bluuebunny/crossref_metadata_2025 huggingface dataset:
What Level of Sulfate Reduction is Required to Eliminate the Need for Scale-Inhibitor Squeezing?
Authors: Boak L. S. , Al-Mahrouqi H. , Mackay E. J. , Inches C. E. , Sorbie K. S. , Bezerra M. C. M. , Mota R. O.
Published: December 2007

Scale deposition is often controlled using chemical scale inhibitors. However, for high scale severity, sulphate reduction in the injected seawater may provide a more attractive economic solution to the problem.

This study uses data based on Marlim Leste (Campos Basin, offshore Brazil) reservoir brine compositions and conditions for both reservoir modelling and experiments. Using reservoir modelling, supersaturation and precipitation potentials in the system are first calculated assuming no precipitation reactions in the reservoir. Sensitivity calculations are then performed to investigate the effect of brine mixing both deep in the reservoir and at the production well. Supersaturation and precipitation levels are then recalculated assuming in situ stripping has reduced [Ba2+] and/or [SO42-] levels at the wellbore.

Static (uninhibited) BaSO4 precipitation experiments have been conducted to determine the limiting sulphate level that removes the requirement for applying squeeze treatments. A simple rate law is found and this is used to define "safe operating envelopes" where the barite precipitation is sufficiently slow that we expect no squeeze treatment is required. Some risk is associated with these envelopes due to uncertainties in the determination of the rate constant, k, for barium deposition. Based on further kinetic analysis using data on the safe envelopes, we establish what rate the barite deposition may occur thus identifying where the system would deposit barite slowly and where it would reach its full equilibrium deposition limit quickly. This work presents both a methodology and also some analytical modelling tools for establishing, on a sound technical basis, the answer to the question: What level of sulphate reduction is required to eliminate the need for scale inhibitor squeezing?
Laboratory and Field Study of the Influence of Simple Carboxylates on Oilfield Corrosion and Inhibition
Authors: Martin R. L. , Logan P. D.
Published: December 2007

The influence of simple carboxylates on oilfield chemistry measurements, steel corrosion, and corrosion inhibition was studied. In most cases, the error in the field measurement of dissolved CO2 was found to be small. In all but two cases examined, the error in bicarbonate ions measurement was small because of the large actual bicarbonate ion to carboxylate ratio.

The presence of acetate and propionate ions in laboratory tests always accelerated the uninhibited corrosion rate of mild steel because of an increase in cathodic kinetics when the steel was behaving actively. In passive systems, anodic increases were seen.

Both acetate and propionate were detected in field samples; in only one case butyrate was observed. Corrosion inhibitors were effective at controlling corrosion even in the presence of these ions in both laboratory and field conditions.
Modeling and Implementing a Scale-Inhibitor Squeeze in a Deep, Hot Gas Well in Mobile Bay.
Authors: Lopez T. H. , Fielder G. D. , Yuan M. , Williamson D. A. , Blair E. S.
Published: December 2007

A major operator was experiencing severe scale deposition in a deep, hot gas well in Mobile Bay, Gulf of Mexico. The deposits primarily consisted of calcium carbonate, with much smaller amounts of mixed calcium fluoride, lead and zinc sulfide scales. A squeeze application was the desired treatment, but test work had to be performed to ensure the chemical would not cause damage to the formation. Although scale deposition in the production wells are common, no such scale inhibitor application had been attempted in this region previously, primarily due to concerns for formation damage in this complex and extremely high temperature (≥204°C) Norphlet sandstone formation.

Core flooding tests were performed in the laboratory at 204°C to simulate the squeeze treatment using actual core material from the well. Once a suitable scale inhibitor product had been identified, core flood tests were performed by injecting gas and brine through the core and assessing the change in permeability.

Historically scale buildup had been found in the subsurface safety valve and production tubing deep downhole. Steady productivity declines were observed after each near wellbore acid stimulation. When the untreated well had to be shut-in, it often experienced a decline in production upon restart if not a complete well loss. Since the squeeze has been performed in the field, the well has maintained the production in spite of being shut-in and reactivated numerous times due to hurricanes or other tropical storms.

This paper documents the first ever successful scale squeeze treatment in this extremely hot and complex reservoir formation. It describes the results from the detailed lab work leading up to the successful implementation of the scale inhibitor treatment in the field. The paper also discusses the results seen in the field following treatment.
Comparing Efficacy of Scale Inhibitors for Inhibition of Zinc Sulfide and Lead Sulfide Scales.
Authors: Lopez T. H. , Yuan M. , Williamson D. A. , Przybylinski J. L.
Published: December 2007

A large independent operator in Mobile Bay, Gulf of Mexico was experiencing a buildup of common and exotic scales where the produced waters are commingled. The scale species encountered included barium sulfate, zinc sulfide, and lead sulfide. Traditionally, scale inhibitor chemistries have not been used in the past to inhibit these exotic sulfide scales in this region. This is due to some amount of belief within the industry that conventional inhibitors alone could not inhibit these scale species.

Prior to the application of the scale inhibitor in the field, the platform's overboard water line required cleanout every two months due to scale buildup. Not a single cleanout has been necessary since a polymeric scale inhibitor has been applied downhole via continuous capillary injection for over one year.

This paper presents the results of laboratory tests which were used to demonstrate how a polymeric scale inhibitor was identified and approved for inhibition of lead sulfide and iron sulfide, as well as the more common scales. The sulfide scale tests performed in an anaerobic dynamic tube-blocking test unit showed this inhibitor chemistry to be as effective as combined scale inhibitor/dispersant products. The paper then presents the field treatment results, which shows good agreement with the lab test results.
Selecting X-Ray Energy Levels for Three-Phase Saturation Measurements
Authors: Lackner A. S. , Haaskjold G. , Torsaeter O.
Published: December 2007

The effect of pressure and rock type on optimal dual energy levels and minimalisation of saturation uncertainties for three-phase core experiments was investigated.

X-ray scanning of a composite core comprising of two chalk plugs and one Berea sandstone core was done. Reference scans using CO2, natural seawater, n-Ci10 and a CO2/n-Ci10 mixture at four pressure stages and five different pre-defined dual energy levels were acquired. Two unique typical given saturations were input together with data from the reference scans in a routine for back-calculating three-phase intensity data. A detailed uncertainty analysis using these synthetic three-phase data and combining low and high energies was performed. The resulting combination of low and high energy level giving the lowest uncertainty was selected as a given setting for all dynamic scans. Saturated with live oil, the core was waterflooded while dynamic X-ray scans were acquired. After the waterflood, the core was depleted below the bubble point to atmospheric pressure while scans were acquired continuously.

The results show that the rock type largely effects the selection of energy levels for both two- and three-phase X-ray scans. To minimise the uncertainty, the chalks generally required a higher low energy level independent of pressure than the sandstone. Also, at high pressures and for all rocks the optimal high energy level was found in the same range. At lower pressures, a lower high energy level was favourable.
New Horizons in Wide-Bore Drilling and Completion Technology
Authors: Sinha D.
Published: December 2007

Cantilever drilling technology (CDT) is a new concept of drilling which will enable us to drill superwide boreholes with radii of the order of a few feet selectively in zones of our choice. We do this using the cantilever drilling tool. This enlarged hole will facilitate better artificial lift and enhance production among other things. This paper discusses CDT and RESIN CASING technology which can be used to case holes with such a unique geometry. Resin Casing is done using an expandable wire frame balloon structure which forms a mould for the specially modified resin forming a hard shell - overcoming the hurdle of casing and cementing the hole.
Calculations of Fluid Saturations from Log-Derived J-Functions in Giant Complex Middle-East Carbonate Reservoir
Authors: Obeida T. A. , Al-Mehairi Y. S. , Suryanarayana K.
Published: December 2007

Calculation of initial fluid saturations is a critical step in any 3D reservoir modeling studies. The initial water saturation (Swi) distribution will dictate the original oil in place (STOIP) estimation and will influence the subsequent steps in dynamic modeling (history match and predictions). Complex carbonate reservoirs always represent a quit a challenge to geologist and reservoir engineers to calculate the initial water saturation with limited or no SCAL data available. The proposed method in this study combines core data (permeability) from 32 cored wells with identifiable reservoir rock types (RRTs) and log data (porosity and Swi) to develop drainage log-derived capillary pressure (Pc) based on rock quality index (RQI) and then calculate J-function for each RRT which was used to calculate the initial water saturation in the reservoir.

The initialization results of the dynamic model indicate good Swi profile match between the calculated Swi and the log-Swi for 70 wells across the field. The calculation of STOIP indicates a good agreement (within 3% difference) between the geological 3D model (31 million cells fine scale) and the upscaled dynamic model (1 million cells). The proposed method can be used in any heterogeneous media to calculate initial fluid saturations.
Improving Drilling Performance in the Chalk Reservoir of the Valhall Field
Authors: Strachan M. , Kinn S. , Eide Ø. , Mason C. , Chen D. C. -K.
Published: December 2007

Historically, drilling long horizontal wells in the Valhall field offshore Norway has been challenging. Due to high drag levels, the Chalk formation is best drilled with rotary steerable systems (RSS). However due to severe stick-slip vibrations, a high number of LWD and RSS failures have occurred. The necessity to "geosteer" in the reservoir has also contributed to tortuous well paths that have further increased drilling and liner-running difficulties. In order to achieve 2,000m long reservoir sections, BP used a multi-disciplined team to leverage improvements in both drilling and linerrunning performance. The initial focus was on reducing stick-slip vibration and frictional drag. Drill string, BHA and bit design, LWD and logging tools, well profile design and mud design were all considered in the analysis. Significant improvements in both drilling and liner-running performance have been achieved.
The Penetration of Coiled Tubing with Residual Bend in Extended-Reach Wells
Authors: Zheng A. , Adnan S.
Published: December 2007

Residual bend exists in every coiled tubing string. When the coiled tubing is placed inside a wellbore, its initial configuration is not straight but has a certain residual bend. This paper's objective is to explain how this residual bend in coiled tubing affects its extended reach.

This paper presents a new modeling technique to account for the effect of residual bend on coiled-tubing post-helical buckling behavior and maximum penetration. The initial configuration of the coiled tubing is assumed to be the form of a helix along the wellbore. By using the energy method, a set of solutions are obtained for the helix configuration and the radial contact force under the conditions of applied axial force and initial residual bend. These solutions are used to analyze axial load transfer and extended-reach capability of coiled tubing on horizontal wells. It is shown that in a horizontal well, with a relatively small residual bend radius, the existence of residual bend significantly reduces the maximum depth the coiled tubing can reach. Results of this work can be used to enhance job design for extended-reach applications.
Dynamic Reservoir Data Assimilation with an Efficient, Dimension-Reduced Kalman Filter
Authors: Zhang D. , Lu Z. , Chen Y.
Published: December 2007

The Kalman filter has been widely applied for assimilating new measurements to continuously update the estimate of state variables, such as reservoir properties and responses. The standard Kalman filtering scheme requires computing and storing the covariance matrix of state variables, which is computationally expensive for large-scale problems with millions of gridblocks. In the ensemble Kalman filter (EnKF), this problem is alleviated with sampling from a limited number of realizations and computing the required subset of the covariance matrix at each update. However, the goodness of the (ensemble) covariance approximated from the limited ensemble depends on the number of realizations used. In this study, we propose an efficient, dimension-reduced Kalman filtering scheme based on Karhunen-Loeve and other orthogonal polynomial decompositions of the state vector. We consider flow in heterogeneous reservoirs with spatially variable permeability. The reservoir responses such as pressure head are measured at some locations at various time intervals. The aim is to dynamically characterize the reservoir properties and to predict the reservoir performance and its uncertainty at future times. In our scheme, the covariance of the reservoir properties is approximated by a small set of eigenvalues and eigenfunctions using the Karhunen-Loeve (KL) decomposition, and reconstruction of this covariance from the KL decomposition can be done whenever needed. In each update, the forward problem is solved using the KL-based moment method, giving a set of functions from which the mean and covariance of the state vector can be constructed, when needed. The statistics of both the reservoir properties and the reservoir responses are then updated with the available measurements at this time using the auto- and cross-covariances obtained from the forward problem. The new approach is illustrated on a heteroge neous reservoir with dynamic measurements and its superior performance in terms of accuracy and efficiency relative to the EnKF method is discussed.
Harnessing the Wisdom of Crowds—Case Study
Authors: Velasquez G. , Odem P.
Published: December 2007

Sustainable innovation is considered one of the most important business differentiators in the market place as market forces continue to push the envelope of productivity and performance. The most important source of sustainable innovation in any organization is its people. Because of that, it is critical that organizations focus on growing the best and most skilled work force in the industry. According to a survey conducted by the US Bureau of Labor Statistics1, informal training accounts for over 70% of all the training an individual gets in his/her job. This indicates the importance of having a system in place that can fulfill the training needs of the work force in a timely manner. Perhaps one of the most viable alternatives to help develop skills and competencies of the organization's workforce are communities of practice.

This case study discusses how Halliburton Energy Services has used communities of practice to boost and strengthen organizational and individual learning. People frequent these communities because they learn about issues that pertain to their jobs2. This paper discusses the importance of the participation in communities and its relation to professional development. The data presented here tell an important story for the Oil and Gas Industry. Within Halliburton, these communities are transforming the culture and the way we do business in addition to being a very important element of professional development for the individuals who participate.
The Application of Flux-Based Sand-Control Guidelines to the Na Kika Deepwater Fields
Authors: Keck R. G. , Colbert J. R. , Hardham W. D.
Published: December 2007

The Na Kika offtake guidelines were developed jointly by Shell and BP using a blending of recent sand control operational methodologies from each company. In this paper, we focus on the use of the bpflux™ guidelines, which give the maximum safe operating rates for sand control completions, and allow wells with excellent completion quality to produce at twice the rate of wells with lower completion quality.

Before the Na Kika field started up, we estimated the completion quality by reviewing 20 different elements of completion design and operations. We used these estimates to set the initial off-take limits for each zone. As the wells started producing, we performed pressure build-ups to measure the actual completion quality (skin), and adjusted the maximum operating rates accordingly.

Using this methodology early in field life, we were able to bring the field up to targeted production rates without unnecessarily compromising long-term sand control reliability. As the field matures, we will identify opportunities to extend the production plateau, which will provide an incremental production impact. Finally, later in the field life, we also expect to lower the number of workovers, which will provide an additional cost savings from using these guidelines.
A Capacitance Model to Infer Interwell Connectivity from Production and Injection Rate Fluctuations
Authors: Yousef A. A. , Gentil P. , Jensen J. L. , Lake L. W.
Published: December 2007

Proposal

This paper presents a new procedure to quantify communication between vertical wells in a reservoir based on fluctuations in production and injection rates. The proposed procedure uses a nonlinear signal processing model to provide information about preferential transmissibility trends and the presence of flow barriers.

Previous work used a steady-state (purely resistive) model of interwell communication. Data in that work often had to be filtered to account for compressibility effects and time lags. Even though it was often successful, the filtering required subjective judgment as to the goodness of the interpretation. This work uses a more complicated model that includes capacitance (compressibility) as well as resistive (transmissibility) effects.

The procedure was tested on rates obtained from a numerical flow simulator. It was then applied to a short timescale data set from an Argentinean field and a large-scale data set from a North Sea field. The simulation results and field applications show that the connectivity between wells is described by model coefficients (weights) that are consistent with known geology, the distance between wells and their relative positions. The developed procedure provides parameters that explicitly indicate the attenuation and time lag between injector and producer pairs in a field without filtering. The new procedure provides a better insight into the well-to-well connectivities for both fields than the purely resistive model.

The new procedure has several additional advantages. It can be applied to fields in which wells are shut-in frequently or for long periods of time,allows for application to fields where the rates have a remnant of primary production, andhas the capability to incorporate bottom hole pressure data (if available) to enhance the investigation about well connectivity.
Effects of Ultrasonic Waves on Immiscible and Miscible Displacement in Porous Media
Authors: Hamida T. , Babadagli T.
Published: December 2007

Insight into the physical principles governing the mobilization of oil by ultrasonic waves is vital for developing novel techniques of oil extraction. Various mechanisms such as peristaltic transport due to mechanical deformation of the pore walls, reduction of capillary forces due to the destruction of surface films, coalescence of oil drops due to the Bjerknes forces, oscillation and excitation of capillary trapped oil drops, forces generated by cavitating bubbles, and sonocapillary effects may be responsible for enhancing the flow of oil through porous media in the presence of an acoustic field.

This paper aims at analyzing the influence of high-frequency, high-intensity ultrasonic radiation on the immiscible and miscible displacement in porous media. Capillary imbibition (co- and counter current) and viscous displacement (Hele-Shaw) experiments were performed with and without ultrasonic waves.

We observed that the increase in ultimate recovery is more pronounced than the increase in recovery rate when ultrasonic waves were applied in capillary imbibition experiments. The cases yielding enhancements on displacement efficiency (higher recovery rate and lower residual oil saturation) due to ultrasonic effects were identified.

To analyze the viscous displacement under ultrasonic waves, experiments were performed on Hele-Shaw models. Immiscible (for mineral oil-brine and mineral oil-surfactant pairs) and miscible (for mineral oil-pentane, mineral oil-kerosene and mineral oil – 2-Propanol pairs) displacement experiments were performed. Changes on the displacement fronts and patterns were observed under ultrasound. Fractal techniques were used to analyze the changes and correlate them to the intensity of ultrasonic waves.
High CGR Facilities Optimization Using a TMFS
Authors: Al-Taweel A. B. , Alvarez-Cohecha C. J.
Published: December 2007

This paper discusses a method for selecting pipeline sizes and receiving facilities suitable to wet gas wells for new field development. It involves the use of a modern Transient Multiphase Flow Simulator (TMFS) for building detailed network models, and its results have been validated by measurements. Gas wells considered in the study cover a wide range of Condensate Gas Ratio (CGR) 20-294 bbl/MMSCF, 8"-30" pipeline sizes, and 4 km-130 km pipeline lengths. Most previously published data on gas-condensate networks were for pipeline length less than 100 Km and liquid content range of 1-130 bbl/MMSCF compared to the subject fields.

A minimum gas velocity of 15-18 ft/sec is required for continuously sweeping liquid and preventing load-up in the studied pipelines to prevent slugging. The gas-liquid ratio does not appear to significantly influence the minimum sweep velocity in the studied range of liquid content, consistent with previous industry published data in a 1-130 bbl/MMSCF range. Variables that have been analyzed include pressure drops, pipeline liquid inventories, hydrocarbon liquid holdups, and slugs generated by rate changes and scraping operations.

Use of modern transient multiphase flow technology provided accurate predictions of gas-well pipeline design. These can be used to select optimum pipeline sizes, which will result in increased gas production and operational flexibility. At high flow rates, the high gas velocity provides an effective liquid transport, allowing a low pipeline liquid content. At low flow rates, the liquid phases, and in particular the aqueous phase will start accumulating in the pipeline increasing pipeline corrosion risk.

Using a Transient Multiphase Flow Simulators eliminated the need for field separation and aided in selecting pipeline sizes based on cost effectiveness analysis. Smooth operation of receiving facilities was also achieved via stable delivery of gas and liquids to process.
Gas-System Safety Evaluation Using a TMFS
Authors: Al-Taweel A. B. , Currie R. D.
Published: December 2007

Transient Multiphase Flow Simulators (TMFS) can be valuable tools in defining operational strategies for multiphase flow systems. The consequences of changes in operating conditions are difficult to predict, but they can be accurately represented using accurate TMFS models. Safety analysis and the ability to describe propagation of pressure fronts are important applications of a TMFS. A TMFS may be useful for safety analysis in the design phase of pipeline project, such as the positioning of valves, regulation equipment and measuring devices. Critical ranges in pipe monitoring equipment may be estimated and emergency procedures investigated.

This paper presents two case studies for applications of a TMFS. The first is development of a well tubing phase envelopes to determine operating parameters for gas wells, and the second is evaluation of the safety design aspects of a high volume, high pressure gas gathering system based on modelling of the system with a TMFS.

Tubing phase diagrams for high pressure gas wells provide a method of selecting operating conditions to prevent corrosive water condensation in tubing strings. A three-phase envelope was created that represented the flow regime in well tubing. Flow analysis, using a TMFS, allowed for selection of the proper operating range for the well for the given tubing.

Building a network dynamic model for a two-phase, high pressure gas gathering system aided in selection of Wellhead Emergency Shutdown system (WSD) and production manifold relief settings. The model allowed evaluation of the gathering system safety devices and consequences of failures for events such as Emergency Shutdown (ESD) valve closures and pipeline ruptures. A secondary benefit of the model development was verification of the design MAOP and sizing of the gas gathering system.
Step Change Towards a Zero Incident Work Environment— Managing the Human Factor
Authors: Grant P. J. , Senior L. M. , Lake J. H.
Published: December 2007

Safety results within the oil & gas industry have shown continuous improvement in the last decade, with particular focus placed on the equipment and process elements. The challenges faced in reaching and maintaining a zero incident work environment will now hinge around managing the "human factor" whilst also maintaining the equipment and process standards achieved to date. To influence the results we will have to influence the people.

In 1999, we presented a paper in the Aberdeen SPE conference based upon a proactive observation and feedback process – people were the focus. In 2004, at the SPE Calgary SPE conference we presented a paper on Performance Leadership Coaching, again focusing on the potential of fully appreciating the human factor.

Now, after extensive research and testing involving over 2000 workers, the ability to better manage the "human factor" has been uncovered, and a method for practical application established using the "e- colours process". We have developed and refined a process for using personality traits, not only as a communication tool but also as a risk management tool. This methodology is being tried and tested offshore today.

It has always been stated that there is no "silver bullet" when it comes to safety. Yet we all seek the next step change in safety excellence and the results that goal implies. If indeed we are to make the paradigm shift required then it will only come through taking the time and effort to understand human being's actions and reactions, in a context that any roustabout, roughneck or supervisor, can appreciate while working on the job at hand.

What has become evident through our extensive research in the field, offshore, is a clear picture of an element that has eluded us in the past.

People of the same personality traits and tendencies (identified by us using the e-colours) do in fact, have the same approach to safety and their perception of risk tolerance, even to a point of predicting, when asked, how they could get hurt.

This process very much supports the ethos of the SPE conference which is founded upon "Living and Working in Harmony". This can only be achieved by understanding the people with whom we work.

We have some clear examples of how this process works and indeed how lives could have been saved if utilised.
Modeling of Initial Saturation Distributions in Oil/Water Reservoirs in Imbibition Equilibrium
Authors: Bech N. , Frykman P. , Vejbæk O. V.
Published: December 2007

A new technique is presented for the modeling of initial saturations in water wet oil/water reservoirs with large transition zones that have been exposed to imbibition as a result of structural tilting, hydrodynamic effects, gas cap leakage or compaction, or water influx during production. The method quantifies the extent of imbibition that the reservoir has undergone and determines the locations of the existing and the original, paleo free water levels. This is done by matching calculated and log derived water saturations utilizing existing empirical correlations for drainage and imbibition capillary pressure curves. From this information, the saturation in reservoir regions without well control may be computed.

In addition, a method is proposed for the identification of imbibition conditions. It is based upon an estimation of the capillary pressure from logged saturations. If a plot of the capillary pressure vs. depth deviates from a linear trend it is an indication of imbibition.

The new method has been tested by field data from the North Sea. It is shown that the method can capture a large residual oil zone and a free water level far above the oil-water contact and that it is able to establish a good approximation to the saturation distribution resulting from the imbibition. It is also shown that a considerable error in the initial saturation distribution, and hence in the oil-in-place estimate, may be introduced if imbibition is not taken into account.
Marine Biodiversity—Exploring the Deeps
Authors: Walls A. , Clarke J.
Published: December 2007

As exploration and production move into ever deeper waters, the tools and techniques for assessing the environmental impacts of deepwater projects are being developed.

This paper outlines the various complimentary techniques that BP Angola is using to describe biodiversity and to monitor the environment in water depths ranging from 1200m to over 2000m. These include: wide ranging, snap-shot in time benthic surveys, which are targeted based on the geophysical information we have in the area mainly looking at seabed microfauna, using a variety of physical and photographic sampling techniques, including the deployment of BP Angola's deepwater short term environmental platform.Short range, extended timescale monitoring with Remotely Operated Vehicles of opportunity mainly photographic looking at larger animals, with trials of traps to gather microfauna. The ROV also photographs animals within the water column as it travels between the rig and the well.Observations of marine mammals, turtles, birds and surface visible fish from seismic and survey vessels.Long term (25 years) monitoring of deep ocean environmental processes with the deployment of deep sea environmental platforms; a cooperative project involving Scripps Institution of Oceanography, Aberdeen University, Texas A&M University at Galveston and Southampton Oceanographic Centre. These platforms should help us understand the linkages between deepwater biodiversity and climate change.

The data gathered is used in managing the environmental impacts from our operations and also in our Environmental Impact Assessments. In addition,the data is shared with the wider scientific community and used in local capacity building to ensure added value.

The described techniques represent a major step forward in the characterisation of deepwater environments and are applicable in other deepwater areas.
Case Study: Detailed Hydraulic Fracture Analysis Leads to a Better Understanding of a Complex Reservoir
Authors: Rovira A. M. , Jacot R. H.
Published: December 2007

A detailed fracture history matching study coupled with initial flowback production data from a five well drilling program led to a better understanding of the Wilcox formation. The purpose of the study was to determine the source of excess water production from the Lower Wilcox. This paper describes a hydraulic fracture study performed on 26 fracture treatments completed in the Middle and Lower Wilcox zones located in South Conroe, Texas.

Treatment data, which included surface treatment pressure, slurry rate, and proppant concentration, were analyzed with a pseudo-3D fracture model1 to determine fracture geometry and conductivity. Minifrac and After Closure Analysis2 (ACA) were performed to provide estimates of fracture fluid efficiency, closure pressure, reservoir transmissibility, and reservoir pressure. Non-ideal leakoff behavior identified in a large percentage of the minifracs complicated the analysis. The limited Repeat Formation Tester (RFT) and core analysis data were used to validate permeabilities estimated through ACA techniques.

The results of the study indicate that the fracture geometries were consistent with the original fracture designs, confirming the fractures were treating the targeted zones. Fractures were slightly more contained in the Middle Wilcox due to lower net to gross sand ratios than seen in the Lower Wilcox. The fracture study influenced a re-interpretation of previous log analysis for the Lower Wilcox, which concluded that the Wilcox in this field contained short gas columns with long transition zones, accounting for the high water production.

This combination of detailed minifrac analysis, ACA, and pseudo-3D fracture modeling led to a better understanding of the complex nature of the formation and an optimized fracture design for any future completions. Learnings and techniques applied in this study can be used to improve and optimize hydraulic fracture treatments in reservoirs in other geographic areas.
A Study of Branched Alcohol Propoxylate Sulfate Surfactants for Improved Oil Recovery
Authors: Wu Y. , Shuler P. , Blanco M. , Tang Y. , Goddard W. A.
Published: December 2007

This investigation considers one class of anionic surfactant, a series of branched alcohol propoxylate sulfate surfactants, as candidates for chemical EOR applications. This experimental results show that these surfactants may be preferred candidates for EOR as they can be effective at creating low interfacial tension (IFT) at dilute concentrations, and without requiring an alkaline agent or cosurfactant. In addition, some of the formulations exhibit a low IFT at several percent sodium chloride concentrations, and hence may be suitable for use in more saline reservoirs.

Adsorption tests onto kaolinite clay indicate that the loss of these surfactants can be comparable to or greater than other types of anionic surfactants.

Surfactant performance was evaluated in oil recovery core flooding tests. Selected formulations could displace most of the waterflood residual oil in place even with dilute, 0.2 wt% surfactant solutions from Berea sandstone cores.
Case Study: Cased-Hole Density Application, North Slope, Alaska
Authors: Hupp D. , Bennett L. , Campaign W.
Published: December 2007

This paper provides a case study of the techniques used to acquire, process, and interpret cased hole density data combined with logging-while-drilling (LWD) resistivity data for completion decisions in a sidetrack well from the North Slope, Alaska. Density data, acquired through 3.5-in. casing, augmented the openhole LWD resistivity and gamma ray data used to investigate possible water breakthrough and formation water saturation before completing this well. The cased hole density data were critical to this decision because they were not available with LWD, could not be acquired in an open hole because of borehole conditions, and were necessary for porosity determination. Formation lithologic effects precluded the use of alternative through-casing porosity measurements such as neutron log data.

After acquisition, the density data were processed to account for casing and cement effects and were then compared with offset density data for quality-control purposes. A petrophysical analysis was performed using this processed density with the LWD resistivity and gamma ray (GR) information to aid in the completion decisions. The objective of determining if water breakthrough had occurred was met, and this well was perforated and fractured accordingly. Well tests indicated the presence of low water cut and competitive oil rates, which confirmed the petrophysical interpretation.

The ability to acquire accurate formation density data after casing had been set reduced completion decision uncertainty. This added another tool to the completion decision process while this field was developed.
A New Algorithm for Retrieval of Air Quality from Landsat TM7
Authors: San L. H. , Jafri M. Z. M. , Abdullah K.
Published: December 2007

An algorithm for remote sensing applications of air quality over land using Landsat TM7 has been developed. The algorithm was developed base on the aerosol characteristics in the atmosphere and the data from visible bands were employed. The surface reflectance values in the visible bands (red and blue), were retrieved using dark targets with reference to the mid-infrared band data at 2.1 micron. This algorithm was tested using a satellite Landsat TM7 data acquired on 6 March 2002. The in situ PM10 measurements were collected simultaneously with the acquisition of the satellite image. The atmospheric component reflectance and apparent temperature values were extracted corresponding to the ground-truth location and later used for algorithm regression analysis of the air quality. The measured and estimated particulates of size less than 10-micron (PM10) were highly correlated with linear correlation coefficient (R) of 0.9. Finally, a PM10 map over Penang was generated using the proposed algorithm. An average filter of window size 3 by 3 was used in this study to remove noise from the image. The image was then colour- coded for visual interpretation. This study indicates that the remote sensing data could be used for air quality mapping.
Production Monitoring Through Openhole Gravel-Pack Completions Using Permanently Installed Fiber-Optic Distributed Temperature Systems in the BP-Operated Azeri Field in Azerbaijan
Authors: Brown G. , Field D. , Davies J. , Collins P. , Garayeva N.
Published: December 2007

This paper describes the use of fiber-optic distributed temperature systems to monitor production from BP's Azeri field in Azerbaijan and highlights the benefits and issues encountered during the start-up of the first production wells.

Production from BP's Azeri field in the Caspian Sea commenced in February 2005. These offshore wells are completed across multiple sand intervals using sand screens with gravel packs. Each fiber-optic monitoring system was installed with the completion in a purpose-built groove in the side of the gravel-pack screen. The screen is connected to the upper completion string via a hydraulic wet-connect enabling fiber passage from surface to total depth.

The primary Azeri reservoir consists of multiple sand bodies in the Pereriv formation. Commingled completions across these sand bodies are providing wells capable of producing more than 40,000bopd. The issues that dictate the requirement for regular distributed temperature (DTS) monitoring are long, high-angle well bores and the need to understand well and reservoir performance by sand body. Additionally, the requirement for minimal production interruptions during the early years of field life does not favor conventional production logging, which would also cause interruptions to the drilling program.

A thermal model is used to analyze the producing well temperature profiles and calculate the flow contribution from each of the producing zones.

The results demonstrate that, once deployed, permanently installed fiber-optic distributed temperature monitoring is a cost-effective and low-risk method of monitoring multiple-pay sand screen completions without having to reduce production rates to allow conventional production logging to be carried out.
Successful Pinpoint Placement of Multiple Fractures in Highly Deviated Wells in Deepwater Offshore Brazil Fields
Authors: Surjaatmadja J. B. , Miranda C. , Rodrigues V. F. , Graças F. C. M. das , Silveira M. A. , Neumann L. F. , Fernandes P. D.
Published: December 2007

The application of hydrajet technique to stimulate highly-deviated and horizontal wells has become a successful method to improve well productivity for different field conditions in the world.

In the past 2 years, an operator company has successfully implemented a relatively new hydrajet stimulation technique in shallow waters off Brazil. In deepwater locations, additional problems had to be overcome, which proved achievable using this new technology.

This paper discusses a reservoir-based methodology to determine the optimum number of transversal fractures for a horizontal deepwater well. The method starts with the review of geology and stratigraphic aspects of the field to better understand the relationship between fracture orientation, geological faults, and regional tectonic effects.

With this preliminary characterization, well-log interpretation of the pilot well and horizontal wellbore is performed to identify porosity and permeability index of the carbonate formation being drilled.

A study using well testing and nodal analysis is conducted to verify reservoir properties based on real production data. Next, a numerical simulator is used to obtain a production forecast varying the number of transverse fractures intersecting the well. Finally an economic evaluation of net present value vs. number of fractures is performed to determine the optimum number of transversal fractures.

Production results are then evaluated and compared to the other stimulation attempts in offshore horizontal completions in the area.
The Impact of Shale Barriers and Injection Strategy on CO2-Flooding and Sequestration Performance
Authors: Janssen P. H. , Bossie-Codreanu D.
Published: December 2007

In this paper the impact of stochastic shale barriers and injection-strategy on recovery-factor and sequestration capacity have been investigated for secondary CO2-floods in horizontal oil reservoirs. Permeability fields, shale size and shale fraction have been varied in several numerical simulations and the calculated oil recovery factors have been correlated to a dimensionless number relating the viscous to gravity forces. The results show that for relatively homogeneous reservoirs the impact of shale barriers can be accounted for using an upscaled vertical permeability and that a unique relationship can be found between recovery factor and ratio of viscous to gravity forces. For layered reservoirs the impact of shales depends very much on the vertical layer permeability arrangement, pressure drop ratio, and optimisation of injection strategy. Based on the best field characterisation (permeability and shale barriers), injection strategies aim at simulating an overall CO2 injection in all layers, followed by an analysis of the flooding mechanisms, and ending with an optimisation of the vertical conformance. This is recommended especially for low to intermediate pressure drop ratio.
Limits on Data Communication Along the Drillstring Using Acoustic Waves
Authors: Gao L. , Gardner W. , Robbins C. , Memarzadeh M. , Johnson D.
Published: December 2007

The first commercial acoustic telemetry system was successfully introduced in 2000 as part of a drillstem testing system. However, duplicating the success of the acoustic telemetry to environmentally challenging LWD applications at high data throughput remains a formidable task. The primary limitation arises from normal drilling operations that produce in-band acoustic noise at multiple sources at intensities comparable to the transmitter output. This noise, together with the signal attenuation along the drill string, adversely affects the data throughput. To determine the communication capacity of the drill string channel using acoustic waves, we examined the impact of channel characteristics, signal attenuation and noise in detail. Based on a communication model which incorporates the effects of both drill string acoustic channel and noise, we extensively studied the capacity of the system using the waterfilling method. For this analysis, realistic downhole transmitter power output, experimentally measured noise at the surface, and measured attenuation of acoustic waves in the drill string were used as input parameters. The results show that a typical drill string channel has a potential capacity of up to several hundred bits per second under noisy drilling conditions. Implications of the channel capacity on acoustic telemetry system designs are discussed. A communication technique that comes close to realizing a high-rate telemetry system is introduced. Methods to optimize various aspects of the system such that maximum channel utilization can be realized under drilling conditions are also discussed. Potential enhancement to data rates through application of error control coding is briefly covered.
Experimental Studies of Water Wetting in Large-Diameter Horizontal Oil/Water Pipe Flows
Authors: Cai J. , Nesic S. , Li C. , Tang X. , Ayello F. , Ivan C. , Cruz T. , Al-Khamis J. N.
Published: December 2007

Internal pipeline corrosion in oil production and transportation is always associated with the presence of water, and the likelihood of corrosion generally increases with the volume fraction of water. When the walls of the pipeline are wetted with oil no corrosion is possible. Highly turbulent flow was associated with negligible corrosion due to water entrainment by the flowing oil, whereas low flow rates or intermittent flow have been associated with corrosive conditions.

In this study, four advanced techniques (wall conductance probes, corrosion monitoring, wall sampling and flow pattern visualization) were used to determine phase wetting on the internal wall of pipe at different superficial oil and water velocities in the large diameter oil-water horizontal flow.

Four flow patterns were observed: stratified flow, stratified flow with mixed layer, semi-dispersed and dispersed flows.

Three types of phase wetting regimes (water wetting, intermittent wetting and oil wetting) were determined. A phase wetting map was obtained based on the overlapping information from these techniques. It is clear that the critical oil velocity of water entrainment increases with increasing input water cuts. The water cut has a significant effect on the critical oil velocity for water entrainment.

Based on the results of corrosion monitoring, it is also found out that no corrosion occurs under oil wetting. At same superficial oil velocity, corrosion rate under water wetting is much higher than that under intermittent wetting.
Automated Microseismic Event Detection and Location by Continuous Spatial Mapping
Authors: Drew J. , Leslie D. , Armstrong P. , Michaud G.
Published: December 2007

Optimal control of oil-field hydraulic fracturing operations will benefit from reliable, automated, real-time microseismic monitoring. Existing microseismic processing techniques are often either unreliable, or impractical for real time use.

In this paper we present the method of Coalescence Microseismic Mapping (CMMapping) for detection and localization of microseismic events. The technique is both automatic and robust, and explicitly allows for the inclusion of velocity model uncertainty into its formulation. We present the general basis for the method and illustrate its use on data acquired during a hydraulic fracture well stimulation.