggering system, a first sliding sleeve transitional from a first position to a second position, and a second sliding sleeve transitional from a first position to a second position, wherein, when in the first position, the first sliding sleeve retains the second sliding sleeve in the first position, wherein, when in the first position, the second sliding sleeve prevents a route of fluid communication via the one or more ports of the housing and, when is in the second position, the second sliding sleeve allows fluid communication via the ports, and wherein the triggering system is configured to allow the first sliding sleeve to transition from the first position to the second position responsive to recognition of a predetermined signal comprising a predetermined pressure signal, a predetermined temperature signal, a predetermined flow-rate signal, or combinations thereof.

Abstract: A wellbore sensing system comprises a wellbore tubular string comprising at least one gauge carrier and at least one adjacent component, and at least one gauge disposed in the gauge carrier. The at least one gauge carrier is configured to provide an annular fluid communication between a housing and a mandrel, and the at least one gauge carrier is sealingly engaged with the at least one adjacent component. The at least one adjacent component comprises at least one of a filter element or a production sleeve, and the at least one gauge is configured to sense at least one parameter within a wellbore.

Abstract: A system and method of performing a microseismic fracture operation for a wellsite having a subterranean formation with a complex fracture network therein are provided. The method involves describing a relationship between microseismic events to determine the complex fracture network of the subterranean formation, generating a fault volume by extracting faults from the fracture network based on the relationship between the microseismic events, generating a discrete fracture network comprising discrete fractures from the complex fracture network by extracting fracture planes from the obtained fault volume, and simulating fracture geometry and proppant placement.

Abstract: Optical analysis systems, methods, and apparatuses for analyzing fluids may be useful for in situ monitoring fluids that relate to cementing operations. For example, a method may include containing a cement fluid composition in a flow path comprising a wellbore; and optically interacting the cement fluid composition with an integrated computational element, thereby generating an output signal corresponding to a characteristic of the cement fluid composition, the integrated computational element being coupled to a tool.

Abstract: Optical analysis systems may be useful in monitoring fluids relating to cementing operations in or near real-time, e.g., for location and/or the status of a cement setting process. For example, method may involve containing a cement slurry within a flow path, the cement slurry having a chemical reaction occurring therein; and optically interacting the cement slurry with an integrated computational element, thereby generating an output signal corresponding to a characteristic of the chemical reaction.

Abstract: Multiphase flow measurement in extreme environments such as subsea or in-well is a difficult task for many reasons including reliability, survivability, and longevity issues; accessibility to the equipment; and complexity of the varying flow field as a function of position and time. Embodiments of the present invention provide techniques and apparatus for performing subsea multiphase flow measurement by combining two technologies. One is based on infrared water-cut measurement technology which is capable of measuring water and oil concentrations in multiphase flow with up to 99.5% gas volume fractions. The second technology is based on in-well fiber-optic flow measurement capable of resolving gas and total liquid flow through the measurements of flow velocity, fluid mixture speed of sound, and absolute pressure and temperature at meter location. This hybrid system represents an approach to subsea multiphase metering that may offer advantages compared to traditional systems for some applications.

Abstract: A drilling rig with rig buffer storage and optional surge tank for receiving and processing drill cuttings and waste made of a drilling rig, having a tank in a frame with an inlet and an outlet, a moveable weir for expanding to accommodate additional drill cuttings, a central sweep member for cutting the drill cuttings and waste opposite a peripheral outer ring with peripheral cutting members, a controller for controlling rates of flow into and out of the rig buffer storage and the central sweep member rotation via a motor with reduction gear and wherein a first transportation system moves waste from the well bore to the rig buffer storage and a second transportation system moves cut waste and cut drill cuttings to a post treatment system, a skip, or a vessel for transport to another location.

Abstract: A clog free waste removal system for removing waste or drilling cuttings from a wellbore at the rate that waste is being produced having an incoming transportation system, a rig buffer, and optional surge tank, an outgoing transportation system, and post treatment device or transport.

Abstract: Systems are provided for using position data of a piston connected to a ram block in a blowout preventer to determine a backlash of the ram block, and/or to record a position of the ram block, and/or to calculate an instant when a supplemental closing pressure is desired to be applied, and/or to determine when maintenance of a ram locking mechanism is due, and/or to determine when sealing elements are worn.

Abstract: Disclosed are methods and systems for accurately locating wellbore servicing tools within a wellbore. A positioning system includes an elongate housing defining a piston bore with first and second axial ends, a sleeve arranged within the piston bore and having an upset extending radially outward therefrom, one or more lugs arranged within the elongate housing and radially movable when acted upon by the upset, a first biasing device arranged within the piston bore at the second axial end, and at least one RFID tag arranged on the production tubular and configured to communicate with at least one RFID reader arranged on the elongate housing, the at least one RFID reader being configured to deploy the first biasing device upon communicating with the at least one RFID tag, and thereby force the sleeve toward the first axial end and the upset into engagement with the lugs which engage a profile.

Abstract: Various systems and methods for cementing plug tracking using distributed strain sensing include a downhole cementing apparatus that includes a distributed strain sensor with an optical cable and a first downhole cementing plug coupled to a fixed point on the optical cable. The apparatus further includes a second downhole cementing plug slidably coupled to the optical cable between the first downhole cementing plug and a sensing end of the optical cable. The second downhole cementing plug causes a detectable feature in a strain profile along the optical cable's length that indicates a position of the second downhole cementing plug.

Abstract: A method of servicing a wellbore extending from a surface and penetrating a subterranean formation is provided. The method comprises placing a assembly in the wellbore, wherein the assembly comprises at least a first downhole tool, a signal receiver subassembly, and a conveyance between the first downhole tool and the surface. The method further comprises the signal receiver subassembly receiving a first signal generated by contact between the wellbore and the assembly and initiating a first function of the first downhole tool based on the first signal.

Abstract: Position indication in multiplexed downhole well tools. A method of selectively actuating and indicating a position in a well includes selecting at least one well tool from among multiple well tools for actuation by flowing direct current in one direction through a set of conductors in the well, the well tool being deselected for actuation when direct current flows through the set of conductors in an opposite direction; and detecting a varying resistance across the set of conductors as the selected well tool is actuated, the variation in resistance providing an indication of a position of a portion of the selected well tool.

Abstract: Generally, assessing the properties of a plug comprising wellbore strengthening materials may enable the design of more efficient wellbore strengthening additives and fluids because the properties of the plug may translate to the near wellbore strengthening effect of the wellbore strengthening materials of the plug. Assessing such properties may involve applying a differential pressure to a plug formed in a passageway of a tool comprising at least one sensor proximal to the passageway plug, and then measuring at least one attribute selected from the group consisting of a normal plug pressure, a normal plug displacement, and any combination thereof with the at least one sensor.

Abstract: A logging system and method for use in a wellbore formed in an earth formation. A tubular conduit that extends from the surface into the wellbore is included in the system. The conduit includes a stabilizer with sensors to obtain data from the wellbore. A communication interface is used to communicate data from the stabilizer to the logging tool string. Also, a surface communication and control device, along with a telemetry device can be included in the system. The telemetry device could be used to send and receive data to and/or from the surface communication and control device, if needed. Also provided is a logging tool string that is capable of passing from a position within the conduit to a position outside the lower end of the conduit. In addition, a memory storage device used to and store data collected from the wellbore for further analysis and communication.

Abstract: Disclosed herein is a fixture structure for reusing an underground micro-seismic sensor, including: a sensor body configured to be inserted in a borehole and having a sensing portion for sensing micro seismic event; a first fixture portion formed at one surface of the sensor body; a second fixture portion coupled to the first fixture portion and configured to be fixed to a grouting member injected into the borehole; and a separation unit installed between the first fixture portion and the second fixture portion and configured to separate the first fixture portion and the second fixture portion from each other by external force.

Abstract: Methods and related systems are described relating to monitoring particulates downhole at in-situ conditions. Solid particles being carried in the fluid as the fluid is produced from the reservoir formation are monitored. The downhole solid particle monitoring can include measuring the quantity (e.g., volume fraction, weight fraction, or the like) of solid particles, measuring the distribution of sizes of the solid particles, and/or measuring the shape of the particles. The solid particles can be monitored using one or more of sensors such as optical spectrometers, acoustic sensors, video cameras, and erosion probes. A sanding prediction is generated based at least in part on the monitoring of the solid particles, and the sanding prediction is then used to design a completion, lift system, and surface facilities for the wellbore and/or select operating conditions so as to control sanding during production.

Abstract: A system and method are provided for producing controlled vibrations within a borehole. In one example, the system includes an encoder plate having a first surface, an anvil plate having a second surface, a movement mechanism configured to enable translational movement of the encoder plate relative to the anvil plate to allow the first surface to repeatedly impact the second surface to produce a plurality of vibration beats, and a vibration control mechanism configured to selectively control an amplitude of the vibration beats to encode information therein.

Abstract: Devices and methods for obtaining diagnostics and control of the pumping process of rod pumped oil or gas wells are described. The diagnostics and control are implemented by means of the well simulation unit where surface load values are gathered through utilization of a load cell mounted on the carrier bar and attaching to the top of the polished rod and surface position values are gathered through the use of a position sensor mounted on the polish rod. Subsequently, an animation representing the entire pumping system is displayed instantaneously either on local display or by utilizing a HMI or a portable laptop, computer or other device connected to SCADA system. Changes of well conditions and pumping system conditions are displayed real time utilizing a direct simulation.

Abstract: Techniques for correlating depth on a tubular in a wellbore include a casing collar locator tool that includes a tubular mandrel defining a bore therethrough; a top sub-assembly and a bottom sub-assembly carried on the tubular mandrel; a profile carried on the tubular mandrel axially between the top sub-assembly and bottom sub-assembly and adjustable between an engaged state defined by the profile extending radially away from the mandrel and a disengaged state defined by the profile refracted towards the mandrel; and a wedge sleeve carried on the tubular mandrel between the top sub-assembly and the bottom sub-assembly and arranged, at least in part, axially adjacent the profile, the wedge sleeve actuatable to urge the profile into at least one of the engaged state or the disengaged state.

Abstract: A method of servicing a wellbore extending from a surface and penetrating a subterranean formation is provided. The method comprises placing a workstring in the wellbore, wherein the workstring comprises at least a first downhole tool, a signal receiver subassembly, and a conveyance between the first downhole tool and the surface. The method further comprises the signal receiver subassembly receiving a first signal generated by contact between the wellbore and the workstring and initiating a first function of the first downhole tool based on the first signal.

Abstract: The level of hydrogen sulfide in drilling fluid within a well formed in the Earth is assessed in an ongoing and/or in situ manner. The well may be constructed for the removal of hydrocarbons from the Earth. The assessment of hydrogen sulfide level may be provided in an ongoing manner such that real time, or near real time, fluctuations in hydrogen sulfide levels in the drilling fluid within the well may be conveyed to users. This may provide various advantages over systems in which drilling fluid must be extracted and separately tested for hydrogen sulfide content, and/or in which assessments of hydrogen sulfide level require time for performance.

Abstract: The level of hydrogen sulfide in drilling fluid within a well formed in the Earth is assessed in an ongoing and/or in situ manner. The well may be constructed for the removal of hydrocarbons from the Earth. The assessment of hydrogen sulfide level may be provided in an ongoing manner such that real time, or near real time, fluctuations in hydrogen sulfide levels in the drilling fluid within the well may be conveyed to users. This may provide various advantages over systems in which drilling fluid must be extracted and separately tested for hydrogen sulfide content, and/or in which assessments of hydrogen sulfide level require time for performance.

Abstract: For long-term abandonment and monitoring of well systems, a series of barriers are formed within a formation and within a casing of a well to prevent materials from leaking from the well. Formation barriers are formed within the formation at the location of perforations in the casing and along the annulus. A series of casing barriers and fluid barriers are formed within the casing of the well. One or more sensors are formed within the barriers to monitor the conditions around the barriers over long periods of time. The sensors can be configured to measure the conditions around the one or more barriers during formation of the one or more barriers and over long periods of time after the one or more barriers are formed.

Abstract: Methods and systems for assessing fluid dynamics aspects of corrosion and shear stress in piping networks are provided. Shear stress hot spots of a piping network may be identified using non-dimensional transfer functions that have been developed for identifying the magnitude and location of these local maxima depending upon the geometrical parameters of commonly used components of piping networks, the fluid properties of the flow, and the operating conditions of the piping network. Upon identification of potential shear stress local maxima, piping network operators may monitor these locations for corrosion or other damage to prevent loss of integrity of the pipes.

Abstract: Apparatus and methods for controlling and communicating with one or more tools in a downhole tool string including a tractor, an auxiliary tractor tool, a logging tool, a safety sub, a release mechanism, a unit containing sensors for monitoring downhole conditions, a setting tool, and a perforating gun. Also provided are apparatus and methods for controlling and communicating with one or more perforating guns, release devices, and explosive devices in a string to be lowered into a wellbore. Control and communication are accomplished by sending signals from the surface to control switches in the control units on the tool, with redundant switches for safety, to state machines in the respective control units, each state machine returning a signal verifying switch status to the surface. Control and power functions are accomplished with voltage of different polarities for safety.

Abstract: A sensor is configured to sense pressure in an isolated or subterranean environment. The sensor is configured to act as a capacitor with a capacitance that varies as a function of pressure. The sensor has a robust design with minimal moving parts, and in which any parts that do move do not communicate electrically through direct electrical conduction (e.g., through conductive leads). Instead, moving parts that participate in the performance of sensor as a capacitor receive and dispense electrical charge only through a dielectric fluid (e.g., a gas or liquid within the sensor). This may reduce hysterysis, lag, and/or friction with respect to pressure-dependent capacitor designs in which wiring is connected directly to moving parts.

Abstract: An apparatus for use in deployment of downhole tools is disclosed. Preferably, the apparatus includes at least an in-ground well casing, a housing providing a hermetically sealed electronics compartment, a tool attachment portion, and a first flow through core. The housing is preferably configured for sliding communication with the well casing. The hermetically sealed electronics compartment secures a processor and a location sensing system, which communicates with the processor while interacting exclusively with features of the well casing to determine the location of the housing within the well casing. A preferred embodiment further includes a well plug affixed to the tool attachment portion, the well plug includes a second flow through core capped with a core plug with a core plug release mechanism, which upon activation provides separation between the second flow through core and the core plug, allowing material to flow through said first and second flow through cores.

Abstract: An apparatus monitors a production flow from a gravel pack into a tubular sand screen disposed concentrically around downhole production tubing in an oil or gas well. A tubular sample layer is disposed concentrically around the sand screen to be exposed to the radial production flow in use. The sample layer is electrically insulated from the production tubing in use. An erosion sensor provides a signal which varies in dependence upon an electrical resistance of the sample layer, which is related to the erosion of the sample layer. An apparatus also monitors a substantially longitudinal production flow through downhole production tubing in an oil or gas well. A method and apparatus are used to monitor the condition of a gravel pack within an oil or gas well. Other methods monitor temperature or pressure conditions within an oil or gas well.

Abstract: Device comprising equipment for measuring parameters of a drilling or coring operation by means of a drillbit fixed to the end of a drill string, measurement equipment (7) being housed in a chamber (5) made in a coupling (1, 18) that is designed to be interposed between two drill string pipes or between the drillbit and a drill string pipe, or to constitute an adapter (18) for a cutting head (15) of the drillbit of a drill string.

Abstract: A rig control interface, system, and method. The rig control interface includes an emergency disconnect sequence button configured to initiate an emergency disconnect sequence signal to be sent to multiplex pods resulting in an emergency disconnect sequence including a plurality of functions being performed by devices in one or both of a lower marine riser package and a blowout preventer stack; and an emergency disconnect sequence timer display triggered by initiation of the emergency disconnect sequence signal, the emergency disconnect sequence timer display configured to indicate one or both of time elapsed after initiation of the emergency disconnect sequence signal and a status of the plurality of functions being performed by the devices in the one or both of the lower marine riser package and the blowout preventer stack.

Abstract: In one embodiment, an apparatus includes an antenna having a conductive winding, with the antenna disposed about a channel. A characteristic improvement material is disposed between the antenna and the channel. In some embodiments, the characteristic improvement material includes at least one of a negative stiffness material or a negative Poisson's ratio material. Various systems and methods are also disclosed herein.

Abstract: A wellbore servicing apparatus comprising a housing comprising one or more ports, a first sliding sleeve that is movable from a first position to a second position, a second sliding sleeve that is movable from a first position to a second position, a chamber within the housing, and an indicator disposed within the chamber, wherein, when the first sliding sleeve is in the first position, the ports are obstructed and the second sliding sleeve is retained in the first position and, when the first sliding sleeve is in the second position, the ports are unobstructed and the second sliding sleeve is not retained in the first position, and, when the second sliding sleeve is in the first position, the identifier tag is retained within the chamber and, when the second sliding sleeve is in the second position, the indicator is not retained in the chamber.

Abstract: A wellbore apparatus may include first and second tubular members joined together in end-to-end relation, the first tubular member having a reduced outer diameter end portion. The wellbore apparatus may further include a removable modular antenna assembly comprising a cylindrical dielectric housing removably positioned on the reduced outer diameter end portion of the first tubular member, at least one antenna coil carried by the cylindrical dielectric housing, and a first electrical connector coupled to the at least one antenna coil. The wellbore apparatus may also include resistivity processing circuitry coupled to the first electrical connector to determine an electrical resistivity of a wellbore based upon the at least one antenna coil.

Abstract: A weight controlled slip interlock system provides increased safety for a snubbing unit. Slips for a snubbing unit is operable between an open position and a closed position, and valves actuates the slips between the open and closed positions. Weight sensors are coupled to the slips, wherein the weight sensors measures the loads on the slips to determine whether one or more of the slips are controlling the weight of a workstring. Interlocks are coupled to the valves to prevent the valves from actuating from the closed position into the open position when the corresponding slip controls the weight of the workstring.

Abstract: A wellbore instrument system includes a pipe string extending from earth's surface to a selected depth in a wellbore. The pipe string includes at least one of an electrical conductor and an optical fiber signal channel. A power sub including an electric power source is coupled proximate a lower end of the pipe string. At least one electrically powered wireline configurable wellbore instrument is coupled to the power source in the sub.

Abstract: A method and apparatus for controlling the operation of a well which is not flowing or in which fluid is pumped or injected into the well utilising a downhole located pressure monitoring device which is operative to monitor a characteristic pressure profile of the well, and to respond and generate a triggering output when a significant deviation to the pressure profile is introduced into the well as a control signal to the monitoring device by comparing two separate pressure profiles within a certain time span, the device only generating a triggering output when the same pressure profile is monitored twice within the time span; and an actuator which is initiated into operation to control any required operation of the well when the monitoring device responds to the control signal and generates the triggering output.

Abstract: A wellbore assembly includes a housing member, an outer wellbore member, and a second wellbore member, with an outer sensor located in the annulus between the outer wellbore member and the second wellbore member. The outer sensor can sense a condition of the annulus, such as pressure or temperature, and transmit data through a solid portion of the sidewall of the outer wellbore member to a signal receiver located on the housing member. In one embodiment, the signal receiver can transmit an electromagnetic field to inductively charge a power supply on the outer sensor.