bluuebunny/crossref_metadata_2025 huggingface dataset:
Using Rotating Control Devices Safely in Today's Managed Pressure and Underbalanced Drilling Operations
Authors: Cantu Joseph A. , May James , Shelton Jaye
Published: December 2007

In today's Underbalanced and Managed Pressure Drilling environments the Rotating Control Device (RCD) is no longer simply a flow diverter, but is a key piece of well control equipment and the critical first safety defense to prevent escape of well fluids during critical drilling operations. The RCD should not be considered just another piece of rental equipment to be called out at the last minute. When planning a UBO or MPD well it is important to consider the RCD, and consult with the supplier early in the planning stages.

This discussion will attempt to identify the information required to properly select the RCD device and trim, define ancillary equipment needed, and assign responsibilities to various parties to ensure that fit for purpose materials and information are available at the rig site when needed. Procedures and safety precautions for installing the device will be addressed. Operational considerations to insure safety while drilling and maintaining the sealing elements and bearings will also be covered.
Benefits and Challenges Associated with CRA Injection Tubing in Corrosive Gas Wells
Authors: Sullivan R. xsB. , Hinson D. L. , Hendrix D. E.
Published: December 2007

The use of chemical injection (1/4" capillary) strings has gained tremendous popularity in the oilfield during the last few years. Application of these duplex stainless steel strings are now routinely used not only for corrosion chemical injection but also for injecting fresh water where downhole salt precipitation is present, as well as injection of foamer to address water loading issues.

This paper describes an exhaustive investigation into the repetitive failure of these orbital welded duplex stainless steel strings due to environmental cracking in Anadarko's prolific Bossier play. Anadarko currently is very active with 12 drilling rigs running in Freestone County, Texas. The Bossier formation is encountered at a depth of 13,000 ft with a bottom hole temperature of 300 deg F. The gas stream typically contains 3% CO2, 3-5 ppm H2S, and the produced water is saturated with chlorides.

Failures have occurred in numerous wells throughout the field. The paper details the root cause failure analysis investigation conducted, and the influence of well environment, tubing manufacturing process, and tubing material properties in failure. A risk-based approach was used in an attempt to predict tubing failure based on well conditions and material properties. The risk matrix was rationalized against a database of approximately 70 tubing failures. Parameters used in the risk matrix included weld type, weld and base metal hardness, and austenite/ferrite volume fraction ratios. The rationale and factors influencing replacement-tubing decisions (alternate metallurgy) to minimize the occurrence of failures is also described.
Fast Method Finds Infill Drilling Potentials in Mature-Tight Reservoirs
Authors: Guan L. , Du Y.
Published: December 2007

Infill drilling has been identified to play an important role in improving oil or gas recovery in the tight hydrocarbon fields. But quantifying the infill drilling potentials in producing tight hydrocarbon fields is often a challenging problem, due to large variability in rock quality, well spacing, well completion practices, and the large number of wells involved. At the same time, with the increasing demand for energy and favorable oil and gas prices, more and more fields all over the world are undergoing infill drilling. It is not uncommon for a company to have hundreds or thousands of infill candidates to choose from. Complete integrated reservoir studies to determine infill potential are often very time-consuming and costly for many tight hydrocarbon fields.

This paper presents an alternative approach to conduct detailed reservoir studies to find infill drilling potentials in tight hydrocarbon basins. This method can quickly evaluate the infill drilling potentials within weeks even with thousands of wells. Several field examples are provided to demonstrate the application of the method in mature-tight gas basins and the primary advantages of the technique are its speed and reliance upon well location and production data only.
Pushing Fracturing Limits to Maximize Producibility in Turbidite Formations in Russia
Authors: Rueda J. I. , Mach J. , Wolcott D.
Published: December 2007

Engineers use boundary-dominated productivity equations for fracture designs in medium permeability formations. These equations are critical to optimize fracture designs and are different for primary depletion and formations under waterflooding processes.

This paper presents two new models to calculate the dimensionless productivity index, JD, of finite-conductivity fractured wells producing either at pseudo-steady or steady state conditions. These models use a new "definition" of the equivalent wellbore radius to incorporate the finite conductivity and fracture penetration dependency of the solution. New easy-to-use correlations (from 1500 numerical simulation runs) to calculate consistent shape factors and f-functions for fractured wells are also presented in the paper. The f-functions are an extension to PSS and SS conditions from the Cinco-Ley’s original work. These equations are used to regenerate JD type curves of a finite-conductivity fractured well under pseudo-steady or steady state conditions. A comparison of the JD type curves of SS versus PSS is also presented. The maximum JD value, for fully penetrated infinite conductivity fractured well was 4/PI for SS versus 6/PI for the same case under PSS.

These productivity equations are also used to understand more post-fracturing production performance and to push the limits in hydraulic fracturing by injecting very large volumes of proppant of very large retained permeability. The paper will present the production results of the evolution of this hydraulic fracturing technique in these turbidite formations in Russia. It will be shown how the dimensionless productivity indices have been improving as the proppant volume per foot and proppant size has been increased. Statistics has shown how productivity index JD has increased from 0.3 to 0.55 when proppant concentration is increased from 4 tons/meter to 8 tons/meter. Definitely, pushing the fracturing limits in Russia has had a great impact on the production increase on these turbidite formations.
Optimization of PDC Drill Bit Performance Utilizing High-Speed, Real-Time Downhole Data Acquired Under a Cooperative Research and Development Agreement
Authors: Roberts T. S. , Schen A. E. , Wise J. L.
Published: December 2007

PDC drill bit performance has been greatly improved over the past three decades by innovations in bit design and how these designs are applied. The next leap forward is most likely to come from using high-speed, real-time downhole data to optimize the performance of these sophisticated bits on an application-by-application basis. By effectively managing conditions of lateral, axial and torsional acceleration, damage to cutting structures can be minimized for improved penetration rates. Avoiding these damaging vibrations is essential to increasing bit durability and improving overall drilling economics.

This paper describes one set of independent drilling optimization results obtained as part of a series of controlled demonstrations of PDC bits. Sandia National Laboratories on behalf of the U. S. Department of Energy (DOE) managed this work. The effort was organized as a Cooperative Research and Development Agreement (CRADA) established between Sandia and four bit manufacturers with DOE funding and in-kind contributions by the industry partners. The goal of this CRADA was to demonstrate drag bit performance in formations with degrees of hardness typical of those encountered while drilling geothermal wells.

The test results indicate that the surface weight-on-bit (WOB), revolutions per minute (RPM) and torque readings traditionally used to guide adjustments in the drilling parameters do not always provide the true picture of what is really taking place at the bit. Instead, a holistic approach combining traditional methods of optimization together with high-speed, real-time data enables far better decisions for improving bit performance and avoiding damaging situations that may have otherwise gone unnoticed.
New Bit Design, Cutter Technology Extend PDC Applications to Hard Rock Drilling
Authors: Clayton Robert , Chen Shilin , Lefort Guy
Published: December 2007

An advanced series of PDC drill bits incorporating a new highly abrasion-resistant PDC cutter has extended effective PDC bit application to hard rock drilling. In direct offset comparisons, the advanced series of PDC bits fitted with the new cutters delivered significant increases in footage drilled and rate of penetration.

To achieve an optimum match in drilling efficiency and bit life to lower costs and mitigate risk in hard rock environments, the series is designed using a combination of advanced modeling capabilities and sophisticated analytical tools. These tools allow the designs to be "customized" for specific applications, optimizing cutting efficiency and durability according to specific rock properties and drilling parameters. A transitional drilling model simulation allows evaluation of how cutting forces are affected during transitional drilling, common in "hard rock" environments. The bit design is globally balanced to optimize axial, lateral, and torsional forces, and can be modified by adjusting features such as profile shape, cutter rake angles, impact arrestors, and cutter type, to optimize bit performance when drilling in hard and transitional environments.

In addition, recognition of a third dimension of PDC performance – Thermal Mechanical Integrity (TMI) -- has lead to development of a new PDC cutter that provides 13.5 times the abrasion resistance of the industry standard, without sacrificing impact resistance. This improved understanding of PDC cutter failure provides a different way of looking at the traditional characteristics of abrasion and impact, enabling cutter durability to be optimized in both abrasive and hard, inter-bedded formations.

The paper discusses the science behind the advanced series of bits, including the impact of TMI on cutter performance. New laboratory capabilities and testing results are described, and actual field case histories presented to demonstrate performance improvements of these PDC bits in hard rock applications.
New Platform Rigs: Design and Construction
Authors: Nichols J. , Emans M. , Witton D.
Published: December 2007

There have been a number of dry tree developments over the past 5 years where new build drilling facilities have been designed and constructed as an integral part of the overall platform.

Each project has approached the specification, design and integration of the rig using different contractual arrangements. For example, the stage at which the drilling design team, the equipment suppliers, the fabricator and the drilling contractor become involved has varied widely between projects.

The degree of success of these integrated drilling facilities projects, both in terms of the rig being delivered on time and within budget, and also then operating as intended, has at best been variable.

The paper will describe the approach taken for the Benguela Belize project that started detailed design in February 2003. The fully mechanised 4,600hp rig is currently being commissioned in Houston and will sail away in February 2005 following the completion of onshore commissioning and acceptance.

The paper will cover how the project has been set up, including the development of an appropriate safety culture, the detailed design, fabrication, onshore commissioning and the training of the senior drill crew members prior to sail away.

The lessons learned from designing an appropriately specified rig and integrating the rig systems with the topsides contractor throughout the design will be discussed.
Understanding Torque and Drag: Best Practices and Lessons Learnt from the Captain Field's Extended Reach Wells
Authors: Rae G. , Lesso W. G. , Sapijanskas M.
Published: December 2007

This paper describes how torque and drag (T&D) analysis was used to successfully drill extended reach (ERD) wells in the Captain field in the North Sea. The issues and best practices associated with using this basic real-time drilling technique, particularly on Captain subsea development wells drilled from 2000 to 2003, are explained. The paper also explains the tactics used in overcoming issues such as how far could we drill and the associated risk. The applicability of available T&D reduction technologies and why many of them were eliminated as possible solutions reinforced the criticality of good T&D analysis on this project.

The Captain subsea wells have the highest aspect ratio (unwrapped displacement [UD] / true vertical depth [TVD]) ever for development wells drilled and completed from a floating vessel. Although the wells are short in displacement for ERD wells, the shallow nature of the reservoir requires the application of T&D analysis, which has been at the core of good ERD drilling principles and practices for some time.

This paper outlines what T&D analysis is and why it is important. The design of the bottomhole assembly (BHA) and drilling string, drilling string buckling, friction factor (FF) analysis, casing sanding considerations, trajectory design, and wellbore tortuosity all must be considered in applying this basic technique to field operations. Other issues such as why it is often misunderstood or badly applied, the importance of calibration with offset data, and conditions that effect FF determination are explained.
Development and Testing of an Expandable Casing Patch System
Authors: Braddick B. O. , Jordan G. D. , Baker S. F. , Stulberg M. A.
Published: December 2007

Since the early years of cased hole completions, casing patches of various designs have been used to seal off annular leaks down hole. Casing patches of prior art would typically restrict the operator the ability to run large diameter tools below the patch leaving the well bore with a less than desirable tubing size for completions. Also, current designs of casing patches that are available are typically weaker with respect to the pressure integrity of the patch itself.

Recent interest along with the technological advances of expandable tubulars have led to a new design of casing patch that permits a more desirable size of completion string. In addition to this, it was also realized in the design and testing phase, that a patch could be developed with pressure integrity that meet or exceed the tubing and/or casing string in which it is set.

This paper will focus on the unique features of this high pressure, large thru bore expandable casing patch system from the initial customer contact, to the trials and tribulations of the design and the research and development testing process. Actual field use of the tool including applications and sizes will also be briefly discussed, as the patch system has been deployed in wells ranging from the Texas panhandle to Wyoming1.

In conclusion, this paper will discuss how the developmental process of this particular tool has led the manufacturer to the design of several other new tools for various down hole applications.
Application of a New Mechanistic Parachor Model to Predict Dynamic Gas-Oil Miscibility in Reservoir Crude Oil-Solvent Systems
Authors: Ayirala Subhash C. , Rao Dandina N.
Published: December 2007

Interfacial tension (IFT), being an important thermodynamic property of the interface between two fluid phases in contact, can be used for phase behavior characterization, interpretation of fluid phase equilibria and miscibility. In order to examine these multitudes of roles played by interfacial tension, gas-oil IFT measurements were carried out for Rainbow Keg River (RKR) and Terra Nova reservoir fluids at elevated pressures and temperatures [1, 2]. A computerized drop shape analysis technique was used to fit the actual drop profiles of pendent oil drops with the iterative solution of the Laplace capillary equation for gas-oil IFT determination. These measurements have enabled the development of a new gas-oil miscibility determination technique called the vanishing interfacial tension (VIT) technique [1, 2].

In this paper, we propose a mass transfer enhanced mechanistic Parachor model to predict the gas-oil IFT at reservoir conditions and to identify the governing mechanism of mass transfer to attain fluid phase equilibria. The proposed model incorporates the ratio of diffusivities between the fluid phases raised to an exponent to account for mass transfer effects. The proposed model resulted in good IFT predictions as well as indicating that vaporization of light hydrocarbon components from crude oil to gas phase is the governing mass transfer mechanism for the attainment of fluid phase equilibria in these two reservoir fluids. The sensitivity studies on model results indicate that the provision of a single experimental IFT measurement is sufficient for accurate IFT predictions at other conditions from the model. Regression equation has been developed relating the exponent in the mechanistic model to the normalized solute compositions present in either of the two fluid phases for RKR and Terra Nova reservoir fluids. This regression equation, if generalized, using more reservoir crude oil-solvent systems, can be used for a-priori prediction of exponent in the mechanistic model by simply knowing the reservoir fluid compositions, without the need for experimental measurements. The use of diffusion coefficients in the mechanistic model indicates dynamic nature of IFT, thus enabling the use of model predictions to determine dynamic gas-oil miscibility in gas injection EOR projects.
Steady-State Propagation of In-situ Combustion Fronts with Sequential Reactions
Authors: Akkutlu I. Yucel , Yortsos Yannis C.
Published: December 2007

The sustained propagation of a combustion front is necessary for the improved recovery of oil during an in situ combustion process. In situ combustion involves the added complexity of chemical reactions. In this paper, combustion will involve two sequential oxidation reactions. High-temperature oxidation represents proper combustion, its fuel generated by the preceding low-temperature oxidation. The interaction between the two reactions in the presence of reservoir heat losses and their overall influence on front propagation are investigated using a perturbation, analytical approach, based on the assumption of large activation energies. The places where the reactions occur are treated as spatial discontinuities for heat and mass fluxes, across which appropriate jump conditions are developed. Under certain conditions, the two reaction regions are coupled and travel coherently with the same velocity. The corresponding parameter space is delineated. The resulting common velocity is investigated as a function of the various parameters, including heat losses. The work finds application to our understanding of in-situ combustion processes and their application to oil and bitumen recovery.
Drilling Further with Water-Based Fluids—Selecting the Right Lubricant
Authors: Knox D. , Jiang P.
Published: December 2007

This paper summarises the results of extensive laboratory work carried out in recent years to determine the performance of a number of experimental and commercially available lubricants for reservoir applications. The laboratory work included a series of tests to determine formation damage potential in both completion brines and low-solids, water-based reservoir drilling fluids, as well as reduction in friction coefficient.

The testing to evaluate formation damage potential included brine miscibility, greasing and emulsion formation potential, as well as return permeability testing on outcrop sandstone.
Planning EOR Projects
Authors: Hite J. Roger , Avasthi S. M. (Sam) , Bondor Paul L.
Published: December 2007

High oil prices and concerns about future oil supply are leading to a renewed emphasis on Enhanced Oil Recovery (EOR), a group of technologies which can significantly increase the recovery factor of oil reservoirs. Some of these EOR technologies are currently producing substantial incremental oil; others have not yet made a commercial impact. As all EOR processes are reservoir- and reservoir fluid-specific, it is necessary to identify the appropriate EOR technology for use in a reservoir, design the project to achieve the required economic incremental recovery, and manage the project to meet or exceed expectations. This paper discusses how to plan, design and manage an EOR project, proceeding from process selection through geologic analysis and modeling, project economics, project design, pilot testing (when and if required), and project implementation and surveillance. In each stage, key risks are identified, and actions to minimize those risks are given.
On the Inverse Problem of the Estimation of Multiphase Flow Functions
Authors: Nieto V. L. , Savioli G. B. , Bidner M. S.
Published: December 2007

An inverse method is described for simultaneously obtaining relative permeability and capillary pressure curves from measurements taken during an unsteady state oil-water flow experiment at the laboratory. This inverse method algorithm has four basic components: 1) an IMPES finite-difference numerical simulator of the flow through the core; 2) functional representations-power law models or piece-wise linear splines-of relative permeability and capillary pressure curves in terms of a set of adjustable parameters found by minimizing an objective function; 3) the objective function, formed by the sum of the square of the differences between the experimentally measured and the numerically simulated data; 4) the Quasi-Newton Approximation for the Least-Squares Problem (QNA) technique to minimize that objective function. The method is tested with synthetic and experimental data.

The QNA optimization technique performs better than other methods of the Newton type. Besides, it is simpler to implement than the genetic and optimal control algorithms. The accuracy of the relative permeability and capillary pressure estimations depends on the objective function definition. That definition, in turn, depends of the different kinds of available measurements (flow rates, pressure drop, saturation profiles at different times) and of the functional representations (power functions or piece-wise linear splines) of relative permeability and capillary pressure curves. Automatic history matching of a laboratory two-phase displacement to obtain relative permeabilities and capillary pressure is a classical ill-posed inverse problem. The solution of the lack of uniqueness and convergence of the method cannot be warranted for all cases by the introduction of more data (i.e. saturation profiles), more refined functional representations (piece-wise linear splines) or better optimization techniques.
The Use of Tracers to Characterize Highly Heterogeneous Fluvial Reservoirs: Field Results
Authors: Badessich M. F. , Swinnen I. , Somaruga C.
Published: December 2007

Proposal

Before the start of an enhanced oil recovery project it is important to adequately describe the architecture of sand bodies, preferential flow directions and permeability barriers.

As a consequence of project implementation operating costs tend to increase so in order to guarantee the economic success of the venture, reservoir surveillance plays a major role. This is mandatory in highly heterogeneous reservoirs where it becomes strictly necessary to identify and adjust any deviation from the anticipated response to injection.

This paper presents the results of the use of chemical and radioactive tracers in Grupo Neuquen reservoir, Loma Alta Sur field, Argentina. The objectives have been to improve the dynamic description of the reservoir previous to the injection of costly polymers and surfactants and to optimise the secondary flood by increasing volumetric sweep efficiency.

This field has been in production since 1990. Water injection started in 1993 and due to field observations of poor reservoir connectivity an intensive programme of tracers was recommended. Three injectors were inoculated, one of them with ammonium thiocyanate and the rest with tritiated water. Fifteen producers were monitored throughout twelve months.

Field data is presented in this report. It shows that hydraulic connectivity is higher than expected although fluid migration among wells is highly variable depending on reservoir transmissibility and channel orientation. For wells separated only 300 feet arrival times of few hours were reported. From these observations it was concluded that many sand bodies still produce under primary recovery. Sands with better transmissibility and continuity are constantly recycling injected water contributing little to reduce oil saturation. As a consequence a full field reservoir description in a sand by sand basis was initiated before the implementation of an EOR process.
New Analytical Pressure-Transient Models to Detect and Characterize Reservoirs With Multiple Fracture Systems
Authors: Dreier Jürgen , Ozkan Erdal , Kazemi Hossein
Published: December 2007

This paper presents two new pressure-transient models for naturally fractured reservoirs. The analytical models consider flow in a quadruple-porosity system that consists of a triple-fracture network with a single-matrix system. The models are used to investigate the pressure-transient characteristics of quadruple-porosity systems. They can also be used to detect, characterize, and simulate naturally fractured reservoirs with quadruple-porosity characteristics. It is shown that the fracture interconnectivity can be determined from pressure-transient tests if the combined fracture storativity is sufficiently large and the matrix contribution can be unambiguously isolated. Regression analysis of pressure-transient tests in naturally fractured reservoir with quadruple-porosity behavior is also discussed. It is demonstrated that the standard regression techniques are very sensitive to the scatter of the pressure vs. time data.
Successful Field Surveillance Using Portable Multi-Phase Flow Meter in a High Gas-Volume Fraction and High Water-Cut Application in East Kalimantan, Indonesia
Authors: Wangsa S. , Latief R. , Kaura J. , Finley D. , Ogilvie A.
Published: December 2007

Total Indonesia had been finding it increasingly more difficult to obtain direct measurement of produced oil from some of their remotely located fields. The production wells that needed testing were in a mature field in a swamp location and had high water-cuts (WC) and extremely high gas-volume fractions (GVF). The WC and GVFs in these fields range from 80 to 100% and 90 to 100%, respectively. Moreover, most of the wells have low potential and are very sensitive to back-pressure. All these characteristics as well as their logistics made accurate measurement of production from the wells in this area extremely challenging. As a result, the time interval between the well tests was ever increasing (more than one month).

In order to achieve more frequent performance data, and thus, enable more effective work-over decisions, the suggestion was made to evaluate use of a portable multi-phase flow meter (MPFM) to resolve the measurement problems.

The initial well tests yielded MPFM total liquid flow-rate readings that were ±30% of the test separator readings; the MPFM gas rates were ±25% of the separator reading. The operator's requirement was for the MPFM to be within ±10% of the test separator readings. Since these disparities were attributed to the extremely high GVFs that had been encountered on these wells, modifications to the present MPFM system were needed to

Reduce the GVF going through the meter Reduce the uncertainty of the meter measurements Improve the accuracy of the meter Increase the meter operating envelope.

Subsequently, a gas knock-out (GKO) vessel was designed and constructed to address the above needs. The GKO vessel was designed within a predetermined set of constraints so as to achieve the desired results.

The GKO vessel was installed immediately upstream of the multiphase meter. After incorporating the GKO vessel with the MPFM, the new "hybrid" system was used to test the same wells that had been tested earlier. The results using the MPFM and the GKO vessel yielded liquid rates and gas rates that were within ±10% of the test separator.
Why so Many Different Types of Wells on Njord?
Authors: Talukdar Saifullah , Brusdal Lill Harriet
Published: December 2007

The Njord Field is one of the most complex reservoirs in the Norwegian North Sea due to a large number of faults. Seismic quality in the heavily faulted areas is poor making seismic interpretation difficult. Typically the uncertainty in top structure is in the order of 10-100 m.

The well design criteria on Njord are dependent on the structural uncertainty and the availability of new technology. Njord started with relatively simple single-bore horizontal wells. This design was not suitable in the intensely faulted areas. High amplitude U-, S- and W-shaped wells have been effective to penetrate all reservoir units in uncertain areas, to minimize the risk of hole-instability and to drain oil from multiple fault compartments.

The need for placing a well in the best reservoir interval, to penetrate longer reservoir section and to drain oil from sparsely located undrained compartments led to drill a tree-branched well in the recent days. A new active visualization assisted geo-steering technology coupled with biostratigraphy has been tremendously successful to steer the well path in the most complicated area. Another well has been drilled in another heavily faulted area where the pressure depletion in some of the compartments was in excess of 300 bar.

The drive for a cheaper way of drilling sparsely located relatively smaller undrained pockets led to initiate a new campaign to find and drill low cost infill targets using the Through Tubing Rotary Drilling technology. Intensive research and development activities have been undertaken to resolve outstanding issues, such as, protection of X-mas tree and down hole safety valve, risk for mud loss and differential sticking, zone isolation by swell packers, etc.

This paper summarizes the reasons for adopting so many different well types, and a comprehensive description on their planning, execution, challenges, successes and failures.
Effect of Ultrasonic Waves on the Capillary-Imbibition Recovery of Oil
Authors: Hamida T. , Babadagli T.
Published: December 2007

Although the effects of ultrasonic irradiation on multiphase flow through porous media has been studied in the past few decades, the physics of the acoustic interaction between fluid and rock is not yet well understood. Insight into the physical principles governing the mobilization of oil by ultrasonic waves is vital for developing novel techniques of oil extraction.

Various mechanisms may be responsible for enhancing the flow of oil through porous media in the presence of an acoustic field. Capillary related mechanisms are peristaltic transport due to mechanical deformation of the pore walls, reduction of capillary forces due to the destruction of surface films generated across pore boundaries, coalescence of oil drops due to Bjerknes forces, oscillation and excitation of capillary trapped oil drops, forces generated by cavitating bubbles, and sonocapillary effects.

This paper aims at identifying and analyzing the influence of high-frequency, high-intensity ultrasonic radiation on capillary imbibition. Laboratory experiments were performed using cylindrical Berea sandstone and Indiana limestone samples with all sides (co-current imbibition) and only one side (counter-current imbibition) open to flow contacting with the aqueous phase. The oil saturated cores were placed in an ultrasonic bath, and brought into contact with the aqueous phase. The recovery rate due to capillary imbibition was monitored against time.

Air-water, mineral oil-brine, mineral oil-surfactant solution and mineral oil-polymer solution experiments were run each exploring a separate physical process governing acoustic stimulation. Water-air imbibition tests isolate the effect of ultrasound on wettability and capillarity, while oil-brine imbibition experiments help understand the ultrasonic effect on viscosity and interfacial interaction among oil, rock and aqueous phase. We observed a substantial increase in final recovery (up to 15%), and a slight increase in recovery rate when ultrasonic waves were applied. A modified form of an exponential model was employed to fit the recovery curves to clarify the factors causing an incremental recovery by ultrasonic waves for different fluid pairs and rock types.
Abandonment of the NW Hutton Platform Wells
Authors: Kirby Steve , Skelly Garry , Campbell Ken
Published: December 2007

This paper discusses the systematic approach adopted by BP Exploration to achieve its objective of safely recovering the tubing, casing and conductors from the wells on a major North Sea Platform. An integrated team, comprising oil company engineers and key service company personnel developed processes and procedures to reach the objective. The project applied conventional and non-conventional technology to address the issues. This approach facilitated the timely and cost effective recovery of 40 wells in a safe and environmentally friendly manner and in achieving world-class performance.
Fracture Closure Stress (FCS) and Lost Returns Practices
Authors: Dupriest Fred E.
Published: December 2007

In the mid 1990's the operator's lost returns mitigation practices were modified to align with a simple, but robust, rock mechanics concept that described the manner in which LCM and other products work. The model holds that regardless of the type of treatment used, integrity is increased by widening the fracture to increase its closing stress. Field practices have been changed to enhance a variety of mechanisms that may play a role in this process. Depending on the product, these mechanisms may include development of an immobile mass, deposition of solids in layers, development of viscous resistance, and the deposition of adhesive solids. The paper presents the development of the rock mechanics perspective, the resulting Fracture Closure Stress (FCS) Practices, a treatment selection guide, worldwide results, and discussion of the key factors that continue to limit performance in some situations.
Achieving Long-Term Isolation for Thin Gas Zones in the Adriatic Sea Region
Authors: Moroni N. , Vallorani F. , Johnson C. , Perez D. , Bilic J.
Published: December 2007

This paper describes the application of a flexible cement system to isolate pay zones, spaced 1 m apart, in the Barbara gas field in the Adriatic Sea, off the coast of Italy. This field presents several challenges to achieving long-term zonal isolation—crossflow between pressured zones, changing mud weights, and a high-pressure cold-fluid injection fracture treatment. One or more of these conditions may contribute to a loss of isolation; hence, there is a need for an effective sealant material that can handle these challenges. Conventional cement systems have been unable to address zonal isolation at such a scale.

In view of these various challenges, the team in charge of cementing these wells redesigned the cement program to mitigate the risks in the field. The main objective was to minimize the Young's modulus (maximize flexibility) and maximize the compressive strength of the set cement. Thus, an extensive program was carried out to measure the mechanical properties of the set cement. The new cement program used a flexible, expandable slurry system that isolated five zones behind 7-in. casing in the Barbara gas field. A cement-bond log evaluation confirmed isolation of the pay zone. No losses were observed during cement placement across the low-fracture-gradient formations. The new slurry system brought substantial value to the operation by enabling use of 7-in. casing as the production casing. It also eliminated any interzonal pressure communication between formations and the need for an additional 5-in. liner, which saved rig time and rig costs.
Maximizing Drill Rates with Real-Time Surveillance of Mechanical Specific Energy
Authors: Dupriest Fred E. , Koederitz William L.
Published: December 2007

The concept of Mechanical Specific Energy (MSE) has been used effectively in lab environments to evaluate the drilling efficiency of bits. MSE analysis has also been used in a limited manner to investigate specific inefficiencies in field operations.3,4 In early 2004, the operator initiated a pilot to determine whether the concept might be used more broadly by rig-site personnel as a real-time tool to maximize the rate of penetration. The results have exceeded expectations. The average ROP on the six rigs selected for the three-month pilot was increased by 133% and new field records were established on 10 of 11 wells.

The MSE surveillance process provides the ability to detect changes in the efficiency of the drilling system, more or less continuously. This has improved performance by 1) allowing the optimum operating parameters to be identified easily, and 2) providing the quantitative data needed to cost-justify design changes to extend the current limits of the system. MSE analysis has resulted in redesign in areas as diverse as well control practices, bit selection, BHA design, makeup torque, directional target sizing and motor differential ratings. The use of MSE surveillance is a key feature in a family of well planning and operational practices that are referred to as the ExxonMobil Fast Drill Process (FDP). These are now being introduced in other operating areas throughout the global organization.
The Pitch of Helically Buckled Pipe
Authors: Mitchell Robert F.
Published: December 2007

The most fundamental question about helically buckled pipe is "What is the pitch?" The original development by Lubinski and Woods1 used the method of virtual work to determine a specific constant pitch. Since any constant pitch will solve the buckling equations, what is special about this solution? Perhaps pipe end conditions determined the pitch? All attempts to connect a constant pitch helix to a packer or centralizer have failed2,3. Would these two different end conditions give different pitches?

Since the buckling differential equation is non-linear, it is not surprising that no other solution has been discovered. Recently, however, new buckling solutions have been found for the vertical well problem4.

Once these solutions are known, the problem of end conditions can be posed and solved. Two possible end conditions are considered in this study: a cantilever boundary condition to model a packer, and a "pinned" boundary condition to model a centralizer. For the first time, analytic solutions were found for both problems, and interestingly, both solutions converged rapidly to Lubinski's constant pitch solution a short distance from the boundary. Furthermore, these solutions are simple and suitable for spreadsheet calculations. Many of the original Lubinski calculations remain essentially correct, such as length change and contact forces. On the other hand, the bending moment near the boundary exceeds the bending moment calculated from the Lubinski solution by as much as 20%. For this reason alone, conventional pipe buckling stress analysis must be revised.

Possible applications for these solutions include the analysis of bottom hole assemblies, drill pipe, casing, and tubing. The boundary solutions are simple formulas, suitable for spreadsheet or hand calculations.
A Method for Formation Temperature Estimation Using Wireline Formation Tester Measurements
Authors: Zazovsky A. , Haddad S. , Tertychnyi V.
Published: December 2007

Production data show that early estimates of formation temperature are often inaccurate. Fluids arriving at production facilities can have temperatures that are significantly different from the expected values; the difference is in part because of inaccuracy in heat-loss estimates. Moreover, the initial formation temperature estimate may also be significantly in error. The pitfalls in formation temperature predictions have great impact on the effectiveness of flow assurance, well completion, and production facility design and performance. Usually formation temperature is estimated from openhole and cased hole logs, slickline temperature measurements, or stabilized wellbore temperature measurement during sampling and testing operations.

A new method for determining formation temperature from wireline formation tester temperature measurements has been developed. Rather than being simulated, the thermal history covering the formation cooling phase is represented by a single unknown parameter—either the average wellbore temperature opposite the interval of production or the average heat flux from the wellbore into the formation. One of these parameters and the initial formation temperature are the only two unknowns to be determined from the temperature measurement data obtained during fluid production phase by wireline formation tester.

An inversion technique has been proposed for the formation temperature estimation based on the simplification of the thermal history simulation and the dimensional analysis of the forward problem.
Analytical Model for Casing Expansion
Authors: Ruan C. G. , Maurer W. C.
Published: December 2007

This paper presents the mechanics of expandable casings in oil and gas wells and outlines the development of a computer model based on a force and energy balance. The computer model includes effects of stress and strain, expansion-cone diameter and angle, friction between the expansion cone and expandable casing, casing length shrinkage, and expansion rate.

The model calculates changes in casing mechanical properties as expansion occurs (burst and collapse pressures) and predicts required expansion force (or liquid pressure if the expansion cone is pumped).

Examples are given that illustrate applications of the model for cone design, mechanical property evaluation, expansion force calculation (for both solid casing and sand screen expansion), and monobore design.

Model predictions have been calibrated with extensive test data and finite element analysis. Comparisons show that the model, as calibrated with real measured data, can accurately predict expansion forces and other parameters.
Challenges and Countermeasures Facing Casing Damage in Daqing Oilfield
Authors: He L. , Ye Y. , Qunyi W. , Jianwen Y. , Huilan D.
Published: December 2007

Casing damage is one of the most important problems influencing oilfield production. On the basis of the Daqing Oilfield characteristics, this paper analyzes the casing damage situation, shapes, horizon and characteristics of the damaged casing and discusses the harm of casing damage and the progress of casing damage mechanism. This article gives some suggestions for preventing and solving the casing damage. The result may be valuable to develop the similar oilfields.
Further Considerations of Heave-Induced Dynamic Loading on Deepwater Landing Strings
Authors: Zheng Nanjiu , Baker Jeffry M. , Everage S. DeWayne
Published: December 2007

The initial treatment of heave-induced dynamic loading (SPE/IADC 87152) introduced a mathematical model for estimating the dynamic axial loads imposed on a deepwater landing string by a drilling vessel's response to ocean waves. The landing string was treated as an open-ended elastic steel column with allowable variations in cross-section as a function of depth inside of a vertical wellbore.

This paper extends the investigation of heave-induced dynamic loading on deepwater landing strings to account for the mass inertia of fluid columns in the wellbore. The results presented suggest that the effect of the fluid column mass is negligible only for cases when the casing is run open-ended. For closed-end casing (especially with low clearance annuli), the resonance frequency of the landing string is lowered significantly by the fluid column, causing it to more closely match the heave excitation frequency observed for most drill ships.

Evidence is also presented to validate the original assumption that drilling vessel resonance behavior exhibits a narrowband response to ocean waves with a fundamental resonance frequency between 0.1 and 0.14 Hz (periods between 7 and 10 sec). This important assumption was based on a single drillship's MRU data and allowed reasonably accurate dynamic load approximation without having to consider high order harmonics. To validate this assumption, a spectral analysis was performed on additional heave data from several floating drilling vessels. The results are presented and suggest that the original assumption is well-founded.

Finally, the original model was calibrated with an actual landing string load case. This allowed for range specification of the model's damping coefficient, which improves the estimates of dynamic load magnitude, much like calibrating friction factors in a torque & drag model.
Technical Limit Specific Energy—An Index to Facilitate Drilling Performance Evaluation
Authors: Curry D. , Fear M. , Govzitch A. , Aghazada L.
Published: December 2007

This paper describes a method developed to represent the inherent drilling difficulty posed by the combination of rock properties, depths and pressures that make up a field's drilling environment, thereby facilitating comparisons of drilling performance from different fields that take account of varying rock "drillability". The method uses the concept of specific energy - the lower the specific energy in a given environment, the more efficient the drilling process. An algorithm has been developed to estimate the technical limit specific energy from wireline sonic, lithology and pressure data. This represents the lowest specific energy that can reasonably be expected for that combination of rock properties and pressures.

Data were analyzed from 10 wells, drilled in varying on and offshore locations, which were selected as good benchmarks for the performance achievable in their drilling environments. Three measures were used to represent drilling performance in these wells – total dry hole (excluding coring, logging and completion activities) days per 1,000 m, normal drilling days per 1,000 m, and rotating days per 1,000 m. These measures showed wide variations across the 10 wells, reflecting the range in drilling difficulty posed by the different geological environments. However, the rotating days per 1,000 m showed encouraging correlation when plotted against the wells' technical limit specific energies. The other performance measures also showed clear trends when plotted against technical limit specific energy. The existence of these correlations demonstrates that technical limit specific energy is a valid measure of whole-well drillability, and provides a benchmark against which other wells' drilling performance can be compared.

The performance measures for the new well are compared with the "benchmark performance" trends at the new well's technical limit specific energy, revealing whether the drilling performance departs substantially from the expectation for a well of similar drilling difficulty.