bluuebunny/crossref_metadata_2025 huggingface dataset:
Multilateral System Allowing 100 Level 5 Laterals Drilled Simultaneously
Authors: Freyer Rune , Kristiansen Tron , Madland Merete Vadla , Omdal Edvard , Omdal Øyvind
Published: May 2009

New completion techniques improving recovery, production rates and reducing cost and complexity are always looked for in the oil and gas industry. This paper is presenting a new concept where 100's of small level 5 laterals can be drilled simultaneously into the formation around a main wellbore. This paper presents the main concept as well as some preliminary results from qualifying the system for service in a high porosity very weak chalk reservoir. The qualification of the system is addressing three main aspects, the ability to jet a 12 meter long and 5–10mm diameter lateral, the ability to produce in high porosity weak chalk without loss of production, and simulation of production that is at least as good as or better than existing technologies like propped fractured horizontal wells, acid fractured horizontal wells and different types of openhole completions with and without liners. The experiments indicate that the system is able to achieve the results we are looking for.
Openhole Gravel Packing With Exposed Shales: Waterpack Case Histories From Underground Gas Storage Wells in Italy
Authors: Zanchi A. , Ripa G. , Colombo M. , Ferrara G. , Belleggia E. , Barbedo R. , Illuminati R. , Rezende J. , Shenoy S.
Published: May 2009

One of the major challenges in underground gas storage wells in Italy is to maximize the sand layers exposure by drilling slanted or sub-horizontal wells through several shale bodies to obtain high gas rate performances during the production and the injection cycles. This challenge has a significant effect in selection of the completion technique in these wells, which require an effective and reliable sand control for long term, and open-hole and large tubular size to minimize friction losses.

Until now, standard open-hole gravel packing was the common completion in a single sand body, however in presence of shales open-hole expandable screens with annular barriers and blanks between each section of sand is the only completion option, except in fine sand environment.

In this paper, we present experimental data of shale stabilizer treated-brine and three open-hole gravel packing case histories from one UGS field in Italy. In the three case studies the wells were gravel packed using shale stabilizer treated-brine in open-hole made up of sand layers containing shale, without negative impact on completion time.
A Self-Mitigating Sand Control Screen
Authors: Yeh C. S. , Moffett T. J. , Petrie D. H. , Entchev P. B. , Long T. A. , Clingman S. R. , Dale B. A. , Harrison L. E. , Barry M. D. , Hecker M. T. , Howell D. A.
Published: May 2009

Sand screens often serve as the primary barrier to sand production from weakly consolidated reservoirs. Screen technology has improved significantly in the areas of sand retention, mechanical integrity, and quality control. As future field developments trend towards more hostile environments, requiring fewer wells at higher rates, the overall reliability and longevity of sand screens will be increasingly more important in this high cost environment.

This paper introduces a self-mitigating sand screen technology, MazeFlo™, that uses redundant sand control and compartment baffles to improve reliability and longevity for sand-prone well production. The technology self-mitigates downhole screen damage by isolating the effects of any mechanical failure of the screen to a local compartment, while allowing continued hydrocarbon flow through the undamaged sections. The compartment maze is comprised of baffles and tortuous flow paths that balance the incoming flow momentum from the outer screen. This flow redistribution mitigates risk of inner screen failure, while posing no additional plugging risk over conventional screens.

These self-mitigating screens reduce the frequency of sand-related workovers, extend well production, and increase recovery. Due to its simplicity and unique passive control capability, self-mitigating sand screens will expand the applicability of less complex and more cost effective standalone screen completions. Self-mitigating screens can also be easily combined with other emerging technologies such as zonal isolation and inflow control devices.
Modelling the Placement of Scale Squeeze Treatments in Heterogeneous Formations with Pressurised Layers
Authors: Vazquez O. , Mackay E. J. , Sorbie K. S.
Published: May 2009

The most common method for preventing scale formation is by applying scale inhibitor squeeze treatments. In this process, a scale inhibitor solution is injected down a producer well and into the near wellbore formation. Generally, reservoir formations consist of a number of layers or zones of different permeability which may or may not be in pressure communication. When the zones are non-communicating within the reservoir, they are often at different pressures. When this is the case, then this can have a strong influence on the flow and placement of any injected fluids. Indeed, it can dominate the dynamics of the placement process and can also cause wellbore crossflow during the shut-in period following the squeeze treatment. In order to design a successful squeeze treatment, it is very important to know where the injected fluid goes; i.e. where the slug of scale inhibitor is placed in the formation. Therefore, our squeeze design and prediction models must incorporate these layer pressure effects along with the other models for the scale inhibitor transport and retention mechanisms.

In this paper, we develop the analytical expressions for calculating the flow partition in radial layered formations, where the layers are non-communicating. This is not in itself original and these equations are "well known". However, we have incorporated them into our multi-layer, two phase scale squeeze design software (SQUEEZE VI) to simulate situations where layers are at different pressures. We demonstrate that this has an important effect on the scale inhibitor slug placement in a heterogeneous system and it drives crossflow between layers at production or injection stages. Furthermore, we go on to show what the consequences of these placement effects on the squeeze lifetime are. We also present a wide sensitivity study of this effect showing how a number of ancillary parameters affect the squeeze lifetime e.g. the magnitude of the differential pressure between layers, the permeability contrast, the retention mechanism. Finally, we give some general field guidelines for various specific situations where formation zone pressures are not equal in terms of squeeze applications.
Impact of Mutual Solvent Preflush on Scale Squeeze Treatments: Extended Squeeze Lifetime and Improved Well Clean-up Time
Authors: Vazquez O. , Mackay E. , Sorbie K. , Jordan M.
Published: May 2009

The most common method for preventing scale formation is by applying a scale inhibitor squeeze treatment. In this process, a scale inhibitor solution is injected down a producer well into the near wellbore formation. Commonly, scale treatments comprise the following stages: preflush, main scale inhibitor pill, overflush tubing displacement and shut-in, followed by back-production of the well. For some years the industry has applied mutual solvent chemicals in the preflush stage of such treatments to (i) avoid emulsion formation or water blocking, thus avoiding slow well clean-up, and also (ii) for enhancing adsorption of the scale inhibitor onto the formation rock.

This paper discusses the effect of a mutual solvent preflush on scale inhibitor squeeze lifetime and also on well clean up time. It builds on a previous publication that introduced a recent model to simulate the impact of a surfactant on improved inhibitor retention, which used data derived from laboratory experiments. The focus of this paper will be to consider the impact of the mutual solvent on well clean up time and the model is used to demonstrate the effect of a mutual solvent in quickly bringing wells back to full oil production. A field example is presented for a deepwater field in West Africa where intervention costs are high and any negative impact of squeeze treatments can have a significant associated deferred oil cost.

A scale inhibitor squeeze design in which a mutual solvent is deployed in the preflush should account for the following phenomena: mutual solvent propagation, diminishing mutual solvent efficiency due to interaction with the fluid phases, impact of the mutual solvent on scale inhibitor retention due to increased rock surface area available for adsorption, and impact of mutual solvent on saturation dependent relative permeability functions and phase mobilities. These aspects are discussed in the paper, and the model is used to demonstrate their impact on a squeeze treatment. Particular attention is paid to the reservoir wettability, and the importance of the shape of the relative permeability curves in determining the clean up time for a well, and the benefit that a mutual solvent may bring in overcoming slow clean up times.

The model is then used to demonstrate how the preflush stage of given specific field squeeze designs may be adapted to ensure optimum efficiency in terms of chemical usage, minimised deferred oil production and extended squeeze life.
Fines Migration in a High Temperature Gas Reservoir – Laboratory Simulation and Implications for Completion Design
Authors: Byrne Michael , Waggoner Steve
Published: May 2009

Fines migration is widespread in oil and gas reservoirs but often misunderstood. It can be difficult to identify and even more difficult to predict and interpret. The phenomenon, which can be considered a "natural" damage mechanism, involves the movement of rock particles through and within the pore matrix of that rock.

This paper presents a case history of fines migration investigation in a reservoir in the Malay basin in South East Asia. High temperature core flood tests and equivalent ambient condition core flood tests were used to evaluate the potential for fines movement in the producing gas phase. This paper outlines the laboratory test procedures, the results and discusses the implications. A comparison is made between the different laboratory techniques and recommendations made for similar reservoir challenges. The importance of scaling down near wellbore flow rates from field conditions to make them relevant in laboratory conditions was considered. Thus the test results are now able to be scaled up and are more relevant. This paper will also show significant differences in permeability reduction and fines movement between ambient conditions and high temperature reservoir conditions. The testing at high temperature reservoir conditions has not been a common practice and no published work has been found within SPE on this topic.

Once fines movement is predicted, the next challenge is to evaluate its potential impact on well performance. The implications for the specific reservoir and particularly for well design and completion options are discussed. Sand control issues as well as the potential impact on water injection or disposal wells are considered.

This paper presents clear evidence for fines migration in the production phase of a high temperature gas reservoir. Laboratory testing and subsequent analysis of tested samples demonstrate the nature of the fines and the process of permeability change. A process for identification of potential fines migration problems in gas reservoirs is proposed. The implications of fines migration in such a reservoir are discussed and potential mitigation is considered together with well completion design implications.
Design and Application of Invert Emulsion Drilling and Aqueous Completion Fluids for Long Horizontal Multilateral Wells
Authors: Hutton Alistair , Vickers Stephen , Davidson Marcus , Wharton Jon , Hatch Andy , Simmonds Roger , Brankling David
Published: May 2009

The Rita gas field was the first dual lateral well aimed at carboniferous reservoirs drilled in the UK Southern North Sea. This method enabled both the East and West fault segments of the field to be produced from the same upper well bore, thus reducing drilling costs and improving field economics. An invert emulsion drilling fluid was chosen for this field application due to the risk of shale instability over the long horizontal sections of each wellbore.

The West segment was drilled and suspended with a whipstock placed above the sand screen completion. The positioning of this whipstock would not allow for re-entry, making remediation of the West lateral impractical. A remediation treatment for this leg was required as the planned suspension fluid was an invert emulsion system that would be in contact with the completion screens and reservoir for more than a month whilst the East leg was drilled and completed. The chosen suspension fluid in the East leg removed the requirement for remediation with enhanced well productivity. This paper describes the design and testing of the reservoir drilling and suspension/completion fluids that were used on this multi-lateral project to minimise drilling time and maximise productivity.
Cases History Studies of Production Enhancement in Cased Hole Wells Using Microemulsion Fluids
Authors: Quintero Lirio , Jones Thomas A. , Clark David E. , Schwertner David
Published: May 2009

A high percentage of oil and gas wells drilled throughout the world have been completed using perforated casing. In older cased-hole wells, the production pressure may be depleted and/or hydrocarbon flow may be impeded by various damaging mechanisms such as in-situ emulsions, water blockage, solids migration, asphaltenes and paraffin deposition. In newer wells, drilled using oil- or synthetic-based drilling fluids, emulsion blockage may cause near-wellbore damage when the filtrate or whole mud interacts with formation fluids or completion brine.

Properties of microemulsions, such as high oil solubilization rates and ultra-low interfacial tension make this type of fluid ideal for addressing all of the described problems in old and new cased-hole wells.

This paper presents development procedures and case history results from numerous field applications that demonstrate the efficiency to reduce skin damage and improve productivity by using a single-phase microemulsion fluid specially designed for cased-hole wells.
Field Development and Productivity Improvement in Offshore Mexico: An Engineering and Laboratory Synergistic Approach to Carbonate Fracture Acidizing
Authors: Inda Antonio , Steffani Octavio , Soriano Eduardo , Robles Fernando
Published: May 2009

The marine light crude (CLM) project in offshore Mexico is a group of 12 oil fields located 75 km off the coast of southern Mexico (Jurassic and Cretaceous period). The fields have been under development since 2003, are high-temperature (160°C or >300°F) carbonate formations producing gas and condensate with permeability that ranges from 1 to 6 mD, and are naturally fractured. These fields were experiencing considerable drawdown, which slowed down the return on investment and, in one case, could have potentially led to well abandonment. Established dogma dictates that carbonate formations in Mexico are best treated by matrix stimulation rather than fracture-stimulation techniques. The two case studies discussed in this paper demonstrate the effective implementation of a production-optimization design and execution methodology that has translated into productivity increase. The design resulted in up to 80% removal of the pressure drop experienced in the formation face, accomplished by establishing a linear flow path, bypassing the formation damage. After treatment, a production increase of 50% more than conventional treatments is the best proof of concept, validating the synergistic approach, entailing data collection and analysis, field and laboratory work, and engineering design and simulation. The selection of appropriate candidates was performed by analyzing productivity data (drillstem testing), which indicated a skin factor of zero but, nevertheless, a remnant and considerable pressure drop caused by the formation's low permeability. Fluid optimization and placement techniques were combined with core studies and rock mechanics in the job design. Candidate wells for acid fracturing had permeability of 1 to 20 mD, while matrix stimulation candidates had 20 to 50 mD, and 50-m etched fractures appear to have provided optimum results. The methodology signifies less risk of incurring damage caused by condensate formation in the formation. As a result, fracture acidizing in Mexico's offshore fields is a completely viable alternative to production improvement.
Flow Performance Of Perforation Tunnels Created With Shaped Charges Using Reactive Liner Technology
Authors: Atwood D. C. , Yang W. , Grove B. M. , Behrmann L. A.
Published: May 2009

We report on a series of laboratory flow experiments comparing the productivity of perforations created with reactive liner charges against those created with conventional liner charges. Three of the tests involved shots into an outcrop carbonate rock called Indiana Limestone. Three of the tests involved shots into an outcrop sandstone rock called Berea Sandstone. Four different charge types were tested, including one standard (conventional) charge and three different designs of reactive liner charges. Among all charges, the only difference of note was the design and composition of the liner. All other charge design parameters were kept constant.

For both rock types, the reactive liner charges produced perforations with lower productivity than the baseline conventional charge. The reduction in the normalized Productivity Ratio (PRn) ranged from 29% to 66%. Furthermore, the reactive liner charges produced characteristic "dynamic overbalance" conditions in the wellbore, in a system configuration which produced dynamic underbalance for the conventional charge. We conclude that the reactive liner charges tested are detrimental to productivity in naturally perforated completions.
Water Induced Formation Damage in Unconventional Gas Reservoirs
Authors: Lakatos István , Bódi Tibor , Lakatos-Szabó Julianna
Published: May 2009

In the 21st century, the global gas demand will be met only by extensive production of unconventional gas (shale and tight sand gas, deep gas, basin concentrated gas accumulation, etc.). All such gas-bearing formations are characterized, however, by extremely low, usually micro Darcy range permeability. Unfortunately, the operators of such reservoirs face with difficulties when routine drilling, well completion, fracturing, and production technologies are used. One source of the problems can be traced back to use of water-base fluids. Therefore, the laboratory studies aimed at elucidating the reasons why water-based fluids are harmful and seriously jeopardize the gas production from such reservoirs.

The water induced formation damage is illustrated in a porous media having 0.001–0.1 mD permeability and obtained from a tight sand gas formation. Its pore structure was analyzed by HP Hg porosimetry and the wettability was determined by digital image analysis. The spontaneous imbibition was tested with standard method. Surface tension of water was determined by automatic ring method. The critical Pc needed to mobilize water was calculated as a function of pore size distribution.

Using the relevant data (pore size distribution, wettability and surface tension) the calculated Pc was in range of 40–75 bar for cores obtained from medium depth (3600 m); meanwhile it was extremely high, 500–600 bar for cores derived from deeper layers (>6000 m). Based on these data it was concluded that the native water saturation should be high (>70%) and immobile in similar formations and because of the high imbibition rate the water behaves as a potential blocking phase in the cores. The mentioned factors seriously influence both the resource/reserve assessment and the production efficiency. Since the water may induce formation damage hard to control, application of water free fluids is recommended in any phase of field operation at unconventional gas reservoirs.
A Comprehensive Methodology to Analyze the Impact of the Sand Control Technique on the Efficiency of an Horizontal Well
Authors: Ferreira M. V. D. , Folsta M. G. , Vianna A. M. , Miura K. , Calderon A. , Martins A. L.
Published: May 2009

Sand production in unconsolidated formations has brought heavy injury for the oil and gas industry around the world. Million dollars have been invested in sand control techniques. Among the several sand control systems existing, Open Hole Gravel Pack (OHGP) is the one adopted for horizontal well completions in the offshore Brazilian fields. With the experience in the development of such fields, some assets start to consider the adoption of less conservative sand control strategies, such as the use of stand alone premium screens (SAS). The present work proposes a methodology for evaluating the impact of the sand control technique in the productivity or injectivity of a horizontal well. Several parameters, such as damage rate (DR) and productivity or injectivity index per horizontal effective length (PI/Lef) were used to compare similar wells equipped with different sand control techniques. The main goal of the study is to address the following questions:

There is any formation damage due to the gravel pack during production lifetime of a well? The wells equipped with stand alone screen exhibit formation damage? Wells equipped with OHGP have the same performance when compared with wells equipped with SAS? Stand alone completion is a good alternative path for multilateral and extend reach wells?
Horizontal Open Hole Gravel Pack Placement Requirements in Selective Completion Projects
Authors: Loureiro B. V. , de Magalhães J. V. M. , Ferreira M. V. D. , Calderon A. , Martins A. L. , dos Santos F. P.
Published: May 2009

Horizontal Open Hole Gravel Pack (HOHGP) is the conventional sand control technique for offshore non consolidated reservoirs in Brazil. Gravel pack placement requirements include the design of pumping pressures inside the operational window formed by the minimum pump rate to avoid premature rat hole screen-out and maximum pump rate to avoid formation fracture. Some special projects require additional equipment to provide selective completion – External casing packers (ECP) installed at different positions along the production screen aim the isolation of certain reservoir zones. In these cases, gravel pack placement present an additional constraint – operational pump rates should be high enough to avoid alpha wave sedimentation around the packers to assure sealing after the packer inflation process. Traditionally, design criteria consider a minimum critical velocity to avoid sand deposition.

The specification of minimum flow for cleaning the ECP, and prevent the deposition of sand in the annular space can be obtained from different criteria. Two methods are proposed to analyze the problem: a constant velocity and a constant shear stress approach. The major contribution includes computational fluid dynamic simulation (CFD) of the 3D flow around the packer, using a finite volume method. The methodology based on the estimation of the local shear stresses at the interfaces, suggests less conservative numbers which allows effective gravel pack placement in selective completion projects for narrow operational windows.
Microemulsion Technology for Improved Fluid Recovery and Enhanced Core Permeability to Gas
Authors: Zelenev Andrei S. , Ellena Linda B.
Published: May 2009

In recent years the use of microemulsions for remediating damaged wells has been a success story. Microemulsions are unique, thermodynamically stable, optically clear single phase blends of water, biodegradable water-immiscible solvent, co-solvent, and specially designed surfactant. Engineered mixtures of these ingredients can form stable microemulsions over a rather broad range of water to solvent to surfactant ratios. Are all microemulsions equally effective in their performance? The main focus of our study was to prepare various microemulsions and to examine a link between microemulsion composition and their performance.

Microemulsion treatments have proved to be effective for improving gas production rates by increasing formation permeability and for enhancing fluid recovery from sand-packed and shale-packed columns. For achieving maximum benefits, microemulsion formulations have to be properly designed. Both microemulsion composition and dose are important for their end performance. The effectiveness of a particular microemulsion may vary depending on the application, and may be sensitive to the type of formation.
An Inflow Prediction Model for Open Hole Gravel Pack and Frac & Pack Completions
Authors: Tovar Juan J. , Moreno Ferney , Haider Syed R.
Published: May 2009

Predicting gravel pack performance is a complex and difficult task. Current practices account for expectation of performance by assigning a range of skin values that consider all the mechanisms that generate formation damage in the gravel pack. Other methods of identifying damage in the gravel pack include pressure build up analysis and the use of logging tools to investigate gravel placement. Using techniques such as NODAL® analysis, overall well performance can be validated and the level of damage within the gravel pack estimated. This practice assumes that other damaging mechanisms present at the sand face are part of the overall gravel pack damage.

This paper presents a methodology that integrates near wellbore damage, such as solid's invasion and mechanical damage during drilling, with damage caused to the gravel pack by solid particles as the well is started up for the first time. The model developed is supported by a laboratory test program of granular filter media to determine the various pore blocking mechanisms present during well start up. The results of this work indicate that impairment of the granular filter media is a function of flow rate, particle concentration and particle sizes. The final inflow model developed takes into account the volume of solids (mud cake and sand particles) that will be dragged into the gravel pack causing impairment. The result is an inflow profile from the gravel pack to the wellbore on a foot-by-foot basis that will dictate the final reservoir contribution and flow rates at the internal side of the screen.
Reactive Perforating: Conventional and Unconventional Applications, Learnings and Opportunities
Authors: Bell M. R. G. , Hardesty J. T. , Clark N. G.
Published: May 2009

A new class of shaped charge was introduced to the industry in late 2007 that generates a secondary reaction in the perforation tunnel immediately after it has been formed. The reaction is highly energetic and drives the break up and expulsion of crushed zone material and compacted debris. This profoundly alters the geometry and quality of the resulting tunnels when compared to conventional perforators and underbalanced perforating techniques. This leads to significant improvements in the percentage of open, effective tunnels, the productivity of the perforated interval, and the ease and reliability with which the perforated formation can be stimulated.

Since their launch, reactive perforating systems have been applied to a variety of well and formation types – both conventional and unconventional – under a wide range of pressure and effective stress conditions. As a result, the applicability of the reactive perforating concept is being demonstrated and accepted for an increasing number of situations. Nevertheless, the industry is only just beginning to understand how reactive perforating can be applied and how well and completion designs should be optimized to take full advantage of the benefits this new technology affords.

This paper describes the application of reactive perforators to a number of geographically and lithologically different situations, for the purpose of transferring generic learnings and identifying opportunities for further study. Several clear opportunity areas are already emerging, such as perforating prior to hydraulic fracturing – notably in unconventional gas plays – and re-perforation of depleted or damaged intervals. Other areas are still to be properly explored, such as perforation prior to acidization – especially in carbonates, perforation of unconsolidated sandstones, and perforation of injection wells.

In conclusion the paper identifies those areas where the technology has shown greatest success and summarizes the key learnings that will assist operators in shortening their own learning curve when applying reactive perforator technology.
Prevention of Production Breakdown Caused by Formate Drilling Fluid
Authors: Schulze Kai , Kersten Christoph , Verient Gery , Oswald Wolfgang , Dammerer-Kerbl Michael , Empl Christoph , Marchel Christian , Karsch Harold
Published: May 2009

The Rotliegend sandstone reservoir of Voelkersen (Northwest Germany) is a low permeability (kabs 2–4 mD), high pressure high temperature gas field (650 bar, 160°C). Its formation water is of high salinity (250 g/l) and characterised by its very high calcium content (≥ 40 g/l). The reservoir section of a partly depleted acceleration well was drilled using saturated water based sodium/potassium formate brine. For corrosion protection the pH value of the brine was adjusted to pH 10.5 using a bicarbonate/carbonate buffer. After gas production of 70 million m3(Vn) the production collapsed as a result of an unexpected build-up of calcium carbonate scale in the well bore area and the tubing. Two mechanisms have been identified as the cause of this scale formation. First the interaction of the caustic filtrate of the formate brine with the calcium rich formation water leading to a direct calcium carbonate precipitation. Second the enrichment of the formation water with bicarbonate by interaction with the caustic mud filtrate. This has resulted in calcium carbonate precipitation caused by the rise of the pH value of the water. The latter is resulting from decarbonisation caused by the pressure relief in the well bore area as a result of production. After subsequent mechanical and chemical scale removal, the gas production was even higher than at the initial state of production. However, having additionally produced 90 million m3(Vn) the production dropped again. This breakdown is attributable to an increase of bicarbonate in the formation water by a slow process of decomposition of formate left in the formation. This has resulted in subsequent scale formation following the decarbonisation process described above. To minimise the scaling potential of the formate brine while maintaining sufficient corrosion protection, careful adjustment of the pH value of the formate brine while drilling the reservoir section was implemented for successive wells. For already damaged wells several potential treatments have been identified and introduced, such as scale inhibition treatment integrated in hydraulic fracturing.
Analysis of Fracture Growth Induced by the Injection of Water Above the Fracture Pressure in Nonconsolidated Sandstones and Soft Carbonates – Deviations from the Linear Elastic Elastic Model or Why Can't I Inject Even Above the Fracture Pressure?
Authors: Pedroso Carlos Alberto , Marques Luiz Carlos do Carmo , Paixão Luiz Carlos Alves da , Pires Paulo Roberto da Motta , Luz Eurípedes Barsanulpho
Published: May 2009

The Injection Above the Fracture Pressure (IAFP) has became one of the most important alternatives to guarantee high injection rates, even when the quality of the injected water is below the minimum requirements for not damaging the rockreservoir. For this reason IAFP has found a vast application in both, the discard or re-injection of oily water or water with high solid content and to maintain the injectivity index of injector wells.

In Campos Basin, an interesting application of IAFP to assure the injection rate has been done in a pair of parallel horizontal wells completed with HOHGP (horizontal open hole gravel pack) in a Maastrichtian reservoir, where the fracture growth has been monitored through Hall Plots. In the first group (IAFP for water discard) some new projects have been planned, such as an "ecological well" (so called because the reduction of discard) which plan to inject large amount of water in dolomites.

All these projects were preceded by a fracture growth analysis. Usually, these analyses are carried-out by using simulators which are based in Linear Elastic Fracture Model theory (LEFM) and consider a single planar fracture. However, in the case of IAFP in non-consolidated sandstones or soft carbonates, these assumptions can be quite unrealistic. Effects of plastic deformation in the fracture tip, compacting or fluidization of porous media, multiple fractures and pore-elastic effects can be predominant in these cases.

An example that ratifies this was the attempt to re-inject produced water above the fracture pressure in an unconsolidated Miocene reservoir. Even with injection pressure 800 psi above the fracturing pressure (measured through a previous minifrac), it was impossible to propagate the fracture. In another well, the IAFP was aborted when a completely unexpected fracture gradient greater than 0.83 psi/ft was attained (it was expected 0.52 psi/ft). This behavior can only be explained if we consider the occurrence of any different phenomena of those foreseen by LEFM.

This work details the IAPF projects here mentioned and depicts the deviations of LEFM observed in IAFP wells in Campos’ Basin.
A Novel Timer Activated Sandface Valve to Improve Wellbore Productivity
Authors: Russell Leigh-Ann , Elliott Grahame , Graham John , Wallace Alex , Coull David , Forsyth David
Published: May 2009

A novel timer activated sandface valve was developed that has significant impact on wellbore productivity by enabling improved wellbore clean up, particularly in high angle and open hole completions. This technology has been field trialled and proven in three wells in a North Sea field. The tool was developed from concept to installation in less than nine months including detailed engineering review and assurance.

Negative impact to productivity due to inefficient wellbore clean up of high angle completions is a common situation for production wells. The current solution can be complex completion architecture or extensive clean up procedures that are both expensive and difficult to implement. The consequence of a poor clean up can be loss in well productivity, access to reserves or a requirement to sidetrack the well.

Poor clean up was observed in several wells in a North Sea field. The wells exhibited high skin and no flow from the toe sections of the well due to the dominance of high productive intervals subject to high drawdown at the heel of the well. The timer activated sand face valve was developed with the key objective to deliver sequential clean up from the toe of the reservoir section without intervention or incremental rig time. The valves also deliver the functionality of a sliding side door for future water shut-off capability along the well bore.

The paper will present an overview of the technical challenge, detail development of the tool and processes used for assurance and include results of the field trial. The valve development combines a field proven timer activation mechanism with conventional sliding sleeve technology. The tool was developed without incremental resource and cost often required for product development utilising specifically designed lean technical assurance tools and failure mode and effects analysis processes. The result is a successfully field proven completion tool that is the basis for a new completion technique that has application in high angle wells in all oilfield applications.
Models and Methods for Understanding of Early Acid Breakthrough Observed in Acid Core-floods of Vuggy Carbonates
Authors: Izgec O. , Zhu D. , Hill A. D.
Published: May 2009

Previously, we have studied the acidization of vuggy carbonates with acid core flood experiments in 4-inch diameter by 20-inch long cores, high resolution computerized tomography imaging, image processing and geostatistical characterization. The obvious major finding from these tests is that acid propagates wormholes through vuggy carbonates much more rapidly than occurs in more homogeneous rocks. Acid-created wormholes were observed to break through to the end of the cores an order of magnitude more rapidly than occurs in more homogeneous cores, highlighting the necessity of understanding the flow and transport in vuggy carbonates. The fact that acid channeled through the vugular cores, following the path of the vug system, was underlined with computerized tomography scans of the cores before and after acid injection. This observation proposes that local pressure drops created by vugs are more dominant in determining the wormhole flow path than the chemical reactions occurring at the pore level. Following this idea, we are presenting a modeling study in order to understand flow in porous media in the presence of vugs. Use of coupled Darcy and Stokes flow principles, known as the Darcy-Brinkman formulation, underpins the proposed approach. The power of the Darcy-Brinkman formulation lies in its natural ability to represent both porous media and tube flow in a single equation with variable coefficients.

The methods presented here shows that acid injected into vuggy limestones follows a preferential pathway guided by the vug network. The PVbt (pore volumes to break through) for vuggy limestone correlates inversely with the fraction of total porosity comprised by vugs – the higher the vuggy fraction of porosity, the lower the pore volumes to breakthrough. Local pressure drops created by vugs are more dominant in determining the wormhole flow path than the chemical reactions occurring at the pore level. The results from the developed model demonstrate that the total injection volume to breakthrough is affected by the spatial distribution, the amount and the connectivity of vuggy pore space.
Taking Advantage of Injectivity Decline for Sweep Enhancing during Waterflood with Horizontal Wells
Authors: Bedrikovetsky P. , Muhammad A. W. , Chang G. , de Souza A. L. S. , Furtado C.
Published: May 2009

Injectivity formation damage with waterflooding using sea/produced water has been widely reported in the North Sea, the Gulf of Mexico and the Campos Basin in Brazil. The damage is due to the capture of solid/liquid particles by the rock with consequent permeability decline; it is also due to the formation of a low permeable external filter cake. Yet, moderate injectivity decline is not too damaging with long horizontal injectors where the initial injectivity is high. In this case, injection of raw or poorly treated water would save money on water treatment, which is not only cumbersome but also an expensive procedure in offshore projects.

In this paper we investigate the effects of injected water quality on waterflooding using horizontal wells. It was found out that induced injectivity damage results in increased sweep efficiency. The explanation of the phenomenon is as follows: injectivity rate is distributed along a horizontal well non-uniformly; water advances faster from higher rate intervals resulting in early breakthrough; the retained particles plug mostly the high permeability channels and homogenize the injectivity profile along the well.

An analytical model for injectivity decline accounting for particle capture and a low permeable external filter cake formation has been implemented into the Eclipse 100 reservoir simulator. It is shown that sweep efficiency in a heterogeneous formation can increase by up to 5% after one pore volume injected, compared to ‘clean’ water injection.
Adsorption of Glyphosate on Variable‐Charge, Volcanic Ash–Derived Soils
Authors: Cáceres‐Jensen L. , Gan J. , Báez M. , Fuentes R. , Escudey M.
Published: May 2009

Glyphosate (N‐phosphonometylglycine) is widely used due to its broad spectrum of activity and nonselective mode of action. In Chile it is the most used herbicide, but its adsorption behavior in the abundant and widespread variable charge soils is not well understood. In this study, three volcanic ash–derived soils were selected, including Andisols (Nueva Braunau and Diguillin) and Ultisols (Collipulli), to evaluate the adsorption kinetics, equilibrium isotherms, and the effect of pH in glyphosate adsorption. The influence of glyphosate on soil phosphorus retention was also studied. Glyphosate was rapidly and strongly adsorbed on the selected soils, and adsorption isotherms were well described by the Freundlich relationship with strong nonlinearity (nfads < 0.5). The nfads values were consistently higher than nfdes values, suggesting strong hysteresis. Adsorption (Kads) increased strongly when pH decreased. The presence of glyphosate (3200 μg mL−1) changed the adsorption behavior of phosphate at its maximum adsorption capacity. Andisol soils without the addition of glyphosate had similar mean Kads values for Nueva Braunau (5.68) and Diguillin (7.38). Collipulli had a mean Kads value of 31.58. During the successive desorption steps, glyphosate at the highest level increased Kads values for phosphate in the Andisol soils but had little effect in the Ultisol soil. This different behavior was probably due to the irreversible occupation of some adsorption sites by glyphosate in the Ultisol soil attributed to the dominant Kaolinite mineral. Results from this study suggest that in the two types of volcanic soils, different mechanisms are involved in glyphosate and phosphate adsorption and that long‐term use of glyphosate may impose different effects on the retention and availability of phosphorus. Volcanic ash–derived soils have a particular environmental behavior in relation to the retention of organic contaminants, representing an environmental substrate that may become highly polluted over time due to intensive agronomic uses.
Hardwood Tree Survival in Heavy Ground Cover on Reclaimed Land in West Virginia: Mowing and Ripping Effects
Authors: Skousen Jeff , Gorman Jim , Pena‐Yewtukhiw Eugenia , King Jim , Stewart Jason , Emerson Paul , DeLong Curtis
Published: May 2009

Current West Virginia coal mining regulations emphasize reforestation as a preferred postmining land use on surface mined areas. Some mined sites reclaimed to pasture are being converted to forests. In the spring of 2001, we compared the establishment and growth of five hardwood tree species on a reclaimed West Virginaia surface mine with compacted soils and a heavy grass groundcover. We planted 1‐yr‐old seedlings of five species (black cherry [Prunus serotinaEhrh.], red oak [Quercus rubraL.], yellow poplar [Liriodendron tulipiferaL.], black walnut [Juglans nigraL.], and white ash [Fraxinus americanaL.]) into sites that were mowed and unmowed on north‐ and south‐facing aspects. We applied a ripping treatment, which loosened the compacted soils and disturbed the heavy ground cover. First year results showed >80% survival for all species. After 7 yr black cherry survival averaged 36%, red oak 47%, yellow poplar 66%, black walnut 80%, and white ash 98% across all sites and treatments. Seedling survival was best on north, unmowed, and ripped areas. Average growth (height × diameter2) of trees after 7 yr was greatest with white ash (434 cm3), followed by yellow poplar (256 cm3) and black walnut (138 cm3), then by black cherry (31 cm3) and red oak (27 cm3). Browsing by wildlife had a negative impact on tree growth especially on south aspect sites. Overall, mowing reduced survival of black cherry, red oak, and yellow poplar, but not for black walnut and white ash. Ripping increased survival of black cherry, red oak, and yellow poplar. Growth of all species was improved with ripping. Using inverse linear‐quadratic plateau models, the time required for tree survival to stabilize varied from 1 yr for white ash to 6 to 9 yr for the other species.
Proinflammatory Cytokines Activate the Intrinsic Apoptotic Pathway in β-Cells
Authors: Grunnet Lars G. , Aikin Reid , Tonnesen Morten F. , Paraskevas Steven , Blaabjerg Lykke , Størling Joachim , Rosenberg Lawrence , Billestrup Nils , Maysinger Dusica , Mandrup-Poulsen Thomas
Published: May 2009

OBJECTIVE

Proinflammatory cytokines are cytotoxic to β-cells and have been implicated in the pathogenesis of type 1 diabetes and islet graft failure. The importance of the intrinsic mitochondrial apoptotic pathway in cytokine-induced β-cell death is unclear. Here, cytokine activation of the intrinsic apoptotic pathway and the role of the two proapoptotic Bcl-2 proteins, Bad and Bax, were examined in β-cells.

RESEARCH DESIGN AND METHODS

Human and rat islets and INS-1 cells were exposed to a combination of proinflammatory cytokines (interleukin-1β, interferon-γ, and/or tumor necrosis factor-α). Activation of Bad was determined by Ser136 dephosphorylation, mitochondrial stress by changes in mitochondrial metabolic activity and cytochrome c release, downstream apoptotic signaling by activation of caspase-9 and -3, and DNA fragmentation. The inhibitors FK506 and V5 were used to investigate the role of Bad and Bax activation, respectively.

RESULTS

We found that proinflammatory cytokines induced calcineurin-dependent dephosphorylation of Bad Ser136, mitochondrial stress, cytochrome c release, activation of caspase-9 and -3, and DNA fragmentation. Inhibition of Bad Ser136 dephosphorylation or Bax was found to inhibit cytokine-induced intrinsic proapoptotic signaling.

CONCLUSIONS

Our findings demonstrate that the intrinsic mitochondrial apoptotic pathway contributes significantly to cytokine-induced β-cell death and suggest a functional role of calcineurin-mediated Bad Ser136 dephosphorylation and Bax activity in cytokine-induced apoptosis.
Prevalence and Predictors of Breast and Cervical Cancer Screening Among Spanish Women With Diabetes
Authors: Jiménez-Garcia Rodrigo , Hernandez-Barrera Valentin , Carrasco-Garrido Pilar , Gil Angel
Published: May 2009

OBJECTIVE

To examine the use of mammography and Papanicolaou (Pap) smear among women with diabetes and to identify predictors of adherence to these tests.

RESEARCH DESIGN AND METHODS

We analyzed data of a nationally representative sample of Spanish women. Diabetes status was self-reported. Screenings were assessed asking whether they had a mammography (≥40 years) and a Pap smear (18–69 years) within the previous 2 and 3 years, respectively.

RESULTS

Women with diabetes were less likely to receive mammography (57.9%) or have a Pap smear (61.5%) than women without diabetes (mammography 61.9%, P < 0.05; Pap smear 65.6%, P < 0.05). After adjusting for age, educational level, income, comorbidity, tobacco use, obesity, and physician visits, the corresponding odds ratios remained significant (0.84, 95% CI 0.72–0.97) and (0.82, 95% CI 0.66–0.98). Higher educational level was a positive predictor for both tests among diabetic women.

CONCLUSIONS

Spanish women with diabetes underuse breast and cervical cancer screening tests.
∞-jets of diffeomorphisms preserving orbits of vector fields
Authors: Maksymenko Sergiy
Published: May 2009

Let F be a C
∞ vector field defined near the origin O ∈ ℝn, F(O) = 0, and (Ft) be its local flow. Denote by the set of germs of orbit preserving diffeomorphisms h: ℝn → ℝn at O, and let , (r ≥ 0), be the identity component of with respect to the weak Whitney Wr topology. Then contains a subset consisting of maps of the form Fα(x)(x), where α: ℝn → ℝ runs over the space of all smooth germs at O. It was proved earlier by the author that if F is a linear vector field, then = .

In this paper we present a class of examples of vector fields with degenerate singularities at O for which
formally coincides with , i.e. on the level of ∞-jets at O.

We also establish parameter rigidity of linear vector fields and “reduced” Hamiltonian vector fields of real homogeneous polynomials in two variables.