bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling Channelized Systems: A Robust Approach
Authors: Chike Ikechukwu , Onyekonwu Mike
Published: December 2007

The importance of capturing the architecture of depositional facies within a system cannot be overemphasized. For a channel system as in most cases in the Niger Delta, the problem of accurately describing the geometry of these channels exists. Ideally, object based models are best suited to reproduce facies architecture, but this is generally hindered by the rigidity of this algorithm. Moreover, the application of outcrop analogue in the object model to reproduce the subsurface could be stalled by the differences in diagenesis between the outcrop and the reservoir. Thus, the need to modify the algorithm in modelling the system arises.

We adopted a robust object and pixel based model to capture the reservoir heterogeneity while honouring hard data. The approach includes integrating several available options for a particular channel setting in the software used (for the object based model) to come up with a flexible descriptor. Depositional trend were also built to capture the upward fining sequence of tidal channel sands. This was accomplished by building a complex transformation sequence to ensure accurate petrophysical description within the facies using a pixel model.

The result is a model that incorporates morphologic information and petrophysical trends from analogue while accurately describing the rock and fluid property using well data.
Displacement Efficiency of Supercritical CO2 Flooding in Tight Carbonate Rocks Under Immiscible and Miscible Conditions
Authors: Zekri A. Y. , Almehaideb R. A. , Shedid S. A.
Published: December 2007

Carbon dioxide flooding is currently being investigated as possible EOR processes in UAE candidate reservoirs. The major reasons for selecting CO2 flooding as an EOR process were low permeability and heterogeneity of these reservoirs that resulted in poor response to traditional water injection. In this study, immiscible CO2 displacement efficiency of low permeability carbonate rocks of a selected UAE field is evaluated experimentally. Laboratory tests were conducted on seven tight cores extracted from the selected oil field with a permeability range from 0.16 to 11.99 mD and porosity range from 7.72 to 18.63%. The effects of pressure, permeability, and initial oil saturation on the residual oil saturation after flooding at immiscible conditions were investigated in this study. The pressure was varied from 1600 to 4000 psi, and permeability was varied from 0.16 to 11.99 mD at constant pressure of 1600 psi. All runs were conducted at isothermal condition of 127 °F while the initial oil saturation ranged from 0.334 to 0.79 % pore volume.

Experimental results indicated that immiscible supercritical (SC) CO2 is capable of mobilizing oil in the very low permeability environment (0.16 mD) with reasonable displacement efficiency. Also, higher displacement efficiencies could be obtained if we start the flooding process earlier, i.e. at higher oil saturation, as there is a critical starting oil saturation required to optimize the displacement efficiency. Side effects from the process are that notable asphaltene precipitation was observed and SC CO2 injection in limestone cores results in the precipitation of calcite in the downstream area. Scanning Electron Microscope (SEM) was used to provide accurate description of pores prior and post CO2 flooding experiments and Energy Dispersive X-Ray Spectrometer (EDS) was used to evaluate the composition of the deposited asphaltene.
Gage Design—Effects of Gage Pad Length, Geometry and Activity (Side Cutting) on PDC Bit Stability, Steerability, and Borehole Quality in Rotary Steerable Drilling Applications
Authors: Mensa-Wilmot G. , James B. , Aggarwal L. , Luu H. Van , Rueda F.
Published: December 2007

Technical and operational success, in rotary steerable drilling (RSD) programs, requires optimization of the following performance qualifiers (PQ)1 – stability, rate of penetration (ROP), steerability, durability and borehole quality. Bottom hole assembly (BHA) design and drill bit development must aid in the optimization process.

Rotary Steerable Systems2,3 (RSS), based on their design and operational principles, exhibit different functional characteristics. This realization necessitates the need for specialized PDC bits4,5, for the different RSS tools. Technologies and/or features incorporated in these bits must enable optimization of the identified PQs.

Three of the listed PQs - stability, steerability and borehole quality6 - are directly influenced by a bit's gage design and configuration. This observation has created an intense industry debate on the contributions of gage design, as they relate to the functionality, dynamic behavior and overall performance of different RSS tools.

This paper will isolate and evaluate the effects of gage design concepts in RSD applications. The discussions will relate gage designs to PQ optimization, based on specific RSD programs.

Gage design theories, and functional characteristics, will be supported by extensive field data.
State-of-the-Art Training for State-of-the-Art Rigs—Options in Training for Cyber Rigs in New Locations
Authors: Cormack D.
Published: December 2007

Almost without exception new build offshore drilling rigs these days are mechanized or sequenced to some degree. This is particularly the case on new build offshore platforms regardless of where in the world they are to operate. For new and remote regions simulator and vendor equipment training along with a high degree of cultural awareness and basic minimum standards training are therefore critical elements in the pre-operational phase of any new build offshore platform project.

Historically equipment training is not included in the tender process for new build rigs and consequently has to be worked out after the event, usually by the first drilling contractor to operate the equipment. This can work out well when the drilling contractor has experience of simulators and understands the range of possible solutions.

Key to success in such projects is flexibility. Flexibility in choice of simulator solutions. Flexibility when scheduling personnel on training. Flexibility in how the cultural aspect is tackled. Flexibility in ensuring how basic minimum standards are attained. Flexibility from training providers to adapt to local conditions.

This paper reviews how one drilling contractor approached crew training for three new build offshore cyber rig projects in three different areas of the world.
PDC Bits: All Comes from the Cutter/Rock Interaction
Authors: Gerbaud L. , Menand S. , Sellami H.
Published: December 2007

PDC drill bit performances in hard rock has been greatly improved during the last decades by innovations in PDC wear, impact resistance and better vibrations understanding. The bit design is generally done by balancing the bit, distributing uniform wear along the profile and achieving high drillability and steerability. To obtain required drilling performances, drill bit designer adjust features such as profile shape, gage and mainly cutter characteristics (shape, type and orientation). Cutter rock interaction model became a critical feature in the design process. But previously used models considered only three forces on a cutter based on the cutter-rock contact area: drag force, normal force and side force. Such models are no longer valid with the introduction of PDC cutters with chamfer and special shape.

This paper presents a new cutter rock interaction model including some several improvements. It is based on the presence of a build-up edge of crushed materials on the cutting face often described in the literature. In addition, the chamfer, which significantly affects bit Rate Of Penetration (ROP), is taken into account (shape and size). Forces applied on the back of the cutter and due to the rock deformation and back flow of crushed materials are considered in the model. Finally, results of numerous single cutter tests (under atmospheric and confining pressure) are presented and compared to the new cutter rock interaction model predictions. An analysis of the influence of the PDC characteristics (shape, size, chamfer, back and side rake angles, ….) is presented.

The model has been applied to optimize the cutting efficiency and bit steerability and some design rules are given to minimize the specific energy and maximize the rate of penetration. Finally, full scale laboratory drilling tests and field results indicate that the use of accurate cutter rock interaction model can help the drill bit designer to find the best drill bit for a specific application. Standard laboratory full scale drilling procedures have been developed. The tests have shown that drillability, stability, steerability and wear can be improved and controlled by acting on the cutter characteristics, cutter setup, trimmer characteristics and gage type.
From 0 to 500 in Under 3 Years—The Caspian Recruitment Challenge
Authors: Richardson R. , Steel T.
Published: December 2007

In early 2003, the drilling contractor was awarded the final in a series of operations and maintenance contracts for 4 "cyber" platform rigs which were at the time in various stages of engineering design and construction with the first to start operations in September 2004 offshore Azerbaijan in the Caspian Sea.

While Azerbaijan has one of the longest histories of oil exploration and production, this was largely on old rigs under Soviet style leadership, operational and safety standards. The Operator's corporate objectives of no harm to people and delivering continuous improvement in drilling operations performance required a safe, effective and trouble free start-up and world leading safety and operational standards delivered through competent highly motivated personnel.

The recruitment challenge in sourcing some 500 expatriates and Azerbaijani nationals to deliver these objectives required a new approach so the contractor assembled a cross-functional project team to identify and solve the potential problems ahead.

This paper will demonstrate how the company's approach to recruitment and retention, particularly the extensive project planning and management up front, can be directly linked to performance in the platform rig start-up. It will conclude by showing how the lessons learned from this approach can be transferred to other start-ups and recruitment campaigns providing opportunities for optimising recruitment and retention strategy, and associated cost and efficiency savings.
Rotary Liner Drilling Application in Deepwater Gulf of Mexico
Authors: Mota J. , Campo D. , Menezes J. , Smith P. , Jackson T.
Published: December 2007

Many wells drilled today have complex well paths or are drilled through depleted or problem formations. In these wells, the liner may have to be reamed or drilled in, either to pass through the previously drilled hole or to make a new hole in the problematic formation. In many cases, the liner cannot be run to bottom as planned because unexpected problems are encountered. This situation can cost millions of dollars due to the required remedial work and deferral of production.

This paper will discuss a rotary liner drilling application utilizing an expandable liner hanger in the Gulf of Mexico. The primary objectives of the trial were to develop a better understanding of the status of current technologies and how these apply to the challenges of this type of application.
How To Unify Low-Shear-Rate Rheology and Gel Properties of Drilling Muds: A Transient Rheological and Structural Model for Complex Well Applications
Authors: Herzhaft B. , Ragouillaux A. , Coussot P.
Published: December 2007

Due to their complex formulations, Drilling Fluids and especially Oil base Muds exhibit very complex rheological properties. They are commonly described as thixotropic shear thinning fluids with a yield stress. A set of standards established by the American Petroleum Institute is available for the rheological characterization of these fluids and classical descriptions with non-Newtonian fluids such as yield power law models are typically employed. Although these descriptions and measurements are adequate for classical drilling situations, they reveal to be insufficient to describe more complex phenomena as barite sag, or pressure peak due to transient gel breaking on restart. In particular ultra low shear rate rheology has been early accepted as a key parameter for determining sag potential, and is poorly described by the classical models and measurements. On the other hand, time-dependent behavior (classically apprehended in static conditions through Gel 0 and Gel 10 measurements), which can be very significant even in dynamic conditions, is not quantitatively linked to the rheological description.

This paper describes how a simple thixotropic and structural model is able to describe completely all the features of the rheological behavior of drilling muds. The parameters of the model can be simply deduced from on site measurement using Fann 35 rheometer. We show that mud viscosity results at any moment from the competition between aging and shear rejuvenation. As a consequence, viscosity bifurcation (abrupt transition towards complete stoppage or rapid shear) may appear at low shear, which might explain the occurrence of barite sag. Finally, it is shown how any transient phenomena like pressure peaks when starting a pump after circulation stoppage may be adequately predicted by using this model in hydraulic calculation.
Innovative Systems Approach Enables Smart Intervention Solutions
Authors: Ellzey T. , Heisig G. , DeGeare J. P. , McGurk M. , McNicol J.
Published: December 2007

One of the most frustrating and costly aspects of any wellbore intervention operation is when little or no progress is made during a trip in the well and tools are returned to surface showing no visible signs of performing work. Conversely but equally frustrating is when a downhole tool becomes worn or damaged beyond its useable life and the operator continues to try to make progress based on readings from traditional surface-based indicators and gauges. These situations are becoming more common as wells become deeper, more complex and technically challenging to intervene.

To address these problems, a "smart intervention" system has been developed that provides a new level of process control to the operator while intervention work is being carried out. The system incorporates a short, modular MWD-style sensor sub that is integrated into the bottom hole assembly (BHA). Measurements such as weight on bit, torque, RPM, bending moment, vibration, annular and bore pressures are gathered downhole to provide a clearer picture of what is occurring at and around the downhole tools. Information is then transmitted to surface using mud pulse telemetry and viewed on a rig floor monitor. The system allows the operator to make informed decisions and take immediate action to optimize the intervention being performed.

This paper discusses initial system integration and field testing, benchmarking and analysis, as well as results of, and lessons learned from, early field case histories. The tests and field runs demonstrate the potential of this systems approach to provide economic benefits through significantly improved efficiency, reduced uncertainty, better reliability and less wear and damage to downhole tools and equipment.
Method To Reduce Milling and Trip Times During the Recovery Operations of Permanent Production Packers
Authors: Haughton D. B. , Connell P.
Published: December 2007

There are many situations that require the removal of a production packer from a wellbore, whether it is a planned workover or a stuck packer during the completion process. In all cases, the packer must be washed over and recovered or milled up and pushed down to the bottom of the wellbore.

Most of the methods used today are the same tools and techniques that have been in use for the last 30 or so years. These methods incorporate a shoe or milling head with a specific type retrieving tool to catch the packer after milling away the slips, and were designed for packers that came with millout extensions or blank bottoms. Today, however, packers are being run with seal bore extensions instead of millout extensions. Packers are being manufactured with more exotic materials and high chrome metals. These materials present a milling challenge -- not only do they create longer milling times, but they also usually require two or more trips to mill and recover the packer.

A new method of milling has been specifically designed to reduce milling and trip times in these modern packers. This new method allows an operator to engage a smooth packer bore and completely remove all of the packer material and slips rather than removing only the outside material and leaving the packer mandrel. This milling procedure is quicker and produces smaller amounts of debris, therefore reducing milling times. The milling heads can be dressed with the most up-to-date cutting structures that will optimize the removal of the packer material depending on whether it is standard grade or of a high-tensile, high-chrome content.

This paper will discuss the process and operational procedures pertaining to this new method, along with case histories. The paper will detail the advantages of this method and the tools used, as opposed to the conventional methods and tools that are widely used through out the world today.
Pipe Rotation and Hole Cleaning in an Eccentric Annulus
Authors: Hemphill T. , Ravi K.
Published: December 2007

The drilling community generally believes that pipe rotation helps hole cleaning during both drilling and cementing. However, there has been a lack of reliable calculations to describe the effect and application in engineering and design and deployment. This paper discusses the effect of pipe rotation on velocity profile and pressure drop in concentric and eccentric annulus during the axial flow of non-Newtonian fluid. The calculations are applied to the design of hole cleaning during drilling and cementing.

In the absence of reliable calculations one can only guess the impact of pipe rotation on hole cleaning. This work gives an engineer the tool to design for improved hole cleaning and hence save time and money during well construction and production.

Pipe rotation is all the more important in an eccentric annulus to remove the drill cuttings and the gelled drilling fluid from the narrow annulus. This is because in an eccentric annulus, in the absence of pipe rotation, the fluid flows preferentially through the wider annulus. The pipe rotation speed (i.e., the RPM) required to move the gelled drilling fluid and the drill cuttings in various annulus configurations and eccentricities are presented. The results discussed in this paper can be applied for effective hole cleaning during drilling and cementing, which should save nonproductive time (NPT) during drilling and cementing and also reduce remedial and intervention costs during well production.
An Operator's View of the Choices for Deepwater Intervention
Authors: Browning G. M. , Moss J. H.
Published: December 2007

Well thought out concept selection is critical in developing a future deepwater intervention system that will be both technically and commercially successful. Short term solutions that are developed for part-time usage may get by but should eventually lose out to systems designed for full utilization. This paper will address critical concept issues and provide one Operator's recommendations for long term success.
Novel Approach To Predict Potentiality of Enhanced Oil Recovery
Authors: Jian H. , Wenfen H.
Published: December 2007

The potentiality prediction of enhanced oil recovery (EOR) is the basis of EOR potentiality analysis as well as the robust guarantee of the reliability of analysis results. In the light of statistical learning theory, establishing an EOR predictive model substantially falls within the problem of function approximation. According to Vapnik's structural risk minimization principle, one should improve the generalization ability of learning machine, that is, a small error from an effective training set can guarantee a small error for the corresponding independent testing set. The up-to-date results from studies on statistical theory in recent decades even recent years are firstly applied to EOR potentiality analysis. The applications of group method of data handling (GMDH), Improved BP artificial neural network, and support vector machine (SVM) are discussed. The comparison of the results from three methods indicates that SVM can pay more attention to both the universality and extendibility of a model when the samples are very limited, which shows a good prospect of its application. A method used to generate a set of sample theoretically is developed in this research by combining quadrate designing, reservoir simulation, and economical evaluation.
An Efficient Model for Gas-Rate Forecasting in Complex Reservoirs
Authors: Jordan C. L. , Fenniak M. J. , Smith C. R.
Published: December 2007

This paper presents a simple, but accurate, computer method for predicting the performance of multiple gas wells in complex reservoir scenarios. Real life gas reservoir characterization and forecasting can be accomplished with the substantial reduction of effort when compared to numerical simulation and a substantial increase in accuracy when compared to traditional decline methods. Conventional analytical methods in many cases are highly unsuitable for new field development, in-fill drilling, or long-term production planning. Numerical simulation methods often require impractical pre-processing or computational time. With the method presented in this paper, production profiles can be generated for arbitrary shaped gas reservoirs with multiple wells. The model presented overcomes many limitations of traditional methods, and extends analytical modeling into multiple well scenarios with interference effects, arbitrary reservoir shapes, and perhaps even varying rock properties.
Stimulating High-Water-Cut Wells: Results From Field Applications
Authors: Arangath R. , Obamba J. F. , Saldungaray P. , Malonga H.
Published: December 2007

A common scenario in many mature oilfields is to have most of the wells producing hydrocarbons with high water cuts. These wells are commonly not considered as good candidates for matrix stimulation. Water based treating fluids would enter preferentially into zones with high water saturations leaving oil zones untreated with a final result of increasing overall water production. However if the water production mechanism is understood and the appropriate fluids are selected then stimulating producer wells with high water cuts can be a rewarding operation. The treatment can be carried out while providing favorable economics to the entire operation.

The key fluid for treating high water cut wells is a Viscoelastic fluid that provides self-diversion from water to oil bearing formations. At the same time this same fluid can be used, on long intervals, to divert matrix stimulation treatments from stimulated to un-stimulated intervals or from high permeability intervals to low permeability intervals. These features are unique and inherent to its nature and the particular break mechanism making them suitable for selective placement and uniform zone coverage even for bull heading operations.

The paper presents the experiences with this Viscoelastic fluid used in nine different mature producer wells with pre-treatment water cuts ranging from 32% to 94%. One additional case in presented on a newly drilled producer that was perforated and completed very close to a water zone that was successfully stimulated without any increase in produced water cut. Treatments presented include both cases in which fluids are bull-headed and placed through coiled tubing. The case histories included in the paper illustrate the pre and post treatment production results obtained. All are characterized by the fluid usage contributing to the stimulation being uniformly conveyed across the oil-bearing portion of the reservoir and away from the watered out intervals.

A description of the well candidate selection process, formation damage identification and the remedial treatment design, execution and results is briefly discussed along with the economic impact that such treatments offer to mature oilfields.
A Case Study of Offshore Production Control Through Advanced Process Automation
Authors: Bumatay R. , Sankaran S. , Mijares G. , Vazquez-Esparragoza J. J.
Published: December 2007

The Malampaya Deepwater Gas-to-Power project, the single biggest industrial investment to date in the Philippines, supplies clean, environment-friendly fuel to service 30% of Luzon's power generation requirements. Subsea wells and a manifold gather gas and liquid and control the flow to a shallow water platform. Here, gas and condensate are separated before transporting dry gas through a 504 km long pipeline to an onshore gas plant. A key challenge of the Malampaya offshore facility is to maintain a smooth, continuous operation under varying demands of gas delivery from the onshore gas plant, which often leads to slugging at low flow rates.

This paper focuses on the successful implementation of Halliburton's advanced process automation solutions to improve operation of the offshore platform. The applied solutions include advanced control applications to better control production and the operation of the methanol recovery column and an alarm management system to improve the effectiveness of the alarm system that enables the operators to better respond to abnormal operating conditions.

A core principle of the advanced control application for production control is to maximize the use of topside installed capacity to better handle production rate changes while maintaining the stability of the export gas compressor and the liquid processing equipments, particularly at low production levels.

As part of the implementation of the advanced control applications, some advanced regulatory control improvements to the compressor systems were required to automate speed control for the compressor and to reduce recycling.

The alarm management system allows regular analysis of alarm activity and identifies "bad actors". The project included the execution of a rigorous alarm rationalization procedure, which reduced the number of unnecessary alarms considerably and allowed the operator to focus on the needed areas of action during abnormal operation.

Significant tangible and intangible benefits have been identified as a result of the implemented solutions. These benefits included increases in production, stemming from improved process stability, and reduction of environmental risks from the methanol column operation and better alarm reaction times. This case study highlights the value that advanced process automation can bring to the upstream industry.
A New Correlation Predicting the Formation of Iron Sulfide Precipitation in Wastewater Disposal Wells
Authors: Bahadori A. , Zeidani K.
Published: December 2007

Scale formation and well plugging due to the incompatibility of injected wastewaters is a critical field problem in wastewater disposal wells. When different wastewaters are mixed it is necessary to evaluate their compatibility prior to the injection in disposal wells. The individual wastewaters may be quite stable at all system conditions and present no scale problems. However, once they are mixed, reaction between ions dissolved in the individual wastewaters may form insoluble products that cause permeability damage in the vicinity of the wellbore.

In this paper, the composition of different wastewaters that were collected from southwest Iranian desalting plants disposal wells were analyzed critically. Laboratory studies as well as field experience has shown that formation damage in wastewater disposal wells may occur mainly due to the conception of Iron Sulfide in the case of mixing a wastewater which contains Iron ions with a wastewater containing H2S. A new correlation is developed estimating the critical concentration of Iron ions, Fe(2+) (ferrous ion), which will stay in solution at various pH values and a wide range of H2S concentration in crude oil desalting plants disposal wastewaters. This correlation eliminates the need for compatibility assessment, which is usually assessed either by solubility calculations or by experimental testing, for water mixtures that contains Iron ions and dissolved H2S. Finally, a real case field problem was analyzed and based on the correlation's results three different potential solutions were recommended for further field trial implementation.
Intelligent Integrated Dynamic Surveillance Tool Improves Field-Management Practices
Authors: Al-Fattah S. M. , Dallag M. M. , Abdulmohsin R. A. , Al-Harbi W. A. , Issaka M. B.
Published: December 2007

This paper describes solutions developed using a dynamic surveillance tool to automate several workflow processes of the reservoir management, production engineering, and R&D Center at Saudi Aramco. The objective is to provide improved efficiency in field management practices, while enhancing collaboration between reservoir and production engineers; ultimately resulting in improved decision-making process.

The solutions provided include a combination of smart tools and automated workflows designed to improve reservoir management and surveillance processes. A candidate recognition system was developed to identify and flag problem wells that require immediate remediation. As new production and injection data become available, the system that is linked to the corporate database can automatically display these data for fast and rigorous validation. In addition, a formation damage indicator function is also calculated using field data and mapped to spot production problem areas and identify damaged wells. A daily surveillance tool, which compares the performance of individual wells to the average performance of a group of wells, is also provided to allow the reservoir and production engineers to easily identify underperforming wells, promptly intervene, and recommend best completion practices. Benefits include efficient well management and cost avoidance resulting from early intervention and remediation, while avoiding full-scale problem resolution.

Another dynamic surveillance tool was designed and views were developed to provide online access to the hydrocarbon phase behavior and petrophysical data for the R&D scientists and reservoir engineers. The tool allows integration of the hydrocarbon phase-behavior data and comparison of petrophysical data with historical production/injection data and production well logs, resulting in enhanced analysis, production optimization and data validation. Additional benefits of the smart tools and automated workflow processes include considerable timesavings, with pertinent data being automatically updated, validated and used in the analysis, leading to improved efficiency in field management practices.
SSC Resistance of QT-900 and QT-1000 Coiled Tubing
Authors: McCoy T. H. , Thomas J.
Published: December 2007

Laboratory sulfide stress cracking (SSC) tests were performed on specimens taken from QT-900 and QT-1000 coiled tubing (CT) test strings in an attempt to define zones of acceptable sour service. Acceptable pH-PH2S zones of service for QT-900 CT were proposed in SPE 93786.1 This paper presents additional QT-900 CT test data to further refine acceptable zones of service, with and without use of a chemical inhibitor. In addition, SSC testing was undertaken on QT-1000 CT. The SSC tests on QT-1000 CT were performed in manner similar to that conducted on QT-900 CT, using acidified aqueous solutions with H2S partial pressures ranging from 0.00345 to 100 bars and pH from 3.5 to 6.5, with and without inhibitor. Both as-milled and pressure-cycled tubing was tested. Test specimens were taken from parent metal and bias weld locations. The test data was used to construct acceptable zones of service on a pH-PH2S diagram.
A Comprehensive Bit Hydraulics Model for Gasified Drilling Fluids
Authors: Dogan H. A. , Gucuyener I. H. , Ozbayoglu M. E.
Published: December 2007

Determination of pressure drop at the bit is one of the major concerns for establishing proper hydraulic design. Little has been known about pressure drop estimation at the bit for single phase muds, and even less is known about gasified fluids. The aim of this study is to fulfill this gap in the literature. Although there are numerous studies on this subject available in the literature, they are either valid for high gas flow rates or developed using very strong assumptions. The proposed theory, which is valid for both sonic (critical) and subsonic (sub-critical) regimes, is based on the solution of the general energy equation for compressible fluid flow. Unlike the existing models in the literature, the proposed model takes the change in kinetic energy, compressibility factor, and internal energy terms into consideration. Moreover, the model uses "a mixture sound velocity" approach for determination of the sonic boundary of the fluid. Based on the proposed model, a computer program is developed for calculating the pressure drop through a nozzle at subsonic flow region. The performance of the proposed model is tested by comparing the model results with existing models estimations using realistic field data. It is observed that, as much as 9% difference occurs between the results of the proposed and existing models.
Drilling Optimization at the Aloctono Block in Venezuela With the Utilization of Latest Technologies in Impregnated Bits and Turbines
Authors: Botelho R. , Barreto J. , Bello S. , Anato W. , Uzcategui G.
Published: December 2007

The Aloctono Block at northern Monagas state in Venezuela is one of the most difficult drilling challenges in this region. It basically consists of a Cretaceous geological structure overlaying younger formations, characterized by heterogeneous lithology and presence of extremely abrasive and compacted formations with fine to very fine sandstone grains, in which the compressibility can be higher than 40,000 psi.

Conventionally this geological column has been drilled with packed and/or pendulum assemblies using roller cone and PDC bits, so that the following problems take place: difficulty of well verticality control, excessive wear of drill string components, poor bit performance with short runs, low penetration rates and excessive bit wear, leading to higher risks of cone loss in roller cone bits and the consequent fishing operations. This scenario generates high drilling costs, long well drilling time with lots of bit trips, drill string inspection and downhole tools replacement. For such reasons, a reevaluation of these conventional drilling practices, as well as the utilization of latest drilling technologies have a huge impact on time and costs reduction.

This work shows how the utilization of latest technologies in impregnated bits and turbines optimized the drilling performance of the Aloctono Block, reducing quantity of bits, trips and others, representing huge savings for the operator. One must note that other benefits were also accomplished, such as well bore quality and verticality control, reduction of surveys, no fishing operations and reduction of replacement and repair costs of drill string components.
Optimization of Tertiary Water-Alternate-CO2 Flood in Jilin Oil Field of China: Laboratory and Simulation Studies
Authors: Guo X. , Du Z. , Sun L. , Fu Y. , Huang W. , Zhang C.
Published: December 2007

Most of the low permeability oil reservoirs in Jilin oil field of China have reached their economic limit of production by waterflooding and even many wells have been abandoned due to low productivity. Interest in recovery enhanced technology of tertiary miscible or immiscible CO2 flooding is increasing in these low permeable reservoirs. In this paper, a laboratory study using a high-pressure PVT cell and a simulation study using full-field fully equation-of-state (EOS) compositional reservoir modeling were undertaken to optimize the design of a miscible or immiscible CO2 flood pilot project for the Xinli Unit in Jilin oil field. The laboratory study includes phase behavior analysis, asphaltene deposition assessment, and minimum miscibility pressure (MMP) determination in the CO2 corefloods. Based on building a full-field 3D geologic model and history matching waterflood performance, a preliminary CO2 flood reservoir modeling has been used to distinguish displacement mechanisms and reservoir performance of natural depletion, continued waterflooding, continuous CO2 and water-alternate-CO2. The simulation study and the pilot test showed water-alternate-CO2 after waterflooding is an effective method of improved oil recovery for the low permeability reservoir and it can appreciably reduce water production and enhance oil recovery. Simulation studies has also been completed to determine an optimal water-CO2 ratio, optimal CO2 slugs and optimal CO2 injection rate. The pilot operation is now well implementing according to above-mentioned study achievements. Future plans for water-alternate-CO2 optimization include continuation of performance monitoring to help optimize tapering strategy in order to enhance further oil recovery in the low permeability oil reservoir.
Approximate Pore-Level Modeling for Apparent Viscosity of Polymer-Enhanced Foam in Porous Media
Authors: Huh C. , Rossen W. R.
Published: December 2007

Foam is used in the oil industry in a variety of applications, and polymer is sometimes added to increase foam's stability and effectiveness. A variety of surfactant and polymer combinations have been employed to generate polymer-enhanced foam (PEF), typically anionic surfactants and anionic polymers, to reduce their adsorption in reservoir rock. While addition of polymer to bulk foam is known to increase its viscosity and apparent stability, polymer addition to foams for use in porous media has not been as effective.

In this pore-level modeling study, we develop an apparent viscosity expression for PEF at fixed bubble size, with the intention of better interpreting the conflicting laboratory coreflood data available. To derive the apparent viscosity, the pressure-drop calculation of Hirasaki and Lawson (1985) for gas bubbles in a circular tube is extended to include the effects of shear-thinning polymer in water, employing the Bretherton's asymptotic matching technique. For polymer rheology, the Ellis model is employed, which predicts a limiting Newtonian viscosity at the low-shear limit and the well-known power-law relation at high shear rates. While the pressure drop due to foam can be characterized fully with only the capillary number for Newtonian liquid, the shear-thinning liquid requires one additional grouping of the Ellis-model parameters and bubble velocity.

The model predicts that the apparent viscosity for PEF shows behavior more shear-thinning than that for polymer-free foam, because the polymer solution being displaced by gas bubbles in pores tends to experience a high shear rate. Foam apparent viscosity scales with gas velocity (Ug) with an exponent [−α/(α+2)], where a, the Ellis-model exponent, is greater than 1 for shear-thinning fluids. With a Newtonian fluid, for which α =1, foam apparent viscosity is proportional to the (-1/3) power of Ug, as derived by Hirasaki and Lawson.

A simplified capillary-bundle model study shows that the thin-film flow around a moving foam bubble is generally in the high-shear, power-law regime. Since the flow of polymer solution in narrower, water-filled tubes is also governed by shear-thinning rheology, it affects foam mobility as revealed by plot of pressure gradient as a function of water and gas superficial velocities. The relation between the rheology of the liquid phase and of that of the foam is not simple, however. The apparent rheology of the foam depends on the rheology of the liquid, the trapping and mobilization of gas as a function of pressure gradient, and capillary pressure, which affects the apparent viscosity of the flowing gas even at fixed bubble size.
Application of Horizontal Waterflooding To Improve Oil Recovery From Old Oil Fields
Authors: Westermark R. V. , Schmeling J. , Dauben D. L. , Robinowitz S. , Weyland H. V.
Published: December 2007

This paper discusses the results of the application of horizontal waterflooding technology to improve the recovery of oil from older fields. A multi-disciplinary approach combining geological interpretations, rock mechanics evaluations, reservoir simulation studies, and drilling technologies was employed. A range of reservoir conditions in which the technology is viable is discussed and the results of the field tests are presented.

The major focus has been on the shallow sandstone reservoirs in northeast Oklahoma and southeast Kansas. It has been demonstrated that additional oil can be recovered in several different reservoir environments in these older fields, by utilizing a combination of horizontal and vertical wells. Two previous SPE papers described the results of a Department of Energy (DOE) supported horizontal waterflooding pilot located in the Wolco Field, Osage County, Oklahoma.

The technology has continued to evolve over time. The key to assessing the potential for a horizontal well application is a thorough understanding of the reservoir description, including the oil saturation, depositional environment, reservoir pressure, permeability, and an evaluation of any prior production and/or injection. Other parameters include the length, spacing, positioning and orientation of the injectors and horizontal producers in the target zone. Use of rotary-steerable drilling equipment has made it possible to drill underbalanced, short-radius horizontal laterals at a low cost. Special procedures have been adopted to permit the transport of openhole logging equipment through the short-radius curve to the end of the lateral, providing a good description of reservoir properties and detecting the presence and orientation of natural fractures.

Results from several successful horizontal well projects are discussed. These include (1) two horizontal waterfloods in shallow Bartlesville sandstone reservoirs, (2) recovery from a rim of moderately heavy oil underlain by water, and (3) an application of horizontal waterflooding in a moderately heavy oil reservoir.
Mass Transfer and Gelation in Sandstone Cores of a Novel Water Shutoff Chemical
Authors: Castelijns H. J. , Pel L. , Huinink H. P. , Zitha P. L. J.
Published: December 2007

An innovative water shut-off chemicals was recently proposed. The chemical is soluble in oil without any chemical reaction and forms gel in the presence of water. When the chemical dissolved in oil is injected in the near well-bore formation it modifies selectively the two-phase flow properties in order to reduce the production of water. The gelation process involves the partitioning of the chemical from the oil phase into the water phase. Upon contact with water a heterogeneous (hydrolysis and condensation) reaction takes place between gelant and water, leading to the formation of a gel in the water phase.

Recently we have demonstrated that NMR imaging is a viable technique for visualizing and quantifying the above reactive mass transfer process in bulk and glass bead systems.1,2

Here we report a new core-flood experimental study consisting of the placement of the chemical dissolved in oil in Bentheim sandstone cores. NMR imaging and (T1 and T2) relaxation time measurements are used to monitor the reactive transport of the chemical in the core. The mass transfer of the chemical from the oil phase to the water phase is derived from the measurement of T1 related to the oil phase. The progress of hydrolysis and gelation is indicated by a decrease in T2 of the water phase.
Simops: Coiled Tubing in Parallel With Rig Activities
Authors: Torgersen K. I. , Weiss A. A.
Published: December 2007

This paper covers SIMOPs, SIMultaneous Operations, and describes the topic of doing well service operations in parallel with main rig activities. There are various descriptions for the term SIMOPs, but this paper focuses on doing well servicing operations with Coiled Tubing, CT, or Wire Line, WL, in parallel with drilling or other rig based operations from the main derrick.

SIMOPs have been performed for several years on some platform. However this is still a new innovation for others, and is often considered to be impossible due to various small platform limitations, such as: deck space, crane capacity, bed space, etc.

This paper highlights the potential upside of working multiple operations in parallel. The focus is on the challenges related to rigging up and operating within the limitations of the platform and rig. This is described through case histories, as examples of how solutions have been developed to perform a large scope of well services activities on rig less platforms in parallel with drilling activities through cantilever rig, from jack up rig.
Business Improvement by Integrated Concession Development
Authors: Beuthan H. C. , Shibani M. , Bremeier M.
Published: December 2007

Concession 97 in the Sirte basin of Libya is subdivided into three different exploitation areas (figure 1). The operator, Wintershall, developed discoveries in each area in 1988, 1990 and 1995 respectively. The producing reservoirs are in the challenging Sarir and Lidam horizons. The Sarir reservoirs are stratified sandstones with medium to very low permeability. The Lidam formation, consisting of a lower limestone and an upper dolomite, has limited net pay. While reservoir rock properties in both Sarir and Lidam reservoirs are of rather poor quality, the oil properties are very favourable.

Ongoing appraisal and the application of advanced exploration methods in recent years resulted in the discovery of additional fields and extensions. Substantial additional volumes have been appraised. However, primary recovery factors are expected to be relatively low.

Recent discoveries and the optimisation of the existing fields led to the completion of an integrated redevelopment of the entire concession. Three decentralized gas-oil separation plants were recently replaced by a central unit including gas utilization. A key challenge of such a scheme is the long distances, of up to 50 km, between oilfields and the separation plant. Trunk-lines with multiphase pumps are utilized to overcome the pressure losses and to allow reasonable backpressures at the wellheads.

Considerable savings in operational expenditures were achieved and the integrated concession development approach will enable the operator to apply different improved recovery strategies. The synergies gained from combining improved recovery methods are seen as a prerequisite for commercial application.

This paper aims to illustrate the integration of new field development and mature field re-development. The integration scheme enables the operator to implement improved recovery methods in difficult reservoirs which are not feasible on a stand-alone basis.
Upscaling of Foam Mobility Control to Three Dimensions
Authors: Li B. , Hirasaki G. J. , Miller C. A.
Published: December 2007

The applications of foam are 3-D on a field scale. However, most previous research focuses only on properties of foam in 1-D. Experiments were performed in 3-D, and the compositional reservoir simulator UTCHEM was modified to predict foam flow in 3-D.

The 3-D experiments demonstrated that, under similar experimental conditions, the mobility of foam in a 3-D tank is greater than that in a 1-D column. They also showed that foam greatly increases lateral gas distribution along the bottom of the tank and the average gas saturation for both homogeneous and heterogeneous packings with the effects being significantly larger in the latter case. The reservoir simulator UTCHEM was modified for foam flow. The foam simulation parameters were measured in 1-D sand columns and the simulator was modified to match the 1-D and 3-D experiments. The proposed model successfully history matched the homogeneous and heterogeneous 3-D sand tank experimental results for average gas saturation, gas injection rate, gas distribution and pressure profile along the tank diagonal 6 inches from the bottom.

The results of this study represent an advance in understanding of foam flow in 3-D. The simulator could be used to design a foam process in 3-D.