bluuebunny/crossref_metadata_2025 huggingface dataset:
TECHNICAL NOTE—Decentralized Inventory Sharing with Asymmetric Information
Authors: Yan Xinghao , Zhao Hui
Published: December 2011

We study the information asymmetry issues in a decentralized inventory-sharing system consisting of a manufacturer and two independent retailers, who privately hold demand information, noncooperatively place their orders, but cooperatively share inventories with each other. We find that although the manufacturer needs retailers' mean demand and standard deviation for her wholesale price decision, each retailer only needs to know the other retailer's demand standard deviation for his order quantity decision. However, an incentive compatibility analysis shows that retailers have incentives to share their demand information untruthfully. Although a truth-inducing scheme can be developed for a system with symmetric retailers who share information between themselves, no such scheme can be developed to ensure truth-telling to the manufacturer. Further, we develop a coordination mechanism (CIS) for the decentralized inventory-sharing system, considering information asymmetry. We show that CIS coordinates the manufacturer-retailers system and leads to an all-win situation under complete information. More importantly, CIS minimizes the value of information such that each party can obtain expected profits very close to their first-best profits even under asymmetric information and hence indirectly solves the information asymmetry problem. To our knowledge, this work is the first to study decentralized inventory sharing and its coordination considering asymmetric information.
TECHNICAL NOTE—An Optimal Policy for Joint Dynamic Price and Lead-Time Quotation
Authors: Feng Jiejian , Liu Liming , Liu Xiaoming
Published: December 2011

For a dynamic joint price and lead-time quotation problem with a fairly general demand function, we show that the policy consisting of a threshold and a reward-maximizing lead-time is optimal. This policy offers some interesting managerial insights. Under this policy, finding the exact optimal quotation can be accomplished by single-variable policy iterations of unimodal value functions.
Generation Capacity Expansion in a Risky Environment: A Stochastic Equilibrium Analysis
Authors: Ehrenmann Andreas , Smeers Yves
Published: December 2011

We cast models of the generation capacity expansion type formally developed for the monopoly regime into equilibrium models better adapted for a competitive environment. We focus on some of the risks faced today by investors in generation capacity and thus pose the problem as a stochastic equilibrium model. We illustrate the approach on the problem of the incentive to invest. Agents can be risk neutral or risk averse. We model risk aversion through the CVaR of plants' profit. The CVaR induces risk-adjusted probabilities according to which investors value their plants. The model is formulated as a complementarity problem (including the CVaR valuation of investments). An illustration is provided on a small problem that captures several features of today's electricity world: a choice often restricted to coal and gas units, a peaky load curve because of wind penetration, uncertain fuel prices, and an evolving carbon market. We assess the potential of the approach by comparing energy-only and capacity market organizations in this risky environment. Our results can be summarized as follows: a deterministic analysis overlooks some changes of capacity structure induced by risk, whether in the capacity market or energy-only organizations. The risk-neutral analysis also misses a shift towards less capital-intensive technologies that may result from risk aversion. Last, risk aversion also increases the shortage of capacity compared to the risk-neutral view in the energy-only market when the price cap is low. This may have a dramatic impact on the bill to the final consumer. The approach relies on mathematical programming techniques and can be extended to full-size problems. The results are illustrative and may deserve more investigation.
Warfarin for Venous Thromboembolism Prophylaxis After Elective Hip or Knee Arthroplasty: Exploring the Evidence, Guidelines, and Challenges Remaining
Authors: Dager William E
Published: December 2011

BACKGROUND:

Guidelines for the prevention of venous thromboembolism (VTE) after elective total hip or knee arthroplasty (THA/TKA) have been developed separately by the American Academy of Orthopaedic Surgeons (AAOS) and the American College of Chest Physicians (ACCP). Differences exist in approaches to preventing postoperative VTE through prophylaxis.

OBJECTIVE:

To compare trials using vitamin K antagonists (VKAs) and differences in guidelines to determine the benefits and drawbacks of warfarin for VTE prophylaxis following THA/TKA.

DATA SOURCES:

Guidelines from the AAOS published in 2009 and revised in 2011 and from the ACCP published in 2008 were compared for recommendations on the use of VKAs. A MEDLINE search from 1960 to November 2009 was conducted to identify pertinent articles on the use of warfarin or VKAs for VTE prophylaxis following THA/TKA. Search terms included warfarin, vitamin K antagonist, total hip or total knee replacement, and total hip or total knee arthroplasty.

STUDY SELECTION AND DATA EXTRACTION:

Only clinical trials in which warfarin was the primary agent for prophylaxis compared to other anticoagulants were included.

DATA SYNTHESIS:

Data on differences between guideline recommendations for the use of VKAs and the importance of a deep vein thrombosis or asymptomatic events were extracted. Thirteen comparative trials using VKAs for VTE prophylaxis and international normalized ratio (INR) targets were assessed. Overall, the incidence of bleeding tended to be lower with the use of VKAs, but thrombosis when including asymptomatic events was numerically higher when comparing INR targets. However, INR targets varied, with no comparative trials assessing the AAOS 2009 recommended INR target of 1.5-2.0. The AAOS guidelines initially recommended a longer duration of therapy and expressed stronger support for the use of aspirin for prophylaxis; however, in 2011, its guidelines were revised, with no specific recommendations as to agent, dose, or INR target goal.

CONCLUSIONS:

Warfarin is an effective agent to prevent VTE after elective THA/TKA. The most effective approach, including extended warfarin use up to 4 weeks or longer, has not been determined.
Lung Transplantation Across Donor-Specific Anti-Human Leukocyte Antigen Antibodies: Utility of Bortezomib Therapy in Early Graft Dysfunction
Authors: Stuckey Linda J , Kamoun Malek , Chan Kevin M
Published: December 2011

OBJECTIVE:

To report the usefulness of bortezomib therapy in a sensitized lung transplant recipient experiencing antibody-mediated rejection.

CASE SUMMARY:

During a pretransplant evaluation, a 62-year-old woman with usual interstitial pneumonitis developed a diverticular bleed requiring transfusions, which elevated her panel reactive antibody to 98% for human leukocyte antigen (HLA) class I and 71% for class II. She underwent desensitization to decrease her panel reactive antibody levels. She received a double lung transplant across a weak HLA class II incompatibility but developed respiratory failure due to early graft dysfunction. On postoperative day (POD) 14 she was found to have donor-specific antibodies (DSA) to HLA class I and class II antigens. She received intravenous immunoglobulin (IVIG), plasmapheresis, and bortezomib to reduce the DSA. Repeat DSA testing on POD 80 demonstrated a 50% reduction in DSA, which became undetectable at POD 255.

DISCUSSION:

Antibody-mediated rejection (AMR) is difficult to diagnose and treat in lung transplantation. Since primary treatment options such as plasmapheresis and IVIG alone may not adequately eradicate DSA, the proteasome inhibitor bortezomib can be of additional value for the treatment of AMR. Bortezomib causes apoptosis of plasma cells, thus eliminating the production of allograftspecific DSA.

CONCLUSIONS:

This is the first report describing the utility of bortezomib for early graft dysfunction in a highly sensitized lung transplant recipient. Although this patient had preformed donor-specific anti-HLA antibodies, AMR was successfully treated with a combination of plasmapheresis, IVIG, and bortezomib. At time of writing, the patient continued to have excellent graft function 2 years posttransplant. Bortezomib is a potent inhibitor of plasma cell production and it appears to be useful for the treatment of antibody-mediated graft dysfunction.
Glycemic Control and Preventive Care Measures of Indigent Diabetes Patients Within a Pharmacist-Managed Insulin Titration Program vs Standard Care
Authors: Salvo Marissa C , Brooks Amie McCord
Published: December 2011

BACKGROUND:

Studies assessing pharmacist-led services have noted positive clinical diabetes outcomes; however, studies assessing pharmacist impact on glycemic control through insulin titration and adherence to American Diabetes Association (ADA) preventive care measures in an indigent population are limited.

OBJECTIVE:

To assess the impact of a pharmacist-managed insulin titration program compared to standard medical care on glycemic control and preventive care measures in an indigent population with diabetes.

METHODS:

This retrospective cohort study compared pharmacist-managed insulin titration to standard care; all patients received primary care services through a county-funded health center serving a low-income minority population. The pharmacist-managed patients, referred by the primary care provider, received telephone calls to assess blood glucose levels, encourage preventive care examinations, and titrate insulin doses through collaborative drug therapy management. Standard care patients received diabetes care solely from the primary care provider. Student t test was used to evaluate the primary outcome, glycemic control, assessed by change in hemoglobin A1c (A1C) between groups from baseline to various time points and study end. Secondary outcomes included attainment of preventive care measures and A1C goal of less than 7% and change in weight and total daily insulin dose from baseline to study end.

RESULTS:

Sixty-nine patients in the pharmacist-managed group (intervention) and 57 standard care patients (control) were evaluated. The pharmacist-managed group showed a significant difference in A1C at all time points, including, study end, compared to standard care (−1.3% vs −0.18%, respectively; p = 0.001). In addition, the intervention group more often completed the ADA's recommended preventive care measures; all differences were statistically significant.

CONCLUSIONS:

Pharmacist-provider collaboration can result in significant clinical improvements, including A1C reduction and adherence to preventive care measures, when compared to standard care in a medically underserved population with diabetes.
Circulating Epithelial Cells in Patients with Benign Colon Diseases
Authors: Pantel Klaus , Denève Eric , Nocca David , Coffy Amandine , Vendrell Jean-Pierre , Maudelonde Thierry , Riethdorf Sabine , Alix-Panabières Catherine
Published: December 2011

BACKGROUND

Detection of circulating tumor cells (CTCs) in the peripheral blood is a rapidly developing research field with clear clinical implications for the staging and monitoring of cancer patients. Current CTC assays, including the US Food and Drug Administration–cleared CellSearch® system, typically use markers [e.g., cytokeratins (CKs), the transmembrane protein EpCAM (epithelial cell adhesion molecule)] that are expressed on normal and malignant epithelial cells but not on the surrounding normal leukocytes.

METHODS

We enrolled 53 patients with benign colon diseases (e.g., diverticulosis, benign polyps, Crohn disease, ulcerative rectocolitis, colonic endometriosis) and analyzed their peripheral blood with 2 previously validated CTC assays: the epithelial immunospot (EPISPOT) assay and the CellSearch system. The EPISPOT assay detects only viable, CK19-releasing CTCs that were enriched by depletion of CD45+ leukocytes, whereas the CellSearch system detects CK-positive CTCs after positive EpCAM-based immunomagnetic enrichment.

RESULTS

In patients with benign colon diseases, positive events that met the criteria for “tumor cells” were detected with both the CellSearch system (11.3%) and the CK19-EPISPOT assay (18.9%), whereas no positive events were detected in samples from healthy volunteers. Positive events were detected most frequently in patients with diverticulosis and Crohn disease. All positive events lacked expression of CD45, a common leukocyte antigen.

CONCLUSIONS

These results indicate that patients with benign inflammatory colon diseases in particular can harbor viable circulating epithelial cells that are detectable with current CTC assays. This finding points to the need for further molecular characterization of circulating epithelial cells and has important implications for the use of CTC testing.
Linking Customer and Financial Metrics to Shareholder Value: The Leverage Effect in Customer-Based Valuation
Authors: Schulze Christian , Skiera Bernd , Wiesel Thorsten
Published: December 2011

Customers are the most important assets of most companies, such that customer equity has been used as a proxy for shareholder value. However, linking customer metrics to shareholder value without considering debt and non-operating assets ignores their effects on relative changes in customer equity and leads to biased estimates. In developing a new theoretical framework for customer-based valuation, grounded in valuation theory, this article links the value of all customers to shareholder value and introduces a new leverage effect that can translate percentage changes in customer equity into shareholder value. The average leverage effect in more than 2000 companies across ten years is 1.55, which indicates that a 10% increase in customer equity is amplified to a 15.5% increase in shareholder value. This research also compares the influence of customer and financial metrics on shareholder value. The findings challenge previous notions about the dominant effect of the retention rate and underline the importance of predicting the number of future acquired customers for a company.
Bryozoan fauna from the Lower Devonian (middle Lochkovian) of Sierra de Guadarrama, Spain
Authors: Ernst Andrej , May Andreas
Published: December 2011

A bryozoan fauna containing 11 species is described from the Lower Devonian (middle Lochkovian) of Arroyo del Agua, Sierra de Guadarrama, Guadalajara, Spain. One genus containing one species is new: rhabdomesine cryptostomeFehlerpora insolitan. gen. n. sp. Six additional new species are described: three cystoporates:Cystiramus gracilisn. sp.,Fistuliramus guadarramaensisn. sp., andFistuliphragma tenuisn. sp.; and three trepostomes:Eridotrypella hispanican. sp.,Boardmanella dubian. sp., andLeptotrypella inesaen. sp. Four further trepostome species were identified:Leioclema incompositumDuncan, 1939,Minussina spinosoformisAstrova, 1964b,Leptotrypella verisimilisAstrova, 1970, andLeptotrypella vulgataAstrova, 1964b. The association is distributed over three different sedimentary environments. The high-energy one representing accumulation of debris from bryozoan-coral-pelmatozoan thickets contains eight species dominated by erect branched forms (six species). Tabulate corals are present, especially branches which most likely belong toSubcladopora?abnormis(Mironova, 1974). The environment with moderate to low wave influence contains only two bryozoan species, one erect branched and one encrusting. The third setting represents bryozoan thickets in situ situated in deeper water, the most tranquil environment characterized by four bryozoan species, dominated by three erect forms. Fenestrate bryozoans are absent from the two higher energy environments, whereas the bryozoan thickets in deeper water contain rare unidentified fragments of fenestrates. The bryozoan fauna shows distinct relations to the Lower Devonian (Lochkovian) of Ukraine, one species is known from the Middle Devonian of U.S.A.
Phase Stability and Inhibition of Calcium Sulfate in the System NaCl/Monoethylene Glycol/H2O
Authors: Lu Haiping , Amy T Kan , Zhang Ping , Yu Jie , Fan Chunfang , Work Sarah , Tomson Mason B.
Published: December 2011

Calcium sulfate is one of the major mineral scales in oil and gas production. Hemihydrate (CaSO4·0.5H2O) and anhydrite (CaSO4) are the predominant sulfate scales formed at high temperature, while gypsum (CaSO4·2H2O) scale may form at low temperatures (<~45°C). However, it has been shown in this study that anhydrite can form at low temperature in the presence of excess amounts of monoethylene glycol (MEG), and this may occur during offshore production with long tie-backs. The prediction and prevention of calcium sulfate scales requires knowledge of the phase behavior of the three major phases of calcium sulfate.

The phase behavior of different calcium sulfate phases is related to the supersaturation state, temperature, and fugacity of water. In this study, the effect of a common hydrate inhibitor, MEG, on calcium sulfate solubility and phase behavior was investigated. This study was run with NaCl/CaSO4/MEG/H2O solutions at 0–6 molality (M) NaCl and 0–95 wt% MEG at 4–70°C. Three approaches were taken to determine the kinetics of calcium sulfate phase transition at various temperatures, ionic strengths, and MEG concentrations: (1) dissolution of gypsum, (2) dissolution of anhydrite, and (3) nucleation and precipitation of calcium sulfate by mixing calcium- and sulfate-containing solutions. The effect of scale inhibitors on phase transition was also evaluated. Phase transition of gypsum to anhydrite was observed in the presence of high concentrations of NaCl and MEG, regardless of the experimental approach. The transition boundary of temperature and concentrations of NaCl and MEG can be estimated from solubility of calcium sulfate and the fugacity of water. The inhibition mechanism of hexamethylene diamine tetra (methylene phosphonic acid) (HDTMP), one of the most effective inhibitors for calcium sulfate scale, was also tested by investigating the kinetics of precipitation and inhibition of calcium sulfate.
Preselection of Reservoir Models From a Geostatistics-Based Petrophysical Seismic Inversion
Authors: Le Ravalec-Dupin M.. , Enchery G.. , Baroni A.. , Da Veiga S..
Published: December 2011

A new geostatistics-based seismic-inversion method is introduced in this paper for determining reservoir models consistent with base seismic information. The proposed methodology entails two steps, with only the second being examined in this paper. First, cubes of acoustic velocities or impedances are derived from seismic inversion. Second, these data are incorporated into a matching process to identify reservoir models leading to acoustic responses close to the reference acoustic data. The parameterization of the facies and petrophysical properties populating the reservoir models is based upon the gradual-deformation method (GDM), which relies on geostatistical concepts. This particular feature makes it possible to change the spatial distribution of the property of interest from a few parameters while preserving its spatial variability. The matching process is driven from a global optimization algorithm known as the particle-swarm optimization (PSO). Such a global approach is reasonable for the problem considered because the forward modeling is very fast. A variant of the PSO algorithm is implemented to take advantage of the GDM properties. This approach yields reservoir models that honor the seismic data better than those derived from stochastic simulation only with seismic used as a secondary variable. A numerical experiment is then presented to stress the applicability of the proposed matching methodology: The GDM-based PSO approach is used to identify facies reservoir models and water/oil contact consistent with some reference acoustic P-wave impedances.
Seismic History Matching of Nelson Using Time-Lapse Seismic Data: An Investigation of 4D Signature Normalization
Authors: Kazemi Alireza , Stephen Karl D. , Shams Asghar
Published: December 2011

History matching of a reservoir model is always a difficult task. In some fields, we can use time-lapse (4D) seismic data to detect production-induced changes as a complement to more conventional production data. In seismic history matching, we predict these data and compare to observations. Observed time-lapse data often consist of relative measures of change, which require normalization. We investigate different normalization approaches, based on predicted 4D data, and assess their impact on history matching.

We apply the approach to the Nelson field in which four surveys are available over 9 years of production. We normalize the 4D signature in a number of ways. First, we use predictions of 4D signature from vertical wells that match production, and we derive a normalization function. As an alternative, we use crossplots of the full-field prediction against observation. Normalized observations are used in an automatic-history-matching process, in which the model is updated. We analyze the results of the two normalization approaches and compare against the case of just using production data.

The result shows that when we use 4D data normalized to wells, we obtain 49% reduced misfit along with 36% improvement in predictions. Also over the whole reservoir, 8 and 7% reduction of misfits for 4D seismic are obtained in history and prediction periods, respectively. When we use only production data, the production history match is improved to a similar degree (45%), but in predictions, the improvement is only 25% and the 4D seismic misfit is 10% worse.

Finding the unswept areas in the reservoir is always a challenge in reservoir management. By using 4D data in history matching, we can better predict reservoir behavior and identify regions of remaining oil.
Understanding the Effects of Leakoff Tests on Wellbore Strength
Authors: Wang Hong , Soliman M. Y. , Shan Zhaohui , Meng Frank , Towler Brian F.
Published: December 2011

Leakoff tests (LOTs) are performed to test the strength or pressure containment of the shoe after a cement job to help ensure that the new hole has been securely isolated from what has been cased off. A successful LOT can also be used to calibrate the least principal stress (many times, in the case of a vertical well, the minimum horizontal stress), or for geomechanics modeling. This will require initiating a fracture at the wellbore. Because of the near-wellbore stress concentration, for the purpose of geomechanics calibration, it is preferred to take the leakoff to the far-field stress region. To perform this extended LOT (XLOT), a relatively long fracture has to be created. Though an XLOT is needed for these reasons, some engineers tend to refrain from performing this test for fear that the test may damage the wellbore and consequently cause drilling problems.

This paper addresses this issue by investigating the effect of wellbore damage on wellbore "strength" or pressure containment. Various issues are discussed to help engineers determine when it may or may not be a concern. This should give practicing engineers the necessary insight into this complex rock-mechanics issue. The discussions are supported with results from analytical and numerical simulations based on rock-mechanics principles.
Protecting the Reservoir With Surfactant Micellar Drill-In Fluids in Carbonate-Containing Formations
Authors: Huang Tianping , Crews James B. , Clark David E.
Published: December 2011

Conventional water-based drill-in fluids (DIFs) contain high-molecular-weight polymers and different-size-distribution solid particles to reduce fluid loss and carry drilling debris back to surface during the drilling process. The polymers and solid particles in the drill-in fluids usually generate near-wellbore formation damage.

This paper introduces a new polymer-free and solids-free surfactant micellar-based drill-in-fluid system to drill a carbonate-containing reservoir. This new fluid system contains relatively low-reactivity acids mixed with surfactants and internal breakers. The drill-in fluid is designed to have low viscosities in the drillpipe. After the fluid flows out of the drill bit, the acids will react with carbonates in the formation and thereby increase the pH of the drill-in fluid. The higher fluid pH combined with the presence of dissolved divalent ions will cause the surfactants to form elongated micelle structures that will significantly increase fluid viscosity at the bottom of the hole and in the downhole annulus between the drillpipe and the formation rock. The viscosified drill-in fluid will reduce fluid loss and will carry nondissolved drilling debris to the surface. After drilling through the targeted formation, the internal breakers in the viscosified drill-in fluid will break down the fluid viscosity to improve ease of removal, and the drill-in fluid should leave very little or no near-wellbore damage.
Boosting Energy Efficiency Using Waste-Heat-Powered Absorption Chillers
Authors: Popli Sahil , Rodgers Peter , Eveloy Valerie , Al Hashimi Saleh , Radermacher Reinhard , Hwang Yunho
Published: December 2011

The oil and gas industry is under increasing pressure to improve the efficiency of its energy-intensive oil- and gas-processing operations through improved energy use and waste-heat recovery. This paper explores the use of waste-heat-powered absorption cooling to boost the efficiency of natural-gas (NG) processing, enhance hydrocarbon recovery, and reduce utility cost in an NG plant. A thermodynamic analysis of a gas turbine waste-heat-powered double-effect water/lithium bromide (H2O/LiBr) absorption chiller in an integrated NG plant is presented. It is found that waste heat recovered from turbine exhaust gases could be used to provide enhanced process cooling capacity to the NG plant through absorption cooling. The results suggest that a double-effect LiBr absorption chiller utilizing 34.6 MW of gas-turbine exhaust heat could provide 45 MW of cooling at 5°C. This could save approximately 9 MW of electric energy required by a typical compression chiller, while providing an equivalent amount of cooling. The associated annual savings are estimated to be approximately USD 7.8 million/yr, with a payback period of 2 years.
Review of Electrical-Submersible-Pump Surging Correlation and Models
Authors: Gamboa Jose , Prado Mauricio
Published: December 2011

Head deterioration observed in electrical submersible pumps (ESPs) under two-phase flow is mild until a sudden performance breakdown is observed in the pump head curve at a certain volumetric gas fraction. This critical condition is termed surging. Consequently, the head that the pump generates with two-phase flow depends on whether the stages operate under conditions before (mild performance deterioration) or after (severe performance deterioration) the surging point.

The surging, for engineering purposes, can be predicted by published correlations, but the lack of a theoretical basis is a limiting factor for their application. Mechanistic models seem to be the proper alternative. However, the poor understanding of the physical mechanism that causes the surging hinders the development of such mechanistic models. This paper reviews some of these correlations and mechanistic models by comparing the correlation predictions against experimental data acquired in a closed loop with water and air using a commercial 24-stage ESP. The data cover a wide range of volumetric gas fractions, rotational speeds, and intake pressures. As a consequence of this analysis, a new correlation has been formulated. This correlation predicts the initiation of the surging as a function of rotational speed and fluid properties.
A Proposed Method for Planning the Best Response to Kicks Taken During Managed Pressure Drilling Operations
Authors: Smith J. R. , Patel B. M.
Published: December 2011

An industry-supported research project has investigated well control methods for managed pressure drilling (MPD) using the constant bottom hole pressure (CBHP) method. This paper proposes a method for pre-selecting the best initial response to be taken when a kick occurs during CBHP MPD based on conclusions from the research. That research (Davoudi et al 2010) concluded that the three most widely applicable initial responses to kicks during MPD were increasing casing pressure until flow out equals flow in, shutting the well in, and using an adaptation of a MPD pump shut down schedule to detect and shut in a low rate kick. Increasing pump rate until flow out equals flow in was concluded to have limited, but potentially still important applications.

The proposed method uses a decision tree to pre-select the best response to be used if an influx of formation fluid is detected. This selection is based on the desired tolerance to kicks, equipment being used, well geometry and conclusiveness of the kick warning signs. The equations necessary to calculate decision parameters, example calculations for an application of the decision tree and comparison of simulation results to application of the decision tree are included. The decision tree indicates the response that maximizes kick tolerance within the well design, gives a basis for revising equipment or well design to maximize kick tolerance, and supports calculation of the expected kick tolerance advantage of the increasing casing pressure response versus a shut in response.
MPD Makes Possible to Drill and Trip Out of the Hole in a Gas Well With a Combination of a Narrow Mud Weight Window and a Serious Ballooning Effect
Authors: Tirado G. R. , Lupo C. P. , Beltran J. C. , Duno H. , Iturrios C. O. , Gallo J. F. , Hernandez T. , Centeno M.
Published: December 2011

This document presents the successful application of pro-active Managed Pressure Drilling (MPD) to drill one section through three different sands; the one in the middle with a low fracture pressure, the lower sand with a formation pressure higher than the frac gradient of the weak formation. The wrong decision to apply MPD in a reactive way leads to NPT, influxes, mud losses and increased risks.

It is shown how the conventional procedures to drill and make the trips are replaced by tailored MPD procedures leading to successful results. The Client understands the high value of proactive MPD, not only to drill but also to during trips. The drilling commenced with a MW of 1.6 g/cc and after 100 m the MW was increased to 1.62 g/cc (it is a routine procedure in the field to increase the mud density prior to reaching the expected high pressure zones while drilling conventionally). Some meters after start drilling the low frac gradient sand total mud losses were observed. The MW was reduced from 1.62 to 1.52 g/cc and MPD was implemented in a proactive manner whereby the BHP was maintained constant. The big challenge was to control the well at all times avoiding a catastrophic condition.
Hybrid Parameterization of Reservoir Properties for Robust History Matching Under Geologic Uncertainty
Authors: Reza M.. , Khaninezhad M.. , Jafarpour Behnam
Published: December 2011

Calibrating reservoir models against production history, also known as history matching, is commonly performed to improve reservoir prediction quality. Data scarcity and over-parameterization typically lead to an ill-posed formulation of history matching inverse problems where too many unknown parameters have to be estimated from limited measurements. As a consequence, many non-unique solutions can be found to match the observed data. Parameterization of reservoir models is often used to improve problem ill-posedness and solution plausibility (i.e., geologic realism). The existing parameterization techniques can be classified as prior-dependent (specialized) and prior-independent (generic) methods. Prior dependent methods such as the principle component analysis (PCA) utilize prior knowledge about the unknown reservoir property distributions (e.g., covariance model) and construct effective parametric descriptions for history matching. These methods immediately lose their effectiveness when the prior model becomes inaccurate. Alternatively, prior-independent methods such as Wavelet or Fourier image compression techniques are more generic (robust) in that they do not assume any prior knowledge in parameterizing reservoir properties. However, because they do not use prior knowledge, these methods are less effective when a reliable prior model is available. What complicates realistic reservoir parameterization is the uncertainty in prior knowledge. Here, we propose a hybrid parameterization approach that, by combining generic and specialized parameterization methods, offers the advantages of two techniques. By combining a set of significant prior-independent generic compression basis elements with a subset of prior-dependent learned basis components we construct a robust hybrid parameterization basis is less sensitive to errors in the prior model and more effective in reproducing more specialized geologic features in the prior. Using the proposed hybrid parameterization in several history matching examples, we show that under (in)correct prior knowledge the generic portion of the hybrid basis becomes (less) more relevant. We conclude that for realistic history matching problems where accounting for geologic uncertainty is imperative, a hybrid parameterization is more appropriate.
Capturing the Effect of Fracture Heterogeneity on Multi-Phase Flow
Authors: Jonoud S. , Wennberg O. P. , Larsen J. A. , Casini G.
Published: December 2011

A typical fractured carbonate reservoir introduces a tremendous challenge to upscaling of single- and multi-phase flow. The complexity comes from both heterogeneous matrix and fracture systems where separation of scales is very difficult, if not impossible. The mathematical upscaling techniques, based on representative elementary volume, must therefore be replaced by a more realistic geology-based approach. In the case of multi-phase flow, an evaluation of the main forces acting during oil recovery must also be performed.

A matrix sector model from a highly heterogeneous carbonate reservoir is linked to different fracture realizations in dual continuum simulations. An integrated iterative workflow between the geology based static modelling and dynamic simulations is used to investigate the effect of fracture heterogeneity on multi-phase fluid flow. Heterogeneities at various scales, from diffuse fractures to sub-seismic faults, as well as fracture barriers, are considered. The diffuse fracture model is built based on facies and porosity from the matrix model together with core data, image log data and data from outcrop analogues. The sub-seismic fault model is conceptual and based on analysis of outcrop analogue data. Fluid flow simulations are run for both single-phase and multi-phase flow, gas and water injection.

Better understanding of fractured reservoirs behaviour is achieved by incorporating realistic fracture heterogeneity into the geological model and analysing the dynamic impact of fractures at various scales. In the case of diffuse fractures, the heterogeneity effect can be captured in the upscaled model. The sub-seismic faults, however, must be explicitly represented, unless the sigma factor is included in the upscaling process. A local grid refinement approach is applied to demonstrate explicit fractures in large scale simulation grid. This study provides guidelines to how to effectively upscale a heterogeneous fracture model and still capture the heterogeneous flow behaviour.
Lessons Learnt from Nine Years of Immiscible Gas Injection Performance and Sector Modeling Study of Two Pilots in a Heterogeneous Carbonate Reservoir
Authors: Konwar Lakshi , Tariq Syed , Khan Sameer , Kompanik Gary Steven , Bengherbia Mourad , Faskhoodi Majid
Published: December 2011

The subject reservoir is a heterogeneous carbonate formation in a giant field located offshore Abu Dhabi. Five gas injection pilots were initiated in late 2001 in the Eastern, Central and Western parts of the field both as secondary and tertiary recovery methods to evaluate the benefit of gas injection for pressure support and for recovery improvement. With less than 10% of HCPV gas injection, the pilots to date have provided valuable insight on production performance and pressure support, gravity override, swelling effect and flow assurance issues (such as asphaltene deposition) in the field. Using a 3D compositional model, a sector modeling study was carried out for comprehensive evaluation of the pilot performance to date and to predict definitive results within reasonable time frame (3-5 years) which will have ramifications on long-term full field development decisions. Additionally, the objectives of simulation efforts were to evaluate different recovery processes (gas/water/WAG) and assess key reservoir uncertainty (volumetric sweep) due to reservoir heterogeneity (high permeability streaks). Initially, the sector model was history matched with nine years of pilot performance while both reservoir heterogeneity and well spacing sensitivities were tested in the model. The history matched sector model was utilized to predict performance under different operating conditions using both gas, water and water alternating gas (WAG) injection methods.

This paper describes the pilot performance, field observations and results of a sector model study including history match, sensitivity and predictions under different injection scenarios on two of the pilots. Based on the performance and surveillance data gathered on the two pilots and sector modeling study, it was established that both pilots have met their objectives and can be concluded. Through the integration of field observations and sector modeling work, the study provided valuable insight on optimum recovery processes, well spacing and well completion requirements for long-term field development.
A Workflow for Fully Consistent Water Saturation Initialization without Capillary Pressure Scaling
Authors: Ghorayeb Kassem , Darous Christophe , Acharya Mihira N. , El-Anzi Ealian
Published: December 2011

Discrepancies in terms of hydrocarbon initially in place volumes (HIIP) between static and dynamic models might take place because of nonlinear dependency of the saturation height function (SHF) versus porosity and averaging of height above free water level. Upscaling tends to eliminate the high and low porosity values in favor of the average porosity, which might lead to substantial changes in the resulting water saturation. Furthermore, pressure and compositional variation with depth in the dynamic model might lead to substantial contribution to the discrepancies, independent of upscaling.

We present a procedure to address the above issues and provide full consistency between static and dynamic models in terms of HIIP, without the use of capillary pressure (Pc) scaling by the reservoir simulator. A "preprocessing" workflow is used to slightly reassign the Pc curve of each grid block so that a very close match is obtained between the two models in terms of HIIP.

Results show that HIIP obtained from the dynamic model through equilibration using the proposed procedure are within 1% of those obtained using the static model without having to use Pc scaling in the reservoir simulator which warranties realistic and physically valid Pc curves in the reservoir dynamic model initialization process.
Integration of Fiber Optic Enabled Coiled Tubing System with Multiphase Production Logging Tool for Remedial Work Candidate Evaluation
Authors: Al-Buali Muhammad H. , Shawly Alaa S. , Dashash Alaa A. , Stuker John , Burov Anton
Published: December 2011

Multiphase production logging is essential to identify the contribution of different zones, types of fluids produced and other production related issues in producing wells. Data collected is used to determine if the well requires other services to enhance production or isolate unwanted zones.

Locating water production and cross flow between thief zones are common problems for carbonate formations. Remedial well services require costly multiple mobilizations of wireline, coiled tubing (CT) and stimulation units. Results might not be accurate due to the time gap between identifying the problem and implementing the action.

The new fiber optic enabled coiled tubing (FOECT) system supports many well intervention services, such as production logging, water shut-offs and/or acid stimulations with a single CT string. Combining FOECT with a real-time multiphase production logging tool (MPLT) reduces well downtime and improves remedial service quality control. Downtime is reduced by using the same surface equipment of FOECT to perform multiphase logging and also remedial work. Only the required bottom-hole assembly (BHA) needs to be changed. This successful logging job for Saudi Aramco allows evaluating remedial well services to be planned right after the production logging job to maximize quality control.

This paper documents the implementation of the FOECT system with real-time MPLTs and demonstrates the following improvements for the Ghawar field: First time in a Saudi FOECT system and MPLTs were used to log a wet oil producer well for immediate evaluation of remedial work needed.Significant reduction of well downtime by eliminating multiple mobilizations of wireline, CT and pumping units.Established best practices for production logging with FOECT and multiphase tools, including equipment rig up and single acquisition system setup.Optimize the required equipment by eliminating the electric line (e-line) logging unit.
Passive Inflow Control Devices versus Multiple Fracturing in Horizontal Wells: Selection Criteria for Optimized Completions in Oil Reservoirs
Authors: Uelker E. B. , Galimzyanov A. , Ostrowski L. , Gordeev Y. , Mirochnichenko A.
Published: December 2011

The industry has faced rapid advances in openhole completions in recent years, mainly in horizontal wells. Among these innovations, multistage fracturing and inflow control devices (ICDs) have gained notoriety as popular methods for field development, especially in unconventional reservoirs.

Fracturing a horizontal well may be considered when formation permeability is low and laminated shales are present. Compartmentalization or anisotropies are also a reason for this type of completion. In the same manner, ICDs can be de-ployed in a heterogeneous reservoir to mitigate the potential for early water and/or gas breakthrough.

To compare the features and benefits of both completion methods, the water breakthrough time was investigated in a full-field simulation model. Initially, a near-wellbore simulator was used to evaluate the applicability of the hydraulic multifrac and ICD completion. Then, a full-field simulation model was used to quantify the benefits of these completion techniques, where flow performance and completion optimization were accounted for. A degree of increase of recovery factor due to optimized completion was investigated.

The multistage frac was modelled with explicit gridding techniques. These used local grid refinement and a single porosity approach around the well and induced fractures. ICDs were modelled with a multisegment well model, which analyzed the lateral well branches, fluid phase changes and pressure variations.

This paper provides an example of the unconventional reservoir development for both a multistage frac option and an ICD completion. The optimization designs were aimed to achieve the optimum well completion strategy to fit specific reservoir conditions and an increasing recovery factor. The work was based on a real field case from Russia. The simulation runs were carried out using a commercial black oil simulator. Evaluation and selection criteria of these optimized completions are discussed in this paper.
Fine Numerical Simulation of Alkaline-Surfactant-Polymer Flooding Considering Emulsion and alkaline scale Mechanism
Authors: Lei Zhengdong , Song Jie , Zhu Bin
Published: December 2011

The mobilization of ASP emulsions and the existing of alkaline scale played important effect on fluid flow characteristics through porous media, which exert import effect on the simulation and prediction of ASP flooding process.

The previous studies were carried out to observe alkaline dissolution and precipitation reaction, emulsion rheology, emulsion drop capture, and stable emulsion flowing through capillary tube. However, few studies had been carried out to quantitatively describe emulsion and alkaline scale effect on enhanced oil recovery. This paper aims to improve simulation accuracy by description of physical chemical reaction processes, and enhance simulation speed and stability by improved solution.

The prediction model of permeability and porosity alternation caused by alkaline scale was established, and emulsion flow mechanisms in porous media including emulsifying startup, emulsifying entrainment, emulsion rheology and emulsion droplets capture was mathematically described. On this basis, an improved ASP flooding numerical simulation model incorporating emulsification and alkaline scale was established. In order to better solve the above model, IMPLICIT difference scheme and improved Parallel computing method IBiCRSTAB was proposed. The simulator was validated by comparing the simulation results with the results from linear core floods performed in the laboratory.

The ASP flooding process was simulated on geological model of DaQing Oilfield. The simulation result shows that emulsification role is favor of further improvement of displacement efficiency on middle-high permeability layer, moreover, it could enhance sweep efficiency of low-middle layer. Alkaline scale could decrease inject capability of injection wells and produce capability of oil wells, and bring higher formation damage for low-permeability layer. The proposed IMPLICIT method is more stable and efficient than the traditional methods of IMPES, and the IBiCRSTAB method could significantly improve efficiency 66% for large-scale simulations.
EOS Modelling for Two Oils with High Concentration of Organic Sulphur - Case Study
Authors: Dias Ana , Alves Fernando
Published: December 2011

A reliable fluid characterization achieved through the use of an Equation of State (EOS) is vital to reproduce the phase behaviour of a reservoir fluid and consequently, to improve understanding of the reservoirs EOR potential.

In this case, an EOS model was developed aimed at accurately reproducing the phase behaviour of two reservoir oils in the same field that contain, besides H2S, substantial amounts of organic sulphur components. The tuning of the EOS for both oils was more difficult to achieve than in cases without such level of sulphur components.

The tuning of the Peng-Robinson EOS was achieved with 9 pseudo-components for both oils, following the selection of the lumping scheme considered adequate for reservoir simulation studies. Organic sulphur components are concentrated in the higher range of molecular weights and, consequently, were incorporated into the heavy fraction. The tuned EOS was then used on a 1 D reservoir simulation compositional model to match the available slim tube experiments, to verify the validity of the EOS tuning. Using the compositional simulation of slim tube displacements, minimum miscibility pressure (MMP) was estimated for both oils and different injection gases.

Although a 9 component scheme is adequate for reservoir performance purposes, engineering of surface facilities requires more detail. Therefore, a delumping methodology was developed to allow engineers to estimate detailed fluid composition from the lumped components obtained from reservoir simulation studies. One of the objectives of this study is to obtain a table of variation of the detailed components distributions that can be used for delumping purposes at different stages of the gas injection project.