bluuebunny/crossref_metadata_2025 huggingface dataset:
One Year Experience With The Injection of Nitrate To Control Souring in Bonga Deepwater Development Offshore Nigeria
Authors: Kuijvenhoven Cor , Noirot Jean Christophe , Hubbard Paul , Oduola Lukman
Published: December 2007

The Bonga field, which is located in deep water off the Nigerian coast, started oil production at the end of 2005. In order to sustain production, seawater injection started from the beginning of the oil production at a rate of 300k bwpd. During the field development it was concluded that seawater injection in Bonga would result in reservoir souring, and that mitigation was necessary. Initially the selected strategy for Bonga seawater injection was to control reservoir souring with biocide and handle low levels of H2S with sour service materials and scavenging facilities topside. The maximum H2S the existing facilities could handle was set at 50 ppm (v).

The decision to control reservoir souring with biocide and handle H2S at surface was re-evaluated in 2003, and it was concluded that there would be a risk that the maximum allowable H2S content in the facilities (i.e. 50 ppm(v)) might be exceeded during the life time of the project. Given the positive experience with the injection of nitrate in other seawater floods throughout the industry, nitrate was selected as the mitigation method and injection started directly at the beginning of the waterflood at the end of 2005. As such Bonga is one of the first waterfloods where nitrate is being used to prevent reservoir souring, the main application so far has been to reduce H2S in already sour fields.

This paper presents the experience gained with the nitrate injection during the first period of the Bonga waterflood. Issues like logistics and how to ensure nitrate is applied correctly are discussed in more detail. In addition laboratory testing executed to define an appropriate nitrate injection rate under Bonga conditions are also presented.

After several months of operation the Minox unit to remove the bulk of the oxygen broke down and oxygen control was done with chemical oxygen scavenger only. With this different mode of operation, the effectiveness of the nitrate as souring mitigation method was expected to be affected. Additional laboratory experiments, also reported in this paper, were performed and did not indicate any issue with respect to the predicted souring.
Assessing Multiple Resolution Scales in History Matching With Metamodels
Authors: Rodriguez Adolfo A. , Klie Hector , Wheeler Mary F. , Banchs Rafael
Published: December 2007

In this paper we present a new multiscale approach to history matching assisted by a neural network metamodel. The method starts with the construction of a fine scale a priori model that includes geological and geostatistical information. We then apply a singular value decomposition (SVD) in order to obtain a parametric representation of the permeability field, in a way that a fixed set of eigenimages are determined with the parameters to be inverted as weights in the expansion. Through this procedure not only is the number of parameters significantly reduced, but also the weights in the SVD expansion define a hierarchy that naturally separates the different resolution scales in the system. We show that the multiscale procedure alone helps to significantly reduce the CPU time required to accomplish the parameter estimation. Furthermore, the reduced parameter space facilitated the training of the neural network engine.
Practical Application of Safety Cultures
Authors: Spadaccini Danny , Robinson Scott
Published: December 2007

The Asia Pacific region consists of 1600 employees, 14 countries, 30 locations, 5 spoken languages with various socio political and cultural differences. The region includes the countries of Australia, New Zealand, Papua New Guinea, Indonesia, Singapore, Malaysia, Thailand, China, Philippines, Saklin Islands, India and Brunei. The HSE Team for Asia Pacific reviewed surveys, administration and implementation of the HSE management systems for the region. This review included traditional HSE data such as LTI's, TRIR, systems / infrastructure auditing in addition to measures of participation in HSE systems. The key findings of the review were: Levels of HSE performance where unacceptable for the region;Participation of personnel in HSE was low; andSystems and infrastructure to support participation was lacking.

It was recognised that no improvements to HSE could be achieved without the relevant infrastructure, training, systems and tools. It would be a waste of time to be seeking participation from personnel in HSE when the organisation has not provided the basics to support HSE. A plan was developed and broken into two key parts being infrastructure and implementation programs.

The HSE systems and infrastructure implemented have become an integral part of day to day business. The systems and processes have been designed and implemented by the personnel who will use them; accordingly the sustainability and continual improvement of the processes will be maintained. The performance improvement has included a TRIR improvement from 4.39 in 2002 to 0.46 in 2005.

The improvements in safety performance have occurred across a wide spectrum of activities, statute laws, cultures and political climates. The participation of all personnel has been the critical element to the success achieved.
Formation Damages Caused by Emulsions During Drilling With Emulsified Drilling Fluids
Authors: Fjelde Ingebret
Published: December 2007

The potential for macroemulsions to cause formation damages during drilling with emulsified drilling fluids (OBM) have been studied for consolidated low-medium permeable sandstone. Two types of emulsified drilling fluids were used, one with mineral base oil and one with synthetic base oil.

The emulsions in tested OBM were found to be stabilized both by emulsifiers and particles (organoclay and drilled solids). At low shear rates, aggregates of water droplets and particles were observed by microscopy. The potential for emulsion invasion will be highest during the spurt period, especially if the emulsions in the muds are not stable. The risk for emulsion invasion will increase with filtration pressure.

In bulk experiments, the stability of emulsions formed by mixing of mud filtrates and reservoir fluids was found to depend on the compositions of emulsified drilling fluid and crude oil. These emulsions were found to cause severe formation damages in core-floods at 90°C. The damages were partly removed during aging at higher temperatures (120°C and 150°C). At 90°C the emulsions appeared to be more stable in cores than in bulk. The potential for creation of emulsion in the oil reservoirs will be highest at high shear rates, e.g. in the spurt period and in the start of the oil production. The risk will increase with the concentrations of emulsifiers in the mud filtrate and reservoir oil.

Formation damages caused by emulsions can be non-permanent. Since emulsions are thermodynamically unstable, the potential for permanent damage caused by emulsions will usually be lower at higher temperatures. Mechanisms for stabilisation and thereby also breaking of emulsions, depend on the compositions of the mud filtrate and the reservoir fluids. If the damaged area is swept by the produced oil, removal of emulsions by dilution with the oil can be possible.

Use of synthetic oil in stead of the crude oil in laboratory experiments, can give incorrect estimates of the potentials for formation damages caused by emulsions. Short laboratory experiments can also give too high estimates of the potential for permanent emulsion related formation damages.
Conformance and Mobility Control: Foams vs. Polymers
Authors: Zhang Guoyin , Seright R. S.
Published: December 2007

This paper considers whether foams can be superior to polymers for improving vertical sweep efficiency in reservoirs. Our focus is on vertical sweep improvement during waterflooding and chemical flooding rather than gas flooding. Both linear and radial flow geometries were considered, with and without crossflow. We found that foams can provide improved sweep compared to polymer solutions if (1) foam forms in high permeability zone(s) but not in low permeability zone(s), (2) no crossflow occurs between high and low permeability zones, AND (3) the foam resistance factor in the high permeability zone(s) is sufficiently high to overcome the permeability contrast and the unfavorable mobility ratio between the gas bank and the oil/water bank in the less permeable zones. Foams will generally not be superior to polymers under other circumstances unless gravity effects provide a fortuitous benefit. Other limitations for foams must be recognized, including (1) challenges with formulating foams to meet the above requirements, (2) limitations on foam propagation, especially due to surfactant retention, (3) compression costs during foam injection, and (4) limitations on foam stability under reservoir conditions.

The paper also examines limitations for polymers. Historically, permeability reduction by polymers was advocated as advantageous since reduction in polymer mobility was greater than anticipated based on solution viscosity. However, this permeability reduction generally increases with decreasing permeability, thereby diminishing sweep efficiency. Applications in linear flow (i.e., fractured wells) can be reasonably forgiving of this effect if the permeability contrast and the polymer solution resistance factors are sufficiently large. For radial flow (i.e., wells that do not intersect fractures) with crossflow between layers, the effect has little consequence. However, for radial flow with no crossflow, the effect is quite damaging to sweep.
Oxidation as a Rheology Modifier and a Potential Cause of Explosions in Oil and Synthetic-Based Drilling Fluids
Authors: Shahbazi K. , Mehta S. A. , Moore R. G. , Ursenbach M. G. , Fraassen K. C. V.
Published: December 2007

In drilling directional and horizontal wells, the oil and synthetic-based drilling fluids are required to exhibit high viscosity at low shear rates to properly suspend the weighting materials and drilling cuttings and to prevent sag and settling of weighting materials. This can be achieved by employing different rheology modifiers such as dimeric and trimeric fatty acids, imidazolines, amides, and synthetic polymers. Moreover, the safety of the drilling operation has been one of the main concerns of drilling companies.

Since oil and synthetic-based drilling muds are widely used in high pressure high temperature wells, a set of drilling fluids commonly used in Western Canada were examined to study the effect of long exposure of the drilling mud with air. They consist of three oil base liquids (Diesel, Drillsol, and Distillate) and one synthetic base liquid (Envirodrill) together with water scavengers, viscosifiers, wetting materials, fluid loss controllers, and weighting materials. The drilling fluids were aged in stationary reactors in the presence of one charge of air for 52 hours at 150°C and 13.5 MPa initial pressure.

This paper presents the results related to changes in rheological properties and occurrence of explosion in the drilling fluids employed. The results at different shear rates, ranging from ultra low shear rates to high shear rates, are presented. It is shown that the aged drilling fluid systems exhibited a tremendous increase in viscosity at ultra-low shear rates and relatively low increases at medium and high shear rates. Furthermore, the amounts of solids precipitated in the base liquids were correlated with the mononuclear aromatics content. While rapid heat releases or explosions in the synthetic-based drilling fluids were observed with 0.5 – 1.6 hours induction delay times with gradual increase in liquid phase temperature, oil-based systems were safe under the conditions tested.

These experimental results imply that oxidation serves as a rheology modifier and induction delay time can be used as a warning parameter for an impeding explosion. Moreover, the impact of each chemical on the extent of increasing the viscosity and the occurrence of explosion is given.
Application of Viscoelastic Surfactants as Mobility-Control Agents in Low-Tension Surfactant Floods
Authors: Lakatos Istvan , Toth Janos , Bodi Tibor , Lakatos-Szabo Julianna , Berger Paul D. , Lee Christie
Published: December 2007

Since the recent trend of oil price opened new vistas in IOR/EOR scenario, the laboratory study looked at different new type of super (S) and viscoelastic (Sv) surfactants that provide both IFT lowering and mobility control. The paper is basically focusing on evaluation of viscoelastic surfactants as mobility controlling agents used as pre-flush, co-surfactant and post-buffer media. The experimental work is extended to their effects on bulk phase and interfacial rheological properties, surface and interfacial tension, phase behavior, wettability, flow properties in porous media and displacement efficiency using various injection protocol. Beside determination of mobility, mobility ratio, normal and differential displacement curves, the solution structure was analyzed by transmission and backscattering photon correlation spectroscopy.

Measurements and core studies confirmed that the viscoelastic surfactants might be used to replace traditional mobility controlling agents (polymers) over a wide temperature and pressure range. Their sensitivity to shear rate and other degrading effects is much less than found for high molecular weight synthetic and biopolymers. Thus, the viscoelastic surfactants may offer an excellent opportunity for mobility control in various enhanced oil recovery techniques independent of injection protocol. Their positive influence on recovery efficiently can be explained by mobility control, front stabilization (buffering) and profile correction. The viscoelastic surfactants may also improve the "microscopic displacement efficiency", which is not widely recognized as a significant part of the displacement mechanism, and hence the recovery efficiency. General conclusion of the laboratory studies is that viscoelastic surfactants may open new vistas in chemical flooding.
Nanoemulsions: A New Vehicle for Chemical Additive Delivery
Authors: Del Gaudio Lucilla , Bortolo Rossella , Lockhart Thomas P.
Published: December 2007

Nano-emulsions are emulsions where the droplet size of the internal phase is 500 nm or less. Because of the small drop size, they are not subject to gravity-driven separation owing to the density differences of the two phases. Nano-emulsions constitute a rapidly expanding field of study, with perceived or consolidated applications to drug delivery, cosmetics, food products, etc. To date, most processes for generating nano-emulsions have relied on brute force mechanical methods (ie., based on high mixing energy in order to overcome the high surface energy generated), including several developed for the E&P industry. These generate nano-emulsions with a broad droplet size distribution and, in general, limited stability. While low energy processes based on phase inversion are well-known, the lack of general preparation methods has limited their applications to specific, high value-added industries.

We report a general, transitional phase inversion method for the preparation of mono-disperse nano-emulsions of very small drop size (30-80 nm) which should prove useful for the delivery of oilfield chemicals in a variety of applications. The nano-emulsions possess very long lifetimes and can be charged with one or more oilfield chemicals. Parameters governing nano-emulsion formation and their properties and stability are reported. Nano-emulsions containing oilfield chemicals may find applications to well treatments (scale inhibition, acidizing, etc.), flow assurance (eg., multiple additive packages), and deposit removal/clean-up. Their long-term stability and ease of preparation from a concentrated precursor are compatible with oilfield logistics requirements.
ICD Screen Technology Used to Optimize Waterflooding in Injector Well
Authors: Raffn A. G. , Hundsnes S. , Kvernstuen S. , Moen T.
Published: December 2007

This paper presents an innovative completion technology, fine tuned by reservoir simulations, for balancing the water injection profile into various sand formation zones in an open-hole completed injector well, increasing sweep efficiency.

Traditional injection wells often suffer from the risk of sanding in, hence sand control is beneficial or even required. Another major challenge is to achieve even distribution of the injected water into all zones along the well-bore. Injector wells are often designed to penetrate, and give pressure support to, several reservoir intervals with various permeabilities which challenges the reservoir management. Permeability contrasts, heel-toe effect, formation damage, creation of thief fractures and well bore injectivity changes need to be managed to avoid early breakthrough in adjacent production wells. Smart-well systems are highly complex and costly, and for this particular case, where raw seawater is used, the high corrosion resistance requirement was considered a show stopper.

The solution was to qualify and install special screens with integrated flow control devices, tailor-made for injection wells, and with correct nozzle sizes for this particular case. These screens were made of materials selected to withstand the corrosive environment and high rate of unfiltered water during lifetime of the well. The screens where gravel-packed to restrict annular flow and give zonal isolation, which optimizes regulation of reservoir heterogeneities.

This new technology is representing a quantum leap forward in field economics, by marrying all the benefits realized with this simple robust and reliable self-regulating injection management system.

The paper will discuss the qualification program inclusive focus on risk of erosion, plugging and corrosion. Further, the completion design of the well, with flow distribution simulations and sensitivities inclusive comparisons with actual field date is also reviewed together with economic value analysis. Future potential, applications and scenarios will also be discussed.
Assisted and Manual History Matching of a Reservoir With 120 Wells, 58 Years Production History and Multiple Well Recompletions
Authors: Gruenwalder Markus , Poellitzer Stefan , Clemens Torsten
Published: December 2007

The 16th Torton horizon of the Matzen Field is the largest oil reservoir in Austria. Oil production commenced in 1949. Up to now, 42 mn m3 have been produced from this reservoir. The reservoir is characterised by transgressive sands and calcite layers extending laterally several meters to several tens of meters. These layers are effective vertical flow barriers. To optimise oil recovery, wells were first completed in deeper sections of the sands which are up to 70 m thick and later perforated in upper sections.

To identify infill drilling locations in this 58 year old field, an integrated study was performed 2005 – 2006. To achieve a good history match, permeabilities and the extent and presence of thin limestones, the so-called "hard layers", were modified (vertical flow barriers). Four infill drilling locations were identified.

To assess the uncertainty in the production forecast for these four wells, assisted history matching and forecasting was performed. Assisted history matching achieved several good matches. Using history matches with the smallest error, several forecasts were generated. In all of the forecasts, the production rates from the infill wells would result in economically attractive projects – hence the four drilling locations were included in the drilling schedule for 2007.

Comparing results of the manual and assisted history matching shows that assisted history matching leads to as good as or better global matches for production rates and pressures. Furthermore, assisted history matching gives a range of forecasts which can be used to quantify uncertainty. However, in this reservoir with multiple re-completions and small scale heterogeneities, the well by well history match was better in manual history matching than in assisted history matching. In addition, manual history matching resulted in significantly improving the understanding of the reservoir behaviour and in identifying wells which suffer from poor cementation.
Using Microgels To Shut Off Water in a Gas Storage Well
Authors: Zaitoun A. , Tabary R. , Rousseau D. , Pichery T. , Nouyoux S. , Mallo P. , Braun O.
Published: December 2007

The present paper describes the first field application of a new water shutoff technology using size-controlled microgels for the treatment of a gas storage well.

The treatment was designed from an integrated study combining laboratory coreflood experiments and near-wellbore reservoir simulations. The candidate well (open hole completion with liner) was drilled in a sandstone reservoir formation made of a succession of layers with different petrophysical quality all connected each other. The presence of a thin high-permeability streak located in the bottom part of the open interval was assumed to be the main factor of excessive water production. A bullhead option was chosen for the treatment. Microgel size (around 2 micron) favored their placement in the high-permeability layer, whereas the penetration in the rest of the reservoir was expected to be very superficial.

The treatment was performed in June 2005. Due to pressure constraints, the volume of the treatment had to be reduced to 26 m3 only. A backflush of gas was necessary to recover gas injectivity. The well was kept on production during the whole winter season 2005-2006. Water production was significantly reduced thus enabling higher gas rate production. A positive impact on sand production was also observed. Well behavior was in good agreement with model predictions.
Effect of Production-Induced Stress Field on Refracture Propagation and Pressure Response
Authors: Weng X. , Siebrits E.
Published: December 2007

In this work, the propagation of an orthogonal fracture and reopening along the initial fracture during a refracture treatment is studied by taking into account the production induced stress field surrounding the initial fracture. It is shown that the propagation pressure of the orthogonal fracture quickly increases to above the closure stress on the initial fracture due to the fracture penetrating into the higher stress region, which leads to fracture reopening along the initial fracture plane (called in-plane frac hereafter). A dual-frac PKN model is developed to predict the growth of the two intersecting fractures in a variable stress field and the associated pressure response in order to obtain an insight into the refracture process. The modeling results show that a refracture treatment can undergo three distinct periods of fracture growth:

Period I: Dominant orthogonal fracture propagation. It exhibits a rapid pressure increase due to the stress increase at the tip of the orthogonal fracture.

Period II: Reopening of the initial fracture. This period shows a relatively flat pressure since the stress at the fracture tip is nearly constant.

Period III: Extension of the initial frac and the orthogonal frac. It exhibits steeper pressure increase (tip screen-out like pressure response) as the stress at the tip increases when the in-plane fracture propagates past the initial fracture tip. The in-plane fracture length growth is significantly slowed.

Two field cases from the Barnett Shale are evaluated by comparing the model prediction to the pressure response. The model prediction agrees well with the observed pressure response and surface tiltmeter observations. The production-induced stress has significant implications on refracture design and candidate selection and they are discussed for various reservoir scenarios.
Three-Phase Equilibrium Calculations for Compositional Simulation
Authors: Haugen K. B. , Sun L. , Firoozabadi A.
Published: December 2007

The combination of successive substitution and the Newton method provides a robust and efficient solution to the non-linear iso-fugacity and mass balance equations for two-phase split computations in compositional simulations. In the successive substitution, the non-linear Rachford-Rice equation introduces some complexity, but the Newton method in combination with the bisection method provides a robust solution. For three-phase split calculations, the literature indicates that the computed three-phase region is smaller than the measured data. Some of the computed results also show some inconsistency in the phase diagram when there is three-phase region. We have found that the solution to the two Rachford-Rice equations in three phases can solve the problem. Our proposal is deceptively simple. We use a two-dimensional bisection method to provide good enough initial guesses for the Newton method in solving the two Rachford-Rice equations. In this work, we provide examples of various degree of complexity to demonstrate how powerful the combined bisection-Newton method is in three-phase split calculations. The proposed method is both infallible and efficient. To the best of our knowledge, the use of the bisection method in two variables has not been attempted in the past.
Evaluation of a Renewable, Environmentally Benign Green Solvent for Wellbore and Formation Cleaning Applications
Authors: Berry Sandra L. , Boles Joel L. , Cawiezel Kay E.
Published: December 2007

Traditional aromatic and chlorinated solvents typically utilized in oilfield applications are facing stricter governmental and environmental restrictions for their use and disposal. Concerns about flammability, acute toxicity, and environmental contamination have made their use less attractive. Furthermore, many countries in Central and South America have begun to closely monitor and regulate the manufacture, importation, and storage of typically utilized oilfield solvents such xylene and toluene due to their utilization in the manufacture of illicit drugs.

In an effort to be environmentally and socially responsible, greener alternative solvents from renewable resources are continually being investigated as possible cleaning and solvent solution substitutes. This paper discusses the properties and evaluation of a 100% biodegradable non-toxic solvent blend that is derived from two renewable resources produced both in the U.S. and world. In the past, due to its price and limited availability, the solvent’s use has been limited to specialized cleaning applications in the electronics industry. However, due to improved manufacturing processes, the product is more available and affordable for wider applications. The totally biodegradable solvent blend is currently being utilized heavily in paint and coatings removal, ink and graffiti removal, and electronics component cleaning. It has a Kauri Butanol (KB) solvency value of approximately 500 and is a EPA approved SNAP solvent.

This paper discusses the evaluation of the biodegradable solvent blend to replace traditional solvents in stimulation packages for wellbore and formation cleaning applications. Laboratory studies were conducted to evaluate the solvent’s efficiency to dissolve and remove pipe dope materials and OB/SOB mud residues and films at room temperature and 150°F. The solvent was also evaluated to determine its efficiency to dissolve and disperse paraffin and asphaltene solids, and to reduce the viscosity and enhance the flow characteristics of heavy crude oils.
Next-Generation Modeling of a Middle Eastern Multireservoir Complex
Authors: Al-Matar Bader S. , Pathak Ashok , Mandal Dipak , Killough John , Fleming Graham , Engle Colin , Brock Nigel , Varma Sanjeev
Published: December 2007

An elusive goal of reservoir simulation has been the ability to accurately model multiple reservoirs producing through a common surface facility. In the past, loosely coupled techniques have often been used which did not fully converge the overall solution of the simulation. This led to instabilities at worst or to inaccuracies in the solution at best because it did not properly account for the complete interaction of the reservoir. In the following paper, we discuss the application of a fully implicit, tightly coupled surface-subsurface simulation with a next-generation reservoir simulation of the north Kuwait Raudhatain multireservoir complex with common surface facilities using actual field data. In addition to surface-subsurface simulation, the reservoir simulator provides a parallel unstructured grid capability and significant computational efficiency from a improved model formulation. For the simulations of this study, four stacked reservoir horizons form the subsurface portion of the model. The surface facilities consist of the production gathering centers, and gas lift and water injection capabilities. A unique feature of the model included the capability to automatically switch the flow lines for the more than 500 wells among six different separator trains at a gathering center, depending on the wellhead pressures and producing water cuts. The resultant 600,000 cell multireservoir model was first validated by comparing fifty years of historical performance for the individual reservoirs from the original simulation models with the next-generation model. In general, the matches between the original simulations and those generated with the next generation simulator were extremely close for each of the four reservoirs. With the validation completed, a simulation surface network was constructed that attempted to capture all of the salient features of the current and future surface facilities for the field by including, for example, actual flowline lengths in the model. In particular, future facilities expansions were included with gas lift, water injection, and the multiple header switching of wells at the gathering center. The complete model, including all four reservoirs and the surface facilities, was run for a prediction period of over sixty years. The resulting predictions provided, for the first time, solutions that show the interaction of the reservoirs with the surface facilities, including reallocation of production and injection based on facilities constraints. The multireservoir model forms the basis of a field planning and optimization tool whose forecasts can be used with greater confidence because of the inclusion of the comprehensive physics of the field production. A comparison of the simulation output with a spreadsheet field planning model shows interesting results which should form the basis of future work.
Biosurfactants Produced From Agriculture Process Waste Streams To Improve Oil Recovery in Fractured Carbonate Reservoirs
Authors: Johnson S. J. , Salehi M. , Eisert K. E. , Liang J. -T. , Bala G. , Fox S. L.
Published: December 2007

We examined the ability of surfactin, an anionic lipopeptide surfactant produced by Bacillus subtilis, to mediate wettability changes that positively affect oil recovery in fractured carbonate rock. On both a weight for weight and a molar basis, surfactin has a greater ability to alter a carbonate rock to a more water-wet state than does sodium laureth sulfate (SLS). Surfactin, was produced by growing Bacillus subtilis on high-starch medium to represent agricultural effluent, and a suitable benchmark chemical surfactant was selected for comparative study. Cores and crushed samples of Lansing-Kansas City (LKC) carbonate reservoir material were cleaned and characterized. Crushed rock was aged in crude oil to ensure that it was strongly oil-wet and rapid wettability tests were performed to assess the wettability change mediated by low concentrations of surfactin and SLS. Static adsorption of surfactants on LKC rock was assessed and dynamic adsorption in intact cores was measured. Surfactin exhibits higher specific adsorption onto crushed LKC.
A Rapid and Robust Method To Replace Rachford-Rice in Flash Calculations
Authors: Li Yinghui , Johns Russell T.
Published: December 2007

Rachford-Rice iterations are widely used in equation-of-state (EOS) flash calculations to determine phase equilibrium compositions from constant equilibrium ratios (K-values). The method, however, can be slow to converge and in some cases may not converge at all.

This paper presents a simpler and more robust method to replace Rachford-Rice and similar methods in flash calculations. The new objective function has two fewer asymptotes compared to Rachford-Rice and is based on one of the equilibrium phase mole fractions, typically the lightest component.

Results with the new objective function demonstrate that rapid convergence using Newton-Raphson iterations (NR) is assured because the correct solution is determined within a small range (window). In that window, no poles exist no matter the overall composition and the objective function is often linear. Improved linearity of the objective function contributes to increased convergence speed even near critical points. The method can be easily incorporated into any compositional simulator without significant modifications.
Effect of Temperature on Degradation of Polymer Drag Reduction and Heat Transfer in Non-Newtonian Fluid
Authors: Hamouda A. A. , Moshood Omotayo. T.
Published: December 2007

Drag reduction is a well known phenomenon. Possible mechanism deduced from heat transfer has been suggested earlier for non isothermal Newtonian fluid treated with polymer drag reducer. Several works have shown the susceptibility of the long chain polymer to shear degradation, hence reduction in its performance. Most of the works were performed in isothermal conditions. Moreover, it mostly covers water soluble polymers. There is an increasing need to address the shear degradation phenomenon for oil soluble polymer, where its performance is related to increase transportation capacity of pipeline as well as energy savings.

In this work the degradation of oil drag reducing polymer in a non-isothermal environment in which rheological change of oil (the carrier fluid in this work) occurs as the fluid is transformed from Newtonian to non-Newtonian is addressed. In another words, the paper addresses the temperature effect on the degradation of the oil soluble drag reducer polymer in a wide range of temperatures. The non-Newtonian fluid behaviour here is defined as the temperature below which paraffin deposits in presence of drag reducer polymer. The validity of equations for estimating Colburn factor is also addressed.
An Ensemble Level Upscaling Approach for Efficient Estimation of Fine-Scale Production Statistics Using Coarse-Scale Simulations
Authors: Chen Yuguang , Durlofsky Louis J.
Published: December 2007

Upscaling is often needed in reservoir simulation to coarsen highly detailed geological descriptions. Most existing upscaling procedures aim to reproduce fine-scale results for a particular geological model (realization). In this work we develop and test a new approach, ensemble level upscaling, for efficiently generating upscaled two-phase flow parameters (e.g., upscaled relative permeabilities) for multiple geological realizations. For this purpose, flow-based upscaling calculations are combined with a statistical estimation procedure (cluster analysis). This approach allows us to numerically compute the upscaled two-phase flow functions for only a small portion of the coarse blocks. For the majority of blocks, these functions are estimated statistically based on single-phase velocity information (attributes), determined when the upscaled single-phase parameters are calculated. The procedure is designed to maintain close correspondence between the cumulative distribution functions for the numerically computed and statistically estimated two-phase flow functions. We apply the method to two-dimensional synthetic models of multiple realizations for uncertainty quantification. Models with different geological heterogeneity and fluid mobility ratios are considered. It is shown that the method consistently corrects the biases evident in primitive coarse-scale predictions and can capture the ensemble statistics (e.g., P50, P10, P90) of the fine-scale results almost as accurately as the full flow-based upscaling procedures, but with much less computational effort. The overall approach is flexible and can be used with any combination of upscaling procedures.
Flexible Treatment Program for Controlling H2S in FPSO Produced-Water Tanks
Authors: Burger E. D. , Andrade C. A. , Rebelo M. , Ribeiro R.
Published: December 2007

Tanks used to store produced water on Floating, Production, Storage and Offloading units (FPSOs) are extremely susceptible for generation of high hydrogen sulfide (H2S) levels due to the activity of sulfate-reducing bacteria (SRB). The FPSOs operated by Petrobras in the Campos Basin, offshore Brazil, all contain slop water tanks, while some also have upstream oil-water separation tankage. Slop water, comprised of produced water, ballast water from oil cargo ships and deck water, contains SRB and their nutrients required for generating H2S. Additionally, solids accumulations at the tank bottoms provide an excellent environment for microbial growth.

A 2002 field trial on an FPSO confirmed the viability of combined batch treatments of anthraquinone and of a THPS blend to control H2S biogeneration better than previous treatment programs. Anthraquinone, a non-toxic SRB inhibitor, and THPS, an oilfield biocide, act synergistically to effectively control the H2S biogeneration in this environment. The combined chemical treatment strategy has now been implemented successfully on six Petrobras FPSOs. Flexibility has been important in developing the treatment programs since operating parameters are different for each FPSO and change due to increased water production rates. Options include the ability to inject the chemicals continuously or batchwise at different locations and to alter the volumes and ratios of chemicals for optimizing control over H2S and corrosion.

This paper describes the individual FPSO water flow and storage systems and discusses the customized chemical treatment programs. Included are field H2S data showing the progression of the programs as they are being continually adjusted to optimize H2S generation and cost effectiveness. Also included are results of laboratory microbial studies showing the synergy of anthraquinone and THPS and of corrosion studies which have impacted the direction of usage of these chemicals.

With over 100 FPSOs operating worldwide, the described treatment program can significantly affect the safety and environmental aspects of processing water containing SRB.
Experimental Investigation of Emulsions Stability in GOSPs—Part I: Analyses of Separated Phases
Authors: Al-Ghamdi A. M. , Noïk C. , Dalmazzone C. , Kokal S.
Published: December 2007

This paper presents the first part of an experimental study performed jointly by IFP and Saudi Aramco to characterize the stability of emulsion samples collected from different Saudi Aramco Gas/Oil Separation Plants (GOSP). Earlier studies1-2 have shown the importance of emulsion characteristics on the performance and optimization of oil-water separation at Saudi Aramco GOSPs. A strict and rigorous methodology was applied to understand the characteristics, behaviour and composition of these systems. Samples were first separated by simple gravity sedimentation in order to identify the amount of separated water, oil and residual emulsion. Each separated phase was then analyzed separately. This included the chemical composition and bulk properties of crude oil and the salinity of the separated water phase. Residual emulsions were characterized using several techniques including Karl Fisher analysis for water content, as well as optical microscopy, DSC (Differential Scanning Calorimetry) and cryo-SEM to assess the size and polydispersity of the dispersed droplets. The objective of the study is to highlight the main physico-chemical parameters responsible for the varying tightness of these emulsions, and provide insights to optimize their treatment costs and resolve emulsion issues in the GOSPs. The second part of this study still under progress will investigate the stability of residual emulsions in terms of chemical demulsification and interfacial properties.
A Program for Acid Formulation in Stimulation Jobs—Merging Oilfield Chemistry and IT Towards Development of "Smart" Fields
Authors: Gupta Adit
Published: December 2007

Acid formulation design for well stimulation requires careful experimentation for quantitative and qualitative identification of different elements present in spent acid and also mineralogical analysis of core samples. In depth lithological studies, experienced personnel and long discussion sessions are a prerequisite for finalization of acid formulation for wells, which proves to be a time consuming process. Development of an intelligent program proves to be an effective and time saving process for acid formulation of wells. Just the input of experimental results would give the necessary acid formulation design for the well. The program has an in-built database and decision making intelligence, which is based on the basics of reservoir stimulation (Basics like McLeod's table). The software can also deal with some exceptional wells. With the application of the software, the acid formulation design is achieved in minutes rather than in hours. Thus, the software proves to be an effective tool for the Oil industry where effective time and money management are the key ingredients for success.
Factors Determining the Reverse Osmosis Performance of Zeolite Membranes on Produced Water Purification
Authors: Liu Ning , Lu Jun , Li Liangxiong , Lee Robert
Published: December 2007

Purification of produced water by zeolite membranes is a novel technology reported recently for reclamation of produced water for beneficial use. Because of the extremely stable chemical, mechanical, and thermal properties, zeolite membranes show great advantages in difficult situations such as operations in a strong solvent environment, or those requiring high temperatures and high pressures. In this paper, we reported reverse osmosis (RO) permeation of solutions containing dissolved salts on a zeolite membrane. The influencing factors, including operating pressure, temperature, and ion concentration, on the RO performance of zeolite membranes are investigated. Potential application of the zeolite membrane technology in large-scale produced water purification is also discussed.
Nitrate-Based Souring Mitigation of Produced Water—Side Effects and Challenges from the Draugen Produced-Water ReInjection Pilot
Authors: Vik E. A. , Janbu A. O. , Garshol F. , Henninge L. B. , Engebretsen S. , Kuijvenhoven C. , Oilphant D. , Hendriks W. P.
Published: December 2007

Currently, the application of nitrate/nitrite is considered one of the most promising souring mitigation solutions during Produced Water Re-Injection (PWRI). Norske Shell tested nitrate based souring mitigation as part of a PWRI feasibility study in the Draugen field. Prior to the pilot, the application of both nitrite and nitrate had been tested on Draugen using a Souring Mitigation Cabinet (SMC) specially developed to mimic the microbial activity in the near well reservoir. From this pre-study, the dosage of nitrate was selected based upon bio-available carbon and the required stoichiometric concentration of nitrate.

During the PWRI pilot, corrosion rates were measured continuously Downstream (D/S) the Water Injection (WI) pumps in the High Pressure (HP) system, and after three months testing, significant increases in corrosion rates were seen. These were thought to be related with the addition of nitrate to the Produced Water (PW). To investigate this more closely, the SMC was modified by including a dedicated Low Pressure (LP) Corrosion Sidestream Monitoring (CSM) system. The results obtained in the CSM system verified the results obtained in the HP corrosion monitoring system in place on Draugen.

The results of the Draugen PWRI pilot also showed that the addition of nitrate to the PW was efficient to control near-well reservoir souring. However, as mentioned above the corrosion rates increased logarithmically when nitrate was used. At the same time, a few ppm nitrite was seen in the nitrate treated PW water. The addition of biocide resulted in an instantaneous decrease in nitrite and corrosion rates to background levels. The result clearly indicates that bacterial activity, resulting from the addition of nitrate, was the causative agent of the increased corrosion seen in the Draugen PW treated for re-injection. It was concluded that the increase in corrosion rates most likely was Microbiologically Influenced Corrosion (MIC). Details of the PWRI pilot and the observed effects when applying nitrate are discussed in this paper.

Because of the negative side-effects observed when applying nitrate to PW, Norske Shell re-evaluated the requirement to mitigate souring with nitrate. The testing during the PWRI pilot showed a low tendency to develop SRB activity, probably because of the low VFA concentration in the PW. Consequently it was decided to terminate the application of nitrate to PW on Draugen and control bacterial activity in the surface facilites with biocide.

As nitrate is still promising to be applied in PW in other field applications, dedicated research has been initiated to learn more about the mechanisms leading to the increased corrosion rates seen when applying nitrate in PW.
Using the EnKF for Assisted History Matching of a North Sea Reservoir Model
Authors: Evensen G. , Hove J. , Meisingset H. C. , Reiso E. , Seim K. S. , Espelid Ø.
Published: December 2007

The ensemble Kalman filter (EnKF) has been used for history matching a simulation model of a North Sea reservoir. Parameters such as initial fluid contacts, vertical transmissivity multipliers and fault transmissivity multipliers have been estimated as well as 3D fields of porosity and permeability.

It is shown that for several of the parameters a large initial uncertainty is reduced to an acceptable level by the assimilation of well-log measurements and production rates of oil, gas and water. The result is an ensemble of history matched realizations which can be used to predict the uncertainty in future production.

It is also shown that the formulation used in the EnKF reduces a nonlinear minimization problem in a huge parameter space, involving the minimization of an objective function with multiple local minima, to a statistical minimization problem in the ensemble space. Thus, by searching for the mean rather than the mode of the posterior pdf, the method avoids getting trapped in local minima and is thus promising for history matching reservoir simulation models.

Furthermore, the EnKF provides an ideal setting for operational reservoir monitoring and prediction, including proper representation and prediction of uncertainty.
On-Site Freshwater Production for Offshore Facilities
Authors: Osegovic J. P. , Hill J. W. , Tatro S. R. , Max M. D.
Published: December 2007

Natural supplies of fresh water are limited while the demand for fresh water is increasing worldwide. Production of fresh water at sea is often achieved through a restricted group of conventional desalination technologies including reverse osmosis and modern versions of distillation. Two methods of unconventional water production, one of which is based on the unique set of resources available at an operating production platform, may provide solutions for provision of potable water and for industrial dewatering of process water.