bluuebunny/crossref_metadata_2025_split huggingface dataset:
PDC Bits: What's Needed To Meet Tomorrow's Challenge
Authors: Warren T. M. , Sinor L. A. 
Published: December 2007

Abstract
When polycrystalline diamond compact (PDC) bits were introduced in the mid-1970s they showed tantalizingly high penetration rates in laboratory drilling tests. Single cutter tests indicated that they had the potential to drill very hard rocks. Unfortunately, 20 years later we are still striving to reach the potential that these bits seem to have. Many problems have been overcome, and PDC bits have offered capabilities not possible with roller cone bits. PDC bits provide the most economical bit choice in many areas, but their limited durability has hampered their application in many other areas.
New and Expected Developments in Artificial Lift
Authors: Lea J. F. , Winkler H. W. 
Published: December 2007

Abstract
Artificial lift is a broad subject. This paper discusses some of the new developments in the major areas of artificial lift. These are (1) Beam Lift, (2) Electrical Submersible Pumping, (3) Gas Lift, (4) Hydraulic Pumping and (5) Miscellaneous Topics.
The beam lift discussion concerns a new rod material, downhole measurements for rod loading, unit design and some miscellaneous topics. The ESP (Electrical Submersible Pump) section includes a discussion on solids handling, downhole sensor technology, new motor temperature limitations, motor efficiency, and other topics. The gas lift discussion includes mention of coiled tubing with gas lift valves internal, a surface controlled gas lift valve concept, and gas lift valve testing and modeling. Hydraulic pumping Is used in many locations with deep pay and fairly small production rates. New hydraulic developments include a wider availability of power fluid pumps other than positive displacement pumps, and small jet pumps specifically designed for de-watering gas wells. Some miscellaneous developments include an insertable PC (progressing cavity) pump and improved plunger lift algorithms and equipment.
Avoiding Hydrates in the Petroleum Industry: Kinetics of Formation
Authors: Christiansen R. L. , Bansal Vibha , Sloan E. D. 
Published: December 2007

Abstract
Natural gas hydrates significantly impact the economics of development of off-shore hydrocarbon resources in deep water. Methods for avoiding hydrates that depend on kinetics of hydrate formation may replace thermodynamic methods. Hydrate growth rates measured on a quiescent drop of water were found to agree qualitatively with rates measured in a vigorously stirred reactor when normalized with respect to the area of contact between the gas and the liquid, or liquid suspension of hydrates. The Gibbs free energy change for hydrate formation is shown to be a good estimate of driving force for hydrate growth. Hydrate growth rates per unit area correlate with the driving force. Driving force calculations suggest that hydrate structures other than the thermodynamically favored structures may form.
Rock Mechanics Characterization of Deep Formations: A Technico-Economical Overview
Authors: Santarelli F. J. 
Published: December 2007

Abstract
Rock mechanics is a central component of many oil industry problems. The correct rock mechanics characterisation of formations in terms of behaviour is thus of paramount technical and economical importance. State-of-the-art characterisation relies upon core testing. After emphasizing the limits of such methods two field cases are used to show that the operational timing of the characterisation is of fundamental importance. To ensure the characterisation efficiency, it is suggested: i. to use data sources normally available during operation as part of a risk prevention policy; ii. to develop new measuring methods compatible with field practice. For both areas, specific examples are given.
Elastic Moduli In Porous Rocks: A Comparison Of Differential, Poroelastic and Semi-Empirical Models
Authors: Ravalec M. Le , Gueguen Y. 
Published: December 2007

Abstract
Computations of effective elastic moduli of porous/cracked rocks have been performed by using three distinct theories. The first one, the differential scheme, accounts at best for fluid content, crack interactions and connectivity. When compared with the second one (poroelasticity), it gives consistent results for round pores. For a crack porosity, there is also a good agreement for the bulk modulus, but not for the shear modulus. The differential scheme shows that this last modulus depends on fluid properties. The third theory is a semi-empirical model (Bound Averaging Method) which can be calculated explicitly from the differential scheme.
Effects of Rock-Fluid Interactions On ohe Petrofabric and Stress-Strain Behaviour of Mudrocks
Authors: Amanullah M. , Marsden J. R. , Shaw H. F. 
Published: December 2007

Abstract
Uniaxial compression tests and SEM analyses were conducted on Tertiary and Jurassic outcrop mudrocks after exposure to different water- and oil-based fluid phases. The tests were conducted as part of an investigation into the role of rock-fluid interactions on drilling and wellbore problems. It was found that increasing intensity of rock-fluid interactions led to a decrease in brittleness of the mudrocks as well as reductions in their strengths and stiffnesses. Interestingly, on exposure to the most reactive fluids (water and 4% NaCl brine), the more competent Jurassic mudrock experienced a greater percentage reduction in strength than the Tertiary material, even though its clay content comprised a lower proportion of swelling minerals. It was demonstrated that behaviour similar to that seen for the mudrocks in their natural states could also be achieved using selected water based systems as well as oil-based muds.
Experimental and numerical study of crack propagation in sandstone
Authors: Schlangen E. , Van Mier J. G. M. 
Published: December 2007

Abstract
A combined experimental and numerical approach is adopted to investigate crack propagation in sandstone. Experiments on two types of sandstones show a similar behaviour as found in tests on concrete specimens. The heterogeneity of the material in combination with the stress situation, as a result of the applied load, governs the direction of crack propagation. Cracks that develop axe not continuous, but overlaps exist mainly around the grain particles in the material. A simple lattice model, in which the material is schematized as a network of small beams, is adopted to simulate the experiments. Using the simulations caxried out with the lattice model, stable four-point-shear tests were designed. The crack patterns obtained with the model are in good agreement with the experimental observations. However further study is needed to predict the load-displacement response more accurately.
The effect of temperature on rock mechanical properties and fracture mechanisms in source rocks – Experimental results
Authors: Lempp Ch. , Natau O. , Bayer U. , Welte D. H. 
Published: December 2007

Abstract
Triaxial compression tests were carried out on Toarcian source rocks (Lias ε) from South Germany under various temperatures between 20 °C and 300 °C and under drained and undrained conditions. The behavior of the source rocks with high total organic carbon (TOC) is strongly temperature dependent and predominantly plastic at elevated temperatures. Microfracture systems are generated which resemble natural assemblages. The fractures are of tensile nature and related to internal pressure built-up in the pore fluid. The experiments provide new aspects to compaction and fluid expulsion from source rocks.
Size dependency of hollow-cylinder stabiliy
Authors: van den Hoek P. J. , Smit D. -J. , Kooijman A. P. , Bree Ph.de , Kenter C. J. , Khodaverdian M. 
Published: December 2007

Abstract
The hollow-cylinder (HC) test is an important means of assessing openhole stability during drilling, completion and production. This paper reviews experimental and theoretical work aimed at quantifying the size dependency of hollow-cylinder stability. The strength of the size effect appears to depend largely on the initial failure mechanism (whether splitting or shear). The preference for one or the other failure mechanism, in turn, depends not only on the type of material but also on hole size. Quantification of such a preference, as a function of size and material, is considered one of the major challenges in this line of research.
Nonlinear effects in the study of borehole stability
Authors: Pellegrino A. , Sulem J. , Barla G. 
Published: December 2007

Abstract
The purpose of the paper is to describe a damage constitutive model adopted for the description of the nonlinear mechanical behaviour of brittle rocks subjected to different stress paths. The main feature of the model consists in the introduction of a damage tensor which allows for representing stress induced anisotropy effects related to anisotropic crack development and propagation.
The model is used first for the simulation of testing of a hollow cylinder, loaded from the outer boundary. Then, consideration is given to borehole stability, when studying the creation of a circular cavity in a rock mass under a hydrostatic stress field. In both cases, the solution of the problem is attained by using a numerical procedure for the integration of the equilibrium equations. It is shown how the results are dependent upon the stress path associated with the specific problem being analyzed.
X-ray Tomographic Study of the Influence of Bedding Plane Orientation on Shale Swelling
Authors: Cook J. M. , Goldsmith G. , Bailey L. , Audibert A. , Bieber M. -T. 
Published: December 2007

ABSTRACT
X-ray tomography (CT scanning) has been used to monitor, in real time, the damage produced by chemical interaction between drilling fluid and Pierre shale in a model wellbore geometry, under downhole stress conditions. This shale is moderately anisotropic, and the experiments examine the effect of the angle between bedding and wellbore. The swollen zone around the wellbore becomes increasingly asymmetric as the angle between bedding plane normal and wellbore axis increases. Swelling and strength tests on the shale at different orientations are described, and the results related to the damage seen in the wellbore experiments.
Role of Hydration State of Shales in Borehole Stability Studies
Authors: Onaisi A. , Durand C. , Audibert A. 
Published: December 2007

ABSTRACT
When in contact with water-based muds, shales can absorb water and ions that causes serious wellbore stability problems. An efficient stability model should combine together mechanical and chemical effects, but to run such a model, shale mechanical properties and hydration tendency as function of mud composition have to be identified. Characteristics would be determined while shale is under hydration and stress states representative of downhole conditions. A laboratory methodology has been developed to restore initial rock hydration state. Modelling of such experiments points out the existence of a suction pressure that can be wrongly assimilated to a swelling pressure. This paper will contribute to specify the representative experimental conditions and show how rock behaviour can be affected if such conditions are not respected.
The Mechanism of Mud Support Reduction Due to Mud Pressure Penetration
Authors: ETan C. , Rahman S. S. 
Published: December 2007

ABSTRACT
This paper describes the fundamental concept and a mathematical model of the mud pressure penetration mechanism and the associated mud support reduction as the drilling mud invades the rock material. The variation of breakthrough pressure with cumulative pore size distribution of a Cretaceous shale from the North West Shelf of Australia has been quantified for a polyacrylamide, an ester-based and an oil-based mud systems. The results indicate that the improvement in the stability of reactive shale sections drilled with ester-based and oil-based muds may not be due solely to the muds inhibiting the hydration and loss of strength of the shale but also due in part to the comparatively better mechanical support provided by the muds.
A Novel Technique for the Investigation of Drilling Fluid Induced Borehole Instability in Shales
Authors: van Oort E. 
Published: December 2007

ABSTRACT
A new experimental technique for the investigation of drilling-fluid induced borehole instability in shales is introduced. Pressure transmission transients are used to study pressure penetration in shales, the latter being a main shale-destabilising mechanism. The pressure transmission method provides a powerful tool for the fundamental study of shale-fluid interactions and for the development of improved water-based mud formulations to promote borehole stabilisation in shales. The capabilities of the method are illustrated by permeability measurements made in low-permeability shales. In addition, a wide range of conventional and new mud systems is screened and the shale-stabilising performance of these systems is assessed. It is argued that the strategy for promoting borehole stability in shales through improved mud formulation should be based on maintaining pressure isolation between wellbore and formation.
Experimental Study of Sand Production Processes Near an Orifice
Authors: Yim K. , Dusseault M. B. , Zhang L. 
Published: December 2007

ABSTRACT
An experimental study was performed using Ottawa sand and a produced sand. A 3-D semi-analytical flow model was developed to analyze the experimental data. The results show that the ratio of sand grain size and outlet hole size, grain size distribution, and angularity are the most important factors affecting the sand arch stability. Pressure increase mode and pressure magnitude also affect arch stability.
A Model for Borehole Breakouts in Brittle Rocks
Authors: Germanovich L. N. , Roegiers J. -C. , Dyskin A. V. 
Published: December 2007

ABSTRACT
A 2-D model of the mechanism of borehole instability due to crack propagation parallel to the free surface is considered. Pre-existing cracks start to grow under the action of the compressive stress concentrations at the borehole boundary. The interaction with the boundary eventually makes the crack propagate unstably and separate a thin rock layer which subsequently buckles. This initial step of failure slightly moves the borehole boundary, enabling the next crack to propagate. Such a process repeats itself until the change in the borehole shape is sufficient to suppress the unstable phase of crack growth. This is regarded as the ultimate extent of the failure. The smaller the sizes of the pre-existing cracks, the larger the extent. This implies that in the cases when the considered failure mechanism prevails, larger failures can be expected for less microcracked rock masses.
Review of Recent Developments in Fracture Mechanics with Petroleum Engineering Applications
Authors: Shlyapobersky J. , Chudnovsky A. 
Published: December 2007

ABSTRACT
Basic concepts of fracture mechanics are discussed to analyze their applicability in modeling fracture initiation and propagation during hydraulic fracturing and waterflooding. Recent advances in modeling fracture initiation and quasi-equilibrium growth are reviewed. Special attention is given to the role of the process zone in fracturing. Process zone observed in laboratory and field hydraulic fracture experiments may explain the discrepancies between simulated and measured net fracture pressures. Process zone is revealed to be the common critical element for proposed mechanisms used for calibrating hydraulic fracture models. Deterministic and probabilistic mechanisms in fracture phenomena are addressed. Scale and rate effects are discussed.
Reorientation of Propped Refracture Treatments
Authors: Wright C. A. , Conant R. A. , Stewart D. W. , Byerly P. M. 
Published: December 2007

ABSTRACT
Refracture treatments have been effectively used for production enhancement for decades. Typical motivations for refracture treatments include: restoring the fracture conductivity to the (possibly) "damaged" proppant pack of the initial fracture treatment; achieving a longer propped fracture by placing a much larger volume of proppant; or simply achieving a more effective proppant pack through the use of vastly improved fracture design procedures1. This paper describes tiltmeter hydraulic fracture mapping field studies which conclusively document a significant additional motivation for refracture treatments, namely: refracture reorientation. Reorientation of propped refracture treatments allows contact with undepleted reservoir from older existing wellbores, which can restore production to near initial rates.
Coupled Geomechanical, Thermal and Fluid Flow Modelling as an Aid toIimproving Waterflood Sweep Efficiency
Authors: Heffer K. J. , Koutsabeloulis N. C. , Wong S. K. 
Published: December 2007

Abstract
Generic studies, involving coupled geomechanical, thermal and flow modelling, together with empirical field data, have elicited the concept that preferred directionality in oilfield waterflooding is stress-related and progressive with time. Specific field applications have illustrated the importance of mechanical and hydraulic interactions between wells, and of the characteristics of natural fractures.
Propagation/Recession of a Penny-Shaped Fracture in a Permeable Diffusive Formation
Authors: Abousleiman Y. , Yuan Y. G. , Roegiers J. -C. 
Published: December 2007

Abstract
This paper examines the poromechanics-related aspects in the propagation/recession of an axi-symmetric hydraulic fracture. Using a penny-shaped geometry, the fluid leakoff is modelled as a pressure-dependent phenomenon coupled with the poroelastic stresses induced by changes of the porepressure. The system of equations that couples the formation poroelastic response with the flow of a Newtonian or power law fluid in a fracture is described. The fracture model is formulated in a moving coordinate system and solved using a pseudo-explicit finite difference scheme. The programme, "McFrac," has the following features: (i) a fixed mesh for a propagating/receding fracture, (ii) the capability for fluid flow-back, and (iii) a pressure-dependent fluid leakoff. The numerical simulation indicates that poroelastic processes coupled with the fluid leakoff affect not only the pressure history at the wellbore, but also the fracture's dimensions.
Experimental Modelling of Casing Deformation in a Compacting Reservoir
Authors: Veeken C. A. M. , Wahleitner J. P. , Keedy C. R. 
Published: December 2007

Abstract
The deformation of casing in a compacting reservoir has been simulated in model experiments to assist with the design of compaction-tolerant completions installed in deep-water, unconsolidated sandstone reservoirs.
Compaction causes severe casing buckling if the lateral casing support is insufficient. Vertical casing with adequate support has been compacted 10% without developing excessive dogleg. Compaction of deviated casing results in casing ellipticity and bending. The model test results are confirmed by field observations (borehole televiewer data). The experimental results indicate that casing damage in a compacting reservoir can be reduced by providing adequate lateral support, by changing the wellbore deviation and by using thick-walled casing.
Application of Seismic Tomography to Induced Seismicity Investigations
Authors: Maxwell S. C. , Young R. P. 
Published: December 2007

Abstract
Two case studies are presented, which highlight the potential application of seismic velocity imaging to induced seismicity investigations. Velocity images may be produced using data currently recorded with seismic monitoring arrays. Comparisons of velocity images and induced seismicity have shown that both natural and induced earthquakes cluster in regions of high seismic velocity, while low-velocity regions predominantly lack seismicity. An interpretation of seismic velocity imaging and induced seismicity can be used to interpret the state of stress throughout a rockmass and identify potential problem regions. Examples are given of using this combined seismic interpretation to validate numerical stress models.
The Use of a Genetic Algorithm for the Optimal Design of Microseismic Monitoring Networks
Authors: Jones Robert H. , Rayne Christopher M. , Lindblom Ulf 
Published: December 2007

Abstract
The quality of microseismic location data from a volume of interest is dependent on the three dimensional geometry of the monitoring array. When the volume of interest contains an arbitrary shaped cavity not all the sensors will detect all the seismic activity. The performance of the array can be modelled so its configuration can be optimised.
A genetic algorithm is used to steer the search for the optimal array of sensors. Various fitness functions were tested in the genetic algorithm and the minimax criterion was found to be the most satisfactory.
Acoustic Emission and Temperature Changes in Hard Coal During Carbon Dioxide Sorption-Desorption
Authors: Majewska Zofia , Majewski Stanislaw , Moscicki Wlodzimierz , Zietek Jerzy 
Published: December 2007

Abstract
The effect of carbon dioxide sorption – desorption on hard coal on acoustic emission (AE) and temperature (T) changes have been carried out on granular coal samples. The study was conducted primarily in order to answer the following questions: Do measurements on AE and T changes provide a good indication of the proneness of coal to outbursts? Is it possible to find correlation between AE and T characteristic and petrographic structure of a coal? Data are presented as plots of AE and T parameters versus time.
The experimental data presented lead to the following conclusions:
– AE and T versus time plots show that they provide a very good measure of the proneness of coal to gas and coal outbursts. – There is a direct influence of porous structure and petrographic composition of coal on its behaviour during carbon dioxide sorption – desorption – AE and T measurements have been shown to be promising for predicting outbursts. – The results obtained in this study are also relevant to coal – methane system.
Computational Modelling of the Thermal and Mechanical Behaviour of Rock Mass Subjected to Cryogenic Temperatures
Authors: van den Bogert P. A. J. , Kenter C. J. 
Published: December 2007

Abstract
A finite-element model has been developed to simulate the behaviour of rock mass to be utilised for underground storage of liquefied natural gas (LNG). The model will be used to assess the technical and commercial viability of LNG storage in unlined rock caverns for different geotechnical conditions. The numerical model includes interface elements to describe the mechanical behaviour of joints. The smeared-crack approach is employed to simulate cracking in intact rock.
The numerical model is validated against large-scale site experiments which are being carried out in cavern B at the Röda Sten Rock Laboratory (Göteborg, Sweden). In an exploratory experiment carried out in 1992, the temperature was lowered to −40°C using a cooling machine. In a subsequent experiment liquid nitrogen will be used to cool the same unlined cavern to −162°C. The paper describes the validation of the model against the exploratory experiment at −40°C. The calculated temperature and strain distribution in the rock mass compare well with the measurements. The results demonstrate an encouraging prospect in adequately simulating the relevant phenomena in jointed rock mass at low temperatures.