bluuebunny/crossref_metadata_2025 huggingface dataset:
Flare Gas Recovery in Tunisia--From Liability to Value
Authors: Bauer Matthias , Köck Mario , Jörg Klaus , Ramakrishnan Chandrasekhar , Mestiri Yassine , Scheed Andreas
Published: March 2015

Thyna Petroleum Services (TPS) is a Tunisian joint-venture corporation of the Tunisian governmental oil and gas company, Entreprise Tunisienne d'Activités Pétrolières (ETAP), and the Austrian oil and gas affiliated group OMV A.G. based in Sfax. One of the future objectives of TPS is to avoid, or at least reduce, flaring of associated gas contained in crude oil during oil production. A particular challenge is to discover a process that enables the use of the associated gas despite its untypical gas composition for valorization processes.

Use of the associated gas will also reduce greenhouse-gas emissions. Therefore, this project also could be considered as a Clean Development Mechanism (CDM) project (United Nations 2010).

CDM is an arrangement under the Kyoto Protocol that allows industrialized countries with an emission-reduction or emission-limitation commitment to invest in an emission-reduction project in developing countries as an alternative to more-expensive emission reductions in their own countries. Such projects can earn saleable certified-emission-reduction (CER) credits, each equivalent to 1 ton of CO2, which can be counted toward meeting the Kyoto targets.

Increasing energy prices over the last few years, as well as enhancements in the process area, make the use of associated gas more and more interesting. Furthermore, the pressure of environmental and political organizations to develop new alternatives to flaring is constantly rising.
Experimental Investigation of Wellhead Twin-Screw Pump for Gas-Well Deliquification
Authors: Morrison Gerald L. , Kroupa Ryan , Patil Abhay , Xu Jun , Scott Stuart , Olsen Sven
Published: March 2015

Onshore gas developments are often characterized by drilling, fracturing, and production of wells before low-pressure gas-gathering systems are in place. As well production declines, liquid-loading issues begin to appear. Gas-well deliquefication (GWD) can be accomplished with compression or in-well artificial-lift methods or both. Wellhead wet-gas compression is desirable in that it does not require well intervention to provide GWD, and it is especially useful in maintaining well production in the interim period before field-wide compression is available. Even when fieldwide compression is available, local wellhead compression is desirable at various locations in a field as high-rate wells are added or for wells located at peripheral locations. The use of a twin-screw pump to provide boost for high-gas-volume-fraction (GVF) multiphase flow was investigated experimentally. Tests were conducted with pressure rises ranging up to 250 psi for GVF’s greater than 90%. Water and air were used as the working fluids. The pumping system is a commercially available 230-gal/min twin-screw pump (60 hp) with a design speed of 3,600 rev/min used in conjunction with a knock-out tank that recirculates liquid from the pump exit to provide seal flush. The amount of electrical power required to operate the pump, the inlet liquid- and gas-flow rates, the pressure rise, and the inlet and exit temperatures were recorded. From these data, the volumetric efficiency (flow rate), pump effectiveness, and mechanical efficiency were calculated. Because there is a fixed clearance between the rotating screws and the pump housing, there is a leakage from the high- to low-pressure regions of the pump that will reduce the volumetric efficiency of the pump. It was found that the volumetric efficiency decreased significantly with decreasing pump speed and increasing GVF. At full speed, the volumetric efficiency was between 70 and 88% at ?P=50 psi. Increasing ?P to 250 psi decreased these values to 55 and 81%, respectively. The mechanical efficiency was relatively constant over the pressure-rise range, varying from a high of 48% at the lowest inlet pressure (10 psig) at 0% GVF to a low of 14% for both inlet pressures (10 and 50 psig) at 100% GVF. Overall, the testing demonstrated the ability of a surface twin-screw pump to provide wet-gas compression.
Simulation of Multiphase Fluid-Hammer Effects During Well StartUp and Shut-In
Authors: Han Guoqing , Ling Kegang , Khor Siew Hiang , Zhang He , Thakur Ram K.
Published: March 2015

In this study, well-known commercial software that is capable of modelingfully transient multiphase flow in wellbore and pipeline has been used to characterize the fluid-hammer effects of well shut-in and startup on the coupled subsurface and surface systems. The original work was performed byapplying sensitivity analysis to a typical production system, including wellcompletion, wellbore, downhole equipment (e.g., packer), and the associated surface equipment (i.e., flowline, riser, and valves). This study summarizesthe general course of key factors that worsen the fluid-hammer effects. Fluidhammer is also known as water hammer, a shock wave produced by the sudden stoppage of, or reduction in, fluid flow.

Field operations, such as pressure-transient analysis, facility maintenance,and workover, require a well shut-in process. For a typical production system,the resultant sudden rises in pressure can be critical because they have adirect impact on equipment (i.e., unsetting of the packer) and may cause damageto instrumentation. This paper provides estimates of the typical ratio oftransient shock in pressure and flow rate to preconditional values, and theduration of such pressure shocks. It also proposes the best location for theshut-in valve and the length of flowline needed to reduce the fluid-hammereffects.

This is a pioneering approach to integrate multiphase-flow modeling oftransient fluid-hammer effects by targeting flow-assurance issues. The software used in the study is a fully transient, commercial flow-assurance simulator,and it has been used extensively for well-dynamics studies. The selected toolenables the integrated approach [i.e., from sandface (bottomhole) to wellheadand topside platform accordingly], which can be applied to surface-facilitydesign and can serve as guidance in field operation to avoid hydrocarbon leakages.
Novel Leak Detection Method for Sulfur Recovery Unit Condensers
Authors: Cheung Timothy , Scheck Michael , Goodmurphy Adam
Published: March 2015

At a Shell sour-gas processing facility in Alberta, Canada, hydrogen sulfide contained within the natural gas is converted into elemental sulfur by means of a sulfur recovery unit (SRU). Tube leaks present in a water-cooled SRU condenser can lead to a variety of process issues, including corrosion and the oxidative formation of acidic species. Leak indicators, such as loss of sulfur flow in the rundown and a frothy sulfur appearance, were observed. This work devised a novel method to verify such leaks within a SRU condenser. Using basic pump equipment and an inexpensive commodity chemical tracer, lithium hydroxide, a leak was diagnosed without the shutdown of the unit and with a minimal of expenditures and hazards to operators. The unit was inspected and the tube leak plugged, which enabled the resumption of normal operations.
New Method To Estimate Surface-Separator Optimum Operating Pressures
Authors: Ling Kegang , Wu Xingru , Guo Boyun , He Jun
Published: March 2015

The significance of setting optimal surface separation pressures cannot be overemphasized in surface-separation design for the purpose of maximizing the surface liquid production from the wellstream feed. Usually, classical pressure volume-temperature (PVT) analysis of reservoir fluids provides one or several separator tests through which the optimum separator pressures are estimated. In case separator tests are not available, or the limited numbers of separator tests are not adequate to determine the optimum separator pressures, empirical correlations are applied to estimate the optimum separator pressures. The empirical correlations, however, have several disadvantages that limit their practical applications.

In this study, we approached the problem with a rigorous method with a theoretical basis. According to the gas/liquid equilibrium calculation, the optimum separator pressures were determined. Comparisons of our results with experimental data indicated that the proposed method can simulate the separator tests very well. Because the method has a theoretical basis and does not require existing two-stage or multiple-stage separator-test data as in the application of empirical correlations, it potentially has wide applications in practice for a variety of conditions and yields a more optimal separation scheme than the empirical correlations. Furthermore, the method is independent of reservoir fluid. In the event that separator tests are available from fluid analysis, our method can be used as a quality-control tool. Because the setting for optimal separation pressures vary as the composition of the wellstream changes during the field life, our method provides a quick and low-computational-cost approach to estimate optimum separator pressures corresponding to different compositions.
Pipeline Integrity Assessment Using Probabilistic Transformation Method and Corrosion Growth Modeling Through Gamma Distribution
Authors: Younsi Karim , Chebouba Ammar , Zemmour Nordine , Smati Abdelnacer
Published: March 2015

This paper presents a methodology to estimate the probability of failure of every individual corrosion defect and the residual likelihood of failure of an overall corroded pipeline segment after selected repairs, using structural probabilistic analysis based on the assumption of a stationary gamma distribution of the corrosion process. Metal loss size is taken as the load condition, and the allowable depth of the defect is taken as the resistance condition. The load condition is obtained applying the probabilistic transformation method (PTM) and the resistance condition is obtained through Monte Carlo simulation.

Using inspection data collected on a gas pipeline segment pigged two times, results of the suggested methodology are compared with those obtained by a classical approach based on a Gaussian distribution. It is determined that the use of Gaussian model overestimates for a short time horizon after inspection the failure probability, and suggests many useless repairs. The model developed in this paper instead authorizes a more rigorous estimation of failure probability and a significant reduction of maintenance costs.
Use of the ALARP Principle for Evaluating Environmental Risks and Impacts of Produced-Water Discharged to Sea
Authors: Valeur Jens R. , Petersen Johannes
Published: March 2015

When produced water from offshore production is discharged to sea, itcontains some oil (aliphatic and aromatic components), production chemicals,and naturally occurring radioactive materials (NORM). These groups of materialsare traditionally treated in different ways in the regulations andstandards.

Regulations of oil in produced water are mainly related to maximumconcentrations and the total discharge of the aliphatic (dispersed) fraction.Regulation of chemicals is based on the environmental risk profile of eachproduction chemical, although efforts are made toward regulations based on riskassessment of the discharge of the mixture of substances. For discharge of NORMdissolved in the produced water, no limit values are imposed. For NORM solids(scale, sludge, sand) from process equipment, discharge to sea is in generalnot allowed--it is reinjected or taken to a deposit onshore.

Management of safety risks takes place on the basis of the principle thatrisks shall be reduced to a level as low as reasonably practicable (ALARP). Theconcept of environmental risk is not as unambiguously defined as safety risks.With respect to accidental environmental impacts, the parallel is relativelystraightforward, but with respect to planned environmental impacts (e.g.,emissions/discharges during operation), the parallel to the safety ALARP levelis not so clear; the consequence (the environmental impact) is not linked to acertain frequency (i.e., we cannot talk about risk as likelihood timesconsequence).

Costs are normally defined as money, effort, and time. But what if the costof a reduced health, safety, and environmental (HSE) risk or impact is anincrease in another HSE risk or impact? Produced-water reinjection might causeincreased carbon dioxide (CO2) emissions. Handling solid NORM duringshipping to shore causes health risks to the people handling the NORM. Can thatrisk be justified on the basis of the possible reduction in environmentalimpact by not discharging the solid NORM to sea instead?

This paper highlights the aforementioned issues and proposes a method called’integrated HSE ALARP assessment’ for supporting such analysis. Theenvironmental risks and impacts of discharge of oil, chemicals, and NORM,respectively, with produced water to sea are used to illustrate theseprinciples.
Simulation of Polymer Injection Under Fracturing Conditions—An Injectivity Pilot in the Matzen Field, Austria
Authors: Zechner Markus , Clemens Torsten , Suri Ajay , Sharma Mukul M.
Published: March 2015

Polymer flooding leads to enhanced oil recovery by accelerating oil production and improving sweep efficiency. However, because of the higher viscosity, the injectivity of polymer solutions is of some concern and is important to understand to predict incremental oil recoveries. Achieving high polymer-injection rates is required to increase oil-production rates.

In the field test performed in the Matzen field (Austria), polyacrylamide polymers were injected for the past 2 years. Coreflood experiments with these polymers showed a significant increase in apparent viscosity because of the viscoelastic properties of the polymer solutions. Also, severe degradation of the polymer solution at high flow velocities was detected. In addition to coreflood experiments, flow experiments through fractures were performed. In these experiments, shear thinning and limited degradation of the polymer solution were observed and quantified.

Detailed polymer-injection simulations were conducted that included complex polymer rheology in the fractures and the matrix. The reservoir stress changes and their effects on the fractures were also taken into account as a result of cold-polymer injection. The results of the simulations matched the field data both for waterfloods and polymer-test floods.

The simulations revealed two distinct phases during the injection of the polyacrylamide-polymer solution:

Injection under matrix conditions in an early phase resulting in severe degradation of the polymers Injection under fracturing conditions after the formation parting pressure is reached, leading to limited degradation of the polymers

The calibrated model was used to investigate the impact of polymer rheology and particle plugging on injectivity and fracture growth.

The results of the field test and the simulations indicate that screening of fields for polyacrylamide-polymer projects needs to include geomechanical properties of the reservoir sand and cap/base rock in addition to the conventional parameters used in screening such as oil viscosity, water salinity, reservoir temperature, and reservoir permeability.
Energy-Efficiency Technologies for Reduction of Offshore CO2 Emissions
Authors: Mazzetti Marit Jagtøyen , Nekså Petter , Walnum Harald Taxt , Hemmingsen Anne Karin T.
Published: March 2015

Summary

This paper will discuss novel technologies for increasing the energy efficiency of offshore oil and gas platforms. Three case studies are in progress that are based on actual oil-producing platforms--two on the Norwegian Continental Shelf (NCS) and one in the Brazilian basin. The current focus is on developing compact, novel bottoming cycles for recovery of waste heat from the gas turbine and heat recovery from the compressor train for gas export. The technologies under investigation use steam and alternative working fluids, such as carbon dioxide (CO2) and hydrocarbons. All the fluids investigated in this project are natural working fluids; hence, they will not cause any unexpected environmental issues in the future. A case study was performed that considered an 18-year period of operation on an actual platform and a scenario in which one gas turbine was removed and replaced with a CO2 bottoming cycle by use of the exhaust heat from a different gas turbine. The beauty of this scenario is that it would not increase the weight on the platform because the crate containing the gas turbine to be removed was of a weight similar to that of the crate containing the CO2 bottoming cycle. The substitution would not affect the ability to cover the heat demand on the platform because a waste-heat-recovery unit (WHRU) could be installed on the platform's other gas turbine. The case study indicates a significant reduction in CO2 emissions of 22% (63 000 t/a), and does not involve adding additional weight or volume to the platform. If operating on the NCS, the annual savings in reduced fuel costs and CO2 tax from implementing this scenario would be USD 17 million, although much lower in other territories.
A Modular Subsea Direct-Current Electrical-Power System
Authors: Lai Rixin , Zhang Di , Dong Dong , Chi Song , Harfman Todorovic Maja , Gupta Ranjan , Garces Luis , Gunturi Satish , Datta Rajib , Wijekoon Thiwanka , Sihler Christof , Rocke Svend Erik , Elgsaas Kristin Moe , Savarit Elise , Anbarasu Arungalai , Song Manguelle Joseph , Pappas James
Published: March 2015

Subsea processing has been increasingly accepted by the offshore oil and gas industry as a solution to boost production and reduce cost. Accordingly, the subsea power demand is growing to support various processing loads, including pumps and compressors. Depending on the application, the power rating of a field ranges from tens of kilowatts to tens of megawatts, and the step-out distance ranges from a few kilometers to hundreds of kilometers. Considering the hostile and remote environment, a reliable subsea electrical-power system that is suitable for subsea deployment is clearly desired. This paper presents a modular direct-current electrical-power system that is designed for use in a subsea field with medium or long step-out distance. The proposed system consists of multiple modular converters in the subsea station to achieve the required power-conversion functions. It features high reliability, high flexibility, and reduced installation weight. The system operation and protection are presented, and the performance is verified by a laboratory-scale demonstration.
The Development of High-Strength Coiled Tubing with Improved Fatigue Performance and H2S Resistance
Authors: Valdez M. , Morales C. , Rolovic R. , Reichert B.
Published: March 2015

In the recent years coiled tubing (CT) has become an integral part of many well completion programs. The trend is to higher-strength CT, larger tube diameters and higher pumping pressures while employing relatively small CT spools to satisfy transportation logistics. Coiled tubing is now routinely used at stress and strain levels that significantly exceed prior experience. These conditions have identified limitations within currently available CT products. Today there is a need for higher-strength CT grades with better resistance to severe environments and better fatigue performance in both the tube body and bias weld.

A detailed study of the metallurgical basis of each production step was performed in order to understand the limitations of the current CT technology and manufacturing process. This understanding, coupled with the goal of developing new CT grades that satisfy new market demands, has resulted in a complete redesign of the CT technology and manufacturing process. Extensive trials have been performed, and a prototype manufacturing facility has been constructed to produce new tubing grades. Comprehensive mechanical testing, metallurgical evaluation, low-cycle fatigue testing, and sour (wet H2S) exposure testing of new 110 ksi and 125 ksi grades produced by the new manufacturing process were conducted. The fatigue testing was performed over a broad range of bending strain and hoop stress that anticipates severe operating conditions. Sour exposure testing included static, sulfide stress cracking (SSC) and hydrogen induced cracking (HIC) testing, as well as dynamic, low-cycle fatigue testing after sour exposure.

Laboratory and field testing of commercial-size strings has shown the fatigue life of the new CT grades exceeds the fatigue life of currently available high-strength grades. Additionally, the bias-weld fatigue life is improved significantly, both in general and relative to the base-tube fatigue life. SSC resistance of the new CT grades is considerably better than the SSC resistance of the conventional CT grades with the same strength, making it possible to increase the tubing material strength by about 20 ksi to 30 ksi without deteriorating the sour resistance.

The paper presents comprehensive information on the new CT grades, their performance in various environments under a wide range of loading conditions, as well as the qualification of the new tubing grades for field use. This allows CT operators and users to select more suitable CT grades for their applications. These new tubing grades also can enable field operations with coiled tubing that cannot be conducted safely and reliably with the currently available tubing grades.
Benefits of Remote Activation and New Downhole Tool for Pinpoint Coiled Tubing Stimulation Technology
Authors: Pawar Bharat , Hriscu Joseph , Brand Shannon
Published: March 2015

The global demand for energy has led to an industry focused on increasing process efficiency with respect to innovative techniques for hydraulic fracturing stimulation. One such innovative process is coiled tubing (CT) deployed pinpoint stimulation. Pinpoint multistage fracturing with hydrajetting perforation technique is a solution that enables fracture placement in virtually an unlimited number of fracturing stages in long lateral sections, with a single trip into the wellbore. The evolution of pinpoint stimulation technology and its benefits have been recognized in many papers published along the years.

In some variations of the pinpoint stimulation technique, the bottomhole assembly (BHA) is activated by ball drop and reverse circulation of the ball. This process has been improved with a new generation design of the BHA, which renders the operation capable of being entirely controlled remotely from the surface using movement of the CT string. The ball drop activation is eliminated. This allows real-time, on-demand control of the tool setting. Based on traditional proven pinpoint solutions and adopting this new way of well stimulation, the pinpoint multistage fracturing method has become more efficient. This improved BHA, in conjunction with a proprietary pinpoint stimulation process, can help reduce water consumption on location and horsepower requirements, reduce idle time between fracturing treatments, reduce pump time per stage, and help prevent ball drop difficulties, all without having to make changes to the fracturing spread, equipment, and CT on location.

The improved BHA enables hydrajet perforation, hydraulic fracturing using real-time downhole proppant concentration control, and proppant plugs to be set for zonal isolation. Additionally, multicycle sequences can be repeated in long lateral and vertical wells. It also helps assist centralization of the BHA during perforating operations to help maintain appropriate jet standoff distance.

This paper presents the development approach of the aforementioned improved BHA, and a means to manipulate it from the surface. Validation during field testing is also outlined.
Performing Riserless Subsea Operations Utilizing Coiled Tubing in Open Water
Authors: Lasseigne Beau , Lindsey BJ , Larke James
Published: March 2015

Due to the versatility of modern coiled tubing (CT) operations coupled with the increasing demand for deepwater activity, CT is becoming a common conveyance method to perform subsea operations without the need of a marine riser or lubricator connected to the subsea wellhead. These operations utilize the CT string as an umbilical deployed through the moonpool of a dynamically positioned multi-purpose support vessel (MSV) to provide a variety of services to the operator without CT entering the wellbore. Without the need for a conventional deepwater rig or riser-based vessel, operations utilizing CT as an umbilical become a valuable time- and cost-saving option to perform subsea intervention work. Job objectives include well stimulation, lower zonal abandonment, subsea dispersant application, subsea equipment testing, flowline intervention, and hydrate-preventative blowout preventer (BOP) flushing.

From 2008-2012, an average of one CT umbilical job per year was performed. The method has increased in popularity and over the past two years, nine CT umbilical operations have been successfully completed. These successful operations include supplying nitrogen gas subsea to perform leak detection testing, utilizing dual CT umbilical strings to perform subsea BOP flushing as a pump down and return line, nitrified acid stimulation treatment, flowline hydrate removal, flowline purge to platform, and cementing zonal abandonment.

The combination of increasing deepwater technology and the adaptability of CT increases intervention and testing methods for operators. This paper will explain the techniques used, system improvements (both operational and HSE), and it will provide an overview of various types of jobs performed.
A Field Case History of Sulfate Reducing Bacteria Attack on Coiled Tubing Bias Welds - Root Causes and Remediation
Authors: Seal Clark , Padron Tomas , Mallanao Genesis , Maddy Tim , Craig Steven
Published: March 2015

Historically in our industry there have been many anecdotal claims of premature coiled tubing pipe failures during plug milling operations with recirculated fluid. Many of these failures shared related failure characteristics but no root cause was believed to have been identified by the service companies involved. In 2013, for one particular client, a series of failures on the coiled tubing string bias welds was observed, with a root cause due to the presence of sulfate-reducing bacteria (SRB) in the recirculated water. Two different mechanisms were identified as causing the premature failures on the bias welds: high-pressure corrosion fatigue that started at severe internal pitting caused by the presence of bacteria, and sulfide stress cracking caused by the SRB producing H2S.

A detailed analysis was also completed of time periods where fluid was spent stagnant in coiled tubing during rig-down/rig-up operations. Procedures were adjusted accordingly to prevent failure from further exposure to similar conditions by modifying recirculated fluid-handling volumes, improved biocide use, and rigorous multicomponent inhibition and purging during and between jobs.

Several specialist colleagues, familiar with SRB corrosion, were surprised at the speed SRB formed and created problems in coiled tubing in these environments. During the investigation process a rigorous fluid-testing protocol was developed. A prevention procedure was implemented during coiled tubing plug milling operations in this field. Afterward, no further coiled tubing failures were observed during similar operations in this area.

These failures have an industrywide impact in terms of personnel safety, operational disruption, and the cost and inconvenience of replacing coiled tubing strings. Information regarding coiled tubing failures related to bacteria exposure is only recently being published in our industry (Sherman 2014, Sherman 2015, Edillon 2015). Establishing the causes of these pipe failures and developing a procedure to minimize and/or eliminate their recurrence will allow safer operations for everyone involved in these operations. This paper presents the characteristics of these failures and the corrective actions taken to prevent further failures in coiled tubing exposed to similar conditions.
Modern Wireline Forces Modeling Using High-Impact Supplementary Utilities
Authors: Castillo H. , Smalley E.
Published: March 2015

With the increased popularity of long, deep and tortuous wells, mainly in high-cost operating environments, the risks associated with wireline logging operations and interventions in these modern complex wells have become more acute. Several risk-reduction technologies and forces-modeling software capable of simulating these operations have been developed and successfully applied.

This paper describes several high-impact supplementary modeling utilities that have been implemented within a leading forces-modeling software that enable users to adequately plan and execute complex wireline operations. The utilities are designed to perform dedicated analyses using the project data already included in the wireline operation models.

The following utilities are presented in this paper: Pump Down AnalysisCable Tension AnalysisFriction Coefficient AnalysisTool Depth Creep AnalysisStuck Pipe AnalysisStuck Wireline/Tool AnalysisTool Free Fall Analysis

The effective use of these utilities significantly reduces the non-productive rig time associated with recovery operations and can assist with optimizing pump down operations, accurate positioning of downhole tools, as well as locating tool strings dropped in the well. Use of the utilities can also improve the accuracy of wireline downhole conveyance models while enhancing the ability to perform high-tension operations in a safe and efficient manner. The economic value resulting from the use of these applications is directly associated with the aggregate daily rig cost and the financial cost of the resulting deferred production volume during non-productive time, which together can be in excess of a million dollars a day.

This paper provides descriptions and application examples of these supplementary wireline modeling utilities, the logic and calculations supporting them, and the resulting economic benefits they deliver.
Using Coiled Tubing to Safely and Efficiently Mill Out Composite Bridge Plugs Set Across Zones with Significant Differential Pressures
Authors: Li Yang , Terry Adrian , Parr Christopher , Stanley Rick , Dunsmore Braden
Published: March 2015

Coiled tubing (CT) is one of the most common and effective methods employed to mill out composite bridge plugs (CBPs) that are used to isolate zones during completion. Typically, the zones are normally pressured or over pressured, i.e., each interval approximately the same pressure. Recently, in a New Zealand field, a plan was set to mill out CBPs that had been set between zones that were tight gas and conventional with as much as 3,780 psi pressure differential between them.

One major challenge relates to the CT CBP milling. While milling the plug that isolates the over-pressured zones, the differential pressure can exert significant forces on the milling assembly, raising the potential for buckling/failure of the CT. To reduce this risk it was decided that a bridge plug with an equalizing path would be used to eliminate the large pressure differential and potential upward forces. Another challenge was the issue of cross flow between the zones after milling was completed, and the potential for well control issues due to some under-pressured zones that could not support a full fluid column, causing loss of hydrostatic pressure.

For the under-pressured zones, nitrogen was used to equalize the pressure across the plugs prior to milling them. To minimize the risk of getting stuck and potential CT failure, the operation was closely monitored and optimized by using a CT real-time downhole communication system. The real-time downhole pressure captured by the system during plug milling provided the firm evidence that equalization had occurred.

This paper reviews the selection of plugs/mills and the milling strategy for safely milling CBPs that have been set across zones with significant differential pressures. The benefits of using a CT real-time downhole communication system is discussed by illustrating the case study of successfully removing 25 CBPs with CT in the three wells within a field.
Application of a Biocide Water Treatment Program to Prevent Coiled Tubing Corrosion: A Case Study
Authors: Edillon Lemuel , McLeod Richard , Henderson Matthew A. , McVicar Warren , Eyre Kellen , Pelletier Robbie , Yao Shunyu , Yan James
Published: March 2015

From December 2013 to February 2014, a major Canadian coiled tubing (CT) service company experienced several premature CT failures that all occurred in the same geographic region of northeastern, British Columbia. The failed CT samples were analyzed both by the manufacturer and a third party to determine the failure mechanism. Upon inspection, internal corrosion on the base material and preferential corrosion of the bias weld filler material was, in multiple cases, determined to be the cause of failure. It was concluded that microbial induced corrosion (MIC) likely caused localized corrosion and pit initiation leading to crack propagation and sudden failure.

When MIC was identified as a potential cause of failure, the service company's engineering team initiated an extensive water testing program to determine a preventative solution. The base fluid used for CT operations in the specified geographical region typically consisted of produced water, often recycled multiple times from fracturing operations. The CT service provider was not responsible for the water supply, nor did it have historical information on the supplied water quality.

In several occurrences, the fluid tested positive for the presence of harmful acid producing, and sulfate reducing bacteria, which further supported the presence of MIC. To eliminate or minimize the potential for harmful corrosive bacteria, the service company implemented a biocide water treatment program.

The service company explored several methods of applying both liquid and powdered biocide establishing a best practice for pre-treating the supplied water and treating it throughout the operation. Field testing proved the application of biocide dramatically decreased bacteria count. To date the biocide treatment program has been successful and no additional premature failures due to corrosion have been recorded. This has allowed the engineering team to optimize biocide loadings and revise the CT retirement criteria.

While the subject of microbial induced corrosion in CT has been widely discussed and published throughout industry literature, the problem has not been prevalent among CT operations in Canada. This paper discusses a specific premature CT failure due to corrosion, an analysis of the base fluid in the area that was believed to cause the corrosion, and the biocide treatment program used to prevent similar CT failures in the future.
Coiled Tubing Inverted Gas-lift System Installation on the Norwegian Continental Shelf
Authors: Babayev Rufat , Sirevaag Bjorn , Grindheim Kjell Ivar , Kerr Scott , Sliper Britt
Published: March 2015

The Statfjord field was the first, and one of the largest, fields developed so far with Statoil as operator. The field was discovered by Mobil in 1974 and Statoil took over operatorship in 1987.

The field was developed with Statfjord A, B and C production platforms, which all have concrete gravity base structures incorporating storage cells. Statfjord A began production in 1979.

The field will remain in production until 2025 and possibilities to further expand the lifetime are being looked into.

One of the techniques that are being applied to rejuvenate some of the older wells is retrofit gas lift solutions.

In this paper detailed information on an Inverted Gas Lift System (IGLS) applied to a well on the Statfjord A platform will be presented. The IGLS solution included a solution to retain downhole safety valve functionality in the well and required qualification of a new type of coiled tubing material.

The following aspects of the project will be discussed in detail in this paper: Background and objectives.Method selection, planning and equipment qualificationOffshore operations for installation of the systemFollow up and results
Overcoming Extended-Reach Challenges for Annular Fracturing
Authors: Castro L. , Craig S. , Micheli R. , Livescu S.
Published: March 2015

More operators are seeing the production benefits of targeted horizontal annular fracturing. The most active method of annular fracturing in the USA involves ported sleeves installed with the completion and activated via an isolation packer. Initial operations were in lateral lengths of 2,000 to 3,000 ft. However, current operations are planned for accessing up to 10,000 ft laterals. Increasing lateral length results in the traditional access challenges faced by all coiled tubing (CT) operations. The traditional method of lubricant use is the primary option due to its simplicity. The second method is to use fluid hammer tools (FHT). These are industry standard for improving efficiency in composite plug milling operations, but their use in genuine extended-reach operations is not as broad.

This paper briefly covers historical ported annular fracturing operations and the various methods of achieving increased lateral reach. Results from four wells with lateral reach of 7,200 to 10,277 ft are detailed in the paper. The balance of the paper details operational results and optimization from several extended-reach wells.

Detailed lateral reach modelling was performed prior to all operations. This permitted the determination of the number of expected stages that would require the use of lubricant in the fracture treatment flush. Given that residual lubricant in the completion is removed by the erosion effects of the proppant in the fracture treatment, each stage would require an additional fluid flush. This gives an opportunity to modify the lubricant concentration, type, and volume in the flush. Before using fluid hammer tools (FHT) for setting the isolation packer, laboratory testing was performed to ensure the bottom-hole assembly (BHA) system compatibility.

The lubricant testing and initial field results were reported previously (Livescu and Craig 2014; Livescu et al. 2014a,b). This paper provides operators with sufficient case histories of the planned use of an advanced lubricant in genuine extended-reach wells in real life situations. This knowledge can improve operator confidence in drilling longer laterals for predictable access for annular fracturing operations.
Optimization of Matrix Acidizing With Fluids Diversion in Real-Time Using Distributed Temperature Sensing and Coiled Tubing
Authors: Medina Eber , Sierra Jose , Garcia Alexis , Gleaves Jorge , Mendez Josue
Published: March 2015

Carbonate formations in southern Mexico are commonly stimulated using matrix acidizing treatments to increase well productivity by removing near-wellbore (NWB) damage. Such damage can be attributed to accumulation of paraffin and asphaltene deposits during the productive life of the well and, in other scenarios, to fluid invasion while performing workover activities. A high perforation length across the reservoir to increase production from this highly natural-fractured carbonate has been the completion option for several years. The use of diverters is a common practice in the Bellota-Jujo field when multiple intervals are open. However, the effectiveness of the diversion had not been evaluated in real-time. A distributed temperature sensing (DTS) option was deployed to measure temperature profiles along coiled tubing (CT) equipped with an internal fiber-optic cable and a modular bottomhole assembly (BHA) consisting of pressure, temperature, and depth correlation sensors. This option was selected to monitor the treatment and help make real-time decisions.

This real-time fiber-optic (RTFO) integrated system used during the stimulation allowed identification of zones with higher and lower admission. Based on this information, decisions were made during the pumping schedule, modifying volumes and rates of diverting agents and stimulation fluids being pumped through the annular space between production tubing and CT, also pumping through CT using a fluidic oscillating tool optimizing the diversion process during different stages of the intervention. This system enabled the operator to correlate depth and continuously monitor the temperature changes across the producing zone of the well.

The findings and results of the stimulation treatment with this technique used in the well, Bricol 2DL, are presented in addition to the thermal analysis of the DTS profiles.

The use of the RTFO integrated system during a matrix stimulation treatment in a carbonate formation with high permeability contributed to successfully evaluating the effectiveness of the fluids and mechanical diversion resulting in a well productivity increase of 60%, thus keeping the well in production since the treatment was performed.
A New Method for Leak Detection in Gas Pipelines
Authors: Ling Kegang , Han Guoqing , Ni Xiao , Xu Chunming , He Jun , Pei Peng , Ge Jun
Published: March 2015

Two types of approaches -- physical inspection and mathematical-model simulation -- are used to identify a leak in a gas pipeline. The former method can result in an accurate detection of the location and the size of the leak, but comes with the expense of production shutdown and the high cost/long time to run the physical detection, which is very crucial in long-distance gas pipeline. The latter approach detects a gas leak by solving the governing equations, thus leading to quick evaluation at much lower costs, but with higher uncertainties. Our literature review indicates that a simple, practical, and reliable method to detect a gas leak under the conditions of unknown inlet or outlet gas rate, or unknown inlet or outlet pressure, is highly desirable. In this study, we develop single and multiple rate test methods to detect leaks in a gas pipeline. By conducting multiple rate tests, the location and size of leaks can be detected. The new method can be applied under the conditions of no inlet or outlet rate available or no inlet or outlet pressure available. Because these conditions are not uncommon in gas-pipeline transportation, our method provides a quick and low-computational-cost approach to detect leaks corresponding to different scenarios.
Evaluation on Risk for Ship Collision with Archbridge and Crash Capability of Anti-Collision
Authors: Jilun Miao , Chuang Cai , Shengxie Xiao
Published: March 2015

The development of the highway traffic has promoted the construction of increasing numbers of river-crossing bridges, but at the same time, large-size ship causes serious threat to structural safety of the bridge. The probability of bridge-ship collision increases, water safety accidents have happened frequently in the recent years. Arch bridge is easier to be subjected to the threat of ship collision because of small navigation clearance on both sides. However, study on the destructive consequences by ship impact on arch bridge is seldom. This paper takes reinforced concrete arch bridge as an example, on the basis of the forecast of the water-level frequency, flow velocity and long-term navigation density of the ship, the ship collision probability on different parts of the arch ring at different water levels are analyzed to deduce the annual collapse frequency of the grand bridge. The risk matrix evaluation result shows that there is medium risk in long-term. The establishment of finite element numerical model concludes the energy absorption and the change process when the arch ring suffers from collision from the ship under different working conditions as well as the relationship among the impact force, crown displacement and collision depth along with time change. According to the result of simulated analysis, the maximum collision force of the main arch ring suffered from the ship is 25.9MN, and the resistance of the main arch ring is 33.6 MN, so the existing structure basically meets the requirement for fortification against the ship collision. The numerical simulation results are qualitatively consistent with the risk of evaluation. The results of the analysis can provide scientific foundation to the maintenance and management of the arch bridge.
Exploration and Grouting of Large-Scale Water Capsule in the Fault Fracture Zone of Yonglian Tunnel
Authors: Zhang Qingsong , Li Peng , Zhang Xiao , Li Shucai , Zhang Weijie , Wang Qian
Published: March 2015

A large-scale water capsule was formed after 8 times inrush of mud and water in Yonglian tunnel. The capsule seriously inhabited the construction of the tunnel. By combining with the geological conditions in tunnel site, the causes and characteristics of the water capsule were analyzed. Its spatial location and size were explorated by comprehensive exploration methods. In order to control the water capsule, the treatment scheme composed by full-face curtain grouting in left tunnel and decompression by drainage in right tunnel was made, and the composite and controlling grouting methods were proposed. The composite and controlling grouting technology was applied in the treatment. It was composed by grouting parameters selection, grouting material and technology optimization by means of numerical simulation, model experiment and SEM microscopic experiment. By means of the grouting effect examination methods including P-Q-t curve, examination holes, surrounding rock deformation monitoring and excavation, the water capsule was proved to be treated successfully. The engineering case provides a reference for the similar engineering to some extent.
Local Use of Ankaferd Blood Clotter in Emergent Beating Heart Coronary Artery Bypass Grafting
Authors: Atalay Hakan , Atalay Atakan , Dogan Omer F.
Published: March 2015

Background:

Severe beeding which requiring massive blood transfusion after emergent beating heart surgery is shown to be 1–3%. Therefore, complications and side effects of transfusion can be seen. The aim of this study was to investigate the effectiveness of Ankaferd blood clotter (ABC) as a new topical herbal blood clotter to decrease mediastinal bleeding in emergent beating heart CABG patients who medicated with clopidogrel and acetyl salisilic acite (ASA) prior to CABG surgery.

Materials and Methods:

25 CABG patients received a high dose clopidogrel (600 mgr) and 300 mgr ASA have been included into the study (ABC group). 25 patients have also been included into the study for comparison (placebo group, PG). After the administration of protamine sulphate, a 10 ml of ABC solution has been sprayed to the surgical area including mediastinum and epicardial sac. We compared mediastinal drenaige, reoperation due to tamponade, and required blood and blood products in both groups.

Results:

The mean amount of bleeding after operation was 230 ml in ABC group, and 490 ml in CG (P=0.001). In ICU, bleeding in ABC group and CG was 410ml and 680ml, respectively (P=0.0022). The mean total bleeding from mediastinum was 530±280 mL and 990±440 mL In ABC and CG group, respectively (P=0.001). The amount of autotransfusion was as follows: 175 mL in ABC group, and 290 mL in CG (P=0.002). No patient needed the surgical revision in ABC group, but four patients (16%) from CG group because of cardiac tamponade. Seventeen patients from CG required blood transfusion due to low hematocrite level postoperatively. In CG, the mean hematocrite level was 17±2,3. Transfusion of fresh frozen plasma and platelets in ABC group and CG were as follows: 0.2 and 0 in ABC group, and 0.3and 0.4 in CG.

Conclusion:

Our study showed that the local use of 10 mL ABC reduces bleeding significantly. Therefore, transfusion requirements of PRBC, platelets, and total blood units in patients on clopidogrel and ASA undergoing emergent beating heart CABG. To provide cardiac tamponade because of excessive mediastinal bleeding and requirement of blood transfusion after emergent CABG patients who previously administered clopidogrel and ASA, we propose local use of ABC solution as a potent coagulant agent.