bluuebunny/crossref_metadata_2025 huggingface dataset:
Project Management Knowledge Retrieval: Project Classification
Authors: Bērziša Solvita
Published: August 2015

Project management knowledge contains a wide range of information that can be accumulated from theory and practice. This knowledge is not always readily available to project manager and that can leave a significant impact on project management efficiency and success. Therefore, this knowledge is necessary to store in the project management knowledge repository and then to retrieve it when necessary. To find this knowledge it is necessary to define attributes for searching relevant projects and knowledge associated with these projects. The objective of this paper is to develop a set of project classification attributes that can be used to describe project characteristics and use them in similarity definition. The project classification attributes are defined as a part of the architecture of project management knowledge retrieval. They are identified by analyzing several project management methodologies and are validated by classifying twenty two empirical information technology projects.
Dynamic Response Of Tower Structures
Authors: Gaile Liga , Radinsh Ivars
Published: August 2015

The present study focuses on the tower type structures response to the dynamic loads. The study analyzes the possible mode shapes regarding to tower structure. The estimation of mode shapes and their dependence from structural changes was made for an existing tower structure. To get an acceptable tower’s vibration level and avoid possibility of resonance effect from usual serviceability loads it was evaluated options to change natural frequencies of the structure. It is performed existing 36m high sightseeing tower dynamic analysis and proposed potential solutions to increase critical natural frequencies of the structure. In this study to obtain dynamic parameters of the sightseeing tower structure have been used finite element models and calculation techniques.
The Diversity Of Weeds In Organic Linseed And Flax Crop
Authors: Gruzdevienė Elvyra , Jankauskienė Zofija
Published: August 2015

The flax is grown in the world for many years. The area of linseed in the world is much more than that of fibre flax. The seeds of ecologically grown linseed have high value as the row material for food, medicine, fodder, oil production. The cold pressed oil and seeds of ecologically grown linseed are especially popular in EU, Canada and USA. The quality of the finished linen product is often dependent upon growing conditions and harvesting techniques. The organic textile trend is starting to develop worldwide, while in Lithuania it is still almost non-existent. Therefore, the chance for Lithuanian farmers appears to export the ecological seed and fiber, not only use them in local market. Lithuanian farmers are in luck for the advices how to grow flax in ecological way. Therefore, in 2007- 2009 some investigations were carried out at the Upytė Experimental Station of the Lithuanian Research Centre for Agriculture and Forestry (Panevėžys district, Lithuania). The results of our investigation showed that it is possible to grow and harvest fibre flax and linseed in organic farms without any pesticides. The incidence of weeds is one of the biggest problems in organic growing of flax and linseed.
Micro-Electromechanical Systems In The Ecology
Authors: Kartunov Stefan
Published: August 2015

In the present paper a definition, a model for building of MEMS (micro-electromechanical systems), types, their advantages and disadvantages have been given. The elements and the components, from which they are built, the development and the prediction of market about them have been considered as well more important firms, that manufacture them. A classification of MEMS is made on the basis of their designation and the region, where they operate. A special place is separated on the application of MEMS in the ecology as well as concrete examples are indicated – developments of firms and own ones.
Clustering-Based Behavioural Analysis of Biological Objects
Authors: Kirshners Arnis
Published: August 2015

The article examines the problem of processing short time series for bioinformatics tasks using data mining methods in the field of pharmacology. The experiments were conducted using heart contraction (contraction and relaxation) power data that were obtained in experiments with laboratory animals with the goal of registering the power changes of heart contractions in different stages of experiment in a given period of time. The selected data were treated using data preprocessing technologies. The short time series were compared using various time-point similarity search methods using agglomerative hierarchical clustering, k- means clustering, modified k-means clustering and expectation-maximization clustering algorithms. Based on the clustering result evaluation the most suitable algorithm was chosen and the optimal number of clusters was determined for the least clustering error. The acquired clusters were used for to create cluster prototypes that aggregate the groups of similar heart contraction power objects. The article offers an examination of the errors produced by algorithms and methods as well as a discussion of the obtained clustering results using different evaluation methodologies. It also gives conclusions about the application of data mining methods in solving bioinformatics tasks and outlines further research directions.
Use of Lignosilicon to Improve the Harvest and Quality Parameters Of Potato
Authors: Lebedeva Galina , Solodovnik Valentin , Telysheva Galina , Vigovskis Jānis , Švarta Agrita
Published: August 2015

Lignosilicon (LSi), a plant growth activator, was synthesized at the Latvian State Institute of Wood Chemistry (LS IWC) on the basis of the wood lignocellulosic complex. It is shown that LSi, used for treatment of potato tubers before sowing at low application rates of 20-40 kg/ha, has a favourable action on the yield and quality of the tubers. In comparison with the control, the additional yield achieved on the background of LSi (20-40 kg/ha) was 18-20%. The best biochemical composition was for the tubers wetted with water and LSi-treated before the sowing, i.e., the content of dry matter and starch increased by 16% and 18%, respectively, but the content of nitrates in the tubers decreased 1.6 times. LSi can be recommended for potato cultivation under conditions of conventional and organic agriculture.
Regional Climate Change (Karelia, Russia)
Authors: Nazarova Larisa
Published: August 2015

The overview of climatic conditions in Karelia is based on the data from meteorological observations carried out in 1951-2009 at Roskomgidromet weather stations situated in the study area. Taking the period in question into account, the mean annual air temperature norm has increased by 0.2-0.3°C. The greatest deviation from multiyear averages of mean monthly air temperature is observed in January and March. The investigation of the changes the basic regional climate characteristics is very important in present time because the global climate is changed. The analysis the data about air temperature and precipitation, that were obtained for the different meteorological stations in the investigated region, shows that the regional climate is changed and the main tendencies are directly proportional to the change of the global characteristics.
DEVICE FOR MONITORING THE CONDITION OF THE NATURAL BACKGROUND
Authors: Nenov Nikolay
Published: August 2015

Life on Earth arose and exists in terms of natural ionizing radiation. Environmental pollution with radioactive substances begins with the emergence of the nuclear industry. Proceeding from the accepted truth that there is no safe dose of exposure to radioactive radiation and accumulated over the years experience (more than 25 years), the author of this article provides an apparatus for monitoring the condition of the natural radiation background based on light and sound indication in all cases when there is increase toward “imperturbable” atmosphere.
Nonlinear Dynamics of Buck Converter
Authors: Pikulin Dmitry
Published: August 2015

This paper is concerned with the problem of modeling and simulation of piecewise linear systems with the pulse width modulation control. Models of this kind of systems are widely used in engineering practice, in particular in power electronic converters. The research provides the study of chaos and bifurcations in one of the switching converters – step-down converter under voltage mode control, operating in discontinuous and continuous current modes, using Matlab and Simulink simulation environment. Various types of models, including discrete – time maps, switched state – space models are examined in order to detect their suitability and reliability in numerical investigation of nonlinear phenomena in DC–DC converters. Some analytical methods for the search of periodic regimes and their stability estimation were also used in order to validate numerically obtained results and evaluate the accuracy of models used. As direct simulation does not accurately pinpoint bifurcation points and computes only stable invariant sets, some aspects and advantages of numerical path-following are also discussed.
Feature Selection Approaches In Antibody Display
Authors: Polaka Inese
Published: August 2015

Molecular diagnostics tools provide specific data that have high dimensionality due to many factors analyzed in one experiment and few records due to high costs of the experiments. This study addresses the problem of dimensionality in melanoma patient antibody display data by applying data mining feature selection techniques. The article describes feature selection ranking and subset selection approaches and analyzes the performance of various methods evaluating selected feature subsets using classification algorithms C4.5, Random Forest, SVM and Naïve Bayes, which have to differentiate between cancer patient data and healthy donor data. The feature selection methods include correlation-based, consistency based and wrapper subset selection algorithms as well as statistical, information evaluation, prediction potential of rules and SVM feature selection evaluation of single features for ranking purposes.
A Review of Nigerian Bentonitic Clays as Drilling Mud
Authors: Agwu Okorie E. , Okon Anietie N. , Udoh Francis D.
Published: August 2015

The heydays of bentonitic clay production in Nigeria occurred in the late 1950s when oil was first discovered. This was short lived as the advent of imported bentonite took the centre stage in the early 1960s. Since then, there has been no widespread use of the Nigerian bentonitic clay as drilling muds in Nigeria. In the recent past, precisely in 2001, the only major use of Nigerian bentonite for drilling oil wells was made by Shell Petroleum Development Company, Nigeria where over 600 wells were drilled with it. In recent years, Nigerian researchers have been actively pursuing the study of using Nigerian clay as drilling muds and finding potential markets for it. Many of these studies have focused on characterizing and beneficiating the clays to the American Petroleum Institute (API) standard. The available studies in this direction have been chronicled in this paper with the major research findings of each individual researcher brought to the fore. Much of the information that has been gathered in this review indicate that all the researchers were in unison in their submission that the Nigerian bentonitic clay is predominantly Calcium based and that it requires some measure of beneficiation to be effective for use as drilling muds. Mention is also made of possible gray areas where more research efforts should be directed. This work is predicated upon the belief that the works of the past combined with that of the present can lay the necessary framework for future studies on Nigerian bentonitic clays. The review this paper presents can serve as a baseline for the oil and gas E & P companies desirous of unlocking the potential of using Nigerian bentonitic clays as drilling muds.
The Effect Of Wellbore Stability In Naturally Fractured Reservoirs
Authors: Fekete Paul , Bruno Lopez A. , Dosunmu Adewale , Odagme Samuel , Sanusi Adewale , Bowe Ediri
Published: August 2015

Wellbore instability all over the world accounts for a significant in Non-Productive Time (NPT) in well drilling and completions and incurring high cost of drilling as well as increasing safe risks. Real time analysis of data and geomechanics (understanding the rock properties and stresses) has continuously improved the stability of wellbores in the world. Some of the issues cost by this instability are the most common of these losses are: borehole enlargement, cavings, washouts, stuck pipes, deformation of the casing and amongst others.

Numerous wellbore instability problems related to drilling through potentially natural fractured reservoirs/formations have been reported. Most of the this reported formations are been characterized by number of macro and micro scale bedding planes and/or networks of natural fractures which weakens the mechanical strength of the rock and the producibility of potential of the rock matrix. This term paper reviews instabilities issues in Naturally Fractured Reservoirs (NFR), natural fracture reservoir failure mechanism and highlights the effect of instabilities in NFR as well as proper well placement in the NFRs. This paper also looked at wellbore solution in permeable and impermeable formations, borehole failure analyses, drilling strategies to mitigate instabilities in naturally fractured reservoirs and other counter-measures dealing with wellbore instability. The review shows that well design, drilling fluid design, minimizing lateral vibrations of drill pipe and good drilling practices are critical in solving wellbore stabilities in naturally fractured reservoirs.
Local Content Policy and Enterpreneurship: Implications for Small and Medium Scale Industries in the Nigerian Oil and Gas Sector
Authors: Udoh Francis D. , Akpanika Offiong I. , Anietie N. Okon
Published: August 2015

The introduction of the Local Content (LC) policy by the Nigerian Government in the early 2000's was primarily aimed at transforming the petroleum industry into the economic engine room for job creation and national growth through capacity building and empowerment of Nigerian indigenous companies. Through stimulating higher participation of small and medium scale industries and promoting the utilization of local human and material resources in the oil and gas sector, Nigeria was to ultimately develop as the hub for service delivery within the West African sub-region and beyond. The high technology, capital intensive/high risk nature of operations in the oil and gas sector have always been the challenge that militate against the rapid development of successful entrepreneurship and the realization of government's goal in the area. The Nigerian Oil and Gas Industry Content Development Act 2010 has the potential for effective value repositioning, thus raising our small and medium scale enterprises in the sector to reputable service providers capable of wealth creation and contributing to growth of the national Gross Domestic Product (GDP).
Alternative Approachto Multi-Rate Testing
Authors: Obeahon P. P. , Daodu O. , Sedgwick A. , Okereke O.
Published: August 2015

In Nigeria it is a statutory requirement to frequently perform multi-rate test (MRT) on gas wells to update well deliverability and for optimal reservoir management. Analysis of MRT test data provides information on well potential, average reservoir pressure, flow correction, skin factors, condensate and water rate. This information is useful when calibrating well models and in reservoir management. Allthisinformation when not properly estimated can have a huge impact in reserve estimation as well as production forecasting. Traditionally, MRT testing is done using a mobile tester. The inability to conduct MRT tests frequently using themobile tester is due to budget constraints and associated deferment or flaring affectingobligation to meet gas sale agreement. Other demerits associated with the traditional approach to MRT include large personnel exposure, mobilization of heavy equipment, high environmental footprint, inability to flow well to potential due to flare limitation and difficulty in reconciling test rates with actual rates. Due to these limitations, an alternative testing method is proposed. The proposed approach makes frequent MRT's possible and attractive from both economic and HSSE standpoint.

The proposed method discussesusing existing gas central processing facility to conduct MRT. This new method offers a major advantage over the former since it requires little or no equipment mobilization, no flaring nor deferment, reduced number of personnel exposure, no test rate limitation nor rate reconciliation, all of which can be achieved at a significantly lower cost, reduced HSSE exposure and testing duration.

Pilot tests were successfully carried out on well X, well Y & well Z. In each case there were zero incidents, zero deferment and zero production loss. This method saved $2.34M and gained some volume of gas which would have been lost to flaring if testing was done using the traditionalmobile tester. These three pilot examples demonstrate that MRT's can be performed more frequently using an existing gas central processing facility provided all of the metering equipment are installed and that the activities is meticulously planned to capture all of the required data.
Analysis on Traditional Reserve Estimation Methods in Stress-sensitive Gas reservoir: Error Analysis and Modification
Authors: Dou Xiangji , Xinwei Liao , Xiaoliang Zhao , Tianyi Zhao , Zhiming Chen , Weiyan Ren , Rui Zhang
Published: August 2015

Thanks to predecessor's researches, several reserve estimation methods have been proposed over the last few decades, which are commonly accurate for conventional reservoir. However, for stress-sensitive reservoir, permeability is the function of pressure, which may lead to significant errors when using traditional methods even though the flow is boundary-dominated.

In this paper, errors caused by applying several traditional reserve estimation methods based on production data including Flowing Material Balance, Normalized Rate – Cumulative Curved in stress-sensitive reservoir are quantified with numerical simulation. Then, based on the sensitive-analysis, modification procedures for these traditional methods are proposed and validated with synthetic data. Finally, the modified methods are applied to Sulige gas field, a typical stress-sensitive tight gas reservoir.

It can be concluded from the error analysis that for stress-sensitive gas reservoir, Flowing Material Balance and Normalized Rat-Cumulative Curve would result in underestimation. For all the methods above, the magnitude of error is influenced by formation properties, hydraulic fracture qualities, operation conditions and the level of stress-sensitivity. Besides, the error caused by the latter method is larger than that caused by flowing material balance for the same condition. We also find that Flowing Material Balance and Normalized Rate–Cumulative Curve can be modified by introducing new pseudo-pressure and pseudo-time, which take stress-sensitivity into account. These methods are proved to be accurate by both numerical simulated data and field data.

The technique contributions of this paper including: (1) the error caused by stress-sensitivity for traditional reserve estimation methods are quantified and the influencing factors are investigated; (2) modified ideals for traditional methods are proposed.
Coupled 3-D Temperature, Viscosity and Pressure to Investigate the Effect of Heating on Pressure Decline in a Closed Reservoir with high Viscosity
Authors: Akonobea Appiah Elizabeth , Igbokoyi A. O. , Akinojo Omololu
Published: August 2015

Even though heavy oil and bitumen are difficult to produce due to their high viscosity which can be reduced by heating, with increased oil price, the production of these heavy oils are seen viable thus the need for a model that would help make predictions for the future and also take into consideration areal and vertical sweep of hydrocarbons. As a result of a heterogeneity of reservoirs, numerical simulators are used to obtain consistent and significant solutions. For this work, a three-dimensional numerical reservoir simulator is developed for an expansion drive reservoir with a high viscous oil. A transient state heat system by conduction with an internal heat source is considered. A temperature simulator is first developed then coupled with a viscosity correlation after which it is then coupled with a diffusivity equation for a single phase flow of an expansion drive reservoir. All the governing equations are discretized using finite difference technique. Iterative linear solver with the aid of MATLAB code is used to solve the system of linear equations. The study evaluates the performance and the proficiencies of thermal recovery method which is the most common for high viscous oil. The results shows reasonable amount of energy being sustained for more recovery. Without heating, pressure decline is rapid but increasing heat source shows pressure decline being slow.
Empirical Wellhead Pressure-Production Rate Correlations for Niger Delta Oil Wells
Authors: Okon Anietie N. , Udoh Francis D. , Appah Dulu
Published: August 2015

Several correlations have been developed to predict wellhead pressure–production rate relationship in the Niger Delta region. Regrettably, most of these correlations were developed from field data that are not from the Niger Delta region and with limited field test data ranges, so their predictions are lower than expected field values when applied to the Niger Delta. Additionally, some developed wellhead pressure–production rate correlations based on Niger Delta field data are made using in-house equations by the operating companies in the Niger Delta region. To ameliorate this anomaly, sixty four (64) field test data: choke size (S), production rate (q), gas-liquid ratio (GLR), flowing wellhead pressure (Pwh), flowing temperature (FTHP) and basic sediment and water (BS&W) were collected from oil producing wells in the Niger Delta region to develop wellhead pressure–production rate correlations based on Gilbert correlation and modified Gilbert equations. The developed correlations using Niger Delta field test data were compared with several authors' correlations. The results obtained indicate that the developed correlations resulted in better predictions than earlier correlations. In addition, the statistical analysis of the developed correlations used to ascertain the extent of their predicted values differ from the field test data and resulted in average error, absolute error and standard deviation of −0.1477, 0.4430 and 0.9582 for Gilbert formula and −0.2515, 0.4737 and 1.0997 for modified Gilbert formula, respectively. Furthermore, the developed correlations are comparable with an average correlation coefficient of 0.9869. Therefore, the developed correlations can be used as a quick tool to estimate the wellhead pressure–production rate relationship in Niger Delta oil fields.
Evaluation of Cased-Hole Expandable Sand Screen (ESS) Application in Gas Wells.
Authors: Wali Asmau , Uzoho Foster , Nwankwo Cosmas , Ekwealor Jude
Published: August 2015

Sand face completions have a major impact on a well's deliverability, by determining its productivity or injectvity throughout its expected life. In the Niger Delta, most reservoirs are shallow (below 10,000 ftss) and poorly consolidated, sand control forms an important part of sand face completion design. Sand management strategy involves using a software FIST (Fully Integrated Sand Prediction Tool) to carry out sand failure prediction analysis. In cases where sand failure is imminent, a sand control selection guide is used to determine the optimal sand control method to be installed. The selection is benchmarked against the performance of existing sand controls designs in analogue wells the in the region.

A number of sand control mechanisms have been successfully deployed in various completions across Niger Delta which includes Chemical Sand Consolidation, Gravel Packs (Internal/External), Slotted liners, Expandable Sand Screens (ESS), etc. The complexity of deployment varies widely from the most complex multiple IGP/EGP to slotted liners. In all, most of the methods have exhibited good sand control properties however, with varied productivity. The ESS has presented a good balance between ease of deployment, productivity and life cycle management of the well.

A field in the greater Gbaran area of the Niger Delta is proposed to be developed by three gas wells targeting three reservoirs. The reservoirs are unconsolidated and below 10,000 ftss, with Sonic log transit times in the range of 93 - 162 μsec/ft. Sand failure prediction on these three reservoirs using FIST indicated a high failure probability (95 – 100%) during the production life, thus requiring sand control. Following the process of selection, and Cased-Hole ESS was proposed. Although cheaper and easier to install with better productivity, a proper evaluation of the erosion tendency especially in Cased-Hole application of ESS in gas wells is essential to ensure full life cycle coverage.

This paper documents the results of the evaluations carried out, optimization methods employed to evaluate the proposed sand control mechanism.
Thermodynamic Modelling for Mapping Wax Deposition Envelope for an Identified Niger Delta Oilfield
Authors: Johnson-Achilike N. N. , Chukwu G. A. , Ajienka J.
Published: August 2015

Wax deposition is a major concern for the pipeline and oil industry. During normal pipeline and production operations in an oilfield containing waxy crude oil, wax precipitation and deposition will occur which may provide conditions conducive for corrosion to commence. Several Niger Delta oilfields have been identified to contain waxy crude oil. Wax can be deposited in the formation, production tubing, wellhead, surface flow lines and in storage facilities, when favorable conditions of pressure and temperature exist. A decline in the reservoir pressure will lead to a decrease in production rate leading to conditions favorable for wax precipitation and deposition. This becomes a huge concern for marginal oilfields producing at low oil rates. The need to proactively predict the temperature at which wax will precipitate, called Wax Appearance Temperature (WAT), leads to the development and application of thermodynamic models for such predictions. Several models have been developed till date and are currently in use in the Niger Delta but most of them have been validated using data from stock tank oil or dead oil. This makes it unreliable for prediction of wax precipitation during production because the effects of pressure and composition have been neglected. This work aims to modify selected thermodynamic models using live crude oil data from an identified Niger Delta Oilfield with a view to mapping the Wax Deposition Envelope (WDE) which will give an idea of the WAT at different points in the production life of the field.
Regional (Niger Delta) Facie Based Vsh Cut-Off For Net Reservoir Sand Definition
Authors: Anyaehie James
Published: August 2015

Different approaches and methods are used across the various Oil and Gas companies for net sand definition resulting in variation of results even on the same data set. The lack of a consistent, concise and systematic approach in the determination of net sand which is a key input to STOIIP or FGIIP parameters leads to lack of credible and transparent audit trail thereby further increase uncertainties in the hydrocarbon reserves determination.

In general, the common practice is to plot a creaming curve of various Vsh cut off versus equivalent HC column (Porosity * Net sand) and pick the cut off at the asymptote (i.e. at the point where further increase in the value of Vsh used for cut-off has minimal impact on incremental equivalent HC column). Other analytical methods are also used. However, most of this methods, estimate their end points and parameters on aggregate level without consideration for clay distribution within the pore spaces resulting from the genetic variation (facies) within the sand packages, which has significant impact on the storage and transmissibility of the hydrocarbon within the porous media.

This report covers the development of a Niger Delta regional core calibrated faces based Vsh cut-off for the HC resource assessment in absent of actual core for calibration. The research derived various cut-off ranges that covers the major facies observed in the Niger Delta deposition. The developed cut-off values which are calibrated with core acquired within the region are facie specific has greatly simplified and standardize Vsh-cut-off used in estimation of net sand which is a key input in Hydrocarbon resource estimation.
Reducing Reservoir Uncertainty through Systematic Data Integration and Analysis: Case Study of a Partially Appraised Gas Field
Authors: Obi Azubike , Inaingo Osuagwu , Olakunle Iyowu , Uche Ozoemene , Anyaehie James , Muyiwa Esho
Published: August 2015

The maturation and development of hydrocarbons in partially appraised fields (PAFs) is often threatened by the high degree of subsurface uncertainty resulting from limited well penetration and paucity of subsurface data in such fields. The uncertainties ranges are sometimes very wide and the resultant cost of further appraisal is so prohibitive that the value and economic indices of carrying out development projects in these fields are severely eroded. For PAFs which are gas-bearing, the challenge is further underscored by the relatively lower price of natural gas and associated higher cost of infrastructure compared to oil. Thus, if not adequately managed, the subsurface uncertainties can go a long way in defining the economic success or failure of planned development projects in PAFs. For this reason, geoscientists and petroleum engineers are tasked with the responsibility of integrating and analysing all available data in the field with the aim of assessing, managing and reducing these uncertainty ranges as much as possible.

The OZ field, which is discussed in this paper, is located in the Niger Delta and has a maximum of 6 well penetrations across sixteen (16) reservoirs in a predominantly gas field. Comprehensive data acquisition (electrical surveys and formation pressures and samples) from the last well drilled in the field in 2012, helped eliminate the fluid typing and contact uncertainties in most of the reservoirs.

However, for the potentially largest reservoir in the field, the actual fluid contacts (Gas Oil Contact or Hydrocarbon Water Contact) were not logged rather a Gas-Down-To (GDT) and Water-Up-To (WUT) were logged in this reservoir at 100ft apart. With a 100ft column of undifferentiated fluid, the resource volumetric uncertainties varied substantially and if the entire 100 ft column contained hydrocarbon then depending on the type (gas or oil) and ratio, the planned development of the reservoir could easily change from primarily gas to an oil development with a gas-cap blowdown in the future. Hence, the fluid typing and contact delineation emerged as one of the major uncertainties associated with the development of the reservoir and the field at large. To reduce this uncertainty, systematic field reservoir pressure analysis coupled with the integration of other electrical surveys and regional knowledge were applied to significantly minimize the fluid type and contact uncertainties.

This paper showcases details of the analysis and its implication in cost reduction and project value enhancement.
Integrated Performance Based Gas Initially In-Place Estimates Update - An Aid To Optimum Natural Gas Field Development
Authors: Ikwan Ukauku , Ehighebolo Thaddeus , Bhattacharya Tirthankar , Das Debasis , Dongen Van , Madiba Gislain , Temitope Jegede , Ernest Ikpolo , Anaevune Austin , Sarkar Sudipto , Fouzdar Amit , Sanwoolu Fola , Esimaje Jolomi
Published: August 2015

Two methods exist for the estimation of Gas Initially In-Place – volumetrics (probabilistic or deterministic) and performance (material balance equation or numerical simulation). The more appropriate method will depend on the maturity of the project reservoir. For potential accumulations with limited information, the GIIP estimate may be volumetric-based using probabilistic methods, covering the range of possible outcomes with P90, P50 and P10 outcomes as low, best and high estimates. For fields where more subsurface data are available, the preferred method will generally shift towards volumetric-based GIIP estimates using deterministic low, best and high cases. Once a field is in production and sufficient data are available, a performance-based GIIP estimate should be established, including the appropriate range of uncertainty.

Over the years, the tendency has been to over-rely on volumetric-based estimates with little attention paid to performance based GIIP update leading to sub-optimal gas field development.

In this paper, we took a case-study reservoir having or tending towards negative reserves in course of its production life to underscore the need for timely update of GIIP based on performance data as an aid to optimal development of a gas field. Reservoir A has volumetrically based GIIP of 1.6 Tscf respectively leading to prediction of early End of Life (EOL) or negative reserves. When compared with performance based GIIP and updated volumetric GIIP of 2.04 Tscf to match performance data, the issue of early EOL or negative reserves was ameliorated and ultimate recoveries were optimized.

Performance based GIIP estimate is reliable when premised on appropriate choice of methods (P/Z material balance for depletion reservoirs, aquifer influx model in water drive gas reservoirs material balance model or dynamic simulation) integrating all available data as illustrated in the case studies.

To allow comparison between volumetric-based (static) and performance-based (dynamic) GIIP estimates and to understand the potential difference between the two, it is recommended that a current volumetric GIIP estimate should be maintained throughout the life of the field in addition to an up-to-date performance-based GIIP estimate to aid optimal gas field development.
Interference Test Pressures of a Reservoir with Vertical and Horizontal Wells
Authors: Giegbefumwen P. U. , Adewole E. S
Published: August 2015

Over the years, interference test analysis has become a veritable analytical tool in reservoir characterization of most brown fields. At interference the area between the wells has been adequately swept. Therefore, results obtained from interference data analysis show a better reservoir representation as compared to that obtained from single well test. This study presents an analysis of interference test data of horizontal and vertical wells for various well spacing using Malekzadeh's model. Malekzadeh assumed an isotropic reservoir condition. For the fact that anisotropy has a major effect on the pressure transient responses of horizontal well, the results of Malekzadeh have limited applicability. Thus, in an attempt to alleviate this limitation, this analytical study was borne.

The reservoir model used in this study is assumed to be anisotropic, laterally infinite and bounded at its top and bottom. Skin and wellbore storage effects are not considered. For proper analysis, three cases are considered: (1) an observation horizontal well and active vertical well, (2) observation vertical well and (3) active horizontal well and an active observation vertical well and an active horizontal well. Type curves are generated for each case.

Our results show a slope of 1.1513/cycle for Cases 1 and 2 and a slope of 2.303/cycle for Case 3 at interference for late time flow regime. However, a check on the effect of anisotropy reveals that directional permeabilities bring about a slightly higher bottomhole responses for late-time flow regimes. For pressure to be felt by adjacent wells, an enomous time is sometime needed pending on the location of the observation well.

In conclusion, our findings show that anisotropy strongly affects interfering pressures between wells.
An Analytical Model of Foam Resistance Factor in Gas Foam Flooding
Authors: Zang Jiali , Li Xiangfang , Chen Zhiming , Huang Liang , Li Yanzun , Telphi Yanick
Published: August 2015

Gas foam flooding is an effective technique to improve recovery and it has been successfully applied in some low permeability oil reservoirs. Among all parameters, foam resistance factor is regarded as an important index to evaluate the gas shutoff and water shutoff capacity of foam system. Until now, Foam Resistance Factor is normally obtained through solving the nonlinear regression equation based on laboratory foam flow experiment. The empirical formulas obtained through this method have low accuracy, limited application range and no repeatability.

In this study, we used the fractional flow theory to analyse the liquid and gas distribution and established a formula of solving water saturation in function of gas liquid ratio, connate water saturation and flowing gas fraction when foam flow is at steady-state. Then foam resistance factor prediction model was approached in absence of oil based on empirical and population-balance foam models which were employed to modify gas relative permeability and gas viscosity. Analytical method was proposed to estimate critical parameters, such as fmmob, Xf and FM, for model solution. A case was designed for illustrating detailed solution procedure. In the end, comparison between calculation FM data and simulation FM data were performed indicating a relatively good match.
Effective Hydrate Management during Gas Expansion
Authors: Olabisi Odutola Toyin , Sunday Ikiensikimama Sunday , Joseph Ajienka Atubokiki
Published: August 2015

As the world increases its natural gas development and exploitation projects, Gas hydrate will constitute a major flow assurance concern in most gas facilities. It is imperative to critically examine the various means of hydrate formation and effective ways of managing gas hydrates. This work considers gas hydrate formation due to gas expansion. It was discovered that hydrate formation may occur at the Joule Thompson's valve due to cooling during gas expansion. Hydrate prevention was effected by determining the critical point at which the expanded gas moves from the hydrate free zone to the hydrate risk zone. A comparative study was carried out to evaluate the effectiveness of methanol (MeOH) and monoethylene glycol (MEG) in hydrate inhibition during gas expansion. Hydrate formation curve and inhibitor performance curves were generated using CSMGem Software. MeOH performed better than MEG as 10wt% MeOH could prevent hydrate formation when the gas was expanded to about 3338 psia whereas, 10wt% of MEG could not prevent hydrate formation when gas was expanded beyond 3750 psia. This work will aid the engineer to assess problem areas upfront and to determine mitigating measures.
Material Balance Modeling and Performance Prediction of a Multi-Tank Reservoir
Authors: Idogun Iroro , Jeboda Olatunji , Charles Dawari , Ufomadu Happiness
Published: August 2015

Recent reservoir studies have shown great strides in capturing complex multi-tank reservoir systems using Material balance (MBAL®) model especially when these tanks are hydraulically connected. The preference of a simple and quick material balance method over numerical simulation is justified when time and budget constraints may hamper full field simulation modelling. The subject reservoir for this study is a mature hydraulically connected tank under waterflood. This paper compares reserves estimation using predictive material balance and dynamic simulation after history matching both models.

Results from this paper shows that for multi-tank modeling using of hydraulically connected reservoirs using MBAL, transmissibility modeling & aquifer modelling are key factors in achieving reasonably reliable MBAL models. A good understanding of the reservoir fault frame work and connectivity, adequate & reliable BHP, injection and production data are very important for attaining a good history match & model calibration. Results of this study show a good comparison between the Reserves estimate from both MBAL and that from dynamic simulation. Under the appropriate conditions, Predictive Material Balance is a quick alternative tool to reservoir simulation in reservoir performance prediction especially when time & resources are limited. Also, predictive material balance analysis should be applied in reservoir where the existing wells have adequate data to build reliable inflow & out flow models.
An Investment Matrix Model for Marginal Field Operators in Nigeria
Authors: Ashore Utomako , Onaiwu Oduwa , Olafuyi Olalekan , Sunmonu Rasak
Published: August 2015

In a bid to promote the participation of indigenous oil and gas companies in the upstream sector, the Nigerian government introduced the marginal field program which is aimed at encouraging local participation in the industry and to increase Nigeria's oil production.

The development of these fields has been quite challenging as petroleum projects require huge funds that are associated with a series of risks and uncertainties which a combination of experience, knowledge and careful evaluations may not be able to overcome.

Economic analysis is an integral part of every field development as it is the pivot on which several other decisions revolve. It helps to reduce the challenges by carrying out economic evaluations to find out the best petroleum investment opportunities in terms of cost, revenue and risk mitigation.

With the uncertainties in the oil and gas industry and in light of the current decline in the world oil price which has been having a negative impact on the Nigerian economy owing to the fact that 85% of Nigeria's revenue is gotten from the sale of crude oil, this study seeks to develop an investment matrix model for marginal fields in Nigeria. It recognizes the current drop in world oil price, analyzes its effects on marginal fields and proffers solutions on how marginal fields can stay afloat even with the current drop in oil price. Forecasts are carried out in case of a future drop in oil price and the results are incorporated into a deterministic model with the economic yardsticks as guiding factors in order to make the best economic decisions.
Steam-alternating-CO2 for heavy-oil recovery
Authors: Lawal Kazeem A , Tendo Fidelis
Published: August 2015

The commercial exploitation of relatively deep heavy-oil reservoirs is often accomplished by injecting only high-quality steam (steam-alone). This practice is associated with prohibitive CO2 emissions. However, tightening constraints on fuel, water, and the environment are inspiring enhancements to the traditional steam-alone recovery methods. As an improvement, this paper introduces and evaluates the steam-alternating-CO2 (SAC) process for developing these resources.

Conceptually, SAC entails injecting steam and CO2 in cycles while oil is produced continuously. Essentially, hot CO2 partially replaces steam as an injectant. Where steam and CO2 are available, another possible enhancement option is the simultaneous steam-CO2 (SSC) process, involving the co-injection of steam and CO2 as a mixture, rather than in cycles. Compared to the steam-alone process, SAC and SSC promise better project performance, largely due to enhanced thermal efficiency and underground carbon sequestration.

Some conceptual thoughts behind SAC are explored, including how the required CO2 injectant would be sourced from the flue-gas emitted during steam generation. It is shown that the overall process is potentially self-sustaining, as the required CO2 is generated and utilised within the same closed system, thus minimising fugitive emissions. Relevant process-engineering aspects are highlighted.

As a case-study, 3-D multi-phase/multi-component thermal-reservoir simulations are conducted using a representative sector of the Nigerian heavy-oil deposit. Performances of the SAC and SSC processes are compared, while using the steam-alone process as the reference case. In terms of oil-recovery and thermal efficiencies, simulation results suggest that SAC is superior to SSC.

Although SAC yields a lower oil-recovery compared to its steam-alone counterpart, the former has higher thermal and environmental efficiencies, as it returns better oil-recovery per unit steam-consumption. Differences in their recovery performances are explained. Based on these results, SAC is considered a promising thermal-recovery method. Thus, for sustainable energy-supply, the proposed in-situ extraction method deserves attention.
Application of Interconnected Fibre-Network to Improve Sand-Control in Water Injectors: Preliminary Insights From Field Data
Authors: Lawal Kazeem A. , Okosun Joshua , Olatunji Idris , Okonkwo Paulinus , Horsfall Ipalibo , Adenuga Ademola , Ogunsina Oluseye , Ekebafe Abraham , Mbanefo Edith , Tendo Fidelis , Pokima Sophie , Bapoo Saeed
Published: August 2015

To minimise well-count, sustain high injectivity and enable high offtake rates from the associated oil producers, cased-hole frac-pack water injectors in deepwater fields are often operated at relatively high injection rates. However, continuous injection at high rates (velocities) may displace the proppants in the sand-control system, increasing the vulnerability of such injectors to impairments by fines invasion. To mitigate this impairment mechanism, a new fibre-based product (interconnected fibre network) was recently introduced for locking proppants in-place. Although the product was extensively tested in the laboratory prior to its release, its field performance and impacts on injectivity remain uncertain.

To improve the reliability and longevity of a critical frac-pack water-injection well in a giant West-Africa deepwater oilfield, this proprietary product was recently deployed. Being the first field application in the exploration-and-production industry, this case-study presents an opportunity to validate the results of prior numerical and laboratory experiments while identifying relevant improvement areas for future developments and field applications. Specifically, the impacts of this product on well injectivity and other performance indicators were investigated.

Within 6 months of start-up, the well injected ca. 7 MMbbl of treated seawater and surveillance data acquired. Although this fibre-reinforced cased-hole frac-pack injector is still at relative infancy, this paper presents initial insights gained from managing the well. For the current evaluation, the surveillance techniques employed include the Hall-plot and deep-bed filtration analysis, complemented by step-rate, injectivity and pressure-transient tests. Among other findings, the performance of this well is generally comparable to the conventional (unreinforced) frac-pack injectors completed in an analogue reservoir in the same field.

To a reasonable extent, this pioneering case-study allays the pre-installation concerns that the product would hamper injectivity. The present observations notwithstanding, there remain some key uncertainties and challenges, which are potentially reducible as more statistically significant performance datasets become available from this field and elsewhere. It is too early to conclude from available data that the fibre-reinforced frac-pack performs better than the (previously used) non-fibre-reinforced frac pack injectors in this field.