Tool Standoff Research Articles

Improvement in the method for borehole caliper measurement based on azimuthal gamma-gamma density well logging

Accurate characterization of the size and shape of the borehole is critical to the effective borehole correction for logging while drilling (LWD) measurements. It is also necessary for the real-time evaluation of geomechanical wellbore stability and for optimizing drilling operation and determining proper completion strategies. The pseudo-caliper measurement can be derived from LWD azimuthal density measurement, where a linear empirical model is employed to calculate the tool standoffs. However, we found that as the tool standoff continues to increase, the model could no longer describe the variation in borehole size accurately. In this paper, the responses of LWD azimuthal density measurement under different logging conditions are studied using the Monte Carlo modeling method. To improve the estimation of borehole geometry, a new model is proposed to determine tool standoffs and measure the borehole caliper. Simulation models with different degrees of borehole enlargement are built to investigate the performance of the model. Compared with the currently used method, the wellbore caliper values calculated using the new method are more consistent with the actual values. A field example with mechanical caliper measured from wireline logs is also presented to validate the effectiveness of the proposed method.

Qualification of bumping processes: Experimental and numerical investigations on mechanical stress and failure modes induced by shear test

In the past few years, novel assembly schemes, such as Flip Chip, 3D assemblies, and advanced low-k/ultralow-k dielectric materials have been introduced in the semiconductor industry. Aiming to develop and grant maturity milestones, standardized procedures are used to assess the assembly reliability. Among them, bump shear test provides a quantitative measure of the bonding strength between the Bump, UBM and pad structure. In this paper, some investigations on the failure mechanism induced by shear test are proposed. At first, it is shown experimentally that, for similar structures, the failure mode depends on the shear tool standoff. More precisely, high height values promote the cratering mode (i.e. fracture in the interconnect layers) whereas low ones induce a ductile mode (i.e. fracture in the bulk Aluminum layer). A numerical model is carried out to provide a better understanding of the mechanisms. Finite element simulations highlight a strong variation of the peeling stress according to the shear height, whereas the shear stress component remains quite stable. Based on these experimental and numerical findings, distinct scenarii and criterion are proposed to explain the fails. This approach is consolidated by extending the comparisons with additional experimental results. At last, the preliminary results of a time dependent study (effect of the shear tool speed and a non linear copper law) are discussed. These first insights aim at giving additional input on the physics occurring during the test.The present work proposes a validated numerical basis to explain and forecast the failure mode preference during a bump shear test. This provides some clues for design guidelines, process integration and product developments.

Electromagnetic fields of loop antenna with axis parallel to planar interface

Wireline resistivity tools in vertical or near vertical holes are run with centralizers to keep the tool near the center of the borehole. In this environment the borehole signal usually behaves in a predictable manner and is not difficult to compensate. An MWD resistivity measurement tool is now often run in highly deviated or horizontal well completions. The rotation of the drill pipe produces continuous lateral as well as axial motion of the resistivity tool. A resistivity tool measurement is a function of the tool standoff distance x s from the borehole wall. When x s is small and the tool surface is near the borehole wall, the effect can be large. In this regime, the magnetic dipole mathematical model, particularly for short array spacings, is not adequate. This paper formulates and computes the finite-size loop electromagnetic response near an idealized interface. Graphical results compare the proximity effect predicted by loop and dipole theories.

Standoff and Caliper Measurements While Drilling Using a New Formation-Evaluation Tool With Three Ultrasonic Transducers

Abstract A new formation-evaluation LWD tool that employs three ultrasonic transducers to determine tool standoff and borehole diameter is presented. The ultrasonic data are used to improve density and neutron-porosity measurements obtained from the same tool. The paper describes the ultrasonic transducer hardware and operating characteristics, as well as a unique technique for setting the ultrasonic threshold. Data processing procedures and caliper equations are also presented. Downhole phenomena that adversely affect the measurements are discussed, along with solutions used to handle them. Log examples illustrate the effectiveness of the ultrasonic measurements and include evidence of sticking, lateral bouncing, and whirling of the toolstring while drilling. Although monitoring of these undesirable bit motions is not currently available, future tools will be able to communicate this information to the surface to aid drillers.

Epithermal neutron lifetime logging in partially saturated formations and large-diameter holes

A prototype logging tool which measures hydrogen content using epithermal neutron lifetime was operated in air-filled holes through partially saturated formations at the US Department of Energy's Nevada test site. Data from model formations of known hydrogen content show that the tool can be calibrated to provide volume fraction of water in partially saturated formations. Such calibrations were obtained for air-filled holes 12 inches in diameter and 8 feet in diameter, which are typical hole sizes at the nuclear weapons test site. Data from the calibration models also allowed determination of the effects on the measurement caused by tool standoff from the wall of the hole. An 8-foot diameter hole was logged for 1000 feet through a partially saturated silica formation. Comparison to the standard, steady-state neutron log, in this hole showed good agreement in calculated water volume. Water volume percentages were generally in the range 10-20%, although values as high as about 30% were encountered for one extended interval. >

Modeling analysis of environmental effects on accelerator porosity logging measurements

MNCP modeling of an accelerator porosity sonde tool was performed in an 8-inch borehole over the complete porosity range in order to investigate its epithermal neutron response to porosity and the most significant environmental variables that affect the porosity measurement, including tool standoff, temperature, and formation lithography. The results obtained in limestone, sandstone, and dolomite formations are compared to experiments. The variations with temperature and standoff are illustrated in the case of limestone formations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Statistical uncertainties of elemental concentrations extracted from neutron-induced gamma-ray measurements

The uncertainties in elemental concentrations obtained from borehole thermal neutron capture measurements have been determined, when the normalization to absolute concentrations is by an associated element closure model that accounts for unmeasured elements in the rock. Typical uncertainties under normal logging conditions are between 2 and 3 wt.% for Ca and Si, an little over 1 wt.% for S, a few tenths of a weight percent for Fe and Ti, and about 0.2 p.p.m. for Gd. Adverse geophysical effects, large effective tool standoff, and large borehole thermal neutron absorption cross section increase the elemental concentration uncertainties because of an increase in the number of borehole gamma rays detected. Acceptable uncertainties can be obtained by slower logging speed or multiple passes. Regardless of geophysical parameter values, correct elemental concentrations are obtained within the measurement statistics.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Statistical uncertainties of elemental concentrations extracted from neutron-induced gamma-ray measurements

The uncertainties in elemental concentrations obtained from borehole thermal neutron capture measurements have been determined, when the normalization to absolute concentrations is by an associated element closure model that accounts for unmeasured elements in the rock. Typical uncertainties under normal logging conditions are between 2 and 3 wt.% for Ca and Si, an little over 1 wt.% for S, a few tenths of a weight percent for Fe and Ti, and about 0.2 p.p.m. for Gd. Adverse geophysical effects, large effective tool standoff, and large borehole thermal neutron absorption cross section increase the elemental concentration uncertainties because of an increase in the number of borehole gamma rays detected. Acceptable uncertainties can be obtained by slower logging speed or multiple passes. Regardless of geophysical parameter values, correct elemental concentrations are obtained within the measurement statistics.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of Borehole Size, Mudcake, and Standoff on the Photoelectric Absorption Index Measurement

Summary The photoelectric absorption index, IPe, is accepted as an accurate measurement for the description of formation lithology. The measured IPe has been shown to deviate slightly for a given lithology because of the effects of porosity. Properly calibrated and measured IPe's, however, have been observed to deviate from predicted values in practice, even considering the influence of porosity. Such departures were traced to variations in borehole size and tool standoff. The nature of the physical method of recording an IPe does not ensure independence from the influence of the borehole environment. A series of laboratory experiments has been conducted in test formations to verify and to characterize the influence of borehole size, mudcake, and standoff on IPe measurement. A set of nomographs has been constructed that allows correction of IPe measurements for the influence of the borehole environment. With these nomographs, a more accurate interpretation of IPe can be performed.

Improved Environmental Corrections for Compensated Neutron Logs

Summary The basic openhole responses and environmental correction algorithms for compensated neutron logging (CNL™) tools have been updated. The improved processing is based on an extensive set of laboratory formation measurements to which mathematical modeling calculations have been added. In all, the new algorithms include basic responses for the three principal formation matrix types and corrections for seven environmental effects and formation-fluid salinity. A total of 467 laboratory formation measurements have been augmented with 245 data points generated through mathematical modeling. This data base has been used to define more accurately the effects on the tool response of variations in logging conditions from those considered standard in the laboratory. More accurate corrections for the effects of formation pressure, temperature, mudcake, natural or barite mud, and borehole salinity have been defined. Certain other effects depend on more than one parameter. For example, the effect of formation salinity is somewhat matrix-dependent; therefore, the corrections are handled differently for sandstone, limestone, and dolomite. The effect of tool standoff depends on the borehole size; consequently, the standoff correction is larger for larger boreholes. The porosity crossplots and environmental correction charts based on the new algorithms represent a significant evolutionary improvement over previous techniques. They should be an important aid to the use and interpretation of neutron logs.

Slimline Dual Detector Density Logging - A Semitheoretical but Practical Approach to Correction and Compensation

A semiempirical approach to particular problems encountered in quantitative density logging with slimline logging tools is made. Equations based on known "physics" are employed to avoid problems encountered if empirical relationships alone are used. The simplest assumptions consistent with satisfactory results are outlined, and sample logs illustrate the effects of dual detector compensation. Introduction The log described in this paper is part of a multifunction sonde (gamma ray and caliper also are included as well as two density logs) developed to fulfill a requirement for a slimline one-run tool for one-man coal logging operations. The log response and compensation theory used also has shown itself to be readily extendable to logging in the higher 2- to 3-g/cm3 density region. The original purpose of the dual detector density log was to provide a thin-bed resolution capability with a good quantitative density measurement from the long-spacing detector. The spacings were chosen with these requirements in mind and were developed in an earlier generation of single-function tools. A semiempirical approach was taken to the density response equation with satisfactory results, and more recently, efforts to utilize the two logs to give densities compensated for tool standoff and (to some extent) for caving have shown some success. Slimline Sonde Design Constraints The one-man operation and slimline requirements indicated a sonde diameter of less than 5 cm and of manageable length (eventually around 3.5 m). The small diameter and desire for relative simplicity made necessary two other basic constraints.1. A limited volume was available for collimation of the source (Cesium 137) and the detector. This meant that a much larger borehole effect was present than is usual with larger-diameter tools and necessitated use of the semiempirical theory described later.2. An articulating detector shoe for the density logs was not used, since the sonde was eccentered as a whole by a single eccentering arm (Fig. 1).To reduce radiation counting statistics, high-efficiency scintillation counters were used for both detectors. Downhole count-rate dividers also were used to eliminate dead-time losses that can be caused by low-bandwidth logging cables. These dividers are such that the resolution and low counting statistics provided by the scintillation counters are in no way provided by the scintillation counters are in no way compromised. The detector dead time still remains, however, and is dealt with later. Response Equation For the preceding reasons, a semiempirical approach was thought to be necessary to allow a reasonably comprehensive relationship between the detector count rate and formation density to be established. The procedure should, however, apply equally to other similar tools. Let us begin with a relationship between count rate and density in an isotropic medium: I = P e (-mp),......................(1) JPT P. 1316