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Drilling for foundation piles and tieback anchors through soils using a continuous casing to support the borehole is often referred to as 'overburden drilling'. Monitoring data from several case studies show that overburden drilling may cause considerable short-term ground settlements indicating a loss of soil volume around the casings. However, further insight is required to understand the mechanisms that govern overburden drilling. Novel physical model tests were carried out to investigate the effects of varying parameters such as flushing media (water or air), flow and penetration rate on the penetration force, pore pressure changes, soil displacements, and drill cutting transport. Tests with water flushing indicate a clear relation between the flow and penetration rate and the resulting influence on the surrounding ground. Increasing flow rates caused larger excess pore pressures at greater radial distances and generated more excess drill cuttings compared to the theoretical casing volume. The obtained results were translated into a non-dimensional framework to estimate optimal flushing parameters in similar conditions. The air flushing tests were considerably limited by the modelling constraints. Notable reduction of pore pressures adjacent to the casing indicate an air-lift pump effect that can lead to extensive ground movements as observed in the field. Key words: model tests, drilling, piles, anchors, settlement, pore pressure. Le forage de pieux de fondation et d'ancrages d'arrimage dans le sol a l'aide d'un tubage continu pour soutenir le trou de forage est souvent appele << forage dans les morts-terrains >>. Les donnees de surveillance provenant de plusieurs etudes de cas montrent que le forage de morts-terrains peut provoquer des tassements considerables du sol a court terme, indiquant une perte de volume de sol autour des tubages. Toutefois, il est necessaire de mieux comprendre les mecanismes qui regissent le forage des morts-terrains. De nouveaux essais sur modele physique ont ete realises pour etudier les effets de divers parametres tels que le milieu de rincage (eau ou air), le debit et le taux de penetration sur la force de penetration, les changements de pression interstitielle, les deplacements de sol et le transport des deblais de forage. Les essais avec rincage a l'eau indiquent une relation claire entre le debit et le taux de penetration et l'influence consequente sur le sol environnant. L'augmentation des debits a entraine des pressions de pores plus importantes a des distances radiales plus grandes et a genere plus de deblais de forage en exces par rapport au volume theorique du tubage. Les resultats obtenus ont ete traduits dans un cadre non dimensionnel pour estimer les parametres de rincage optimaux dans des conditions similaires. Les essais de chasse d'air ont ete considerablement limites par les contraintes de modelisation. Une reduction notable de la pression des pores adjacents au tubage indique un effet de pompe a air qui peut entrainer des mouvements importants du sol, comme on l'a observe sur le terrain. [Traduit par la Redaction] Mots-cles: essais sur maquettes, forage, pieux, ancrages, tassement, pression interstitielle., 1. Introduction In areas where soft soil deposits of limited depth are overlying competent bedrock so-called overburden drilling is often carried out to install tieback anchors for sheet pile walls [...]

A fully implicit, three-dimensional simulator with local grid refinement around the wellbore is developed to solve reservoir and horizontal well flow equations simultaneously, for single-phase liquid and gas cases. The model consists of conservation of mass and Darcy's law in the reservoir, and mass and momentum conservation in the wellbore for isothermal conditions. Establishing the continuity of pressure and preserving mass balance at the sandface satisfy the coupling requirements. The proposed simulator is tested against and verified with the results obtained from a commercial code ECLIPSE-100[TM], and available public domain simulators and semi-analytical models. The proposed model can be used for multiple purposes such as well productivity prediction, transient analyses, well length optimization, completion design and optimization, and production logging interpretation. Different completion scenarios and reservoir anisotropy are simulated and their effects on the productivity of the horizontal wells are discussed. Completion cases include open-hole and partial completions. During the production logging of a horizontal well, the coil tubing reduces the wellbore cross sectional area and may cause substantial changes in the wellbore flow behavior. Depending on the well and coil tubing diameters, a significant difference between the actual production rates and the rates obtained from a production log can be observed.

The original purpose of this work was to propose an equation system to describe the kind of drilling in which the tools are with pronounced shaft length. The equation system turned out to disclose the low frequency mechanism of hole lobes. The proposed system is composed of Euler-Bernoulli beam equation representing tool shaft, and an excitation force in form of Fourier series. An empirical cutting force was established and related cutting force components were calculated. And the accumulated contribution of modes and harmonics was evaluated. The solution for the proposed equation system allowed a prediction of hole roundness which was consistent with experimental results for different conditions. The solution also allowed an investigation into the waviness and lobes. The results suggested that the bizarre phenomenon of lobes on hole is in reality waviness described by Tlusty for milling. The rigorous mathematical nature of the proposed equation built solid foundation for former empirical observation of waviness and lobes on work pieces. [DOI: 10.111511.1765142]

A model is developed for predicting the heat that flows into the workpiece during dry drilling processes. The model can be applied to any drill of known geometry. The measured drilling thrust and torque are used as inputs in an oblique cutting analysis, and an advection heat partition model is developed to calculate heat flux loads on a finite element model of the workpiece. Experiments using embedded thermocouples have verified that the model accurately predicts the temperature field in the workpiece for a range of drilling speeds and feeds.

Large-amplitude vibrations in drilling often occur at frequencies near multiples of the rotation frequency, even when these are much lower than the system's first natural frequency. These vibrations are responsible for out-of-round, 'lobed' holes. A simplified model of the mechanics of this phenomenon is presented in this paper. The model includes cutting and 'rubbing 'forces on the drill, but inertia and damping of the tool are neglected at low speeds. This quasi-static model remains dynamic because of the regenerative nature of cutting; the force on each cutting element depends on both the tool's current position and its position at the time of the previous tooth passage. Characteristic solutions, including unstable retrograde 'whirling' modes, are found in terms of eigenvalues and eigenvectors of a discrete state-transition matrix. These unstable modes correspond closely to behavior observed in drilling tests. [DOI: 10.1115/1.1459087]

A finite element thermal model is devised to capture the transient temperatures in the workpiece in drilling. Experimental observations along with an inverse heat conduction procedure is utilized in identifying the strength of the heat fluxes from the three distinct regions of the drill (drill body, cutting lips and chisel edge) at various process conditions in both wet and dry conditions with coated and uncoated drills. The identified heat fluxes along with a calibration scheme are used in predicting the transient temperatures in the workpiece in both dry and wet conditions. The model demonstrates the ability to predict the temperatures within 20 percent of the measured temperature rise. [DOI: 10.1115/1.1455645]

A finite element thermo-elastic model is devised to capture the radial errors induced in the workpiece in drilling. The temperature rise in the workpiece modeled in Part 1 of this paper is utilized in obtaining the thermo-elastic deformations in the workpiece at various process conditions. The predicted errors are compared to the average errors measured with the aid of a CMM. The predicted profiles agree well with the experimentally observed tapered hole profiles in the absence of cutting fluids. In the presence of cutting fluids the predicted radial errors only account for 10 percent of the experimentally observed errors. [DOI: 10.1115/1.1458014]

This paper attempts to explain the complicated behavior of oilwell drillstring motion when both torsional stick-slip and lateral whirl vibration are involved. It is demonstrated that the observed phenomena in experimental drillstring data could be due to the fluid forces of the drilling mud. A Stick-slip Whirl Model is presented which consists of a submodel for the whirling motion and a submodel for the stick-slip motion, both as simple as possible. The Stick-slip Whirl Model is a simplification of a drillstring confined in a borehole wall with drilling mud. The model is as simple as possible to expose only the basic phenomena but is discontinuous. Bifurcation diagrams of this discontinuous model for varying rotation speeds reveal discontinuous bifurcations. The disappearance of stick-slip vibration when whirl vibration appears is explained by bifurcation theory. The numerical results are compared with the experimental data from a full-scale drilling rig. [DOI: 10.1115/1.1452745]

This paper develops a finite-difference time-domain (FDTD) approach suitable for modeling general antenna structures which include cylindrical dipoles. The medium averaging is a key factor of the method since the FDTD grid size is comparable to the dimensions of the antenna. It is essential in the FDTD calculation to account for the effective media seen by different electric field components. The input impedance calculated by the FDTD approach agrees well with the published results for a cylindrical dipole, although only one cell in the transverse direction is assigned as the metallic conductor. This FDTD approach is then used to model and analyze a novel broadband antenna which can be used in a borehole radar system for oil-field imaging while drilling. The antenna is essentially a horizontal cut on a metallic drill collar with a vertical cylindrical dipole placed across the cut and loaded at the ends. Based on the modeling results, we found that a proper resistive loading is the key in order to increase the bandwidth of the antenna and reduce ringing. When properly loaded, the antenna has a fairly flat input impedance ranging from 50 MHz to 600 MHz. The real part of the input impedance varies favorably around 75 [OMEGA]. In addition, the input impedance of the antenna is not very sensitive to the surrounding medium. The simulated antenna radiation of the electric field shows good azimuthal discrimination. For a lossless medium with a permittivity of [20[member of].sub.0] the front-back ratio climbs from around 15 dB at 100 MHz to about 45 dB at 600 MHz. Index Terms--Borehole radar, broadband antenna, finite difference, imaging while drilling, input impedance, subsurface.

In this paper, a method for on-line compensation of cylindricity errors in machined bores is formulated and demonstrated. The cylindricity errors addressed are those caused by the elastic deformation of the bore wall due to forces applied to the workpiece both during and after the machining process. Compensation is achieved using a piezoelectric boring bar servo capable of varying the depth of cut rapidly for on-line compensation at acceptable industrial machining speeds. Control of the boring bar servo consists of both learning and repetitive control. Learning control is used to determine the cutting tool reference trajectory required to achieve compensation, and repetitive servo control is used to accurately track the reference trajectory. The stability and convergence of the error dynamics of the learning control system are analyzed using a model for the flexure-induced machining errors. Experimental results demonstrate that the proposed method can significantly improve bore cylindricity in machined components.