Browse Prior Art Database

A ROBUST METHOD TO DESIGN CALIBRATION BOX FOR ARRAY LATEROLOG

IP.com Disclosure Number: IPCOM000236904D
Publication Date: 2014-May-21

Publishing Venue

The IP.com Prior Art Database

Abstract

Array laterolog tools need calibration. Calibration is performed by using calibration boxes. A calibration box is designed to represent a homogeneous formation around a borehole. The invention disclosure herein introduces a method to design array laterolog calibration box. The method utilizes difference equations along with imposed currents equations, non-negativity-constrained equations and symmetric equations. All of these equations are used in the assembly of the overdetermined system . These equations are necessary, but not sufficient for a successful solution. By boosting the imposed current equations, this method can lead to substantially close apparent resistivities to corresponding formation apparent resistivities. The method is robust and reliable.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 15% of the total text.

Page 01 of 13

A ROBUST METHOD TO DESIGN CALIBRATION BOX FOR ARRAY LATEROLOG

ABSTRACT

Array laterolog tools need calibration. Calibration is performed by using calibration boxes. A calibration box is designed to represent a homogeneous formation around a borehole. The invention disclosure herein introduces a method to design array laterolog calibration box. The method utilizes difference equations along with imposed currents equations, non-negativity-constrained equations and symmetric equations. All of these equations are used in the assembly of the overdetermined system Ax b


= . These equations are necessary, but not sufficient for a successful solution. By boosting the imposed current equations, this method can lead to substantially close apparent resistivities to corresponding formation apparent resistivities. The method is robust and reliable.


1. INTRODUCTION

The calibration box consists of a network of resistors, which simulates electrical loading of the LAT (Array Laterolog Tools), corresponding to various formations. The resistor electrically simulates the corresponding borehole-formation impedance between all electrode pairs. Usually several different calibration boxes for different borehole-formation conditions should be designed to implement shop calibration of the LAT, the boxes with low resistor values are used to calibrate the tool while the highest resistor available calibration box is employed to extend the accuracy range of the tool. Ideally, the calibration boxes should produce substantially similar results (apparent resistivity) with the results obtained by using formations [1].


1.1 Array Laterolog Tools

Array laterolog tools typically include a central electrode A0 around a tool body, with current excitation electrodes A1, A2, ..., AN and electrodes A1', A2', ... , AN' symmetrically spaced above and below the central electrode and voltage monitoring electrodes M1, ... ,M2*(N-1), and M1', ... ,M2*(N-1)'. The tool drives auxiliary currents between the current excitation electrodes and the center electrode to "focus" the current from the center electrode, i.e., to reduce dispersion of the current from the center electrode until after the current has penetrated some distance into the formation. Generally, a greater depth of investigation can be achieved using more widely-spaced current excitation electrodes, but the vertical resolution of the measurements may suffer. Therefore, existing tools have multiple sets of current excitation electrodes at different spacings from the central electrode to enable multiple depths of investigation without unduly sacrificing vertical resolution. Figure 1 shows the configuration of an Array Laterolog Tool.

A1' M4'A2' M5' AN-1

M2*(N-1)'

AN

AN-1

M2*(N-1)

M5 M3 A0

Figure 1: Configuration of Array Laterolog Tool

A2 A1

M2'

M1' M3'

M1

        M2
M4

AN'


Page 02 of 13

Figure 2: Configuration of the Calibration Box of the LAT


Page 03 of 13


1.2 Background - Basic Procedures of the Calibration Box Design....