bluuebunny/crossref_metadata_2025 huggingface dataset:
Economic Cycles and the Valuation of Oil and Gas Properties
Authors: Miller Richard J.
Published: December 2007

During the period of the 1980's and 1990's the oil business endured or, at times, benefitted from several economic cycles which brought about extreme fluctuation in the prices for oil and gas, changes in interest rates from as low as 3% to over 20%, substantial declines in domestic U.S. production and continually increasing regulation of the physical and economic aspects of the industry worldwide. This paper will examine the effects of the cycles in prices, interest rates, regulation and other economic factors on the process and component of the valuation of oil properties for sale/acquisition, taxes and litigation and other purposes. The paper will draw on information developed as part of recent analysis work as well as published studies and SPE papers from the past 30 years. Specific areas of study and discussion will include the effects of various methods to identify and account for risk and the influence of interest rates on discount rates.
Advanced Optimization Methodology in the Oil and Gas Industry: The Theory of Scatter Search Techniques with Simple Examples
Authors: April J. , Glover F. , Kelly J. , Laguna M. , Erdogan M. , Mudford B. , Stegemeier D.
Published: December 2007

A primary purpose of senior management is to make decisions around capital allocation that will improve the performance of the corporation. Portfolio analysis tools are designed to aid senior management in the development and analysis of portfolio strategies, by giving them the capability to assess the impact on the corporation of various investment decisions. To date most of the commercial portfolio optimization packages have been relatively inflexible and are often not able to answer the key questions asked by senior management. In this paper we will present new techniques that increase the flexibility of optimization tools and deepen the types of portfolio analysis that can be carried out. A new optimization engine, which contains state-of-the-art optimization functionality, allows users to simultaneously address financial return goals, catastrophic loss avoidance, and performance probability. These innovations enable users to confidently design effective plans for achieving financial goals, by employing accurate analysis based on real data. Traditional analysis and prediction methods are based on mean variance analysis, which is known to be faulty. The new techniques take a more sophisticated and strategic direction. State-of-the-art technology integrates optimization and simulation techniques into a global system that guides a series of evaluations to reveal truly optimal investment scenarios. Specifically, the new optimization techniques use an evolutionary approach called scatter search, reinforced by the adaptive memory strategies of tabu search. The software integrates state-of-the-art metaheuristic procedures, including Tabu Search, Neural Networks, and Scatter Search, into a single composite method. We will give some examples that highlight the importance and flexibility of the techniques applied to E&P portfolios.
Portfolio Optimization Techniques for the Energy Industry
Authors: Lessard Rodney W.
Published: December 2007

Energy companies typically face asset investment decisions which must satisfy a number of constraints in the form of annual corporate goals and complex asset dependencies. The aim of portfolio optimization is to select a portfolio, which maximizes/minimizes one or more value or risk measures, and satisfies these constraints.

In many cases, these problems can be readily expressed in the form of a set of linear equations, such that, global optimum values can be determined through the method of Linear Programming. As the complexity of corporate goals increase, non-linearities are often introduced, which require more advanced optimization techniques. In this paper we will describe a linear model for solving many optimization problems. In the case of non-linear problems we will describe the utilization of Genetic Programming as an efficient search algorithm to seek global optimum values. Finally, we will combine the two methods into a strategy for solving complex optimization problems, utilizing hybrid techniques that combine both linear and non-linear methods.
Integrated Prospect Portfolio Management for 3D Seismic Volumes Combining Geologic, Engineering, and Economic Risk
Authors: Garcia Javier , Holtz Mark H. , John A. , Jackson Katherine G.
Published: December 2007

This paper describes a practical methodology that links probabilistic play analysis, volumetric calculations, and economical evaluation to portfolio optimization using information from a 3-D seismic cube. In order that geologic chance of success might be calculated using a new probabilistic risking scale, a description of the geological framework is presented both in terms of play characteristics and the dependence on setting between geologic risk factors.

Probabilistic volumetric evaluation and expected monetary value were calculated for each of the targets in a 3-D seismic prospect portfolio by assigning probability distributions to geological, engineering, and economical characteristics. Monte Carlo simulation was also applied so that uncertainty could be modeled for probabilistic input values. Finally, an efficient frontier analysis was generated by building optimal portfolios having various degrees of risk.

Efficient portfolios are built by applying linear programming as an optimization tool. The balance between value and risk is considered for an optimal working interest to be obtained that fits investor constraints and risk attitude instead of a netpresent-value ranking being used. This trade-off maximizes value and minimizes risk for the entire portfolio.

Prospect risk is modeled as chance of loss, or semi-standard deviation, and value is defined as the mean expected monetary value derived from probabilistic economical evaluation.

A new geologic probabilistic risking scale was developed that adds standardization to the Monte Carlo simulation of geologic probability of success. This scale improves on previous methods by taking into account the uncertainty in judgment, as well as the quantity and quality of available information.

The methodology presented in this paper combines optimal portfolio management with probabilistic risk-analysis methodology, thus helping to guide management in evaluating a portfolio of exploration prospects, not just according to their value, but also by their inherent risk. This practical analysis is simple to apply using economical tools such as spreadsheets and Monte Carlo simulation software.
Decision Mapping - A Practical Decision Analysis Approach to Appraisal & Development Strategy Evaluations
Authors: Coopersmith E. M. , Cunningham P. C. , Pena C. A.
Published: December 2007

The time between discovery and development of a petroleum asset is wrought with many decisions, all with an aim to reach first oil with minimum expenditure, and maximum value. Not surprisingly, sorting through all the decisions and uncertainties is a daunting task for asset teams worldwide and lends itself to the use of a systematic approach. The focus on this phase is obvious. The majority of investment in a petroleum asset is in the appraisal and development phases, where the potential for value degradation due to lengthy, unfocused evaluation or sub-optimization of the project is great.

Key to accomplishing the goal of maximizing discovered asset value is the development of an appropriate appraisal and delineation strategy – ideally, geared toward gathering information, which adds value by optimizing development strategy selection. This requires a clear understanding of the development decisions ahead, and the existing uncertainties in the field, making the selection of development strategy difficult. Only with a clear understanding of the direct linkages between appraisal and development strategy, can teams set up their evaluations correctly. This requires a practical process and tools to identify and understand those interrelationships.

This paper proposes a practical methodology to frame (set up) appraisal and development strategy evaluations, and provides an illustrative example utilizing the approach. The methodology combines classic decision analysis with a new team-based, efficiency tool, referred to as "Decision Mapping". Decision Mapping is a simple framing tool, which helps multi-discipline teams identify the development decisions facing them, the key choices "in play" for each of those decisions, the interrelationship between those choices and the key uncertainties driving their value.

The Decision Map focuses teams on "why they cannot make each development decision today". This in turn helps them identify the inter-related decisions and key uncertainties, around which appraisal needs to focus. As appraisal and flexibility decisions are both "Valuing Information" decisions, the proposed approach also incorporates previously described methodologies to frame and value information-gathering decisions 1 and expands them to address related project sanction decisions. One of which, valuing appraisal well placement, will be addressed specifically.
Benefits of Using Deliquescing Desiccants for Gas Dehydration
Authors: Acor Lori G. , Mirdadian David
Published: December 2007

Historically deliquescing desiccants had limited applications due to poor desiccant quality, integrity, equipment design problems, operational difficulty, and limited drying ability. Advances in formulation, material blending, tableting, and equipment design have expanded the application range of deliquescing desiccants. Desiccants are now used to dry sales gas, fuel gas, sour gas, "peak" gas, and for hydrate control. The operational simplicity of deliquescing desiccants offer many advantages over traditional drying methods such as triethylene glycol, including: no VOC or BTEX emissions, no ground contamination, no fire hazard, low capital expense, and low maintenance. Used for hydrate control in gathering systems, desiccants offer an inexpensive method to dry gas to meet pipeline dew point specifications. Desiccants have advantages for drying sour gas both for hydrate control and pipeline sales. Vessels can be over-sized to extend service interval to only several times per year, reducing employee exposure to hydrogen sulfide. Desiccant drying of fuel gas yields increased revenues by using suction gas, not sales gas for compressor fuel. Desiccant dehydration is well suited for remote, unmanned locations, where operators can schedule maintenance and service weekly or even monthly. This reduces total operating costs and labor requirements.
The Application of High Power Sound Waves for Wellbore Cleaning
Authors: Champion Brian , van der Bas Fred , Nitters Gerrit
Published: December 2007

This paper presents the results of a wide-ranging investigation into the application of high power sound waves for the removal of plugging material from the wellbore and near wellbore region. The paper describes the process of generating high power sound waves using a high voltage electrical discharge and also summarizes the results of the laboratory and test well trials conducted on both simulated plugging materials and also on mud cake. The paper also references progress on the development of a prototype wireline conveyed wellbore cleaning system. The results of the investigation concluded that high power sound waves represent a viable wellbore cleaning technology with the potential to be applied effectively in the removal of various forms of wellbore plugging material. Since this process can be applied selectively and in a controlled manner in the wellbore, without environmental impact and using standard wireline deployment techniques, it offers considerable benefits over some of the existing solutions.
Use of Microfluidic Devices to Investigate Formation Damage
Authors: Zeilinger S. , McNeil R. I. , Belkin A. , Brasseur M. , Rosoff M. , Gentalen E. , Tripathi A. , Spaid M.
Published: December 2007

Developments in recent years allow chemical experiments that have traditionally been performed in the laboratory to be carried out on small chip-type instruments. This miniaturization of flow and chemical reactions in microchannels is called microfluidics. Only small quantities (i.e. microlitres) of reagent are necessary to perform these tests fast, reliably and cost effectively.

This paper outlines the basics of microfluidics, describing what it is and how it works as a tool for chemical analysis applied to drilling- and production chemistry. The focus is for applications as a measurement tool for the concentrations of ions, scaling ions and scale inhibitors. Results of measurements of chloride concentrations, zinc content, total ion content and calcium concentrations and scaling are discussed. The advantage of a microfluidic test of scaling is discussed using a field example, where unexpected reactions between unspent acids and completion brine were observed in the well and also in microfluidic devices.
The Role of Underbalanced Technology in the Completion Process
Authors: Cade Randall
Published: December 2007

Underbalanced technology is typically understood as a drilling technique, not a completion technique. Yet in many fields where underbalanced (UB) technology is applied, the completion aspect can have considerably greater economic impact - after all, the completion is the crucial link between the reservoir and hydrocarbon flow throughout the life of the well.

The advent of new technology and techniques have allowed UB to be applied to completions in both hard rock environments and in wells requiring support from screens or liners. Successful UB-completed wells have been documented in heavy oil, light oil and gas environments, and in horizontal and vertical wells. In every environment, understanding and controlling pressures and fluids are the keys to success.

This paper discusses the elements of the completion process that are unique to underbalanced operations and then examines five field case histories that highlight the role of UB.
Perforating in Overbalance - Is It Really Sinful?
Authors: Chang F. F. , Kageson-Loe N. M. , Walton I. C. , Mathisen A. M. , Svanes G. S.
Published: December 2007

Drilling and completing long horizontal wells in the North Sea oil fields are extremely costly. When perforating these long horizontal sections (>1000 m) deployment of the perforation guns on drill pipe has been regarded as the safest and most cost efficient method. The well is then kept in overbalance until the completion is installed.

In order to maintain well control during the perforation operation a kill fluid with fluid loss control capability to seal off against the formation is required. However, perforating with the kill fluid in the wellbore presents a great challenge in minimizing formation damage. Therefore, optimizing the perforating design and properly choosing the completion fluids are crucial tasks to ensure good well productivity. A thorough laboratory-testing program has been performed to reevaluate perforating strategy and completion fluids selection for several fields in the North Sea. The fluid systems investigated include oil-based mud, low solid oil based mud, and kill pills formulated from formates and bromide brines.

The laboratory results have shown that if the perforating is properly designed and executed, formation damage can be reduced to a minimum even during overbalance perforating. In this work the major damage appears to be from the kill fluids. When using a water based kill pill, the reduction in relative permeability appears to be an important damage mechanism. Therefore the productivity is influenced strongly by the fluid loss control capability. In contrast, the filtrate invasion from the oil-based mud does not alter relative permeability, therefore the productivity impairment for these tests is less pronounced.

Furthermore, zinc and steel cased charges have been used to investigate their compatibility with kill fluids and their impact on formation damage. These studies have shown that interaction between zinc and CaBr2 based kill pill can cause failure of fluid loss control and excessive invasion of filtrate leading to reduced productivity.

This paper presents some of the results of the testing program.
Controlling Proppant Flowback in High-Temperature, High-Production Wells
Authors: Nguyen Philip D. , Weaver Jimmie D.
Published: December 2007

Curable resins have been used to coat onto proppant for controlling proppant flowback after hydraulic fracturing treatments as well as in screenless, frac-pack completions. As more wells are drilled into deeper reservoirs, severe conditions including high temperatures and high production flow rates impose more constraint requirements on the use of curable resin systems. This paper presents the results of an extensive study, including both laboratory and field testing, of a new liquid resin coating system that is particularly useful in controlling proppant flowback in high-temperature, high-flow rate wells. Additives included in the liquid resin system can eliminate fracturing fluid interference and permit good consolidation properties to be achieved without any formation closure stress.

Results of this work demonstrate the difficulty in designing fracturing treatments such that the curing of resin does not occur too fast relative to fracture treatment time and the time for formation closure to achieve good consolidation, but fast enough to prevent flowback upon fluid recovery operations. The useful window for resin-coated proppants has been greatly expanded by the incorporation of simple chemical additives into the resin that react with fracturing fluids, rendering them noninterfering to the consolidation process. These additives permit resin-coated proppant to achieve good consolidation properties without closure stress.

This study provides new answers as to why resin precoated proppant (RCP) consolidations sometimes fail in the field. Operators can use the information presented to help them select the appropriate curable resin systems for their applications where consolidations are expected to withstand production conditions of high temperatures, high flow rates, and stress loading.
A Holistic Review of the Water Injection Process
Authors: Palsson B. , Davies D. R. , Todd A. C. , Somerville J. M.
Published: December 2007

Water injection is an essential part of many modern oilfield development plans. The high costs and often tight economic margins associated with offshore developments require that the chosen waterflood design not only provides an optimum sweep efficiency and reservoir pressure support, to maximise the oil production revenue, but also carries an acceptable level of risk in terms of the project costs and technical uncertainties. The objective of this paper is to show how an optimisation process can be used to maximise the value of the injection water. This paper describes a holistic approach for an economic evaluation of the water injection process, integrating the key technical and economical elements.

A six–stage process to evaluate the "Value of Injection Water" is presented. For illustrative purposes, this process is applied to show how a holistic technical–economic evaluation of the water injection operational option for a North Sea field case can be carried out. The study concludes that the injection of a mixture of produced and aquifer water is the preferred source for injection water when applying a matrix injection process into a high quality formation. However, this introduction of the produced water increases significantly the uncertainty in the eventual economic outcome.

This process for developing an integrated technical and economic comparison of the options available is a tool by which the operator can decide on a decision on future water injection strategy. It can also assign a quantitative value to each volume of injection water - providing a quantitative framework for making day-to-day operational decisions..
SQUEEZE Modelling: Treatment Design and Case Histories
Authors: Mackay E. J. , Jordan M. M.
Published: December 2007

Modelling of scale inhibitor squeeze treatments is routinely performed to assist with chemical selection and to optimise treatment design, many examples having been presented in the literature previously. However, the modelling techniques are not always used to best effect, due to lack of experience, time or a methodical procedure for calculating sensitivities.

This paper presents a systematic approach to the use of squeeze models that makes use of laboratory data and field experience to assess, simply and effectively, the options for treatment design. Examples are presented that demonstrate the use of such models in aiding the selection of an appropriate inhibitor and the design of the first treatments as part of an integrated scale management philosophy. Very good accuracy in modelling the core flood is usually achieved. While the match between the model prediction and the first squeeze treatment is typically less accurate, history matching of the model parameters based on the first treatment is shown, by means of examples from two North Sea fields, to enable accurate predictions of numerous subsequent treatments in the same formation. The ability to accurately model treatments means that squeeze performance can be predicted with a high degree of confidence, and thus the treatment design may be optimised. This ability to accurately predicted treatment life is critical as wells mature, and the focus on cost per barrel of treated fluid becomes more critical. The most sensitive parameters are shown to be inhibitor type, inhibitor volume and overflush volume, and the paper discusses how they should be optimised to achieve the desired protection while striking a balance with chemical cost and deferred oil production.
A Stochastic Model for Deep Bed Filtration and Well Impairment
Authors: Bedrikovetsky P. , Santos A. , Siqueira A. , Souza A. L. , Shecaira F.
Published: December 2007

Injectivity decline during sea/produced water flooding is a wide spread phenomenon in offshore waterflood projects. The injectivity decreases due to solid and liquid particles that are present in the injected water. Capture of particles by porous rock results in permeability damage.

In this work, a new pore level model for deep bed filtration of water with particles in porous media is developed. The model accounts for particles and pore size distribution, as well as size exclusion mechanism (a particle is captured by a smaller size pore). The system of equations derived consists of the continuity particle number equations and of the kinetics of particle entrapment and pore plugging. The particle velocity reduction and the particle accessibility, due to restriction for particles to move via large pores only, are incorporated in the model.

An analytical solution of the pore level stochastic system is obtained for a medium with small pore size variation. It allows derivation of the averaged concentration equations which differs from the traditional ones.

Finally, the modification of the classical deep bed filtration model that accounts for velocity reduction and particle accessibility effects is proposed.
30 Years of Predicting Injectivity after Barkman & Davidson: Where are we today?
Authors: Hofsaess T. , Kleinitz W.
Published: December 2007

The reinjection of produced water is an important prerequisite for maintaining pressure and for flooding reservoirs. Thirty years ago Barkman and Davidson introduced the first compre-hensive theory for predicting the behaviour of injection wells. This theory was employed and tested for many years in actual injection projects at 'Preussag-Energie', including the develop-ment of a special-purpose instrument. In the present article, a survey of operational experience is given, and necessary ex-tensions of the model are delineated. Furthermore, the article highlights some important aspects which should be considered in laboratory investigations.
A 3D Network Model of Rock Permeability Impairment Due to Suspended Particles in Injection Water
Authors: Siqueira A. G. , Bonet E. J. , Shecaira F. S.
Published: December 2007

A 3-D network model is used to simulate the impairment of porous medium permeability during the flow of water with suspended particles.

Digitized 2-D images of the porous systems are obtained by petrographic image analysis of rock thin sections. Geostatistical procedures are applied to construct 3-D virtual realizations of the medium. The pore body and throat sizes distributions of the virtual medium and its connectivity, expressed by the average coordination number, are determined. Alternatively, these characteristics are obtained by using capillary driven porosimetry data and empirical correlations. A regular cubic network of sites (pore bodies) and bonds (pore throats) that reproduces these characteristics is structured.

Network absolute permeability can be calculated by solving a system of linear mass balance equations for the sites, along with equations of hydraulic conductivity for the bonds. Realistic permeability estimates are obtained.

Motion and contingent capture of injected particles inside the medium are simulated. Both physicochemical interception and size exclusion mechanisms of particle retention are modeled, the former with the aid of two empirical parameters. Particle capture modifies the flow in the network, that is recurrently calculated, resulting in permeability decline as more particles are retained.

Network simulated data and their comparison with those obtained in laboratory tests are reported. Besides particle to pore throat size ratio, concentration and flow velocity, other important factors governing the permeability impairment are: 1. medium coordination number and 2. shape of pore throats.
Scale Formation in Oil Reservoir and Production Equipment during Water Injection Kinetics of CaSO4 and CaCO3 Crystal Growth and Effect on Formation Damage
Authors: Moghadasi J. , Jamialahmadi M. , Müller-Steinhagen H. , Sharif A.
Published: December 2007

In the oilfield, due to the extensive use of water injection for oil displacement and pressure maintenance, many reservoirs experience the problem of scale deposition when injection water starts to breakthrough. In most cases the scaled-up wells are caused by the formation of sulphate and carbonate scales of calcium and Strontium. Due to their relative hardness and low solubility, there are limited processes available for their removal and the preventive measure such as the 'squeeze' inhibitor treatment has to be taken. It is therefore important to have a proper understanding of the kinetics of scale formation and its detrimental effect on formation damage under both inhibited and uninhibited environment.

This paper presents an experimental and theoretical study of permeability reduction of porous medium caused by scaling. Two incompatible solutions, calcium and sulfate/carbonate rich ions were injected into and calcium sulphate or carbonate generated within the porous medium by chemical reaction. Mechanisms by which a precipitate reduces permeability include solids depositing on the pore walls because of attractive forces between the particles and the surface of the pore, a single particle blocking a pore throat, and several particles bridging across a pore throat. The characteristics of the precipitate influence the extent of formation damage. Conditions such as large degree of supersaturation, presence of impurities, a change in temperature, and the rate of mixing control the quantity and morphology of the precipitating crystals.
Reinjection of Finely Disposed Produced-water Reduces Formation Damage in Low Permeability Zones
Authors: Wan Jun , Sui Xinguang , Liu Bing , Bai Yanming , Liang Shaohui
Published: December 2007

Daqing Oilfield is a water flooded oilfield, the injected water is usually the produced-water. It reduces the injection cost and performs a good environmental effect as well. The formation of tertiary infill wells are usually of a effective thickness less than 0.5m, and a permeability less than 0.050 Darcy, and the permeability in 60% of the formation is less than 0.010 Darcy, this kind of formations are vulnerable to be damaged, it requires a higher quality of injected water,. In tertiary infill wells, reinjection of produced-water does a more serious damage to the formation, the water absorbing thickness decreases from 76.4% of the secondary infill wells to that of 59.3% of tertiary infill wells, this result in a serious adverse waterflood development.

Through a considerable research and analyses of the injection operation , this paper suggests a finely treatment of produced-water by decreasing the suspended particle to less than 7-8mg/l, and increasing the water absorbing thickness of tertiary infill wells to 81.2%, this performs a better water absorbance. This makes the water absorbing thickness reach 66% in those formations with a permeability less than 0.010 Darcy, and the producing thickness in those formations with a permeability less than 0.010 Darcy reach to 61% in oil well, this eases the damage degree of produced-water to low permeable formations, thus performs a good waterflood effect in low permeable formations.
Formation Damage vs. Solid Particles Deposition Profile during Laboratory Simulated PWRI
Authors: Al-Abduwani F. A. H. , Shirzadi A. , van den Broek W.M.G.T. , Currie P. K.
Published: December 2007

The importance of produced water re-injection (PWRI) is unquestionable. It is in many cases the cheapest and most environmentally friendly solution for wastewater disposal. It is also a feasible method for EOR as a water flooding mechanism.

PWRI, however, suffers from a major limitation, which is the current inability in accurately predicting the lifespan and performance of its injection wells. This is due to the multitude of parameters that affect it. Current models 1-2 exist that incorporate the thermal effects 3 of PWRI leading to fracture growth. However, the leak-off pattern of this injection differs from that of clean water (seawater) injection due to the damage caused by the produced water onto the formation and especially the fracture faces. Thus, static filtration experiments with refined post-mortem analysis have been conducted to obtain quantitative deposition profiles along the core. This allows for the testing and verification of existing models 4-7.

The post-mortem analysis introduced in this paper will be used for future dynamic filtration experiments as well as experiments specifically devised to simulate the fracture tip area. A unified model that will accurately reproduce the permeability decline and deposition profile for all three sets of experiments will flow, thus advancing the predictability of injectivity decline associated with PWRI.

A detailed description of the post-mortem analysis will be presented. Testing of existing heuristic models Wennberg5 and Bedrikovedski7 will be published in the near future.
Conductivity Maintenance: Long-Term Results from the Use of Conductivity Enhancement Material
Authors: Lehman Lyle V. , Shelley Bob , Crumrine Tim , Gusdorf Matthew , Tiffin Judy
Published: December 2007

In 1997, a surface modification agent was introduced into the global stimulation market. The agent was designed to enhance and sustain fracture conductivity by making the proppant surface tacky. Several conductivity-enhancing mechanisms were suggested. Two important mechanisms resulting from increased surface tackiness are 1) increased proppant pack porosity resulting in increased pack permeability and 2) increased proppant pack stability that prevents encroachment of formation fines into the pack and migration of fines within the proppant pack. In terms of extended conductivity maintenance, the fines control aspect has proved to be the most valuable property developed from the product.

This paper presents a brief discussion on the theory of applying a tacky surface on proppants to mitigate conductivity loss from fines migration in the propped fracture. The paper then offers direct comparison case histories, which contain long-term production data that illustrate the benefits from lower operating expenses and increased production over the use of previous completion methods. Case histories are discussed in reservoirs that are known for fines migration, such as coal-bed methane (CBM) and high permeability-unconsolidated sandstones. The histories also include zones not widely known for fines migration problems, where the authors feel that this condition does exist.
Revitalizing a Mature Sand-Prone Field by Installing Enhanced Gravel-Pack Completions - A Case Study
Authors: Md Noor Mohamed Zaini B. , Selamat Kasim B. , Kasim Abdullah B. , Salahudin Sharifudin
Published: December 2007

The Dulang oilfield is located some 130 km offshore Terengganu in Peninsular Malaysia and is structurally complex. Production from the field began in March 1991, and oil production averaged 26,000 STB/D with peak production reaching approximately 50,000 STB/D. As with the other field developments in the Malay Basin, sand production was not anticipated under normal drawdown or producing conditions, and thus, all the wells in Dulang field were completed without any sand-control measures.

In the later stages of the field's life, however, a significant amount of sand production was observed. This condition gradually increased over time, resulting in reduced hydrocarbon production, additional costs for routine wellbore sand clean-outs, and platform shutdowns for surface vessel sand clean-up.

In 1991, eight years after initial development, a wellbore opportunity study was initiated to revitalize a section of Dulang field. The objectives of the study were to 1) identify remaining reserves, and 2) identify new completion options to maximize recovery. The study identified three major activities that would improve oil production: Develop by-passed reserves behind casingReactivate idle wells that had been closed in, some as a result of sand production.Provide additional drainage points for undeveloped reserves.

From the proposed wellbore opportunities study, ten wells were identified for a workover campaign, and six wells were identified for infill drilling or sidetracks.

Sand production mitigation using a gravel-pack technique was identified as a requirement in the completion plan for the majority of the targeted reservoirs. However, the increase in mechanical skin that would result from a sand control installation was also recognized. Hence, it was determined that the best approach for production optimization in these wells would be a combination of a sand control and a stimulation technique. Several technologies, which included frac-and- pack, extension pack with conductivity enhancer, and highrate water-pack (HRWP) gravel packing, were suggested. The use of a special completion tool that would enable greater flexibility on short string selective production in multi-zone gravel-packed wells was also identified.

After careful review of the options, a combination of sand control and stimulation technique (frac pack, extension pack and high-rate water pack) was selected, and the combined strategies have successfully increased the productivity and prevented sand production in the Dulang wells.
A Single Additive Non-ionic System for Frac Packing Offers Operators a Small Equipment Footprint and High Compatibility with Brines and Crude Oils
Authors: McElfresh P. M. , Williams C. F. , Wood W. R. , Ruzic M. , Baycroft P. D.
Published: December 2007

There are many advantages to using a single component, non- ionic viscoelastic surfactant gel (VES) for sand control and stimulation applications. The VES is highly compatible with a wide range of completion brines and crude oils, is virtually non-damaging to the formation and demonstrates shale- stabilizing characteristics with many types of shale. Another advantage of having a single additive VES system is that it requires a small equipment footprint. With this combination of compact equipment set-up and simplified fluid mixing, complex, high rate, high sand concentration frac jobs are possible where rig space is limited or equipment is limited because of the remote location from full stimulation service. A treatment using a single additive system can typically be performed with only one or two frac pumps, a frac blender, proppant silo or a modified sand infuser and data acquisition equipment.

Many offshore facilities have commingled gathering systems many of which must be treated for emulsions with chemicals. This treatment process may be substantially reduced or simplified when a non-ionic VES fluid is used for stimulation compared to a crosslinked gel fluid. The high compatibility with completion brines and crude oils, coupled with the non- damaging nature of the VES itself, reduces the likelihood of formation damage in the well. The VES promotes a fast and more thorough recovery of the stimulation fluid from the formation and if emulsions are generated, it will allow for easier treatment in the surface facility.

Since December 2000, non-ionic VES gels have been used in over 30 applications in the Adriatic Sea and in the Gulf of Mexico in brines ranging from seawater with varying amounts of KCl to 10.5 ppg CaCl2. Each application has resulted in enhanced production due to the excellent performance of the fluid. Clean-up rates have been directly related to bottom hole pressure, and have not been complicated with typical clean-up problems such as clay swelling, water blocks, and filter cake plugging of proppant packs. This type of treatment with a minimum equipment set-up has made high rate/volume frac treatments possible without the need of a stimulation vessel.
Real Time Monitoring of Permeability, Elastic Moduli and Strength in Sands and Shales Using Digital Rock Physics
Authors: Dvorkin Jack , Kameda Ayako , Nur Amos , Mese Ali , Tutuncu Azra Nur
Published: December 2007

The Digital Rock Physics (DRP) technology is based on a rigorous numerical simulation of physical experiments in a realistic pore space, at the pore-scale level. The output is usually a macroscopic property conventionally measured in the lab. For example, single-phase viscous fluid flow simulation through a digitized pore space provides absolute permeability. A simulation of electrical current provides conductivity, and a simulation of the stress field provides the elastic moduli and strength. DRP complements lab measurements and, at the same time, enormously enhances the geoscientist's capabilities because digital experiments can be conducted in real time and on small fragments of rock, such as drill cuttings.

In this paper, results of a feasibility study on DRP technology is reported using for the first time the drill cutting samples in obtaining petrophysical properties including permeability and porosity of formations. This real-time technology may become very beneficial to the industry once it is established that the results are reliable.

The 3D digital pore space needed for numerical simulation has been recreated from 2D images by means of statistical simulation. An example is also presented where the 3D digital pore space was obtained by direct CT scanning of drill cutting. The resulting macroscopic rock properties have been compared to independently obtained core data from laboratory measurements and log data from the same interval where cuttings are obtained.
Modelling of Near-Wellbore Formation Damage for Open Hole Horizontal Wells in Anisotropic Media
Authors: Ding Y. , Renard G.
Published: December 2007

It is well known that formation damage due to drilling fluid has a huge impact on well productivities, especially for open hole completed horizontal wells. To evaluate this impact to keep maximum oil productivity, a numerical model has been developed to simulate formation invasion and damage during the drilling phase of a well. This model can be used to study the impact of various parameters related to drilling fluid properties or drilling conditions on well performances.

In previous papers1,2, a methodology combining both experimental and numerical approaches has been proposed to model the near-wellbore formation damage for both water- based mud (WBD) and oil-based mud (OBM) and filter cakes removal by natural clean up procedures. However, anisotropic permeability was not considered, although heterogeneities were taken into account. The main difficulty of near-well modelling of anisotropic media is that the generally recognised elliptic flow behaviour in the well vicinity is not valid as the well cannot be considered as a point (or line) source. Flow behaviour is radial at the wellbore boundary and becomes gradually elliptic when going away from the well. To accurately model near-wellbore formation damage, a new grid system, which is obtained based on elliptic coordinate transformation, is proposed in this paper, and a new numerical scheme is given for the modelling of near-well flow in anisotropic media.

The proposed model can be used to study non-uniform formation damage and cleanup results around the well due both to permeability anisotropy and gravity effect. Examples are presented to study sensitivity of various parameters (fluid properties, drilling conditions, …) on well performances. This model is developed for the modelling of horizontal wells as well as slanted wells. It can be used as a tool for well design and construction. Finally, a field example in a deep offshore reservoir is presented to show an application of the developed model.
Modeling of polymer adsorption under near-wellbore flow conditions
Authors: Zitha Pacelli L. J. , Mandzi Daniel , Vermolen Fred , Darwish Mohamed I. M.
Published: December 2007

An investigation of the adsorption of long flexible polymer chainlike molecules during flows in low permeability porous media under near-wellbore conditions is reported. The theory for this phenomenon (canonical filtration theory) previously developed is firstly surveyed. This theory encompasses four partial differential equations describing the overall mass conservation, the conservation of the longest chains and the layer and bridging adsorption kinetics. Simple analytical expressions were derived mainly for flow in flat cores (having a length that is much smaller than the diameter), for which the problem reduces to the adsorption kinetic equations. Numerical computations were conducted to predict the transport and sorption behavior in long cores. Experiments conducted using a high molecular weigh cationic polyacrylamide and siliceous cores have been performed. The flat core experiments were used to determine the kinetic adsorption coefficients, which were then used in the numerical computations. Long core flow experiments were used to determine concentration profiles. The theoretical prediction and experiments in the long cores are in excellent agreement, which proves the validity of the canonical filtration model.
Predicting Asphaltene Deposition and Assessing Formation Damage
Authors: Garrouch Ali A. , Al-Ruhaimani Feras A.
Published: December 2007

This study formulates a mass balance model in integral form, for predicting permeability reduction caused by asphaltene deposition in vertical and horizontal wells. The theory accounts for both the effect of radius and time on all the parameters affecting the deposition process. This approach accounts, implicitly, for the effects of pressure, temperature, and fluid composition as a function of position in the reservoir. The model accounts for pore-size distribution, rock original permeability, and asphaltene particle-size distribution. The model is general and can be used to estimate the permeability reduction for both homogeneous and heterogeneous formations.
Formation Damage Resulting From Unexpexted Acid Incompatibilities At Brutus, Gulf Of Mexico
Authors: Fair P. S. , McNeil R. I. , Nitters G. , Stroman S. R. , Davis C. L.
Published: December 2007

Formation damage problems in the Brutus A-8 well in the Gulf of Mexico have provided a rich opportunity to study mechanisms of pore plugging. Field data and laboratory experiments have led to the following conclusions. Unexpected reactions can take place between spent organic acids and completion brine, resulting in polymerization and other reactions that can plug formations.These precipitates can be prevented by appropriate acidizing practices, including the use of sufficient (ammonium chloride or other innocuous brine) spacers to maintain separation of the (spent) acid and completion brine and the use of an appropriate post-flush acid to maintain a low pH in the spent acid.If a precipitate does form, it can be cleaned up readily by acid treatment if the acid reaches the occluding precipitate.Organic acids should not be mixed. That is, if completion uses one organic acid, no other organic acids should be used in subsequent stimulation treatments.
Stimulation Efforts in Carbonate Gas Reservoir Experiencing Subsidence in Offshore North West Java Field - Indonesia
Authors: Susilo Yoliandri , Rahamanda Zahazny , Wibowo Wahju , Tjahyadi Riza , Silitonga Frans J.
Published: December 2007

Subsidence and reservoir compaction continues to be significant concern for the oil and gas industry. The decrease of pore pressure during hydrocarbon production (depletion) leads to compaction of the reservoir. When compaction occurs, it changes the porosity and permeability properties of the reservoir rock and can affect recovery efficiency and well productivity. The results of stimulation efforts to improve gas deliverability in carbonate reservoir experiencing subsidence in Offshore North West Java (ONWJ) field are presented here.

The wells in this study were completed in the Parigi Formation, which is a thick carbonate buildup formation with large columns of gas about 250-300 feet thick underlain by aquifer.It has high porosities (32-45%) and good gas permeabilities up to several Darcies with the initial well production were around 20-30 MMSCFD. The continuous production of gas from this shallow, thick and low strength carbonate reservoir has resulted in reservoir compaction, surface subsidence, several well mechanical failures and a sharp production decline (from 15 MMCFD to 2 MMCF). The other impact of declining gas rate that is nearing its critical velocity is causing water condensation that cannot be lifted out of the well; it then accumulates in the wellbore and creates more back pressure on the reservoir.

Treatment efforts, starting from nitrogen kick-off with CT to unload the condense water in the wellbore followed by re- perforation and acidizing job, that were conducted in the first two well have resulted a significant production response. Gas production increases by 4-9 times after the treatment. The previous fear/perception that acidizing would perhaps even worsen the conditions of the reservoir and thus reduce production proved not to be true. These successful treatments have led to stimulation campaigns for other wells in the area.

This paper will also discuss several surveillance projects to monitor and assess the magnitude and progression of surface subsidence, reservoir compaction and wellbore damage in this area.
Acid Sensitive Aluminosilicates: Dissolution Kinetics and Fluid Selection for Matrix Stimulation Treatments
Authors: Hartman R. L. , Lecerf B. , Frenier W. , Ziauddin M. , Fogler H. S.
Published: December 2007

Dissolution kinetics of analcime (a zeolite), chlorite and illite (layered aluminosilicates) are determined in hydrochloric and mixtures of hydrochloric and hydrofluoric acid systems. Dissolution kinetics were determined from batch reactor experiments in the temperature range of 25 to 100 °C. The reaction progress was monitored by analysis of Al, Si, Fe, Mg, and Na concentrations in the aqueous phase. The reactivity of these aluminosilicates was compared with that of kaolinite under similar experimental conditions.

Models for the reaction of the aluminosilicates with each acid will be presented. The reaction kinetics incorporated into a geochemical simulator predicts matrix stimulation results for formations containing these minerals. Guidelines for design of matrix stimulation treatments for acid sensitive formations will be presented.