bluuebunny/crossref_metadata_2025 huggingface dataset:
Maximizing Reservoir Potential Using Enhanced Analytical Techniques with Underbalanced Drilling
Authors: Ansah J. , Shayegi S. , Ibrahim E.
Published: December 2007

Improved oil and gas recovery begins at the point of first contact with the reservoir. If drilling of the wellbore used to access reserves is accomplished with minimal formation damage, then oil and gas recovery will be maximized at all stages of reservoir development: from primary exploitation through to tertiary recovery. Underbalanced drilling (UBD) is a technique that has shown excellent results in this area for vertical and horizontal wells.

This paper describes the use of UBD technology to improve the overall hydrocarbon recovery. It focuses on how this technology can be used to maximize reservoir performance, illustrating these gains with the results of a field case where this technology has been applied.

At its inception, UBD technology was focused primarily on drilling issues such as increasing the rate of penetration, avoiding drilling problems including differential sticking, lost circulation incidents, and facilitating drilling through difficult zones. More recently, however, UBD has seen increased application in cases where the primary objective is to avoid or minimize damage to the reservoir. This change of focus to the reservoir means that from the outset, recovery from the reservoir can be maximized with data and information gathered much earlier than in the typical field development life cycle. To take advantage of the availability of the "well testing type" data during underbalanced drilling, analytical and numerical models were developed. Results from these models, which permit analysis of each of the productive zones as they are traversed, are reviewed. Finally the current developments in further characterization of the reservoir being embarked upon are described. The results from the modeling in conjunction with a new system being developed for on-site analysis of produced fluids while drilling, allows characterization of the produced effluent which can be used to determine waterflood status, interconnectedness of a system, sweep efficiencies of the current water or gas floods, bypassed oil, and to aid in optimizing completion methods and multi-well infill drilling campaigns.
Horizontal Gravel Packs Successfully Deployed in Trinidad's First Multilateral Well — Planning, Implementation, and Remedial Strategies
Authors: Lougheide Delano , Lutchman Krishna , Anthony Elred , Waterman Bert , Cavender Travis , Flores Denar , Ramsook Vishnu
Published: December 2007

This paper discusses the first multilateral well drilled in Trinidad and the unique integration of techniques that allowed sand control procedures to be implemented as well. The well was recently drilled and completed in the 759 area of the northern Soldado Field, offshore Trinidad in approximately 60 feet of water. A multilateral completion was selected over conventional well construction to horizontally access heavy-oil reserves in the Forest 4B and 4C sands, located at true vertical depths of 3850- and 4000-ft respectively. Since the formation parameters included poorly sorted, non-uniform formation characteristics, the completion would have to employ some method of sand control.

This well represents several "firsts" for this area as it not only represents the first multilateral well in Trinidad but also is the first in the area that integrates sand control into a multilateral.

After reviewing many possibilities, horizontal openhole gravel-pack technology had been selected to provide sand-exclusion. A TAML 4 multilateral well junction was selected originally because it offered a cemented junction with full casing-drift access across the mainbore/lateral interface. When sand was encountered above the junction area, a completion workover was required to convert the existing TAML 4 multilateral junction into a TAML 5 to gain pressure integrity across the junction area.

The paper will present the initial planning, special considerations, methods for implementation of horizontal gravel pack into multilateral technology, and finally, the rework operation later required for junction conversion.
Poromechanics Modeling of Wellbore Stability in Naturally Fractured Formations
Authors: Nguyen V. , Abousleiman Y. , Mody F. K.
Published: December 2007

With recent advances in drilling technology, directional drilling in deep and highly fractured formation has received considerable attention concerning the stability of the wellbore. The majority of the existing wellbore stability predictions are based on the solutions obtained using single-porosity elastic or poromechanics theory which considers rock formations to be homogenous with one degree of porosity distribution. However, the solutions may fall short when the rock formation is also fractured. The dominant characteristics of fractured rock formations, i.e., the coupling between various induced hydro-mechanical processes and interporosity flow can be well represented under the realm of dual-porosity poromechanics. Due to the complexity of the physical phenomena and mathematical formulations associated with a dual-porosity system, to date the solution for industry field applications e.g. mudweight estimation, pore pressure and stress distribution in wellbore drilling in fractured formations does not exist. This paper aims at using a consistent dual-porosity poromechanics and/or poroelastic analytical model to analyze wellbore stability in naturally fractured rock formations.
Application of Vacuum Insulated Tubing to Mitigate Annular Pressure Buildup
Authors: Azzola J. H. , Tselepidakis D. P. , Pattillo P. D. , Richey J. F. , Tinker S. J. , Miller R. A. , Segreto S. J.
Published: December 2007

Vacuum insulated tubing (VIT) has been used successfully to mitigate the potentially harmful effects of annular pressure buildup (APB). In a recent deepwater installation, the subject well had lost alternate APB mitigation capability through a series of events. VIT was then chosen as the only viable technology.

A common design companion of VIT is gelled brine, chosen to decrease annular natural convection driven by heat loss around the VIT connections. There are, however, several drawbacks to the indiscriminate use of gelled brine: Tight clearances around the tubing hanger running tool, creating the potential for debris plugging and/or tool recovery issues from the subsea wellhead,Limitations imposed by VIT collapse and hydrostatic packer setting pressures,Unknown temperature/viscosity response and associated quality control requirements for displacement through a subsea wellhead, andA need to reduce operational time and cost.

These issues led to the consideration of alternative means of controlling natural convection, and an effort was made to understand, improve, and deploy external coupling insulators.

An in-ground vertical experiment with two connected joints of VIT was conducted with and without coupling insulators. Temperatures were monitored at multiple locations. Test results confirm the effectiveness of external coupling insulators. Several theoretical models using different numerical techniques (finite difference, lumped mass/resistance, finite element, and computational fluid dynamics) were found to be consistent with experimental results. These were compared with critical APB temperatures calculated with a commercial wellbore simulator. The net result of these studies was to adopt the external insulators.

This paper reviews the experimental data and presents several models of a vertically aligned VIT in a deepwater completion. A comparison of thermally effective APB solutions, together with a critical assessment of modeling accuracy, is presented.
Perforating and Hydraulic Proppant Fracturing in Western Siberia, Russia
Authors: van Gijtenbeek Klaas A. W. , Pongratz Reinhard
Published: December 2007

Hydraulic proppant fracturing is developing rapidly in the oil fields in western Siberia and is seen as the most important means to improve oil production from both existing and newly drilled wells. The oil fields vary in size and reservoir quality, with a majority of the developed fields showing permeabilities of 1 to 30 mD. Reservoirs are layered, and fracturing vertical wells in general seems to give higher productivity compared to horizontal wells that are not being hydraulically fractured. This result is most likely because the vertical permeability is much lower than the horizontal permeability.

To maximize production from these wells, coarse-sized proppant must be placed using the least-damaging and lowest-viscosity fluid systems. For production optimization, the trend is currently "larger (proppant sizes) and bigger (jobs)," using the lowest acceptable polymer loading in the frac fluids, which minimizes gel damage.

This paper describes the conflicts that can arise between the requirement to place large amounts of coarse propping material using low viscosity fluids and the perforation size and condition that is needed to do so. These conflicts can lead to job scenarios in which screenouts take place.

During fracturing operations in wells in west Siberia, some screenouts did take place. An investigation of the screenouts revealed that the major cause of the screenouts is reduced width development at the perforations associated with the "stress cage." Guidelines were developed to reduce the influence of the near-wellbore stress cage and prevent screenouts. In addition to these guidelines, future solutions are proposed that may avoid the stress cage and place coarse proppant more efficiently.
Is Bitumen a Petroleum Reserve?
Authors: Etherington John R. , McDonald Ian R.
Published: December 2007

Like most reserves issues, the answer depends on the specifics of the project relative to an interpretation of the applicable regulatory guidelines.

The US Security and Exchange Commission (SEC) regulation S-X, 4-10 a) states that: "Oil and gas producing activities do not include the extraction of hydrocarbons from shale, tar sands, or coal". Thus, it has been generally accepted that oil derived from processing of mined bitumen cannot be included in petroleum reserves of companies listed on the US stock exchanges. However, the quantities of synthetic oil derived from the upgrading the same bitumen produced out of wellbores using thermal processes are routinely included in reserves disclosures. The logic is that the activities largely duplicate those involved in producing and processing heavy oil.

The new Canadian Security Administrators' regulations (NI 51-101), take a different approach: "The intended product of both conventional and non-conventional oil projects is essentially the same – a liquid hydrocarbon. We believe that investors are likely to consider a reporting issuer focused on oil sands to be more comparable to a conventional oil producer than to a hard rock mining issuer. Accordingly, NI 51-101 applies to activities directed at the extraction or production of hydrocarbons from either conventional or non-conventional sources (such as surface mines and in-situ projects)".

Which approach provides more clarity for investors? Should the sales product quantities derived from mined and thermally recovered bitumen be treated differently? What would be the international impact of including all bitumen in petroleum reserve estimates and production statistics?

This paper presents background and reviews industry practices for the estimation and disclosure of bitumen resources. The issue is of most interest to the Canadian industry; it is forecast that by 2012 over 50% of that nation's crude production may be derived from bitumen.
A Comparative Study of Sea-Going Natural Gas Transport
Authors: Subero Gloria , Sun Kai , Deshpande Asim , McLaughlin John , Economides Michael J.
Published: December 2007

Rapidly increasing worldwide natural gas demand and tight domestic supplies in many consuming countries suggest that trans-national transportation of gas will rapidly become important. From a technical perspective, the most economically attractive gas transport option depends on a specific project's reserve base, production capacity, and required shipping distance.

This paper examines and quantifies how distance, reserves, and gas production rate affect the technology selection and project economics. Sea-going natural gas transport technologies are: liquefied natural gas (LNG), compressed natural gas (CNG), sub sea pipelines (PNG), gas-to-liquids (GTL), gas-to-wire (GTW), or gas-to-solids (GTS). Available data on capital, operating, and shipping costs for proposed, conceptual, and actual gas-transport projects are analyzed. These cost functions are then integrated into an economic model, which is used to determine the economic constraints of a number of theoretical developments that cover a range of gas rates and shipping distances.

Given pricing, financing, and escalation assumptions, net present values (NPV) of the four options are generated over a range of daily gas rates and shipping distances. By examining which option delivers the highest NPV some conclusions are reached: Pipeline and CNG projects are best suited to maximize returns for shorter distances (e.g., 1,000-2,000 km); LNG is better suited for long distance projects.

We find that meaningful comparisons between CNG and LNG are for relatively small volumes of gas, i.e., less than 500-600 MMscf/d. For large quantities and for any reasonable distances LNG is still by far the best option. For distances >3,000 km, it is necessary to have at least a >500-600 MMscf/d gas stream available for 20-30 years; this translates to a requirement of a reserve base on the order of 5-10 TCF to supply these long haul projects. For CNG much smaller reserve bases are attractive.
Flow Assurance and Subsea Productivity: Closing the Loop with Connectivity and Measurements
Authors: Ratulowski J. , Amin A. , Hammami A. , Muhammad M. , Riding M.
Published: December 2007

Flow assurance is a key priority for the subsea community as it is being challenged to provide answers to the following question: Can we manage the risk of hydrocarbons flow interruptions while optimizing the system performance using current flow assurance practice?

Traditionally, flow assurance has focused on evaluating potential production problems associated with produced fluid issue such as waxes, asphaltenes, hydrates and scale. A combination of fluid sampling, laboratory techniques, and predictive modeling are then used for system selection and design of prevention and remediation strategies. These are often based on conservative modeling practices using incomplete or inconsistent data sets. No allowance for continuous monitoring that will provide data needed to recalibrate the system or to change the course of the process over the subsequent years is made. The result is often an overly conservative system design and operating strategy.

The paper discusses a more dynamic approach to answering the above question as it explores the integration of the design and surveillance processes. Advances in sampling, analysis and modeling that reduce conservatism in design are reviewed. The role of real-time measurements during production from the reservoir, the wellbore, and the subsea infrastructure, in monitoring and optimization of a system is then discussed. Specific case examples are presented throughout to illustrate these points.
A Multiscale Methodology for Simulating Miscible Gas Injection Projects Applied to a North African Oil Field
Authors: Bronchalo Jesus , Venkataraman Ramachandran , Blunt Martin J.
Published: December 2007

We present a methodology for the simulation of miscible gas injection applied to a water alternate gas (WAG) project being considered for oil field in North Africa. First we run one-dimensional (1D) simulations using an eight-component Peng-Robinson equation-of-state and tune the fluid characterization to match the results of slim tube experiments at different pressures. We use the simulations to determine the minimum miscibility pressure (MMP) by finding the pressure at which a piston-like advance of the injected gas is observed. We find that while acceptable recoveries that match the experiments may be obtained using 100 grid blocks, even when using 10,000 blocks a converged saturation profile is not obtained, especially close to the MMP.

We then run 2D compositional simulations above the estimated MMP to model viscous fingering. We compare the results with those of a black-oil model that assumes a first-contact miscible displacement (FCM). The compositional simulation predicts much less fingering than the FCM black-oil model. This is because the resolution of the 2D compositional simulation, even with a very fine grid, is insufficient to resolve the sharp transition in viscosity from injected gas to reservoir oil and thus severely underestimates the apparent viscosity contrast. We recommend using a simpler FCM simulation if the system is above the MMP. The degree of fingering in the FCM model is accurately predicted using the Koval model.

At the field scale we use FCM simulation with a Todd & Longstaff mixing parameter ω that accounts for small-scale fingering. For WAG floods the value of ω is adjusted to account for the reduced mobility ratio between injected gas and water and displaced oil. Overall we show how to account systematically for the development of miscibility and sub-grid-block fingering in field-scale simulation of a miscible gas injection project.
Secondary Porosity and Permeability of Coal Vs. Gas Composition and Pressure
Authors: Mavor Matthew J. , Gunter William D.
Published: December 2007

We have been investigating sequestration of atmospheric pollutants by injection into coal seams while at the same time enhancing hydrocarbon productivity by displacement of methane by the pollutants. During the course of our field measurements, we have been using single well injection, soak, and production tests to collect data required to understand and predict enhanced coalbed methane (ECBM) recovery potential and sequestration capacity. We found that changing the composition of the gas sorbed into the coal changes the porosity and permeability of the coal natural fracture system due to gas content changes, which cause matrix swelling or shrinkage due to relative adsorption of different gases.

We collected sufficient information to develop a method for predicting the permeability and porosity of a coal bed as a function of the secondary porosity system (SPS) pressure and the gas content and composition of the primary porosity system (PPS). The method uses data from injection/falloff tests using water and/or a weaker adsorbing gas (WAG) than CH4 and a stronger adsorbing gas (SAG) than CH4. Estimates of effective permeability to gas and water obtained from these tests are used with an iterative computation procedure subject to constraints to solve for equivalent SPS porosity and absolute permeability at atmospheric pressure.

Once calibrated, the model can be used to predict a coal bed's permeability and porosity as a function of injection pressure and injected fluid composition that in turn are used to predict injection performance. The model is applicable to production forecasts to account for SPS permeability and porosity changes as reservoir pressure declines with changes in gas composition.

This paper describes the new model and discusses well test procedures to obtain the data required for model calibration. Also included are coal property estimates resulting from Alberta Medicine River (Manville) coal core and test data and an example model calibration.
Zonal Allocation and Increased Production Opportunities Using Data Mining in Kern River
Authors: Popa Carrie , Popa Andrei , Cover Andrew
Published: December 2007

This paper presents a fast and effective methodology to estimate zonal allocation for commingled producers in a multilayer reservoir using minimal, readily available data (well completion, historical production, sand depths, and location data). A set of data mining tools including regression, neural networks, and fuzzy logic was used to identify candidates for remedial work and the corresponding production increase expected. This approach was applied and executed in a portion of the Kern River field in California with very promising preliminary results.
Sand Production Prediction: A New Set of Criteria for Modeling Based on Large-Scale Transient Experiments and Numerical Investigation
Authors: Nouri Alireza , Vaziri Hans , Belhaj Hadi , Islam Rafiqul
Published: December 2007

Using novel physical model experiments and numerical analyses, a set of criteria are proposed that can be used to determine the onset of sanding and its severity in terms of rate and duration.

Experiments on large-scale hollow cylinder specimens were conducted involving real time sand production measurement under various conditions. Synthetic sandstone was used in the experiments whose strength properties were comprehensively determined. A numerical approach was used for simulating the proposed experiments. The material behaviour was simulated using an elasto-plastic stress-strain relationship. The model simulates interaction between fluid flow and mechanical deformation of the medium in predicting sand production. The criteria considered for sanding are more comprehensive than conventionally used and included modeling strain softening of the material accompanied with shear bands formation as well as tensile failure. In the post disaggregation phase, additional features are considered including allowing for the removal of the disaggregated material and making the necessary adjustments to the size and properties of the domain under consideration. Hence, the model is considered to be suitable for time-dependent analysis of the rock as it undergoes disaggregation and production induced by depletion, drawdown, and water-cut. By relating the sand rate to production over the life of a field, the tool can be used in assisting with the completion and operation design of the wells.

The model shows good agreement with experimental results in terms of rock deformation and sand rate. It predicted the onset of shear failure and the subsequent strain softening initiated from the cavity face and propagated inside the medium. Strain softening proved to be the main mechanism for material disaggregation. The good agreement between the numerical and experimental results under comprehensive and complex conditions bodes well for its field applications.
A Combined Geological, Geophysical and Rock Mechanics Approach to Naturally Fractured Reservoir Characterization and Its Applications
Authors: Shen Feng , Li Shuiquan
Published: December 2007

In this paper, we present a combined geological, geophysical and rock mechanics approach to natural fractured reservoir characterization. The local structure entropy analysis on 3D seismic data is used to detect distributions of fault and sub-fault systems. The curvature attribute along with modeled strain and stress field, constrained with the log data measuring P- and S-wave velocities and rock density and the inverted elastic modulus from pre-stack seismic data, reveal effects of the geological structure, bed thickness and lithology on fracturability of the reservoir layer. These analyses quantify the relationships between the geologic factors and rock fracturability and describe physically the weighting factors for geologic parameters in controlling the rock fracturing. The comparison of the seismic azimuthal analysis results to these of geological and rock mechanics modeling provides an opportunity to verify whether the seismic anisotropy derived from seismic data is caused by structure related natural fracture patterns or by other mechanisms. The consistency among different techniques provides the confidence in the interpretation of the distribution of fractures induced by structures. If azimuthal seismic attribute data can be combined, the application of this procedure results in the development of the fracture connectivity anisotropy by considering relationships between the present and palaeo-stress fields. In addition, the scale depend analysis technique in this approach can improve the ability to identify the distribution of fractures with multiple length scales. In this paper, case studies are used to illustrate applications of these technologies and their efficiency.
Compositional Modeling by the Combined Discontinuous Galerkin and Mixed Methods
Authors: Hoteit H. , Firoozabadi A.
Published: December 2007

In this work, we present a new numerical procedure that combines the mixed finite element (MFE) and the discontinuous Galerkin (DG) methods. This numerical scheme is used to solve the highly nonlinear coupled equations that describe the flow processes in homogeneous and heterogeneous media with mass transfer between the phases. The MFE method is used to approximate the phase velocity based on the pressure (more precisely average pressure) at the interface between the nodes. This approach conserves the mass locally at the element level and guarantees the continuity of the total flux across the interfaces. The DG method is used to solve the flow equations which are generally convection dominated. The DG method associated with suitable slope limiters can capture sharp gradients in the solution without creating spurious oscillations. We present several numerical examples in homogeneous and heterogeneous media that demonstrate the superiority of our method to the finite difference (FD) approach. Our proposed MFE-DG method becomes orders of magnitude faster than the FD method for a desired accuracy in 2D.
Simulation-Based EOR Evaluation of a North Sea Field
Authors: Skinner Roger C , Jerauld Gary R. , Bush Michael D.
Published: December 2007

A North Sea oil field was evaluated for continued gas injection for an EOR scheme. Two key aspects of the evaluation used genetic algorithm optimization to support the workflow. The initial application was in determining the range of model variables that equally well matched history and are known to impact EOR performance. The second application was to generate pseudo's to translate fine scale sector model simulation results to enable full field EOR evaluation. The genetic algorithm approach to the history match enables any clusters of variables that together match history to be defined, as well as their individual sensitivity in achieving a match. The outcome is a range of possible models that fit the historical data equally well, which then define a range for predicted EOR performance. The results of this exercise will be presented. The pseudo application enabled the rapid up-scaling of the fine scale sector model results such that they could be confidently applied directly in full field model compositional simulation. The good up-scaling match that was achieved will be presented. The overall outcome was a rapid evaluation of EOR performance in the field together with the expected uncertainty ranges.

The genetic algorithm technique used is very general and can therefore be applied to any problem that has a quantitative measure of success that is dependant on varying input parameters. The challenge is determining the parameters than control performance along with their uncertainty rage and in setting up the software to automatically compute at appropriate measure of success which can be optimized. The generation of multiple variable sets that equally well fit the history data enables a range in EOR prediction to be generated rather than the usual approach of using one history matched base case or performing monte carlo analysis unconstrainted to history. The up-scaling of fine scale simulation results of a complex process, such as EOR, is difficult. The presented technique automates the up-scaling, enabling multiple scenarios to be evaluated
Phase Equilibrium between Gas Condensate and Brine at HT/HP Conditions
Authors: Pedersen K. S. , Milter J.
Published: December 2007

Petroleum reservoir fluids are often produced together with formation water. The mutual solubility between water and hydrocarbons is somewhat affected by the salt contained in the formation water. The paper presents phase equilibrium data for the mutual solubility of brine and a gas condensate mixture at temperatures ranging from 35 °C to 200 °C and pressures of 700 bar and 1000 bar. The phase compositions are compared with compositions measured at the same conditions for the same gas condensate mixed with pure water. The experimental data are modeled using the SRK and PR equations with the non-classical mixing rule of Huron and Vidal. The salt ions are treated as hypothetical molecules having critical properties close to those of high boiling liquid hydrate inhibitors. The model takes into consideration possible association of salt ions and water molecules in the water phase. The simulations results are in good agreement with the experimental data even at high pressure and high temperatures.
Integrated Approach for Optimization of Field Development Portfolios in Complex Production Systems
Authors: Jacobs Richard A.
Published: December 2007

This work presents general steps, criteria and information tools to ensure consistent treatment of investment proposals and availability of key information when optimizing investment portfolios in complex production systems. The approach considers facilities and production related cash flows separately, and uses them as building blocks to describe the cash flows of individual projects, local field development plans, and the regional or corporate portfolios.
Multiscale Flow and Transport in Highly Heterogeneous Carbonates
Authors: Zhang Liying , Bryant Steven L. , Jennings James W. , Arbogast Todd J. , Paruchuri Ramoj
Published: December 2007

Large-scale (cm and greater) heterogeneities raise both practical and theoretical problems for understanding fluid flow through rocks that contain them. Standard sampling methods such as thin sections, core plugs, and even whole core are at a scale too small to resolve these heterogeneities, and direct measurement of flow properties is not straightforward. Moreover it is not obvious what physical formulism (e.g., Darcy's law, Forchheimer's Law, Stokes flow) is appropriate for modeling flow or interpreting flow measurements, nor is it clear that traditional homogenization approaches (e.g., effective medium theory, renormalization, dual-porosity) are applicable in such systems. We report simple measurements on a large 25 cm diameter by 36 cm high sample of Cretaceous carbonate containing centimeter-scale vugs, and compare them to flow fields computed from high-resolution CT images of the same sample. These computations use a single-physics Darcy-flow model. We also compute passive tracer transport in the same model to evaluate preferential flow paths within the rock. The direct computations are based on a porosity grid extracted from a set of CT images (512 × 512 × 240 pixels, 0.5 mm resolution) of the large sample. We also use the single-physics model to estimate the length scale of connections between vugs in this sample. The results demonstrate the need for upscaling methods that preserve connectivity of features in highly heterogeneous rocks.
Problems with the Elicitation of Uncertainty
Authors: Welsh M. B. , Begg S. H. , Bratvold R. B. , Lee M. D.
Published: December 2007

The Oil and Gas industry has a poor record when it comes to accurately assessing uncertainties. An assessment of the risks that arise from these uncertainties is a major factor influencing investment decisions in the O&G industry. Thus, throughout the industry, experts’ understanding of the probabilities of uncertain events are elicited via a range of methods. However, industry sources continue to report ‘surprise’ values (outside the P(80) range) far more often than the 20% indicated by this interval. This suggests problems in the elicitation process: either experts’ beliefs do not capture the distributions they are attempting to define or the processes used in the industry are failing to elicit the experts’ subjective probability distributions (SPDs) accurately.

The authors discuss the ways in which experts’ subjective beliefs about the probability of events are commonly elicited in the industry, and the biases expected to be observed therein, in light of psychological findings and theories of decision-making. Special note is made of the limitations imposed on decision-making by the nature of human short-term memory and predictable biases resulting from reliance on heuristic (rule-of-thumb) reasoning techniques.

The results of an experiment comparing two commonly used elicitation techniques with one, designed by the authors, which utilizes heuristic reasoning as a strength rather than a weakness, are presented and discussed. Accuracy, both in terms of subjective and objective measures, was improved on our experimental tasks by use of the new, More-or-Less Elicitation (MOLE) technique over both of the currently used methods. We conclude that an approach to elicitation that recognizes the tendency of people to use heuristic reasoning, rather than forces them to reason in probabilistic, non-intuitive ways, may yield superior results.

Finally, we discuss possible refinements to the MOLE process and further research required to elucidate the impacts of various biases on elicited distributions.
Validation of Clustering of Fractures in Discrete Fracture Network Model by Using Fracture Density Distributions along Boreholes
Authors: Tamagawa T. , Tezuka K.
Published: December 2007

This study reports a procedure for validating a reliability of a location distribution of fractures in highly populated portions (clusters) of a constructed discrete fracture network (DFN) model. In the procedure, we focus on a relationship between a fracture density distribution along boreholes and spatial extents of clusters of fractures in a DFN model. The numerical experiments show that a shape of a fracture density distribution function evaluated using fractures crossing boreholes mainly depends on a location distribution of fractures, and is less affected by a size distribution and an orientation distribution of fractures.

The DFN model is constructed by the procedure we had proposed previously. At the procedure, geostatistics method is used for predicting extents of clusters of fractures. However, it is pointed out that the extents of clusters have uncertainty due to the prediction by using only the observed locations of fractures along boreholes. This uncertainty reduces a reliability of a constructed DFN model.

To meet the issue, the fracture density distributions along boreholes are calculated for constructed DFN models with different extents of clusters and compared with the observations. Through the studies, it is confirmed that the fracture density distributions along boreholes are useful to constrain the uncertainty of the extents of the clusters and that the optimum extent of the cluster can be extracted by focusing the fracture density distribution along boreholes. Additionally, fluid flow behaviors of the constructed DFN model with the optimum extents of clusters is verified by flow simulations.
Application of MJPs in Oil&Gas Fields
Authors: Andreussi P. , Ansiati A. , Faluomi V. , Senna S. , Sodini S. , Dellarole E. , Battaia C. , Guaita P.
Published: December 2007

ENI E&P in 1993 launched an R&D project on production boosting using multiphase jet pumps. In these devices a high pressure oil or gas well can be used to enhance both the production and the total recovery from a depleted well. The multiphase ejector is characterized by a simple design, absence of moving parts and small dimensions, coupled with a high degree of reliability and low cost. The main disadvantages related to the use of multiphase ejectors are due to the lack of reliable design methods and to the sharp decrease of the performance when operative conditions change.

In the last three years the ejector technology can be considered a standard for ENI resulted in several successful installations worldwide: -West Africa (onshore oil wells)-GOM (offshore, condensate gas )-Italy and Mediterranean Sea (onshore and offshore, wet and dry gases)

In the present work a status of these installations is reported, pointing out the following main items: -design and installation peculiarities-predicted and measured performances-optimisation actions performed during the considered period

The results of this review have been used to identify the new strategies on ejector design and operability, which will be also reported. In particular, new design to increase productivity and component operability life is described, together with laboratory test results
Portfolio Management Using Questionable Quality Data
Authors: DuBois James R.
Published: December 2007

Many, if not all portfolio managers spend a great deal of time worrying about the quality of their economic input data. These concerns cover the gamut from systemic over or under estimation, to project or region specific bias, to simple sloppy and inconsistent data gathering. Many postpone initiating advanced decision making techniques "until the data are in better shape". However, investment decision data quality rarely improves substantially until that data starts being used consistently, systematically, and seriously.

How then are we initiate use of advanced decision making techniques if we don't trust the data? Business decisions are made every day, using the data that is available at the time. If we think of Portfolio Management and Optimization as techniques to improve the quality of our decisions, instead of as ways to find "the right answer", we can begin to use these techniques to improve those decisions in spite of reservations we may have about the quality of data currently at hand. Once a system is in place and functioning, data quality improvement measures can start to take hold with sufficient feedback to guide the process.

In this paper we will investigate ways to use Portfolio Management and Optimization techniques to improve the quality of decisions being made even if the data used is questionable. We will describe methods to combine sensitivity analysis and optimization to address several possible quality issues persistent under and over estimation, specific bias, and random data failures. We will look at techniques to systematically investigate the effects of bias in reserve, probability, and cost estimation on the decision being considered. Finally, we will describe methods to choose portfolios that honor submitted data while reducing the impact of suspected bias and quality issues. .
Prediction of Wellbore Position Accuracy When Surveyed With Gyroscopic Tools
Authors: Torkildsen Torgeir , Håvardstein Stein T. , Weston John L. , Ekseth Roger
Published: December 2007

This paper describes a new method for estimation of well bore position accuracies, when using gyroscopic tools. The developed method represents a solution to the industry's need for a general and flexible error model which is applicable for all gyroscopic surveying tools and services.

The general gyro error model consists of a new set of error terms and a mathematical description of how the different error sources contribute to position uncertainties dependent on sensor configurations and operational modes. The model is suitable for appropriate modelling of most gyro surveying services.

The error propagation mechanisms are chosen to be identical to those in the ISCWSA’s MWD error model (SPE 67616), which has become an industry standard during the last five years. Thus future standardisation and software implementation are simplified. The description of the model and the attached numerical examples should be sufficient to implement the model.

The paper is a product of a collaborative work in ISCWSA (Industry Steering Committee on Wellbore Surveying Accuracy).
Upscaling Multiphase Flow Simulations in Heterogeneous Stratified Reservoirs by Optimal Layering
Authors: Artus Vincent , Nœtinger Benoit
Published: December 2007

Using some recent theoretical findings, we define an optimal vertical partition of stratified reservoir. This approach consists in merging several neighbor geological layers to define hydrodynamic layers. These hydrodynamic layers correspond to zones where the water oil front propagates without being deformed, even if these layers can be composed at smaller scale of several geological layers having different permeability values. This phenomenon is due to viscous crossflow effects that can stabilize the front. In a next step, a coarse vertical grid can be defined in accordance with this layering, optimizing the quality of coarse simulations.

We developed a simple numerical tool allowing a fast determination of different hydrodynamic layers as a function of the input permeability distribution and fluid mobility properties. Possible extensions to isotropic structures are also investigated.
History Matching and Quantitative Use of 4D Seismic Data for an Improved Reservoir Characterization
Authors: Mezghani M. , Fornel A. , Langlais V. , Lucet N.
Published: December 2007

In reservoir characterization, the value of each piece of data does not lie in its isolated use, but rather in the value it adds to the analysis when integrated with other data. Earth scientists from different disciplines have made many efforts to better predict the spatial distribution of petrophysical properties. However, the interpretation of isolated piece of knowledge, without a real integration of disciplines, cannot lead to a quantitative answer in terms of reservoir characterization. In this paper we present a joint inversion scheme for estimating petrophysical properties by integrating both production and 4D seismic related data in geological modeling. Simultaneous history matching of production and 4D seismic related data leads to a better prediction of petrophysical reservoir properties and of production forecast.
Enhanced Hydrate Inhibition in Alberta Gas Field
Authors: Budd Dana , Hurd Danica , Pakulski Marek , Schaffer Thane D.
Published: December 2007

Gas wells located in Southern Alberta, Canada pose challenges for well operators. High bottomhole pressure in new wells, low bottomhole temperatures and Joule-Thompson expansion cooling effect often lowering gas stream temperatures to below brine freezing create favorable conditions for formation of gas hydrates in the wells and transportation pipelines. The problems are aggravated during cold winter months when wells and pipelines have strong tendencies to plugging with hydrates and ice. Operators experience significant monetary losses due to disrupted production and have to spend considerable amount on chemicals and time to clean up hydrates from plugged wells and pipelines.

With subcooling temperatures often exceeding 14°C, kinetic hydrate inhibitors are incapable of preventing hydrates formation. A typical solution to such severe hydrate problems is pumping massive amounts of methanol or glycols to the well and production lines. Adding large amounts of thermodynamic inhibitors creates problems by itself like oxygen corrosion or solvent induced scaling. Earlier work in the field indicated a possibility of synergism between thermodynamic hydrate inhibitors and Low Dosage Hydrate Inhibitors (LDHI). Systematic laboratory work was undertaken to explore possible synergistic effects between methanol and LDHI. A strong synergistic effect was discovered at a certain ratio of methanol and low molecular weight oligomer type hydrate inhibitor. These observations allowed a formulation of a superior hydrate inhibitor. Field results show the reduction up to 80% of the original and often insufficient methanol dosages. Due to this novel approach to hydrate problems, the operator experienced more trouble-free field operation and increased gas production, improved economics with less down time, lower total cost of chemicals and delivery.
Level 6 Multi-Lateral Experiences in the Niger Delta – A Review
Authors: Erivwo Ochuko , Ugboaja Remmy , Ikoh Editi , Banks Andy
Published: December 2007

Multi-Lateral technology was selected in SPDC as one of its strategic cost leadership initiative to drive down the development costs of its hydrocarbon assets. Its main objective was to reduce well construction costs by 30 – 40% in terms of unit footage costs and unit development costs and to increase string months available per rig. The technology implementation was set within legislative requirements peculiar to the area and its reservoir geology, which constrained the available options.

To date five level 6 multi-lateral wells have been successfully drilled and completed while a sixth one was aborted due to a junction installation failure. Two of the wells were Deep Set Splitter (DSS) installations in the same field while the others were Formation Junction (FJ) applications in two different fields. Field execution for the Formation Junction wells encountered significant challenges, which resulted in several innovative approaches including design and procedural modifications to achieve success. Commercial improvement was also observed as the implementation progressed.

This paper presents the application of level 6 multi-lateral technology and it’s impact in SPDC. It reviews the concept selection, engineering planning, risk analysis and mitigation for the wells. It dwells on the technical experiences from the execution phase with a special focus on the failed attempt. It also presents learnings and best practices from the technology implementation with recommendations for future applications in the industry.
Optimisation of Well Placement and Improved Well Planning within a Collaborative 3D Environment Employing Real-Time Data: A Case Study from the Visund Field, Norway
Authors: Girling S. B. , Lambert A. D. , Andersen K. , Båtevik A.
Published: December 2007

The overall success of an oil and gas company is largely judged by their ability to prolong revenue from producing fields. Reducing operating cost has the single most significant impact on this objective but has become more challenging to minimize, as the deviated wells required to economically exploit reserves, necessitate highly accurate placement and increasingly advanced engineering. Rapid evaluation cycle times and operational lost time prevention are critical to cost reduction.

This paper will detail how the well design process and WITSML enabled real-time drilling information is conducted and visualized in one 3D view. It will demonstrate how this increased efficiency, contributed to better well placement and reduced operational cost, by complementing technical expertise and increasing collaboration, through a multidiscipline workflow approach.

This change in working practice culminated in the success of achieving the worlds fastest drilled well of more than 8000m measured depth, from a sub sea template.
The Evaluation of a New Environmentally Friendly Combined Product for Application in the North Sea for Effective Scale and Corrosion Control
Authors: McNaughtan D. , Winning I. G. , Sim M.
Published: December 2007

The introduction of more stringent environmental regulation within the North Sea has resulted in increased focus on developing environmentally acceptable inhibitors for application to oil and gas applications. One approach in fulfilling these criteria has been the emergence of multifunctional combined products. This paper demonstrates how this approach can be used effectively to control both scale and corrosion problems. A new environmentally friendly product was developed within the laboratory that gave improved scale control performance against conventional products while also affording excellent corrosion control. A series of tests were conducted to establish the performance of the product as well as compatibility with produced fluids from a North Sea platform. The results of the laboratory investigation are discussed in detail including the advantages and disadvantages offered by this approach as well as the potential environmental benefits.