bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Design in Deterministic Modelling: Assessing Significant Uncertainties
Authors: Peng Cheong Yaw , Gupta Ritu
Published: December 2007

This study investigates the feasibility of using experimental design and analysis methods within the 3D geological modelling framework, which includes the discussions and guidelines of: (1) how to select appropriate designs; (2) how to determine the number of experimental runs; and, (3) how the experimental response can be modelled accurately with the statistical modelling methods to develop a surrogate equation model. This methodology can systematically and significantly reduce the number of models that must be generated to cover the effects due to all the input uncertainties in multiple deterministic modelling. The approach is valuable in assessing the various sources of uncertainty in 3D geological modelling, and to study how they affect the hydrocarbon in-place volume. In brief, the approach uses expert knowledge and a decision tree to consider the input variables and the full range of possible geological models. Then, experimental design methods and expert opinion are used to select a subset of models that must be built to cover the whole uncertainty range. A response surface equation model is fitted to develop a surrogate equation model, which represents the ‘actual’ modelling experiment. This can provide a valuable insight into the behaviour of the input uncertainties, and the output response distribution. Finally, this surrogate equation model must be evaluated to justify the results.

The above approach is demonstrated using: (1) a simple multiplicative hydrocarbon in-place volume equation, (2) an Excel spreadsheet built to mimic the 3D geological modelling workflow to provide some guidelines on the possible effects (interaction, nonlinear) and design selection; (3) 3D geological modelling (multiple deterministic) to assess the input variables of a fluvial reservoir. A few key variables were found to be significantly affecting the hydrocarbon in-place volume. The designs used were Placket-Burman, 2k-p and 3k-p fractional factorial designs, either with or without some modifications. These selected designs were ranging from 9 to 27 runs/models.

In conclusion, a simple two-level fractional factorial design, such as Placket-Burman, is sufficient to assess and rank the input uncertainties in 3D geological modelling, as only the main linear effects are dominant. This permits future data acquisition to be optimised to reduce uncertainty. On the other hand, where the aim is to predict hydrocarbon in-place volume, nonlinear and interaction effects are significant, and a more sophisticated design, such as a modified two-level fractional factorial design with central and axial points, is required. The surrogate equation model can be used to determine the in-place volume distribution and to extract the possible P5, P50 and P95 models.
A Computer Aided System of Geology-Engineering-Economy-Production Synergy for Optimization of Integrated Reservoir Management
Authors: Du Zhimin , Liang Baosheng , Xie Dan , Chen Xiaofan
Published: December 2007

Reservoir management widely accepted as a concept has been paid close attention in Chinese petroleum industry. However, there are innumerable barriers in operation mainly because of the lack of powerful platform to effectively support multidisciplinary cooperation. As a result, after a period of fast development, the geology-engineering-economy synergy arrives to a plateau and becomes a mirage suitable only in theory, which in turn reduce the confidence in the viability of optimum reservoir management.

This paper provides a systematic approach to integrated reservoir management by a computer aided system, based on a database of China National Petroleum Corporation. The system includes seven organic sub-systems: geology information integration, development information integration, reservoir engineering calculation, production performance analysis, economic evaluation, real-time monitoring, data management and maintenance. The function of each part and tightly mutual collaboration are presented. More specifically, through the access to the database in which data of different specialized areas are originally separate, all the information since reservoir exploration is shared orderly on the platform of this computer aided system. Graphs, curves, spreadsheets and other engineering and economic analyses can be generated automatically with any selected area or well groups. Teamwork is realized conveniently, and the dynamic-static performance combination is obtained through comfortable communications among geologists, field engineers and economists on the computer aided reservoir management system. Furthermore, because the routine production management is optimized through real-time monitoring, especially its visualized performance analysis, it is a handy assistant for high-level managers to know how the operation process works, to make reasonable decision and to adjust the strategy timely. In this way, geology, engineering, production and economy are integrated expediently and the traditional bottleneck is solved. Additionally, the successful applications of reservoir management system designed in this paper are briefly introduced in some oil fields such as Dagang Oil Field and Zhongyuan Oil Field in China.
The Effect of Fracture Characteristics on Reduction of Permeability by Asphaltene Precipitation in Carbonate Formation
Authors: Zekri Abdulrazag Y. , Shedid Shedid Ali
Published: December 2007

Crude oils produced in many parts of the world contain asphaltene. Asphaltene plugging is a known cause of near-wellbore formation damage. The deposition phenomenon of asphaltene has been extensively investigated in homogenous porous media. However, we have not found any reported experimental work on asphaltene plugging in naturally or artificially fractured reservoirs. The main objective of this study is to investigate the effect of fracture characteristics on reduction of permeability by asphaltene deposition in carbonate formation.

A single fracture system is made with different fractures characteristics such as porosity, permeability, and fracture angel using saw-cut limestone core samples with metallic plate. The fracture aperture was kept constant for most of the studied systems. The effect of flow rate, fracture angel, matrix to fracture permeability, asphaltene concentration and the state of stress on the retained permeability is presented. Different fracture angle orientations of 45°, 90°, and 180° relevant to the axis of the flow were investigated. A non-invasive imaging technique-Scanning Electron Microscopy (SEM) was employed to visualize changes on the surface of the fracture as a result of aspheltenic crude oil flow through the system.
Reducing Evaluation Cycle-Time in Complex Reservoir Settings: A Case Study from South West Ampa Field, Brunei
Authors: Holyoak S. C. , Hayon S.
Published: December 2007

The content of this paper is based on the ongoing evaluation of the South West Ampa Field, Brunei, and encompasses the processes executed from seismic interpretation through to structural and reservoir modeling. South West Ampa is a large, complex oil and gas field, with more than 100 stacked, highly compartmentalized reservoir intervals. Original fluid contacts are typically not common between adjacent fault blocks. In this challenging setting, the approach used in the past to evaluate reservoir fluid distribution and volumetrics relied heavily on conventional mapping packages and intensive draughting efforts. The constraints imposed by software and processes resulted in cycle-times of several years. Recently however, Brunei Shell Petroleum (BSP) has conceived innovative solutions to manage the inherent complexity, and significantly reduce evaluation cycle-time. The workflow described maximizes use of legacy data, and culminates in a tightly integrated full-field 3D model. A new approach to utilizing corporate fluid contact data has resulted in breakthrough performance in the area of fluid distribution modeling and volumetric calculations. The majority of the processes covered in this paper are also applicable to less complex settings. At South West Ampa Field, the cycle-time of the evaluation process has been significantly reduced.Working in a highly integrated 3D environment facilitates quality control of the model.The model and the resultant maps / cross-sections are based directly on corporate data. Any inconsistencies are highlighted, and can be corrected at source. The model and its derivatives can be rapidly updated with new or re-evaluated data.

The paper is fully supported by examples from the South West Ampa Field.
Extracting Capillary Pressure and Global Mobility from Spontaneous Imbibition Data in Oil-Water-Rock Systems
Authors: Li Kewen , Horne Roland N.
Published: December 2007

An approach was developed to extract the imbibition capillary pressure and the global mobility data from spontaneous water imbibition tests in oil-water-rock systems. Capillary pressure and global mobility data were calculated using this method with the experimental data of countercurrent spontaneous water imbibition tests in different rocks and at different interfacial tensions. The calculated capillary pressures were consistent with the change in interfacial tension. The oil-water-rock systems with greater interfacial tensions had greater capillary pressures. However the oil-water-rock systems with greater capillary pressure may not have greater imbibition rate. The calculated values of the global mobility and the imbibition index explain why the oil recovery or the imbibition rate in systems with high interfacial tension was smaller than that in systems with low interfacial tension, which has been considered a paradoxical result for many years.
Internal Environmental Corrections for a New Carbon Oxygen Logging System
Authors: Jacobson Larry A. , Truax Jerome , Durbin Dennis P.
Published: December 2007

Modern Pulsed-Neutron Spectrometry (PNS) well logging tools produce measurements (e.g., Carbon/Oxygen (C/O) ratio, lithology (Ca/Si) ratio, elemental yields, etc) that are impacted by internal as well as external factors. The external ones are well known: porosity, lithology, borehole size, casing size, cement thickness, borehole fluid type, centering, tubing size, to name a few. These factors have been discussed extensively in the literature and will not be addressed here.

Internal effects have not, however, been extensively discussed in the literature. They arise from unit-to-unit variations in component characteristics. Some examples are scintillator and photomultiplier performance, dead-time and pulse pileup effects, electronic, and analog-to-digital converter linearity. All of these will be discussed here. These internal effects generally lead to differences, from unit-to-unit, in the absolute magnitude of output quantities measured (C/O ratio, lithology ratio, for example). Fortunately, the log character (i.e. the variations with depth) is usually preserved. Unit-to-unit variability is of concern in well monitoring projects because of the likelihood that logs will be obtained with different tools (perhaps even different vendors) over the lifetime of a well.

These internal effects are examined using a database of measurements made in the same zone of a single test well. The database was generated from several dozen tools; each calibrated in the same fixture. Using this database, corrective schemes were devised that minimize internal effects, thereby producing measurements that are more consistent from unit to unit. The corrective schemes are parameterized in the calibration process for each tool and applied to all log data run with that particular tool.
Zero Discharge Strategy on Water Quality, A Case Study in Minas OU
Authors: Santoso E. A. , Fanandi A. , Nasoetion S. , Moersidik S. S. , Hamzah U. S.
Published: December 2007

Discovered in 1944 and placed on production in 1952, the Minas Field has produced 4.25 billion barrels of oil to date (47% recovery). Current production average is 126 MBOPD with 5,200 MBWPD. This huge volume of water needs to be managed effectively because its potential environmental impact and water handling cost. These two reasons triggered the need of extensive water management program.

The water management programs in Minas are divided on surface and subsurface strategy. The surface strategy emphasizes more on avoiding any environmental impact. Starting on late 1995 "Zero Water Discharge" program was implemented by means of re-injecting all of produced water from all 6 (six) gathering stations. The subsurface activities emphasize on reducing water production, which is unavoidable process in oil industry. In early 2000, the subsurface strategy of limited open sand perforation was implemented and is able to flattening oil production decline while also reducing water production significantly.

This paper describes the strategy of the Minas Operating Unit (OU) on surface and subsurface activities on continuing its effort on handling its produced water while also attaining zero water discharge to the environment as part of its water management program.

Surface activities are included monitoring produced water in each gathering system, stream water and sediment, quality of injection water and shallow ground water, as well as improving water injection equipment. Ensuring no subsurface water injection leaking to ground water by conducting surveillance, improving injectivity, reducing water production, and effort on water injection reduction to productive zone are the current subsurface activities.

All the above effort have added tangible and intangible value to Minas operation. Tangible value came from reduction in operating cost by $ 14.6 million in year 2001 by reducing 800 MBWPD. Preserving our environment for future generations is the highest value (intangible) of this program.
Behavioral Change in Managing Waste From Risk to Challenge
Authors: Parwitosari Agustina , Waluyo Waluyo
Published: December 2007

Helios, the BP brand, has four attributes namely Green, Performance, Innovative and Progressive. To put real meaning into Green value, BP commits to continuously drive down the environmental impacts of its operation. Accordingly, improvement targets will be set for individual Business Unit. In this role, BP Indonesia is applying the Environmental Management System (EMS) ISO 14001 as a tool for managing wastes in its operations and ensuring its compliance with Indonesia's environmental regulations.

BP Indonesia, a production-sharing contractor to Indonesia's state oil and gas company (Pertamina), is one of the main oil and gas producers. BP employs approximately 600 labor force and contracts additional 600 people in its operating area in Pagerungan, Offshore Northwest Java and the Shorebase (Warehouse). Distances between these sites of operations are indeed impediments in the waste management efforts. In line with EMS framework, a work process for waste management was developed with a primary function to identify current practices, the gap with regulatory requirements, the priority to manage and improvement potential.

Initial work aimed to put into practice waste segregation from the waste sources. Program implementation was the greatest challenge to the entire workforce of BP Indonesia and its contractors since people's behavior is the most contributing factor to the success of the program. In places where a typical problem such as different level of education and understanding exists, it is very challenging to view the environmental awareness with the same optimism and the same perception. All efforts in managing waste used to be considered as additional work and financial burden. In the initial period, those attempts to protect the environment by implementing waste management seemed highly unlikely. Nevertheless, by strong commitment from the management as well as persuasive and enduring approach, it is surely a successful one. Yet, when it is about behavioral change, the efforts should be relentless.
Estimating Air Emissions for Permian Basin Oil and Gas Properties
Authors: Johnstone James E. , Stobbe Alan
Published: December 2007

A system to estimate emissions from large numbers of oil and gas producing properties was developed by the BP's Permian Basin environmental group. The system developed by BP estimates air emissions on a quarterly basis for both internal and external reporting requirements. Additional benefits from the system have been the reduction of fuel gas use and other measures to improve operating efficiencies. This paper describes the key components of the air emission data gathering system, the results of the calculations showing the relative emission levels, and the economic benefits by implementing such a system.

The results of the emission reporting system enabled BP to accurately estimate the emissions from each property. Overall emissions for the Permian Basin were quantified. Operations people determined that fuel gas costs could be reduced through the use of lower or no bleed gas operated equipment. The study also helped to prioritize additional engineering work to look at fuel consumption in fired equipment. Internal and external reporting requirements were integrated.
Offshore Environmental Monitoring Around Oil And Gas Installations On The Western Continental Shelf, Arabian Sea, India.
Authors: Dulip Awinash
Published: December 2007

Oil & Natural Gas Corporation (ONGC) has been exploring and producing Oil and Gas on the western continental shelf of the Arabian Sea since mid 1970's. There are about 150 production platforms (including 13 major complexes) and approximately 3,000 km of sub-sea pipeline producing over 20 million tonnes of crude oil and about 20 billion cubic metres of natural gas per annum from this region.

ONGC has established an Institute of Petroleum Safety, Health and Environment Management (IPSHEM) as its commitment towards promoting higher standards of Health, Safety and Environment for the Petroleum Sector in India. The Institute apart from imparting training in HSE has regularly undertaken a two-season offshore monitoring study since 1994 for its Offshore Installations.

Offshore Environment Monitoring may have many meanings but generally, it means repeated measurement of pollutants for their effects, and changes over a time frame. In a more regulatory sense, monitoring includes collection of data in relation to some standards or guidelines imposed on the project authorities.

This paper describes the strategies, procedures, methodologies adopted in the design of the monitoring program, surveys, analysis etc. and the salient findings during the study period 1994–2001.

The parameters of interest covering environmental impact of offshore operations are identified. From the study, it is clear that there is little or no effect of offshore operations on the general hydrography of water column, and availability of nutrients for phyto-plankton growth in the marine environment. Environmental Impact of offshore operations on the biological productivity was found to be insignificant from the recorded observations. Most pollutants were well within the background levels in this offshore region of the Arabian Sea.

INTRODUCTION

The Oil and Natural Gas Corporation (ONGC) Offshore oil field development incorporates various phases such as geophysical /geological exploration, drilling of wells, production testing, processing of oil, gas and produced water and transportation of oil and gas by pipelines or tankers. Deployment of a series of rigs in the region led to delineation of several major and marginal oil fields in the region. There are about 150 production platforms (including 13 major complexes) and approximately 3,000 km of sub sea pipelines producing over 20 million tonnes of crude oil and 20 billion cubic metres of natural gas per annum from this region.
Development Practices and Achievements for Reducing the Risk of Oilfield Chemicals
Authors: Hill Donald G. , Dismuke Keith , Shepherd William , Witt Irena , Romijn Henk , Frenier Wayne , Parris Mike
Published: December 2007

An effective approach to the global issue of chemical management, based on Gulf Coast and North Sea experience in wellbore stimulation, is described. This paper presents the results of aggressive chemical development and replacement programs for stimulation chemicals for worldwide application. Development of more environmentally acceptable products requires working with regulatory agencies, clients, and chemical suppliers to achieve regulatory compliance for MSDS, labels, and environmental testing protocol. This paper recognizes that international environmental statutes and guidelines combined with clear corporate goals to minimize environmental impact are key requirements in regulating industrial use and discharge of environmentally harmful chemicals. The development of more environmentally acceptable products requires a thorough screening of environmental fitness and status of compliance with relevant laws and regulations.

Oilfield chemicals have primary active ingredients that may be harmful if discharged to the environment. Improving the characteristics of these products to reduce risk or damage to marine life requires changes in previously acceptable products, such as elimination of restricted materials and incorporation of components with improved ecotoxicity values.

Details are given on the aggressive programs developed to address a wide range of environmental opportunities and issues. International environmental statutes and guidelines are the strongest driving force to restrict industrial use and discharge of environmentally harmful chemicals. The primary tool of environmental risk reduction is an aggressive product development program incorporating more environmentally friendly chemical solutions. The paper will also present three years of field results achieved using environmentally improved stimulation products.
Electronic Applications of EIMS Available to the Oil and Gas Industry
Authors: Belieu S. , Jehn P. , Kerr T. , Gillespie D.
Published: December 2007

The Ground Water Protection Council's Environmental Information Management Suite (EIMS) of applications, with its flagship application, the Risk Based Data Management System (RBDMS), has expanded to include other electronic business applications that extend the use of oil and gas database information. These project development efforts will allow industry to produce more oil and gas more cost-effectively by providing industry with the tools that enable electronic business.

EIMS is the information management system used by most of the state agencies that regulate oil and gas production and injection throughout the country. The design goal of this suite of software is to enhance environmental protection and provide industry with the tools necessary to leverage resource development work by expediting reporting and permitting processes through access to the data contained in agency databases. Examples of GWPC's success in this regard include the eReport XML schema for production and injection data and Web-based reporting system, Web-based oil and gas well permitting (ePermit), RBDMS Online State Web sites, a Web-enabled schematic drawing utility that renders scaled drawings of wells from construction information stored in an ODBC/ADO data source, and Web-enabled GIS utilities for evaluating risk assessment and produced water quality.

GWPC, state personnel, and design consultants are developing e-business software applications that will serve small, medium, and large oil and gas operators. These customizable applications can be mapped to any Level 2 ODBC data source to meet the varying requirements of differing agencies without incurring duplicative programming efforts. Options under development include XML schema expansion, run-time databases, and online Web interfaces. This paper describes some of these electronic business software tools and their benefits to industry, user agencies, and the public.
Environment and Sustainable Management of Oil and Gas Reservoirs in Italy
Authors: Brighenti Giovanni , Macini Paolo , Mesini Ezio
Published: December 2007

Approximately 80% of the energy consumed in Italy today comes from hydrocarbons (49% oil, 31% gas). In 2001, domestic production covered about 23% of gas and only less than 4% of oil consumptions. From a mere technical standpoint, the exploitation of the existing fields and the development of some recently discovered oil and gas reservoirs could increase domestic production. Moreover, it is estimated that the application of advanced technologies might double the reserves, mainly with new discoveries. However, in a small country like Italy, where the population is heavily concentrated, very often the oil or gas reservoirs are located in environmentally sensitive areas, so that their exploitation might pose problems. After a brief review of some case histories related to such critical areas, the paper examines the technical challenges, together with the solution taken so far, with particular reference to the following hazards: a) onshore and offshore reservoirs located along the shoreline or in marshes and lagoons, where land settlements would cause a regression of the coast and flooding (e.g., Po Delta area, Venice and its lagoon, Ravenna, etc.); b) reservoirs located in natural parks where pollution due to release of oil, mud or other pollutants on the soil, or excavation and deforestation, could damage the environment (e.g., Ticino River natural park, Val d'Agri natural park, etc.); c) reservoirs located near urban settlements, where there are serious restrictions to drilling and production, limits to noise, traffic, water and soil pollution etc. At last, the paper examines the local and national constraints and the environmental limitations for a sustainable management of oil and gas reservoirs in Italy.
Determining How Different Plunger Manufacture Features Affect Plunger Fall Velocity
Authors: Rowlan O. L. , McCoy J. N. , Podio A. L.
Published: December 2007

Tracking the fall of the plunger down the tubing can be used to optimize the operation of plunger lifted wells. Acoustic fluid level instruments can be used on plunger lifted wells to acquire a series of plunger/fluid level soundings and/or to record the acoustic signal produced as the plunger falls down the tubing. Five different data acquisition and analysis methods can be used to monitor the position of the plunger, as the plunger falls down the tubing during the controller’s shut- in time period. The acquired data is used to determine the 1) fall velocity of the plunger 2) depth to the plunger and 3) time for the plunger to fall to fluid. Results acquired from field case studies from 15 sessions at various wells are used to correlate the various construction features of different types of plungers with their fall velocity. Some construction features cause a plunger to fall rapidly through the tubing, while other features cause the plunger to have a slow fall velocity.

By accurately measuring the plunger fall velocity, the proper shut-in time for the plunger lift installation can be determined. The plunger trace measurements will ensure that the plunger has reached the fluid at the bottom of the tubing by the end of the shut-in period. Setting the well’s controller to have the shortest possible shut-in time period to allow the plunger to fall to bottom can maximize oil and gas production from plunger lift installations.
Characterization of Leaky Boundaries Using Transient Pressure Analysis
Authors: Escobar Freddy H. , Djebbar Tiab , Jokhio Sarfraz A.
Published: December 2007

Some faults or boundaries have been recognized to be sealing to the migration of underground fluids. Other faults are indicated to be non-sealing or leaky to fluid flow by providing a path for fluid migration. Determining whether a fault or barrier is sealing or non-sealing and their effects in the subsurface is a major problem for the engineer in petroleum exploitation.

From the transient pressure analysis point of view, few publications have been referred to this issue. The determination of the non-sealing degree has been performed by type-curve matching which leads to a limited number of type curves and involves a trial-and-error procedure.

This paper presents a pressure transient analysis method to characterize a leaky boundary by identifying a fault or boundary scalable dimensionless conductivity parameter which goes from −1 for constant pressure fault/boundary to +1 for a fully sealing barrier. The model used here assumes that the mobility and diffusivity ratios of reservoirs on two sides of the barrier are the same. The interpretation method used is the Tiab's Direct Synthesis Technique4 which basically utilizes characteristic points obtained of intersection of various straight line portions of the pressure and pressure derivative curve, slopes and starting times of these straight lines. These points, slopes and times are then used with appropriate equations to solve directly for permeability, wellbore storage, skin, boundary distance and leakage degree.

A step-by-step procedure to determine distance from wellbore to the barrier and the boundary scalable dimensionless conductivity is presented and successfully tested by means of simulated examples. The scalable dimensionless conductivity provides a degree, or even percentage, of the leakage condition of a boundary or fault. This is determined from the ratio between the radial line and the second radial line. The scalable dimensionless conductivity can be used to estimate the value of boundary conductivity.
A Generalized Hyperbolic Decline Equation with Rate-Time Dependent Function
Authors: Chen Shing-Ming
Published: December 2007

Nearly all the decline curve equations used today are based on the Arps hyperbolic equation1, given as:

Using this equation, the production rate ‘Q’ at anytime ‘t’ can be calculated from the hyperbolic exponent ‘b’, the initial production rate ‘Q0’ and its corresponding decline rate ‘D0’ at time zero.

Although Equation (1) is easy to use, the variation of the decline rate with time (except b = 0) limits the applicability of the equation. For a hyperbolic decline curve (b>0), if a different production rate ‘Qi’ on the curve is used an initial rate, a different corresponding decline rate ‘Di’ needs to be identified for the equation to represent the same decline curve. Moreover, if there is a rate or reference time change in the production forecast period, the identified hyperbolic equation from the production history is no longer applicable.

(1) Q(t)=Q 0 × (1+b × D 0 × t) − 1 / b

In this paper, a generalized hyperbolic equation is derived to overcome the above limitations. Once a set of ‘Q0’, ‘D0’ and ‘b’ is identified from the production history, the equation can be used to predict the future rate regardless of the initial rate or time change.
Pressure Behavior of Well Near a Leaky Boundary in Heterogeneous Reservoirs
Authors: Boussila A. K. , Tiab D. , Owayed J.
Published: December 2007

This paper provides an analytical solution for a well near a linear leaky boundary, in otherwise infinite laterally composite systems. The leaky boundary is viewed as an infinitesimal damaged discontinuity (linear skin discontinuity) located at the interface between two adjacent media. The zone thickness may or may not be equal, and the infinitesimal damaged zone width is a restatement to the assumption of low fault conductivity and storativity.

The problem was solved using the two-dimensional diffusion equation with successive integral transformations, and the one dimensional green’s function. Both solutions, uniform and non-uniform diffusivity cases merge exactly at early and late time. Solutions presented in this study have been validated by comparing a number of its simplified forms with those available in the literature. Confirmation of the solution is also demonstrated by investigating three limiting cases: (1) a well near a sealing boundary, (2) well near undamaged linear discontinuity in a composite system, and (3) well near a constant pressure linear boundary.

As shown in this paper, a single leaky fault can give appearance of naturally fractured reservoir on a pressure transient response for a unit-mobility ratio case and a linear flow regime may also develop for a low diffusivity contrast. Further investigation of the correlating skin parameter ‘sa’ representing the product (Sf* ad) proves that Yaxley’s definition addressed to the fault (α) is equivalent to the term (1/Sa) derived in this work. Consequently, computing the discontinuity damage leads to an indirect measurement of the fault conductivity. Pressure and pressure derivative type curves have also been generated showing the effect of all the parameters affecting the wellbore responses. Making the use of the flexibility of the final solution, we have also investigated the pressure response of a linear boundary in an infinite naturally fractured composite reservoir. The step-by-step procedure for calculating reservoir parameters is also developed in this study. The Tiab’s Direct Synthesis (TDS) technique is applied to interpret pressure derivative behavior of a vertical well near a linear leaky boundary in laterally composite systems.

Lastly, for a practical implication, the procedure developed is illustrated with one simulated example and one field case.
Analysis of Experimental Data of ESP Performance Under Two-Phase Flow Conditions
Authors: Beltur Raghavan , Prado Mauricio , Duran Javier , Pessoa Rui
Published: December 2007

Electrical Submersible Pumps (ESP's) are well known to have a good predictable performance for single phase, low viscosity liquids. In the oil industry, oil production is associated with the production of gas. The presence of gas deteriorates the performance of the pump. The performance deterioration varies with the amount of gas and the intake pressure at which the pump is operated. So far no good predictive method is available to predict the performance of the ESP under two-phase conditions. Presently the industry is using the homogeneous model, correlations and other models to predict this performance. In the homogeneous model the two-phase flow head is assumed to be the same as single-phase head (provided by the manufacturer) at a total mixture flow rate. The available correlations are specific to the tested type of pump and to the tested number of stages. Finally to predict performance on model, no general model has been developed to predict two-phase performance of the ESP due to complexity of two-phase flow, pump geometry and speed at which it is operated. Researchers, Lea and Bearden (1982), Cirilo (1998)), Romero (1999) and Pessoa (2000) have concluded through experimental results that the application of the homogeneous model gives good prediction only at low gas fractions (in the order of 2 to 5 %) at the intake. At higher gas fraction the experimental results shows that performance is well away from the homogeneous model predicted performance.

The University of Tulsa Artificial Lift Projects – TUALP is currently conducting experimental and theoretical research on the two-phase behavior of electrical submersible centrifugal pumps, using a 22-stage Mixed flow type, series 513 pump with best efficiency flow rate of 6100 BPD to gather data on stage wise performance under two-phase flow conditions. Air and water were used as working fluids. This is a unique facility that has pressure gauges fitted across each stage. It not only helps to study the stage wise behavior but also the effect of number of stages on cumulative performance of pump under two-phase flow conditions. This paper focuses on analysis of data collected at TUALP facility.
Intelligent-Thinking Restored Well Productivity in Horizontal Completions Plugged-off by Sand-Deposits: Huge Reward
Authors: Nwoke Linus , Arukhe James , Uchendu Chike
Published: December 2007

This paper presents improved CTU foam cleanout operation for horizontal producers completed with pre-drilled liners and provides insight into the technicalities of optimized removal of sand-deposits in horizontal wells. Excessive sand production (800-lbs/MSTBO) characterized JKJ reservoir in Niger-Delta, with sand-deposits in the doglegs, drastically plugging the wellbore to abandonment and subsequent shut-in on LTP. Wireline runs and previous unsuccessful attempts to gas/nitrogen-lift the wells confirmed existence of sand-plugs along the wellbore. Rigless CTU sand-cleanout operation was performed on five wells using key design and placement techniques. Limiting sand-cleanout to optimized depths at first point where hole-inclination is 90° within the heel gives valuable results. Further cleanout beyond this depth to the toe breaks apart already-formed cohesive sand-configuration (acting as filters) outside the pre-drilled liners into the wellbore, generating massive sand returns of about 30 bbls to the surface thereby increasing treatment costs and adds negligible value to productivity. Each well was treated within six days at an average total cost of $130,000.00. Incremental 1200 bopd was achieved on average per well, given rise to 4 ½ days Pay Out with respect to oil price of $24 per barrel.

Summarily; Good eccentricity, under-balanced cleanout, stable foam quality and incremental oil were achieved with valued engineering thinking and decision.Because much of the production comes from the heel of horizontal wells, cleanout of sand-deposits to the toe adds little value to productivity with excessive / high additional job costs.Treatment duration is reduced and production time accelerated by limiting cleanout of sand-deposits to optimized depths.Severe production fall-off in horizontal pre-drilled liner completions is caused by sand-plugs in the doglegs, which act as mechanical bridge-plugs.Observation not to cleanout horizontal wellbore completed with pre-drilled liners beyond the depth at first point where hole-inclination is 90° within the heel has been established, and reveals that cleanout beyond this optimal depth creates excessive sands to be handled on surface and adds negligible value to productivity.There is threat of possible formation deconsolidation and early production decline when low bed sands are washed out in horizontal section.
Modeling of Hydraulic Fracture Height Containment in Laminated Sand and Shale Sequences
Authors: Miskimins Jennifer L. , Barree Robert D.
Published: December 2007

The results of hydraulic fracture modeling in a hydrocarbon reservoir consisting of laminated sand and shale sequences are presented. Work previously published by other authors addresses hydraulic fracture growth characteristics in layered intervals, but little published information is available for growth in thin-bedded reservoirs. For the purposes of this paper, thin beds are considered to be on the order of less than 6 inches (15 cm) in thickness. In certain reservoirs, there may be thousands of these thin beds involved in influencing hydraulic fracture growth.

The hydraulic fracture modeling is based on data from the North LaBarge Shallow Unit (NLBSU) located in the Green River basin of Wyoming. The NLBSU produces hydrocarbons from the Cretaceous-age Mesaverde interval. This reservoir is comprised of laminated sand and shale sequences. Hydraulic fracturing is necessary for economic production. Actual field data from two NLBSU wells is used in the analysis. The data includes stimulation treatment pressures and information, as well as a radioactively tagged fracture treatment.

The hydraulic fracture modeling software GOHFER is used in the analysis. GOHFER is used based on its ability to approximate decoupled rock deformation with shear-slip, and its extensive use in the industry.

The results of this study strongly indicate that the sand and shale laminations present in the Mesaverde reservoir act as a hydraulic fracture height containment mechanism. Two events are presented as the reasons for this observed containment. First, shear slippage is prevalent due to the numerous interfaces present in the subject depositional environment. These interfaces inhibit fracture growth through shear failure. Second, the contrast in rock mechanical property values between the sand and shale intervals reduce the fracturing energy available for fracture propagation.

Further research in this area is strongly recommended due to the significant oil and gas reserves associated with this type of reservoirs. These additional research areas include laboratory investigations and field work with tiltmeter and microseismic analysis. Meanwhile, fracture modelers are strongly encouraged to evaluate the effects of laminations in their modeling efforts.
Fluid Loss Control – Improvement for HTHP Wells
Authors: Evans Brian
Published: December 2007

Fluid loss control is often a consideration, if not a major engineering exercise, for a wellbore workover or completion operation. When the mix includes high bottomhole wellbore temperature, high reservoir pore pressure and high reservoir permeability and porosity, then the well killing operation can become very complicated. For these reasons many operations include mechanical means of fluid loss control, thereby achieving positive well control for a long period of time without the worry of reservoir damage by fluid invasion and kill fluid byproducts. However, there are some instances, such as tripping drill pipe or tubing in or out of a well, that mechanical tools are not applicable.

Enter chemical fluid loss control. Often referred to as "fluid loss pills," chemical fluid loss control has been associated with everything from shredded newspapers to the latest biopolymers, which may carry carefully engineered bridging solids. While completion operations will hopefully not use bridging solids usually reserved for lost circulation while drilling, the point is that just about everything at hand on a rig location or in a laboratory has been tried as a fluid loss control agent.

For most of these chemical fluid loss pills, the upper limit of endurance is 275°F (135°C), which is the melting point of processed starch commonly found in fluid loss pills. Also, most commercially available fluid loss pills lose temperature stability as fluid density is increased with water soluble salts. A new fluid loss control pill has been designed to provide effective fluid loss control for 24 hours at 300°F (149°C) in a fluid density up to 12.5 pounds per gallon (1.50 specific gravity).
P/Z Analysis of a Mature Gas Condensate Field, Offshore Trinidad
Authors: Baptiste Brian J. , Jagai Tennyson
Published: December 2007

Graphical application of the gas Material Balance Equation (MBE), P/Z plots, have typically been used to predict the gas in place (GIP) of volumetric reservoirs. Few reservoirs however, are truly volumetric and several workers have developed procedures to correct such P/Z plots, particularly in over pressured regimes, for the pressure maintaining effects of rock collapse and/or shale water influx.

The paper examines and discusses the applicability of eight (8) such procedures to the mildly overpressured, relatively low yield, gas condensate Kiskadee Field in which the original GIP is known from late life P/Z data and in which pressure maintaining effects on the early life P/Z data were not previously recognised.

Production, bottom hole pressure, PVT and pore volume compressibility data are used to analyse the early and late life P/Z data of each identified fault block and to determine the extent and causes of apparent early life pressure maintenance as well as observed variations in the degree of pressure maintenance in individual blocks. A modification is proposed to the Bourgoyne procedure that accurately corrects the early life P/Z data of mildly overpressured reservoirs. A further modification is proposed to correct late life P/Z data for the effects of decreasing shale water influx and increasing water saturation. This further modification is successfully applied and results in GIP estimates that are within 3 % of the known volume.
Amherstia Field, Trinidad: Breaking Barriers in the New Millennium
Authors: Pucknell John , Holder Glen , Seesahai Tony
Published: December 2007

Trinidad's giant Amherstia field began production in October 2000. Eight gas wells and two oil wells have now been drilled and completed, with production capability in excess of 700 MMscf/d. Well performance has far surpassed pre-field development predictions, with current forecasts indicating that the current platform capacity of 825 MMscf/d will be exceeded. The paper describes the many innovative steps taken by the Trinidad based, Amherstia team, bringing world-class technology to Trinidad and developing some of its own, including: Completing the largest gas well operated by bp (225 MMscf/d peak rate) and the largest in Trinidad, achieved by drilling Trinidad's first horizontal gas well and using 7" tubing as the production string;Introducing the use of near bit, hole opening reamers to eliminate back reaming;Extending the step out capability of the in house drilling fleet, developing distant oil reserves in an area formerly deemed unreachable.Introducing Shunt tube open hole gravel pack technology to Trinidad;The use of 4 Component, Ocean bottom Seismic and Pre Stack Depth migration to obtain clear and undistorted images of strata below shallow gas.

Due to the risk of sand production all wells are fitted with Acoustic sand detectors and flowlines operated with erosion limits for nominally sand free production. Permanent downhole pressure gauges are used to ensure pressure build up data is collected whenever a well is shut in. This data, together with the "wet gas" meters used at the surface, mean that the well is, in effect, permanently being tested. Plans are under way to increase platform capacity to 1.1 bscf/d.
On the Mechanisms of Mobilization of Residual Oil Left After Waterflooding
Authors: Bidner M. S. , Savioli G. B.
Published: December 2007

To mobilize the oil trapped after secondary recovery by waterflooding, chemicals (surfactants, alcohols, alkalis, etc.) are injected into the reservoir. Chemical flooding has two main effects: 1) the interfacial tension between oil and water phases is decreased, and 2) these phases become partially miscible. A numerical model is proposed to analyze those effects on oil recovery.
Numerical and Experimental Modeling of Non-Darcy Flow in Porous Media
Authors: Belhaj H. A. , Agha K. R. , Nouri A. M. , Butt S. D. , Islam M. R.
Published: December 2007

A numerical simulation of the newly derived Forchheimer's diffusivity equation has been achieved, careful selection of the non-Darcy coefficient (β) and a fruitful discussion on the use of this coefficient has been presented. Although the proposed model has been designed for single phase flow in porous media, with minor modification it can be applied to multi-phase flow cases. Results show that the proposed numerical model is valid for single-phase flow and is functioning in all ranges of flow in porous medium. The point at which the flow breaks from the Darcian trend has been determined and a new dimensionless term, "Be", has been suggested to define the point of deviating from Darcian flow. "Be" has been found to be 0.0526 at 5% deviation from the Darcian behavior.

An experimental model has been designed to examine certain critical parameters experimentally for the purpose of comparing results with the numerical model predictions. A horizontal fracture has been induced to a homogeneous synthetic sample in the direction of flow with changing aperture to study the effect of fractures on flow behavior.

Experimental results have been compared to the numerical model predictions; a satisfactory agreement within the domain of testing has been concluded which in turn encourages the implementation of this model on a field scale.

Unlike other approaches, the non-Darcy coefficient "β" has been determined experimentally which reflects the authors' belief that when possible, "β" should be evaluated based on the same set of data used to determine permeability in the laboratory.