bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of North Sea Turbo Diamond Bit Designs
Authors: Vennin Henri C. , Rowley David S. , Walker Bruce
Published: December 2007

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

This paper explains how 9 5/8" turbine diamond bit designs for the North Sea were optimized through the combined results of practical field developments and analytical practical field developments and analytical design studies. Various mechanical characteristics such as bit face contour, diamond size, and diamond pattern were analyzed with the aid of the diamond drilling theory, taking into account the particular conditions encountered in North Sea drilling.

The mathematical model for rotary and turbine diamond drilling as used in this study was developed during recent years, and is now considered an effective aid to design optimization. The drilling theory is based on previously reported studies on the cutting actions of single diamonds in rocks, now expanded to encompass the total effect of all diamonds on the cutting surfaces of the bit. Using specific drilling conditions and rock properties, expressions for bit torque, properties, expressions for bit torque, penetration rate, rotary power and other penetration rate, rotary power and other performance characteristics are obtained in performance characteristics are obtained in terms of bit weight, rotary speed and the design parameters, like diamond size, fluid handling characteristics and geometric factors.

The evolution of the bit designs leads to a bit style which, within the known limitations on diamonds, has best theoretical performance and best field performance.

Introduction

In view of the expanding use and importance of turbo diamond drilling techniques, particularly in modern offshore development, particularly in modern offshore development, it is important to study the way in which diamond bits work under the specific conditions imposed by turbines, and to use this knowledge to improve the performance of the diamond tools. In this study, several practical turbo diamond bit design approaches are practical turbo diamond bit design approaches are studied analytically in an effort to isolate the best performing or "optimum" combination of bit design variables. The goal of optimization is to find the particular set of design variables which yields the highest penetration rate under the selected operating conditions, without violating any of the assumed practical limitations on loading and application of the diamonds, the diamond bits and the turbines.
Offshore Riser Slug Flow Avoidance: Mathematical Models for Design and Optimization
Authors: Yocum B.T.
Published: December 2007

Yocum, B.T., Member AIME, Yocum International Asso.

Losses in capacity of up to 50% in offshore oilfield production systems have been caused by poor design of two phase flow risers. Operators often do not realize the reduced capacity and additional costs caused by slug flow formation in risers, because the total system has been adjusted for slug flow avoidance, to a non optimum operating point. This paper (1) proposes a riser point. This paper (1) proposes a riser slug flow prediction chart with accept able slug and stratified flow range (2) develops a mathematical model for the elevation pressure drop and frictional pressure loss in the riser as a function pressure loss in the riser as a function of flow capacity (3) discusses the influence and characteristics of entering conditions (4) proposes several alternative designs to eliminate slug flow at minimum pressure loss and cost (5) recommends a inter company data gathering and testing program on risers, and, other vertical sections, in order to formulate more exact design models for optimization.

Introduction

During the 1960's progress was made in advancing the technology, and, rapid computer calculation, of two phase flow oilfield production systems. These utilize the flashing of the two phase mixture of oil and gas, to produce flow with pressure drop. Several large scale oilfield installations have been made both onshore and offshore. An example of a multiwell-flowline-trunkline system is shown in Figure 1. Such configurations of interdependent wells, branchlines, junctions, main trunklines, and gas/oil separators, often prove to be optimum cost solution in many fields; especially offshore fields. Large capital savings often are possible, both for initial and future facilities, as well as operating cost savings, when compared with the single well, single or looped flowline concept, producing to a centrally located gas/oil separator plant. Separate gas lines may be avoided by us of the trunk lines.
Cementing Research in Directional Gas Well Completions
Authors: Carter L. Greg , Cook Clyde , Snelson Lawrence
Published: December 2007

This paper was prepared for the Second Annual European Meeting of the Society of Petroleum Engineers of AIME, to be held in London, England, April 2–3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

This paper reviews some of the accepted causes of gas migration through a cemented column. Possible causes leading to gas migration in deviated borehole conditions have been considered in a laboratory model study. Emphasis has been primarily placed on cementing slurry properties and mechanical requirements necessary for a successful primary cementing job. Synthetic formation cores having various permeabilities were incorporated in the tests. permeabilities were incorporated in the tests. The permeable formation sand allowed early detection of gas diffusion into the wellbore as well as the migration of gas through the vertical cemented column.

Factors found to be most important for prevention of gas migration were: prevention of gas migration were:Mud-Cement Density (Effectivehydrostatic head)Cement Filtration ControlCement Viscosity or GelationBorehole Mud RemovalSetting Time or TemperaturePipe MovementCentralization

Introduction

Gas communication through a cemented annulus has been recognized as a major problem for a considerable number of years. With increased drilling activity taking place throughout the North Sea it has become increasingly difficult to combat because of the directional drilling of a number of wells from one location.

The completion of wells for the recovery of gas in a directional hole is similar in many respects to that used for the recovery of gas in a straight hole. The primary concern in any well is the isolation of zones and this is particularly difficult in the case of particularly difficult in the case of completing a well with a deviated borehole.

Previously gas migration in a wellbore was considered to exist only at the casing-cement or cement-formation interfaces, and bonding was considered to be a major cause for gas communication. This is still a major factor to contend with; however, it is not the only problem that may he responsible for gas communication between multiple permeable formations.
Kinetic Rate Expressions for Reactions of Selected Minerals with HCl and HF Mixtures
Authors: Lund K. , Fogler H.S. , McCune C.C. , Ault J.W.
Published: December 2007

This paper was prepared for the Oilfield Chemistry Symposium of the Society of Petroleum Engineers of AIME, to be held in Denver, Colo., May 24–25, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

The chemical kinetics of solid-liquid reactions were studied for different mud acid-mineral systems in a rotating disk apparatus. The minerals studied included calcite, dolomite, microcline, and albite. The kinetic rate equations, regimes of diffusion and reaction control, and possible mechanisms of dissolution are presented for these various minerals.

At temperatures above 100 degrees C, the rotating disk rate data show that the rate of reaction of HCl with dolomite is controlled by the mass transport of HCl to the dolomite surface. The HCl-dolomite reaction becomes surface reaction controlled at temperatures below 100 degrees C. At the conditions existing in petroleum reservoirs, the HCl-calcite reaction can be considered controlled exclusively by mass transport of HCl. The feldspar-mud acid reaction rate results reveal that the dissolution of feldspars is surface reaction rate limited and depends on both the HF and HCl concentrations in the mud acid.

Introduction

Acid stimulation of oil and gas reservoirs is concerned with the application of acids and acid mixtures to dissolve porous and non-porous minerals. It has great utility in enhancing the productivity of oil reservoirs through increasing the permeability of the formation by the permeability of the formation by the processes of matrix and fracture processes of matrix and fracture acidization. In matrix acidization, acid such as hydrochloric acid or a mud acid (HCl and HF) is forced to flow within the pore structure of the rock matrix. The reservoir rock characteristics are altered as the acid reacts with the clays and minerals present. In fracture acidization, the present. In fracture acidization, the acid is forced to flow along hydraulically induced fractures.
Solubility of Calcium Sulfate in Brine
Authors: Carlberg B.L.
Published: December 2007

Brine solubility of calcium sulfate is a function of several variables, including brine composition, temperature, and the hydration state of the precipitating phase. Solubility data covering these variables is included, and the need for inclusion of an additional variable—turbulence—is shown for temperatures above the normal boiling point. These data are then used to derive an expression for that solubility to about 250 degrees F.

Introduction

Calcium sulfate is one of several sparingly soluble salts commonly deposited from oil field waters. That deposition is the result of a supersaturated condition approaching equilibrium by precipitating some of its dissolved salt burden. Precipitation continues until stability has been achieved.

A number of parameters influence the solubility of calcium sulfate. Certainly one of these is the hydration state of the calcium sulfate molecule. Figure l shows solubility of the three most common forms in distilled water as a function of temperature. Solubility of calcium sulfate is also affected by temperature; salinity; excess common ion; concentration of magnesium ion; and, to some extent, pressure. This latter effect has been well covered by Vetter.

In this study of calcium sulfate solubility, we have searched the literature for data on the effects of the above-mentioned parameters. We have supplemented the available parameters. We have supplemented the available information with new, experimental data. The purpose of this paper is to present these purpose of this paper is to present these data, to note the trends revealed, and to use the information to improve prediction of calcium sulfate deposition over a wide range of temperatures, salinities, and magnesium ion concentrations. With this procedure, we can now calculate calcium sulfate scaling tendencies from waters with temperatures as high as 225 degrees F. At the elevated temperatures, an additional solubility parameter—turbulence— must also be considered.

CALCIUM SULFATE SOLUBILITY

Anhydrite

Solubilities of anhydrous calcium sulfate in water and in sodium chloride solutions are shown in Figures 2 and 3. The bulk of these data were taken from the literature shown in the attached bibliography.
Analysis of Alternate Gas Development and Market Plans by Optimizing Techniques
Authors: Wattenbarger Robert A. , Pacheco E.F. , Parsons Steven D.
Published: December 2007

This paper was prepared for the 48th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Las Vegas, Nev., Sept. 30-Oct. 3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgement of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

An economic study of development and market plans was performed on a complex area of oil and gas fields. The purpose of the study was to compare different plans for marketing gas and developing the fields prior to negotiating long term gas contracts prior to negotiating long term gas contracts for export to other countries. A nonlinear mathematical program for optimizing drilling and development schedules was applied to various cases. The study resulted in definite plans regarding minimum prices for negotiating purposes, a ranking of prices for negotiating purposes, a ranking of the desirability of each gas contract, and the order in which these negotiations should be approached.

Introduction

The problem of planning the development of multiple gas fields for a specified future market demand schedule is complicated because it requires the coordination of planning for development drilling, gathering planning for development drilling, gathering facilities, processing facilities and pipelines. The usual planning approach is pipelines. The usual planning approach is to use the "case study method" which normally involves a limited number of cases to reach the best solution possible within the available time.

The problem is complicated further when the market demand schedule has not yet been determined. Nevertheless it is a great advantage to an operator who has the responsibility for developing all aspects of the gas production and pipeline facilities, to be able to coordinate the entire planning problem prior to negotiating long term gas problem prior to negotiating long term gas contracts. A prior knowledge of optimal alternatives gives the operator an estimate of the cost of delivering gas and his ability to meet specified delivery schedules.

This paper reports a systematic approach to this type of planning problem by using a nonlinear programming computer system which has been developed for the purpose of optimizing oil and gas field purpose of optimizing oil and gas field investments.
Numerical Simulation of Edge Water Drive with Well Effect by Galerkin's Method
Authors: Vermuelen J.L.
Published: December 2007

This paper was prepared for the 48th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Las Vegas, Nev., Sept. 30-Oct. 3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

By using an Irons quadrature rule and a semi-implicit linearized scheme for relative permeabilities and capillary pressure, a permeabilities and capillary pressure, a three-dimensional two-phase variational simulator has been developed, which requires only a little more computation time than the standard finite difference models. However some difficulties arise in solving edge water drive problems by the Galerkin's methods.

Introduction

This paper presents a numerical simulator of "water tongue" displacement with well effect in a three-dimensional reservoir. Standard finite difference models do not fit to treat such problems. Indeed the three-dimensional models require many grid points for accurately describing the saturation distribution, which results in large computer times. Furthermore coning models cannot be used because of their radial symmetry.

Recently some authors tried a new approach, the Galerkin's variational method, to solve the flow equations. For classical flow problems this technique has been proved to be numerically superior to finite difference methods but it requires more computation time.

This work describes a variational simulator developed to solve the above edge water drive problem. It is a three-dimensional, problem. It is a three-dimensional, two-phase, compressible model which treats the reservoir as inhomogeneous and anisotropic. Substantially higher computing efficiency than in other known variational models has been obtained in two ways :Integrations have been more efficientlyperformed by using Irons quadraturerules. These formulae simpler than the standard gaussian rules having the sameorder of truncation error, highly reduce the computing time absorbed inintegrating the coefficients of the equations.Time-step sizes have been enlarged byusing a semi-implicit linearized scheme for relative permeabilities and capillary pressure.

Some problems have been treated and theirresults compared to those from a finitedifference model.
Development and Applications of a Downhole Tool to Detect Gas while Drilling
Authors: Tanguy D.R. , Kishel J.F. , Young D. , Kisling J.
Published: December 2007

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

A new downhole tool has been developed to indicate the presence of gas in the mud immediately above the drill bit. The new tool has many potential applications beyond the early anticipation of a kick. For instance, under favorable conditions, shallow gas bearing sands can be located without interrupting drilling operations. Consequently, drilling schedules and mud programs can be optimized for safe and programs can be optimized for safe and efficient rig operation.

No electronics is used in the downhole gas detector and no modification of the drill string is necessary. operating the tool requires only a minor variation in routine drilling operations.

Introduction

Whenever formation gases flow into the well bore during drilling operations, a potentially hazardous condition exists. As the gas rises up the well with the drilling mud, it expands, reduces the apparent density of the well fluids and, consequently, reduces the pressure which the mud can exert pressure which the mud can exert against drilled formations. Most often, the reduction of hydrostatic pressure is small and the flow of gas into the well is quickly stopped by the buildup of a mud cake on the bore walls.

However, if the initial amount of gas which enters the well as the bit cuts into the formations is high or if the mud density is abnormally low, the reduction in the well fluid hydrostatic pressure caused by the expansion-of the pressure caused by the expansion-of the gas permits more gas to enter the mud system. The additional gas causes a further reduction in the hydrostatic pressure and a corresponding additional pressure and a corresponding additional flow of gas. Unless the well is closed off, a blowout situation quickly develops.

It is obviously very important to measure as accurately and as early as possible how much gas is being added to possible how much gas is being added to the mud stream near the bit in the process of drilling. If the amount is process of drilling. If the amount is small or if the flow is only temporary, the situation will correct itself and there is no reason to stop drilling operations. However, if the flow of gas is steady, it is inevitable that a dangerous condition is developing and immediate measures must be taken. Even when the gas kick is kept under control, the time required to correct the situation and the costs incurred to do so increase rapidly with the amount of gas which is permitted to enter the well bore. The laws of physics which apply to the expansion of formation gases in the well bore do not permit a simple and early detection of the kick.
In-situ Stress and Pore Pressure in the South Eugene Island Field, Gulf of Mexico
Authors: Finkbeiner T. , Zoback M.D.
Published: December 2007

Analysis of minifracs and pore pressure surveys from sand reservoirs in a Gulf of Mexico oil field show effective stress ratios, K, that scatter significantly and do not correlate with previously published fracture gradient models for this area. The lower-bound value of K is 0.33, which corresponds to the expected value for Coulomb failure for a coefficient of friction of 0.6 in normal faulting environments. However, in some sands K approaches unity, thus indicating an essentially isotropic stress field. Hence, the data indicate a highly variable state of stress that cannot be simply related to depth or pore pressure, but appears to reflect an interaction between deformational processes and material properties.

Borehole breakout analysis in vertical wells reveals stress orientations that are predominantly perpendicular to normal faults and, hence, consistent with an extensional stress regime. Analysis of breakouts in inclined wells in two sand reservoirs allows to constrain the magnitude of the maximum horizontal principal stress, SHmax. and further indicates an active normal faulting environment with a clear, but small degree of horizontal stress anisotropy (i.e., Sv>SHmax>Shmin).

P. 69
Tectonic Controls on Fault-Zone Permeability in a Geothermal Reservoir at Dixie Valley, Nevada
Authors: Hickman Stephen , Zoback Mark , Benoit Richard
Published: December 2007

To determine factors controlling permeability variations within and adjacent to a fault-hosted geothermal reservoir at Dixie Valley, Nevada, we conducted borehole televiewer observations of wellbore failure (breakouts and cooling cracks) together with hydraulic fracturing stress measurements in six wells drilled into the Stillwater fault zone at depths of 2 to 3 km. Measurements in highly permeable wells penetrating the main geothermal reservoir indicate that the local orientation of the least horizontal principal stress, Shmin, is nearly optimal for normal faulting on the Stillwater fault. Hydraulic fracturing tests from these wells further show that the magnitude of Shmin is low enough to lead to frictional failure on the Stillwater and nearby subparallel faults, suggesting that fault slip is responsible for the high reservoir productivity. Similar measurements were conducted in two wells penetrating a relatively impermeable segment of the Stillwater fault zone, located 8 and 20 km southwest of the geothermal reservoir (wells 66–21 and 45–14, respectively). The orientation of Shmin in well 66–21 is near optimal for normal faulting on the nearby Stillwater fault, but the magnitude of Shmin is too high to result in incipient frictional failure. In contrast, although the magnitude of Shmin, in well 45–14 is low enough to lead to normal faulting on optimally oriented faults, the orientation of the Stillwater fault near this well is rotated by 40 from the optimal orientation for normal faulting. This misorientation, coupled with an apparent increase in the magnitude of the greatest horizontal principal stress in going from the producing to nonproducing wells, acts to inhibit frictional failure on the Stillwater fault zone in proximity to well 45–14. Taken together, data from the nonproducing and producing wells thus suggest that a necessary condition for high reservoir permeability is that the Stillwater fault zone be critically stressed for frictional failure in the current stress field.

P. 79
Mitigation of Heavy Oil Production Environmental Impact through Large-Scale Slurry Fracture Injection of Wastes
Authors: Dusseault Maurice B. , Bilak Roman A.
Published: December 2007

Slurry fracture injection (SFI) involves placement of solid wastes and water wider fracture pressures into deep geological formations. Currently, materials permitted for SFI include oily waste sand, "slops", produced muds, and produced water or waste water. Five years field experience has led to a good understanding of the SFI technology, and a regulatory frame- work is evolving in Alberta to permit SFI projects to proceed in an environmentally secure manner to meet the goals of the regulatory bodies as well as the goals of the oil companies.

The approach to SFI operations is described, including geological arguments related to environmental security. Security is also based on careful regulatory control, design, site selection, and analysis. The application of SFI to other waste streams should help mitigate environmental issues for heavy oil development, as well as for other oil feld applications.

P. 87
Measurement of Stress Direction and Mechanical Damage Around Stressed Boreholes Using Dipole and Microsonic Techniques
Authors: Plona T.J. , Winkler K.W. , Sinha B.K. , D'Angelo R.
Published: December 2007

In this paper the effects of borehole stress concentrations on both dipole flexural waves and azimuthally resolved, axially propagating compressional waves (i.e., microsonic) are studied. Dipole sonic logging tools provide the capability to measure acoustic anisotropy in the borehole. However, one needs to distinguish between two forms of anisotropy: intrinsic or stress-induced. A method is presented, based on an analysis of dipole dispersion curves, which can make this distinction. Once stress-induced anisotropy is determined, then the fast shear direction is the maximum stress direction. In addition, an azimuthal microsonic measurement technique is used to measure the azimuthally resolved, axially propagating, refracted compressional wave which can identify both stress direction and detect mechanical damage (i.e., zone of plasticity). Laboratory borehole experiments are presented for both dipole and compressional measurements. The experiments compare favorably with the theory of acoustoelasticity. The maximum stress direction is important in hydraulic fracturing while detection of mechanical damage can be important for wellbore stability.

P. 123
High Horizontal Stress in the Visund Field, Norwegian North Sea: Consequences For Borehole Stability and Sand Production
Authors: Wiprut D.J. , Zoback M.D.
Published: December 2007

We examine drilling-induced tensile fractures in five vertical and inclined exploration wells in the Visund oil field in the northern North Sea. Each well yields a consistent azimuth of the maximum horizontal stress both laterally and with depth.

The magnitudes of the three principal stresses (Sv, Shmin, and Shmax) are consitent with depth and reflect a strike-slip faulting stress regime. The magnitude of the maximum horizontal stress is significantly higher than the vertical (Shmax = 1.3 Sv) and minimum horizontal stresses in our models.

We determine optimally stable trajectories for borehole stability during drilling, after reservoir pore pressure drawdown.

P. 199
Wellbore Stability Predictions Using a Modified Lade Criterion
Authors: Ewy Russell T.
Published: December 2007

The two most commonly used rock failure criteria in wellbore stability analyses are the Mohr-Coulomb criterion and the Drucker-Prager criterion. Neither of these is compatible with 3-dimensional rock strength measurements that have explored the influence of the intermediate principal stress. This paper presents a modified Lade criterion which has the following desirable qualities:

it correctly describes the influence of the intermediate stress on rock strength, and therefore on wellbore stability, it can be rearranged to give a closed-form solution for critical mud weight, for any wellbore orientation, and only two rock strength parameters are required, such as cohesion and friction angle.

The modified Lade criterion predicts critical mud weight values that are less conservative than those predicted by the Mohr-Coulomb criterion yet are not as unconservative as those predicted by the Drucker-Prager criterion. It also reveals that the required increase in mud weight when going from low hole angle to high hole angle is not as great as predicted by either the Mohr-Coulomb or Drucker-Prager criteria.

P. 247
Integrated Rock Mechanics and Drilling Fluid Design Approach to Manage Shale Instability
Authors: Tan C.P. , Rahman S.S. , Richards B.G. , Mody F.K.
Published: December 2007

In recognising the petroleum industry's need for a technology to design optimal drilling fluid (weight, type and chemistry) to solve and manage shale instability problems, a collaborative project has been undertaken to develop the technology which will provide the basis for state-of-the-ant drilling fluid design criteria. The key drilling fluid-shale interaction mechanisms included in the study are mud pressure penetration, chemical potential and swelling-hydrational stress.

Fundamental concepts, processes, models and a range of novel test equipment and procedures for laboratory simulation of the mechanisms were developed. The laboratory test results were used in the refinement and verification of the models. The verified models, which have been integrated in a wellbore stability analysis software, were used to conduct analyses to demonstrate the effects of shale and drilling fluid properties on time-dependent wellbore (in)stability.

The understanding of the drilling fluid-shale interaction mechanisms and the development of the capacity to model them enabled the development of drilling fluid design charts. These charts, together with a shale property database and property correlations, provide a pragmatic and effective approach for designing optimal drilling fluids to manage shale instability efficiently.

P. 291
An Investigation of Leak-off Test Data for Estimating In-situ Stress Magnitudes: Application to a Basinwide Study in the North Sea
Authors: Edwards S.T. , Meredith P.G. , Murrell S.A.F.
Published: December 2007

The leak-off test (LOT) procedure has been examined within the theoretical framework pertaining to hydraulic fracturing stress measurements (HFSMs). LOT records have then been compared with the results of HFSMs where both measurements have been made in the same boreholes. From this comparison, we make recommendations on the use of LOT data, and suggest a new method of estimating the minimum horizontal stress magnitude () from LOT pressure/volume plots. In-situ stress magnitudes have been investigated by applying these methods to data from over 1000 LOTs in North Sea boreholes. The results of this investigation imply that tectonic stress increases significantly with depth in some parts of the North Sea. which is consistent with the mapped distribution of borehole breakouts.

P. 357
The Influence Of The Reservoir Stress-Depletion Response On The Lifetime Considerations Of Well Completion Design
Authors: Addis M.A. , Choi X. , Gunning J.
Published: December 2007

The selection of horizontal wells as barefoot and multilateral well candidates requires consideration of the well integrity over the producing life of the field. The evaluation of the production lifetime of a well requires that both the mechanical and chemical changes which the well experiences be modeled and predicted during the well design. The mechanical changes which the well will experience during production is primarily a function of stress and strength changes; the stress changes which result from depletion, the stress-depletion response, are addressed in this paper. Stress-depletion responses from reservoirs in the Gulf Coast region and in the North Sea have been collated and show a range of stress reductions which fields undergo accompanying the field-wide pore pressure depletion. The stress-depletion response of a field only addresses the minimum stress changes, consequently, the maximum horizontal stress change accompanying depletion can only be estimated using models.

The ability to predict the stress-depletion response of a field requires an understanding of what processes control the initial stress magnitudes, and the boundary conditions which the reservoir experiences during the production lifetime. The factors which define and influence the stress-depletion response of reservoirs are addressed, specifically the geological boundary conditions. The ability to model and predict the stress-depletion response of the reservoirs is then discussed, specifically focusing on the role and influence of the overburden surrounding the reservoir on the predicted response. Analytical and numerical models illustrate the influence of the material properties in the reservoir and overburden, and the reservoir size on the stressdepletion response. The ability to predict stress changes during depletion is erratic primarily due to insufficient data.

Uncertainty in the pre-production estimation of the stress- depletion response of the reservoir has a considerable impact on the predicted stability of wells in the reservoir interval. The ability to determine an accurate stress-depletion response is a principal consideration for reliable stability predictions and design recommendations for horizontal and multilateral wells.

P. 433
Investigating the Mechanics of Microcrack Damage Induced under True-Triaxial Unloading
Authors: Pettitt W.S. , Young R. Paul , Marsden J. Robert
Published: December 2007

The stress path experienced by a rock mass, during and immediately after excavation is complex and cannot be replicated by a simple loading of samples to induce microcracking. We have simulated excavation stresses in the laboratory by true-triaxial unloading. To do this we have utilised an existing polyaxial system at Imperial College and modified it to undertake acoustic emission (AE) monitoring. We have then used triaxial strain, measurements, three- dimensional ultrasonic surveys and Ali studies to investigate laboratory induced cracking. In particular we have developed and applied a moment tensor inversion procedure to located AE. This allows a direct analysis of the mechanics driving the cracking. We present and compare results from two tests (triaxial loading and triaxial unloading) using Springwell sandstone to show the capabilities of the laboratory and processing techniques. The AE source mechanisms in both tests are shown tu have a significant isotropic component. The mechanics of the cracking fits neither a Mode I tensile or shear source, but a combination of the two. The mechanism orientations agree with cracking parallel to.

P. 509
Micromechanical Modelling of Acoustic Emissions
Authors: Hazzard J.F. , Maxwell S.C. , Young R.P.
Published: December 2007

Micromechanical models of high porosity chalk and low porosity granite are presented to examine the mechanics of cracking and failure that occur in the rocks when they are subjected to stress. The models are run dynamically (with low numerical damping) to allow for dynamic fracture propagation and so that acoustic emission (AE) information can be obtained. Seismic parameters such as source location, magnitude and crack type are calculated internally within the models. It is also shown how it is possible to calculate this information externally through waveform inversion of synthetic AE. These methods are used to compare the acoustic behaviour of compacting chalk models with different porosities. It is shown that low porosity chalks are more seismically active than those with high porosities. The methods are also applied to observe the cracking and eventual macrofailure that occurs in axially loaded granite samples. The micromechanics of tensile cracks occurring during loading of the granite are examined directly by observing the particle motions at the source, and indirectly by recording waveforms and calculating seismic parameters.

P. 519
Elastoplastic Finite Element Analysis of Inclined Wellbores
Authors: Zervos A. , Papanastasiou P. , Cook J.
Published: December 2007

An effective finite element model which can be used for elastoplastic analysis of inclined wellbores is presented. The same discretised model can be used for any wellbore inclination and azimuth by varying only the applied initial stress field or boundary conditions. The model is applied for calculating the optimum drilling mud-pressure assuming an elastoplastic rock behaviour and different failure criteria. The rock material parameters were derived from triaxial compression tests. The results show that the difference in mud- pressure predictions between elasticity and plasticity depends strongly on the employed failure criteria. The difference between elasticity and plasticity becomes more pronounced with a criterion which allows the material near the borehole wall to reach a critical plastic strain determined from the calibration tests. In such a case differences from 45% to 80% were encountered. Calibration factors given by the ratio of plasticity predictions over the elasticity predictions have been derived and can be used with analytical models for quick field wellbore stability computations.

P. 535
Measurement of Velocity Changes Induced In Cores By Saturation Changes, Water Flood, and Drawdown.
Authors: Jones C. , Somerville J.M. , Smart B.G.D. , Hamilton S.A.
Published: December 2007

4 D seismic measurements are used to monitor changes during the production and stimulation of a reservoir. Parameters such as the type of fluid fill, porosity and pressure distribution are obtained from the results. Interpretation is difficult and is complicated by stress sensitive matrix properties, and phase sensitive fluid properties. Interpretation depends on some theoretical scheme such as Gassmann's equation. Such formulations require a detailed knowledge of the velocity of sound in the fluids present and compression and shear wave velocities in the matrix. These velocity values are obtained from a combination of field and laboratory measurements.

P. 555
Direct Observation and Modeling of Sand Production Processes in Weak Sandstone
Authors: Nicholson E.D. , Goldsmith G. , Cook J.M.
Published: December 2007

Sanding experiments were carried out on weak sandstones with uniaxial compressive strengths in the range of 2 MPa to 25 MPa. The sandstones were either reservoir rocks or those with appropriate physical and mechanical properties to be good model materials.

The experiments involved simulating a perforation or openhole well, by flowing fluid/gas down a hole in a cylindrical rock sample. No radial flow component was present. The flow velocity could be varied, while the sample was hydrostatically stressed to values up to 70 MPa. Deformation of the hole, and the initiation and subsequent flow of sand are viewed and monitored using a specially designed optical method.

Significant differences in behavior were seen for the different rock types. The weakest rock showed compactant behavior, whereas the stronger rocks showed a more brittle response with the formation of breakouts in sanding tests.

The data will be used in the future in the elastoplastic modeling of the perforation geometry.

Experiments of this type provide a simple route to direct observation of sanding in experimental perforations or openhole wells, and give new insight into the mechanisms of failure and the diversity of these mechanisms with different rock types.

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A Constitutive Model For Swelling Shales
Authors: Molenaar M.M. , Huyghe J.M. , van den Bogert P.A.J.
Published: December 2007

The main operational parameters controlling borehole stability in drilling shales are the density and the chemical composition of the drilling fluid. The density of the drilling fluid provides support of the borehole wall, while the chemical composition of the drilling fluid can be adopted to reduce the infiltration rate and to maintain hole stability for prolonged exposure time of the drilling fluid to the shale.

To describe the interaction between the drilling fluid composition and the mechanical behaviour of shales, an electro-chemo-mechanical formulation of quasi-static finite deformation of swelling compressible porous media has been derived from the theory of mixtures. The model presented in this paper, which is applicable to biological tissues and synthetic hydrogels also, consists of an electrically charged porous solid, saturated with an ionic solution. The mixture as a whole is assumed electro-neutral.

Four phases following different kinematic paths are defined: solid, fluid, anions and cations. Balance laws have been derived for each constituent and for the mixture as a whole. A Lagrangian form of the second law of thermodynamics has been derived to formulate the constitutive relations for the swelling behaviour of shales as well as the transport equations for the fluid and the ions.

P. 127
Application of Yield Design For Understanding Rock Cutting Mechanism
Authors: Challamel N. , Sellami H.
Published: December 2007

This paper deals with the analysis of the response of rock material subjected to the cutting action of a PDC (Polycristalline Diamond Compact) cutter. Following a phenomenological characterization, we show the importance of the maximum loading in understanding the rock cutting mechanism. This parameter is analytically approached using the formalism of the yield design. Cutting tests carried out in Vosges sandstone at atmospheric pressure showed the existence of additional forces acting on the cutter and not predicted by the model. These forces, related to the rock microstructure, induce a change of the rock failure. As they cannot be neglected at this solicitation scale for many geomaterials, they are a major stake of rock cutting.

P. 153
Predicting Rock Mechanical Properties from Wireline Porosities
Authors: Edimann K. , Somerville J.M. , Smart B.G.D. , Hamilton S.A. , Crawford B.R.
Published: December 2007

The rock mechanical behaviour of reservoir rocks is important in the design and implementation of drilling and production programmes. Traditionally rock mechanical properties are obtained from direct measurement on core samples or from mechanical calculations on acoustic wireline log measurements. This paper reports the rock mechanical properties of many different reservoir rocks of different porosities. This has led to the development of a new method of predicting rock mechanical properties directly from porosity. The paper discusses the measurement of experimentally derived porosity, elastic moduli and fracture strength parameters and the intetpretation of these mechanical properties results into direct correlations with porosity. The application of these results to obtain continuous rock mechanical property plots of the reservoir from wireline derived porosity is discussed. The practical use of these rock mechanical property profiles in drilling, production and enhanced reservoir simulation is also emphasised.

Porosity (), modulus of elasticity (E), Poisson's Ratio (v), uniaxial compressive strength (UCS), cohesion (), angle of internal friction (), and triaxial stress factor (k), were measured on samples from a wide range of North Sea reservoirs using a conventional triaxial testing machine. This paper describes the procedure used and presents the correlations obtained from plotting each of the rock mechanical properties against porosity. The derivation of wireline porosities along with empirical corrections are presented and the results of applying the correlations to these wireline derived porosities to produce continuous rock mechanical property plots are discussed. Logs were calibrated to core-measured values to reveal realistic elastic and inelastic moduli profiles. The continuous property logs provide a reasonable estimate of the possible behaviour at discrete points throughout the reservoir interval, but they are limited in their description of the behaviour of individual beds as coherent bodies. A technique has been developed to pick out these individual beds and assess how they will perform as Rock Mechanical Coherent Units, i.e. sets of beds that perform in a similar or dissimilar manner to adjacent layers. Finally a discussion on how the results are used to aid production and generate enhanced reservoir simulation will be presented.

P. 169