bluuebunny/crossref_metadata_2025 huggingface dataset:
Methodology and Benefits of a Drilling Analysis Paradigm
Authors: Iyoho A. W. , Millheim K. K. , Virginillo B. K. , Adeleye A. R , Crumrine M. J.
Published: December 2007

This paper discusses a segment of drilling engineering -- drilling analysis -- that is assumed to be practiced routinely, but in many cases is not given the necessary attention, time, and resources required.

Routinely acquired drilling, geologic, mud-log, and logging data, are shown to be amenable to organization into a knowledge-based structure that permits: Use of statistical analysis to develop challenging but achievable technical limits, or best composite time (BCT), for similar wells – location, depth, hole size.Statistics-based best composite cost (BCC), the dollars equivalent of BCT. Both the BCC and BCT represent practical, challenging but achievable benchmarks that are continuously upgraded, providing significant steps in the process of drilling costs reduction.Specialized learning-curve analysis, trouble-time analysis, flat-time analysis, time vs. depth analysis, cost vs. depth analysis, rig and crew performance evaluation, bit-on-bottom and tripping analysis, time distribution plots, etc.Convenient drilling data cross-correlation with wireline logs, geology and mud-log data, to further delineate drilling problem zones and improve drillingoperational performance.A historical understanding of well construction that can contribute to continuing drilling improvement, and a method to provide feedback and collaboration with company drilling personnel, rig contractors, and service companies.

This paper reviews existing variations, key elements, and typical field applications of drilling analysis, and puts forth the case that drilling analysis should become an integral part of drilling engineering, the same way well-test analysis is an integral part of reservoir engineering. The need for a university curriculum and training on this key discipline is stressed, along with the necessity for management to champion the use of drilling analysis as an on-going process to improve organizational drilling performance.
The Completion of Subsea Production Wells Eased by the Use of a Unique, High-Density, Solids-Free, Oil Based Completion Fluid
Authors: Taugbøl Knut , Lilledal Lars , Juel Henning , Svanes Kåre , Jakobsen Tom Magne
Published: December 2007

Hole stability issues and the need to reduced drillpipe torque have made oil-based drilling fluids the systems of choice for highly deviated or horizontal reservoir sections offshore Norway. However, the tendency of barite sag in non-aqueous drilling fluids has led to plugging of sand-control screens, thereby creating in some cases the need for a solids-free environment for the completion. Unfortunately, because of problems related to emulsion blocking when mixing filtrate from oil-based drilling fluid and water-based completion fluid, displacing to brine after drilling with oil-based fluid can damage productivity.

This paper describes the design and successful application of a unique high-density solids-free, oil-based completion fluid. This fluid obtains its density from an emulsified internal phase of heavy brine. This eliminates the requirements for solid weight materials for fluid density, providing a solids-free, oil-continuous environment for the completion.
The Effect Of The Synthetic- And Oil Based Drilling Fluid's Internal Water Phase Composition On Barite Sag
Authors: Albertsen Tron , Omland Tor Henry , Taugbøl Knut , Saasen Arild , Svanes Kåre
Published: December 2007

One important issue for drilling operations is control of down hole pressures. When drilling with synthetic or oil-based drilling fluids, the ability to maintain all the weighting agents in suspension is particularly difficult since these fluids are more vulnerable for sag than water-based drilling fluids.

In the current study, it has been shown that the ability to keep barite in suspension also depends on the chemical composition of the water phase. The sag tendency of a mineral oil-based drilling fluid, a linear paraffin-based drilling fluid and both an ester and a LAO-based synthetic drilling fluid has been evaluated. For comparison, all fluids were formulated with equivalent water activity in the internal brine phase. The results show that for all these fluids, improved performance was observed if the traditional calcium chloride salt was replaced with a selection of other salts. Formates as the internal salt, gave generally better performance than if calcium chloride was used. The best performance with respect to sag stability in the tests was observed using an ammonium calcium nitrate as the internal salt phase.

The paper describes in detail the effect that different salts in the internal brine phases in synthetic and oil-based drilling fluids was found to have on sag performance in a series of tests.
Evaluation of Heave-Induced Dynamic Loading on Deepwater Landing Strings
Authors: Everage S. DeWayne , Zheng Nanjiu , Ellis Sean E.
Published: December 2007

With current landing string tensile loads approaching 1.5MM lbs., deepwater drilling programs are quickly eliminating comfortable design margins. Consideration of static loading alone in these cases can sometimes be insufficient. This paper provides a mathematical model to predict dynamic axial loads imposed on a deepwater landing string by a drillship's response to ocean waves. The model can be adapted to a given landing string's geometric and mechanical constraints. The model will help the user identify the correct window for pausing a landing operation when sea states are increasing, or alternatively, may allow the user to continue deepwater landing operations with increased confidence during what may be considered marginal conditions.
Wellbore Enlargement for a Deepwater Casing Program: Case Study and Developments
Authors: Courville David F. , Childers Ronald D. , Miller Gregory C.
Published: December 2007

The success of deepwater exploration and development operations is greatly dependent on utilizing larger OD casing to reach the ever-increasing depths of today's prospects. Recently in the Mississippi Canyon region of the U.S. Gulf of Mexico's deepwater arena, a leading exploration company utilized new hole enlargement technology to simultaneously drill and enlarge a wellbore to facilitate the installation of a multiple string casing program.

A case study is detailed to illustrate how proper planning and the utilization of new hole enlargement technology matched with a rotary steerable system, culminated in the successful execution of this critical well construction operation. As part of the planning process, hydraulics analyses and BHA stabilization optimizations using special computer software are discussed. The application of a new design concentric reamer in a deepwater tight clearance casing program that enlarged more than 18,000 ft of four different-sized wellbore intervals will be presented.
Taut Leg Moorings Using Polyester and VLA Anchors
Authors: Agnevall Thomas
Published: December 2007

The use of catenary moorings systems in deep and ultra deep water requires long and heavy mooring lines. As a consequence the floater has to support a large weight and the mooring footprint becomes large and may interfere with neighbouring infrastructure. Installation of these mooring systems becomes very expensive due to the vessels that are required. For deep and ultra deep water mooring systems the more appropriate moorings system is the taut leg mooring, using shorter and lighter mooring lines. The mooring loads arrive at an angle between 30 and 45 degrees at the bottom, requiring the anchor points to resist not only horizontal, but also considerable vertical loads. This paper discusses the use of synthetic ropes and anchors in deep water mooring systems. The characteristics of the ropes and anchors are presented and how they can be used in both catenary and taut leg mooring systems.

When oil and gas exploration and production took place in shallow to deep water, the most common mooring line configuration was the catenary mooring line consisting of chain and wire rope (Fig. 1). For exploration and production in deep to ultra deep water, the weight of the mooring line starts to become a limiting factor in the design of the floater. To overcome this problem new solutions were devised consisting of synthetic ropes in the mooring line (less weight) and/or a taut leg mooring system (Fig. 2).

The major difference between a catenary mooring and a taut leg mooring is that where the catenary mooring arrives at the seabed horizontally, the taut leg mooring arrives at the seabed at an angle. This means that in a taut leg mooring the anchor point has to be capable of resisting both horizontal and vertical forces, while in a catenary mooring the anchor point is only subjected to horizontal forces. In a catenary mooring, the restoring forces are generated by the weight of the mooring line. In a taut leg mooring, the restoring forces are generated by the elasticity of the mooring line.
Planning and Execution of a Long, Tight Clearance Liner Through a Whipstock Milled Window
Authors: Dooley Lynn B. , Faul Gary L. , Courville David , Harrell Danny , Shipley Jonathan A.
Published: December 2007

A long, tight clearance liner was recently installed through a whipstock-milled window in a deepwater well. The length and weight of the liner, coupled with the tight clearances, pushed the limits of current technology. The liner was successfully run through a deep whipstock milled window and cemented at a depth below 24,000'. This paper describes the planning and execution involved in this critical well construction operation.
Integrated BHA Concept of the Latest Generation Rotary Closed-Loop System for Hole Sizes from 5 7/8" to 18 ¼"
Authors: Hahne Ulrich , Risdal Georg , Ruszka Jon , Wahlen Liv Sivertsen
Published: December 2007

During the past 7 years, rotary steerable drilling technology has emerged from prototype status to a standard application world wide. This paper focuses on the latest generation integrated Rotary Closed-Loop System which now enables the industry to benefit from this technology in hole sizes from 5 7/8"-18 ¼". The paper discusses the integrated BHA concept and the sequential implementation of additional BHA components. Modular positive displacement motors placed immediately above the steering device simultaneously gives another step change in drilling performance while reducing casing wear and extends the drilling envelope. The paper provides an insight into applications where the integration into the rotary closed-loop BHA, of real-time Logging While Drilling (LWD) formation pressure measurements and real time acoustic property services has complimented, or indeed eliminated the need for, wireline logging runs.

Using such an integrated Rotary Closed-Loop System in the Norwegian Troll Field created incremental production revenue of 6 Billion USD.
Overcoming Shallow-Gas Drilling Difficulties in the Gulf of Thailand
Authors: Tiraputra Pornpoch , Thiravutpinyo Pattanapong , Pongorapin Sunchai , Fraboulet Bernard , Dooply Mohammed , Friedl Walter , Elmarsafawi Youssef
Published: December 2007

Shallow gas-bearing formations in the Gulf of Thailand present numerous drilling and cementing challenges. In the first three wells drilled on platform WP11 in Bongkot field, initial cementing of surface casing did not achieve effective zonal isolation of the shallow-gas zone. Several techniques were unsuccessful, including the use of conventional lightweight gas-tight cement slurries, two-stage cementing operations with conventional gas migration control slurries, and injection of sodium silicate to damage the shallow gas sand. All methods failed to control the gas migration through permeable upper sand layers.

This paper presents case histories describing the solutions-oriented approach to this problem, which resulted in changes to both the drilling program and the cementing operations. There is discussion of the extensive laboratory testing performed to formulate the lightweight gas-tight cement slurry at low bottomhole temperature, the best drilling practices learned, and changes to selection of drilling fluid. Results of post-job cement logs are also included.

The new approach involved consolidating and damaging the formation with drilling fluid and using low-temperature, lightweight, gas-tight cement slurry. This water-reduced formulation required optimization of the particle size distribution, gas migration control, and short transition time. Modifications were made to drilling techniques and cementing practices, and an openhole external casing packer (ECP) was employed as an additional barrier. Successful zonal isolation was achieved in seven wells drilled from WP-11 Platform in the Gulf of Thailand with excellent cement coverage above and below the gas sands and no increase in wellhead pressure.
Experimental Assessment of Fluid Velocity to Control Gas Accumulation and Removal While Drilling "Horizontal" Wells
Authors: Ustun Firat , Nikitopoulos Dimitris E. , Smith John R. , Bourgoyne Adam T.
Published: December 2007

Horizontal wells often include sections with angles greater than 90 degrees due to steering uncertainties or the well path following the reservoir updip. If gas is present inside the well-bore either because of underbalanced drilling or taking a kick, the gas can accumulate in the resultant high spots and complicate effective well control.

A series of experiments were conducted to understand accumulation and removal of gas in a flow tube simulating a fully eccentric well bore annulus at inclinations of 91.5 to 100 degrees. Water, or polymer-viscosified water, and air were circulated in a 6 inch by 2.375 inch annulus at a range of liquid velocities representative of both well control and routine drilling operations. The studies demonstrated that low flow rates favor counter-current flow in either slug or elongated bubble flow patterns that would cause accumulation at high spots. As the liquid flow rate increases, co-current flow develops, and ultimately the counter-current flow disappears. The co-current flow patterns observed were stratified, stratified wavy, and bubble.

Flow maps were made to show co-current and counter-current flow windows and void fractions as a function of superficial gas and liquid velocities, fluid type, and inclination angle. Some counter-current flow was found at superficial liquid velocities below 1.2 ft/sec almost regardless of other conditions. Non-Newtonian fluids with a higher yield point were found to sometimes encourage counter-current flow and accumulation in contrast to conclusions published by other authors. Gas was effectively removed at inclination angles up to 96 degrees by a superficial liquid velocity of at least 3.3 ft/sec. Failure to continuously remove gas during underbalanced drilling can result in accumulation that ultimately "spills" into the vertical section of the well. A case history showing excessive surface pressures encountered during underbalanced drilling for gas is presented as an example of this effect.
An Investigation to Determine the Effect of Synthetic Mud Compressibility in Deepwater Cementing Operations
Authors: Singamshetty Kalyan C. S. , Authement Gervais J. , Dieffenbaugher Jeffrey T. , Dupre Ronald J.
Published: December 2007

Accuracy in displacement calculations is required to ensure proper displacement of cement with wiper plugs and drilling fluid. With deepwater operations moving to deeper seas the effect of temperature variations and high pressure induce another difficult to model parameter: compressibility of a synthetic mud. Dynamic temperature modeling has facilitated better 3D modeling of mud compressibility with respect to pressure and temperature during the cementing process. Ultimately the theoretical modeling results are compared with actual field data from Gulf of Mexico (GOM). The comparative matrix shows the nature of the complexity of this analysis and serves as a pioneering attempt in quantifying the effect of mud compressibility in deepwater cement displacement operations.
Reverse Circulation of Primary Cementing Jobs—Evaluation and Case History
Authors: Davies Jason , Parenteau Kim , Schappert Guy , Tahmourpour Farzad , Griffith James
Published: December 2007

Proposal

Conventional means of primary cement placement pump the cementing fluids down the casing and well returns are taken from the annulus. This is the most common way of cement placement for the industry and has been used for more than 80 years. Much less commonly used by the industry, but recently gaining in use is the Reverse Circulation of Cement (RCC) technique. When using the RCC technique, the cementing fluids are pumped into the annulus of the well and returns are taken through the casing.

The recent acceptance of the RCC technique is mainly driven by economics and state-of-the-art technology bringing an alternative technique. Benefits of the RCC technique can include lowering bottom-hole placement pressure, reducing cement retarder concentration, lowering the time for cement placement, and increasing location safety. The main drawback to the technique is determining when uncontaminated cement is at and around the casing shoe.

This paper discusses the benefits and shortcomings of the RCC technique in relation to fluid friction, cement slurry design, location safety, and zonal isolation. The paper illustrates, through a case history, how RCC technique's strengths are obtained while shortcomings are minimized. Field data from a recent job using the RCC technique on a 3100-m gas well in Alberta, Canada, as well as lessons learned from the job, are presented.
Helical Buckling of Pipe with Connectors and Torque
Authors: Mitchell Robert F. , Miska Stefan
Published: December 2007

It has been generally recognized that connectors should have some effect on the buckling of pipe. For instance, the connector outside diameter may be as much as 50% greater than the pipe body diameter. As a result, the radial clearance of the connector can be substantially smaller than the radial clearance of the pipe body.

The analysis of buckling has received extensive attention in the last 20 years. The effect of connectors on pipe stresses has received somewhat less attention. Lubinski used the beam-column equations to analyze the effect of connectors on pipe bending stresses for a pipe in tension in a twodimensional constant curvature wellbore. Bending stresses were significantly magnified by the connector stand-off. Paslay and Cernocky completed this analysis by analyzing the pipe in compression. Mitchell extended these results to threedimensional helical buckling.

Torque adds a new dimension to the buckling problem. Without torque, buckling occurs only for positive effective axial force (compressive axial force plus pressure effects). A pipe with applied torque can buckle in tension! The contact force between pipe and wellbore can be increased or decreased, depending on the direction of the applied torque. And, of course, pipe used in rotary drilling always has applied torque; so buckling analysis without torque is always questionable.

This paper looks at three-dimensional buckling of pipes with connectors with applied torque. The problem formulation is similar to Lubinski's buckling analysis: the wellbore is vertical and straight. The beam-column equations considered in the plane buckling analysis are used, but now there are deflections out of the plane. A solution for helical buckling is developed that produces pipe sag, maximum dogleg angle, contact force, and bending stress magnification as a function of pipe effective axial force and torque. An application problem is solved and the relative effects of compressive axial force and torque on sag between connectors, contact loads, and maximum bending stress are examined.

Applications include the analysis of bottom hole assemblies, drill pipe, casing, and tubing. The solutions are simple enough that they are suitable for spreadsheet calculations.
Installation of Solid Expandable Tubular Systems Through Milled Casing Windows
Authors: Waddell Kevin , Schuurmans Rutmer
Published: December 2007

Proposal

During development, the potential of solid expandable tubular technology promised to revolutionize the design, construction, and remediation of wells through conservation of hole size and maximization of pass-through and flow area. The increased use of this technology and value-based applications by major and independent operators is making this promise a reality. One installation after another, operators are realizing significant value creation in new well construction and increased production from remediated wells.

Initially, the envelope of well criteria in which solid expandable tubular systems were qualified was limited to relatively straight holes. However, the full application potential of this technology can only be realized by a continual broadening of the expandable operational envelope. Ongoing testing and actual field installations continue to reduce the limitations of using solid expandable tubular systems in candidate wells.

Currently, the performance of solid expandable tubular systems is proven for use in high-angle and horizontal wells, deepwater wells, multiple installations in the same well, situations that require a relatively long expandable casing string, various cementing scenarios, among others. One application of solid expandable tubular systems that was not qualified in the past was a sidetrack through a milled window. However, recent testing and successful field applications proves the viability of using solid expandable tubular systems in these circumstances.

This paper discusses factors that potentially threaten the reliable installation of solid expandable tubular systems through a milled casing window into a sidetrack or lateral wellbore, the steps taken to mitigate these factors, the procedures used to test and qualify the performance in this situation, and the results of surface and field testing. The current limitations of using solid expandable tubular systems in this application are also presented.
Important Aspects Related to the Influence of Water Depth on ERW
Authors: S. Rocha Luiz Alberto , Andrade Renata , Helena Lobato V. Freire
Published: December 2007

Over the last years, the drilling of extended reach wells (ERW) has become almost common practice in the oil industry. Although it still poses many technical challenges, successful applications such as the ones at Witch Farm, UK or in the South China Sea spurred the interest in ERW by the operators. In parallel, with the push for even further lateral displacement of wells, another technology frontier emerged for drillers: Extended reach wells in deepwater.

The majority of the extended reach wells are drilled from onshore sites to reservoirs that are situated under sensible locations like preserved nature or urbanized areas. Extended reach wells drilled from fixed platform installations in shallow water usually are aimed to reach outer parts of reservoirs that otherwise could not be developed economically. In deepwater, ERW allows the use of dry completion platforms such as TLP or SPAR. It improves flow assurance and reduces the cost of the well and the future interventions.

The paper at hand gives an overview on the effects of water depth on extended reach drilling (ERD).
Risk Based Inspection - A Valuable Approach
Authors: Santos Alfredo Dos , Al Hajri Abdul Aziz
Published: December 2007

Pressures on cost reductions, and tougher environmental regulations are driving an upsurge in the application of risk management approaches to optimise the utilisation of plant assets. Risk based inspection (RBI), and fitness-for-service (FFS) assessments are key risk management approaches to assist in minimising the risk of loss, and in maintaining plant availability at reduced maintenance costs.

In 1998 GASCO initiated the process of changing the traditional practice of inspection planning based only on probability of failure to the semi-probabilistic Risk Based Inspection planning method that uses a multi-disciplined team to identify the criticality of operating assets based on both the likelihood of failure, and the consequences of failure.

This paper describes the successful experience of the implementation of Risk Based Inspection at GASCO Bab and BuHasa plants, and identifies the key success factors which led to clear technical benefits and savings of over one million dollars per year.
Analysis of Gas Lift Installation Problems
Authors: Al Abdin Mazin Zain
Published: December 2007

GAS Lift is an important mean of artificial lift method being used for most of the producing wells of two major QGPC offshore oil fields. This was best-suited method to keep and extend the plateau production rate as much as possible. By means of a variety of field examples, this paper describes how quickly the trouble shooting action is required before gaslifting problems arise.

The proper analysis of a gas lift installation can become extremely important in determining whether or not it is performing satisfactorily. The general opinion and accepted practice in most cases have been to wait until some type of trouble develops before analyzing a gas lift installation. Preferably, the gas lift installation of each well should be analyzed while it is performing satisfactorily. Not only will this show whether or not the installation has been properly designed, but provide valuable information for future reference in the event of trouble. Where improvement appears possible, design changes may then be made with complete confidence. If this information is not obtained, and the tubing and gas lift valves are pulled because of some trouble, a change of design, including such things as valve spacing, valve pressure, and type of gas lift valve would still involve some guess work. There are many ways of analyzing gas lift installation problems. These can be divided into surface and subsurface methods. Surface observation methods include backpressure, total injected and produced gas volume as well as operating gas injection pressure and its behavior analysis.

Subsurface methods include flowing pressure/temperature survey analysis. Nodel analysis can also used as an effective tool for evaluating the gas lift valves performance.
Reservoir monitoring of the Draugen field through time-lapse seismic and it's business impact
Authors: Koster Klaas , Gabriels Pieter , Horvei Aksel
Published: December 2007

In a time-lapse 3D seismic (TL3D) project a ‘monitor’ seismic survey is compared to a ‘base’ survey. Ideally, the base survey is a 3D dataset acquired before production from the field started. Normally, the monitor survey is acquired after several years of production. The observed differences between the base and the monitor survey can be interpreted in terms of changes in fluid saturation and pressure.

When embarking on a seismic monitoring project it is important to keep the following questions in mind:

What field information might technically be obtained?

What impact will it have on reservoir management?

What is the optimal timing with respect to the drilling sequence and development decisions?

What is the probability of successfully obtaining that information from TL3D?

In this article we will work these questions out and illustrate them with an example.
Potential Application of Viscosified Treatments for Improved Bullhead Scale Inhibitor Placement in Long Horizontal Wells – A Theoretical and Laboratory Examination
Authors: Stalker R. , Graham G. M. , Oliphant D. , Smillie M.
Published: December 2007

Scale control in subsea horizontal wells is recognised as a particular technical and economic challenge, especially if effective chemical placement cannot be achieved through conventional bullhead squeeze treatments. When long horizontal or highly deviated wells produce from areas of high permeability contrast and high wellbore crossflow, coil tubing operations can often be the only manner in which effective chemical placement can be guaranteed. The costs associated with such treatments are extremely expensive and often prohibitive when compared with conventional bullhead operations. Such aspects were recognized as a particular risk for successful chemical treatments in the Draugen field, operated by Norske Shell. The Draugen field is located in the environmentally sensitive Haltenbank area of the Norwegian Continental Shelf, and produces oil from 6 horizontal (>1,000 ft.) wells completed with pre-packed resin screens to achieve effective sand exclusion. A moderate barium sulphate scaling potential was anticipated following sea water breakthrough requiring squeeze treatments. In order to improve chemical placement in this field and reduce the requirement for coil tubing interventions for squeeze treatment, work was initiated to investigate the potential use of viscosified fluids to improve downhole chemical placement.

A range of viscosifying agents was selected following detailed literature review based upon the rheology that was expected to lead to improved chemical placement. This included common water control additives such as xanthan and HEC (hydroxyethylcellulose) biopolymers and formulated water in oil (WIO) or oil in water (OIW) emulsions. Various formulations were selected that would either remain stable (higher viscosity) or to break (to low viscosity) at reservoir temperature. It should be noted, however, that viscosities were selected far below those normally applied in water shut off or multi-stage chemical diversion treatments. A series of formation damage core flood experiments has been conducted using analogue cores to ensure that the various formulations were non damaging, allowing rapid recovery to pre-treatment effective oil permeability. In addition, more sophisticated core flooding equipment was designed to examine chemical placement and recovery in zones of different permeability.

In summary, this paper presents a literature review describing the properties of different viscosifying agents and their potential applicability for improving bullhead scale inhibitor squeeze treatments. Core flood studies on viscosifying agents with selected rheological properties will then be presented to demonstrate the potential advantages of such applications for improved chemical placement by bullhead application in horizontal wells.
Injection of Aquifer Water and GOSP Disposal Water into Tight Carbonate Reservoirs
Authors: Raju K. U. , Nasr-El-Din H. A. , Hilab V. V. , Siddiqui S. , Mehta S.
Published: December 2007

Disposal of produced water from oil fields is a major concern to oil companies for environmental and economic reasons. One way to dispose off this water is to mix it with injection water. A carbonate reservoir in Saudi Arabia produces wet oil where the salinity of the produced water is high (TDS up to 230,0 mg/L). The produced water contained dissolved gasses (H2S and CO2), and suspended solids (oil, corrosion products). GOSP disposal water has CaCO3 scaling potential. It contains 750 mg/L of H2S. The aquifer water contains 2 mg/L of iron. Iron sulfide scale forms once the disposal water is mixed with the aquifer water. The objective of this study is to assess potential formation damage that can result when the two waters are mixed and injected into the tight carbonate reservoir.

The current study included detailed analysis of field waters, determination of scaling potential of various waters, and extensive coreflood testing using reservoir cores. A unique feature of this study is that the cores were examined after the injection of the mixed waters by CT and SEM techniques.

Injection of mixed water into reservoir cores created wormholes which increased core permeability. This new finding indicates that disposal water is not always damaging. The effect of iron sulfide particles was found to be a function of the initial core permeability. Iron sulfide particles (0.25 micron) caused damage to cores with permeability < 20 mD after injecting 1,000 PV of the mixed water. No damage was noted in high permeable cores (> 100 mD) even after the injection of 600 PV of the same water.

The results of the study identifies various types of scale related to mixing GOSP disposal water and aquifer water, and determine conditions where these waters can be injected. Also, the study highlights an unexpected benefit from injecting H2S containing waters into carbonate reservoirs.
Scale Inhibitor Core Floods in Carbonate Cores: the Influence of pH on Phosphonate-Carbonate Interactions
Authors: Baraka-Lokmane S. , Sorbie K. S.
Published: December 2007

Scale inhibitor core floods were performed using outcrop Jurassic Portlandian chalk cores. The effect of pH on the phosphonate-carbonate interaction was studied by performing core floods at various fixed injected pH values (pH ∼6, 4, and 2). The scale inhibitor (SI) used in these core floods was 5000 ppm active DETPMP adjusted to the application pH for that core flood. Effluent concentrations of scale inhibitor, lithium tracer, calcium and magnesium are measured, as are the effluent pH values. This thorough set of measurements makes it possible to interpret the inhibitor/carbonate interaction mechanisms quite clearly.

Some carbonate dissolution is evident in all core floods which is quantified in our floods and, as expected, the degree of dissolution increases as pH decreases. The pH 2 core flood (C4) showed the highest carbonate dissolution to the extent that the fluid induced the formation of a worm hole through the core. Flood C3 carried out at pH 4 showed more carbonate dissolution than in floods carried out at pH 6, as well as giving high pH (~7) effluents. There is higher interaction between the injected solutions and the rock material in flood C3 (SI retention, Γ ≈ 4.5 mg/g), and an increase in permeability between the pre-treatment and post treatment stages (~13 %).

All floods were modelled using a well established methodology [1, 2]. For the high pH floods (pH 6) the SI return curves were modelled very accurately using an adsorption isotherm which appears to provide an excellent description of the SI/carbonate rock interaction. For the lower pH floods (pH 4 and 2), a reasonably good, but not perfect, match was obtained using a "pseudo-adsorption isotherm" approach. However, a more complete description of the SI /rock interaction involving the role of Ca2+ is required in order to accurately model all of the features of the phosphonate/carbonate interaction.
Understanding Inhibitor Action on Components of Erosion, Corrosion and Their Interactions in CO2-Containing Slurries
Authors: Wang C , Neville A , Ramachandran S
Published: December 2007

Erosion-corrosion is a complex mechanism of material degradation resulting from interactions between electrochemical and mechanical processes. The consequences of erosion-corrosion are severe with economic penalties resulting from premature failure of components, increased downtime and increased maintenance costs.

The use of carbon steel in conjunction with corrosion inhibitors in preventing erosion-corrosion has been observed as an economically viable solution for oil and gas piping systems. In order to produce highly effective corrosion inhibitors for erosion-corrosion environment, it is important to understand how inhibitors act on each of the material loss components in erosion-corrosion. Although research into corrosion inhibition has been extensively conducted, there is less published work dealing with inhibitors retarding erosion-corrosion.

This paper is to evaluate the efficiency of a corrosion inhibitor under severe liquid-solid impingement. It investigates the adsorption properties of films in addition to the inhibitor action on the components of erosion-corrosion using surface analysis techniques. The experiments have been conducted using a jet impingement rig capable of producing a jet with velocity of 20m/s in a CO2-saturated environment. An assessment of the total damage is made using gravimetric techniques and visual observation. The performance of the inhibitor in this extremely aggressive erosion-corrosion condition is discussed. This paper will identify the role that inhibitors can play in reducing damage in addition to that caused by corrosion and improving erosion-corrosion performance.
Guidelines For The Prevention, Control And Monitoring Of Preferential Weld Corrosion Of Ferritic Steels In Wet Hydrocarbon Production Systems Containing CO2
Authors: Queen David , Lee Chi-Ming , Palmer Jim , Gulbrandsen Egil
Published: December 2007

Preferential weldment corrosion (PWC) of carbon and low alloy steels used for pipelines and process and piping systems in CO2-containing media has been observed increasingly in recent years. In particular, PWC has been detected on weldments made by the manual metal arc (MMA) process using electrodes containing Ni or Ni plus Cu. With information available and industrial experience to 2000, the mechanisms of this corrosion phenomenon were still unclear. It was not possible to predict the preferential corrosion rate that may be experienced, the exact location of attack (i.e. weld metal or HAZ), or the effectiveness of corrosion inhibitors.

A programme of work sponsored by oil and gas operating companies, together with a UK health and safety regulator was conducted collaboratively by three international research organisations. The aim of this programme was to identify if methods of mitigation and prevention could be found in terms of a better understanding of the corrosion mechanisms, the effects of weldment microstructure and composition, including various small alloying additions, and the role of corrosion inhibitors. The results from this programme have been distilled into guidelines for the prevention or control of PWC, in carbon and low alloy steels systems transporting produced hydrocarbons with entrained water and CO2 but in the absence of H2S. The paper briefly describes the experimental approach and summarises the practical guidance derived from the project. The effects of brine conductivity, liquid film thickness, temperature, corrosion scales, and corrosion inhibition are discussed. Appropriate control of inhibition was established as the most reliable means of avoiding PWC. PWC should be considered during selection of inhibitors, since the inhibitor performance may vary between the sections of the weld, and inadequate inhibition may, in some cases, increase selective corrosion rates. Recommendations on inhibitor testing, selection and deployment to avoid PWC are given.
Comparison of Segmented Weld Corrosion Tests with Short and Long Pre-Corrosion and The Influence of Synergist in Corrosion Inhibitors
Authors: McNaughtan D. , Winning I. G.
Published: December 2007

A standard 1% Ni weld consumable typical of that used in the Oil industry was utilised to investigate the factors which influence the efficiency of corrosion inhibitors in preventing weld corrosion. Testing was conducted on a 5-segment weld electrode in standard brine under sweet conditions. Precorrosion times of between 2 hours to 5 days were employed to assess the affect of different levels of synergist in the inhibitor and what affect this had on corrosion inhibition. Electrochemical techniques including linear polarisation resistance, galvanic current and potential measurements were made to assess the influence of pre-corrosion time and the chemistry of the inhibitor. The results indicated that the length of pre-corrosion had a significant influence on the time required for the corrosion inhibitor to reduce corrosion. It was also concluded that the rate of inhibition could be controlled by application of the appropriate amount of synergist for a particular system.
The Impact of Inorganic Scale Deposits and Their Removal on General CO2 Corrosion Rates and Corrosion Inhibitor Performance
Authors: Stalker Robert , Graham Gordon M. , Simpson Caroline
Published: December 2007

The inter-relationship between scale and corrosion and their control in oil field production systems has been well documented in relation to increased localized "under deposit" corrosion and the potential for detrimental performance interferences between scale and corrosion inhibitors. The impact of various chemical interferences (impact on corrosion inhibitor performance by the presence of scale inhibitor) is routinely assessed in laboratory pre-screening tests. However, although the importance of iron carbonate scales and other passivating scales is well documented, the impact on corrosion control due to the deposition of more conventional inorganic scales and their removal is not generally assessed in detail. In addition, the presence of scaling ions in test brines can significantly impact the recorded corrosion rates in conventional electrochemical tests owing to the build up of deposits on the various electrode surfaces. Omitting the scaling ions can lead to a dramatic change in test conditions (for example much lower test pH's in CO2 saturated systems if bicarbonate ions are omitted from the test brine) therefore reducing the appropriateness of the test.

The work reported describes a range of laboratory tests conducted to assess the impact of inorganic precipitates (scales) and their removal on both inhibited and uninhibited corrosion rates. Initial work summarises the impact of the inclusion or exclusion of scaling ions from test brines on the corrosion rates recorded using conventional electrochemical laboratory techniques. Further tests are then reported which examine the impact on general corrosion rates and corrosion inhibition using partially pre-scaled samples and those in which scale deposits have been chemically removed.

In summary the presence of scale deposits can have a significant impact on the recorded corrosion rates and the performance of conventional corrosion inhibitors which may have important implications for chemical screening.
Integrated CO2 Corrosion - Multiphase Flow Model
Authors: Nesic Srdjan , Wang Shihuai , Cai Jiyong , Xiao Ying
Published: December 2007

An integrated CO2 corrosion - multiphase flow model was built which takes into account the effect of most important variables. The model is mechanistic in nature and resides on clear theoretical foundations. All the assumptions in the model are explicitly stated and are open to future adjustments and improvements.

The overall model was extensively verified with a large experimental database and was able to perform reasonably well in all cases. The multiphase flow model was also benchmarked against a well-established commercial package.

Introduction

A variety of prediction models for CO2 corrosion of carbon steel exist. 1–19 Most of these models are semi-empirical, or even fully empirical with only a handful of the more recent models being based on mechanistic descriptions of the processes underlying CO2 corrosion 14–19. A recent paper by Nyborg20 reviews the performance of a representative group of models concluding that most of the models predict well the "worst case" CO2 corrosion rate but vary widely when more complex effects (e.g. protective films, water entrainment/wetting, H2S, etc) are included. The main reason for this spread lies in the arbitrary nature of the empirical correction factors that are employed to account for the various complicating effects.

The present paper describes a newly developed CO2 corrosion multiphase flow model that takes into account the effect of most important variables. The majority of the model is mechanistic in nature, fully transparent and resides on solid theoretical foundations. Some aspects of the model that cover areas where insufficient knowledge exists (e.g. H2S effect) employ a semi-empirical approach. It should be noted that the current model is a decade long project building on previous developments published in the open literature21–23.

Integrated Model

The integrated model consists of two main models: the corrosion model and the multiphase flow model. An interface module enables the transfer of the data between the two.

Corrosion model.

The transient mechanistic CO2 corrosion model of Nesic et al.21–23 is used as the backbone of the corrosion model of the integrated package. The corrosion model comprises of the following sub-models covering:Kinetics of electrochemical reactions at the steel surface including:H+ reductionH2CO3 reductionHAc reductionFe oxidationTransient one-dimensional transport of species between the bulk solution and the steel surface, through the turbulent boundary layer and through a porous surface film.Kinetics of chemical reactions including precipitation.Growth of iron carbonate films.Effect of traces of H2S.Effect of steel type.Effect of inhibition by crude oil and/or corrosion inhibitors.Possibility and morphology of localized attack.

The physical, mathematical and numerical aspects of the electrochemical, transport and chemical models have been published previously, and only a very brief outline is given below to facilitate the understanding of the text to follow.
The Development and Application of a Novel Model for Tubular Corrosion Prediction
Authors: Zhang Yuping , Brodie Alan , McMahon Andrew , Russell Leigh-Ann
Published: December 2007

The corrosion of carbon steel tubulars is an important completion integrity management issue. It is critical for the safe lifetime containment of well fluids, to avoid risk to people, property and the environment, and to avoid costly workover and repair during the well's life.

An effective tubing lifetime corrosion prediction model (VirtualCalliper) was developed to improve the management of integrity in carbon steel wells. The model has proved to be an order of magnitude more accurate than many widely used corrosion models, when predicting the internal corrosion of producer and injector wells.

The main reasons for this are: In addition to the standard parameters considered in most corrosion prediction models, VirtualCalliper accounts for the influences of well architecture, water cut development, water salinity, erosion corrosion and H2S corrosion.The model has been rigorously tuned with extensive field corrosion inspection data from a large number of well calliper surveysThe use of a well performance simulator output as the input files for key well parameters, ensures accurate modelling of temperature, pressure and flow characteristics across the whole well profile.The software is capable of time stepping to consider the impact of historical and future changes to parameters such as lift gas, oil, gas and water rates.The corrosion model output can be integrated with completion stress analysis (CSA), to enable the remaining tubing life to be predicted and to assess potential problems during well operations or workover.

VirtualCalliper has been proven in a number of fields. It has been used to plan a risk-based sequence of well workover priorities in a large, mature North Sea field. This has been achieved without the cost, HSE risk and lost production associated with well interventions to obtain calliper survey data.

This paper describes the structure and main functions of the model. Three case studies, used during the model development to compare the predicted tubing metal loss from VirtualCalliper and tubing metal loss measured from calliper surveys, are also presented.
Development of Green Corrosion Inhibitors for Preventing Under Deposit and Weld Corrosion
Authors: Jenkins A E , Mok W Y , Gamble C G , Dicken G E
Published: December 2007

Under-deposit/scale, pitting and weld corrosion are a major cause of localised corrosion failure in oil and gas production systems. Since advancement in instrumentation and the successful development of the localised corrosion test protocol in 2002, the technique has been widely used to study the inhibition of localised corrosion. The latest examples of its application are presented. Green corrosion inhibitors have been screened and their ability to inhibit under scale pitting has been determined. The work has allowed the key monitoring parameters in the inhibition of localised corrosion to be identified, which has resulted in a refinement of the test protocol. Additionally, the ability of corrosion inhibitors in preventing weld corrosion was also assessed. The ability of the corrosion inhibitors to be effective against weld corrosion and under deposit corrosion was demonstrated. The results established that specialised laboratory tests should be used to qualify inhibitors prior to field deployment.