Abstract: A method may comprise plotting treatment data to form a plot of the treatment data, fitting a function to the plot of the treatment data, determining an intercept of the function, calculating one or more coefficients, plotting the one or more coefficients on a histogram, and identifying one or more active flowpath elements on the histogram. A system may comprise a fluid handling system and an information handling system. The fluid handling system may comprise a fluid supply vessel, wherein the fluid supply vessel is disposed on a surface; pumping equipment, wherein the pumping equipment it attached to the fluid supply vessel and disposed on the surface; wellbore supply conduit, wherein the wellbore supply conduit is attached to the pumping equipment and disposed in a formation; and a plurality of flowpath elements, wherein the flowpath elements fluidly couple the wellbore supply conduit to the formation.

Abstract: The present disclosure relates to a method and system for predicting a disturbance response to an injection of carbon dioxide into a multi-scale rock mass. The method includes: predicting a disturbance response to an injection of supercritical carbon dioxide into a multi-scale rock matrix; predicting a disturbance response to an injection of supercritical carbon dioxide into a multi-scale rock mass structure; and predicting a disturbance response to an injection of supercritical carbon dioxide into a multi-scale rock matrix-rock mass structure system. The method in the present disclosure can accurately analyze a cross-scale spatio-temporal evolution process of the multi-scale rock mass and seepage mechanics under disturbance of the injection of supercritical carbon dioxide.

Abstract: The invention concerns a computer implemented method for underbalanced drilling. In one embodiment, the method includes determining a plurality of gas injection rate versus bottom hole pressure curves for a plurality of liquid injection rates for a specified minimum and maximum gas injection rate and a minimum and maximum liquid injection rate. Next, the method determines a set of four interception curves including a minimum motor equivalent liquid rate interception curve, a minimum vertical liquid velocity intercept curve, a minimum horizontal liquid velocity intercept curve, and a maximum motor equivalent liquid rate intercept curve for a specified minimum and maximum mud motor rate range and a minimum horizontal and vertical annulus velocity.

Abstract: A method for recording data relating to the performance of an oil and gas flow network uses statistical data to represent raw data in a compact form. Categories are assigned to time intervals in the data.

Abstract: Systems and methods of the present disclosure are directed to reservoir simulation modeling using upon rock compaction tables derived from physical pore compressibility tests. The illustrative methods transform rock mechanics-based pore compressibility tests into compliant rock compaction tables for reservoir simulators using Dimensionless Stress to Pore Pressure Conversion, to thereby transfer geomechanical changes due to confining stress into expressions of geomechanical changes due to pore pressure.

Abstract: A technique facilitates hydrocarbon fluid production. A well is formed in a subterranean region by drilling a borehole, e.g. a generally vertical wellbore. At least one tunnel is formed and oriented to extend outwardly from the borehole at least 10 feet into a formation surrounding the borehole. The orientation of the at least one tunnel is selected such that it extends at a desired angle with respect to a direction of horizontal stress in the formation. A fracture stimulation of the at least one tunnel is performed to create a network of fractures. The orientation of the at least one tunnel ensures that the network of fractures extends through a target zone in a hydrocarbon bearing region of the formation.

Abstract: A method for performing a physical operation on a geologic formation includes: receiving image data of the formation obtained by an imaging tool disposed in a borehole penetrating the formation, the image data having images of fractures intersecting a wall of the borehole to provide borehole fracture data; simulating multiple fracture scenarios of the fractures intersecting the wall of the borehole with each scenario based on keeping the borehole fracture data constant to provide a plurality of simulations, each fracture scenario varying at least one of fracture dimensions, fracture shape, and fracture placement with respect to the borehole; determining a property from each simulation; calculating the property for the plurality of simulations at a selected statistical level, wherein the receiving, simulating, determining, and calculating are performed using a processor; and performing the physical operation on the geologic formation using physical operation apparatus based on the calculated property.

Abstract: A method of estimating a material mechanical property of a porous material, for an application or objective with a specific application frequency and application strain amplitude, includes estimating an application frequency and an application strain amplitude for use in a targeted application or objective, and constructing a frequency transfer function relating the material mechanical property to measurement frequencies, the measurement frequency range including a measurement frequency different from the application frequency.

Abstract: A method of determining fracture complexity may comprise receiving one or more signal inputs from a fracturing operation, calculating an observed fracture growth rate based at least partially on the one or more signal inputs, calculating a predicted fracture growth rate, determining a fracture complexity value, and applying a control technique to make adjustments a hydraulic stimulation operation based at least in part on the fracture complexity value. Also provided is a system for determining a fracture complexity for a hydraulic fracturing operation may comprise a hydraulic fracturing system, a sensor unit to receive one or more signal inputs, a calculating unit, a fracture complexity unit, and a controller unit to apply a control technique to adjust one or more hydraulic stimulation parameters on the hydraulic fracturing system.

Abstract: A remote temperature monitoring system includes a first unit operatively connected to one or more temperature sensors for sensing the temperature of one or more materials or food items being cooked or heated. The first unit transmits the sensed temperature to a second unit that is located remotely from the first unit during heating. The second unit is programmable with the desired temperature and/or heating parameters of the item. By monitoring the temperature status of the item over time, the system determines when the food has reached the desired temperature or degree of cooking, and notifies the user.

Abstract: Systems and methods for transferring logging data from an offset well location to a target well location by adjusting the logging data to account for the difference in correlated depths between the target well and the offset well where logging data is acquired.

Abstract: A method for assessment of an oil and gas flow network comprises: gathering historical data and/or live data relating to the status of multiple control points at different branches within the flow network and to one or more flow parameter(s) of interest in one or more flow path(s) of the flow network d; identifying time intervals in the data during which the control points and the flow parameters are in a steady state; and extracting statistical data representative of some or all steady state intervals identified in step to thereby represent the original data from step in a compact form.

Abstract: The present invention a method for determining the gas saturation of a tight reservoir. The method comprises the steps of: determining the pore size distribution of the tight reservoir rock sample, and calculating the free water saturation; calculating the water-membrane water saturation; calculating the corner water saturation; calculating the gas saturation of the tight reservoir rock sample according to the following equation: Sg=100?Sw wherein Sw is the water saturation in %; Sw is the sum of the free water saturation, the water saturation and the corner water saturation; Sg is the gas saturation in %. The method for determining the gas saturation of a tight reservoir uses model calculations, which avoids errors in the determination results of the gas saturation caused by water volatilization, surface adsorption, and observation of water flow during experiments.

Abstract: A system and method is provided for enhancing hydrocarbon production. The method and system involve geochemistry analysis and include multiply substituted isotopologue and position specific isotope geochemistry. The method and system involve using clumped isotope and position-specific isotope signatures to enhance reservoir surveillance operations.

Abstract: This invention relates to the oil and gas production industry and can be used in geophysical surveys of horizontal and deviated (including vertical) wells for their injectivity profiling and assessment of total fluid loss into the lower zone of a target interval, inaccessible for survey, and below the bottom hole. The proposed technology can be used in the presence of both behind-casing and wellbore cross-flows.

Abstract: Provided are techniques that include determining a first set of operating parameters for a hydrocarbon well for a first period; determining, based on the first set of operating parameters, a skin factor (S1); determining, based on the skin factor (S1), a well model for the well; determining, a second set of operating parameters for the well for a second period; determining, based on the second set of operating parameters, well performance characteristics for the second period that include: a well pressure and a production flowrate for the second period of time; determining that the well performance characteristics for the second period are not consistent with the well model and, in response: determining, based on the second set of operating parameters, an updated skin factor; and determining, based on the updated skin factor (S2), an updated well model for the well.

Abstract: A system controlling equipment to serve energy loads of a building includes a cost function generator configured to obtain a cost function of decision variables representing an amount of resources consumed or produced by the equipment, an optimizer configured to perform a first optimization of the cost function subject to a first set of constraints defining first values of constraint variables to generate a first result defining first values of decision variables, a constraint modifier configured determine a cost gradient, recommend changes to constraint variables, and modify constraint variables to modified values in response to changes. The optimizer is configured to perform an optimization of the cost function subject to a second set of constraints to generate a second optimization result defining second values of the decision variables. The system includes a controller that operates equipment to consume or produce resources defined by second values of the decision variables.

Abstract: Techniques for developing a hydrocarbon reservoir that include: obtaining, by way of a downhole pressure sensor of a hydrocarbon well, pressure transient test data that reflects prior changes in the flow rates corresponding to measurements of bottomhole pressure across a given interval of time during pressure transient testing of the well, conducting, for the pressure data points, a time function superposition that includes application of a superposition time function to generate superposition times for the measurements of pressure across the interval, determining, based on the superposition times and corresponding measurements of pressure, first order derivative (FOD) values for the measurements of pressure across the interval, determining, based on the FOD values for the measurements of pressure, second order derivative (SOD) values for the measurements of pressure across the interval, and generating a log plot of the SOD values for the measurements of pressure across the interval of time.

Abstract: A device for determining the composition of a mixture of fluids that flow along a pipe includes: a radiation source for illuminating the mixture with radiation; a detector for detecting radiation that has been attenuated by the mixture; and a device for monitoring the flow rate of fluid along the pipe and outputting a signal indicative of the flow rate. The device for determining further includes a device for adjusting the intensity of radiation emitting by the radiation source in response to the signal indicative of the flow rate so that the intensity of the radiation source is reduced if the flow rate reduces.

Abstract: Methods and apparatus are provided for optimizing operations for a fracturing injection waste disposal well especially where the formation is damaged or tight such that pressure fall-off tests are impractical due to extended leak-off rate times. Formation closure pressure and formation stress are calculated using Instantaneous Shut-in Pressure rather than traditional methods requiring actual fracture closure.

Abstract: Systems and methods relate to testing and/or monitoring acoustic emissions detected at composite structures, such as carbon fiber structures, intended for use in extreme conditions, such as in high pressure conditions, high or low temperature conditions, conditions in which the composite structure is subjected to mechanical impacts, or the like. The systems and protocols are suitable for use with composite structures comprising, e.g., carbon fiber structures, such as hollow or partially hollow structures used in submersible vehicles, spacecraft, gas-fillable storage containers, pressure vessels, and the like, that are subjected to extreme conditions during use.

Abstract: Techniques for automatically updated a remote data source are provided. Multiple data type-field name pairs are received. The field names correspond to names of fields in a database system. In response to receiving first input, a text string is displayed on a screen of a client device that is remote relative to the database system. A portion of the text string is identified. A data type of the portion is determined. Based on the determined data type, a subset of the data type-field name pairs that share the data type is determined. One or more options, each corresponding to a field name in the subset, are displayed. In response to receiving second input that selects a particular option of the one or more options, the portion is stored in a particular field of a particular record of the database system, where the particular field corresponds to the particular option.

Abstract: Provided are methods for drilling a well having a wellbore that extends into the earth and that encounters a salt layer. Such methods include determinations of subsurface salt mobility and salt balance load mud weight and the performance of salt mobility tests to determine salt creep and wellbore enlargement problems. A salt formation may be determined from well log data and a drilling rate. The presence of salt creep may be determined from torque generated by the drilling assembly and a hook load. The initial mud weight of a drilling fluid may be adjusted to a salt balance load mud weight (SBLMW) to mitigate or prevent salt creep during drilling.

Abstract: A subsurface hydrocarbon reservoir is simulated by sequential solution of reservoir and well equations to simulate fluid flow inside the reservoir and well production rates. Sequential solution of reservoir and well equations treats wells as specified bottom hole pressure wells. This avoids solving large matrices resulting from the simultaneous solution of the reservoir and well equations which can be computationally very expensive for large number of unknowns and require special sparse matrix solvers. Such sequential solution involves regular reservoir system solvers complemented by small matrices for the numerical solution of the well bottom hole pressures. The solution is performed on tridiagonal matrices for the adjacent reservoir cells to the well cells at the perforated well intervals; and a vector of the unknown reservoir potentials for the adjacent reservoir cells.

Abstract: A subsurface hydrocarbon reservoir with horizontal wells is simulated by sequential solution of reservoir and well equations to simulate fluid flow inside the reservoir and well production rates. Sequential solution of reservoir and well equations treats wells as specified bottom hole pressure wells. This avoids solving large matrices resulting from the simultaneous solution of the reservoir and well equations which can be computationally very expensive for large number of unknowns and require special sparse matrix solvers. Such sequential solution involves regular reservoir system solvers complemented by a small matrix for the numerical solution of the well bottom hole pressures.

Abstract: Provided are embodiments of operating an injection well of including partitioning a length of a sample of formation rock of the reservoir into length increments and determining (for a time increment) fluid saturations of the length increments based on fluid injected. The determining including, for each length increment, determining a volume of fluid injected into, fractional flow of fluid produced from, and a fluid saturation for the length increment during the time increment. The method including determining whether the volume of the fluid injected is saturated into the length of the sample during the time increment, and if so determining a flood front saturation model for the reservoir based on the fluid saturations and a fluid injection rate corresponding to the flood front saturation model, and operating the injection well according to the fluid injection rate.

Abstract: A subsurface hydrocarbon reservoir is simulated by sequential solution of reservoir and well equations to simulate fluid flow inside the reservoir and well production rates. Sequential solution of reservoir and well equations treats wells as specified bottom hole pressure wells. This avoids solving large matrices resulting from the simultaneous solution of the reservoir and well equations which can be computationally very expensive for large number of unknowns and require special sparse matrix solvers. Such sequential solution involves regular reservoir system solvers complemented by small matrices for the numerical solution of the well bottom hole pressures. The solution is performed on tridiagonal matrices for the adjacent reservoir cells to the well cells at the perforated well intervals; and a vector of the unknown reservoir potentials for the adjacent reservoir cells.

Abstract: In accordance with one embodiment, a method of locating mineral deposits suitable for production comprises obtaining via a computer an image of an area of land, determining from the image at least one fluid-expulsion structure present on the land, designating an area proximate the fluid-expulsion structure as a mineral exploration location; while in accordance with another embodiment a method of locating a hydrocarbon reservoir suitable for production is described which comprises obtaining via a computer an image of an area of land, determining from the image at least one fluid-expulsion structure present on the land, and designating an area proximate the fluid-expulsion structure as a hydrocarbon exploration location.

Abstract: To improve or optimize a wellbore treatment operation, a target net treating pressure may be determined and the constant net treating pressure maintained to effectively enhance formation breakdown and fracture complexity as well as provide a reduction in wear and tear of equipment and completion time. The target net treating pressure may be based on one or more treatment parameters and these parameters may be adjusted during the wellbore treatment operation to maintain a constant net treating pressure at or about the target net treating pressure. The injection rate or pressure of a treatment fluid may be adjusted to maintain the constant net treating pressure. Measurements associated with the wellbore treatment operation may be compared to an operational constraint and adjustments to the wellbore treatment operation may be made based on the comparison. The wellbore treatment operation may be terminated based on a parameter falling below or exceeding a threshold.

Abstract: A method for estimating reservoir quality from a reflection seismic survey includes determining seismic interval velocity (or their inverse, interval transit time “ITT”) with respect to depth from the reflection seismic survey. A normal compaction trend of the seismic interval velocity with respect to depth is determined. A fractional amount of sand and a fractional amount of shale at at least one depth is determined based on deviation of the seismic interval velocity (or ITT) at the at least one depth from the normal compaction trend.

Abstract: A method for characterizing a hydraulic fracture in a subsurface formation, includes inducing a pressure change in a well drilled through the subsurface formation. Pressure and/or a time derivative thereof is measured at a location proximate to a wellhead for a selected length of time. A conductivity of at least one fracture is determined using the measured at least one of pressure and the time derivative of pressure. A change in the determined conductivity with respect to time is determined.

Abstract: In some aspects, a one-dimensional proppant transport flow model represents flow of a proppant-fluid mixture in a subterranean region. The one-dimensional proppant transport flow model includes a fluid momentum conservation model and a proppant bed momentum conservation model that account for viscoelastic effects of the proppant-fluid mixture. The one-dimensional proppant transport flow model may also include a proppant momentum conservation model. In some cases the one-dimensional proppant transport flow model may account for any of settling and resuspension of a proppant bed and interphase momentum transfer between the proppant, proppant bed, and the fluid.

Abstract: A dual core flooding apparatus and process are disclosed that provide for testing of two core plugs using different orientations and multiple fluids. The dual core flooding apparatus includes at least two core holders each configured to contain a core plug. The dual core flooding apparatus includes a fluids delivery system configured to inject one or more fluids into the core holders and core plugs. The dual core flooding apparatus includes an image capture system, a density and viscosity measurement system, and at least two oil/water separators. The dual core flooding apparatus also includes at least two back pressure regulators and an automated confining pressure system. A dual core flooding process may include introducing at least one fluid into the core holders, maintaining confining pressure and back pressure, and measuring density and viscosity of existing fluids.

Abstract: Near real-time methodologies for maximizing return-on-fracturing-investment for shale fracturing. An example system can calculate, based on sonic data and density data, mechanical properties and closure stress of a portion of shale rocks for fracture modeling. The system can generate one or more rock mechanical models based on the mechanical properties and closure stress of the portion of shale rocks, and perform one or more fracture modeling simulations based on one or more treatment parameter values. Based on the one or more fracture modeling simulations, the system can generate a neural network model which predicts a fracture productivity indicator of an effective propped area (EPA) and/or an effective propped length (EPL), and calculate a return-on-fracturing-investment (ROFI) based on the EPA or EPL predicted by the neural network model.

Abstract: The present invention relates to an experimental device for testing the lubricity in horizontal well drilling with a cuttings bed taken into consideration, which comprises a simulated wellbore with a pulley provided at one end and a hydraulic cylinder fixed and a drill rod mounted at the other end; a cuttings feeding port is arranged above the simulated wellbore; a low end of the simulated wellbore is connected with a liquid return pipeline; the simulated wellbore is provided with an ultrasonic probe and is connected with a rock core holder. The present invention is in line with the actual operating conditions because it not only takes consideration of the friction force between the drill string and the drilling fluid, wellbore wall and slurry cake, but also takes consideration of the friction force between the drill string and the cuttings bed.

Abstract: A tracer method for online monitoring of downhole zonal contributions of oil, condensate, gas, or water mass flux of a production flow in a petroleum production well, includes arranging distinct tracer carrier systems, each in different production zones in said well, the distinct tracer carrier systems arranged for releasing unique tracers to a fluid of the production zones, the tracers having affinity after downhole release to separate phases of oil, condensate, gas, or water, using an online tracer monitor, conducting sampling of tracer concentrations for at least one of the tracers in said zonal mass fluxes at a high sampling rate, based on said concentration values, estimating the corresponding zonal tracer fluxes for each delivery data point and using said one or more estimated zonal mass fluxes to control one or more Petro Technical processes.

Abstract: A system is presented that monitors the condition of a plurality of pumps in a system of pumps using a remote telemetry unit (RTU) associated with each pump. The RTUs have a sensor configured to detect when a power failure occurs and a power backup system that includes at least one capacitor that is configured to power the RTU in response to a power failure long enough for the RTU to transmit a power failure signal to a computer system that monitors the status of the pumps. The computer system initiates a delay timer in response to receiving a power failure signal and transmits a power failure signal to a technician if a power up signal is not received within the time set by the delay timer. Using capacitors instead of batteries allows the RTU to be sealed within a container and/or a potting compound.

Abstract: A method, including: obtaining initial estimates of a plurality of subsurface parameters; obtaining a recorded wavefield decomposed into a plurality of discrete components; performing, with a computer, a cascaded inversion where the initial estimates of the subsurface parameters are individually updated, wherein each of the subsurface parameters are updated using a different discrete component of the recorded wavefield of the plurality of discrete components; and generating, with the computer, updated subsurface models from the cascaded inversion for each of the subsurface parameters.

Abstract: A method for rapid, high throughput screening of the activities of enzymes, especially ligninases and its enzyme cocktails, using nanostructure initiator mass spectrometry (NIMS) surfaces, substrates and methodology.

Abstract: Subsurface exploration using In-Situ tests such as SPT, CPT, CPTu, DMT, and PMT predicts inaccurately engineering properties of soils and intermediate geomaterials and thereby predicts incorrect load-settlement relationship of piles; variations or errors in engineering properties predicted by one empirical correlation to another correlation could be up to 50% or greater. For soft to very soft soils, engineering properties cannot be predicted as the SPT only provides information such as WOR and WOH. To overcome this problem, the invention of the application consists of performing subsurface exploration using load tests on short model piles with or without instrumentation at various depths of a soil deposit for determining accurately the above-mentioned properties. For very soft soils, a hung balance is used to hang drill rods and short model pile from a drill rig boom or from a platform with soil anchors to prevent its overturning, and then perform the load test.

Abstract: A method can include receiving mechanical information of a geologic environment and location information of natural fractures of the geologic environment; using a model of the geologic environment, calculating at least strain associated with hydraulic fracturing in the geologic environment; calculating at least microseismicity event locations based at least in part on the calculated strain; calibrating the model based at least in part on the calculated microseismicity event locations and based at least in part on measured microseismicity information associated with the geologic environment to provide a calibrated model; and, using the calibrated model, determining an increase in reactivated fracture volume associated with hydraulic fracturing in the geologic environment.

Abstract: A method is provided for controlling a managed pressure drilling system. The method comprises providing a fast system interpretation model for the operation of the managed pressure drilling system, obtaining real-time measurements from one or more sensors regarding the operation of the managed pressure drilling system, using the measurements to calibrate the fast system interpretation model for the managed pressure drilling system in real-time and using a predictive controller to run the calibrated fast system interpretation model to a time horizon in the future.

Abstract: A method may include collecting measurement data using a first operational sensor and a second operational sensor of a downhole tool, standardizing optical responses of each operational sensor to a master sensor in a tool parameter space to obtain a standardized master sensor response, transforming the standardized master sensor response to a synthetic parameter space response of the master sensor, applying a fluid model with the synthetic parameter space response of the master sensor to predict a fluid characteristic, comparing a first prediction obtained with the fluid model from the first operational sensor with a second prediction obtained with the fluid model from the second operational sensor, determining a fluid characteristic from the first prediction and the second prediction, and optimizing a well testing and sampling operation according to the fluid characteristic.

Abstract: A method and system provide automated mapping of fluid distributions in an oil field reservoir. The processes include receiving initial fluid and pressure characteristics of well-pairs in the field. Measurements from sensors detect the amount of fluid injection versus fluid produced for the well-pair during a timestep. The remaining fluid volume for the well-pair may be determined. In an exemplary embodiment, a grid map of well-pairs in the oil field are automatically generated which shows in real-time the remaining volume of fluid for each well-pair in the map. A user may thus manage the production from the oil field with increased efficiency based on the improved accuracy of the mapped data.

Abstract: A method includes: performing a machine learning process using information for enhanced oil recovery (EOR) materials to be used for an EOR process on a defined oil reservoir; determining EOR materials suitable for a condition of the oil reservoir; listing the EOR materials; and outputting an indication of the EOR materials. The materials comprise a first complex fluid to be introduced into the oil reservoir. Determining the EOR materials suitable for the condition is based on similarities between a first set of vector values for the first complex fluid, a second set of vector values for a second complex fluid already in the oil reservoir, and geological data, each of the vector values of the first set being defined by parameters of the first complex fluid and each of the vector values of the second set being defined by parameters of the second complex fluid and the geological data.

Abstract: A downhole tool includes a membrane to separate water from a formation fluid and a meter that operates as a densitometer and a Coriolis effect flowmeter.

Abstract: There is described an apparatus for monitoring at least a portion of a wellbore, the apparatus comprising a body including at least an anchoring means for releasably positioning the apparatus with respect to a tubular in the wellbore. The apparatus comprises detecting means for detecting at least one parameter of a substance in the portion, and in that the apparatus comprises transceiver means configured to at least transmit data related to the parameter.

Abstract: A method, apparatus, and program product for determining a formation pressure for a reservoir. Measurement data for a pretest of a formation of the reservoir is received. The measurement data is analyzed to determine a last-read event and a corresponding last-read pressure. Derivative data for flow regime identification is determined based at least in part on the measurement data. The derivative data is analyzed to determine a pressure derivative response, and a formation pressure is determined based at least in part on the last-read event, the last-read pressure, and the pressure derivative response.

Abstract: Systems and methods for a hybrid approach to assisted history matching in large reservoirs based on a reservoir model built using connectivity between each production well and each corresponding injection well, aquifer or gas cap.

Abstract: A method for estimating one or more properties as a function of depth of an earth formation penetrated by a borehole includes: receiving nuclear magnetic resonance (NMR) logging data having NMR echo trains as a function of depth in the borehole; receiving non-NMR logging data having non-NMR measurement values for one or more types of non-NMR measurements as a function of depth in the borehole; generating an evolution matrix (E) representing a mathematical relationship between the one or more properties in property matrix (P) to be estimated and the NMR logging data and non-NMR logging data matrix (M); generating a matrix equation of the form M=E·P; and inverting the matrix equation to estimate the one or more properties as a function of depth.