bluuebunny/crossref_metadata_2025 huggingface dataset:
Medienwandel sichtbar machen. Standardisierte Nutzungsmessung von Bibliothekswebsites / To visualize media transition. A standardized measure for library website usage / Rendre visible la transformation des médias. Mesure standardisée de l’utilisation des sites web des bibliothèques
Authors: Hennies Markus , Mundt Sebastian
Published: September 2013

Bibliotheken wenden heute erhebliche Mittel zum Ausbau elektronischer Ressourcen auf, erweitern ihre Angebote für internetaffine Zielgruppen und betonen ihre Rolle als „hybride“ Informationsdienstleister. Bisher fehlte jedoch eine vergleichbare, einfach zu kommunizierende und ohne hohen Aufwand zu ermittelnde Kennzahl, die Bibliotheken und Informationseinrichtungen für ihre strategische Planung und die Kommunikation mit Unterhaltsträgern und der allgemeinen Öffentlichkeit nutzen konnten. Der Forschungsschwerpunkt Digitaler Medienwandel befasst sich mit den Treibern und Erscheinungsformen des digitalen Medienwandels und ihren Auswirkungen auf die Gesellschaft. Am Forschungsschwerpunkt wurde ein standardisiertes Verfahren zur Nutzungsmessung für Bibliothekswebseiten entwickelt, das inzwischen von rund 420 Bibliotheken bundesweit und im europäischen Ausland genutzt wird.
Verbally closed subgroups of free groups
Authors: Myasnikov Alexei G. , Roman'kov Vitaly
Published: September 2013

We prove that every verbally closed subgroup of a free group
Rationality of the probabilistic zeta functions of finitely generated
profinite groups
Authors: Dung Duong Hoang , Lucchini Andrea
Published: September 2013

We prove that if the probabilistic zeta function

P
G

(
s
)

${P_G(s)}$

of a finitely generated profinite group G is rational and all but finitely many nonabelian composition factors of G are groups of Lie type in a fixed characteristic or sporadic simple groups, then G contains only finitely many maximal subgroups.
Fitting quotients of finitely presented abelian-by-nilpotent groups
Authors: Groves J. R. J. , Strebel Ralph
Published: September 2013

We show that every finitely generated nilpotent group of class 2 occurs as the quotient of a finitely presented abelian-by-nilpotent group by its largest nilpotent normal subgroup.
Event Mining Through Clustering
Authors: Umamaheswari E. , Geetha T.V.
Published: September 2013

Traditional document clustering algorithms consider text-based features such as unique word count, concept count, etc. to cluster documents. Meanwhile, event mining is the extraction of specific events, their related sub-events, and the associated semantic relations from documents. This work discusses an approach to event mining through clustering. The Universal Networking Language (UNL)-based subgraph, a semantic representation of the document, is used as the input for clustering. Our research focuses on exploring the use of three different feature sets for event clustering and comparing the approaches used for specific event mining. In our previous work, the clustering algorithm used UNL-based event semantics to represent event context for clustering. However, this approach resulted in different events with similar semantics being clustered together. Hence, instead of considering only UNL event semantics, we considered assigning additional weights to similarity between event contexts with event-related attributes such as time, place, and persons. Although we get specific events in a single cluster, sub-events related to the specific events are not necessarily in a single cluster. Therefore, to improve our cluster efficiency, connective terms between two sentences and their representation as UNL subgraphs were also considered for similarity determination. By combining UNL semantics, event-specific arguments similarity, and connective term concepts between sentences, we were able to obtain clusters for specific events and their sub-events. We have used 112 000 Tamil documents from the Forum for Information Retrieval Evaluation data corpus and achieved good results. We have also compared our approach with the previous state-of-the-art approach for Router-RCV1 corpus and achieved 30% improvements in precision.
A Comparison of Semi-Supervised Classification Approaches for Software Defect Prediction
Authors: Catal Cagatay
Published: September 2013

Predicting the defect-prone modules when the previous defect labels of modules are limited is a challenging problem encountered in the software industry. Supervised classification approaches cannot build high-performance prediction models with few defect data, leading to the need for new methods, techniques, and tools. One solution is to combine labeled data points with unlabeled data points during learning phase. Semi-supervised classification methods use not only labeled data points but also unlabeled ones to improve the generalization capability. In this study, we evaluated four semi-supervised classification methods for semi-supervised defect prediction. Low-density separation (LDS), support vector machine (SVM), expectation-maximization (EM-SEMI), and class mass normalization (CMN) methods have been investigated on NASA data sets, which are CM1, KC1, KC2, and PC1. Experimental results showed that SVM and LDS algorithms outperform CMN and EM-SEMI algorithms. In addition, LDS algorithm performs much better than SVM when the data set is large. In this study, the LDS-based prediction approach is suggested for software defect prediction when there are limited fault data.
Reading imaginatively: The imagination in cognitive science and cognitive literary studies
Authors: Troscianko Emily T.
Published: September 2013

I argue that literary studies can contribute to the “imagery debate” (between pictorialist, propositionalist, and enactivist accounts of mental imagery). While imagery questionnaires are pictorially configured and conflate imagining and seeing with pictorial representation, literary texts can exploit language's capacity for indeterminacy and therefore elicit very different imaginative experiences, thus illuminating the non-pictorial qualities of mental imagery.
The rhetorical neuroscience of style: On the primacy of style elements during literary discourse processing
Authors: Burke Michael
Published: September 2013

Much work has been conducted in the social psychological sciences both modelling and predicting how the storage and retrieval of images and words in the mind operate (e.g. Baddeley 1974, 2000, Damasio 1999, Barsalou 1999). The focus has largely been on the interactions between short-term and long-term regions of memory. Such studies have also on occasion been complemented by behavioural experiments. More recently, a growing body of work has started to emerge from the biological cognitive neurosciences which looks at these same processes with the aid of scanning technologies (e.g. Dehaene 2003, 2009, Ledoux 1998, Eichenbaum 2011). The questions that will be considered in this paper are can these scientific findings be extended to aesthetic objects that are studied in the humanities, and in particular to the style of literary texts, and also can the way literary style figures operate shed light on how the mind and brain might function.
Learning History through Digital Preservation: Student Experiences in a LGBT Archive
Authors: Cocciolo Anthony
Published: September 2013

Archivists have become increasingly interested in their role as educators. This project builds upon this interest by asking what students can gain in history learning when they are put in the role of archivist. To study this, 43 MSLIS students engaged in digital preservation of oral histories from the Lesbian Herstory Archives in Brooklyn, NY, and were surveyed at the completion of the project to uncover their perceived learning of LGBT history. Results indicate that students perceived increases in their understanding of and interest in LGBT history and issues. This study has implications for further partnerships between archivists and educators.
Archival Digital Preservation Programs: Staffing, Costs, and Policy
Authors: Sanett Shelby
Published: September 2013

A three-part longitudinal research study- conducted from 1999-2007-gathered information on management practices in national archives that were developing digital preservation programs. In the first two rounds, data was collected from surveys and interviews. The third round was an in-depth case study conducted at the National Archives of Australia (Sanett 2008). Three core areas of practice in the emerging digital preservation programs were selected for further exploration after the first round: staffing, costs, and policy. Generally, the data indicated that these three areas remained underdeveloped in archival digital preservation programs. This article discusses results of the study and is an overview of what has changed in these areas since the study ended in 2007.
Cushing's syndrome due to ectopic ACTH production by a nasal paraganglioma
Authors: Serra F , Duarte S , Abreu S , Marques C , Cassis J , Saraiva M
Published: September 2013

Ectopic secretion of ACTH is an infrequent cause of Cushing's syndrome. We report a case of ectopic ACTH syndrome caused by a nasal paraganglioma, a 68-year-old female with clinical features of Cushing's syndrome, serious hypokalaemia and a right paranasal sinus' lesion. Cranial magnetic resonance image showed a 46-mm mass on the right paranasal sinuses. Endocrinological investigation confirmed the diagnosis of ectopic ACTH production. Resection of the tumour normalised ACTH and cortisol secretion. The tumour was found to be a paraganglioma through microscopic analysis. On follow-up 3 months later, the patient showed nearly complete clinical recovery. Ectopic ACTH syndrome due to nasal paraganglioma is extremely uncommon, as only two other cases have been discussed in the literature.

Learning points

Ectopic Cushing's syndrome accounts for 10% of Cushing's syndrome etiologies.

Most paraganglioma of the head and neck are not hormonally active.

Nasal paraganglioma, especially ACTH producing, is a very rare tumour.
First reported case in Ireland of MEN2A due to a rare mutation in exon 8 of the RET oncogene
Authors: Casey R , Prendeville S , Joyce C , O'Halloran D
Published: September 2013

We present the case of a 30-year-old female who was diagnosed with hereditary phaeochromocytoma secondary to a rare gene mutation in exon 8 of the RET oncogene. This genetic mutation was picked up as part of an extended genetic screen using a method known as next generation sequencing. Detection of this genetic mutation prompted further screening for the manifestation of multiple endocrine neoplasia type 2A (MEN2A). The patient subsequently underwent a thyroidectomy with histology confirming C-cell hyperplasia.

Learning points

Genetic analysis is an important step in the diagnostic work up of phaeochromocytoma.

Extended genetic analysis is important when there is a strong suspicion of hereditary phaeochromocytoma.

Mutations in exon 8 of the RET gene are associated with phaeochromocytoma as part of MEN2A syndrome.
Sinus Augmentation With Platelet-Rich Fibrin in Combination With Bovine Bone Graft Versus Bovine Bone Graft in Combination With Collagen Membrane
Authors: Bolukbasi Nilufer , Ersanlı Selim , Keklikoglu Nurullah , Basegmez Cansu , Ozdemir Tayfun
Published: September 2013

The purpose of this study was to compare the efficacy between the use of bovine bone graft material and platelet-rich fibrin (PRF) mixture (test group) and bovine bone graft material and collagen membrane combination (control group) in 2-stage maxillary sinus augmentation. According to specific inclusion/exclusion criteria, patients treated between 2008 and 2012 were selected. Panoramic radiographs were used for radiologic assessments. To evaluate the relationship between sinus-graft height and each implant, the bone level (BL) was divided by implant length (IL). To evaluate the change in the height of grafted sinus, the grafted sinus floor above the lowest part of the original sinus height (GSH) was divided by the original sinus height (OSH). Samples taken during implant surgery were used for histologic and histomorphometric analyses. Twenty-five patients, 32 augmentation surgeries, and 66 one-stage implants were included in the study. No implant loss or complication was observed in either group. There were no statistical differences according to new bone formation (P = .61) and biomaterial remnant (P = .87). During the evaluation period, the test group showed statistically less change in the BL/IL ratio (P = .022). The difference of GSH/OSH ratio was found to be insignificant between groups (P = .093). It was observed that the grafted sinus covering the implant apex and sinus floor was above the original sinus height in both groups. It may be concluded from this study that both combinations can be successfully used for sinus augmentation. Further studies evaluating different graft materials and PRF combinations in the early phases of healing would be beneficial.
Estimation of Water Saturation in Water Injector Wells, Drilled Across Tight Carbonate Formations, Using Resistivity Inversion
Authors: Serry Amr Mohamed , Al-Farisi Omar , Al-Marzouqi Mariam , Budebes Sultan
Published: September 2013

Accurate water saturation estimation in thin carbonate reservoirs is one of the major formation evaluation challenges in horizontal wells. This is mainly due to the strong shoulder bed effect of thick dense sections on the resistivity logs recorded in thin porous reservoir layers, particularly in horizontal wells. The performed work implies correction of the high resistivity log data acquired while drilling horizontal well sections by means of resistivity modeling. This has been achieved by building a forward model for the resistivity data acquired in the deviated section of the overlying reservoirs in water injector wells, where the porous section is thick and the shoulder bed effect is minimal. The resistivity model construction is based on the relationship of the deep and shallow Laterolog resistivity to the neutron porosity log responses measured in the thick reservoir sections. The established model equations are used to construct deep and shallow resistivity logs in the horizontal sections of thin reservoirs by resistivity inversion using the neutron porosity log data.Several well data sets have been tested and the results were complimented by test data, formation tester fluid sample analysis, Dean Stark measurements and core data. The results obtained confirmed that the resistivity inversion technique is applicable to compute water saturation in both the flushed zone (Sxo) and the un-invaded zone (Sw) for horizontal well sections drilled across carbonate reservoirs. The application of the inversion process allows generating resistivity log responses corrected for the tight shoulder bed effects, and providing more accurate water saturation estimation.
A Case Study from October Field: Modeling Heterogeneity Results in Improved Reservoir Management
Authors: Nassar I. S. , Noureldien Darhim M.
Published: September 2013

October field is a large oil field located in North Gulf of Suez (N-GoS) of Egypt. The reservoir was discovered in the mid-1980s. More than 20 wells have been drilled in the reservoir, revealing considerable complexity and heterogeneity. Until late 1999, the production mechanism was natural depletion above bubble point. At that time water injection was started and has since been extended to all the field.

Based on pressure performance data, the reservoir could be divided into five relatively independent producing areas. In initial field development, material balance techniques were used to evaluate group "5" performance. Using graphical techniques, a dynamic STOIIP close to the mapped STOIIP was obtained. However, due to reservoir heterogeneity, material balance techniques were not adequate for providing reliable predictions under water injection.

A reservoir model that could accurately predict future production had to include reservoir heterogeneity. Within an integrated subsurface team environment, a geological static model was constructed and a numerical reservoir simulation study was performed.

This model led the team to conclude that this area was affected by water injection wells in the adjacent block and that the current reservoir pressure could be about 400 psi higher than previously expected. As a result, an immediate static survey was run that confirmed the simulation results. A recommendation was made to return previously shut-in wells to production resulting in an oil gain of 1,500 BOPD.
Successful Application Of Different QI Techniques To Improve The Static Reservoir Model For A Clastic Onshore Oil Field In Oman
Authors: Scholten-Vissinga M.
Published: September 2013

A quantitative interpretation (QI) study has successfully predicted the distribution of sands and shales in the Upper Gharif. This was indisputably confirmed by three wells drilled after completion of the QI study. By integrating a range from low to high "tech" QI technologies, a workflow in a land environment could be developed that enables us to delineate channel sands with challenging rock properties at a fairly deep target. Integral part of this workflow comprehends the alignment of the petrophysical data, seismic data and production data in a consistent manner. Then, joining the maps from RMS amplitudes, spectral decomposition and seismic facies classification with products from the AVO inversion allowed us to construct a confidence map, which assigns areas with different probabilities to encounter these channel sands.

Building further on this QI success, the first 3D Close-the-Loop (3DCtL) project in Petroleum Development Oman (PDO) ever was initiated. This methodology strives to obtain an accurate as possible static reservoir model, which is consistent with all available subsurface data. The workflow consists of two main steps. Firstly, a rock property model is derived from well data and then the reservoir properties (net-to-gross, porosity and hydrocarbon saturation) in the static model are used to generate synthetic 3D seismic data and compared with the measured surface seismic data. In case of disagreement, the second phase involves a stochastic seismic inversion which updates the reservoir properties and makes them consistent with the measured seismic data. While running through this workflow, a number of deficiencies in the static reservoir model came to surface. Besides improvement in the thicknesses of the layers away from well control and in the velocity model used for time-depth conversion, the main enhancements from the stochastic inversion amounts to more realistic net-to-gross and porosity estimates and improved insight in the sand distribution in the Al Khlata reservoir. Ultimately, the subsurface uncertainties are considerably reduced and result into improved reserve estimates.

The significance for PDO is that although this technology is well established in most major oil companies, this is the first time it has been successfully applied on a PDO seismic data volume.
Reservoir Characterization for Improved Petrophysical Properties Predictability & Validations: Capillary Pressures and Permeability (Niger Delta Province as Case Study)
Authors: Haruna Onuh , Ogbe David , Chike Nwosu
Published: September 2013

Permeability and initial saturation are two key reservoir parameters to be defined in subsurface reservoir models. The prediction of these parameters is particularly challenging since they cannot are not abtained directltly from downhole well logs. In this paper, we focus on characterization of pore systems at core plug scale to provide improved models for permeability and saturation prediction. The wider implication of the workflow presented is that they offer better integration between methods used for saturation prediction and methods used for permeability prediction.

We examine the use of Mercury Injection Capillary Pressures (MICP) for genetic unit classification and for predicting permeability and saturation. The method is based on a NORMALIZED PORE THROAT APPROACH (Rtot¯) with Niger Delta as case study. Petrographic observations of pore types are analysed alongside MICP data and air permeability for a number of genetic reservoir units. A correlation coefficient, R2 of 0.81 is obtained for permeability - Rtot¯ plot compared to R2 of 0.56 for the porosity-permeability plot. We also investigated Volotikin's method for generating primary drainage capillary pressure curves from NMR logs, to generate pore throat radius as input to Rtot¯.

Model Validation with reference to existing Flow Zone Indicator (FZI) based approach, NMR based methods by SDR and Coates, and the existing core derived permeability correlation for an Offshore Niger Delta Field.
ICD Completions` Optimization for an Offshore Abu Dhabi Well Using Dynamic Modeling
Authors: Hashemi Mohamed Al , Bellah Samir , Gurses Sule , Akhtar Muhammad Nadeem
Published: September 2013

A study was conducted to determine the optimum re-completion for an offshore Abu Dhabi well. The candidate well was completed as open hole in a complex carbonate reservoir with faults and fractures and suffering from rapid increases in water cut. To quantify the value of re-completing the well with ICDs completions, a dynamic simulation modeling and optimization workflow was applied.

To evaluate the best completion design, the dynamic model was refined and history matched in the sector area of the well using multi-segmented well technique. The number of downhole compartments (sections between packers), location of packers and ICDs flow area were simultaneously optimized to determine the best completion options for the candidate well using an objective function that included both; the value of oil and the cost of water. The ICD flow area per compartment was reverse engineered into an appropriate number of ICD joints and set of nozzles as part of the completion design process.

The workflow provided a quantitative method for choosing the most appropriate horizontal well completion and demonstrated significant value for installing downhole flow control devices. The presentation of the results in terms of oil gain and water reduction for the different objective functions provided a clear indication about the best completion options, depending on the cost or aversion for water production versus the value of oil.
Minimum Miscibility Pressure Measurement with Slim Tube Apparatus - How Unique is the Value?
Authors: Ekundayo Jamiu M. , Ghedan Shawket G.
Published: September 2013

Over the years, the slim tube experiment has been the most commonly used laboratory technique for determination of minimum miscibility pressure (MMP) for designing field miscible floods. However, till now, the design of these experiments is not standardized, neither in terms of set-up nor procedure. Often, the set-up, characteristics of the slim tube coil and even the experimental procedures are left to the discretion of the experimentalist, leading to very uncertain and non-unique MMP values, to say the least. Not just the uniqueness is of great concern, but also the lack of measurement repeatability; two measurements using same fluid samples under the "same experimental conditions" may result in too different MMP values. Matching these experiments with any PVT simulation package may pose a challenge, which even if a match is achieved, may be of questionable reliability. It is on this premise that this work was based.

Slim tube experiments were designed and performed to study the effects of some parameters on the uniqueness and repeatability of the MMP measurements. It was found that MMP measurements are different with different injection rates. The lowest tested rate showed slightly lower MMP and better recovery performance than the other tested rates. No clear trend was noted, however. MMP was found to be lower for the larger coil diameter of the two investigated. MMP decreased as the coil length increased. The decrease in MMP with increase in coil length followed a parabolic trend.

It was, therefore, concluded that laboratory measurements of MMP using the slim tube apparatus is a function of not just the characteristics of the interacting fluids but also those of the coil used as well as the choice of injection rates. The experimental design and procedure need to be unified to produce more reliable MMP data. It is the recommendation of the authors to design the experimental injection rate based on the expected field gas injection, to use the largest coil diameter possible, and to design the coil length, based on the expected well spacing between the injector and producer.
Safeguarding Reserves of a Large Carbonate Waterflood Field by Preventing Induced Fractures
Authors: Al Waheibi Hamed , Garimella Sai , Wardy Widad
Published: September 2013

The case study carbonate field has been developed by waterflooding. Presently, only the produced water is re-injected into 50 wells with voidage replacement ratio being less than unity at field level. Declining pressure trends due to suboptimal voidage replacement balancing and continuous drilling activities require rigorous monitoring to avoid dropping below a critical reservoir pressure (13000 Std. Units ) level at which the hydrostatic head could initiate fractures in the reservoir. Injection under fracturing condition is not an option for field recovery furthermore preventing artificial fractures will be safeguarding 40% of expectation reserves in three specific injection patterns.

A geo-mechanical study was conducted to understand the dependency of fracture pressure on reservoir pressure depletion, including temperature effects. A geo-mechanical model was generated using well logs such as density & sonic that was calibrated with lab tests for rock mechanical properties and leak-off tests together with pore pressure for stress model. This model was then used in the estimation of fracture pressure dependency on reservoir pressure using poro-elastic theory. A pragmatic diagnostic tool was then developed for establishing the field pressure operating envelope, where the injection pressures are plotted against reservoir pressures and compared to the field operating envelope at pattern level.. This tool helps identify which patterns are at potential fracturing risk. i.e. above fracture pressure model. Consequent to identification of risky patterns, mitigation measures are implemented by reducing water injection rates and/or reducing offtake rates to adjust sector pressure within the operating envelope. This remediation is practiced rigorously every quarter for all the patterns with the availability of updated reservoir pressure data. So far no indication of induced fractures from downhole temperature gauges or anomalous water-cut behavior is seen. With the effective injection pressure/rate management, field ultimate recovery is estimated to be 33%, exceeding the top quartile recovery factor (32%) and a sustained expectation oil production forecast for the coming 7+ years. To further enhancing the voidage replacement, two supply water wells were drilled for supplementing water injection

In summary, better management of waterflood projects dictates controlling injection strictly below fracture pressure compared to maintaining injection closely above bubble point pressure. The proposed waterflood field management methodology adopted is generic and the diagnostic tool developed can be utilized routinely for preventing induced fractures in matrix waterflood projects.
Does the Double Layer Expansion Mechanism Contribute to the LSWI Effect on Hydrocarbon Recovery from Carbonate Rocks?
Authors: Al-Shalabi Emad W. , Sepehrnoori Kamy , Delshad Mojdeh
Published: September 2013

Wettability alteration mechanism is still believed to be the main contributor to low salinity water Injection (LSWI) effect on oil recovery from carbonate rocks. This paper makes an attempt to explain the double electric layer expansion as a main mechanism and contributor to LSWI effect on oil recovery from carbonate rocks. The existence of double electric layer expansion mechanism in carbonate rocks is investigated through history matching recently published coreflood experiments using the wettability alteration option in the UTCHEM simulator. The history match results suggest that wettability alteration has negligible effect on water relative permeability. The negligible change in the water relative permeability is also consistent with the double electric layer expansion whereas the immobile water film thickness increases and hence the relative permeability remains constant. This paper provides a basis to develop a LSWI model to predict oil recovery from carbonate rocks.
Risk Analysis for a Fracture Offshore Abu Dhabi Reservoir
Authors: Abou Ali Mouyhna , Games Federico German , Bourdarot Gilles Jean
Published: September 2013

This field case present a risk analysis on production, plateau duration and ultimate recovery factor performed on a fractured carbonate reservoir.

The field has been under early production for more than 48 years, with less than 2% cumulative produced Oil. Historical data measurements on Well Production Oil Rate, Well Gas Oil Ratio (GOR), Well Static Pressure and Well Bottom Hole Flowing Pressure have been utilized in order to constrain uncertain parameters during historical period and then propagate into prediction.

The risk analysis takes into account reservoir uncertainties and geological uncertainties on Discrete Fracture Network (DFN). Several surface/controllable parameters have been considered for the Risk analysis evaluation on Plateau Length hypothesis and Recovery Factor.

The risk analysis accounts for two main recovery mechanisms: gas injection from the crest for Gas gravity drainage and periphery down dip water injection with imbibition.

Several scenarios of DFN's and 43 uncertain reservoir parameters with probability distribution were considered.

Experimental Design and Response Surface Methodology have been extensively applied to minimize the number of Reservoir simulation runs of the study.

Plackett and Burman Experimental Design has been used for the Screening Phase. During the screening phase, it has been revealed that 7 uncertain parameters account for more than 80 % of the total variation of Cumulative Oil Production.

A detailed Latin Hypercube has been performed with 3 discrete fracture network, controllable uncertain parameters and these 7 most relevant parameters.

This risk analysis identified the best cases of each phase of the development, P10 and P90, and the major uncertainties impacting the field development plan. Mitigation, acquisition and monitoring plan have been defined accordingly to reduce the major impacting uncertainties.
Computer Assisted History Matching - A Field Example
Authors: Lind R. H. , Allottai O. , Gaaim A. M. , Almuallim H.
Published: September 2013

Computer assisted history matching has received much interest in the recent past. Several commercial programs are now available. We have tested some of these programs – most did not meet our expectations and we discontinued using them.

The latest software tested helps in fine-tuning individual well behavior in a simulation model that has been globally matched. The program identifies model cells which have the highest influence on individual well behavior and modifies permeability in three directions (and porosity) such that the match is improved. Maximum allowed changes of permeability (and porosity) are controlled by the user. The procedure is repeated 10 to 20+ times until the match is considered satisfactory or the model no longer improves.

A flow simulation model is globally matched when all wells can flow historical rates, the pressure history in different compartments or layers can be reproduced, external aquifer properties are adjusted, and fluid and rock properties are verified. In such a model computed well watercut can be grossly in error, some wells are too high others too low. Manual fine-tuning of individual well behavior is a lengthy and frustrating process. We have tested the new computer assisted history matching program on several models. Improvements to most well matches were spectacular.

Model set up and history match procedures used are outlined on a moderately complex reservoir containing more than 1 billion STB oil initially in place. Production history spans 14 years, current recovery is ~25% of OOIP. Some 40 wells are active, four of them peripheral injectors. Injection voidage replacement is ~30%; there is a strong bottom and edge aquifer. The reservoir consists of 3 geological layers; the upper one has a permeability of several Darcy; the middle layer is highly heterogeneous and forms a partial seal to the lower layer with permeability of ~100 mD. We show examples of individual well matches before and after computer assisted fine tuning. We also discuss limitations of the program used and manual interferences required for selected wells.
Determination of Waterflooding Residual Oil Saturation for Mixed to Oil-Wet Carbonate Reservoir and its Impact on EOR
Authors: Masalmeh S. K
Published: September 2013

It is widely recognized that the determination of the amount and distribution of residual oil saturation (Sorw) is a significant factor in managing ongoing waterflooding and the selection of EOR methods that are applicable and economically suitable for oil reservoirs. Laboratory core flooding tests are often used to estimate the amount of Sorw. The same core samples are then usually subjected to EOR flooding experiments to estimate the extra amount of oil that can be recovered with the specific EOR option. Failure to accurately determine Sorw will lead to wrong estimates of recovery factor of both waterflooding and the subsequent EOR methods.

Significant amount of data is available in the literature on determining Sorw and on the critical capillary or bond number to mobilize Sorw. However, most of the data are measured on sandstone rock and for water-wet conditions. In this study the focus is on 1- determination of Sorw in the laboratory for carbonate reservoirs, 2- The factors that affect Sorw, including capillary end effect, capillary and Bond numbers, initial oil saturation, rock permeability, rock heterogeneity and experimental techniques and 3- The use of numerical simulation as tool to aid proper interpretation of laboratory experiments.

The main conclusions of the study are: 1- Performing the water flooding experiments at reservoir rates of ~1 ft/d will lead to overestimation of Sorw as the data can be dominated by capillary end effect; 2- The relative contribution of capillary end effect increases as the permeability increases especially for heterogeneous carbonate rocks; 3- There is no correlation between Sorw and rock permeability or porosity for the case understudy; 4- The critical capillary or bond number of non-water-wet carbonates is much higher than those reported in the literature for water-wet sandstone; thus experiments can be performed at higher rates than those expected in the field without the risk of de-saturation of Sorw and 5- Once an equilibrium between capillary and viscous (or gravity) forces is established, the remaining oil saturation is independent of the number of pore volumes injected.

The data presented in this paper has significant impact on the design of any subsequent EOR process. It shows that the EOR target (after waterflood) is significantly reduced if the measurements are performed using high rates (or high centrifuge speed) to overcome capillary end effect. Moreover, for non-water wet rock surfactant flooding will require much higher reduction in IFT to mobilize residual oil saturation than for water-wet rocks.
Coupled Geomechanical and Reactive Geochemical Model for Fluid and Heat Flow: Application for Enhanced Geothermal Reservoir
Authors: Xiong Yi , Fakcharoenphol Perapon , Winterfeld Philip , Zhang Ronglei , Wu Yu-Shu
Published: September 2013

A major concern in development of fractured reservoirs in Enhanced Geothermal Systems (EGS) is to achieve and maintain adequate injectivity, while avoiding short-circuiting flow paths. The injection performance and flow paths are dominated by the permeability distribution of fracture network for EGS reservoirs. The evolution of reservoir permeability can be affected by rock deformation, induced by the change in temperature or pressure around the injector, and chemical reactions between injection fluid and reservoir rock minerals. Thus the change in permeability due to geomechanical deformation and mineral precipitation/dissolution could have a major impact on reservoir long-term performance. A coupled thermal-hydrological-mechanical-chemical (THMC) model is in general necessary to examine the reservoir behavior in EGS.

This paper presents a numerical model, TOUGH2-EGS, for simulating coupled THMC processes in enhanced geothermal reservoirs. This simulator is built by coupling mean stress calculation and reactive geochemistry into the existing framework of TOUGH2 (Pruess et al., 1999) and TOUGHREACT (Xu et al., 2004a), the well-established numerical simulators for geothermal reservoir simulation. The geomechanical model is fully-coupled as mean stress equations are solved simultaneously with fluid and heat flow equations. After solution of the fluid, heat, and stress equations, the flow velocity and phase saturations are used for reactive geochemical transport simulation in order to sequentially couple reactive geochemistry at each time step.

We perform coupled THMC simulations to examine a prototypical EGS reservoir for permeability evolution at the vicinity of the injection well. The simulation results demonstrate the strong influence of rock deformation effects in the short and intermediate term, and long-term influence of chemical effects. It is observed that the permeability enhancement by thermal-mechanical effect can be counteracted by the chemical precipitation of minerals, initially dissolved into the low temperature injected water. We analyze the sensitivity of temperature of injected water on the coupled geomechanical and geochemical effects, and conclude that the temperature of injected water could be modified to maintain or even enhance the reservoir permeability and the injection performance.
Compositional Phase Trapping in CO2 WAG Simulation
Authors: Brown J. S. , Al-Kobaisi M. S. , Kazemi H.
Published: September 2013

A three-dimensional, three-phase, parallel compositional simulator has been developed to handle large computational efforts involving carbon dioxide (CO2) water-alternating-gas (WAG) injection. Algorithms have been developed to calculate three-phase relative permeability and capillary pressure, including the effects of phase trapping and relative permeability hysteresis for use in the simulator.

Injecting CO2 in oil reservoirs has two advantages: increasing oil production by miscible and immiscible displacement and sequestering CO2 as an environmental measure. Typically a WAG injection scheme is used to control the mobility of the injected fluids. Reservoir simulation models allow us to predict the future performance of CO2 enhanced oil recovery (EOR) and sequestration projects which are of high interest in the Middle East and throughout the world. Test cases applicable to Abu Dhabi carbonate reservoirs were simulated.

It is important to correctly account for trapped oil, water, and gas in reservoir simulation models. An incorrect estimate of trapped fluids in a sequestration project leads to over- or under-estimation of the CO2 stored in the reservoir. An incorrect estimate of trapped fluids in an EOR project leads to over- or under-estimation of CO2 required and inaccurate timing and amount of incremental oil recovery.

Industry simulators assume that mobile and trapped oil and gas in a grid cell are in thermodynamic equilibrium while in this model they are not. The formulation presented in this paper allows tracking the changes in composition of the trapped and mobile fluids during different WAG cycles.
A Comprehensive Approach for History Matching A Giant and Complex Oil Reservoir
Authors: Aissaoui Karim , Moreno Manuel
Published: September 2013

History matching complex reservoirs with hundreds of active wells over decades of production history may reveal to be tedious and complex given the amount of data to be honoured, the level of uncertainty as well as software and hardware requirements. This paper aims at sharing ADCO's experience in achieving a satisfactory match quality on a giant carbonate oil reservoir in Middle East. The approach encompasses manual as well as assisted history matching techniques in a two way communication leading to consistent reservoir images that honour all observed data and mitigate any potential pitfalls which may lead to geologically unrealistic solutions.

Main outputs enabled a better understanding of key influencing reservoir uncertainties that can improve the match quality as well as identifying a few alternative reservoir images that can replicate the observed data both at well and full field level, in addition to an impact assessment on production forecasting uncertainty. Furthermore key remaining uncertainties were pin-pointed so that they can be acted upon.

The reservoir model history matching was undertaken on a single deterministic geological realisation via manual history matching to start with, and then assisted history matching was introduced as a way to rank uncertainty parameters based on their impact on match quality and to provide some directionality for history matching improvement. Moreover, the approach enabled identifying alternative equally history matched reservoir models.

Given the high number of mis-match parameters to satisfy both at reservoir and well levels and the number of reservoir uncertainties to be tested, a structured (staged) assisted history matching approach was implemented. A physically-sound and proper set of parameters with realistic ranges have been considered at each stage of the history-match process in a logical order.

Ranges of selected parameters were designed in a way that satisfactory solutions at each stage can be carried over to the next stage to continue the history-match. This process started with the Latin Hypercube technique as a browsing phase to assess uncertainty impact on response parameters and then discard those with no impact on match quality. The next step evolved proxy modelling - a mathematically / statistically defined functions based on existing realisations that replicated the simulation model outputs for selected input parameters. This helped reducing time required to get the solution to converge. Afterwards, sequential adjustments have been implemented from global then flow units, followed by local changes in model properties using Evolutionary Strategy algorithm. During each stage of this process the "heavy-hitters" with the highest impact on the history-match process were identified and thouroughly investigated.
A Multiple-Continuum Model for Simulation of Gas Production from Shale Gas Reservoirs
Authors: Li Ning , Ran Qiquan , Li Jianfang , Yuan Jiangru , Wang Cong , Wu Yu-Shu
Published: September 2013

Gas production from unconventional shale gas reservoirs is controlled by multi-scaled fractures, i.e., hydraulic fractures, natural fracture, micro fractures, etc., as flow pathways. On the other hand, shale matrix provides the majority of shale gas storage of both free and adsorbed gas. In addition, field data show that there exists significant amount of micro fractures within low-permeable shale matrix and these micro fractures may connect to large, global-connected fracture network. However, these micro fractures have been either ignored or lumped into the "matrix block" in the current simulation models. In this paper, we present a physically based multiple-continuum concept to include both natural and micro fractures as well as low-permeability shale matrix. The multiple-continuum conceptual model implemented considers shale gas rock consisting of (1) globally connected natural fractures, (2) micro fractures locally connected between matrix and/or kerogen to global fractures, and (3) low-permeability shale rock matrix. Similar to the classic double-porosity concept, the global fracture continuum is responsible for global gas flow to hydraulic fractures or wells, while low-permeability shale matrix, providing main storage space, is locally connected to micro-fractures and interacting with globally connecting fractures. In addition, our model formulation also includes the following processes: (1) nonlinear adsorption/desorption effect, (2) Klinkenberg effect, (3) non-Darcy flow (at high flow rate and low flow rate), and (4) pressure-sensitive rock deformation. We use a hybrid modeling approach to describe different types of fractures, including hydraulic fractures, natural fracture network, and micro fractures. We will demonstrate model application to quantify flow behavior in fractured shale gas reservoirs.
Investigation of Optimum Salinity of Injected Water in Carbonate Reservoirs using Wettability Measurement and Core Flooding
Authors: Sharifi Mohammad , Shaikh Murtdha
Published: September 2013

Waterflooding is the most popular secondary oil recovery method. Attempts were made to increase the sweep efficiency of waterflooding by focusing on various physical and chemical aspects of this process. Low salinity waterflooding was an important research topic in recent years, with a focus on the possible effect of various compositions of injected fluid on oil recovery. In this study, the effect of the salinity level on oil recovery in a limestone reservoir was investigated. The methodology utilized multiple limestone core samples. After x-ray analysis, four samples with high calcite content (more than 98% calcite) were used in flooding experiments and the impact of the salinity level on oil recovery was measured.

This study is a continuation of a project at The University of Tulsa (Al Shaikh, 2012). The design of the coreflooding study was constructed base on the contact angle measurement results of the wettability study. The Tagochi method was used to design wettability measurement experiments that span varieties of salinity combinations. The current study showed that coreflooding recovery has a clear relationship with the contact angle measurement of calcite plate. We showed that contact angle values are better indicators for choosing optimum injected water composition in compare to the salinity level. Sequential injection of water with the lower measured contact angles led to the highest recovery. This relationship is not necessarily valid for the salinity level because our wettability experiments show that there is no direct relationship between the measured contact angle and the salinity level of water.

During this experiment, incremental oil recovery from 12 to 18 percentages was reported. This shows the high potential of success for this method. We showed that Tagochi method is an effective way to design an experiment for measuring the contact angle and finding the optimum level of salinity. Similar experiments are required before applying this method to the field. In practice, there is an optimum salinity beyond which purifying the brine water further will not lead to incremental oil recovery. Finding the optimum salinity scenario is essential for increasing recovery with minimum cost.