bluuebunny/crossref_metadata_2025 huggingface dataset:
History Match Tuning Through Different Upscaling Algorithms
Authors: Allam Farid A. , El-Banbi Ahmed H. , Bustami Sami S. , Saada Tamer H. , Fahmy Ismail I.
Published: December 2007

Although computer power has significantly increased in recent years, the need for upscaling is still mandatory to save run time for many reservoir-modeling studies. In this paper we demonstrate the results of reservoir upscaling using nine different algorithms. A comprehensive evaluation for these upscaling methods was performed using several models with increasing complexities and heterogeneity.

Several simulation models were constructed to investigate the effect of the upscaling technique on the quality of the simulation results (including history matching). A very fine model, closest to the geological model, was constructed as a benchmark. Simulation models were then upscaled using nine different upscaling techniques for both natural depletion and water injection driving mechanisms. The models were run for a period of time and the results were compared with those of the fine model. The results were treated statistically to quantify the resultant deviation (errors) from the benchmark results. It was found that some of the upscaling techniques gave better results than others.

In this paper, we also suggest a road map to follow when upscaling geological models and discuss the upscaling for different levels of refinement. The suggested procedures can be applied to many modeling problems and is expected to save time in simulation studies.
Experimental Analysis of Primary and Secondary Oil Recovery from Matrix by Counter-Current Diffusion and Spontaneous Imbibition
Authors: Hatiboglu C. U. , Babadagli T.
Published: December 2007

Matrix–fracture interaction is a commonly encountered process in fractured subsurface reservoirs during oil, gas, and geothermal fluid recoveries and contaminant transport. It occurs in counter-current manner if the interaction between matrix and fracture takes place from the same side. In the first part of this paper, the effects of the matrix shape factor, wettability, and interfacial tension on the rate of capillary imbibition and development of residual non-wetting phase saturation were studied experimentally. In the second part, secondary oil recovery by diffusion of a solvent from the samples exposed to capillary imbibition is investigated. Primary diffusion experiments were also performed on selected core sizes for comparison.

To achieve all these, experiments were conducted on Berea sandstone samples. Cylindrical samples with different shape factors were obtained by cutting the plugs ½, 1 and 2 inches in diameter and 2, 4, and 6 inches in length. All sides were coated with epoxy except one end. Static imbibition experiments were conducted on vertically and laterally situated samples where the imbibition took place upward and lateral directions, respectively. Brine-kerosene, brine-mineral oil and surfactant solution-mineral oil pairs were used as fluids. The rate of imbibition was evaluated for different matrix size, shape factor, wetting/non-wetting phase types and IFT. Conditions at which the shape factor controls the residual oil development were identified.

Diffusion experiments were conducted using n-heptane as a solvent. In addition to the cores exposed to full capillary imbibition, oil saturated (virgin) cores were also tested. To serve as a benchmark, uncoated versions of two different core sizes were used.

It was observed that the residual oil after capillary imbibition is controlled by the matrix shape factor for the vertically positioned samples unlike horizontal samples. Surfactant concentration plays a role on the rate of imbibition and the development of residual oil saturation.

Primary and secondary diffusion experiment showed that it could be more efficient to begin the oil recovery process by capillary imbibition (primary recovery) then continue with diffusion (secondary recovery) depending on the matrix shape factor.
The Boris Field Well Management Philosophy-the Application of Permanent Downhole Flowmeters to Pressure Transient Analysis: An Integrated Approach
Authors: Coludrovich E. J. , McFadden J. D. , Palke M. R. , Roberts W. R. , Robson L. J.
Published: December 2007

Considering the large capital investments and returns for high rate completions in overpressured, unconsolidated sandstone reservoirs, a testing methodology with defined objectives, designed to define acceptable risk levels for rates of individual completions is necessary. Critical parameters, such as permeability and skin, are dynamic properties in these types of reservoirs and require frequent measurement. BHP Billiton has implemented a program in the Boris Field that relies on the use of permanent downhole pressure gauges and flow meters. The well management philosophy and integration of pressure transient results is described, and our approach and experiences since first oil will be reviewed.

Our program relies on several novel well test approaches. A) Intermittent, unplanned build-ups can be analyzed to arrive at a continuous history of permeability and skin. B) Permanent downhole flowmeter data allows for analysis of unplanned build-ups which otherwise would be uninterpretable. C) Methods to quality control the results such as specialized trend plots of skin and permeability are reviewed.

Wellbore management is constrained by limits established by drawdown, flux, water handling, and flow assurance. Surveillance is performed by corroborating the instantaneous well performance from the permanent flowmeters with the most recently interpreted properties. Observations are presented about the utility of intermittent, unplanned shut-ins compared to planned tests.

This process is evolving and requires the advancement of available industry tools with regard to data handling and the use of classical analytical pressure transient techniques combined with numerical methods. Historical data files for individual completions using continuous downhole data are very large which makes manual manipulation of the files undesirable. Management of the data and the impact on the methodology is reviewed
Corrosion Inhibition in Deep, Hot Wyoming Wells
Authors: Kelley Joe A.
Published: December 2007

Downhole inhibitor treatment of several relatively deep, hot gas wells in Wyoming was used in a study of factors to consider in establishing an effective corrosion control program. Basically, one needs an effective inhibitor, a good application method, and a means to evaluate the lifetime of the treatment.
Pushing the Limits of Hydraulic Fracturing in Russia
Authors: Economides M. J. , Demarchos A. S. , Mach J. M. , Rueda J. , Wolcott D. S.
Published: December 2007

We have established the concept of Unified Fracture Design (UFD) to maximize the dimensionless productivity index (JD) following a hydraulic fracture treatment. For a given mass of proppant there is a specific dimensionless fracture conductivity, which we called the optimum, at which the JD becomes maximum. The Proppant Number is a seminal quantity unifying the propped fracture and the drainage volumes and the two permeabilities, those of the proppant pack and the reservoir.

For each injected proppant mass there is a corresponding Proppant Number and, at the optimum conductivity, the dimensionless PI can be readily determined. Increasing the proppant mass or the proppant-pack permeability would result in an increase in the JD, which has a maximum limit of approximately 1.9. In a recent publication we have shown how to push the limits in hydraulic fracturing by injecting very large volumes of proppant of very large retained permeability.

There are physical constraints to our approach, one of which is an upper limit of the net pressure resulting from both the physical limitations of injection equipment and tubulars but also from the need to prevent undesirable fracture height migration. However, the use of much larger proppant pack permeability leads to a correspondingly smaller width for the same fracture conductivity. The smaller width requirement allows the injection of far larger proppant masses before the net pressure constraints are met. This is a departure from current industry practices, which are aimed to "save" injection costs for a specific rate. Our approach, in medium to high permeability formations is to maximize the rate within the injection constraints. Rudimentary economics suggest that such treatments pay for themselves in just a few days of incremental production.

We present here field case studies and results showing the application and success of our design approach.
Gelled Organic Acid System for Improved CaCO3 Removal in Horizontal Openhole Wells at the Heidrun Field
Authors: Selle Olav M. , Wat Rex M. S. , Nasvik Haavard , Mebratu Amare
Published: December 2007

To remove calcium carbonate (CaCO3) damage from openhole wells, proper contact with treatment fluids must occur. Poor results are often caused by the improper placement of acid. Such was the case in the horizontal, openhole wells with sand screens on the Heidrun Field (Norwegian Sea). In these wells, bullheading plain HCl acid to dissolve carbonate kill pills provided only temporary effectiveness.

Recently, an operator and a service company initiated a joint project to study Heidrun's CaCO3 removal problem. Two wells were selected as candidates because of their severe CaCO3 plugging. Repeated attempts to remove the damage with HCl bullheading resulted in improved productivity that lasted only until the wells quickly became plugged. The temporary gain seemed to come from the heel of the wells. The team surmised that treatment could be improved with more uniform placement of acid. To provide a more even distribution of the acid treatment, the team developed a gelled organic acid system.

This paper describes the product qualification process and the chemistry of the new gelled organic acid system. A diversion technology study screened possible treating methods, and different gelling products were tested for potential formation damage, viscosity profile, and gel-breaking characteristics. A purified xanthan polymer with an added breaker was selected for further evaluation. When used to viscosify HCl, the gel-breaking time of the xanthan gel was too short for bullheading applications at Heidrun. Subsequently, an organic acid blend with acceptable CaCO3 dissolution power was formulated, and an environmentally acceptable corrosion inhibitor was incorporated.

Two case histories are presented to show that the system was applied with success. The gelled organic acid system is now qualified for use in the Heidrun Field. This system is applicable to most types of completions and the paper includes a discussion of its benefits.
Soft Sensing for Gas-Lift Wells
Authors: Bloemen H. H. J. , Belfroid S. P. C. , Sturm W. L. , Verhelst F. J. P. C. M. G.
Published: December 2007

This paper considers the use of extended Kalman Filtering as a soft-sensing technique for gas-lift wells. This technique is deployed for the estimation of dynamic variables that are not directly measured. Possible applications are the estimation of flow rates from pressure measurements or the estimation of parameters of a drift-flux model. By means of simulation examples different configurations of sensor systems are analyzed. The estimation of drift-flux model parameters is demonstrated on real data from a laboratory set-up.
Improved Drilling Performance in Troublesome Environment
Authors: Russell K. A. , Cockburn C. , MacLure R. , Crawford A. , Davison M. , Jolley S. J. , Kazi M. , Koster M. , McGrath B.
Published: December 2007

This paper describes an example of drilling hazard mitigation. It demonstrates how a completely fresh approach, involving geomechanical analysis, planning of a new revised well trajectory, and real-time well monitoring, can reduce non-productive time and cost, and mitigate against unplanned terminal events.

Recent drilling operations in a mature field in the North Sea were severely disrupted by wellbore deterioration, stuck pipe, and lost circulation incidents. A complex geological sequence of tilted fault blocks and partially depleted reservoir sands made well trajectory and wellbore stability planning difficult. After two unsuccessful sidetrack attempts, an integrated operator-contractor team performed a detailed audit of the drilling problems and built a geomechanical earth model to evaluate drilling hazards and develop strategies to mitigate any further wellbore instability. Well objectives were re-evaluated and a new approach to the drilling process was developed. The key was simplification of the well path. The operational solution featured management of drilling hazards through a real-time risk-mitigation process. Additional engineers at the wellsite managed drilling parameters, continuously monitored cavings, cuttings, and drill fluids, and analyzed drilling mechanics and logging while drilling (LWD) log data for indications of impending problems. A Web-based real-time data-transfer system was used to deliver data to the onshore drilling and subsurface teams. These methods, combined with advanced communication techniques, enabled tight control of drilling parameters and trajectory, and enhanced collaborative understanding within the multi-disiplinary team. The third sidetrack was completed without incident, within time, and under budget.
Seismic Scale Sand Injectites in the North Sea
Authors: Cheret T. , Carrillat A.
Published: December 2007

In recent years, there has been increased interest in sandstone injectite geological features in the North Sea. They are interpreted as post-depositional features, and are characterized by chaotically distributed, unconsolidated, remobilized sands mostly in the Paleocene and Eocene formations. Porosity, when, present is often high. On seismic sections, they appear as dykes crosscutting the surrounding reflectors and as sills with short lateral extent. Until recently, they have not been considered as potential targets for hydrocarbon production for several reasons: -In some cases, they were thought to be processing artifacts.-They are often difficult to image seismically as their thickness is considered beyond the resolution of conventional seismic data and there is generally a low acoustic impedance contrast between the sand and the overlying shale.-Because they have not been imaged on seismic data, they have often been neglected in favor of deeper targets.-They have often been considered drilling hazards, as they could be over-pressured.

In this paper, we review three case studies from three different areas in the North Sea: Area 1: Block G34_12 east of Kvitebjoern field, Area 2: Central North Sea, and Area 3: Grane field. In these three areas, we show sandstone injectite features, each having different seismic characteristics: for example, geometry, thickness, and acoustic impedance contrast. We demonstrate that in each case, the injectite can be imaged and visualized as a single object or geobody.
Miscible Gas Injection in Undersaturated Gas-Oil Systems
Authors: Hoier L. , Cheng N. , Whitson C. H.
Published: December 2007

This paper discusses miscible gas injection in reservoir fluid systems exhibiting compositional variation with depth characterized by an undersaturated "critical" transition from gas to oil, where all fluid properties exhibit a continuous variation with depth.

In an undersaturated gas-oil fluid system all fluids throughout the reservoir are initially first-contact miscible with their neighboring fluids. This implies that full-pressure maintenance, gravity-stable updip gas injection will lead to miscible displacement throughout the reservoir, even for down-dip fluids which are not miscible with the injection gas. The pressure maintenance required is to avoid depletion below initial saturation pressure throughout the reservoir, i.e. maintaining a single-phase fluid system. Compositional reservoir simulation studies have been used to verify this behavior for one-dimensional (1D) flow.

Similar results were originally suggested by Hoier and Whitson1. In this paper we study the same mechanism for non-ideal reservoir systems characterized by (1) partial pressure maintenance where reservoir pressures locally drop below initial saturation pressure and two phases form prior to injection gas arrival; and (2) two-dimensional (2D) flow in reservoirs with heterogeneities and strong layer-property contrasts. Both situations may have a negative impact on oil recovery compared with full-pressure maintenance and gravity-stable miscible displacement with expected near-100% recovery.

1D and 2D compositional simulations are used based on the reservoir characteristics of a field with an undersaturated gas-oil fluid system – Smorbukk South Field, located in the Norwegian Sea. This field produces rich gas condensate and volatile oil through an undersaturated gas-oil transition from two main geological layers. We present five years of production history with pressure maintenance by gas injection.
REACH is Real: The Proposed Reach System and its Effect on a Service Company
Authors: Killaars Janine
Published: December 2007

Guided by the white paper, "Strategy for a Future Chemical Policy,1 in October 2003, the European Commission drafted a new regulatory framework for chemicals known as the Registration, Evaluation and Authorisation of Chemicals (REACH) policy.

REACH is an integrated system that requires all substances produced or imported in quantities above one ton per year to be registered in the European Union (EU). The adoption of REACH will divert the burden of proof for putting safe chemicals on the market from the public authorities to industry.

The formal REACH proposal is expected to be presented for legislation in December 2005. If adopted, an 11-year transition (phase in) period will be implemented in three stages, determined by production volume and chemical hazard. A new European Agency will act as the central point in the REACH system.

This paper describes the proposed REACH system and its potential impact on an oilfield service company, both as an importer and downstream user of chemicals. The following topics will be discussed: Effects of REACH on producers/importersEffects of REACH on downstream usersImpact assessment of the REACH regulation on a service company as a case study
Advancements in Electromagnetic Propagation Logging
Authors: Wharton Russell P. , Hazen Gary A. , Rau Rama N. , Best David L
Published: December 2007

The basic theory upon which the microwave Electromagnetic Propagation Tool (EPT) has been founded is reviewed, and the measurement technique is discussed in terms of a functional block diagram. Two methods of interpreting the propagating wave's measured phase and attenuation are reviewed. Specific log examples which distinguish between hydrocarbon and water-bearing zones in several lithologies are presented.
Stochastic-Aided Design and Bayesian Updating: New Tools to Use Expert Knowledge in Quantitative Models That Incorporate Uncertainty
Authors: Galli Alain , Armstrong Margaret , Mattos Portella Ricardo Cunha , de Souza Olinto Gomes , Yokota Honorio Kouki
Published: December 2007

In this paper we propose to use a new stochastic methodology for constructing reservoirs models that combines ideas coming from the pilot point method and dual kriging. Using this approach, specialists can directly build models of surfaces that reflect their knowledge of the field and honour available well data and can be based on information like seismic that is generally available at that step. They can also incorporate a range of uncertainty on specific parts of the surface. As well as being flexible and easy to apply, this method provides a consistent framework for measuring the effect of additional information.

The method has been tested on a Brazilian gas reservoir (that has modified for confidentiality reasons) where two wells had been drilled and two more were planned. In addition we used a Bayesian approach to incorporate geological ideas about the maximum and minimum extent of sand bodies. Production profiles were modelled using response surface analysis where the plateau length and the decline rate depend on parameters like the size of reserves and the average permeability but still have residual uncertainty. One of the key results obtained was the quantitative impact of drilling a new well on the reservoir. These are used as input in a companion paper in which real option and Bayesian methodology are combined to evaluate the economic value of drilling two wells, and to select the best development scenario.
Successful Implementation of Resurgent Relative Permeability Modifier (RPM) Technology in Well Treatments Requires Realistic Expectations
Authors: Kalfayan Leonard J. , Dawson Jeffery C.
Published: December 2007

Industry interest in relative permeability modifier (RPM) treatments for water control is revived. However, as in the past, a majority of the treatments are applied to wells with extremely high water cuts (95% and greater) – with the unrealistic expectation that use of such agents will substantially reduce percent water cut or even prevent (shut off) unwanted water flow altogether.

Recent field experience with newly-developed RPM-based treatments is leading to clearer definition of the proper applications necessary to overcome the existing barriers to success which include, but are not limited to, treatment penetration depth, treatment placement, formation permeability and wettability characteristics, pre- and post-treatment reservoir fluid flow mechanisms, and a history of skepticism.

With these aspects in mind, this paper points to the largely unrecognized economic benefits that can be realized through creative and strategic deployment of low-risk or risk-reducing RPM-based technologies in multi-well scenarios. Examples include oil and gas producer matrix treatments, especially in high permeability and clean sands.
A New Skin Factor Model for Gravel-Packed Completions
Authors: Furui K. , Zhu D. , Hill A. D.
Published: December 2007

Gravel packing is widely used in well completions to prevent sand production. An efficient gravel pack completion retains formation sand without creating significant additional pressure drop through the completion itself. To predict gravel-packed well performance, a completion model that calculates pressure drop for a gravel pack completion is necessary. In this paper, a theoretical turbulence skin factor model for cased-hole gravel-packed wells is presented that can be used to determine the effects of the gravel pack on well performance. The overall pressure drop through the gravel pack completion is divided into three parts; the pressure drop through the gravel between the casing and the screen, which is usually small and can be neglected; the pressure drop occurring through gravel in the perforation tunnels penetrating through the casing and cement and out into the formation; and the pressure drop outside the casing caused by flow converging to the perforations. This study is focused on the latter two pressure drops. Based on extensive 3D finite element simulation studies, the flow field in and around a gravel pack completion is approximated by a series of linear, radial, and hemispherical flow geometries, and the Forchheimer equation is then integrated along a simplified flowpath to obtain the pressure drop both inside and outside of the casing.

The FEM simulation results show that the flow geometry of a cased, perforated, and gravel packed well greatly depends on the ratio of the formation permeability to the permeability of the gravel in the perforation tunnels. As the perforation tunnel permeability approaches the formation permeability, the flow geometry near the perforation through the casing is no longer linear but spherical as if there is no perforation in the formation. As a result, the conventional model of flow in the gravel packed perforations may give inaccurate results under these conditions. The new skin factor model accounts for the transition from linear to spherical flow as a function of the ratio of the formation to perforation tunnel permeabilities. This model also includes permeability damage in a perforation tunnel that significantly increases rate dependent (turbulent) skin effects. We used the model to determine the gravel pack conditions needed to insure that gravel pack skin factor is low and to minimize the effects of turbulence in the gravel pack in high rate wells. Guidelines for gravel permeability are presented based on these results.
The Effect of Cementation on Static and Dynamic Properties in Jauf and Unayzah Formations at Saudi Arabia
Authors: Al-Tahini A. M. , Sondergeld C. H. , Rai C. S.
Published: December 2007

The variability in mechanical properties measured on sandstones from the Jauf and Unayzah formations in Saudi Arabia is observed to be dependent on cementation. Static and dynamic measurements from triaxial testing data, measured acoustic velocities, and examination of core in thin section were used to relate the detailed microstructure and cementation to differences between static and dynamic moduli. The differences between static and dynamic moduli have numerous origins and vary from formation to formation. Properly converting from dynamic (log based) to static moduli is crucial for proper well stimulation analysis and design.

Elastic moduli and velocities (compressional and shear) were measured on sixty-five plugs from five different wells encountered through Jauf and Unayzah formations. Simple models based on moduli-porosity relations failed to adequately explain our observations. We used thin section analysis to evaluate the influence of cementation on the static-dynamic moduli differences. Forty-seven samples were selected for thin section analysis and fifteen representative samples were point counted to characterize and quantify cementation.

Cements in these two formations have variable composition and habits; both affect the moduli and acoustic velocities. It is not sufficient to know that cements exist; it is also necessary to know where the cement occurs. Pure quartz overgrowths cement plays a major role in increasing the moduli and velocities while clay cement plays a minor role. Simple functions suffice to describe the effect of these cements on velocity and the difference between static and dynamic moduli. Effective quartz overgrowth index was defined to quantify the effect of different type of cements. The difference between the static and dynamic moduli is reduced to a value of 2% to 15% when effective quartz overgrowth index is in the range of 16% to 26%. On the other hand, the difference increases to about 80% when high clay cements are present and the percentage of quartz overgrowth index less than 2%. Understanding these often ignored microstructural contributions, helps to understand the variation in moduli and allows for the design of more effective hydraulic fracturing treatments in the Jauf and Unayzah formations.
Field Applications of Low Molecular-Weight Polymer Activated with an Organic Crosslinker for Water Conformance in South Mexico
Authors: Ortiz Polo Roger P. , Monroy Rafael Rodriguez , Toledo Nelson , Dalrymple E. Dwyann , Eoff Larry , Everett Don
Published: December 2007

One of the major challenges faced in the Mexico South region is water management. Water in the oil stream results in extra disposal costs, scale buildup, reduced oil production, and eventually well shut-in (with associated workover costs). Consequently, producing zones are often abandoned in an attempt to avoid water contact, even when the intervals still retain large volumes of recoverable hydrocarbons.

Although natural fractures have a positive effect on oil flow, they also include a negative water or gas flow caused by coning effects or conductive streaks between the producing hydrocarbon zone and intervals above or below. If these zones are water producers, they soon impact the productivity of the hydrocarbon zone. An additional problem must be addressed as well: early water breakthrough caused by edge water flowing through faults, natural fractures, etc. Depending on the desired objective, placement techniques vary. However, placement techniques generally can be divided into two types: those involving a workover rig and those that are rig-less.

This paper will discuss case histories from southern Mexico that have used a low molecular-weight polymer, activated with an organic crosslinker. The candidate selection process, general job designs, laboratory testing results, etc. performed for water-reduction treatments in this area will be presented. These cases include depleted, highly fractured reservoirs.
Petroelastic Modelling as Key Element of 4D History Matching: A Field Example
Authors: Falcone Gioia , Gosselin Olivier , Maire Flavien , Marrauld Jean , Zhakupov Mansur
Published: December 2007

4D (or time-lapse) seismic is sensitive to changes in reservoir pressure and saturation. It allows monitoring of a reservoir during production, helps define areas of unswept hydrocarbons, and aids planning of infill drilling or pressure support solutions.

By improving the reservoir model, 4D reservoir monitoring can improve the accuracy of reserves evaluation and help with the optimisation of reservoir management.

This paper describes the preliminary work carried out as part of an ongoing project on 4D reservoir monitoring. The ultimate aim of the project is to history match a field flow model using both production and 4D seismic data.

The proposed approach, based on the integration of a reliable petroelastic model (PEM) with a dynamic flow simulator, uses an iterative, gradient-based optimisation method to adjust the initial reservoir parameters.

This paper focuses on the assessment of the impact of petroelastic modelling within the framework of 4D quantitative history matching. It shows the results of the procedure that was followed to validate the PEM for the Girassol field in offshore Angola. It addresses the problems of scale usually encountered within a 4D workflow. It also illustrates the results of the sensitivity analysis carried out on the acoustic properties predicted by the PEM when applied to the dynamic flow simulator.

In view of the application of the full 4D history matching loop to the field example, possible ways of determining the acoustic parameters and the areas of the reservoir that are most sensitive to 4D effects were assessed and are presented herein.

This paper highlights the importance of deriving a reliable PEM when dealing with 4D reservoir monitoring and suggests a way forward for integration with computer-aided history matching processes using both production and seismic data.
Managing Maintenance Expenditures with an Integrated Decision Analysis and Portfolio Approach
Authors: Mitchell James C.
Published: December 2007

Energy corporations with large scale operations, like major pipeline systems, refineries and oil fields are faced with high operating & maintenance costs in order to ensure reliable, safe operations. Often maintenance programs are justified by custom, safety or environmental hazard, or a requirement to comply with a current code.

The challenge is to be able to control spending on operations and maintenance while maintaining reliable and safe operations that meet regulatory codes and environmental standards. We advocate an integrated decision management and portfolio approach to analyze the risks of reducing or discontinuing a practice, or conversely, increasing maintenance spending where necessary.

With a traditional approach it is difficult for management to manage costs when risks are not quantified, often overstated or are not known.

Our approach integrates elements of decision analysis and portfolio preference. By developing a simplified model that captures the key areas of risk and benefits each maintenance element is assessed on a consistent basis. Using a portfolio approach to roll-up the program it is easy to identify the most productive projects as well as the projects that should be modified, delayed or dropped. The method also identifies underfunding e.g. where there are higher risks than the corporate risk tolerance allows.

The application of the process within a large transcontinental pipeline system resulted in an initial savings of 20% and ongoing savings of 50% from the original baseline that translated into hundreds of millions of dollars of sustained value.
Geared Turbodrilling Applications and Case Histories in the North Sea
Authors: Seale R. , Beaton T. , Strang G. , Salomons G. , Van Den Bos M.
Published: December 2007

In the late 1800s, the drilling industry recognized the inherent benefits promised by downhole drive systems. Turbodrills, and later, positive displacement motors (PDMs), were introduced to capitalize on these benefits. Both Turbodrills and PDMs convert hydraulic energy in the drilling fluid into mechanical power at the bit. With a Turbodrill, this power conversion is accomplished through the use of turbine blades, and with a PDM, it is accomplished through a seal between an eccentrically rotating steel rotor and an elastomer stator. While there are many benefits to the use of turbine blades to create mechanical power from hydraulic power, their superior efficiency at relatively high output speeds stands out. The rotational speed generated at the bit is not ideal for certain applications, however. The industry recognized this situation in the 1920s, and the development of the geared Turbodrill was initiated. By including reduction gearing in a Turbodrill, high rotating speeds generated by the turbine can be converted into lower RPM and higher torque at the bit.

For decades, there have been attempts to develop a successful geared Turbodrill. Until recently, these efforts have realized little success. Design work performed with the latest software technology and modern materials have now resulted in a very successful, high power, high torque geared Turbodrill. With the new possibility of decreasing output RPM, and increasing the available torque, the range of applications in which Turbodrills perform favorably is significantly expanded. The focus of this paper will be to identify applications in which the deployment of a gear reduced Turbodrill will be advantageous.

This paper will also analyze three recent North Sea case histories, in which geared Turbodrills, together with PDC bits, were run successfully to drill a 12-1/4" hole section through the upper Cretaceous chalk down to the upper Permian Zechstein formation. One of these cases involved running the new geared Turbodrill (NGT) with a rotary steerable system. Analysis of these runs will detail proposed versus actual drilling curves including an in-depth discussion on all parameters encountered during drilling.
Deepwater Four Zones Selective Washpipeless Frac-Pack Completion Inside a Bad Cemented Liner: A Case History
Authors: Vilela Alvaro , Hightower Chad , Montanha Roberto , Luiz Ronaldo , Queiroz Ricardo , Pereira Alexandre
Published: December 2007

Fracpack completions are not new to the oil and gas industry; however, they are operations that are very critical to the results of well longevity, productivity, and are considered operationally "high-risk" completions. Some fields in deepwater Campos basin (Figure 1) - Brazil have tightly spaced productive zones that require sand control and selectivity of production. Two systems were used on the four-zone completion to allow for the tight spacing between zones. On the lower and upper middle zone a modified washpipeless isolation system (Crippled) was utilized and on the lower middle and upper zones a high pressure retrievable washpipeless isolation system (HPRWIS) was used. Both systems utilize a concentric string for isolation, not using washpipe to the bottom of the screen, like a normal land or Gulf of Mexico completion stems from unsuccessful attempts resulting in stuck washpipe in 7" liners with 2 3/8" isolation tubing on floating platforms or drillships and rough seas.

The HPRWIS system also provides "live-annulus" capabilities and a method to isolate the production screen from the tubing after fracing by placing a concentric string into a lower seal bore after the treatment is over. All installation is done at the surface in both systems, but the HPRWIS is initially spaced out to allow communication through the lower most part of the production screen. After reversing operations to remove excess proppant from the workstring, a shifting prong actuates the concentric string down by means of well hydrostatic working across an atmospheric chamber connected to the gravel pack assembly. Actuation is accomplished by mechanically removing a lock ring attached to the atmospheric chamber with the previously mentioned shifting prong. The concentric string may also be retrieved on pipe by utilizing a HPRWIS retrieving tool with straight upward pull to the inner assembly.

This paper outlines the utilization of "State-of-the-art" frac pack downhole equipment technology used to successfully complete, without unscheduled events, a four zone well with bad cemented liner (Figures 2–5) in the Campos Basin, Macae, Brazil.
Effect of IFT Variation and Wettability on Three-Phase Relative Permeability
Authors: Cinar Y. , Marquez S. , Orr F. M.
Published: December 2007

In this paper, we report experimental results that demonstrate combined effects of variations in interfacial tension (IFT) between one pair of three phases and wettability of porous medium on three-phase relative permeabilities. We employed two analogue three-phase systems, in which the IFT between two of the phases could be varied systematically while holding the IFTs between the other pairs of phases roughly constant. We report measured three-phase relative permeabilities for systems with IFTs between two of the three phases varying from 0.005 to 2 mN/m. Phase recovery and pressure drop data were interpreted by the combined Welge/Johnson-Bossler-Naumann (JBN) method to yield relative permeability curves. The results obtained indicate that as IFT between the analogue "gas"/"oil" pair of phases decreases, relative permeabilities for those phases increase at a given saturation. The relative permeability for the analogue "water" phase remains nearly unchanged for water-wet porous systems, but decreases especially at low phase saturations for oil-wet porous systems.
Erosion by Proppant: A Comparison of the Erosivity of Sand and Ceramic Proppants During Slurry Injection and Flowback of Proppant
Authors: Vincent M. C. , Miller H. B. , Milton-Tayler D. , Kaufman P. B.
Published: December 2007

During fracture stimulation treatments, particle-laden slurries may damage pumping equipment and have been shown to erode perforation tunnels. During subsequent flowback operations, minor to severe erosion of surface equipment may be observed if formation sand and/or proppants are produced. This paper compares the erosivity of sand-based and ceramic proppants.

This paper will examine the erosion mechanisms and demonstrate that theoretical and laboratory measurements are in agreement that low density ceramic proppants, due to the superior roundness and sphericity, are less erosive than more angular sand products.

Real-world results from the oilfield, the waterjet industry, pump and valve manufacturers, and the abrasive industry will be reviewed to substantiate the conclusion that proppant angularity is a dominant parameter that increases erosion in typical pumping and flowback conditions.

Impingement tests designed to simulate flowback conditions demonstrate that substituting a spherical lightweight ceramic may reduce wellhead or other impingement surface erosion by up to 95% compared to an angular sand. The highest quality frac sand was nine times more erosive than lightweight ceramic (LWC) in impingement studies. Additional studies utilizing intentionally crushed proppant to increase angularity demonstrate that proppant shape is a dominant factor which controls erosion. Surprisingly, flowback testing has shown that resin coatings applied to proppant have the potential to increase erosion by 15-fold. The authors believe this is partially due to a focusing effect attributed to electrostatic charge. Test alterations with multiphase flow have reduced, but not eliminated, this effect.

Slurry abrasion testing has shown that the highest quality frac sands are over 250% as abrasive as LWC. Although frac sands are often specified to withstand several thousand pounds of closure stress, significant sand degradation was observed after exposure to a reciprocating five pound weight. Erosivity and abrasivity of all proppant types were shown to increase with proppant damage. Erosion within chokes was found to be three times higher with sand than with lightweight ceramic.

Despite conventional wisdom to the contrary, a number of recent laboratory studies have demonstrated that spherical proppants are less likely to flow back from the fracture as compared to more angular products. All data indicate that equipment erosion occurring during the stimulation treatment and subsequent flowback can be substantially reduced through the use of spherical lightweight ceramic proppants.
Corrosion Control in Cotton Valley Production
Authors: Hilliard Harold M.
Published: December 2007

Corrosion in gas-condensate wells producing from the Cotton Valley Formation has been relatively low in spite of the presence of factors favoring a significant corrosion rate. Producers should be aware of the potential for severe corrosion if the fortuitous natural protection encountered should break down.
Fracture Propagation and Formation Disturbance during Injection and Frac-Pack Operations in Soft Compacting Rocks
Authors: Abou-Sayed Ahmed , Zaki Karim , Wang Gay , Meng Fanhong , Sarfare Manoj
Published: December 2007

The widespread use of FracPack technology in deepwater reservoir has been a growing practice. Its purpose is sand control and well stimulation. To-date, field applications and fracture treatments have been designed using traditional hydraulic fracturing simulators that apply LEFM theories. While this is adequate for hard rocks (e.g., tight gas formations), the fracture geometry predictions fall short when applied to fracturing soft rocks. Soft rocks are normally at incipient plasticity and, hence, are prone to compaction.

Compaction, or plastic rock deformations during sand control FracPacks operations and disposal of drilling cuttings slurries in soft layers. The capacity of the created fracture to store or accept solids, the conditions of the rock strength near the fracture faces and the near well/fracture rock porosity or permeability are all highly impacted by the rock compaction during the fracture propagation process.

The objective of the presented research is to assess the impact of compaction and plasticity on fracture geometry and formation properties around the fracture. In particular, it is important to quantify the details of the geometry of factures generated during FracPack and waste disposal operations as well as the porosity/permeability changes in the vicinity of the fracture faces.

In the current paper, rock behavior is described by a variation of the Cam-Clay model. This model represents an inelastic, work hardening model that, depending on the loading path, could predict both compaction and dilatency, in a given formation. This is particularly useful in modeling soft or elasto-plastic compacting formations since the fracture propagation is heavily driven by the leak off into the formation and the in situ stress profile. Formation low permeability leads to lower leak off rates, especially if the injected slurry has a leak-off control additive. This scenario leads to compaction of the rock along the fracture sides. High permeability at the tip results in a large amount of fluid leak off into the formation causing the near-tip zone to dilate during slurry injection and fracture propagation.

The current paper presents results of fracture simulation in compacting rocks including fracture geometry, fracturing pressure and porosity/permeability alteration around the fracture. In the previous paper, results of finite element model provided a benchmark to simulation results. The present work, on the other hand, shows the extent of formation disturbance and porosity/permeability alteration, as well as propped fracture characterization in FracPacks. Finally, the model results addressed the disparity between conventional FracPacks designs and actual treatment data. The observations confirm the need for careful consideration of rock plasticity in fracture simulation to avoid FracPack failures and minimize the absence of TSO response in some field implementations.
3D Visualisation: A Common Language for the Drilling and Subsurface Communities
Authors: Telford C. , Burns M. , Whiteley N.
Published: December 2007

3D visualisation has enabled the Andrew field team in the North Sea to develop a common understanding of geologically related drilling hazards to achieve Best in Class drilling performance on the 16/28-A16 well. Improvement continued in subsequent well 16/28-A17 with a further reduction in geologically related non-productive time (NPT). The common language provided by the 3D visualisation tools enabled the different disciplines onshore and offshore to communicate effectively, integrating the team.

This paper is a case history, describing how the reservoir model, 3D pressure cube and structural model were used with the 4D seismic to identify the geological targets in the reservoir. These models, together with the mapping of the overburden and the historical drilling NPT were used to determine the optimal trajectory to reach the prize. The ability of the multi-disciplinary team to view the subsurface field data alongside the drilling NPT provided a greater understanding of the potential risks and challenges, and ensured buy-in by all in the project from planning through to production. Visual images developed during the planning process were then used to brief the drilling and subsurface contractor services in technical limit, pre-spud and refresher sessions prior to each drilling phase.

Following the problematic A15y well with two sidetracks, the A16 well was drilled and completed with only 13.1% total NPT including waiting on weather, comfortably beating the aggressive 20% target and high historical levels of NPT recorded on mature fields in the same area. Only 9.4% of the total A16 NPT time was geologically related. A17 was drilled and completed with 21.4% total NPT including waiting on weather with only 3% of the total well NPT geologically related NPT.

This paper will be of interest to all personnel involved in planning and execution of a well and system developers wishing to enhance workflows for integrated teams.
A Methodology for Selecting Interventionless Packer Setting Techniques
Authors: King James G. , Arrazola Alvaro J.
Published: December 2007

Eliminating intervention during well completion reduces operating expense and risk. In deepwater, horizontal, and extended-reach applications, interventionless actuation systems for setting completion tools are reducing well intervention and completion time and associated costs without compromising reliability or safety. This paper details the operation of three commercially successful technologies that permit interventionless actuation and provides a methodology for selecting the optimum solution for a particular application.