[신간안내] Computational Electrodynamics (the finite difference time - domain method)

This invention is directed to a downhole method and apparatus for simultaneously determining the horizontal resistivity, vertical resistivity, and relative dip angle for anisotropic earth formations. The present invention accomplishes this objective by using an antenna configuration in which a transmitter antenna and a receiver antenna are oriented in non-parallel planes such that the vertical resistivity and the relative dip angle are decoupled. Preferably, either the transmitter or the receiver is mounted in a conventional orientation in a first plane that is normal to the tool axis, and the other antenna is mounted in a second plane that is not parallel to the first plane. This invention also relates to a method and apparatus for steering a downhole tool during a drilling operation in order to maintain the borehole within a desired earth formation. The steering capability is enabled by computing the difference or the ratio of the phase-based or amplitude-based responses of the receiver antennas which are mounted in planes that are not parallel to the planes of the transmitter antennas. Although this invention is primarily intended for MWD or LWD applications, this invention is also applicable to wireline and possibly other applications.

Electromagnetic wave resistivity tool having a tilted antenna for geosteering within a desired payzone

Extensions of finite-difference time-domain (FDTD) and finite-element time-domain (FETD) algorithms are reviewed for solving transient Maxwell equations in complex media. Also provided are a few representative examples to illustrate the modeling capabilities of FDTD and FETD for complex media. The term complex media refers here to media with dispersive, (bi)anisotropic, inhomogeneous, and/or nonlinear properties present in the constitutive tensors.

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Time-Domain Finite-Difference and Finite-Element Methods for Maxwell Equations in Complex Media

This invention is directed to a downhole method and apparatus for simultaneously determining the horizontal resistivity, vertical resistivity, and relative dip angle for anisotropic earth formations. The present invention accomplishes this objective by using an antenna configuration in which a transmitter antenna and a receiver antenna are oriented in non-parallel planes such that the vertical resistivity and the relative dip angle are decoupled. Preferably, either the transmitter or the receiver is mounted in a conventional orientation in a first plane that is normal to the tool axis, and the other antenna is mounted in a second plane that is not parallel to the first plane. Although this invention is primarily intended for MWD or LWD applications, this invention is also applicable to wireline and possibly other applications.

Electromagnetic wave resistivity tool having a tilted antenna for determining the horizontal and vertical resistivities and relative dip angle in anisotropic earth formations

A system and method that permits measuring properties and thickness of a dielectric layer, particularly a dielectric layer close to a pipeline wall, and more particularly fluids flowing inside a pipe is provided. The present invention attains the above described objective by a system comprising a sensor operating in a material characterization mode in a first frequency range and a sensor operating in a thickness characterization mode in a second frequency range, and a method for operating said system.

Permittivity measurements of layers

We simulate the response of logging-while-drilling (LWD) tools in complex thee-dimensional (3-D) borehole environments using a finite-difference time-domain (FDTD) scheme in cylindrical coordinates. Several techniques are applied to the FDTD algorithm to improve the computational efficiency and the modeling accuracy of more arbitrary geometries/media in well-logging problems: (1) a 3-D FDTD cylindrical grid to avoid staircasing discretization errors in the transmitter, receiver, and mandrel geometries; (2) an anisotropic-medium (unsplit) perfectly matched layer (PML) absorbing boundary condition in cylindrical coordinates is applied to the FDTD algorithm, leading to more compact grids and reduced memory requirements; (3) a simple and efficient algorithm is employed to extract frequency-domain data (phase and amplitude) from early-time FDTD data; (4) permittivity scaling is applied to overcome the Courant limit of FDTD and allow faster simulations of lower frequency tool; and (5) two locally conformal FDTD (LC-FDTD) techniques are applied to better simulate the response of logging tools in eccentric boreholes. We validate the FDTD results against the numerical mode matching method for problems where the latter is applicable, and against pseudoanalytical results for eccentric borehole problems. The comparisons show very good agreement. Results from 3-D borehole problems involving eccentric tools and dipping beds simultaneously are also included to demonstrate the robustness of the method.

/pdf/three-dimensional-simulation-of-eccentric-lwd-tool-response-2bdyuf0bhe.pdf

Three-dimensional simulation of eccentric LWD tool response in boreholes through dipping formations

Logging-while-drilling (LWD) borehole sensors are used to provide real-time resistivity data of adjacent earth formations for hydrocarbon exploration. This allows for a proactive adjustment of the dipping angle and azimuth direction of the drill and, hence, geosteering capabilities. The analysis of borehole eccentricity effects on LWD sensor response in full 3 3 anisotropic earth formations is important for correct data interpretation in deviated or horizontal wells. In this paper, we present a cylindrical-grid finite-difference time-domain model to tackle this problem. The grid is aligned to the sensor axis to avoid staircasing error in the sensor geometry but, in general, misaligned to the (eccentered) borehole/formation interface. A locally conformal discretization is used to compute effective conductivity tensors of partially-filled grid cells at those interfaces, involving an isotropic medium (borehole) and a full 3 3 anisotropic medium in general (dipped earth formation). The numerical model is used to compute the response of eccentered LWD sensors in layered earth formations with anisotropic dipping beds.

Numerical Modeling of Eccentered LWD Borehole Sensors in Dipping and Fully Anisotropic Earth Formations

Oil-based mud imaging systems and methods having standoff compensation. In some embodiments, disclosed logging systems include a logging tool in communication with surface computing facilities. The logging tool is provided with a sensor array having at least two voltage electrodes positioned between two current electrodes energized by an excitation source to create an oscillatory electric field in a borehole wall. The two current electrodes are each shielded with conductive shields to prevent current leakage into the logging tool body. A common mode voltage is measured, and the phase and amplitude of the excitation source is controlled to reduce the difference between the common mode voltage and reference voltage of a voltage detector. The logging tool is further provided with electronics coupled to the voltage detector and the current electrodes to determine a differential voltage between the voltage electrodes and two current flows from separate ones of the current electrodes. From the differential voltage and multiple current flows, the computing facilities determine borehole wall resistivity, and may display the resistivity as a borehole wall image.

Standoff compensation for imaging in oil-based muds

A method for determining a formation profile 185 surrounding as well is used to establish a first formation profile 185 using a neural network inversion method 155. A synthetic log 170 is generated from the first formation profile and if the synthetic log converges 180 with a real log 150, the formation profile parameters associated with the synthetic log are output 185. Otherwise, the first formation profile is modified and a new synthetic log 170 is generated.

Method for determining parameters of earth formations surrounding a well bore using neural network inversion

Oil-based mud imaging systems and methods that measure formation permittivity. In some embodiments, disclosed logging systems include a logging tool in communication with surface computing facilities. The logging tool is provided with a sensor array having at least two voltage electrodes positioned between at least two current electrodes that create an electric field in a borehole wall, and is further provided with electronics coupled to the voltage electrodes to determine a differential voltage magnitude and phase. From the magnitude and phase, formation resistivity and permittivity measurements can be determined and used to construct a borehole wall image.

Luis Emilio San Martin

Papers

Three-dimensional simulation of eccentric LWD tool response in boreholes through dipping formations

Numerical Modeling of Eccentered LWD Borehole Sensors in Dipping and Fully Anisotropic Earth Formations

Standoff compensation for imaging in oil-based muds

Method for determining parameters of earth formations surrounding a well bore using neural network inversion

Permittivity measurements with oil-based mud imaging tool